Phosphorus removal by ceramic tight
ultra-filtration (CTUF) membranes for RO
pre-treatment
Zheyi Zeng
For the degree of:
Master of Science in Civil Engineeing
Date of submission: 23.08.2012
Date of defense: 29.08.2012
Committee:
Prof. dr. ir. Luuk Rietveld
Delft University of Technology
Sanitary Engineering Section
Dr. ir. Bas Heijman
Delft University of Technology
Sanitary Engineering Section
Dr. ir. Hans Vrouwenvelder
Delft University of Technology
Environment Biotechnology Section
Ir. Ran Shang
Delft University of Technology
Sanitary Engineering Section
Sanitary Engineering Section, Department of Water Management
Faculty of Civil Engineering and Geosciences
Delft University of Technology, Delft
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Abstract
Reverse Osmosis systems are wildly used for sea water desalination and water reclamation
but they meet problems regarding bio-fouling. Bio-fouling increases their work pressure and
operational costs and decreases their removal efficiencies. Phosphorus limitation is one
strategy to control bio-fouling. This report focuses on phosphorus removal by ceramic tight
ultra-filtration (CTUF) membranes (1kD and 3kD MWCO) as a pretreatment before RO. In this
research we investigated different factors affecting phosphorus rejection by CTUF such as flux,
cross flow velocity, ion strength, zeta potential and pH. The results show that increasing the
flux, the cross flow velocity and the zeta potential increased the removal rate of phosphate.
Increasing ion strength decreased the double layer thickness and decreased the removal rate of
phosphate. All these results are in agreement with the theory of membrane filtration. The pH
affected both the zeta potential of the membrane and the charge of the phosphate ion.
Increasing pH increased the removal rate of phosphate but after pH 8.3, the removal rate of
phosphate began to decrease. There is no explanation for this decrease in rejection at higher
pH at this moment.
Key words: CTUF; phosphate removal; zeta potential; double layer thickness
1
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Preface
This report is a product of my master thesis for my master programme of Sanitary
Engineering in Water Management department in Civil Engineering and Geosciences Faculty of
TU Delft University, The Netherlands. The research work is supported by the whole Sanitary
Section, especially the drinking water treatment group.
Here I want to say thank you to my mother. She supported me for the three year master
study a lot. Also, to my father, who helped me for the last year.
Thanks to Prof. dr. ir. Luuk Rietveld, Dr. ir. Bas Heijman, Ir. Ran Shang, who unreservedly
helped me to finish the research and this report.
Thanks to Siyan, my girlfriend. When I was in bad emotion for the delay of experiments,
she tried to make me calm down and bore me a lot.
Thanks to other friends I met in last three year. You made my life in The Netherlands not
be alone.
Zheyi Zeng
Delft, The Netherlands
August 2012
2
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
MENU
1. Introduction.......................................................................................................... 5
2. Background .......................................................................................................... 9
2.1 RO systems for water reclamation.................................................................. 9
2.2 Bio-fouling .................................................................................................. 11
2.2.1 What is bio-fouling ............................................................................. 11
2.2.2 Drawbacks of bio-fouling in RO systems ............................................... 11
2.2.3 Strategies for bio-fouling control.......................................................... 13
2.3 Current technologies of RO pre-treatment and bio-fouling control ................... 13
2.4 Ceramic Tight ultra-filtration (CTUF) to controlbio-foulingthrough combination of
particle, organic matter and phosphorus removal ................................................. 17
3. Phosphorus removal in water treatment ................................................................. 18
3.1 Fractions of phosphorus in effluent water ...................................................... 18
3.2 Phosphorus limitation in biofilm growth ......................................................... 19
3.3 Phosphorus removal methods ....................................................................... 20
3.3.1 Conventional chemical treatment for phosphorus removal ..................... 20
3.3.2 Enhanced biological treatment for phosphorus removal ......................... 21
3.3.3 Ultra-filtration/ Nano-filtration membranes for phosphorus removal ....... 22
4. Theory of factors affecting phosphorus rejection by tight ceramic UF membrane....... 24
4.1 Factors affecting rejection efficiency of membrane filtration ............................ 24
4.2 Theory of double layer ................................................................................. 27
4.3 Theory of zeta potential ............................................................................... 29
5. Materials and methods ......................................................................................... 32
5.1 membranes ................................................................................................. 32
5.2 Experiments planning................................................................................... 32
5.3 Experimental set-up ..................................................................................... 34
5.4 Measurements ............................................................................................. 35
6. Results and discussions ........................................................................................ 37
6.1 Flux and cross flow velocity effects ............................................................... 37
6.2 The effect of phosphorus concentration in the feed water ............................... 39
6.3 Ions effects to phosphorus removal ............................................................... 41
6.4. pH effects .................................................................................................. 45
6.5 Zeta potential .............................................................................................. 46
7. Conclusions and recommendation .......................................................................... 49
3
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Reference ................................................................................................................ 51
Appendix ................................................................................................................. 62
4
List of Figures
Figure 2.1: Four membranes differences ................................................................................... 9
Figure 2.2: Schematic process diagram of DWP Sas van Gent, ........................................... 10
Figure 2.3: Bio-fouling on RO membrane ................................................................................ 11
Figure 2.4 Normalized flux and Salt passage upon deposition of formaldehyde fixed PA01
dead cells and PA01 biofilm growth on the RO membrane in a synthetic wastewater
medium: (a) Normalized flux; (b) Percent salt passage (ionic strength of 14.6 mM and
pH 7.4) .................................................................................................................................. 12
Figure 2.5: Comparative flux decline of different size fractions of seawater with a SWRO
membrane ............................................................................................................................. 14
_Toc333421889
Figure 3.1: Results of the phosphorus distribution ................................................................. 18
Figure 3.1: Enhanced biological phosphorus schematic diagram ......................................... 21
Figure 4.1: Influence of cross-flow velocity on NF rejection ................................................. 25
Figure 4.2: Schematic of water and ions passing membranes ............................................. 26
Figure 4.3: Hypothesis of charge exclusion ............................................................................. 27
Figure 4.4: Detailed illustration of interfacial DL ..................................................................... 28
Figure 4.5: Dependency of zeta potential of TiO2 suspensions upon pH suspensions at
various concentrations of different KCl , mol/l: ▲ 1*10-5; ◆ 1*10-4; ■ 1*10-3; ●
1*10-2..................................................................................................................................... 30
Figure 4.6: Zeta potential of new and fouled membrane at different pH values (measured
with 1 mmol/l KCl electrolyte solution) ............................................................................. 31
Figure 5.1: Experimental membrane ........................................................................................ 32
Figure 5.2: Experimental set up ................................................................................................ 34
Figure 6.1.1: Phosphorus removal of different fluxes ............................................................ 37
Figure 6.1.2: Phosphorus removal of different cross flow velocities .................................... 38
Figure 6.2.1: phosphorus removal rate in different phosphorus concentration of 3kD
membrane and 1kD membrane (Error bar represents standard deviation, sample
number: 3) ............................................................................................................................ 40
Figure 6.3.1: Removal rate of phosphate with different NaCl concentrations or Na2SO4 for
1kD and 3kD membranes ................................................................................................... 41
Figure 6.3.2: Effects of ionic strength on double layer thickness......................................... 43
Figure 6.3.3: Effects of ionic strength on phosphate removal of 3kD membrane in solution
NaCl and Na2SO4 .................................................................................................................. 44
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Figure 6.3.4: Effects of ionic strength on phosphate removal of 1kD membrane in solution
NaCl and Na2SO4 .................................................................................................................. 44
Figure 6.4.1: Removal rate of phosphate with 6 mmol/l NaCl at different pH for 1kD and
3kD membranes ................................................................................................................... 45
Figure 6.4.2: Phosphoric acid speciation .................................................................................. 46
Figure 6.5.1: Zeta potential of 1kD membrane with different solutions.............................. 47
Figure 6.5.2: Zeta potential of 3kD membrane with different solutions.............................. 47
Figure 6.5.3: Zeta potential of 0.05g/l Degussa P25 TiO2 as a function of pH and ionic
strength in 0.001-0.01 M NaCl ........................................................................................... 48
6
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
List of Tables
Table 2.1: Comparison chart for disinfectants used for bio-fouling control of SWRO
membranes ..................................................................................................... 15
Table 5.1: Membrane parameters ............................................................................ 32
Table 5.2: flux and cross flow settings ...................................................................... 33
Table 5.3: Phosphorus concentration settings ........................................................... 33
Table 5.4: Measuring range ..................................................................................... 35
Table 6.1: Ionic strength, double layer thickness and phosphate removal of different
settings........................................................................................................... 42
7
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
1. Introduction
Reverse Osmosis is widely used in the water desalination and water reuse due to its high
ions rejection rate (>99%). However, it has a high operational cost because it is easy to get
fouling (scaling and bio-fouling). Once fouling occurs, especially bio-fouling, it will lead to the
use of higher operating pressure of RO systems, more frequent chemical cleaning and shorter
membrane life. Therefore, controlling bio-fouling is necessary for RO systems.
This MSc program is part of ICAN project (Innovative application of ceramic ultra- and
nano- filtration). The project is aiming at wastewater reclamation. The RO system is chosen to
treat the wastewater. The effluent of the RO system will be reused as industrial water supply.
The feed water to the reclamation treatment is the effluent of the wastewater treatment plant.
Due to the large number of inorganic and organic matters in the feed water, bio-foiling will
occur which needs to be controlled. This program focuses on the feed water pretreatment.
Ceramic tight ultra-filtration (CTUF) will be used as a pre-treatment of the RO system.
Some researchers propose nutrients (carbon, nitrogen, phosphorus and oxygen) limitation
might be helpful for bio-fouling control. Liu et al. (2011) found that decreasing each nutrient
concentration in feed water respectively would decrease the bio-fouling in cooling water
systems. If any of the nutrient will be limited to a certain concentration values (in their
experiment for cooling water system, nutrient concentrations of carbon, nitrogen and
phosphorus should be below 30 mg/l, 8 mg N/l and 1.0 mg P/l respectively), the microbial cells
cannot survive and duplicate thus there will be no bio-fouling.
This thesis focuses on phosphorus limitation by tight ultra-filtration membranes prior to the
RO system. Two membranes with different MWCO, 1kD and 3kD, are selected.
The key tasks of the research are to investigate the performance of tight ultra-filtration
membrane for phosphorus removal.
The research questions are,
a. What could be the highest removal rate of phosphorus with these two membranes in
different filtration conditions?
b. What are the influence factors of phosphorus removal and how do them influence the
removal rate of phosphorus?
The answers to these two questions are prepared to answer the research question c for
project ICAN, which is not the content of this thesis.
c.
Is phosphorus limitation with CTUF available for bio-fouling control of RO system and
how much bio-fouling can it control?
8
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
2. Background
2.1 RO systems for water reclamation
Membrane filtration nowadays is widely used in water treatment. There are four
membranes filtration methods: Micro-membrane filtration (MF), Ultra-membrane filtration (UF),
Nano-filtration membrane (NF) and Reverse osmosis (RO). The four membranes are classified
with pore size differences. Figure 2.1 shows the differences for the four membranes in terms of
pore sizes, molecular weight cut-off (MWCO) and operational pressures.
Figure 2.1: Four membranes differences (Pore size of nanofiltration is considered as 200 to
1000MWCO usually but Figure 2.1 shows 200 to 10000 MWCO) (van Dijk et al. 2009)
The Figure describes that the pore size of micro filtration is between 0.1μm to 1μm while
ultra-filtration is between 1nm to 0.1μm, nano-filtration is from 1nm to 0.01μm and reverse
osmosis is smaller than 1nm.The removal differs with the pore sizes. MF will remove suspended
matter and bacteria. UF will even remove some of the natural organic matter and viruses. NF
has the ability to remove additionally organic micro-pollutants, multivalent ions and a part of
the monovalent ions and reverse osmosis has the ability to remove all the ions and dissolved
salts (van Dijk et al. 2009).
Seawater desalination and water reclamation are two main applications for RO systems.
9
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Water reclamation is a process by which domestic and industrial wastewater is cleaned
using biological and chemical treatment so that the water can be reused for other purposes.
The reclaimed water can be used for irrigation, industry water and domestic water such as
toilet flushing water (Wikipedia D).
Reclamation water has a high requirement of treatment to reach the desired water quality.
The feed water is always from the effluent of a wastewater plant thus it contains suspended
matters, ions, organic matter, organic micro-pollutants and pathogens. RO systems are
recommended as the key process to treat the water used for reclamation.
Shang et al. (2011) summarized an industrial water treatment plant, DWP Sas van Gent in
the Netherlands, which treats effluent from a starch-producing plant to produce demi-water for
the PW Plant (Polished Water Plant). The main processes in the plant are an inline flocculation
with iron, dual media filtration with anthracite and sand, ultra-filtration, antiscalant dosing, a
first-stage RO system, degasifiers and a second-stage RO system. For its RO system,
antiscalant Genesys LF at a dose of 3.68mg/l and a pH value of 7.2 are used to RO feed water
to control scaling. Bio-fouling (which will be introduced in the following chapter) is observed,
especially in the warm season. The WWTP effluent is successfully reclaimed and reused for
industry.
Figure 2.2: Schematic process diagram of DWP Sas van Gent (Shang et al., 2011),
RO has an excellent removal of all components in the water, but the costs are high. The
costs include both investment as maintenance and operation. Fouling is an important aspect of
operation and maintenance. There are three main mechanisms: (A). Scaling on top of the
membrane; (B). Bio-fouling in the spacers; (C). Particulate fouling on top of the membrane. If
fouling occurs, the resistance of the membrane will increase thus the removal of the ions will
decrease. Therefore, there will always be some pre-treatment before RO such as coagulation,
flocculation, filtration, sedimentation or ultra-filtration pretreatment.
10
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
2.2 Bio-fouling
2.2.1 What is bio-fouling
Fouling has many types in the membrane system: inorganic, organic, particulate, colloidal
and bio-fouling (Kramer et al., 1995). It is agreed that bio-fouling is most difficult to be
controlled (Baker et al., 1998). The first three types of fouling can be controlled by
pretreatment but bio-fouling is not easy to be reduced by pretreatment alone because
deposited microbial cells can grow, multiply and relocate (Goosen et al., 2005).
Figure 2.3: Bio-fouling on RO membrane (From website http://www.waterworld.com)
Donlan (2002) described the bio-fouling is referred to the unwanted deposition and growth
of bioflims. Biofilm formation results in an unaccepTable degree of system performance loss
(Davies et al., 2009). Biofilms are primarily composed of microbial cells and EPS (extracelluar
polymeric substances). The physical properties of the biofilms are largely determined by the
EPS, while the physiological properties are determined by the bacterial cells (Beer et al., 2006).
2.2.2 Drawbacks of bio-fouling in RO systems
Bio-fouling leads to the use of higher operating pressure of RO systems, more frequent
chemical cleaning and shorter membrane life (Martin et al., 2011). Thus increasing normalized
pressure drop (NPD) and/or decreasing normalized flux (MTC) (Vrouwenvelder, 2008). In US,
58 of the 70 RO membrane installations which were surveyed by Paul were reported having
―above average‖ problems with bio-fouling (Paul, 2011). In the Middle East, 70% of the
seawater RO membrane installations suffer from bio-fouling (GamalKhedr, 2011). Martin et al.
(2011) summarizes that bio-fouling will bring a decline in permeate flux and decrease in salt
11
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
rejection in membrane systems, thus the system pressure will be increased by an increase of
the pump performance in order to compensate the flux decline, which will result in an increase
in energy consumption. Herzberg and Elimelech (2007) found biofilms on the RO membranes
resulting in a decrease of both the RO permeate water flux and salt rejection. They used dead
cells of Pseudomonas aeruginosa PA01 and biofilm growth on the membrane surface
respectively in the feed water and observed the flux decline as well as percent of salt passage
in RO systems. Figure 2.4 (a) and (b) show their results.
Figure 2.4 Normalized flux and Salt passage upon deposition of formaldehyde fixed PA01 dead
cells and PA01 biofilm growth on the RO membrane in a synthetic wastewater medium: (a)
Normalized flux; (b) Percent salt passage (ionic strength of 14.6 mM and pH 7.4)
(Herzberg and Elimelech, 2007)
Figure 2.4 (b) shows a sharp increase in the salt passage with the increase in dead cells on the
membrane. In addition, biofilms will also grow on other components such as the permeate
12
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
surfaces of cross flow membranes, the woven polyester support fabrics, the permeate
collection material and the feed channel spacer materials (Aleem et al., 1998).
2.2.3 Strategies for bio-fouling control
RO systems are sensitive to bio-fouling. Herzberg and Elimelech (2007) distinguished two
fouling mechanisms: (i) Bacterial cells hinder the back diffusion of salts, which results in
elevated osmotic pressure on the membrane surface (increase in TMP), and hence a decline in
permeate flux (ii) EPS contributes to the decrease in flux by increasing hydraulic resistance to
permeate flow. The microorganisms are considered as an indication of biofouling on the
membrane surfaces in many studies. However, Vrouwenvelder et al. (2008) summarized that
microorganismes are present on all the surfaces in contact with water and their presence is not
an indication for bio-fouling. The most important mechanism is the clogging of feed spacers in
the RO system (Radu, 2010). They also indicated three mechanisms by which the development
of a biofilm in a RO system contributes to the flux decline and increased salt passage into the
permeate: (A). biofilm-enhanced concentration polarization; (B). increase of hydraulic
resistance to trans-membrane flow; (C). increased feed channel pressure drop.
Even if 99.9% of the bacteria are eliminated by pre-treatment, the surviving cells might
also induce bio-fouling (Flemming, 1997).
Martin, et al. (2011) summarized that since the late of 1990s, there had been two
strategies which were strongly proposed for the prevention and control of membrane
bio-fouling: (1). Physical removal of bacteria from the feed water of membrane systems; (2).
Metabolic inactivation of bacteria by applying biocide dosage or UV irradiation. Otherstrategies
are also considered such as membrane surface modification, and chemical cleaning (Mansouri
et al., 2010).
2.3 Current technologies
bio-fouling control
of
RO
pre-treatment
and
2.3.1 Feed water pretreatment with MF/UF membrane
One strategy for bio-fouling control of RO systems is feed water pre-treatment to reduce
the substances and bacteria which will cause membrane fouling (Kumar et al., 2006). The
pre-treatment processes include coagulation/flocculation, filtration, activated carbon,
disinfection and membrane filtration (MF or UF). However, Schneider et al. (2005) found that
13
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
none of the conventional processes (coagulation/flocculation, filtration, activated carbon,
defection) could get a satisfied reduction of microbial numbers. On the contrary, they found
that GAC (Granular Activated Carbon) filters and chlorination would actually contribute to
bio-fouling. GAC would be one source of microbial contamination and chlorination would be one
contributor to AOC (Assimilable Organic Carbon), which could be nutrient for micro-organisms.
Membrane filtration is more effective than the conventional processes to control
bio-fouling. Kumar et al. (2007) investigated the effect on flux decline of RO systems with
different membranes as pretreatment. They found that the lowest flux decline was when a tight
UF membrane was used and there would be a larger flux decline when MF membrane was used.
Figure 2.5 shows their results.
Figure 2.5: Comparative flux decline of different size fractions of seawater with a SWRO
membrane (Kumar et al., 2006)
Figure 2.5 shows that the larger pore size of the pre-treatment membrane causes a larger
flux decline of the RO system. The tight ultra-filtration membrane (20kD) caused almost 10%
flux decline while micro filtration membrane (1 micron) caused almost 22% flux decline.
Other researchers also obtained the same results. Teng et al. (2003) used MF and UF
pretreatments for seawater desalination with RO and found that the UF pilot system had a
better performance to control the bio-fouling than the MF pilot system.
Furthermore, membrane pretreatment processes need less space and chemicals compared
to the conventional pretreatment systems (Ebrahim et al., 2001). In all, MF and UF membranes
have more advantages to control bio-fouling as the pretreatment of a RO system.
However, actually UF and MF are not sufficient to prevent bio-fouling because nutrients
can still pass these membranes. Nowadays, for wastewater a biological treatment to remove
nutrients or prevent bio-fouling with a biocide are recommended.
14
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
2.3.2 Ozone and UV as biocide to control bio-fouling
Due to its strong oxidation potential, ozone is frequently used to disinfect drinking water. It
is a strong biocide and Kaur et al. (1992) reported that ozone could weaken the biofilms matrix
thus remove the biomass.
However, ozone has some disadvantages. It is reported that ozone may break down the
membrane surface due to its strong oxidizing properties (Martin et al., 2011). Ozonation of
seawater was found to generate the by-product bromate which could deteriorate the
membrane surface and is considered to be carcinogenic (Tyrovola et al., 2005).
Compared to ozone, UV (ultraviolet) light is nowadays more applied. Martin, et al. (2011)
summarized its advantages: no disinfection by-products, independent of pH, elimination of
toxic chemical usage. UV irradiation at 254nm will break the bacterial DNA genetic code and
inhibit their production (Oh et al., 2007). Moreover, with H2O2 as photocatalyst, UV could
completely remove the model organic compound, which serves as nutrients for bacterial
growth (Kang et al., 2003).
Chlorine is also used to control biological growth. Lund et al. (1995) found no biofilm was
formed when using chlorinated water containing a residual of 0.04-0.05mg/L free chlorine
(HOCl, OCl-). However, nowadays chlorine is less and less used in drinking water treatment.
Chlorine addition and dechlorination processes are known to enhance bio-fouling (Jr, I.M., et al.,
1995) and disinfection by-products are formed. Also, it was reported that free chlorine could
not control waterborne pathogens such as Mycobacterium avium, which will contribute the
biofilims (Shnanon, 2008).
Kim et al. (2009) summarized a Table with the advantages and disadvantages of
disinfectants used for bio-fouling control.
Table 2.1: Comparison chart for disinfectants used for bio-fouling control of SWRO membranes
(Kim et al.,2009)
Disinfection
Advantages
Disadvantages
Easy install and
maintenance
Physical
UV
Scale formation
Effective inactivation
Oxidation of organic
No residual effect
matter
Chemical corrosion of RO
Chemical
HOCl, OCl−
High inactivation efficiency
membrane
Organic matter removal
THMs, HAAs formation
Relatively low cost
Ozone
Effective inactivation
15
Very small half life
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
High oxidation potential
for organic matter
Damage by residual ozone
2.3.3 Membrane surface modification
Surface modification is studied to prevent biofilms. Some results show that making the
surface more hydrophilic, negatively charged or smooth will decrease the bacterial adhesion of
bio-fouling (Kochkodan et al., 2006). In addition, using antimicrobial nanomaterials is also one
method to control bio-fouling (Mahendra et al., 2008).
TiO2 is recommended to be a membrane surface material due to its photocatalytic effects,
which can kill the bacteria and decompose organic chemicals (Mills et al., 1997). It usually
co-operates with UV light and generates various active oxygen species such as hydroxyl radical
(OH) (Kikuchi et al., 1997). Kwak et al. (2001) used E.coli as a model bacterium and measured
the cell numbers after a RO system composed of aromatic polyamide thin films underneath TiO2
nanosized particles, both with and without UV illumination. The results showed that without UV,
E.coli could survive for 40% and with UV+TiO2, E.coli could not survive. The difficulty of the
technology is combining TiO2 with polymeric membranes and its risk is that the formed OH
radicals might damage the membranes.
Ag (Silver) can also be used in the form of nano-particles. It is reported silver ions play an
essential role in bacteria inactivation (Cho et al., 2005) and Ag+ ions could prevent DNA
replication and affect the structure and permeability of the cell membrane (Feng et al.,2000).
Zodrow et al. (2009) found that the incorporation of Ag into polysulfone UF membranes not
only exhibited antimicrobialproperties towards a variety of bacteria but also increased
membrane hydrophilicity thus reducing the potential for other types of membrane fouling.
2.3.4 Membrane cleaning
Membrane cleaning is used to restore membrane performance when unwanted operation
conditions occur such as flux decline and feed pressure increase (Al-Amoudi et al., 2005). Much
of the decline in membrane performance will be recovered by cleaning (Sadhwani et al., 2001).
Chemicals for cleaning are of the next six types: alkalis, acids, metal chelating agents,
surfactants, oxidation agents and enzymes (Mohammadi, 2002). Whittaker et al. (1984) found
that
two
combinations
for
cleaning
were
most
effective
in
removing
biofilms:
enzyme–antiprecipitant–dispersant, and bactericidal agents with an anionic detergent. Madeni
et al. (2001) found that the combinations of chelating agent and surfactant with alkali provide
the best cleaning efficiency when compared to acids and alkalis, when cleaning fouled
polyamide RO membranes.
16
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
2.4 Ceramic Tight ultra-filtration (CTUF) to control
bio-fouling through combination of particles, organic
matters and phosphorus removal
This MSc program is part of ICAN project (Innovative application of ceramic ultra- and
nano- filtration), which is introduced in chapter 1. As mentioned in Chapter 2.3, there are four
strategies to prevent bio-fouling. This program chooses the feed water pretreatment. Ceramic
tight ultra-filtration (CTUF) will be used as a pre-treatment of the RO system.
Some researchers propose nutrient (carbon, nitrogen, phosphorus and oxygen) limitation
might be helpful for bio-fouling control. Liu et al. (2011) found that decreasing each nutrient
concentration in feed water respectively would decrease the bio-fouling in cooling water
systems. If any of the nutrient will be limited to a certain concentration values (in their
experiment for cooling water system, nutrient concentrations of carbon, nitrogen and
phosphorus should be below 30 mg/l, 8 mg N/l and 1.0 mg P/l respectively), the microbial cells
cannot survive and duplicate thus there will be no bio-fouling. Vrouwenvelder et al. (2010)
reported that low phosphate conditions (below 0.3μg /L) in the feed water could prevent
pressure drop increase of RO systems and biomass accumulation, even at high substrate
(organic carbon) concentrations.
The project focuses on phosphorus limitation by tight ultra-filtration membranes before
the RO system. Other researchers have studied phosphorus removal by membranes. More than
95% of phosphate can be removed using NF90 membranes (Hong et al., 2009). Some
experiments compare model water with real wastewater. HL membranes can remove 69.7% of
the 25mg/l P2O5 dissolved in demi-water, while in real wastewater, which also includes 25mg/l
P2O5, can remove 88.8% of the phosphorus (Dolar et al., 2011) at a pH of 5.4.
CTUF is a new definition in membrane researches. The pore size of TUF is closed to
bondage pore size of nano-flitraion membrane, which is similar with ―loose‖ nanofiltration.
Tight ultra-filtration is seldom used for phosphorus removal so it is a creative method in this
thesis. The expected results for phosphorus limitation will be discussed in chapter 3.2.
17
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
3. Phosphorus removal in water treatment
3.1 Fractions of phosphorus in effluent water
Phosphorus can be found in different forms in surface water and WWTP effluent. These
forms can be divided into dissolved, colloidal and particulate phosphorus. Colloidal phosphorus
is within the size range of 0.01 – 1.0μm, dissolved phosphorus is smaller than 0.01μm and
particulate phosphorus is larger than 1μm (Scherrenberg, 2011).Colloidal and particulate
phosphorus can be separated by filtration or centrifugation (Scherrenberg, 2011).
Scherrenberg (2011) also summarized that soluble or dissolved phosphorus can be divided
into dissolved reactive phosphorus or orthophosphorus (PO43-, HPO42-, H2PO4-, H3PO4),
dissolved acid hydrolysable phosphorus (polyphosphorus, pyrophosphorus etc.) and dissolved
organic phosphorus (Organic polyphosphorus, phosphoric compounds). The first type of
phosphorus is available for the biological metabolism without further break down and is the end
of many decomposition reactions. It is the only phosphorus form which is not considered
completely biological because many parts of sedimentary orthophophorus are not from
biological transformations (Ahlgren, 2006). The second type can take part in precipitation
reactions or can adsorb to particles (Bratby et al., 2006). The presence of the third type is an
indication for biological and microbial activity (Ahlgren, 2006).
Figure 3.1: Results of the phosphorus distribution (S. Scherrenberg, 2011)
However, there are not many studies on the fractions of phosphorus that give support to
microbial growth. Another parameter named MAP (microbially available phosphorus) is now
18
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
frequently analyzed. Polanska et al. (2005) summarized that the analysis of MAP in drinking
water would be a useful tool, when estimating the potential of microbial growth in the water
phase in distribution systems with high organic carbon content.
3.2 Phosphorus limitation in biofilm growth
It is reported that molar proportion for microbial growth in water of organic carbon,
nitrogen and phosphorus is 100:10:1. Limiting each of the nutrient can control the growth
(Beardsley et al., 1985). Therefore, researchers are now interested in phosphorus growth
limitations of heterotrophic bacteria instead of the main energy source – organic carbon,
especially in water with high organic carbon contents (Polanska et al., 2005).
Phosphorus concentrations could be treated to a low level before high-pressure membrane
systems by coagulation, sedimentation or filtration (Jacobson et al., 2008). What is the exact
limitation have been studied by many researchers. The results for phosphorus limitation are
different for the various water systems. One reason is that the functions are different.
Phosphorus limitation in membrane systems seems to be stricter than it in distribution systems.
Miettien et al. (1997) performed experiments to prove that concentrations of phosphorus
would effect on microbial growth. Even an addition of 1μg /L PO4-P would increase the
microbial growth.
Fang.W et al. (2009) did the experiments to examine the effects of phosphorus on biofilm
disinfection with free chlorine and monochloramine. Phosphorus addition was found to increase
the biofilm cell number but decrease the exopolysaccharides (EPS) production.
J.Wang et al. (2010) investigated the impact of various forms of phosphorus on biological
growth in distribution systems. They found that when the same phosphorus concentrations of
different forms of phosphorus were added to the feed water, bacterial growth was in the
following order: TP (Total phosphours) of river water > PP (Particulate Phosphorus) > SRP
(Soluble Reactive Phosphorus) > Poly-P (Polyphosphate). They concluded that TP 10μg /l or
SRP 5μg /l could be ea meaningful and practical index for biological stability.
Rubulis and Juhna (2007) also concluded that total bacteria numbers and heterotrophic
plate counts increased with the increase of the phosphorus concentration in water and biofilm
formation in experimental waters were limited by phosphorus. They decreased MAP
concentrations with coagulation below 1μg /L and found that it did not significantly reduce
biofilm formation. They doubted if chemical coagulation might reduce phosphorus effectively to
prevent bacterial regrowth and biofilm formation.
19
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
For RO systems, not only preventing bio-fouling but also preventing phosphate scaling in
RO systems is the reason for phosphorus limitation (Vrouwenvelder et al., 2010). Phosphate
scaling was found as the main problem of RO systems when treating effluent water by Katz and
Dosoretz (2008).
Vrouwenvelder et al. (2010) reported that low phosphate conditions (below 0.3μg /L) in
the feed water could prevent pressure drop increase of RO systems and biomass accumulation,
even at high substrate (organic carbon) concentrations. In addition, they found that it should
be considered that antiscalants might increase the phosphate concentration in RO systems.
With the results of literatures, this thesis expects to achieve below 1μg /L phosphorus in
effluent water of CTUF.
3.3 Phosphorus removal methods
There are three main strategies for phosphorus removal: Chemical phosphorus removal,
enhanced biological phosphorus removal and phosphorus removal by nanofiltration membrane.
3.3.1 Conventional chemical treatment for phosphorus removal
Coagulation/flocculation and sedimentation are conventional processes in the drinking
water plant and wastewater tertiary treatment. Coagulation is the process which makes that
the suspended particles become flocs in order to improve the particle separation. The common
coagulants are FeCl3, Al2(SO4)3, PACl (Polymeric Aluminum Chloride), PFS (Polymeric Ferric
Sulfate), PAC (Polymeric Aluminum Chloride) .
The main chemical reaction between coagulants and phosphate are (Tran et al., 2012):
3Fe 2  2PO43  Fe3 ( PO4 ) 2
Fe3  PO43  FePO4
Al 3  PO43  AlPO4
The produced precipitates are able to settle so that part of the phosphorus can be
removed.
Different coagulants bring different results. Wang et al. (2011) found that PFS gives the
best result for phosphorus removal (78.99%) compared to PAC (polymeric aluminum chloride),
PAFSI (polymeric aluminum ferric) and PAFC (polyaluminium ferric chloride). The feed water
was a village sewage treatment plant effluent with a TP around 4.7 mg/l and after coagulation
20
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
the phosphorus concentration could reach 0.98 mg/l. Li et al. (2012) found that PSAF
(polymeric aluminum ferric) gives the best results in their experiments compared to PAC
(polymeric aluminum chloride) and PFS (polymericferric sulfate). The feed water was from the
secondary settling tank of a sewage treatment plant with a TP of 1.09 mg/l. The phosphorus
removal rate by coagulation with PSAF, PFS and PAC were respectively 67.32%, 64.15% and
62.64%. The phosphorus in effluent was reduced to a level below 0.5mg/l. In drinking water
treatment, coagulation also removes TP. Jiang et al. (2012) investigated a drinking water plant
with a TP of 65.36μg/l in feed water. After coagulation, 77.1% of the TP was removed and after
filtration, another 12.4% of TP was removed. TP in the effluent water reached a value of
6.87μg/l. Paar et al. (2011) used in-line coagulation and an ultra-filtration membrane with FeCl3
as a coagulant and removed approximately 87% of the orthophosphorus until levels below
30μg P04-P/l. In the above mentioned in-line system, coagulation contributed more to removal
rate of the phosphorus than the UF. The UF only removed the part of the phosphorus which was
in the colloidal form (Zheng et al., 2012).
Different operational parameters also affect the coagulation efficiency. Li et al. (2012)
found that a higher removal rate of phosphorus was achieved in weak acidic conditions with
PAC and in neutral or slightly alkaline condition with PFS. Wang et al. (2011) concluded through
their experiments that the effect order of factors influencing coagulation was: mixing time >
pH > stir intensity > coagulant dosage.
3.3.2 Enhanced biological treatment for phosphorus removal
Enhanced biological phosphorus removal (EBPR) is usually used in wastewater treatment,
in which the total phosphorus concentrations in the influent for many domestic wastewater
plants are in the range 10-15mg/l (Blackall et al., 2002).
Figure 3.1: Enhanced biological phosphorus schematic diagram
21
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Figure 3.1 shows the order of enhanced biological phosphorus removal. Xu et al. (2011)
summarized its mechanism. The metabolism of poly-phosphate accumulating organisms (PAOs)
is used to change the phosphorus in liquid (wastewater) to solid (sludge). At first, in anaerobic
conditions, the PAOs decompose its Poly-P and create ATP. PAOs will use the ATP to adsorb
volatile fatty acids (VFAs) in water and store as Poly-β-hydroxyalkanoates (PHAs) in the
bacterial body. Then aerobic conditions are needed. PAOs will decompose the stored PHAs to
be a carbon source and energy source for aerobic activities and use ATP to adsorb phosphate as
well as other nutrients in water. Therefore, the phosphorus will be in the sludge after the
aerobic condition. It will be removed by sludge removal.
Blackall et al. (2002) reported that the EBPR processes could reduce the TP concentration
in the effluent until 0.1-0.2 mg/l. Lu et al. (2006) used high concentrations of PAOs (90%) to
obtain a phosphorus removal of almost 100%. You et al. (2008) also used high concentrations
of PAOs (>80%) and obtained >98% removal of phosphorus. However, the removal results are
not sTable (Hartley and Sickerdick, 1994). One of the key reasons for the unsTable results is the
presence of glycogen accumulating organisms (GAOs), which also grow in anaerobic/aerobic
conditions and fight with PAOs for carbon sources. However, GAOs do not adsorb/release
phosphorus (Xu et al., 2011).
EBPR systems always work under strict anaerobic/aerobic alternating environment.
However, Ahn et al. (2007) found that PAOs also remove phosphorus to a low concentration
during continuous aerobic conditions with the injection of additional organic matters and
phosphorus, Compared with under anaerobic/aerobic conditions, it needs extra organic matters
and phosphorus injection under aerobic condtions. Oehmen et al. (2007) elaborated that
denitrifying PAOs (DPAOs) become of interest for phosphorous removal. DPAOs can adsorb
phosphorus and denitrify at the same time so they need less the carbon sources and aeration
time, which decrease the sludge production and save the operational costs.
3.3.3 Ultra-filtration/ Nano-filtration membranes for phosphorus
removal
Nano-filtration membranes are studied for phosphorus removal. At first, Vrijenhoeke et al.
(2000) put forward a definition: ―loose‖ nano-filtration membrane. They used such membranes
to remove arsenic.
Phosphorus is in the same column of the periodic system as arsenic. Therefore in these
years, many researches were performed on phosphorus removal with loose NF membranes.
22
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
More than 95% of the phosphate can be removed using NF90 membranes (Hong et al., 2009).
NF90 has the best result in low pH (Chai et al., 2011). Some experiments compare model water
with real wastewater. HL membranes can remove 69.7% of the 25mg/l P2O5 dissolved in
demi-water, while in real wastewater, which also includes 25mg/l P2O5, can remove 88.8% of
the phosphorus (Dolar et al., 2011) at a pH of 5.4.
The Efficiency of phosphorus removal by membranes depends on the membrane
properties such as membrane charge and membrane pore radius (Tsuru et al., 1991). A smaller
pore size membrane will have ea better ability to retain ionic species (Bowen et al., 1997).
Some experiments show that membranes with larger pore sizes (such as DK5 and MPF34)
cannot get good phosphorus removal results in the higher concentration range of phosphorus
in feed water while NF270, NF200 performed well Chai, et al., 2011). . A highly charged
membrane is summarized to have a better ability to exclude co-ions from the membrane
surface (Bowen et al., 1996). The best pH in feed water is also different for different
membranes. The best pH for the best efficiency is lower than 2 for MPF34 membranes
(Niewersch et al., 2008) and is 4 for DK5, DL and NF270 (Niewersch et al., 2010).
Other experiments prove that larger permeate fluxes, which means a higher operating
pressure, will improve the ion rejection of NF membranes. Different ions in the feed water also
affect the phosphorus removal efficiency. Additional acetic acid decreases the phosphorus
removal while additional sulfuric acid improves it (Chai et al., 2011).
This thesis focuses on membranes of which pore sizes are a little larger than ―loose‖
nano-filtration membranes and they are called tight ultra-filtration membranes. The effect of
these membranes on phosphorus removal will be measured and discussed in the following
chapters.
23
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
4. Theory of factors affecting phosphorus rejection
by tight ceramic UF membrane
UF membranes are in between MF membranes and NF membranes with pore size from
1nm to 0.1μm. The so-called molecular weight cut-off (MWCO) can also be used as an
indication for the ability of membranes to reject compounds. MWCO is defined as the molecular
weight of spherical molecules which are 90% rejected by the membrane’s pores. The unit of
MWCO is Dalton (1 Dalton is the mass of one hydrogen atom = 1.66x10-27kg).
Many researches have focused on the role of several important factors which influence the
removal efficiency of phosphorus, such as water chemistry (pH, foulant concentrations),
membrane properties (pore size, hydrophilicity and charge) and hydrodynamic conditions (TMP,
flux and cross-flow velocity) (Huang et al., 2012). Some key factors will be discussed in the
following section.
4.1 Factors affecting rejection efficiency of membrane
filtration
Pore size: The pore size determines the removal of different compounds by the sieving
effect. Membranes with smaller pore sizes reject more particles or ions but also have a higher
risk of membrane fouling. The Pore size also affects the Surface Charge Exclusion effect,
because a larger pore size leads to a weaker charge intensity in the pores. Therefore, the
elimination of ions by surface charge becomes lower. Chai et al. (2011) used five membranes
with different pore sizes to remove phosphorus: NF90 (MWCO 100Da), NF270 (MWCO 155Da),
NF200 (MWCO 200Da), DK5 (MWCO 150-300Da), MPF34 (MWCO 300Da). They found that the
membrane of the smallest pore size, NF90, always gave the best removal rate while DK5 and
MPF34 performed worse.
Cross flow velocity: Concentration polarization is the accumulation of excess
particles/ions in a thin layer adjacent to the membrane surface. It leads to high concentrations
of ions at the feed side of the membrane. Therefore, concentration polarization decreases the
rejection rate. A proper cross flow velocity can reduce the concentration polarization formed by
ions and organic matter and also can reduce membrane fouling. Chang et al. (2012) observed
24
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
rejections of resorcinol, acetaminophen, glucose, triclosan and sucrose under various
cross-flow velocities by NF270. They found that the rejection increased as the cross-flow
velocity increased under a constant flux (See Figure 4.1).
Figure 4.1: Influence of cross-flow velocity on NF rejection (Chang et al., 2012)
Flux: Flux is defined as the water flow through a squaremeter of membrane surface.
J
Q TMP

A  * Rtot
Where,
J,
flux (m3/(m2.s))
Q,
volume flow (m3/h)
A,
membrane surface area (m2)
TMP, trans membrane pressure (Pa)
ν,
dynamic viscosity (Pa*s)
Rtot, total resistance (m)
25
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Figure 4.2: Schematic of water and ions passing membranes
Figure 4.2 shows how flux affects the removal rate of ions by a membrane. Most of the ions
are rejected by the membrane on the feed water side. During the filtration, the ions diffuse into
the permeate side. At the same time, water is crossing the membrane at a constant flux. The
ion diffusion rate is constant, which depends on the concentration gradient and temperature. In
contrast, the larger flux allows more water to permeate through the membrane. Therefore, a
higher flux leads to a better rejection of ions. Kumar et al. (2011) observed that a larger TMP
(larger flux) leads to larger rejections of the target compound which was cyanide with all the
tested membranes, NF-1, NF-2, NF-3 and NF-20 under the following operational conditions: pH
10, flow rate 700l/h, and temperature 35°C. They also reported the connection between flux
and cross flow. Larger cross flows could result in larger fluxes and larger rejections of cyanide.
Effect of pH: The effect of pH on rejection is related to the feed water ions. For cations
such as Fe3+, Cr3+, Badawy et al. (2011) used a ceramic membrane with 1kDa MWCO and got
47% rejection of Fe3+ at pH 2 and 36% rejection of Cr3+ at pH 3.7. As the pH increased to 2.96
and 5.7 respectively, Fe3+ and Cr3+rejections increased to 98.77% and 95.55%. In weak
alkaline conditions, the removal rates of the two cations reached 99%. They explained that a
higher pH would cause the formation of a cake layer of metal hydroxides and precipitates of
metal hydroxides. For anions, pH also has effects. Vrijenhoek et al. (2000) used loose
nanofiltration membrane NF-45 to remove AsO43-. At pH 4.5, the rejection was 25%, an
increased pH also increased the rejection rate. At pH 8.3, the rejection rate became 80%. Their
experimental conditions were: flux 8μm/s, cross flow 20.4cm/s, and temperature 25°C.
That ,more anions can be removed in weak alkaline conditions can be explained by the fact that
26
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
membranes have a negative charge so the zeta potential of the membrane becomes more
negative, which the result that charge exclusion plays a more important role in rejection . In
addition, the As (V) changes from monovalent (H2AsO4-) to divalent (HAsO42-) with the increase
in pH. Monovalent ions are rejected by the NF-45 membrane at a much lower rate compared to
divalent ions, due to the smaller hydrated radii of the monovalent ions compared to divalent
ions, as well as stronger exclusion.
Factors affecting the membrane surface charge: Besides pH, the surface charge of
the membrane can be affected by inorganic ions (SO42-, Ca2+, Na+, Cl-, etc.) and organic matter
(such as NOM, EPS, humic acids). Surface charge exclusion is one of the key hypotheses to the
removal of small size ions with large pore size membranes.
Figure 4.3: Hypothesis of charge exclusion
Figure 4.3 shows that, if the membrane is negative, it will exclude the negative ions and
then the excluded ions will take the positive ions with the Donnan theory, and the cross flow will
flush them to the concentrate.
Other ions also affect the target compound removal. Many rejection studies have
concluded that the rejection rate of a monovalent anion, such as Cl- , is reduced while
increasing the concentration of a multivalent anion, such as SO42- (Mohammad et al., 2007, Chai
et al., 2011).
4.2 Theory of double layer
A double layer (DL, also called an electrical double layer, EDL) is a structure that appears
on the surface of an object when it is placed into a liquid (Wikipedia A). Figure 4.5 shows the
detailed illustration of the interfacial double layer.
27
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Figure 4.4: Detailed illustration of interfacial DL (Wikipedia B)
The Figure assumes that there is a positive charged surface and its first layer (stern layer)
comprises of anions due to electrical attraction. The second layer is called the diffuse layer. It
begins to have some cations in the diffuse layer. The diffuse layer is associated with the object
loosely. Its free ions could move to the liquid, which is not likely for the firmly anchored anions
in the stern layer. Double layer is composed of stern layer and diffuse layer.
The boundary of the diffuse layer with bulk of the liquid is called the slipping plane and the
electric potential at the plane is the zeta potential (ζ-potential).
Inorganic ions always get a double layer on the membrane surface. If the membrane is
negative, the double layer is positive and vice versa. The negative ions hardly appear in the
double layer. Therefore, if the double layer can fill in the membrane pores, the negative ions will
be well removed due to exclusion. A higher ionic strength makes the thickness of the double
layer thinner. Therefore the negative ions will have more chances to pass the membrane. .
The thickness of the double layer is named the Debye length. Li et al. (2011) mentioned an
equation for the thickness.
1000 N Ae 2

2I
 0 r K B T
28
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Where,
κ,
inverse Debye length (κ-1 means DL thickness);
NA, Avogadro number (6.0*1023 mol-1);
I,
ionic strength (mol/L);
e,
elementary charge (1.60*10-19 C)
εo, vacuum permittivity (8.85*10-12 CV-1m-1);
εr, relative permittivity of the background solution (80 for water);
KB, Boltzmann constant (1.38*10-23 J/K);
T,
absolute temperature (K)
From the equation, the only unknown factor is the ionic strength, which can be calculated
by the next equation and the corresponding κ can be determined (Li et al., 2011).
Equation for ionic strength is,
I
1 n
 ci zi2
2 i 1
Where,
ci, molar concentration of ion I (mol/L);
zi, the charge number of that ion.
Increasing the concentration or valence of the counter ions compresses the double layer
and increases the electrical potential gradient (Wikipedia C).
The two equations will be used to calculate the thickness of the double layer for the
membrane and focus on its exclusion results in this thesis. The connection between the
phosphorus removal rate and DL thickness and the connection between the phosphorus
removal rate and ionic strength will be pointed out.
4.3 Theory of zeta potential
The electric potential at the membrane surface is not easy to measure directly but the
electric potential at the hydrodynamic plane of shear, which is called the zeta potential
(ζ-potential) can be determined from streaming potential measurements (Fievet et al., 2003).
Though zeta potential is different from surface potential, it is an important and reliable indicator
29
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
for the membrane surface charge (Fievet et al., 2003). Tkachenko et al. (2006) summarized
that the zeta potential is the electric potential in the interfacial double layer (DL) at the location
of the slipping plane versus a point in the bulk fluid away from the interface. A higher positive or
negative potential leads to better charge exclusion for the interacting ions. They did the
experiments for the effects of pH on the zeta potential of membranes. The pH affects the
membrane surface charge directly with the neutralization reaction. Figure 4.4 shows how the
zeta potential is affected by pH.
Figure 4.5: Dependency of zeta potential of TiO2 suspensions upon pH suspensions at various
concentrations of different KCl , mol/l (Tkachenko et al. (2006)): ▲ 1*10-5; ◆ 1*10-4; ■
1*10-3; ● 1*10-2
This membrane has the most positive (40mV) zeta potential in acid conditions at around
pH 2 and in alkaline conditions the membrane has a zeta potential of -60mV at around pH 10.
However, a lower pH or higher pH does not lead automatically to a higher positive or a more
negative zeta potential. From Figure 4.4, it is shown that pH 12 will have a lower zeta potential
than at pH 10.
Organic matter also affects the zeta-potential due to fouling. Natural organic matter (NOM)
is a complex matrix of organic compounds (Song et al., 2012). NOM is known to be detrimental
to membrane filtration via adsorption in/on the membrane pores or surfaces, pore blocking,
and gel layer formation (Gao et al., 2012). NOM also interacts with other components in natural
water such as inorganic particles and forms a compact layer that exacerbates fouling (Kim et al.,
2007).
30
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Figure 4.6: Zeta potential of new and fouled membrane at different pH values (measured with
1 mmol/l KCl electrolyte solution) (Li, 2011)
Li (2011) found that fouled membranes have a lower zeta potential than new membranes
at the same pH. He measured that membranes fouled with NOM had a Zeta potential of
-12.5mV (at pH 8 and an electrical conductivity of 960 μs/cm), while the zeta potential of a new
membrane at the same conditions was between -15 and -16 mV (Figure 4.6).
Some researchers investigated the effects of zeta potential on membrane removal rates.
Verliefde et al. (2008) did the experiments with the membranes Trisep TS80 TSF and Desal HL
to remove organic acid at pH 5 and pH 8. At first they concluded that the zeta potential of these
two membranes were higher at pH 8 compared to pH 5. Then they found that all the target
organic acids could be removed better at pH 8 than at pH 5. One of the key reasons for the
results they concluded was the lower membrane surface charge (lower zeta-potential) at pH 5
so charge exclusion was weaker.
31
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
5. Materials and methods
5.1 membranes
Two commercial membranes (Brand: TAMI) were selected: tight ultra-filtration membranes
made of TiO2, of which the MWCO are 1kD and 3KD (Table 5.1).
Table 5.1: Membrane parameters
Water Flux
MWCO
Material
l/(h.m².bar)
Surface
area m2
pH
Temperature
range
(max) °C
Configuration
1 kDa
TiO2
30
0,013
Inside-Out
0-14
350
3 kDa
TiO2
30
0,013
Inside-Out
0-14
350
Figure 5.1: Experimental membrane
5.2 Experiments planning
The following steps were taken during the experiments:
A. With different fluxes (25.3, 50.8 and 62.3 l/(m2*h) ) and a constant cross flow velocity
2m/s through the membrane, find the effects of flux on the removal efficiency for the two
different membranes. Feed water was 50L demi-water with 1mg/L PO4-P (NaH2PO4). The
concentration of PO4-P in the feed water and the permeate was measured every half an
hour as well as electrical conductivity, pH value and temperature. The concentration of
phosphate in feed water was kept as 1mg/L.
32
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
B. With different cross flow (0.5m/s, 1m/s, 2m/s) velocities and a constant flux 50.8 l/(m2*h)
of the membrane, find the effects of cross flow velocity on the removal efficiency for the
two different membranes.Feed water was 50L demi-water with 1mg/L PO4-P. The
concentration of PO4-P in the feed water and the permeate was measured every half an
hour as well as electrical conductivity, pH value and temperature. The concentration of
phosphate in feed water was kept as 1mg/L.
Table 5.2: flux and cross flow settings
flux(l/(m2*h))
cross flow(m/s)
Setting 1
50.8
2
Setting 2
62.3
2
Setting 3
25.3
2
Setting 4
50.8
1
Setting 5
50.8
0.5
C. With different concentrations of phosphate in the demi-water and a constant cross flow
velocity 2m/s as well as a constant flux 50.8 l/(m2*h), find the effects of the phosphate
concentration on the removal efficiency for the two different membranes. Feed water was
50L demi-water with 0.5mg/L PO4-P, 1mg/L PO4-P, 1.5mg/L PO4-P. The concentration of
PO4-P in the feed water and the permeate was measured every half an hour as well as
electrical conductivity, pH value and temperature.
Table 5.3: Phosphorus concentration settings
flux(l/(m2*h)
cross flow(m/s)
pore size(kD)
phosphorus concentration(mg/l)
setting 1
50.8
2
1
0.5
setting 2
50.8
2
1
1
setting 3
50.8
2
1
1.5
setting 4
50.8
2
3
0.5
setting 5
50.8
2
3
1
setting 6
50.8
2
3
1.5
D. Choose a certain, optimal, flux (50.8l/(m2*h)), cross-flow velocity (2m/s) and phosphorus
concentration (1mg/L) in the feed water with the results of B,C,D. Add ions in the feed
water and see the effects on the phosphorus removal with the ions. Different
33
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
concentrations of NaCl were dosed. Feed water was 50L demi-water with 1mg/L PO4-P with
NaCl (0.5mmol/L, 1 mmol/L, 1.5 mmol/L and 6mmol/L). The concentration of PO4-P in
the feed water and permeate were measured every half an hour as well as electrical
conductivity, pH value and temperature.
E. With flux 50.8l/(m2*h), cross-flow velocity 2m/s, phosphorus concentration 1mg/L and
1.5mmol/L Na2SO4 in 50L feed water, find effects of SO42- on the phosphorus removal. Feed
water was also 50L and the concentration of PO4-P in the feed water and the permeate was
measured every half an hour as well as electrical conductivity, pH value and temperature.
F. Then adjust the feed water pH (6, 7.5, 8.5, and 9.5) in a constant concentration of
phosphate (1.5mg/L). 6mmol/L NaCl was dosed to feed water in order to simulate the true
Na+ concentration in the real effluent of the wastewater plant. Feed water was 10L and
nitrogen was aerated in the feed water tank during the experiment.
G. Measure zeta potential of the two membranes in the solution of NaCl, Na2SO4 and NaH2P04.
5.3 Experimental set-up
Figure 5.2: Experimental set up
Figure 5.2 is the schematic diagram of the experimental set-up. The feed water tanks are
100L and 10L. The feed water of steps A-E used the 100L tank and was filled with 50L. The step
F used the 10L tank and during the experiments it was aerated with nitrogen in order to avoid
CO2 dissolving in water and changes in the pH of the feed water. Before the membrane there is
a pressure meter as well as after the membrane. Permeate and concentrate both have valves to
control the flow. A flow meter in the range of 0m3/s- 300m3/s was installed after the CTUF
membrane. Both the concentrate and permeate recycled to the feed water tank. There were
34
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
two sampling points for the feed water and the permeate water respectively.
5.4 Measurements
Phosphorus was measured using the equipment Phosphate Cell Test made by
Spectroquant. The equipment was used to measure total phosphate and orthophosphate, but
here only orthophosphate was measured. In a sulfuric solution orthophosphate ions react with
molybdate
ions
to
form
molybdophosphoric
acid.
Ascorbic
acid
reduces
this
to
phosphomolybedenum blue (PMB) that is determined photometrically. The measuring range is
in Table 5.5. Samples must be decomposed by digestion before total phosphate can be
measured. The tests must be at 15°C to 25°C and in the pH range of 0-10.
Table 5.4: Measuring range
Measuring range
0.05-5.00 mg/l PO4-P
0.2-15.3 mg/l PO43dw0.11-11.46 mg/l P205
The flux was measured by a simple volumetric experiment. 1 minute permeate flow
volume Q was measured. With the equation J= Q/A, where A is the membrane surface area
0.0013m2, the flux J was calculated. Flux was measured every half an hour to make sure the
flux was constant.
The Zeta potential was measured by SurPPAS, which is from Anton Paar Company. The
equipment measures the streaming potential coefficient (SPC) of the target membrane surface.
The Zeta potential was calculated with the following equation.The streaming potential
coefficient is the left of the equation Δφ/ΔP. Δφ and ΔP were measured by electrodes and
pressure meters installed at both ends of the target surface. Other parameters were constant
so the zeta-potential could be calculated. Due to the size requirement of the SurPPAS
equipment for the membrane, in this thesis, the zeta potential was measured on a flat
membrane (10.04mm width and 20.03mm length) with the same membrane parameters and
the same manufacturer (both 1kD and 3kD membranes had their substitutes respectively).
35
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
  0 r

P EC
Where,
Δφ, measured potential difference along membrane surface (V);
ΔP, respective measured pressure difference along membrane surface (Pa);
ξ, zeta potential of the measure surface (V);
εo, vacuum permittivity (8.85*10-12 CV-1m-1);
εr,
relative permittivity of the background solution (80 for water);
η,
the dynamic viscosity of the solution (Pa*s);
EC,
conductivity of solution (S*m-1)
36
Zheyi Zeng
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
6. Results and discussions
6.1 Flux and cross flow velocity effects
The feed water is demi-water with P-P04 (NaH2P04) 1mg/l. Only 1kD membrane was used.
The cross flow velocity was kept constant (2m/s) and the flux was increased (25.3l/(m2*h),
50.8l/(m2*h) and 62.3l/(m2*h)). The results are given in Figure 6.1.1.
Effects of different flux on phosphorus removal
50.00%
Removal
40.00%
30.00%
20.00%
10.00%
0.00%
0
10
20
30
40
50
60
70
2
Flux(l/(m *h))
Figure 6.1.1: Phosphorus removal of different fluxes
The detailed data are shown in Table 1 in Appendix. It shows that the higher flux had a
higher phosphorus removal. A Flux of 25.3 l/(m2*h) gave a removal of 38.3% and a flux of
62.3 l/(m2*h) had a removal of 46.6%. The removal rate had a more or less linear increase
with the flux increase, which is in agreement with the diffusion effect theory (see Figure 4.2).
Due to the concentration polarization around the membrane pores, some phosphate ions are
diffused to the permeate. If there is a higher flux, which means more demi-water goes to
permeate, the concentration of phosphate in the permeate will be lower. Therefore, the
removal rate of the phosphate will be higher.
In the following experiment the feed water was demi-water with P-P04(NaH2P04) 1mg/l.
Only 1kD membrane was used. The flux was kept constant at 50.8 l/(m2*h), and the cross flow
velocity was increased (0.5m/s, 1m/s and 2m/s). The results are represented in Figure 6.1.2.
37
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Phosphorus removal of different cross flow
50.00%
Removal
40.00%
30.00%
20.00%
10.00%
0.00%
0
0.5
1
1.5
2
2.5
Cross flow(m/s)
Figure 6.1.2: Phosphorus removal of different cross flow velocities
The detailed data are shown in Table 2 in Appendix. It can be concluded that the higher the
cross flow velocity was the higher phosphorus removal. A cross flow velocity of 0.5m/s had a
removal of 31.4%. A cross flow velocity of 1 m/s had a removal of 43.3%. A cross flow
velocity of 2m/s had a removal of 44.1%. The results were expected. A high cross flow velocity
could flush the phosphate on the membrane surface to concentrate hence reduce the
concentration polarization around the membrane surface, which increases the phosphate
removal rate. The removal rate curve has a larger increase slope between cross flow velocity
0.5m/s and cross flow velocity 1m/s compared to the increase slope between cross flow velocity
1m/s and cross flow velocity 2m/s. A speculation is that after a certain critical cross flow
velocity A (>2m/s), the increase of the cross flow velocity will not increase the phosphate
removal rate.
The concentration polarization factor β could be used to explain the connection between
concentration polarization and cross flow velocity. The β value indicates how much extra
phosphorus is near the membrane surface. For instance a β value of 1.2, 1.1 and 1.05 results in
respectively an extra 20%, 10% and 5% concentration increase near the membrane surface.
The factor decreases at higher cross flow velocities. Smaller extra concentration of phosphorus
near the membrane surface leads to less phosphorus to be diffused into the permeate, which
means a larger removal rate. Therefore, an increase in cross flow will result in a better removal
rate of phosphorus. Going to higher cross flows will have a smaller effect (smaller β) on the
concentration decrease near the membrane surface and will result in only little increase in
removal rates. Hence, Figure 6.1.2 shows an obvious increase of phosphorus removal rate from
cross flow velocity 0.5m/s to 1m/s and becomes a smooth curve from cross flow velocity 1m/s
38
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
to 2m/s.
The type of water flow regime along the membrane can be evaluated with the Reynolds
number.
Re 
vDH

Where,
Q,
volumetric flow rate (m3/s), here is 216 l/h.
v,
mean velocity of object relative to the fluid (m/s).
DH,
hydraulic diameter of pipe. For a round tube, DH=D=2mm
ν,
kinematic viscosity (m2/s), here is 10-6 m2/s.
Laminar flow occurs when Re<2300 and turbulent flow occurs when Re>4000. In the range
of 2300 to 4000, laminar and turbulent flows are possible and are called "transition" flows.
If Re=2300, with the equation, v=1.15 m/s
If Re=4000, with the equation, v=2 m/s.
Therefore, if cross flow velocity is below 1.15m/s, the water has a laminar flow. If cross
flow velocity is in the range of 1.15m/s to 2m/s, the water is in the transition flow regime. If
cross flow velocity is above 2m/s, the water is turbulent. With the results and water flow
regimes, it can be inferred that an increase in turbulence of the cross flow could increase the
phosphorus removal rate. However, the relationship between β value and turbulence of the
cross flow is not clear yet.
6.2 The effect of phosphorus concentration in the feed
water
During the third experiment the feed water was demi-water with P-P04 (NaH2P04) in
0.5mg/l, 1mg/l and 1.5mg/l. Both a 1kD membrane and a 3kD membrane were tested. The flux
was kept constant at 50.8 l/(m2*h) with a cross flow velocity of 2m/s. Figure 6.2.1 shows the
results.
39
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Phosphorus removal rate in different phosphorus concentration
of 3kD and 1kD membranes
50.00%
removal rate of PP04 with different
phosphate
concentration for
3kD membrane
Removal
40.00%
30.00%
removal rate of PP04 with different
phosphate
concentration for
1kD membrane
20.00%
10.00%
0.00%
0
0.5
1
1.5
2
Concentration(mg/l)
Figure 6.2.1: phosphorus removal rate in different phosphorus concentration of 3kD membrane
and 1kD membrane (Error bar represents standard deviation, sample number: 3)
The detailed data are shown in Table 3 and Table 4 in Appendix. From Figure 6.2.1 it is
found that the removal rate of phosphorus for both membranes had a small increase when the
phosphorus concentration in the feed water changed from 0.5 mg/l to 1 mg/l. The removal
rates were almost the same when the phosphorus concentration in the feed water changed
from 1 mg/l to 1.5 mg/l. For the 1kD membrane, a Cp (concentration of phosphate) of 1 mg/l
gave a removal of 43.3% and a Cp of 1.5 mg/l gave a removal of 40.8%. For 3kD membrane, a
Cp of 1 mg/l gave a removal of 43.1% and a Cp of 1.5 mg/l gave a removal of 42.8%. The error
bars in the Figures show errors of 3%~4%. The removal rates are considered to be
approximately the same. In the double layer theory, a stronger ionic strength gives a thinner
double layer thickness so the exclusion effect should be weaker, which is different from the
results (shown in Figure 6.2.1) for both two membranes. One explanation is that the possible
double layer thicknesses in the three different ionic strengths are much larger than the
membrane pore sizes. Therefore, the exclusion effects are almost the same for the three
different ionic strengths and the phosphate removal rates therefore were almost the same.
Figure 6.2.1 also shows that the 3kD membrane had a better ability for phosphorus
removal than the 1kD membrane. The result is interesting because the 3kD membrane has a
larger pore size than the 1kD membrane, which means that the phosphorus should have had
more opportunity to pass the membrane pores in the 3kD membrane. However, the result was
opposite and the 3kD membrane had a lower phosphorus concentration in the permeate water.
This implies that the inorganic phosphorus removal was not affected by the sieving effect, but
40
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
highly probably by the charge of the membrane and double layer exclusion. One possibility is
that the 3kD membrane has a larger zeta potential than the 1kD membrane in the phosphate
solution. Therefore, the zeta potentials of the 3kD membrane and 1kD membrane were
measured with the same phosphate concentration solutions.
6.3 Ions effects to phosphorus removal
In the forth experiment the feed water was demi-water with P-P04 (NaH2P04) 1mg/l with
different NaCl concentrations: 0.5mmol/l, 1mmol/l, 1.5mmol/l and 6mmol/l, where 6mmol/l
was close to the real waste water NaCl concentration. Both the 1kD and the 3kD membranes
were used.
In the fifth experiment the feed water was demi-water with P-P04 (NaH2P04) 1mg/l and
Na2SO4 concentration: 1.5mmol/l. Both 1kD and 3kD membranes were used.
The results are shown in Figure 6.3.1.
Phosphorus removal rate in different concentrations of NaCl or Na 2SO4 for 1kD membrane and 3kD
membrane
1kD membrane
50.00%
3kD membrane
45.00%
40.00%
Removal
35.00%
30.00%
25.00%
20.00%
15.00%
10.00%
5.00%
0.00%
1
2
3
4
5
NaCl and Na 2SO4 Concentration (type 1:0.5mmol/l NaCl; type 2: 1mmol/l NaCl; type 3: 1.5mmol/l
NaCl; type 4: 6mmol/l NaCl; type 5: 1.5mmol/l Na 2SO4 )
Figure 6.3.1: Removal rate of phosphate with different NaCl concentrations or Na2SO4 for 1kD
and 3kD membranes
The detailed data are shown in Table 5 to Table 8 in Appendix. From Figure 6.3.1, it can be
concluded that with an increasing NaCl concentration, the phosphate removal by the 1kD
membrane had a little decrease, while for the 3kD membrane, the top removal was at 1mmol/l
NaCl while at 6 mmol/l NaCl, the removal of phosphorus was the lowest. The Figure also shows
that, no matter what concentration of NaCl was injected into feed water, the 3kD membrane
always had a better performance in phosphate removal than the 1kD membrane. Without NaCl
dosing and 1mmol /l phosphate, the average removal of phosphate was 40.3% for the 1kD
41
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
membrane, and 43.7% for the 3kD membrane. All the removals with NaCl dosing were lower
than without NaCl except for with the 1mmol/l NaCl with the 3kD membrane. Therefore, the
results for this setting might have an error. With the NaCl dosing of 0.5mmol/l, 1mmol/l and
1.5mmol/l, the phosphate removal rates were considered to be almost the same for both
membranes, but with the NaCl dosing of 6mmol/l the removal rates decreased obviously. Two
speculations are that a) the zeta potential of the 3kD membrane is still larger than the 1kD
membrane in the solution with phosphate and NaCl at different concentrations; b) The double
layer thickness in 6mmol/l NaCl solution became thinner than the membrane pore size so the
exclusion effect of double layer decreased considerably.
Figure 6.3.1 shows that Na2SO4 had a larger effect on phosphate removal than NaCl. The
removal rate for the 1kD membrane decreased to 24.2% and the removal rate for the 3kD
membrane decreased to 32.4%. The 3kD membrane performed better again than the 1kD
membrane. The is postulated that, again, the zeta potential of the 3kD membrane is larger than
the 1kD membrane in the solution with phosphate and Na2SO4 .
Na2SO4 has more influences on phosphorus removal rate than NaCl. A speculation is that
the surface charges of the membranes in the NaCl are stronger than in Na2SO4 solutions and
the zeta potentials of two membranes in the two solutions were therefore measured in the last
experimental step. Another explanation could be that the ionic strength in the Na2SO4 solution
increased, the thickness of the double layer would therefore be thinner, which decreased the
exclusion forces.
With the two equations mentioned in chapter 4, all ionic strengths and double layer
thicknesses were calculated in Table 6.1.
Table 6.1: Ionic strength, double layer thickness and phosphate removal of different settings
Concentration(mmol/l)
Ionic
Thickness(m
strength(mol/L)
)
Phosphate(NaH2PO
NaC
Na2SO
4)
l
4
0.016
0
0
0.000016
7.59446E-08
0.032
0
0
0.000032
5.37009E-08
0.048
0
0
0.000048
4.38466E-08
42
Romoval rate(%)
1kD
3kD
34.59
39.62
%
%
40.25
43.07
%
%
40.84
42.79
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
0
0
0.032
0.000096
3.10043E-08
0.032
0
1.5
0.004532
4.51244E-09
0.032
0.5
0
0.000532
1.31705E-08
0.032
1
0
0.001032
9.45621E-09
0.032
1.5
0
0.001532
7.76117E-09
0.032
6
0
0.006032
3.91135E-09
%
%
24.21
32.41
%
%
38.41
42.14
%
%
37.94
44.09
%
%
37.28
42.75
%
%
36.20
39.49
%
%
With the ionic strength and double layer thickness data, the connection between the ionic
strength and the double layer thickness can be shown in Figure 6.3.2.
Effect of ionic strength on DL thickness
8.00E-08
Thickness (m)
7.00E-08
6.00E-08
5.00E-08
4.00E-08
3.00E-08
2.00E-08
1.00E-08
0.00E+00
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
Ionic strength (mol/l)
Figure 6.3.2: Effects of ionic strength on double layer thickness
The curve shows that the double layer thickness decreases as the ionic strength increases.
The thickness is large when the ionic strength is not so strong. Increasing ionic strength in a
small range could lead to a large thickness drop. When ionic strength increases to 1mmol/l, the
slope of double layer thickness comes almost zero.
The pore size of the 1kD membrane is 1-3nm and pore size of the 3kD membrane is 4-5nm.
The results prove that the speculation in chapter 6.2 is correct, the double layer thickness in
phosphate solution (0.5mg/l (0.016mmol/l), 76nm; 1mg/l (0.032mmol/l), 54nm; 1.5mg/l
(0.048mmol/l), 44nm) is much larger than pores size of the membranes. Therefore, the
43
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
exclusion effects were strong enough to have a sTable removal rate of phosphate as is shown in
the Figure 6.2.1.
Removal rate (%)
Effects of ionic strength on phosphate removal of 3kD
membrane in solution NaCl and Na 2SO4
50.00%
45.00%
40.00%
35.00%
30.00%
25.00%
20.00%
15.00%
10.00%
5.00%
0.00%
NaCl solution
Na2SO4 solution
0
0.002
0.004
0.006
0.008
Ionic strength (mol/l)
Figure 6.3.3: Effects of ionic strength on phosphate removal of 3kD membrane in solution NaCl
and Na2SO4
Removal rate (%)
Effects of ionic strength on phosphate removal of 1kD
membrane in solution NaCl and Na 2SO4
45.00%
40.00%
35.00%
30.00%
25.00%
20.00%
15.00%
10.00%
5.00%
0.00%
NaCl solution
Na2SO4 solution
0
0.002
0.004
0.006
0.008
Ionic strength (mol/l)
Figure 6.3.4: Effects of ionic strength on phosphate removal of 1kD membrane in solution NaCl
and Na2SO4
Figure 6.3.3 and 6.3.4 are based on Table 6.1 and show the effects of ionic strength on
phosphate removal for the 3kD and 1kD membranes in a solution of NaCl and Na2SO4. In the
NaCl solution, the phosphate removal rate had a little decrease as ionic strength increased.
From Table 6.1 it is shown that even with 6mmol/l NaCl and 0.032mol/l phosphate, the double
layer thickness (4nm) was still larger or almost the same compared to the membrane pore sizes,
so the exclusion effects were still enough. Therefore, the removal rates did not change so
44
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
much.
Figure 6.3.3 and 6.3.4 also show that in the same ionic strengths of the NaCl and Na2SO4
solutions, the removal rates of phosphate of the two membranes in solution Na2SO4 both
decreased around 15% than it in solution NaCl. One possible reason is zeta potential effect. The
zeta potential in the NaCl solution might be stronger than in Na2SO4 solution under the same
ionic strength. It will be discussed in chapter 6.5.
6.4. pH effects
Because CO2 is easy to dissolve in the feed water which can change the pH, the pH
experiments were done in a sealed 10L tank. During the experiments, nitrogen was aerated in
the tank to make sure that CO2 could not be dissolved. The flux and cross flow velocity were the
same as in the former experiments: 50.77l/(m2*h) and 2m/s respectively. 6mmol/l NaCl was
injected in order to simulate NaCl concentration in the effluent of a wastewater plant and to
buffer the ionic strength in feed water. pH was adjusted from 6- 9.5.
Phosphorus removal at differen pH value in 1kD membrane and 3kD membrane
100.00%
90.00%
80.00%
Removal
70.00%
60.00%
3kd
50.00%
1kd
40.00%
30.00%
20.00%
10.00%
0.00%
0
2
4
6
8
10
12
pH value
Figure 6.4.1: Removal rate of phosphate with 6 mmol/l NaCl at different pH for 1kD and 3kD
membranes
The detailed data are shown in Table 9 and Table 10 in Appendix. The two membranes
both acquired the lowest removal rates of phosphate at pH 6 (34.8% for the 1kD membrane;
and 40.2% for the 3kD membrane). With the pH increase, the removal rates increased and at
pH 8.3, the rates got to the top. The 3kD membrane could remove 86.9% of phosphate and the
1kD membrane could remove 77.9% of phosphate. After a pH of around 8.3, both of the
removal rates decreased. At all pH values, the 3kD membrane had a larger removal rate of
45
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
phosphate than the 1kD membrane.
Figure 6.4.2: Phosphoric acid speciation
Figure 6.4.2 shows that with increasing pH value, the phosphate species in water change
forms: H2PO4- to HPO42- and to PO43-. In relation to the double layer theory, more divalent ions
means that the ionic strength at high pH becomes stronger, which leads to a thinner double
layer thickness and a lower removal rate. However here the concentration of phosphorus was
extreme low compared to the concentration of NaCl. Therefore, the double layer thickness did
not change much even though the phosphorus charge increased. In contrast, multivalent ions
will be excluded more than monovalent ions, when the double layer thickness is the same so
the exclusion between double layer and phosphate increases and the removal rate increases.
Zeta potentials of membranes are used to explain Figure 6.4.1 and it will be discussed in
chapter 6.4.1.
6.5 Zeta potential
Results of zeta potentials of 1kD and 3kD membranes are shown in Figure 6.5.1 and 6.5.1.
The electrolytes used for measurements were respectively, (A) 1.5 mmol/L Na2SO4; (B) 1.5
mmol/L Na2SO4+0.0032 mmol/L NaH2PO4; (C) 4.5 mmol/L NaCl; (D) 4.5 mmol/L NaCl+0.0032
mmol/L NaH2PO4.
46
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Zeta potential of 1kD membrane with different electrolytes at different
pH value
0
zeta potential(mV)
-5 5
6
7
8
9
10
Na2SO4(1.5mmol/L)
-10
-15
-20
Na2SO4 (1.5mmol/L)+PPO4
-25
NaCl(4.5mmol/L)
-30
NaCl(4.5mmol/L)+P-P04
-35
-40
-45
pH value
Figure 6.5.1: Zeta potential of 1kD membrane with different electrolytes
Zeta potential of 3kD membrane with different electrolytes at different
pH value
pH value
-20
zeta potential(mV)
-25
5
6
7
8
9
10
Na2S04(1.5mmol/L)
-30
-35
Na2S04(1.5mmol/L)+PP04
-40
NaCl(4.5mmol/L)
-45
NaCl(4.5mmol/L)+P-P04
-50
-55
Figure 6.5.2: Zeta potential of 3kD membrane with different electrolytes
Original data are shown in Appendix table 11-18. All the zeta potentials in different
electrolytes for different membranes increased as pH increased. Figure 6.4.1 shows the
rejection rates of phosphorus increased from pH 5.8 to 8.3. Larger zeta potentials could be the
key reason to larger removal rate of phosphorus in this range of pH. The removal rate
decreased under higher pH (>8.3) but zeta potential not. Therefore, in this range, the removal
rates might be affected dominantly by other reasons.
The zeta potentials of 3kD membrane are larger than those of 1kD membrane, which is
expected. Under all same experimental conditions, the phosphate removal rates of 3kD
membrane were higher than phosphate removal rates of 1kD.
47
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
For 1kD membrane, zeta potential with electrolyte Na2SO4 (1.5mmol/L) was smaller than it
with electrolyte NaCl (4.5mmol/L). For 3kD, the result was converse that zeta potential with
electrolyte Na2SO4 was a little smaller than it with electrolyte NaCl. The results were not
expected because under the same ionic strength, phosphorus rejection rates with electrolyte
Na2SO4 were lower than them with electrolyte NaCl. The other reason to explain Figure 6.3.3
and 6.3.4 might be the competition between monovalent ions and divalent ions. As it
mentioned in chapter 4.1, Chloride rejection might be reduced by sulfate injection (Mohammad
et al., 2007). As (V) will have competition with carbonate and H2AsO4- rejection (use loose
nanofiltration) rate also could be reduced when CO32- is the feed water (Vrijenhoek et al., 2000).
Therefore, SO42- might compete with H2P04- and cause smaller rejection rate of phosphorus.
Another phenomenon was found from the zeta potentials results that zeta potentials of
two membranes became stronger when additional phosphorus was injected in the electrolytes,
with both the electrolyte of NaCl and of Na2SO4. One possible reason is adsorption of
phosphorus onto TiO2 might contributed to the enhanced zeta potential.
Guo J.Liu et al. (2008) did experiments with As(V) adsorption onto a commercially
available TiO2 (Degussa P25). They concluded three important things. First was that As(V)
adsorption onto TiO2 increased with the increase of ionic strength under alkaline conditions (pH
7.0-11.0). Second was that As(V) can shift the point of zero charge (pHpzc) of TiO2 to a lower pH
value. Third was that the presence of 2-15 mg/l NOM as C significantly decreased the fraction
of As(V) adsorbed onto TiO2 at pH 6.0 regardless of the initial As(V) concentration (1-15μm).
They obtained a Figure as 6.5.3.
Figure 6.5.3: Zeta potential of 0.05g/l Degussa P25 TiO2 as a function of pH and ionic strength
48
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
in 0.001-0.01 M NaCl (Liu et al., 2008,)
Phosphorus is in the same column of periodic Table with arsenic and the membranes in this
thesis are also made of TiO2. Figure 6.5.1 and 6.5.2 have the similar curve with Figure 6.5.3.
Therefore, phosphorus is expected to be adsorbed onto TiO2 and the zeta-potential of
membranes enhance with phosphorus adsorption onto TiO2. Some infrared studies on
phosphate adsorption on TiO2 particles show that phosphate binds with the surface via the
formation of bidentate complex with Ti ions. Since arsenate, silicate and phosphate possess
tetrahedral structure (typical of a bidentate complex formation), competitive sorption is
expected, thereby lowering arsenic removal from contaminated solutions (Jegadeesan, G., et
al., 2010).
All the zeta potentials seemed to have a same value at high pH (>9) under all the
electrolyte conditions. One possible reason is that at higher pH (see Figure 6.4.3), phosphate
changes to HPO42- so the exclusion between phosphate and membrane become stronger, which
might make phosphorus desorp from membrane, thus effects on zeta potential from
phosphorus adsorption get weaker so zeta potentials with electrolyte phosphorus of both
membranes get close to zeta potentials without electrolyte phosphorus of both membranes at
high pH.
7. Conclusions and recommendations
The research used tight ultra-filtration membrane for phosphorus limitation. Two
membranes with 1kD MWCO and 3kD MWCO pore sizes were selected. The research
changed different operational conditions to observe effects on removal rate of phosphorus
of different factors. The factors included flux, cross flow velocity, concentration of
phosphorus in feed water, pH and ionic strength. Zeta potentials of both membranes in
different electrolytes were measured to explain the results.
Phosphorus was proved to be removed by CTUF. It was removed no more than 50%
without any pH adjustment and other ions injection for both membranes. Effect of Cl- on
phosphorus removal is smaller than effect of SO42- on phosphorus removal. Both removal
rates of phosphorus of two membranes decreased around 15% when there was SO42compared with Cl- and pH value influenced the removal rate largely. The highest removal
rates could be 86.9% for 3kD membrane and 77.9% for 1kD membrane.
49
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
From the research the following conclusions can be drawn:
a. Increase flux and cross flow velocity will increase phosphate removal rates for both
1kD and 3kD membranes.
b. Strong ionic strength will bring thin double layer thickness so the removal rate of
phosphate will decline. However, if the thickness is much larger than membrane pore size,
the exclusion strength is strong enough which means the rejection rate will not be
influenced so much. Under the same ionic strength, removal rate of phosphorus in solution
NaCl is higher than it in solution Na2SO4. The reason might be competition between SO42and H2PO4- rather than zeta potential effect.
c. pH could have huge effects on the phosphate removal. Removal rate increases as
pH increases and after a turning point (pH=8.3), the removal rate begins to decrease. One
reason is zeta potential of membrane increases as pH increases. Another reason is alkaline
condition makes H2PO4- be HPO42-. It means ionic strength becomes higher so the double
layer thickness of membranes decrease and the exclusion strength decrease. When pH is
higher than 8.3, the removal rate of phosphorus goes to decline while the zeta potential
not. One possible reason is disorption of phosphorus from TiO2, which leads to more
phosphorus is diffused to permeate.
d. Different solutions might affect zeta potential of membranes. High zeta potentials
will have high phosphate removal rate under pH 8.3 for both membranes. Electrolytes with
additional phosphorus will cause larger zeta potential, which is explained to contribution
from adsorption of phosphorus onto TiO2.
The further experiments are planned to add organic matters into feed water such as NOM
and EPS. Organic matters will bring fouling to the membranes. Therefore, backwash is needed
to recover irreversible fouling.
Organic matters do not affect ionic strength in theory as well as double layer thickness. As
it mentioned in chapter 4, fouled membranes with NOM have lower zeta potential (Figure 4.5).
Due to the two main reasons, fouling and lower zeta potential, the phosphate removal rate
might decrease under the same operational conditions.
Also, NOM also affects the adsorption of the arsenic onto TiO2. Therefore, in the following
experiments, it is expected to find NOM also has effects on adsorption of the phosphorus onto
TiO2 membranes, which also results lower zeta potential of the membrane thus leads to lower
rejection rate of phosphorus.
Coagulation is another method to improve the rejection. It can remove part of phosphate
50
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
(90%) by coagulant. Also, coagulation can removal a lot of organic matters hence reduce the
fouling and avoid zeta potential of membranes decreasing so much.
In all, the following steps for follow-up experiments are,
a. Add organic matters (NOM or EPS) to feed water to observe the effects of organic
matters on phosphate removal. Possible work condition is the feed water is 50L demi-water
with P-P04(NaH2P04) 1mg/l.Keep cross flow velocity as a constant 2m/s, flux 50.8l/(m2*h), pH
6~9.5.
b. Add coagulation before membrane filtration. Feed water is 50L demi-water with
P-P04(NaH2P04) 1mg/l and the same concentration NOM or EPS in step a.Keep cross flow
velocity as a constant 2m/s, flux 50.8l/(m2*h), pH 6~9.5. Observe the phosphorus removal
rate.
c. Feed water changes to real effluent water. Keep cross flow velocity as a constant 2m/s,
flux 50.8l/(m2*h), pH 6~9.5. Observe the phosphorus removal rate.
d. Taking the effluent of c to be influent of RO systems of project ICAN, observe whether
bio-fouling could be controlled.
Reference
Ahlgren, J., 2006. Organic phosphorus compounds in aquatic sediments: Analysis, Abundance
and Effects. Acta Universitatis Upsaliensis. Digtial Comprehensive summaries of Uppsala
Dissertations from the Faculty of Science and Technology 160. 57pp. Uppsala. ISBN
91-554-6508-0.
Ahn, J., Schroeder, S., Beer, M., McIlroy, S., Bayly, R.C., May, J.W., Vasiliadis, G., Seviour, R.J.,
2007. Ecology of the microbial community removing phosphate from wastewater under
continuously aerobic conditions in a sequencing batch reactor. Appl Environ Microbiol 73
(7), 2257-2270.
Al-Amoudi, A.S., Farooque, A.M., 2005. Performance, restoration and autopsy of NF membranes
used in seawater pretreatment, Desalination 178, 261–271.
Aleem, F.A.A., Al-Sugair, K.A., Al-Ahmad, M.I., 1998. Bio-fouling problems in membrane
processes for water desalination and reuse in Saudi Arabia, Int. Biodeterior. Biodegrad. 41,
19–23.
51
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Badawy, S.S., Shokry, S.A., Ismail, A.A., Zeiada, M.S., 2011. Study on The Removal of Iron (III)
and Chromium (III) from Aqueous Streams Using Inorganic Nanofiltration Membrane,
Australian Journal of Basic and Applied Sciences, 5(11): 236-243.
Baker, J.S., Dudley,L.Y., 1998. Bio-fouling in membrane systems– a review, Desalination 118,
81–90.
Beardsley, M.L., Coffey, J.M., 1985. Bioaugmentation: optimizing biological wastewater
treatment, Pollution Engineering 17, 30~33.
Beer, D., Stoodley, P., 2006. Microbial biofilms, Prokaryotes 1, 904–937.
Blackall, L.L., Crocetti, G.R., Saunders, A.M., Bond, P.L., 2002. A review and update of the
microbiology of enhanced biological phosphorus removal in wastewater treatment plants,
Antonie van Leeuwenhoek 81, 681–691.
Bowen, W.R., Mohammad, A.W., Hilal, N., 1997. Characterisation of nanofiltration membranes
for predictive purposes - Use of salts, uncharged solutes and atomic force microscopy, J.
Membr. Sci., 126(1) 91-105.
Bowen, W.R., Mukhtar, H., 1996. Characterisation and prediction of separation performance of
nanofiltration membranes , J. Membr. Sci.112(2) 263-274.
Bratby, J., 2006. Coagulation and flocculation in water and wastewater treatment. IWA
Publishing. London. UK
Chang, E.E., Liang, C.H., Huang, C.P., Chiang, P.C., 2012, A simplified method for elucidating
the effect of size exclusion on nanofiltration membranes, Separation and Purification
Technology 85, 1–7.
Cho, M., Chung, H., Choi, W., Yoon, J., 2005. Different inactivation behavior of MS-2 phage and
Escherichia coli in TiO2 photocatalytic disinfection, Appl. Environ. Microbiol. 71, 270–275.
52
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Davies, D.G., Marques, C.N.H., 2009. A fatty acid messenger is responsible for inducing
dispersion in microbial biofilms, J. Bacteriol. 191 (5), 1393–1403.
Dolar, D., Kosutic, K., Vucic, B., 2011. RO/NF treatment of wastewater from fertilizer
factory-removal of fluoride and phosphate, Desalination 265, 237-241.
Donlan, R.M., 2002. Biofilms: Microbial Life on Surfaces, Emerging Infectious Diseases 8,
881-890.
Ebrahim, S., Abdel-Jawad, M., Bou-Hamad, S., Safar, M., 2001. Fifteen years of R&D program in
seawater desalination at KISR. Part I. Pretreatment technologies for RO system,
Desalination 135 ,141-153.
Fang, W., Hu, J., Ong, S.L., 2010. Effects of phosphorus on biofilm disinfections in model
drinking water distribution systems, Journal of Water and Health 8 (3), 446-454.
Feng, Q.L., Wu, J., Chen, G.Q., Cui, F.Z., Kim, T.N., Kim, J.O., 2000, A mechanistic study of the
antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus, J. Biomed.
Mat. Res. 52, 662–668.
Fievet, P., Sbaı, M., Szymczyk, A., Vidonne, A., 2003. Determining the -potential of plane
membranes from tangential streaming potential measurements: effect of the membrane
body conductance, Journal of Membrane Science 226, 227–236.
Flemming, H.C., Schaule, G., Griebe, T., Schmitt, J., 1997. Tamachkiarowa, A., Bio-fouling- the
Achilles heel of membrane processes, Desalination 113, 215.
Gao, Y., Chen, D., Weavers, L.K., Walker, H.W., 2012. Ultrasonic control of UF membrane
fouling by natural waters: Effects of calcium, pH, and fractionated natural organic matter,
Journal of Membrane Science 401– 402, 232– 240
Goosen, M.F.A., Sablani, S.S., Al-Hinai, H., Al-Obeidani, S., Al-Belushi, R., Jackson, D., 2005.
Fouling of reverse osmosis and ultra-filtration membranes: a critical review, Sep. Sci.
Technol. 39 (10). 2261-2298.
53
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Hartley, K.J., Sickerdick, L., 1994. Performance of Australian BNR plants. In: Bayly R& Pilkington
N (Eds) Second Australian Conference on Biological Nutrient Removal from Wastewater (pp
65–72). Albury, Victoria.
Herzberg, M., Elimelech, M., 2007. Bio-fouling of reverse osmosis membranes: role of
biofilm-enhanced osmotic pressure, J. Membr. Sci. 295, 11–20.
Jacobson, J.D., Kennedy, M.D., Amy, G., Schippers, J.C., 2008. Phosphate limitation in reverse
osmosis: an option to control bio-fouling. In: Proceedings EuroMed 2008 Conference
Desalination for Clean Water and Energy Cooperation among Mediterranean Countries of
Europe and the MENA Region, 9-13 November 2008, Dead Sea, Jordan.
Jegadeesan, G., AI-Abed, S.R., Sundaram, V., Choi, H., Scheckel, K.G., Dionysiou, D.D., 2010.
Arsenic sorption on TiO2 nanoparticles: Size and crystallinity effects. Water Research 44 (3),
965–973
Jiang, D., Chen, Y., Ni, G., 2012. Phosphorus in Drinking Water And It's Removal in Conventional
Treatment Process, Advanced Materials Research 461, 453-456.
Jr, I.M., Hamida, A.B., Pohland, H., 1995. Proceedings of the IDA World Congress on
Desalination, Vol. IV, UAE, Abu Dhabi, Nov. 18–24, 59–72.
Kang, S.F., Yen, H.Y., Yang, M.H., 2003. Treatment of textile effluents by H2O2/UV oxidation
combined with RO separation for reuse, J. Environ. Sci. Health A Tox. Hazard. Subst.
Environ. Eng. 38, 1327–1339.
Katz, I., Dosoretz, C.G., 2008. Desalination of domestic wastewater effluents: phosphate
removal as pretreatment, Desalination 222, 230-242.
Kaur, K., Bott, T.R., Leadbeater, B.S.C., Effect of ozone on Pseudomonas fluorescens, in: L.F.
Melo, M.M. Fletcher, T.R. Bott, B. Capdeville (Eds.), Biofilms: Science and Technology,
Kluwer, Dordrecht, 1992, pp. 589–594.
54
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Khedr. M.G., 2011. Membrane fouling problems in reverse osmosis desalination plants,
Desalination & Water Reuse 10 (3), 8–17.
Kikuchi, Y., Sunada, K., Iyoda, T., Hashimoto, K., Fujishima, A., 1997. Photocatalytic bactericidal
effects of TiO2 thin films: dynamic view of the active oxygen species responsible for the
effect, J. Photochem. Photobiol. A. Chem. 106, 51–56.
Kim, D., Jung, S., Sohn, J., Kim, H., Lee, S., 2009. Biocide application for controlling bio-fouling
of SWRO membranes — an overview, Desalination 238, 43–52.
Kim, J., Shi, W., Yuan, Y., Benjamin, M.M., 2007. A serial filtration investigation of membrane
fouling by natural organic matter, J. Membr. Sci. 294 (1-2), 115–126.
Kochkodan, V,M., Hilal, N., Goncharuk, V.V., Al-Khatib, L., Levadna, T.I., 2006. Effect of the
surface modification of polymer membranes on their microbiological fouling, J. Colloid 68,
267–273.
Kramer, J.F., Tracey, D.A., 1995. The solution to reverse osmosis bio-fouling, Proceedings of IDA
World Congress on Desalination and Water Reuse Abu Dhabi, UAE IV, 1995, pp. 33–44.
Kumar, K., Adham, S.S., Pearce, W.R., 2006. Investigation of seawater reverse osmosis fouling
and its relationship to pretreatment type, Environ. Sci. Technol. 40, 2037–2044.
Kumar, R., Bhakta, P., Chakraborty, S., Pal, P., 2011. Separating Cyanide from Coke
Wastewater by Cross Flow Nanofiltration, Separation Science and Technology, 46,
2119–2127.
Kwak, S.Y., Kim, S.H., Kim, S.S., 2001. Hybrid organic/inorganic reverse osmosis (RO)
membrane for bactericidal anti-fouling. Part 1. Preparation and characterization of TiO2
nanoparticle self-assembled aromatic polyamide thin-film composite (TFC) membrane,
Environ. Sci. Technol. 35, 2388–2394.
Leo, C.P., Chai, W.K., Mohammad, A.W., Qi, Y., Hoedley, A.F., Chai, S.P., 2011. Phosphorus
removal using nanofiltration membranes, Water Science and Technology 64 (1), 199-205.
55
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Li, Q., Mahendra, S., Lyon, D.Y., Brunet, L., Viga, M.V., Li, D., Alvarez, P.J.J., 2008. Antimicrobial
nanomaterials for water disinfection and microbial control: Potential applications and
implications, Wat. Res. 42, 4591–4602.
Li, S., 2011. A new concept of ultra-filtration fouling control: Bachwashing with low lonic
strength water, Phd thesis 59-97, Published by: Water Management Academic Press;
Printed by Gildeprint Drukkerijen BV; ISBN 978-90-8957-024-6.
Liu, F., Zhao, C.C., Xia, L., Yang, F., Chang, X., Wang, Y., 2011. Bio-fouling characteristics and
identification of preponderant bacteria at different nutrient levels in batch tests of a
recirculating cooling water system, Environmental Technology, 32 (8), 901-910.
Liu,G., Zhang, X., Mcwilliams, L., Talley, J.W., Neal, C.R., 2008. Influence of ionic strength,
electrolyte type and NOM on As(V) adsorption onto TiO2, Journal of environment science
and health part A 43, 430-436.
Li, K., Xu, H., Gu, C., 2012. The depth of phosphorus removal by three coagulations, Advanced
Materials Research Vols. 356-360, 1575-1580.
Lund, V., Ormerod, K., 1995. The influence of disinfection processes on biofilm formation in
water distribution systems, Water Res. 29, 1013.
Madaeni, S.S., Mohamamdi, T., Moghadam, M.K., 2001. Chemical cleaning of reverse osmosis
membranes, Desalination 134, 77–82.
Mansouri, J., Harrisson, S., Chen, V., 2010. Strategies for controlling bio-fouling in membrane
filtration systems: challenges and opportunities, J. Mater. Chem. 20, 4567–4586.
Martin, A., Khan, K., Zaidi, S.M.J., Boyce, M.C., 2011. Bio-fouling in reverse osmosis membranes
for seawater desalination: Phenomena and prevention, Desalination 281, 1–16.
Miettinen, I.T., Vartiainen, T., Martikainen. P.J., 1997. Phosphorus and Bacterial Growth in
Drinking Water，Applied and environment microbiology 63, 3242–3245.
56
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Mills. A., Hunte, S.L., 1997. An overview of semiconductor photocatalysis, Journal of
Photochemistry and Photobiology A: Chemistry 108, 1–35.
Mohammad, A. W., Hilal, N., Al-Zoubi, H. & Darwish, N. A, 2007. Prediction of permeate fluxes
and rejections of highly concentrated salts in nanofiltration membranes. Journal of
Membrane Science 289 (1–2), 40–50.
Mohammadi, T., Madaeni, S.S., Moghadam, M.K., 2002. Investigation of membrane fouling,
Desalination 153, 155–160.
Niewersch, C., Koh, C.N., Wintgens, T., Melin, T., Schaum, C., Cornel, 2008, P. Potentials of using
nanofiltration to recover phosphorus from sewage sludge, Water Science and Technology
57 (5), 707-714.
Niewersch, C., Meier, K., Wintgens, T., Melin, T., 2010. Selectivity of polyamide nanofiltration
membranes for cations and phosphoric acid, Desalination 250, 1021-1024.
Oehmen, A., Lemos, P.C., Carvalho, G., Yuan, Z.G., Keller, J., Blackall, L.L., Reis, M.A.M., 2007.
Advances in enhanced biological phosphorus removal: From micro to macro scale. Water
Research, 41 (11): 2271~2300.
Oh, B.S., Jang, H.Y., Jung, Y.J., Kang, J.W., 2007. Microfiltration of MS2 bacteriophage: effect of
ozone on membrane bio-fouling, J. Membr. Sci. 306, 244–252.
Paar, H., Benecke, J., Ernst, M., Jekel, M., 2011. Pre-coagulation and ultrafiltration of effluent
impaired surface water for phosphorus removal and fouling control, Water Science &
Technology: Water Supply 11(2), 211-218.
Paul, D.H., 2011. Reverse Osmosis: scaling, fouling and chemical attack. International
Desalination & Water Reuse 1, 8–11.
Polanska, M., Huysman, K., Van Keer, C., 2005. Investigation of microbially available
phosphorus (MAP) in flemish drinking water. Water Research 39 (11), 2267-2272.
57
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Radu, A.I., Vrouwenvelder, J.S., van Loosdrecht, M.C.M., C.Picioreanu, C., 2000. Modeling the
effect of biofilm formation on reverse osmosis performance: flux, feed channel pressure
drop and solute passage, Journal of Membrane Science 365, 1-15.
Rubulis, J., Juhna, T., 2007. Evaluating the potential of biofilm control in water supply systems
by removal of phosphorus from drinking water, Water Science & Technology 55, 211–217.
Sadhwani, J.J., Vesa, J.M., 2001. Cleaning tests for seawater reverse osmosis membranes,
Desalination 139, 177–182.
Scherrenberg, S.M, 2011. Reaching ultra low phosphorus concentrations by filtration
techniques, phD thesis, Printing:GILDEPRINT Drukkerijen b.v., Enschede, the Netherlands;
Copyright © by Water Management Academic Press; ISBN/EAN: 978-90-8957-019-2.
Schneider, R.P., Ferreira, L.M., Binder, P., Bejarano, E,M., Goes, K.P., Slongo, E., Machado, C.R.,
Rosa, G.M.Z., 2005. Dynamics of organic carbon and of bacterial populations in a
conventional pretreatment train of a reverse osmosis unit experiencing severe bio-fouling,
J. Membr. Sci. 266 18–29.
Shang, R., van den Broek, W.B.P., G.J.Heijman, S.G.J, van Agtmaal, S., Rietveld, L.C., 2011.
Wastewater reuse through RO: a case study of four RO plants producing industrial water,
Desalination and Water Treatment, 34, 408-415.
Shannon, M.A., Bohn, P.W., Elimelech, M., Georgiadis, J.G., Marinas, B.J., Mayes, A.M., 2008.
Science and technology for water purification in the coming decades, Nature 452,
301–310.
Song, H., Shao, J., He, Y., Liu, B., Zhong, X., 2012. Natural organic matter removal and flux
decline with PEG–TiO2-doped PVDF membranes by integration of ultrafiltration with
photocatalysis, Journal of Membrane Science 405– 406, 48– 56.
Teng, C.K., Hawlader, M.N.A., Malek, A., 2003. An experiment with different pretreatment
methods, Desalination 156, 51–58.
58
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Tkachenko, N. H., Yaremko, Z.Y., Bellmann, C., 2006. Effect of 1-1-charged ions on aggregative
stability and electrical surface properties of aqueous suspensions of titanium dioxide,
Colloids and Surfaces A: Physicochem. Eng. Aspects 279, 10–19.
Tran, N., Drogui, P., Blais, J.F., Mercier, G., 2012. Phosphorus removal from spiked municipal
wastewater using either electrochemical coagulation or chemical coagulation as tertiary
treatment, Separation and Purification Technology 95, 16–25.
Tsuru, T., Nakao. S., Kimura, S., 1991. Calculation of Ion Rejection by Extended Nemst-Planck
Equation with Charged Reverse Osmosis Membranes for Single and Mixed Electrolyte
Solutions, J. Chem. Engineering Japan., 24(4), 511.
Tyrovola, K., Diamadopoulos, E., 2005. Bromate formation during ozonation of groundwater in
coastal areas in Greece, Desalination 176, 201–209.
Wang, H., Li, B., Ma, W., Zeng, F., Fan, H., Deng, C., 2011. Optimization of Chemical
Phosphorous Removal Medicament, Applied Mechanics and Materials 71-78, 3213-3218.
Wang, J., Zhang, Y., Xu, P., Wang, H., Han, F., 2010. Impact of various forms of phosphorus on
biological growth in water, Digital Object Identifier: 10.1109/ICBBE.2010.5515026,
Publication Year: 2010 , Page: 1- 4.
Whittaker, C., Ridgway, H., Olson, B.H., 1984. Evaluation of cleaning strategies for removal of
biofilms from reverse-osmosis membranes, Appl. Environ. Microbiol. 48, 395–403.
Wikipedia A, http://en.wikipedia.org/wiki/Double_layer_(interfacial)
Wikipedia B, http://en.wikipedia.org/wiki/File:DoubleLayer.gif
Wikipedia C, http://en.wikipedia.org/wiki/Ionic_strength
Wikipedia D, http://en.wikipedia.org/wiki/Water_reclamation
59
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
van Dijk, J.C., Verberk,.J.Q.J.C., Heijman, S.G.J., Rietveld,. L.C., de Ridder, D., Grefte, A.,
Andeweg, P., 2009. Drinking water treatment. Lectures of course CT4475 for TU Delft
university
Verliefde, A.R.D., Cornelissen, E.R., Heijman, S.G.J., Verberk, J.Q.J.C., Amy, G.L., Van Der
Bruggen, B., Van Dijk, The role of electrostatic interactions on the rejection of organic
solutes in aqueous solutions with nanofiltration, Journal of Membrane Science 322,
(2008), 52-66.
Vrijenhoek, E.M., Waypa, J.J., 2000. Aresnic removal from drinking water by a ―loose‖
nanofiltrationmemrbrane, Desalination 130, 265-277.
Vrouwenvelder, J.S., Beyer, F., Dahmani, K., Hasan, N., Galjaard, G., Kruithof, J.C., van
Loosdrecht, M.C.M., 2010. Phosphate limitation to control bio-fouling，Water research 44,
3454-3466.
Vrouwenvelder, J.S., Manlarakis, S.A., van der Hoek, J.P., van Paasen, J.A.M., van der Meer,
W.G.J., van Agtmaal, J.M.C., Prummel, H.D.M., Kruithof, J.C., van Loosdrecht，M.C.M, 2008.
Quantitative biofouling diagnosis in full scale nanoflitration and reverse osmosis
installations, Water research 42 (19), 4856-4868.
Xu, L., Guo, C., Peng, Y., Yuan, Z., 2011. Review on the Microbiological and Biochemical
Characteristics of Enhanced Biological Phosphorus Removal System, Chin J Appl Environ
Biol, 17(3), 427~434.
You, Y., Peng, Y. , Yuan, Z. , Li, X., Peng, Y., 2008. Cultivation and characteristic of aerobic
granular sludge enriched by phosphorus accumulating organisms. J Environ Sci, 33 (8),
2242-2248.
Zheng, X., Plume, S., Ernst, M., Croué, J.P., Jekel, M., 2012. In-line coagulation prior to UF of
treated domestic wastewater– foulants removal, fouling control and phosphorus removal,
Journal of Membrane Science 403– 404, 129– 139.
Zodrow, K., Brunet, L., Mahendra, S., Li, D., Zhang, A., Li, Q., Alvarez, J.J.P., 2009. Polysulfone
60
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
ultrafiltration membranes impregnated with silver nanoparticles show improved bio-fouling
resistance and virus removal, Wat. Res. 43, 715–723.
61
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Appendix
Table 1: Phosphorus removal in different flux
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923
cross flow
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
19:00
1.18
0.74
37.29%
22:00
1.18
0.76
35.59%
11:15
1.18
0.67
43.22%
13:55
1.18
0.65
43.32%
Average
43.27%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
62.30769
cross flow
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
14:20
1.18
0.63
46.61%
15:40
1.18
0.62
47.46%
16:30
1.18
0.61
48.31%
Average
47.46%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
25.38462
cross flow
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
10:30
1.13
0.67
40.71%
11:40
1.13
0.71
37.17%
12:55
1.13
0.71
37.17%
Average
38.35%
Table 2: Phosphorus removal in different cross flow
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
19:00
1.18
0.74
37.29%
62
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
22:00
1.18
0.76
35.59%
11:15
1.18
0.67
43.22%
13:55
1.18
0.65
43.32%
Average
43.27%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow
1m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
14:10
1.13
0.71
40.17%
15:10
1.13
0.71
40.17%
16:10
1.13
0.71
40.17%
Average
40.17%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow
0,5m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
16:50
1.13
0.85
30.78%
17:50
1.13
0.84
31.66%
20:30
1.13
0.84
31.66%
Average
31.37%
Table 3: phosphorus removal rate in different phosphorus concentration of 1kD membrane
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923
cross flow velocity
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
0.791666667
1.18
0.74
37.29%
0.916666667
1.18
0.76
35.59%
0.46875
1.18
0.67
43.22%
0.579861111
1.18
0.65
43.32%
Average
43.27%
phosphate
0,5mg/l
pore size
1kD
flux(l/(m2*h))
50.76923
cross flow velocity
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
63
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
15:15
0.53
0.34
35.85%
15:40
0.53
0.36
32.08%
21:00
0.53
0.34
35.85%
phosphate
1,5mg/l
pore size
1kD
flux(l/(m2*h))
50.76923
cross flow velocity
2m/s
Average
34.59%
phosphate
1,5mg/l
pore size
1kD
flux(l/(m2*h))
50.76923
cross flow velocity
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
11:30
1.51
0.9
40.40%
14:10
1.51
0.89
41.06%
20:00
1.51
0.89
41.06%
Average
40.84%
Table 4: phosphorus removal rate in different phosphorus concentration of 3kD membrane
phosphate
1mg/l
pore size
3kD
flux(l/(m2*h))
50.76923
cross flow velocity
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
11:40
1.13
0.64
43.36%
15:50
1.13
0.65
42.48%
16:50
1.13
0.64
43.36%
Average
43.07%
phosphate
0,5mg/l
pore size
3kD
flux(l/(m2*h))
46.15385
cross flow velocity
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
12:05
0.53
0.29
45.28%
13:20
0.53
0.33
37.74%
14:40
0.53
0.34
35.85%
Average
39.62%
phosphate
1,5mg/l
pore size
3kD
flux(l/(m2*h))
50.76923
cross flow velocity
2m/s
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
13:40
1.48
0.86
41.89%
64
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
15:00
1.48
0.84
43.24%
16:00
1.48
0.84
43.24%
Average
42.79%
Table 5: Phosphorus removal with different NaCl concentrations for 1kD membrane
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
0.5
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
15:30
1.09
0.77
29.36%
20:30
1.09
0.71
34.86%
21:40
1.09
0.71
34.86%
12:00
1.05
0.64
39.05%
15:00
1.05
0.66
37.14%
16:30
1.05
0.64
39.05%
Average
38.41%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
1
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
14:20
0.94
0.59
37.23%
15:20
0.94
0.58
38.30%
16:20
0.94
0.58
38.30%
Average
37.94%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
1.5
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
17:10
0.93
0.59
36.56%
18:10
0.93
0.58
37.63%
19:10
0.93
0.58
37.63%
Average
37.28%
phosphate
1mg/l
pore size
1kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
6
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
11:15
0.93
0.6
35.48%
12:10
0.93
0.6
35.48%
15:25
0.93
0.58
37.63%
Average
36.20%
65
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Table 6: Phosphorus removal with different NaCl concentrations for 3kD membrane
phosphate
1mg/l
pore size
3kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
0.5
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
13:40
1.06
0.62
41.51%
15:40
1.06
0.62
41.51%
17:40
1.06
0.62
41.51%
19:40
1.06
0.62
41.51%
10:30
1.06
0.6
43.40%
Average
42.14%
phosphate
1mg/l
pore size
3kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
1
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
12:00
0.93
0.53
43.01%
13:15
0.93
0.51
45.16%
14:15
0.93
0.52
44.09%
Average
44.09%
phosphate
1mg/l
pore size
3kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
1.5
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
17:10
0.92
0.54
41.30%
18:10
0.92
0.53
42.39%
19:10
0.92
0.51
44.57%
Average
42.75%
phosphate
1mg/l
pore size
3kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
6
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
16:55
0.92
0.56
39.13%
17:55
0.92
0.55
40.22%
18:55
0.92
0.56
39.13%
Average
39.49%
Table 7: Phosphorus removal with 1.5mmol/l Na2SO4 for 1kD membrane
phosphate
2
flux(l/(m *h))
1mg/l
pore size
1kD
50.76923077
cross flow velocity
2m/s
66
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
Na2SO4(mmol/l)
1.5
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
13:50
1.06
0.81
23.58%
14:50
1.06
0.81
23.58%
15:50
1.06
0.79
25.47%
average
24.21%
Table 8: Phosphorus removal with 1.5mmol/l Na2SO4 for 3kD membrane
phosphate
1mg/l
pore size
3kD
flux(l/(m2*h))
50.76923077
cross flow velocity
2m/s
Na2SO4(mmol/l)
1.5
Time
Feed water(mg/l)
Permeate water(mg/l)
Removal
15:55
1.08
0.71
34.26%
16:55
1.08
0.74
31.48%
20:00
1.08
0.74
31.48%
average
32.41%
Table 9: Phosphorus removal in different pH for 1kD membrane
phosphate
1mg/l
pore size
1kD
flux(l/(m *h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
6
pH
Feed water(mg/l)
Permeate water(mg/l)
Removal
6.08
0.92
0.6
34.78%
7.80
1.08
0.28
74.07%
7.65
1.08
0.32
70.37%
7.65
1.08
0.3
72.22%
8.43
1.11
0.3
72.97%
8.20
1.133
0.25
77.93%
8.20
1.156
0.29
74.91%
9.45
1.189
0.53
55.42%
9.36
1.212
0.45
62.87%
9.31
1.26
0.4
68.25%
2
Table 10: Phosphorus removal in different pH for 3kD membrane
phosphate
1mg/l
pore size
3kD
flux(l/(m *h))
50.76923077
cross flow velocity
2m/s
NaCl(mmol/l)
6
pH
Feed water(mg/l)
Permeate water(mg/l)
Removal
6.08
0.92
0.55
40.22%
7.3
1.11
0.32
71.17%
7.6
1.11
0.3
72.97%
2
67
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
7.8
1.11
0.28
74.77%
8.51
1.07
0.16
85.05%
8.34
1.07
0.14
86.92%
9.64
1.16
0.28
75.86%
Table 11: Zeta potentials at different pH for 1kD membrane in 1.5mmol/L Na2S04 solution
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
0.1231
1
500
0.0015
0
0.2578
2
500.03
0.0015
0
0.3964
3
500.07
0.0015
0
0.5394
4
500.12
0.0015
0
0.6778
5
500.16
0.0015
0
0.8167
6
500.2
0.001499
0
0.9525
7
500.24
0.001499
0
1.093
8
500.29
0.001499
0
pH
5.75
2
6.11
5
6.55
7.17
5
8.24
6
8.72
5
8.96
6
9.17
ZP (FM)_[mV]
-14.17
-15.69
-17.54
-19.77
-23.54
-29.18
-32.08
-34.43
Table 12: Zeta potentials at different pH for 1kD membrane in 1.5mmol/L Na2S04
solution+0.032 mmol/L NaH2SO4
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
0.1242
1
500
0.0015
0
0.2578
2
500.03
0.0015
0
0.3964
3
500.07
0.0015
0
0.5386
4
500.12
0.0015
0
0.6839
5
500.18
0.001499
0
0.8292
6
500.24
0.001499
0
0.9714
7
500.3
0.001499
0
1.116
8
500.36
0.001499
0
68
pH
5.68
3
5.97
1
6.29
9
6.61
6
6.92
7
7.20
8
7.50
6
7.88
ZP (FM)_[mV]
-13.28
-14.98
-17.67
-20.05
-23.38
-25.85
-28.04
-30.28
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
4
1.259
9
500.41
0.001499
0
1.397
10
500.45
0.001499
0
1.537
11
500.5
0.001499
0
1.678
12
500.55
0.001498
0
8.31
8
8.65
5
8.96
1
9.15
3
-32.6
-35.16
-36.96
-38.65
Table 13: Zeta potentials at different pH for 1kD membrane in 4.5 mmol/L NaCl solution
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
pH
ZP (FM)_[mV]
5.72
-2.285
0.1242
1
500
0.0045
0
0.2586
2
500.03
0.0045
0
0.3969
3
500.07
0.004499
0
0.5394
4
500.12
0.004499
0
0.6786
5
500.16
0.004499
0
0.8169
6
500.2
0.004498
0
0.9547
7
500.24
0.004498
0
1.094
8
500.29
0.004497
0
6.03
4
6.42
6
6.92
8
7.58
1
8.42
8.79
4
9.06
4
-5.264
-8.834
-11.93
-15.73
-21.09
-25.82
-31.4
Table 14: Zeta potentials at different pH for 1kD membrane in 4.5mmol/L NaCl solution+0.032
mmol/L NaH2SO4
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
pH
ZP (FM)_[mV]
5.68
-10.87
0.1208
1
500
0.0045
0
0.2561
2
500.03
0.0045
0
0.3942
3
500.07
0.004499
0
0.5358
4
500.12
0.004499
0
0.6817
5
500.18
0.004498
0
0.825
6
500.24
0.004498
0
69
5.98
8
6.32
7
6.65
3
6.97
7
7.28
-13.47
-16.47
-19.79
-22.9
-25.61
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
0.9683
7
500.3
0.004497
0
1.113
8
500.36
0.004497
0
1.255
9
500.41
0.004496
0
1.394
10
500.45
0.004496
0
1.534
11
500.5
0.004496
0
Zheyi Zeng
7.61
2
8.07
7
8.57
9
8.86
9.09
8
-28.32
-30.5
-33.56
-35.76
-37.15
Table 15: Zeta potentials at different pH for 3kD membrane in 1.5mmol/L Na2S04 solution
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
0.1244
1
500
0.0015
0
0.2628
2
500.04
0.0015
0
0.4044
3
500.09
0.0015
0
0.5428
4
500.13
0.0015
0
0.6808
5
500.17
0.001499
0
0.8189
6
500.21
0.001499
0
0.9606
7
500.26
0.001499
0
pH
5.76
9
6.29
6.89
4
7.94
2
8.68
9
8.97
6
9.19
3
ZP (FM)_[mV]
-30.05
-32.21
-34.73
-37.33
-42.15
-45.19
-47.42
Table 16: Zeta potentials at different pH for 3kD membrane in 1.5mmol/L Na2S04
solution+0.032 mmol/L NaH2SO4
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
pH
ZP (FM)_[mV]
5.67
-32.86
0.1247
1
500
0.0015
0
0.2633
2
500.04
0.0015
0
0.4056
3
500.09
0.0015
0
0.5469
4
500.14
0.0015
0
0.6925
5
500.2
0.001499
0
0.8378
6
500.26
0.001499
0
0.9833
7
500.32
0.001499
0
70
6.08
9
6.49
6.79
5
7.11
6
7.42
9
7.81
-35.05
-36.94
-38.78
-40.76
-42.71
-43.92
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
2
1.125
8
500.37
0.001499
0
8.27
-45.63
1.264
9
500.41
0.001499
0
8.67
-46.67
1.402
10
500.45
0.001499
0
1.545
11
500.5
0.001499
0
8.94
7
9.18
1
-48.33
-48.31
Table 17: Zeta potentials at different pH for 3kD membrane in 4.5 mmol/L NaCl solution
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
0.1242
1
500
0.0045
0
0.2619
2
500.04
0.0045
0
0.4039
3
500.09
0.004499
0
0.5453
4
500.14
0.004499
0
0.6839
5
500.18
0.004498
0
0.8214
6
500.22
0.004498
0
0.9667
7
500.28
0.004497
0
pH
ZP (FM)_[mV]
5.83
5
6.24
1
6.74
7.59
8
8.50
9
8.85
3
9.15
-33.56
-34.58
-36.8
-39
-42.19
-45.18
-47.48
Table 18: Zeta potentials at different pH for 3kD membrane in 4.5mmol/L NaCl solution+0.032
mmol/L NaH2SO4
Time_[h
]
Point #
Volume_[ml
Conc._[mol/l
]
]
Vol. manual_[ml]
pH
ZP (FM)_[mV]
5.64
0.1233
1
500
0.0045
0
6
-37.72
0.2617
2
500.04
0.0045
0
6.09
-39.9
6.49
0.4036
3
500.09
0.004499
0
5
-41.6
6.80
0.5456
4
500.14
0.004499
0
5
-43.62
7.13
0.6911
5
500.2
0.004498
0
7
-44.92
7.47
0.8364
6
500.26
0.004498
0
4
-46.82
7.91
0.9817
7
500.32
0.004497
0
5
-48.03
1.124
8
500.37
0.004497
0
8.45
-49.35
71
Phosphorus removal by ceramic tight ultra-filtration (CTUF) membrane for RO pre-treatment
Zheyi Zeng
5
8.81
1.263
9
500.41
0.004496
0
1.405
10
500.46
0.004496
0
2
-50.18
9.09
72
8
-51.2