The Study on the Operating Characteristics of
Algae-Contaminated Reservoir Water Using GAC-sand
Dual Media Filter Flofilter
YONG LEI WANG1,2,*, KEFENG ZHANG1,2, WENJUAN CHEN3, HONGBO WANG1,2, MEI LI1,2 and RUIBAO JIA4
1College
of Environmental and Municipal Engineering, Shandong Jianzhu University, 250101
2Co-Innovation Center of Green Building, 250101
3China Everbright Water (Ji'nan) Co., Ltd., 250032
4Shandong Province City Water Supply and Drainage Water Quality Monitoring Center, 250101, Jinan, China
ABSTRACT: The problem of reservoir water quality caused by massive algae pollution
keeps going serious, and the traditional solid-liquid separation technology generally fails
to meet water quality standards. In the present study, GAC-sand-double-filtration flofilter
was built to treat reservoir water derived from the Yellow River that has been polluted
by high levels of algal biomass, with the running characteristics and operating results
specifically investigated. The experimental results showed that, running effect was relatively superior when the dosage of PAFC was 4 mg/L (Al3+), the pressure of dissolved
air was 0.4 Mpa, and the reflux ratio was 8%. Algal biomass fixed onto GAC and sand
filter layer was mainly found in the carbon layer, which accounted for 97.4% of the total
biomass (the highest value was 50.2 nmol p/g), and the biomass fixed onto carbon layer
was 16.7 times of that fixed onto the sand layer (3.0 nmol p/g). Clearly, the removal of
pollutants mainly occurred in the carbon layer. Also, the removal efficiency of particulate
matter such as blue-green algae, turbidity, CODMn, UV254, NPOC, ammonia nitrogen
was 96.48%, 92.40%, 92.56%, 57.40%, 52.50%, 51.60% and 75.67%, respectively. The
odor was reduced from 4 to 0, and the content of geosmin and methylisoborneol was
less than their detection limit, with the removal efficiency of chloroform and chlorodibromomethane as 60% and 55.1%, respectively. In general, the results showed that the
flofilter process had imposed an efficient effect on the removal of algal biomass, odor
substances and disinfection byproducts precursors.
INTRODUCTION
T
problem of reservoir water pollution has become increasingly worse, with algae pollution as a
typical culprit. Since the Yellow River is continuously
polluted, the plain reservoirs has generally displayed
characteristics of shallow depth, with high levels of
algal biomass found during the summer, and algal density would decline during the winter due to low levels
of temperature and turbidity. With the acute exacerbation of water eutrophication problem, algal reproduction has posed a serious threat to aquatic ecosystems,
especially during the spring and autumn when temperature changes dramatically and algae outbreaks occur
frequently and such phenomenon could pose a severe
threat to water treatment plant operation and water
safety. Due to the fact that the density of algal community is usually small, the removal efficiency of algae by
HE
*Author to whom correspondence should be addressed.
E-mail: [email protected]; Tel: +86-531-86361857; Fax: +86-531-86361631
using the traditional solid-liquid separation technology
is not satisfactory, ensued by a series of problems, such
as filter blockage, backwash cycle shortage, soaring
processing cost and worsening water quality. Under
certain circumstances, the safety of water supplies is
under great threat of microcystins produced by some
algae species [1~4]. The technology of flofilter with
the process of flotation and filtration integrated seems
promising, which could not only handle water quality
problem with high levels of algal biomass present, but
also display a good removal efficiency of water turbidity, odor and colour. Meanwhile, the operation mode is
flexible in terms of reducing operating costs effectively
[5]. Researchers have carried out numerous studies on
the flotation and filtration process [6~8]. For example,
Zhang et al. developed GAC-sand dual media with
dissolved air flotation/ filtration technology to process
water body with high levels of organic matter and algal biomass in MiYun Reservoir, and the overall result
was satisfactory [9,10]. On the basis of water quality
Journal of Residuals Science & Technology, Vol. 13, Supplement 1
1544-8053/16/01 S093-07
© 2016 DEStech Publications, Inc.
doi:10.12783/issn.1544-8053/13/S1/14
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Y. WANG, K. ZHANG, W. CHEN, H. WANG, M. LI and R. JIA
analysis of reservoir water samples collected from the
Yellow River, the present study tests the coagulation
conditions, reflux ratio, algal biomass and decontamination capability of carbon and sand filter layer when
the technology of flofilter is implemented, with an indepth analysis of the operational characteristics of flofilter being used. Therefore, the present study could provide new perspective and technical support regarding
the development of water plant treatment technology.
MATERIALS AND METHODS
Raw Water Quality
Conventional Indicators
Raw water samples were collected from Jinan
Queshan Yellow River reservoir, and the test period
was between May and September. Water temperature was in the range of 19.2~27.0°C, pH value was
in the range of 8.18~8.40, and the value of turbidity,
CODMn and UV254 was in the range of 2.17~4.30 NTU,
2.63~3.28 mg/L and 0.039~0.045 cm–1, respectively.
would first adhere to the floc particles and then floate
to the separation zone. Generated scum on the surface
was then removed by using scraping slag. After such
flotation process, water would then flow down into
the filtration area. Filter layer was filled with activated
charcoal and quartz sand, and the height of activated
carbon filter layer was 600 mm (the range of diameter
was 0.8~1.2 mm). The height of quartz sand filter layer
was 300 mm (the range of diameter was 0.8~1.2 mm),
and the supporting layer filled with gravel of 400 mm
was below the filter layer. Backwash of air and water
was conducted with long-handled filter head, with coagulant dosed by the metering pumps. The schematic
diagram of floating flofilter pilot plant was shown in
Figure 1.
Analysis Method
The test items and methods of pilot test followed
standard methods for the Examination of Water and
Wastewater APHA/AWWA/WEF (2005).
All assays were carried out in triplicate, with the
averages and corresponding standard deviations sta-
Algae Indicators
The dominant algal species found in Queshan reservoir is cyanobacteria, also known as blue-green algae, and it often blooms during the summer [11]. With
an increasing water temperature since May, the content of algae began to rise, and the variation trend of
chlorophyll A and cyanobacteria was generally consistent. Chlorophyll A content of raw water samples
collected in September was in the range of 6.46~14.37
µg/L, with the average value as 9.35 µg/L. The density of blue-green algae was in the range of 1173~3398
cells/mL, with the average value as 2593.49 cells/mL.
Algae content rose in line with the changes in the season or the temperature.
Test Equipment
The processing capacity of pilot testing device was
about 5 m3/h, with its dimensions as 2.6 m × 0.8 m
× 4.3 m, and all structures such as the mixing tank,
flocculation tank and floating flofilter were established
together. The upper part of the floating filter was flotation zone, and the lower part was the filter area. After
the flocculation process, water flew into the contact
chamber, where water was mixed with pressurized
water containing dissolved gas, and produced bubbles
Figure 1. Testing device of flofilter. 1. Inlet pipe; 2. Dosage; 3. Dosage; 4. Mixing tank; 5. Flocculation tank; 6. Contact tank; 7. Flotation
tank; 8. Backwashing drain pipe; 9. Scum; 10. Filter layer; 11. Outlet
pipe; 12. Backwashing Inlet pipe; 13. Vent pipe; 14. Backwashing
inlet pipe; 15. From dissolved gas cylinders.
The Study on the Operating Characteristics of Algae-Contaminated Reservoir Water
tistically determined. All chemical reagents were of
analytic reagent grade. All glassware and polyethylene
tubes were soaked in 3% HCl overnight prior to use.
Excel 2003 was used to produce figures and perform
relevant statistical analyses.
EXPERIMENTAL RESULTS AND DISCUSSION
Optimization of Coagulant Dosage
Through the pre-experimental research, we chose
PAFC (PAFC) as the flocculant [12], and the dosing
method was used as the wet cast. The speed of mixing
was 50 r/min, and the stirring rate of the reaction was
15 r/min, with PAFC dosage specifically optimized.
CODMn
As can be seen from Figure 2, when PAFC dosage
was 4 mg/L, the removal rate of CODMn reached the
highest point, during which stage the total removal rate
reached 51.91% ± 4.26%, and the flotation removal
rate was 33.33% ± 2.58%. When PAFC dosage was
5~7 mg/L, the total removal rate remained in the range
of 33~45%, and it didn’t increase with the addition of
dosage. Meanwhile, the removal rate of flotation unit
decreased slightly, and the removal rate was in the
range of 10~30%. This is because the flotation process
required flocs with relatively small size after the coagulation process. With an increase of dosage, the generated floc gradually grew bigger, and the amount of gas
that contained in the floc would not provide sufficient
buoyancy. As a result, the stability of the carrier gas
floc went unsteady.
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ble when various amounts of dosage were used (Figure
2), and the total removal rate was about 80%. When
PAFC dosage was 4 mg/L, the removal rate was up to
84.82% ± 4.85%, and the removal rate using flotation
also reached 33.99% ± 3.21%. When the dosage was
5~7 mg/L, the average removal rate was approximately
80%. Although the removal effect was relatively good,
the flotation efficiency actually declined during this
stage. This is because the generated floc was becoming
bigger, and the amount of adhesion bubble was insufficient, all of which led to the fact that the buoyancy declined, and the stability of bubble-floc went unsteady.
With the addition of coagulant dosage, it would not
only increase the operating costs, but also produce a
large amount of metal ions due to the existence of excess amount of coagulant, resulting in aluminum residues in effluent [13]. Therefore, the optimum PAFC
dosage was determined as 4 mg/L (account as Al3+).
Optimized Reflux Flotation Ratio
When the dissolved air pressure was about 0.4 Mpa,
the dissolved air system produced small but dense bubbles in milky white color. Therefore, the reflux ratio of
the dissolved gas system was optimized under a stable
operation pressure of 0.4 Mpa.
CODMn
The removal of turbidity (by using flofilter) was sta-
It can be seen from Figure 3 that the maximum value
of CODMn in filter effluent was 1.33 mg/L, the minimum value was 0.97 mg/L, and the average value was
1.08 mg/L during the test period. When the reflux ratio
was in the range of 6~10%, the total removal rate of
CODMn was relatively high, and it might reach 62.53%
± 4.20%. This indicated that the removal of organic
matters using carbon-sand filter was not only related
to the adsorption and interception of carbon-sand filter
Figure 2. CODMn and Turbidity removal efficiency under different
dosage.
Figure 3. CODMn, Turbidity and UV254 removal under different reflux
ratio.
Turbidity
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Y. WANG, K. ZHANG, W. CHEN, H. WANG, M. LI and R. JIA
layer on the suspended solids, but also to the growth of
microorganisms attached to the filter. As a result, the
formed biofilm attached to the filter layer would play a
key role during the biodegradation process.
Turbidity
With an increase of reflux ratio, turbidity of flotation unit showed a decreasing trend (Figure 3), mainly
because the adhesion chance of micro-bubbles with
flocs was enhanced when the amount of dissolved gas
increased. Under different operating conditions with
varying reflux ratios, there were few differences in the
removal rate of flofilter, and the average removal rate
was maintained around 90%. The maximum turbidity
value of filter effluent was 0.36 NTU, the minimum value was 0.27 NTU, and the mean value was 0.31 NTU.
UV254
It can be seen from Figure 3 that the UV254 value of
influent was stable with the mean value as 0.040 cm–1.
The maximum UV254 value of enfluent was 0.022 cm–1,
the minimum value was 0.014 cm–1, and the average
value was 0.019 cm–1. With an increase of reflux ratio,
the total removal rate also increased. A relatively high
level of removal rate was obtained when reflux ratio
was between 8~12%, and the average removal rate was
66.5% ± 3.10%, beyond which the UV254 value of enfluent started to decrease.
According to the removal efficiency of CODMn,
turbidity and UV254, a relatively good removal effect
could be achieved during the operation process when
the reflux ratio was in the range of 8~10%. Therefore,
8% was chosen as the optimum reflux ratio when the
economic cost was taken into account.
Research on the Filter Unit Characteristics
GAC-sand filter materials were used in the filter
unit of flofilter device, and a certain amount of biofilm started to grow on the surface of the filter after
some running time. The organic compounds in the raw
water could provide nutrients for the development of
biofilms. Meanwhile, microbial metabolism could effectively reduce the pollutant content in the water
body. The quartz sand filter layer could effectively intercept the shedding biofilm, thus providing a protection mechanism for maintaining the quality of filtered
water. After some running time, the distribution of
microbial biomass and the removal efficiency of con-
taminants attached to different filter layer were investigated. Also, the characteristics of GAC-sand filter were
analyzed during different flotation states.
The Distribution of Microbial Biomass in the
Filter Layer
In order to investigate the growth conditions of biofilms attached to the surface of the filter, samples collected from different filter layers were used for biomass
detection and analysis. Sampling points were described
as following: the distance between the activated carbon
top of sampling point 1, 2 and 3 was 100 mm, 200 mm
and 500 mm, respectively, and sampling point 4 was
at the distance of 150 mm from the top of the quartz
sand. Also, the distribution patterns of microbial biomass from different carbon layers were studied. In order to quantify microbial biomass, filter samples were
collected for four consecutive months. The results
showed that microbial biomass mainly existed in the
activated carbon filter, which could account for 97.4%
± 1.21% of the total biomass. The highest value of microbial biomass was 50.2 nmol p/g, 15.7 times that of
the quartz sand (3.0 nmol p/g). Also, the particle size
of activated carbon and quartz was 0.8~1.2 mm. Due
to oxidation and activation process, the activated carbon formed a complex pore structure, with complex
functional groups and hydrocarbons established on
the carbon surface, which displayed following physical properties such as porous, light weight and larger
specific surface area. As a result, the pore structure was
capable of absorbing impurities in the water body due
to its strong adsorption capacity [14].
Contributions of Filter Layers to the Removal of
Pollutants
To further study the contributions of different filter
layers to the removal of pollutants, pollutants removal
efficiency at different filter layer depth was investigated, with test conditions shown as following: the reflux
ratio was 8%, PAFC dosing was 4.0 mg/L, and the filter
speed was 5 m/h. Simultaneously, water samples from
the raw water were collected and analyzed to obtain
parameters such as the DAF effluent, the effluent of
carbon filter layer 1, the effluent of carbon filter layer
2, the effluent of quartz sand layer and the effluent of
supporting layer. Test results were shown in Figure 4,
with sampling port numbers 1 to 6 representing the influent, and sampling points 1 to 4 representing the effluent.
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The Study on the Operating Characteristics of Algae-Contaminated Reservoir Water
efficiency. Turbidity could be further reduced by 12%
± 2.5% when water flew through the supporting layer,
suggesting that the supporting layer could not only
play a key role in supporting filter media and preventing erosion, but also intercept some particulate matters.
UV254
It can be seen from Figure 4 that UV254 was mainly
removed in the activated carbon layer, and the removal
rate of UV254 in the lower layer was higher than that in
the upper. One possible explanation is that suspended
biofilm debris had blocked the activated charcoal pore,
resulting in a decline of adsorption capacity of the activated carbon. By contrast, the quartz sand filter layer and
supporting layer contributed less to UV254 removal.
Figure 4. Removal efficiency curves of CODMn, Turbidity, and UV254.
CODMn
As shown in Figure 4, the CODMn of flofilter influent was in the range of 3.13–3.44 mg/L, the CODMn
of enfluent was in the range of 3.13–3.44 mg/L, and
the average total removal rate was 56%. The removal
of CODMn mainly occurred in the activated carbon
layer, and active carbon played a key role during the
biodegradation process since microbes could attach to
the surface and internal structure of the filter materials
after a long running time. Meanwhile, raw water with
high content of dissolved oxygen provided ideal conditions for biological metabolism. The removal rate of
CODMn in the upper layer of active carbon was higher
than that in the lower part due to the fact that most
microorganisms were living in the upper layer, indicating an asymmetric distribution of microbial biomass
within filter layers.
The Removal Efficiency of Water Polluted by Highdensity Algae Using Floating Filter Technology
The Removal Efficiency of Conventional Pollutants
After a period of steady operation process, PAFC
dosage was 4.0 mg/L, the reflux ratio was 8%, and the
filtration rate was 8.0 m/h. The removal efficiency of
CODMn, turbidity, UV254, ammonia nitrogen, NPOC,
particulate matters and blue-green algae by using flofilter technology were shown in Table 1.
Existing experimental results showed that flofilter
technology generally displayed a high removal rate of
conventional pollutants such as turbidity, particulate
matter and blue-green algae, with the average removal
rates above 90% for all cases. Although the removal
rate of other indicators was lower than 60%, the effluent quality could meet the requirement of drinking water quality standards, and the removal rate of CODMn
was significantly higher than that of common carbon
sand filter. The blue-green algae, particulate matters
and other organic pollutants were discharged with the
scum. As a result, their content in flotation effluent was
efficiently reduced. GAC-sand filter that integrated in
the filtration unit was adopted for further processing
Turbidity
It can be seen from Figure 4 that the effluent turbidity reached 0.33–0.42 NTU when the turbidity of raw
water was changed from 3.29 to 3.51 NTU with the
average removal rate as 90.0%. Turbidity removal contribution rate of activated carbon layer reached 63% ±
1.0%, whereas sand filter layer accounted for 25% ±
1.6%. Since some small inorganic particles had penetrated carbon filter layer, sand filter layer still had a
relatively large contribution to the turbidity removal
Table 1. The Removal Efficiency of Conventional Pollutants by Using Flofilter Technology.
Items
Raw water
DAF effluent
Flofilter effluent
Removal rate
CODMn
(mg/L)
Turbidity
(NTU)
UV254
(cm–1)
Ammonia Nitrogen
(mg/L)
NPOC
(mg/L)
Particulate Matter
(a/mL)
Blue-green Algae
(106 cells /L)
3.24
2.45
1.38
57.41
4.30
1.81
0.32
92.56
0.040
0.022
0.019
52.50
0.185
0.129
0.045
75.67
2.81
2.16
1.36
51.60
24217
—
853
96.48
2.593
—
0.197
92.40
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Y. WANG, K. ZHANG, W. CHEN, H. WANG, M. LI and R. JIA
Table 2. Removal Efficiency of Unconventional Pollutants by Floating Filter Technology (Unit: Mg/L).
Items
Raw water
Flofilter effluent
GB5749-2006
Analytic Hierarchy
Process (AHP) Odor
Earthy taste, Level 4
Odorless, Level 0
Odorless
Soil
Smelly
10–6
<5×
< 5 × 10–6
0.00001
Dimethyl
Borneol
Trichlormethane
Bromodichloromethane
Chlorodibromomethane
Tribromethane
0.035
0.014
0.02
0.0203
0.0180
0.06
0.0207
0.0093
0.01
0.0041
0.0111
0.01
10–6
<5×
< 5 × 10–6
0.00001
of pollutants, and such filter not only played a key role
in the interception and adsorption of inorganic and organic pollutants, but also degraded some organic substances. Moreover, the content of dissolved oxygen
was increased to a sufficient amount after the flotation
process. Therefore, the removal rate of GAC-sand filter was significantly higher than that of ordinary sand
carbon filter.
Removal Efficiency of Odor Substances and
Precursors of Disinfection Byproducts (DBPs)
Due to the growth of algae and actinomycetes, abnormal odor was disseminated from the surface water
of reservoirs contaminated by massive algal species
[15]. The smelly and dimethyl borneol was secreted
by actinomycetes, and the smelly substances were produced by algae during the metabolism process. Trihalomethanes (THMs) is a representative of the volatile
disinfection by-products, which displays some obvious
carcinogenicity. Similarly, tribromethane is also carcinogenic [16]. Therefore, it is necessary to study the
removal efficiency of DBPs precursors since trichloromethane, bromodichloromethane and chlorodibromomethane are all directly related to the yield of DBPs.
The removal efficiency of odor substances and precursors of DBPs by using flofilter technology was shown
in Table 1 and Table 2.
As shown in Table 1 and Table 2, flofilter technology displayed a good purification effect regarding odor
substances and precursors of DBPs. Also, it showed
a strong capacity to remove precursors of trichloromethane and chlorodibromomethane. The odor level
was lowered down from level 4 to level 0. Specifically,
the earthy odor was removed completely, and the soil
smelly and dimethyl borneol content was less than the
detection limit. Also, the removal rate of trichloromethane and chlorodibromomethane was 60% ± 4.50% and
55.1% ± 3.8%, respectively.
CONCLUSIONS
1. Through the optimization of relevant technology
parameters such as coagulation conditions, reflux
ratio and dosage, the right type of flocculant was
determined, PAFC was selected, the dosage was
chosen as 4.0 mg/L (Al3+), the dissolved air pressure was 0.4 Mpa, and the reflux ratio was 8%.
Under such test conditions, an excellent removal
efficiency was achieved.
2. Through studies of the distribution patterns of
microbial biomass in the filter, it was evident that
biomass mainly existed in the activated carbon
filter, which accounted for 97.4% ± 1.21% of the
total biomass, with the highest value of biomass as
50.2 nmol p/g, which was about 15.7 times that of
the quartz sand (3.0nmol p/g). Therefore, maximum amount of CODMn, turbidity, UV254, ammonia nitrogen and NPOC was efficiently removed in
the activated carbon layer.
3. The removal rate of particulate matters, bluegreen algae, turbidity, CODMn, UV254, ammonia
nitrogen and NPOC was 96.48%, 92.40%, 92.56%,
57.40%, 52.50%, 75.67% and 51.60%, respectively when algal density in the water reached the
peak. Odor level was lowered down from level 4
to level 0, and the effluent content of geosmin and
methylisoborneol was less than the detection limit.
Specifically, the removal efficiency of chloroform
and chlorodibromomethane reached 60% and
55.1%, respectively. The results thus showed that
flofilter technology had generally displayed an excellent removal efficiency of odor substances and
disinfection byproducts precursors.
ACKNOWLEDGEMENTS
This work was financially supported by the Natural
Water Pollution Control and Treatment Technology
Major Projects (2012ZX07404-003-006), Ministry
of Housing and Urban-Rural Development Technology Projects (2014-K5-026), Department of housing
and Urban-Rural Construction Department Technology Projects (KY022), Shandong province key development projects (2015GSF117003), Dr. Fund of
The Study on the Operating Characteristics of Algae-Contaminated Reservoir Water
Shandong Jianzhu University in 2015(XNBS1511)
and Universities Innovation Programme of Jinan City
(201303076), Natural Science Foundation of Shandong Province (ZR2014EEM009) and A Project of
Shandong Province Higher Educational Science and
Technology Program (J13LC01).
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