Removal of ammonium and organic matter from water using ozoneceramic membrane and biological activated carbon filtration
X. H. Zhang, J. N. Guo
Research Center of Environmental Engineering and Management, Graduate School at Shenzhen, Tsinghua
University, Shenzhen 518055, P R China
Abstract: The removal of ammonium and organic matter from polluted water using ozone-ceramic
membrane and biological activated carbon filtration hybrid system was studied. Ozone-ceramic
membrane could hardy remove any of the ammonium in the feed water. The average removal
efficiency of total organic carbon (TOC) and UV254 were about 15% and 30% for single ozone-ceramic
membrane process. The efficiencies can be enhanced to 48.3% and 51.8% by the hybrid system. About
1.0mg•L-1~2.0mg•L-1 ammonium can be removed by the hybrid system. Dissolved oxygen (DO) is an
important factor which can affect the removal of ammonium. The amount of ammonium removed by
the biological activated carbon (BAC) column increased with increasing DO. Increasing the dissolved
oxygen (DO) to 30.0mg·L-1 by pure oxygen aeration can lead to complete removal of ammonium with
concentration as high as 5.5 mg·L-1. Some organic matters were oxidized by ozone and this resulted in
reduced membrane fouling and increased membrane flux by 25%~30%. However, ozonation can affect
the microorganism in the BAC, which may impact the removal of nitrite. The concentration of nitrite
would increase sharply when the ammonium concentration of the influent increased to a certain value.
Keywords: ozone; ceramic membrane; biological activated carbon filtration
Introduction
In order to meet the new national standards for drinking water quality, so many old
small drinking water treatment plants in China are facing up to the challenges to
upgrade or change the traditional process widely adopted now.
Membrane filtration is a good alternative to provide safe drinking water to
customers while dealing with these challenges. Membrane filtration is an effective
method to remove particles, microorganisms and organic matter from drinking waters.
Compared with conventional treatment methods, membrane processes (i) can provide
better quality water, (ii) minimize disinfectant demand, (iii) are more compact,
(iv)provide easier operational control and less maintenance, and (v) generate less
sludge(Karnik and Davies et al., 2005, Nakatsuka and Nakate et al., 1996).
Substitution by a membrane filtration technology such as ultrafiltration (UF) or
micro-filtration (MF) membrane for the conventional particle separation process can
reduce operating units and consumption of coagulants, and lead to an efficient
advanced water treatment system. Compared with most organic membranes, ceramic
membranes are ozone resistant and when combined with ozonation, generate very
high and stable permeate fluxes without causing membrane damage(Sartor and
Schlichter et al., 2008, Karnik and Davies et al., 2005, Karnik and Davies et al., 2005,
Schlichter and Mavrov et al., 2003, 2004). The use of ozone-ceramic membrane
filtration process in drinking water treatment is accepted now and there are some pilot
test(Schlichter and Mavrov et al., 2004) and demonstration plant(Sartor and Schlichter
et al., 2008) running now.
Though the ozone-ceramic membrane filtration process have been used in some
districts, there are still some problems: 1) only less than 30% of the organic matter in
the feed water can be removed by UF; 2) some micro-pollutants, such as ammonium,
can hardly be removed by ozone-ceramic membrane process.
In this work, ozone-ceramic membrane was combined with biological activated
carbon (BAC) filtration to form a hybrid system. The primary objective of the present
study was to investigate the removal efficiency of organic matter and ammonium of
the hybrid system. In addition, the impact of DO on the removal efficiency of
ammonium was considered, too. Prior to the BAC column, the DO was adjusted
according to the concentration of ammonium.
Material and Methods
A single-channel tubular ceramic membrane module (SCHUMASIV, Pall
Filtersystems, Inc., Germany) with average 100nm pore size was used in the tests. A
centrifugal pump with frequency converter was used to change the trans-membrane
pressure (TMP). Pure oxygen gas was used to generate ozone and adjust DO of the
raw water prior to the BAC column. A chromatography column with 11mm internal
diameter was used as the BAC column. The BAC was collected form another BAC
column which continuously running for about one year. Figure 1.1 is the schematic
diagram of the hybrid system.
gas pipe
ozone
absorption
ozone
generator
oxygen
cylinder
valve
pressure
gauge
ozone
contact
tank
flowmeter
membrane
housing
water pipe
oxygen
contact
tank
ceramic
membrane
BAC column
raw water
peristaltic pump
centrifugal
pump
peristaltic pump
Figure 1.1 Schematic diagram of the hybrid system.
The ammonium concentration of the simulated feed water was controlled by adding
seriously polluted water from an urban river into the clean river water at different
ratios. The filtrate was aerated with oxygen to keep the DO concentration at different
levels. The total organic carbon and ammonium were analysed by a TOC analyser and
Nessler’s reagent-spectrophotometry. The operating conditions used are given in
Table 1.1.
Table 1.1 Operating conditions of the hybrid system.
Parameters
Water temperature
Room temperature
Water turbidity
About 10 NTU
Ozone dosage
2mg/L
TMP
1×105Pa
EMBCT of the BAC column
15-20min
Flow rate of the BAC column
2.5-3.0mL/min
Results and Conclusions
The varieties of different forms of nitrogen are shown in Figure 2.1~ Figure 2.3.
Figure 2.1 ~ Figure 2.3 show that ozone-ceramic membrane filtration cannot remove
any forms of nitrogen. But as is shown in figure 1.1, about 50% of the ammonium can
be removed by BAC column. When the DO was enhanced to about 20mg/L on the
16th day (Figure 2.6), more than 4mg/L of ammonium could be removed by the BAC
column. In order to evaluate the max removal efficiency of the BAC column, the DO
was increased to more than 30mg/L while the ammonium was about 15mg/L. The
results showed that about 9mg/L of ammonium could be removed by the BAC
column. Though much ammonium could be removed by the BAC column, the nitrite
concentration of the effluent sharply increased to more than 5mg/L. Ozone might
cause some damage to the certain bacteria in the column because the nitrite
concentration of the control group without ozone was much lower (data is not shown
here) than that of the experimental group.
NH4+-N/(mg·L-1)
16.0
Ammonium
14.0
Raw water
12.0
Membrane filtrate
BAC column filtrate
10.0
New raw
water injected
8.0
6.0
4.0
2.0
0.0
0
2
4
6
8
10
12 14
T/d
16
18
20
22
24
Figure 2.1 Comparison of the ammonium concentrations of the hybrid system.
9.0
Raw water
Membrane filtrate
BAC column filtrate
Nitrate
8.0
NO3--N/(mg·L-1)
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0
2
4
6
8
10
12 14
T/d
16
18
20
22
24
Figure 2.2 Comparison of the nitrate concentrations of the hybrid system.
6.0
Nitrite
NO2--N/(mg·L-1)
5.0
Raw water
Membrane filtrate
4.0
BAC column filtrate
3.0
2.0
1.0
0.0
0
2
4
6
8
10
12 14
T/d
16
18
20
22
24
Figure 2.3 Comparison of the nitrite concentrations of the hybrid system.
Figure 2.4 and Figure2.5 show the removal of organic matter by the hybrid system.
The results showed that about 15% of TOC and 30% of UV254 could be removed by
ozone-ceramic membrane process, respectively. Both the average removal rates could
increase to more than 50% after filtrated by the BAC column.
5.0
4.0
TOC/(mg·L-1 )
TOC
Raw water
Membrane filtrate
BAC column filtrate
3.0
2.0
1.0
0.0
0
2
4
6
8
10
12 14
T/d
16
18
20
22
24
Figure 2.4 Comparison of the TOC concentrations of the hybrid system.
0.12
Raw water
0.10
UV254
membrane filtrate
UV254/cm-1
0.08
0.06
0.04
0.02
0.00
0
2
4
6
8
10
12 14
T/d
16
18
20
22
24
Figure 2.5 Comparison of the UV254 of the hybrid system.
40
Influent
35
Effluent
DO/(mg·L-1)
30
25
20
15
10
5
0
0
2
4
6
8
10
12 14
T/d
16
18
20
22
24
Figure 2.6 Variety of the DO in the influent and effluent of the BAC column.
This study demonstrates that when operated appropriatly, the hybrid system of ozone–
ceramic membrane and BAC column filtration can remove ammonium and organic
matter effectively. BAC column is a good choice to compensate the disadvantage of
ozone–ceramic membrane in removing ammonium and organic matter. DO playes an
important role in the removal of ammonium and when the concentration of
ammonium is high enough, the nitrite concentration will increase to a dangerous level.
Ozone may cause some damage to the bacteria in the feed water and then affect the
ammonium removal efficiency.
As is shown in Figure 2.7, the membrane flux can be improved by ozone. The initial
membrane flux is 2045.5L·m2·h-1 with the transmembrane pressure (TMP) of
0.1MPa. The membrane flux decreased to 584.4L·m2·h-1 after ten minutes. The ozone
can increase the membrane flux by 25%~30%.
700
ozone+membrane
Flux/(L·m-2·h-1)
600
Membrane
500
400
300
200
100
0
10
15
20
25
30
35
40
45
50
55
60
T/min
Figure 2.7 Effect of ozone on membrane flux.
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