An empirical model for COD removal in a biological aerated filter （BAF） in the presence of 2,4,6-trinitrophenol （TNP） was developed, which related effluent COD to influent COD or hydraulic loading rate along the b...An empirical model for COD removal in a biological aerated filter （BAF） in the presence of 2,4,6-trinitrophenol （TNP） was developed, which related effluent COD to influent COD or hydraulic loading rate along the bed height. The overall reaction rate for substrate biodegradation could be described as pseudo first order. The experimental data of COD removal against reactor height were used to calculate the parameters in the empirical model. The COD concentration at different reactor height was expressed as a function of influent COD concentration and hydraulic loading rate, ln（C0/C）=0.124H/QC0^0.77 and ln（C/C0）=-5.63H/L^0.94, respectively, under the experimental condition. The models may be used to predict the COD removal profiles along the reactor height at different hydraulic loading rates and influent COD concentration for design, selection and sizing of BAF.展开更多
Some aromatic compounds, phenol, aniline and nitrobenzene, were oxidized in supercritical water. It was experimentally found that the chemical oxygen demand (COD) removal efficiency of these organic compounds can achi...Some aromatic compounds, phenol, aniline and nitrobenzene, were oxidized in supercritical water. It was experimentally found that the chemical oxygen demand (COD) removal efficiency of these organic compounds can achieve a high level more than 90% in a short residence time at temperatures high enough. As temperature, pressure and residence time increase, the COD removal efficiencies of the organic compounds would all increase. It is also found that temperature and residence time offer greater influences on the oxidation process than pressure. The difficulty in oxidizing these three compounds is in the order of nitrobenzene ＞ aniline ＞ Phenol. In addition, it is extremely difficult to oxidize aniline and nitrobenzene to CO2 and H2O at the temperature lower than 873.15 K and 923.15 K, respectively. Only at the temperature higher than 873.15 K and 923.15 K, respectively, the COD removal efficiencies of 90% of aniline and nitrobenzene can be achieved.展开更多
The electrochemical treatment of COD contained in biologically pretreated coking wastewater treated by a three-dimensional electrode system with modified coke as the particle electrode was investigated. And the electr...The electrochemical treatment of COD contained in biologically pretreated coking wastewater treated by a three-dimensional electrode system with modified coke as the particle electrode was investigated. And the electrochemical perromance of the coke modified with various active components was studied. The results show that the coke modified with Fe（NO3）2 has the lowest energy consumption and higher COD removal rate under the same condition, and the modified coke has better surface characteristics for the purpose of this study. In addition, the kinetic constant was also calculated. The study shows that the three-dimensional electrode system with Fe （NO3）z-modified coke can give a satisfactory solution in biologically pretreated coking wastewater.展开更多
The main objective of this research was to study the removal of turbidity and COD （chemical oxygen demand） from a synthetic water sample. The water sample was treated chemically by coagulation. Two inorganic coagula...The main objective of this research was to study the removal of turbidity and COD （chemical oxygen demand） from a synthetic water sample. The water sample was treated chemically by coagulation. Two inorganic coagulants were used, ferric chloride and the double salt potassium-aluminium sulphate. The optimum coagulant dosage and working pH were examined. The results for ferric chloride as coagulant showed that the maximum removal efficiency （%） of COD was achieved at pH 6 with a dosage of 100 mg-L-1 and the maximum removal efficiency （%） of turbidity at pH 5 with a dosage of 500 mg.L-1. For double salt, as coagulant, the maximum removal efficiencies （%） of COD and turbidity were achieved at pH 6 with a dosage of 3,500 mg.L-1. An extensive comparison with results from previous studies was also described in this research.展开更多
Nitrobenzene-containing industrial wastewater was degraded in the presence of ozone coupled with H2O2 by high gravity technology. The effect of high gravity factor, H2O2 concentration, pH value, liquid flow-rate, and ...Nitrobenzene-containing industrial wastewater was degraded in the presence of ozone coupled with H2O2 by high gravity technology. The effect of high gravity factor, H2O2 concentration, pH value, liquid flow-rate, and reaction time on the efficiency for removal of nitrobenzene was investigated. The experimental results show that the high gravity technology enhances the ozone utilization efficiency with O3/H202 showing synergistic effect. The degradation efficiency in terms of the COD removal rate and nitrobenzene removal rate reached 45.8% and 50.4%, respectively, under the following reaction conditions, viz.： a high gravity factor of 66.54, a pH value of 9, a H2O2/O3 molar ratio of 1：1, a liquid flow rate of 140 L/h, an ozone concentration of 40 rag/L, a H2O2 multiple dosing mode of 6 mL/h, and a reaction time of 4 h. Compared with the performance of conventional stirred aeration mixers, the high gravity technology could increase the COD and nitrobenzene removal rate related with the nitrobenzene-containing wastewater by 22.9% and 23.3%, respectively.展开更多
Heterogeneous Fenton-like process using fly ash as a catalyst was studied to degrade n-butyl xanthate form aqueous solution. The different reaction parameters on the degradation efficiency of the process were investig...Heterogeneous Fenton-like process using fly ash as a catalyst was studied to degrade n-butyl xanthate form aqueous solution. The different reaction parameters on the degradation efficiency of the process were investigated. The fly ash/H2O2 catalyst possesses a high oxidation activity for n-butyl xanthate degradation in aqueous solution. It is found that both the dosage of catalyst and initial solution pH significantly affect the n-butyl xanthate conversion efficient. The results indicate that by using 1.176 mmol/L H2O2 and 1.0 g/L fly ash catalyst with mass fraction of 4.14% Fe(III) oxide at pH 3.0, almost 96.90% n-butyl xanthate conversion and over 96.66% COD removal can be achieved within 120 min with heterogeneous catalysis by fly ash. CS2 as an intermediate of n-butyl xanthate oxidation. Finally, it is demonstrated that the fly ash/H2O2 catalytic oxidation process can be an efficient method for the treatment of n-butyl xanthate containing wastewater.展开更多
Wastewater with high NH_4^+-N is difficult to treat by traditional methods.So in this paper,a wild strain of photosynthetic bacteria was used for high NH_4^+-N wastewater treatment together with biomass recovery.Isola...Wastewater with high NH_4^+-N is difficult to treat by traditional methods.So in this paper,a wild strain of photosynthetic bacteria was used for high NH_4^+-N wastewater treatment together with biomass recovery.Isolation,identification,and characterization of the microorganism were carried out.The strain was inoculated to the biological wastewater treatment unit.The impacts of important factors were examined,including temperature,dissolved oxygen,and light intensity.Results showed that photosynthetic bacteria could effectively treat high NH_4^+-N wastewater.For wastewater with NH_4^+-N of 2300 mg·L^(-1),COD/N=1.0,98.3%of COD was removed,and cell concentration increased by 43 times.The optimal conditions for the strain's cell growth and wastewater treatment were 30℃,dissolved oxygen of 0.5-1.5 mg·L^(-1) and a light intensity of 4000 lx.Photosynthetic bacteria could bear a lower C/N ratio than bacteria in a traditional wastewater treatment process,but the NH_4^+-N removal was only 20%-40%because small molecule carbon source was used prior to NH_4^+-N.Also,the use of photosynthetic bacteria in chicken manure wastewater containing NH4+-N about 7000 mg·L^(-1) proved that photosynthetic bacteria could remove NH_4^+-N in a real case,finally,83.2%of NH_4^+-N was removed and 66.3%of COD was removed.展开更多
In this study,an up-flow anaerobic sludge blanket(UASB) reactor was applied to treat the high salinity wastewater from heavy oil production process.At a HRT of ≥24 h,the COD removal reached as high as 65.08% at an in...In this study,an up-flow anaerobic sludge blanket(UASB) reactor was applied to treat the high salinity wastewater from heavy oil production process.At a HRT of ≥24 h,the COD removal reached as high as 65.08% at an influent COD ranging from 350mg/L to 640mg/L.An average of 74.33% oil reduction was also achieved in the UASB reactor at an initial oil concentration between 112mg/L and 205mg/L.These results indicated that this heavy oil production related wastewater could be degraded efficiently in the UASB reactor.Granular sludge was formed in this reactor.In addition,two models,built on the back propagation neural network(BPNN) theory and linear regression techniques were developed for the simulation of the UASB system performance in the oily wastewater biodegradation.The average error of COD and oil removal was-0.65% and 0.84%,respectively.The results indicated that the models built on the BPNN theory were wellfitted to the detected data,and were able to simulate and predict the removal of COD and oil by the UASB reactor.展开更多
Electrochemical treatment of distillery .spentwash was carried out using different combinations of aluminum and iron electrodes in batch mode of operation. The spent wash was characterized for various parameters as pe...Electrochemical treatment of distillery .spentwash was carried out using different combinations of aluminum and iron electrodes in batch mode of operation. The spent wash was characterized for various parameters as per standard method of analysis and the treatment results were analyzed in terms of chemical oxygen demand （COD） removal efficiency o.f thespent.wash. The experiments were performed to s.tudy the effect of operating parameterssuch as current density, pH of the spent wash, agitation speed, electrolysis time and the distance between the elec- trodes on the COD removal efficiency of the spent wash. It was observed that aluminum electrodes were more suitable for treatment of distillery spent wash as compared to iron electrodes. The maximum COD removal effi- ciency of 81.3% was obtained with A1-A1 electrodes at the current density of 0.187 A.cm-2 and pH 3 for an elec-trolysis time of 2 h.展开更多
[Objective] The aim was to obtain higher COD removal rate so as to guide the process of citric acid industrial wastewater. [Method] The effects of controllable factors, acidification time, hydraulic retention time, an...[Objective] The aim was to obtain higher COD removal rate so as to guide the process of citric acid industrial wastewater. [Method] The effects of controllable factors, acidification time, hydraulic retention time, and influent COD concentration, in-anaerobic treatment process of citric acid wastewater on COD removal rate were studied and the COD removal rate was optimized by response surface method. [Result] There was no interaction between acidification time and the other two factors. It was showed that hydraulic retention time and influent COD concentration had significant effect on COD removal rate and there was interaction between the two factors. The optimum COD removing process conditions was as follows: acidification time 1.53 h, hydraulic retention time 3.52 h and influent COD concentration 2 698 mg/L. Under the optimized conditions, the COD removal rate was 93.31% and it was much closed to the experimental result, 93.29%. [Conclusion] Using response surface method to optimize the anaerobic treatment of citric acid wastewater can result in optimized achievement.展开更多
After conducting a lot of screening experiments the appropriate flocculating formulations for treating high-concentration wastewater discharged from a certain refinery were selected. The oil removal rate and COD remov...After conducting a lot of screening experiments the appropriate flocculating formulations for treating high-concentration wastewater discharged from a certain refinery were selected. The oil removal rate and COD removal achieved by these flocculating formulations were better than that achieved by the conventional compound formulation consisting of polyaluminium chloride(PAC) and polyacrylamide(PAA) . Addition of an oil/water separating agent to the formulation could improve its oil removal performance to facilitate the oil/water separation of the oil-in-water emulsion in the high-concentration wastewater along with improved adaptability of the formulation to the wastewater containing high concentration of pollutants. This flocculating agent has promising prospects for commercial application.展开更多
In this study low-concentration wastewater was investigated in the integral two-phase anaerobic baffled reactor by determining the removal of COD at various HRT,reflex ratios,and temperatures. Results indicate that th...In this study low-concentration wastewater was investigated in the integral two-phase anaerobic baffled reactor by determining the removal of COD at various HRT,reflex ratios,and temperatures. Results indicate that the removal efficiency of COD is more than 90% at 25 ℃ and 10-h HRT with no wastewater recycled,and the removal efficiency is up to 88% at 8-h HRT and reflex ratio of 150%. The removal efficiency is decreased with the decreasing temperature and HRT. The removal efficiency of COD is approximately 60% at 10 ℃,which proves that the temperature does not affect it apparently. This research has significance for reducing the cost of wastewater and sludge treatment in cold area.展开更多
In order to investigate the effect of stripping and catalytic ozone oxidation technology on COD and ammonia nitrogen removal after coagulation and sedimentation, the efficiency of ozone oxidation and catalytic ozone o...In order to investigate the effect of stripping and catalytic ozone oxidation technology on COD and ammonia nitrogen removal after coagulation and sedimentation, the efficiency of ozone oxidation and catalytic ozone oxidation were compared. The experimental results showed that： stripping and catalytic ozone oxidation technology has a significant effect on landfill leachate treatment. The removal rate of the COD and NH3-N can reach 88.60% and 98.00% under the initial concentration of COD and NH3-N were 2053.35 mg/L and l 123. 76 mg/L separately.展开更多
[Objective] The aim was to study the COD removal effect of emulsifier wastewater and provide experimental basis for the design, adjustment and operation of project. [Method] Using UASB+SBR technology to process emulsi...[Objective] The aim was to study the COD removal effect of emulsifier wastewater and provide experimental basis for the design, adjustment and operation of project. [Method] Using UASB+SBR technology to process emulsifier wastewater, the problems in operation process were discussed. [Result] The experiment carried out for 71 d, under the situation of large changes of COD concentration (the highest: 10 924 mg/L, the lowest: 2 880 mg/L, mean value: 5 751 mg/L), COD removal efficiency of UASB was around 70% and the COD removal efficiency of SBR was above 70%, which met the emission standard. [Conclusion] The combined technology had good treatment effect on the emulsifier wastewater.展开更多
基金Supported by Innovation Grant for Graduate of Jiangsu Province (AD20246)
文摘An empirical model for COD removal in a biological aerated filter （BAF） in the presence of 2,4,6-trinitrophenol （TNP） was developed, which related effluent COD to influent COD or hydraulic loading rate along the bed height. The overall reaction rate for substrate biodegradation could be described as pseudo first order. The experimental data of COD removal against reactor height were used to calculate the parameters in the empirical model. The COD concentration at different reactor height was expressed as a function of influent COD concentration and hydraulic loading rate, ln（C0/C）=0.124H/QC0^0.77 and ln（C/C0）=-5.63H/L^0.94, respectively, under the experimental condition. The models may be used to predict the COD removal profiles along the reactor height at different hydraulic loading rates and influent COD concentration for design, selection and sizing of BAF.
基金the Research Foundation of SINOPEC(No. X596006) and Cao Guangbiao's Advanced Research Foundation of Zhejiang University.
文摘Some aromatic compounds, phenol, aniline and nitrobenzene, were oxidized in supercritical water. It was experimentally found that the chemical oxygen demand (COD) removal efficiency of these organic compounds can achieve a high level more than 90% in a short residence time at temperatures high enough. As temperature, pressure and residence time increase, the COD removal efficiencies of the organic compounds would all increase. It is also found that temperature and residence time offer greater influences on the oxidation process than pressure. The difficulty in oxidizing these three compounds is in the order of nitrobenzene ＞ aniline ＞ Phenol. In addition, it is extremely difficult to oxidize aniline and nitrobenzene to CO2 and H2O at the temperature lower than 873.15 K and 923.15 K, respectively. Only at the temperature higher than 873.15 K and 923.15 K, respectively, the COD removal efficiencies of 90% of aniline and nitrobenzene can be achieved.
文摘The electrochemical treatment of COD contained in biologically pretreated coking wastewater treated by a three-dimensional electrode system with modified coke as the particle electrode was investigated. And the electrochemical perromance of the coke modified with various active components was studied. The results show that the coke modified with Fe（NO3）2 has the lowest energy consumption and higher COD removal rate under the same condition, and the modified coke has better surface characteristics for the purpose of this study. In addition, the kinetic constant was also calculated. The study shows that the three-dimensional electrode system with Fe （NO3）z-modified coke can give a satisfactory solution in biologically pretreated coking wastewater.
文摘The main objective of this research was to study the removal of turbidity and COD （chemical oxygen demand） from a synthetic water sample. The water sample was treated chemically by coagulation. Two inorganic coagulants were used, ferric chloride and the double salt potassium-aluminium sulphate. The optimum coagulant dosage and working pH were examined. The results for ferric chloride as coagulant showed that the maximum removal efficiency （%） of COD was achieved at pH 6 with a dosage of 100 mg-L-1 and the maximum removal efficiency （%） of turbidity at pH 5 with a dosage of 500 mg.L-1. For double salt, as coagulant, the maximum removal efficiencies （%） of COD and turbidity were achieved at pH 6 with a dosage of 3,500 mg.L-1. An extensive comparison with results from previous studies was also described in this research.
基金financially supported by the National Natural Science Foundation of China(21206153)Science and Technology Development Program Fund of Taiyuan City(120164053)
文摘Nitrobenzene-containing industrial wastewater was degraded in the presence of ozone coupled with H2O2 by high gravity technology. The effect of high gravity factor, H2O2 concentration, pH value, liquid flow-rate, and reaction time on the efficiency for removal of nitrobenzene was investigated. The experimental results show that the high gravity technology enhances the ozone utilization efficiency with O3/H202 showing synergistic effect. The degradation efficiency in terms of the COD removal rate and nitrobenzene removal rate reached 45.8% and 50.4%, respectively, under the following reaction conditions, viz.： a high gravity factor of 66.54, a pH value of 9, a H2O2/O3 molar ratio of 1：1, a liquid flow rate of 140 L/h, an ozone concentration of 40 rag/L, a H2O2 multiple dosing mode of 6 mL/h, and a reaction time of 4 h. Compared with the performance of conventional stirred aeration mixers, the high gravity technology could increase the COD and nitrobenzene removal rate related with the nitrobenzene-containing wastewater by 22.9% and 23.3%, respectively.
基金Project(CZQ13002)supported by the Special Fund for Basic Scientific Research of Central Universities,China
文摘Heterogeneous Fenton-like process using fly ash as a catalyst was studied to degrade n-butyl xanthate form aqueous solution. The different reaction parameters on the degradation efficiency of the process were investigated. The fly ash/H2O2 catalyst possesses a high oxidation activity for n-butyl xanthate degradation in aqueous solution. It is found that both the dosage of catalyst and initial solution pH significantly affect the n-butyl xanthate conversion efficient. The results indicate that by using 1.176 mmol/L H2O2 and 1.0 g/L fly ash catalyst with mass fraction of 4.14% Fe(III) oxide at pH 3.0, almost 96.90% n-butyl xanthate conversion and over 96.66% COD removal can be achieved within 120 min with heterogeneous catalysis by fly ash. CS2 as an intermediate of n-butyl xanthate oxidation. Finally, it is demonstrated that the fly ash/H2O2 catalytic oxidation process can be an efficient method for the treatment of n-butyl xanthate containing wastewater.
基金Supported by the National Natural Science Foundation of China(51278489)
文摘Wastewater with high NH_4^+-N is difficult to treat by traditional methods.So in this paper,a wild strain of photosynthetic bacteria was used for high NH_4^+-N wastewater treatment together with biomass recovery.Isolation,identification,and characterization of the microorganism were carried out.The strain was inoculated to the biological wastewater treatment unit.The impacts of important factors were examined,including temperature,dissolved oxygen,and light intensity.Results showed that photosynthetic bacteria could effectively treat high NH_4^+-N wastewater.For wastewater with NH_4^+-N of 2300 mg·L^(-1),COD/N=1.0,98.3%of COD was removed,and cell concentration increased by 43 times.The optimal conditions for the strain's cell growth and wastewater treatment were 30℃,dissolved oxygen of 0.5-1.5 mg·L^(-1) and a light intensity of 4000 lx.Photosynthetic bacteria could bear a lower C/N ratio than bacteria in a traditional wastewater treatment process,but the NH_4^+-N removal was only 20%-40%because small molecule carbon source was used prior to NH_4^+-N.Also,the use of photosynthetic bacteria in chicken manure wastewater containing NH4+-N about 7000 mg·L^(-1) proved that photosynthetic bacteria could remove NH_4^+-N in a real case,finally,83.2%of NH_4^+-N was removed and 66.3%of COD was removed.
基金the support provided by the Research & Technology Development Project of China National Petroleum Corporation (06A0302)Postdoctor Innovation Funds in Shandong Province (201002039)the Fundamental Research Funds for the Central Universities (27R1204023A)
文摘In this study,an up-flow anaerobic sludge blanket(UASB) reactor was applied to treat the high salinity wastewater from heavy oil production process.At a HRT of ≥24 h,the COD removal reached as high as 65.08% at an influent COD ranging from 350mg/L to 640mg/L.An average of 74.33% oil reduction was also achieved in the UASB reactor at an initial oil concentration between 112mg/L and 205mg/L.These results indicated that this heavy oil production related wastewater could be degraded efficiently in the UASB reactor.Granular sludge was formed in this reactor.In addition,two models,built on the back propagation neural network(BPNN) theory and linear regression techniques were developed for the simulation of the UASB system performance in the oily wastewater biodegradation.The average error of COD and oil removal was-0.65% and 0.84%,respectively.The results indicated that the models built on the BPNN theory were wellfitted to the detected data,and were able to simulate and predict the removal of COD and oil by the UASB reactor.
文摘Electrochemical treatment of distillery .spentwash was carried out using different combinations of aluminum and iron electrodes in batch mode of operation. The spent wash was characterized for various parameters as per standard method of analysis and the treatment results were analyzed in terms of chemical oxygen demand （COD） removal efficiency o.f thespent.wash. The experiments were performed to s.tudy the effect of operating parameterssuch as current density, pH of the spent wash, agitation speed, electrolysis time and the distance between the elec- trodes on the COD removal efficiency of the spent wash. It was observed that aluminum electrodes were more suitable for treatment of distillery spent wash as compared to iron electrodes. The maximum COD removal effi- ciency of 81.3% was obtained with A1-A1 electrodes at the current density of 0.187 A.cm-2 and pH 3 for an elec-trolysis time of 2 h.
文摘[Objective] The aim was to obtain higher COD removal rate so as to guide the process of citric acid industrial wastewater. [Method] The effects of controllable factors, acidification time, hydraulic retention time, and influent COD concentration, in-anaerobic treatment process of citric acid wastewater on COD removal rate were studied and the COD removal rate was optimized by response surface method. [Result] There was no interaction between acidification time and the other two factors. It was showed that hydraulic retention time and influent COD concentration had significant effect on COD removal rate and there was interaction between the two factors. The optimum COD removing process conditions was as follows: acidification time 1.53 h, hydraulic retention time 3.52 h and influent COD concentration 2 698 mg/L. Under the optimized conditions, the COD removal rate was 93.31% and it was much closed to the experimental result, 93.29%. [Conclusion] Using response surface method to optimize the anaerobic treatment of citric acid wastewater can result in optimized achievement.
文摘After conducting a lot of screening experiments the appropriate flocculating formulations for treating high-concentration wastewater discharged from a certain refinery were selected. The oil removal rate and COD removal achieved by these flocculating formulations were better than that achieved by the conventional compound formulation consisting of polyaluminium chloride(PAC) and polyacrylamide(PAA) . Addition of an oil/water separating agent to the formulation could improve its oil removal performance to facilitate the oil/water separation of the oil-in-water emulsion in the high-concentration wastewater along with improved adaptability of the formulation to the wastewater containing high concentration of pollutants. This flocculating agent has promising prospects for commercial application.
基金Sponsored by the National Natural Science Foundation of China(Grant No. 50778080)China's Jilin Province Office of Education(Grant No.200696)Scientific Research Project of the Chinese Ministry of Education(Grant No.03034)
文摘In this study low-concentration wastewater was investigated in the integral two-phase anaerobic baffled reactor by determining the removal of COD at various HRT,reflex ratios,and temperatures. Results indicate that the removal efficiency of COD is more than 90% at 25 ℃ and 10-h HRT with no wastewater recycled,and the removal efficiency is up to 88% at 8-h HRT and reflex ratio of 150%. The removal efficiency is decreased with the decreasing temperature and HRT. The removal efficiency of COD is approximately 60% at 10 ℃,which proves that the temperature does not affect it apparently. This research has significance for reducing the cost of wastewater and sludge treatment in cold area.
文摘In order to investigate the effect of stripping and catalytic ozone oxidation technology on COD and ammonia nitrogen removal after coagulation and sedimentation, the efficiency of ozone oxidation and catalytic ozone oxidation were compared. The experimental results showed that： stripping and catalytic ozone oxidation technology has a significant effect on landfill leachate treatment. The removal rate of the COD and NH3-N can reach 88.60% and 98.00% under the initial concentration of COD and NH3-N were 2053.35 mg/L and l 123. 76 mg/L separately.
文摘[Objective] The aim was to study the COD removal effect of emulsifier wastewater and provide experimental basis for the design, adjustment and operation of project. [Method] Using UASB+SBR technology to process emulsifier wastewater, the problems in operation process were discussed. [Result] The experiment carried out for 71 d, under the situation of large changes of COD concentration (the highest: 10 924 mg/L, the lowest: 2 880 mg/L, mean value: 5 751 mg/L), COD removal efficiency of UASB was around 70% and the COD removal efficiency of SBR was above 70%, which met the emission standard. [Conclusion] The combined technology had good treatment effect on the emulsifier wastewater.
