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Treating high-strength nitrate wastewater by three biological processes
~
Pergamon
War. Sci Tech. Vol.39.No.IG-II.pp.311-3t4.1999
C 1999 Published by ElsevierScience Ltd on bchalfofthe IAWQ Printed in Greal Britain. All rights reserved 0273-1223/99 $20.00 + 0.00
PH: S0273-1223(99)00291-7
TREATING HIGH-STRENGTH NITRATE WASTEWATER BY THREE BIOLOGICAL PROCESSES Shing-Der Chen, Chiu-Yang Chen, Yu-Feng Wang Department ofEnvironmental Engineering, National Chung Hsing University. 150 Kuokuang Road. Taichung, Taiwan 401. Republic ofChina
ABSTRACT Three different types of bioreactors including an activated sludge reactor (ASR). a biologically mediated activated carbon Iluidized bed reactor (BAFBR) and an upllow immobilized cell reactor (UICR) were studied. The results suggest that the carbon-nitrogen equivalent (CNE) ratio (in terms of CODIN) when using ASR to treat the wastewater will decrease as the sludge age increases while it will increase slightly as the influent concentration increases. The CNE ratios for BAFBR and VICR are 3.67 and 3.61 respectively. For the test between the two different growth types. the CNE ratio of suspended growth will be lower than the one of attached' growth. The alkalinity-nitrogen equivalent (ANE) ratio (in term of Alk .lN) for ASR is 3.78. for BAFBR it is 3.54. and for VIeR it is 3.63. These ANE ratios are comparable with the theoretical value 00.57. Under different operating conditions. slight changes of microorganisms arc detected in Scanning Electron Microscope observation, but the dominant species, bacillus group. showed superior growth in all cases. Tests with the immobilized cells. biofilms will grow on the surface of them at the end of operation and the subsequent biochemical reactions will concentrate on the outer layer of biofilms. C 1999 Published by Elsevier Science Ltd on behalf of the IA WQ. All rights reserved
KEYWORDS Activated sludge; denitrification; fluidized bed reactor; immobilized cell; nitrate; scanning electron microscope. INTRODUCTION Apart from the nitrifying effluent, higher concentrations of nitrate are contained in many industrial wastewater discharges, such as those from petrochemical and explosives factories. When these discharges flow into receiving waters, a major effect is the depletion of DO in these waters. Toxicity to aquatic animal life and adverse public health are some of the other negative effects of these discharges (EPA, 1993). Biological denitrification is widely used for removing nitrate from domestic wastewater and contaminated groundwater (Metcalf & Eddy, 1991; Lazarova et al.; 1992), However, very limited information is available for its application to wastewater containing high nitrate levels . The objective of the present study is hence, to determine the feasibility of application of biological denitrification to high nitrate level wastewater. The bioreactors used in the present study are: an activated sludge reactor (ASR), a biologically mediated activated carbon fluidized bed reactor (BAFBR), and an upflow immobilized cell reactor (UICR). 311
S.-D.CHEN et al.
312
Maintaining a continuous flow operation of these treatment systems, the influence of biological denitrification on the systems' operation as well as the different modes of growth of denitrifying organisms can be determined. EXPERIMENTS There were three different types of reactors used in this investigation as shown in Figures 1,2 and 3. Their effective volumes were 10 L, 2.75 Land 2.26 L respectively, while volumes of the filled particles (activated carbon or immobilized cell) were 25% of the effective volumes. The activated carbons used in BAFBR were type F400, obtained from the Calgon Company of USA, while the immobilized cell beads used in VICR were realized by entrapping the suspended denitrifying organisms by polyvinyl alcohol (PVA) phosphate esterification (Lin and Chen, 1993). The PVA material used was type BF-20, obtained from Chang-Chuen Petrochemical Company of Taiwan. RESULTS AND DISCUSSION Carbon-nitrogen equivalent ratio in biological denitrification treatment systems
In the present investigation, methanol was assumed to be the only C-source for the denitrifying organisms. The "carbon nitrogen equivalent (CNE) ratio" is defined as ACOD/~o..-N, which can also be expressed as (COD m - CODout)/(NOJ-N,n - NOx-Nout). In the experiment using ASR, the CNE ratio was found to decrease as the sludge age increased and the CNE ratio was linear with sludge age, i.e., the CNE ratio increased slightly as the influent concentration increased as shown in Figure 4. In the experiment using BAFBR and VICR, the CNE ratios were 3.67 and 3.61 respectively, as shown in Figures 5 and 6. The results obtained by using the two reactors were not much different. The criteria for testing the two different growth types would be that, the CNE ratio of suspended growth should be lower than the one of attached growth. The probable reason, as reported earlier, was the diffusional resistance of substrate caused by attached growth (Characklis and Marshall, 1990). The substrate had to overcome this resistance and then be consumed by the organisms inside the biofilm. The transport mechanisms of different substrates were also different, thus becoming the most important step in controlling the efficiency ofthe biological treatment system. Alkalinity-nitrogen equivalent ratio in biological denitrification treatment system Alkalinity increases during biological denitrification. The "alkalinity-nitrogen equivalent (ANE) ratio" is defined as, AAlldANOx-N, which can also be expressed as (AIkin' Alkout)/(NO)-N m - NOx-Nout). In the experiment using ASR, the ANE ratio was not observed to depend upon sludge age, and removal of 1 mg of nitrate-nitrogen produced 3.78 mg of alkalinity as CaCO). This value was slightly higher than the theoretical value of 3.57 mg of alkalinity as CaCO). The ANE ratio of ASR remained almost constant under different operational conditions. As shown in Figures 7 and 8, the ANE ratios in the experiment using BAFBR and VICR were 3.54 and 3.63 respectively, which were closer to the theoretical value as compared to those for ASR. Moreover, a pH controller which was installed in BAFBR controlled the pH in the system more precisely than in VICR and hence the BAFBR was afforded a lower ANR ratio.
Treat ing high-strength nitra te wastewater
313
4.----------------, elll uent
-.
"" 3.6
~
3.2
wastewater tank
reactor
waste sludge
Q 2.8
8
influent NO,-N = 500 mg/L y ~ 3.29 - 0.02 x
R' = 0 .955
5
Figure 1. Flow-sheet of the ASR.
10
15
20
25
30
sludge age (day)
Figure 4. Regression analysis of the CNE ratio for the ASR. 6000
~
r---------------. y =3 .67 x R' ~ 0.998
4000
oS Cl o
~ 2000 o l<:---~--'----'------l
o
400
800
1600
1200
£l.NOx-N (mglL)
Figure 5. Regression analysis of the CNE ratio for the BAFBR. Figure 2.
Flow-sheet of the BAFBR.
5000 , - --
-
-
-
-
-
-
-
-
-
-,
y = 3.6 1 X R' = 0.994
4000
~oS 3000 Cl
02000 u
ol<::.....---,,-----,,-----,,-----''-----,'----l
o
200
400
600
800
1000
1200
.6 NOx-N (rng/L)
Figure 6. Regression analysis of the CNE ratio for the UICR. wastewater lan k
Figure 3.
Flow-sheet of the UICR.
S.-D. CHEN et
314
5000
6000 , . . - - - - - - - - - - - - - , y
~
3.54 x
r---------------.., y = 3.63 X
4000
Rl_0.990
~ 4000
g
~ g 3000
~ 2000
~
Rl·0998
2000 1000
0""---'----"-----"--------'
o
400
800
~NOx-N
1200
1600
(mgIL)
Figure7. Regression analysisof the ANE ratio for the BAFBR.
Ol<::.._ _"--- _ _"'---_ _"'---_---l
o
300
600 ~NOx-N
900
1200
(mgIL)
Figure 8. Regression analysis of the ANE ratio for the VlCR.
Observation of microorganism species with Scanning Electron Microscope (SEM) Based on the SEM photographs of the denitrifying organisms using three reactors, it can be seen that under different operational conditions, slight changes occur in the microorganisms, however, the dominant species, i.e., bacillus group, retained its superior growth for all cases. Further, there were also many extracellular polymers existing between denitrifying organisms and the bioparticles of attached growth. The profile section of SEM photographs of immobilized cells indicates that the denitrifying organisms existed in the entire bioparticle, when the immobilized cells were initially entrapped. Following a period of initial operation, these denitrifying organisms no longer existed inside the bioparticle and a layer of biofilm was formed outside the bioparticle. This was a notable difference from the initial period when immobilized cell was first entrapped. SUMMARY AND CONCLUSIONS According to the CNE analysis of biological denitrification, the CNE ratio of ASR was found to decrease as the sludge age increased. The corresponding ratios for BAFBR and UIeR were 3.67 and 3.61 respectively. These results are very close to the values reported in the literature. The ANE analysis of biological denitrification revealed that. the ANE ratio for ASR is 3.78. The corresponding ratios for BAFBR and VICR are 3.54 and 3.63 respectively. If a precise pH control system is installed on the bioreactor, the results obtained should agree with the theoretical values. Under different operational conditions, slight changes in the microorganisms were detected through SEM observation, however, the dominant species, namely the bacillus group, retained its superior growth for all cases. From the experiment using the immobilized cells, it was observed that biofilms grow on the surface of these cells at the end of operation and the subsequent biochemical reactions concentrate on the outer layer of biofilms. REFERENCES Characklis, W. G. and MarshallK. C. (1990). Biofilms. John Wiley & Sons, Inc., New York. EPA (1993). Nitrogen control. US EPAl62S/IRl93 1010. Lazarova, V. Z., Capderille,B. and Nikolor, L. (1992). Biofilmperformanceof a fluidizedbed biofilm reactor for drinking water denitrification. Wat. Sci. Tech ., 26(3/4), 555-566. Lin, Y. F. and Chen, K. C. (1993). Denitrification by immobilized sludge with polyvinyl alcohol gels. Wat. Sci. Tech ., 28(7), 159-164. Metcalf & Eddy (1991). Wastewaler engineering: treatment, disposaland reuse. 3rdedn, McGraw-Hili, Inc., New York.
Pergamon
War. Sci Tech. Vol.39.No.IG-II.pp.311-3t4.1999
C 1999 Published by ElsevierScience Ltd on bchalfofthe IAWQ Printed in Greal Britain. All rights reserved 0273-1223/99 $20.00 + 0.00
PH: S0273-1223(99)00291-7
TREATING HIGH-STRENGTH NITRATE WASTEWATER BY THREE BIOLOGICAL PROCESSES Shing-Der Chen, Chiu-Yang Chen, Yu-Feng Wang Department ofEnvironmental Engineering, National Chung Hsing University. 150 Kuokuang Road. Taichung, Taiwan 401. Republic ofChina
ABSTRACT Three different types of bioreactors including an activated sludge reactor (ASR). a biologically mediated activated carbon Iluidized bed reactor (BAFBR) and an upllow immobilized cell reactor (UICR) were studied. The results suggest that the carbon-nitrogen equivalent (CNE) ratio (in terms of CODIN) when using ASR to treat the wastewater will decrease as the sludge age increases while it will increase slightly as the influent concentration increases. The CNE ratios for BAFBR and VICR are 3.67 and 3.61 respectively. For the test between the two different growth types. the CNE ratio of suspended growth will be lower than the one of attached' growth. The alkalinity-nitrogen equivalent (ANE) ratio (in term of Alk .lN) for ASR is 3.78. for BAFBR it is 3.54. and for VIeR it is 3.63. These ANE ratios are comparable with the theoretical value 00.57. Under different operating conditions. slight changes of microorganisms arc detected in Scanning Electron Microscope observation, but the dominant species, bacillus group. showed superior growth in all cases. Tests with the immobilized cells. biofilms will grow on the surface of them at the end of operation and the subsequent biochemical reactions will concentrate on the outer layer of biofilms. C 1999 Published by Elsevier Science Ltd on behalf of the IA WQ. All rights reserved
KEYWORDS Activated sludge; denitrification; fluidized bed reactor; immobilized cell; nitrate; scanning electron microscope. INTRODUCTION Apart from the nitrifying effluent, higher concentrations of nitrate are contained in many industrial wastewater discharges, such as those from petrochemical and explosives factories. When these discharges flow into receiving waters, a major effect is the depletion of DO in these waters. Toxicity to aquatic animal life and adverse public health are some of the other negative effects of these discharges (EPA, 1993). Biological denitrification is widely used for removing nitrate from domestic wastewater and contaminated groundwater (Metcalf & Eddy, 1991; Lazarova et al.; 1992), However, very limited information is available for its application to wastewater containing high nitrate levels . The objective of the present study is hence, to determine the feasibility of application of biological denitrification to high nitrate level wastewater. The bioreactors used in the present study are: an activated sludge reactor (ASR), a biologically mediated activated carbon fluidized bed reactor (BAFBR), and an upflow immobilized cell reactor (UICR). 311
S.-D.CHEN et al.
312
Maintaining a continuous flow operation of these treatment systems, the influence of biological denitrification on the systems' operation as well as the different modes of growth of denitrifying organisms can be determined. EXPERIMENTS There were three different types of reactors used in this investigation as shown in Figures 1,2 and 3. Their effective volumes were 10 L, 2.75 Land 2.26 L respectively, while volumes of the filled particles (activated carbon or immobilized cell) were 25% of the effective volumes. The activated carbons used in BAFBR were type F400, obtained from the Calgon Company of USA, while the immobilized cell beads used in VICR were realized by entrapping the suspended denitrifying organisms by polyvinyl alcohol (PVA) phosphate esterification (Lin and Chen, 1993). The PVA material used was type BF-20, obtained from Chang-Chuen Petrochemical Company of Taiwan. RESULTS AND DISCUSSION Carbon-nitrogen equivalent ratio in biological denitrification treatment systems
In the present investigation, methanol was assumed to be the only C-source for the denitrifying organisms. The "carbon nitrogen equivalent (CNE) ratio" is defined as ACOD/~o..-N, which can also be expressed as (COD m - CODout)/(NOJ-N,n - NOx-Nout). In the experiment using ASR, the CNE ratio was found to decrease as the sludge age increased and the CNE ratio was linear with sludge age, i.e., the CNE ratio increased slightly as the influent concentration increased as shown in Figure 4. In the experiment using BAFBR and VICR, the CNE ratios were 3.67 and 3.61 respectively, as shown in Figures 5 and 6. The results obtained by using the two reactors were not much different. The criteria for testing the two different growth types would be that, the CNE ratio of suspended growth should be lower than the one of attached growth. The probable reason, as reported earlier, was the diffusional resistance of substrate caused by attached growth (Characklis and Marshall, 1990). The substrate had to overcome this resistance and then be consumed by the organisms inside the biofilm. The transport mechanisms of different substrates were also different, thus becoming the most important step in controlling the efficiency ofthe biological treatment system. Alkalinity-nitrogen equivalent ratio in biological denitrification treatment system Alkalinity increases during biological denitrification. The "alkalinity-nitrogen equivalent (ANE) ratio" is defined as, AAlldANOx-N, which can also be expressed as (AIkin' Alkout)/(NO)-N m - NOx-Nout). In the experiment using ASR, the ANE ratio was not observed to depend upon sludge age, and removal of 1 mg of nitrate-nitrogen produced 3.78 mg of alkalinity as CaCO). This value was slightly higher than the theoretical value of 3.57 mg of alkalinity as CaCO). The ANE ratio of ASR remained almost constant under different operational conditions. As shown in Figures 7 and 8, the ANE ratios in the experiment using BAFBR and VICR were 3.54 and 3.63 respectively, which were closer to the theoretical value as compared to those for ASR. Moreover, a pH controller which was installed in BAFBR controlled the pH in the system more precisely than in VICR and hence the BAFBR was afforded a lower ANR ratio.
Treat ing high-strength nitra te wastewater
313
4.----------------, elll uent
-.
"" 3.6
~
3.2
wastewater tank
reactor
waste sludge
Q 2.8
8
influent NO,-N = 500 mg/L y ~ 3.29 - 0.02 x
R' = 0 .955
5
Figure 1. Flow-sheet of the ASR.
10
15
20
25
30
sludge age (day)
Figure 4. Regression analysis of the CNE ratio for the ASR. 6000
~
r---------------. y =3 .67 x R' ~ 0.998
4000
oS Cl o
~ 2000 o l<:---~--'----'------l
o
400
800
1600
1200
£l.NOx-N (mglL)
Figure 5. Regression analysis of the CNE ratio for the BAFBR. Figure 2.
Flow-sheet of the BAFBR.
5000 , - --
-
-
-
-
-
-
-
-
-
-,
y = 3.6 1 X R' = 0.994
4000
~oS 3000 Cl
02000 u
ol<::.....---,,-----,,-----,,-----''-----,'----l
o
200
400
600
800
1000
1200
.6 NOx-N (rng/L)
Figure 6. Regression analysis of the CNE ratio for the UICR. wastewater lan k
Figure 3.
Flow-sheet of the UICR.
S.-D. CHEN et
314
5000
6000 , . . - - - - - - - - - - - - - , y
~
3.54 x
r---------------.., y = 3.63 X
4000
Rl_0.990
~ 4000
g
~ g 3000
~ 2000
~
Rl·0998
2000 1000
0""---'----"-----"--------'
o
400
800
~NOx-N
1200
1600
(mgIL)
Figure7. Regression analysisof the ANE ratio for the BAFBR.
Ol<::.._ _"--- _ _"'---_ _"'---_---l
o
300
600 ~NOx-N
900
1200
(mgIL)
Figure 8. Regression analysis of the ANE ratio for the VlCR.
Observation of microorganism species with Scanning Electron Microscope (SEM) Based on the SEM photographs of the denitrifying organisms using three reactors, it can be seen that under different operational conditions, slight changes occur in the microorganisms, however, the dominant species, i.e., bacillus group, retained its superior growth for all cases. Further, there were also many extracellular polymers existing between denitrifying organisms and the bioparticles of attached growth. The profile section of SEM photographs of immobilized cells indicates that the denitrifying organisms existed in the entire bioparticle, when the immobilized cells were initially entrapped. Following a period of initial operation, these denitrifying organisms no longer existed inside the bioparticle and a layer of biofilm was formed outside the bioparticle. This was a notable difference from the initial period when immobilized cell was first entrapped. SUMMARY AND CONCLUSIONS According to the CNE analysis of biological denitrification, the CNE ratio of ASR was found to decrease as the sludge age increased. The corresponding ratios for BAFBR and UIeR were 3.67 and 3.61 respectively. These results are very close to the values reported in the literature. The ANE analysis of biological denitrification revealed that. the ANE ratio for ASR is 3.78. The corresponding ratios for BAFBR and VICR are 3.54 and 3.63 respectively. If a precise pH control system is installed on the bioreactor, the results obtained should agree with the theoretical values. Under different operational conditions, slight changes in the microorganisms were detected through SEM observation, however, the dominant species, namely the bacillus group, retained its superior growth for all cases. From the experiment using the immobilized cells, it was observed that biofilms grow on the surface of these cells at the end of operation and the subsequent biochemical reactions concentrate on the outer layer of biofilms. REFERENCES Characklis, W. G. and MarshallK. C. (1990). Biofilms. John Wiley & Sons, Inc., New York. EPA (1993). Nitrogen control. US EPAl62S/IRl93 1010. Lazarova, V. Z., Capderille,B. and Nikolor, L. (1992). Biofilmperformanceof a fluidizedbed biofilm reactor for drinking water denitrification. Wat. Sci. Tech ., 26(3/4), 555-566. Lin, Y. F. and Chen, K. C. (1993). Denitrification by immobilized sludge with polyvinyl alcohol gels. Wat. Sci. Tech ., 28(7), 159-164. Metcalf & Eddy (1991). Wastewaler engineering: treatment, disposaland reuse. 3rdedn, McGraw-Hili, Inc., New York.