Electrodialysis (ED) of NaNO3 solutions was performed to stress the role of the membrane pair as a unit i.e. the behavior as a whole of Anion Exchange Membrane (AEM) and Cation Exchange Membrane (CEM), in the process ...Electrodialysis (ED) of NaNO3 solutions was performed to stress the role of the membrane pair as a unit i.e. the behavior as a whole of Anion Exchange Membrane (AEM) and Cation Exchange Membrane (CEM), in the process at room temperature. The membrane pair was also tested in the reclamation of nitric acid and sodium hydroxide. It was found that the membrane pair ranking in Limiting Current Density does not agree with that of ions leakage and both rankings are not the same as for Current Efficiency or Specific Power Consumption, each parameter for a specific membrane pair depends on the associated membrane and at a lesser degree on the flow rate. Results show that one cannot select a membrane or a membrane pair only by its limiting current density i.e. it is necessary to evaluate several parameters of the process by characterizing the whole membrane pair and to decide the parameter of interest, i.e. denitrification speed, ions leakage, proton back migration, current efficiency or specific power consumption.展开更多
The optimal operation conditions in an anoxic sulfide oxidizing (ASO) bioreactor were investigated. The maximal removal rates for sulfide and nitrate were found to be 4.18 kg/(m3·d) and 1.73 kg/(m3·d), respe...The optimal operation conditions in an anoxic sulfide oxidizing (ASO) bioreactor were investigated. The maximal removal rates for sulfide and nitrate were found to be 4.18 kg/(m3·d) and 1.73 kg/(m3·d), respectively. The volumetrical volumetric loading rates (LRs) observed through decreasing hydraulic retention time (HRT) at fixed substrate concentration are higher than those by increasing substrate concentration at fixed HRT. The sulfide oxidation in ASO reactor was partially producing both sulfate and sulfur; but the amount of sulfate produced was approximately one third that of sulfur. The process was able to tolerate high sulfide concentration, as the sulfide removal percentage always remained near 99% when influent concentration was up to 580 mg/L. It tolerated relatively lower nitrate concentration because the removal percentage dropped to 85% when influent con- centration was increased above 110 mg/L. The process can tolerate shorter HRT but careful operation is needed. Nitrate conversion was more sensitive to HRT than sulfide conversion since the process performance deteriorated abruptly when HRT was decreased from 3.12 h to 2.88 h. In order to avoid nitrite accumulation in the reactor, the influent sulfide and nitrate concentrations should be kept at 280 mg/L and 67.5 mg/L respectively. Present biotechnology is useful for removing sulfides from sewers and crude oil.展开更多
Denitrification is an important process of nitrogen removal in lake ecosystems.However,the importance of denitrification across the entire soil-depth gradients including subsurface layers remains poorly understood.Thi...Denitrification is an important process of nitrogen removal in lake ecosystems.However,the importance of denitrification across the entire soil-depth gradients including subsurface layers remains poorly understood.This study aims to determine the spatial pattern of soil denitrification enzyme activity(DEA) and its environmental determinants across the entire soil depth gradients in the raised fields in Baiyang Lake,North China.In two different zones of the raised fields(i.e.,water boundary vs.main body of the raised fields),the soil samples from 1.0 m to 1.1 m depth were collected,and the DEA and following environmental determinants were quantified:soil moisture,p H,total nitrogen(TN),ammonia nitrogen(NH4+-N),nitrate nitrogen(NO3–-N),total organic carbon(TOC),and rhizome biomass of Phragmites australis.The results showed that the soil DEA and environmental factors had a striking zonal distribution across the entire soil depth gradients.The soil DEA reached two peak values in the upper and middle soil layers,indicating that denitrification are important in both topsoil and subsurface of the raised fields.The correlation analysis showed that the DEA is negatively correlated with the soil depth(p < 0.05).However,this phenomenon did not occur in the distance to the water edge,except in the upper layers(from 0.2 m to 0.7 m) of the boundary zone of the raised fields.In the main body of the raised fields,the DEA level remained high;however,it showed no significant relationship with the distance to the water edge.The linear regression analysis showed significant positive correlation of the DEA with the soil TN,NO3–-N,NH4+-N,and TOC;whereas it showed negative correlation with soil p H.No significant correlations with soil moisture and temperature were observed.A positive correlation was also found between the DEA and rhizome biomass of P.australis.展开更多
In this study,the biochar (BC) produced from sawdust,sludge,reed and walnut were used to support sulfidation of nano-zero-valent-iron (S-nZVI) to enhance nitrate NO_(3)^(-) removal and investigate the impact on greenh...In this study,the biochar (BC) produced from sawdust,sludge,reed and walnut were used to support sulfidation of nano-zero-valent-iron (S-nZVI) to enhance nitrate NO_(3)^(-) removal and investigate the impact on greenhouse gas emissions.Batch experiment results showed the S-nZVI/BC(sawdust (2:1,500)),S-n ZVI/BC(sludge (2:1,900)),S-n ZVI/BC(reed (2:1,700)),and S-n ZVI/BC(walnut (2:1,700))respectively improved NO_(3)^(-) removal efficiencies by 22%,20%,3%and0.1%,and the selectivity toward N_(2)by 22%,25%,22%and 18%.S-nZVI uniformly loaded on BC provided electrons for the conversion of NO_(3)^(-) to N_(2)through Fe0.At the same time,FeSxlayer was formed on the outer layer of ZVI in the sulfidation process to prevent iron oxidation,so as to improve the electrons utilization efficiency After adding four kinds of S-nZVI/BC into constructed wetlands (CWs),the NO_(3)^(-) removal efficiencies could reach 100%and the N_(2)O emission fluxes were reduced by 24.17%-36.63%.And the average removal efficiencies of TN,COD,TP were increased by 21.9%,-16.5%,44.3%,repectively.The increasing relative abundances of denitrifying bacteria,such as Comamonas and Simplicispira,suggested that S-nZVI/BC could also improve the process of microbial denitrification.In addition,different S-nZVI/BC had different effects on denitrification functional genes (narG,nirk,nirS and nos Z genes),methanotrophs (pmoA) and methanogenesis (mcrA).This research provided an effective method to improve NO_(3)^(-) removal and reduce N_(2)O emission in CWs.展开更多
In this study,a sequential process(heterotrophic up-flow column and completely mixed membrane bioreactors)was proposed combining advantages of the both processes.The system was operated for 249 days with simulated and...In this study,a sequential process(heterotrophic up-flow column and completely mixed membrane bioreactors)was proposed combining advantages of the both processes.The system was operated for 249 days with simulated and real groundwater for nitrate removal at concentrations varying from 25 to 145 mg·L^(-1) NO_(3)^(-)-N.The contribution of heterotrophic process to total nitrate removal in the system was controlled by dozing the ethanol considering the nitrate concentration.By this way,sulfur based autotrophic denitrification rate was decreased and the effluent sulfate concentrations were controlled.The alkalinity requirement in the autotrophic process was produced in the heterotrophic reactor,and the system was operated without alkalinity supplementation.Throughout the study,the chemical oxygen demand in the heterotrophic reactor effluent was(23.7±22)mg L^(-1) and it was further decreased to(7.5±7.2)mg·L^(-1) in the system effluent,corresponding to a 70%reduction.In the last period of the study,the real groundwater containing 145 mg·L^(-1) NO_(3)^(-)-N was completely removed.Membrane was operated without chemical washing in the first 114 days.Between days 115-249 weekly chemical washing was required.展开更多
Global water bodies are increasingly imperiled by nitrate pollution,primarily originating from industrial waste,agricultural runoffs,and urban sewage.This escalating environmental crisis challenges traditional water t...Global water bodies are increasingly imperiled by nitrate pollution,primarily originating from industrial waste,agricultural runoffs,and urban sewage.This escalating environmental crisis challenges traditional water treatment paradigms and necessitates innovative solutions.Electro-catalysis,especially utilizing copper-based catalysts,known for their efficiency,cost-effectiveness,and eco-friendliness,offer a promising avenue for the electro-catalytic reduction of nitrate to ammonia.In this review,we systematically consolidate current research on diverse copper-based catalysts,including pure Cu,Cu alloys,oxides,single-atom entities,and composites.Furthermore,we assess their catalytic performance,operational mechanisms,and future research directions to find effective,long-term solutions to water purification and ammonia synthesis.Electro-catalysis technology shows the potential in mitigating nitrate pollution and has strategic importance in sustainable environmental management.As to the application,challenges regarding complexity of the real water,the scale-up of the commerical catalysts,and the efficient collection of produced NH3 are still exist.Following reseraches of catalyst specially on long term stability and in situ mechanisms are proposed.展开更多
Excessive nitrate(NO3-)is among the most problematic surface water and groundwater pollutants.In this study,a type of magnetic cationic hydrogel(MCH)is employed for NO3-adsorption and well characterized herein.Its ads...Excessive nitrate(NO3-)is among the most problematic surface water and groundwater pollutants.In this study,a type of magnetic cationic hydrogel(MCH)is employed for NO3-adsorption and well characterized herein.Its adsorption capacity is considerably pHdependent and achieves the optimal adsorption(maximum NO3--adsorption capacity is95.88±1.24 mg/g)when the pH level is 5.2-8.8.The fitting result using the homogeneous surface diffusion model indicates that the surface/film diffusion controls the adsorption rate,and NO3-approaches the center of MCH particles within 30 min.The diffusion coefficient(Ds)and external mass transfer coefficient(kF)in the liquid phase are1.15×10-6 cm2/min and 4.5×10-6 cm/min,respectively.The MCH is employed to treat surface water that contains 10 mg/L of NO3-,and it is found that the optimal magnetic separation time is 1.6 min.The high-efficiency mass transfer and magnetic separation of MCH during the adsorption-regeneration process favors its application in surface water treatment.Furthermore,the study of the mechanism involved reveals that both-N+(CH3)3 groups and NO3-are convoluted in adsorption via electrostatic interactions.It is further found that ion exchange between NO3-and chlorine occurs.展开更多
Bioaugmentation of denitrifying bacteria can serve as a promising technique to improve nutrient removal during wastewater treatment. While denitrification inhibition by bacterial quorum sensing(QS) in Pseudomonas aeru...Bioaugmentation of denitrifying bacteria can serve as a promising technique to improve nutrient removal during wastewater treatment. While denitrification inhibition by bacterial quorum sensing(QS) in Pseudomonas aeruginosa has been indicated, the application of bacterial QS disruption to improve nitrate removal from wastewater has not been investigated. In this study, the effect of bioaugmentation of P. aeruginosa SD-1 on nitrate removal in sequencing batch reactors that treat nitrate rich wastewater was assessed. Additionally, the potential of a quorum sensing inhibitor(QSI) to improve denitrification following bacterial bioaugmentation was evaluated. Curcumin, a natural plant extract, was used as a QSI. The chemical oxygen demand(COD) and initial nitrate concentration of the influent were 700 ±20 mg/L and 200 ±10 mg/L respectively, and their respective concentrations in the effluent were 56.9 ±3.2 mg/L and 9.0 ±3.2 mg/L. Thus, the results revealed that bioaugmentation of P. aeruginosa SD-1 resulted in an increased nitrate removal to 82% ±1%. Further, nitrate was almost completely removed following the addition of the QSI, and activities of nitrate reductase and nitrite reductase increased by 88% ±2% and 74% ±2% respectively. The nitrogen mass balance indicated that aerobic denitrification was employed as the main pathway for nitrogen removal in the reactors. The results imply that bioaugmentation and modulation of QS in denitrifying bacteria, through the use of a QSI, can enhance nitrate removal during wastewater treatment.展开更多
A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank （0.04 m2 tank surface area）, packed to a depth of 5 cm with a b...A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank （0.04 m2 tank surface area）, packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions （e.g. 〉 2 mg/L） while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested （soil, sand, pumice stone and vermiculite）, pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD：N ratio of 5：1, a nitrate removal rate of 4591 ± 133 mg-N/m2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD：N ratio of 5：1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 ± 945 mg-N/m2 tank bottom area/day or 126 ± 18 mg-N/L of pumice packing volume/day.展开更多
This study focuses on identifying the factors under which mixed microbial seeds assist bio-chemical denitrification when Scrap Iron Filings(SIF)are used as electron donors and adsorbents in low C/N ratio waters.Batch ...This study focuses on identifying the factors under which mixed microbial seeds assist bio-chemical denitrification when Scrap Iron Filings(SIF)are used as electron donors and adsorbents in low C/N ratio waters.Batch studies were conducted in abiotic and biotic reactors containing fresh and aged SIF under different dissolved oxygen concentrations with NO_(3)^(-)−N and/or PO_(4)^(3−)influent(s)and their nitrate/phosphate removal and by-product formations were studied.Batch reactors were seeded with a homogenized mixed microbial inoculum procured from natural sludges which were enriched over 6 months under denitrifying conditions in the presence of SIF.Results indicated that when influent containing 40 mg/L of NO_(3)^(-)−N was treated with 5 g SIF,79.9%nitrate reduction was observed in 8 days abiotically and 100%removal was accomplished in 20 days when the reactor was seeded.Both abiotic and seeded reactors removed more than 92%PO_(4)^(3−)under high DO conditions in 12 days.Abiotic and biochemical removal of NO_(3)^(-)−N and abiotic removal of PO_(4)^(3−)were higher under independent NO_(3)^(-)−N/PO_(4)^(3−)loading,while 99%PO_(4)^(3−)was removed biochemically under combined NO_(3)^(-)−N and PO_(4)^(3−)loading.This study furthers the understandings of nitrate and phosphate removal in Zero Valent Iron(ZVI)assisted mixed microbial systems to encourage the application of SIF-supported bio-chemical processes in the simultaneous removals of these pollutants.展开更多
In recent years there has been an increasing interest in the use of autohydrogenotrophic bacteria to treat nitrate from wastewater. However, our knowledge about the characteristics of extracellular polymeric substance...In recent years there has been an increasing interest in the use of autohydrogenotrophic bacteria to treat nitrate from wastewater. However, our knowledge about the characteristics of extracellular polymeric substances（EPS） releasing by these activities is not yet very advanced. This study aimed to investigate the change in EPS compositions under various p H values and hydrogen flow rates, taking into consideration nitrogen removal. Results showed that p H 7.5 and a hydrogen flow rate of 90 m L/min were the optimal operating conditions, resulting in 100% nitrogen removal after 6 hr of operation. Soluble and bound polysaccharides decreased, while bound proteins increased with increasing p H. Polysaccharides increased with increasing hydrogen flow rate. No significant change of bound proteins was observed at various hydrogen flow rates.展开更多
The problem of nitrate accumulation in aerobic tank and total nitrogen excessive discharge in effluent was very common in traditional livestock and poultry farming wastewater treatment systems owing to the lengthy pro...The problem of nitrate accumulation in aerobic tank and total nitrogen excessive discharge in effluent was very common in traditional livestock and poultry farming wastewater treatment systems owing to the lengthy process flow and low process control level.A strain LYX of aerobic bacterium was isolated from the activated sludge of a wastewater treatment system in a pig farm,which could remove nitrate effectively in aerobic tank and was identified Pseudomonas mendocina by 16S rRNA sequencing.Under the condition of nitrate as the sole nitrogen source,this strain removed over 90%of NO_(3)^(−)-N with an initial concentration of 110 mg/L under aerobic conditions within 48 hours.Among them,37.9%of NO_(3)^(−)-N was assimilated into Bio-N,about 51.9%was reduced to gaseous nitrogen and less than 0.5%of nitrogen was replaced by NO_(3)^(−)-N and NH_(4)^(+)-N,9.7%NO_(3)^(−)-N remained in the effluent at the end.At the same time,four key genes(napA,nirK,norB and nosZ)related to nitrate nitrogen removal were expressed during the denitrification process of P.mendocina LYX,in which the transcription level of the indicator genes of this aerobic denitrifying bacterium(napA)was the highest.In addition,it was found with the 15N tracer technique that inoculation of this strain on sludge increased the amount of nitrogen loss from 9.26 nmol N/(g·h)to 23.835 nmol N/(g·h).Therefore,P.medocina LYX is a potential bioagent for advanced nitrogen removal by assimilating and reducing nitrate simultaneously in aerobic tanks.展开更多
Effective control of eutrophication is generally established through the reduction of nutrient loading into waterways and water bodies. An economically viable and ecologically sustainable approach to nutrient pollutio...Effective control of eutrophication is generally established through the reduction of nutrient loading into waterways and water bodies. An economically viable and ecologically sustainable approach to nutrient pollution control could involve the integration of retention ponds, wetlands and greenways into water management systems. Plants not only play an invaluable role in the assimilation and removal of nutrients, but they also support fauna richness and can be aesthetically pleasing. Pandanus amaryllifolius, a tropical terrestrial plant, was found to establish well in hydrophytic conditions and was highly effective in remediating high nutrient levels in an aquatic environment showing 100% removal of NO^-N up to 200 mg/L in 14 days. Phosphate uptake by the plant was less efficient with 64% of the PO4-P removed at the maximum concentration of 100 mg/L at the end of 6 weeks. With its high NO^-N and PO43--P removal efficiency, P. amaryllifolius depleted the nutrient-rich media and markedly contained the natural colonization of algae. The impediment of algal growth led to improvements in the water quality with significant decreases in turbidity, pH and electrical conductivity. In addition, the plants did not show stress symptoms when grown in high nutrient levels as shown by the changes in their biomass, total soluble proteins and chlorophyll accumulation as well as photochemical efficiency. Thus, P. amaryUifolius is a potential candidate for the mitigation of nutrient pollution in phytoremediation systems in the tropics as the plant requires low maintenance, is tolerant to the natural variability of weather conditions and fluctuating hydro-periods, and exhibit good nutrient removal capabilities.展开更多
文摘Electrodialysis (ED) of NaNO3 solutions was performed to stress the role of the membrane pair as a unit i.e. the behavior as a whole of Anion Exchange Membrane (AEM) and Cation Exchange Membrane (CEM), in the process at room temperature. The membrane pair was also tested in the reclamation of nitric acid and sodium hydroxide. It was found that the membrane pair ranking in Limiting Current Density does not agree with that of ions leakage and both rankings are not the same as for Current Efficiency or Specific Power Consumption, each parameter for a specific membrane pair depends on the associated membrane and at a lesser degree on the flow rate. Results show that one cannot select a membrane or a membrane pair only by its limiting current density i.e. it is necessary to evaluate several parameters of the process by characterizing the whole membrane pair and to decide the parameter of interest, i.e. denitrification speed, ions leakage, proton back migration, current efficiency or specific power consumption.
基金Project supported by the National Natural Science Foundation of China (No. 30070017)the Science and Technology Foundation for Key Project of Zhejiang Province (No. 2003C13005), China
文摘The optimal operation conditions in an anoxic sulfide oxidizing (ASO) bioreactor were investigated. The maximal removal rates for sulfide and nitrate were found to be 4.18 kg/(m3·d) and 1.73 kg/(m3·d), respectively. The volumetrical volumetric loading rates (LRs) observed through decreasing hydraulic retention time (HRT) at fixed substrate concentration are higher than those by increasing substrate concentration at fixed HRT. The sulfide oxidation in ASO reactor was partially producing both sulfate and sulfur; but the amount of sulfate produced was approximately one third that of sulfur. The process was able to tolerate high sulfide concentration, as the sulfide removal percentage always remained near 99% when influent concentration was up to 580 mg/L. It tolerated relatively lower nitrate concentration because the removal percentage dropped to 85% when influent con- centration was increased above 110 mg/L. The process can tolerate shorter HRT but careful operation is needed. Nitrate conversion was more sensitive to HRT than sulfide conversion since the process performance deteriorated abruptly when HRT was decreased from 3.12 h to 2.88 h. In order to avoid nitrite accumulation in the reactor, the influent sulfide and nitrate concentrations should be kept at 280 mg/L and 67.5 mg/L respectively. Present biotechnology is useful for removing sulfides from sewers and crude oil.
基金Under the auspices of National Science Fund for Distinguished Young Scholars(No.51125035)National Science Foundation for Innovative Research Group(No.51121003)Major Science and Technology Program for Water Pollution Control and Treatment(No.2009ZX07209-008)
文摘Denitrification is an important process of nitrogen removal in lake ecosystems.However,the importance of denitrification across the entire soil-depth gradients including subsurface layers remains poorly understood.This study aims to determine the spatial pattern of soil denitrification enzyme activity(DEA) and its environmental determinants across the entire soil depth gradients in the raised fields in Baiyang Lake,North China.In two different zones of the raised fields(i.e.,water boundary vs.main body of the raised fields),the soil samples from 1.0 m to 1.1 m depth were collected,and the DEA and following environmental determinants were quantified:soil moisture,p H,total nitrogen(TN),ammonia nitrogen(NH4+-N),nitrate nitrogen(NO3–-N),total organic carbon(TOC),and rhizome biomass of Phragmites australis.The results showed that the soil DEA and environmental factors had a striking zonal distribution across the entire soil depth gradients.The soil DEA reached two peak values in the upper and middle soil layers,indicating that denitrification are important in both topsoil and subsurface of the raised fields.The correlation analysis showed that the DEA is negatively correlated with the soil depth(p < 0.05).However,this phenomenon did not occur in the distance to the water edge,except in the upper layers(from 0.2 m to 0.7 m) of the boundary zone of the raised fields.In the main body of the raised fields,the DEA level remained high;however,it showed no significant relationship with the distance to the water edge.The linear regression analysis showed significant positive correlation of the DEA with the soil TN,NO3–-N,NH4+-N,and TOC;whereas it showed negative correlation with soil p H.No significant correlations with soil moisture and temperature were observed.A positive correlation was also found between the DEA and rhizome biomass of P.australis.
基金supported by the Natural Science Foundation of Shandong Province (Nos. ZR2020MD006, ZR2019MD042)the Science and Technology Support Plan for Youth Innovation of Colleges in Shandong Province (No. DC_(2)000000961)。
文摘In this study,the biochar (BC) produced from sawdust,sludge,reed and walnut were used to support sulfidation of nano-zero-valent-iron (S-nZVI) to enhance nitrate NO_(3)^(-) removal and investigate the impact on greenhouse gas emissions.Batch experiment results showed the S-nZVI/BC(sawdust (2:1,500)),S-n ZVI/BC(sludge (2:1,900)),S-n ZVI/BC(reed (2:1,700)),and S-n ZVI/BC(walnut (2:1,700))respectively improved NO_(3)^(-) removal efficiencies by 22%,20%,3%and0.1%,and the selectivity toward N_(2)by 22%,25%,22%and 18%.S-nZVI uniformly loaded on BC provided electrons for the conversion of NO_(3)^(-) to N_(2)through Fe0.At the same time,FeSxlayer was formed on the outer layer of ZVI in the sulfidation process to prevent iron oxidation,so as to improve the electrons utilization efficiency After adding four kinds of S-nZVI/BC into constructed wetlands (CWs),the NO_(3)^(-) removal efficiencies could reach 100%and the N_(2)O emission fluxes were reduced by 24.17%-36.63%.And the average removal efficiencies of TN,COD,TP were increased by 21.9%,-16.5%,44.3%,repectively.The increasing relative abundances of denitrifying bacteria,such as Comamonas and Simplicispira,suggested that S-nZVI/BC could also improve the process of microbial denitrification.In addition,different S-nZVI/BC had different effects on denitrification functional genes (narG,nirk,nirS and nos Z genes),methanotrophs (pmoA) and methanogenesis (mcrA).This research provided an effective method to improve NO_(3)^(-) removal and reduce N_(2)O emission in CWs.
基金supported by Harran University Scientific Research Projects Coordination Unit(HUBAP,project no 18018)。
文摘In this study,a sequential process(heterotrophic up-flow column and completely mixed membrane bioreactors)was proposed combining advantages of the both processes.The system was operated for 249 days with simulated and real groundwater for nitrate removal at concentrations varying from 25 to 145 mg·L^(-1) NO_(3)^(-)-N.The contribution of heterotrophic process to total nitrate removal in the system was controlled by dozing the ethanol considering the nitrate concentration.By this way,sulfur based autotrophic denitrification rate was decreased and the effluent sulfate concentrations were controlled.The alkalinity requirement in the autotrophic process was produced in the heterotrophic reactor,and the system was operated without alkalinity supplementation.Throughout the study,the chemical oxygen demand in the heterotrophic reactor effluent was(23.7±22)mg L^(-1) and it was further decreased to(7.5±7.2)mg·L^(-1) in the system effluent,corresponding to a 70%reduction.In the last period of the study,the real groundwater containing 145 mg·L^(-1) NO_(3)^(-)-N was completely removed.Membrane was operated without chemical washing in the first 114 days.Between days 115-249 weekly chemical washing was required.
基金supported by the National Natural Science Foundation of China(52372090,52073177)the National Natural Science Foundation of Guangdong,China(2023A1515010947)+1 种基金the Shenzhen Basic Research Program(JCYJ20220531102207017)The authors also gratefully acknowledge the Shenzhen postdoctoral research funding(Grant No.0001330501).
文摘Global water bodies are increasingly imperiled by nitrate pollution,primarily originating from industrial waste,agricultural runoffs,and urban sewage.This escalating environmental crisis challenges traditional water treatment paradigms and necessitates innovative solutions.Electro-catalysis,especially utilizing copper-based catalysts,known for their efficiency,cost-effectiveness,and eco-friendliness,offer a promising avenue for the electro-catalytic reduction of nitrate to ammonia.In this review,we systematically consolidate current research on diverse copper-based catalysts,including pure Cu,Cu alloys,oxides,single-atom entities,and composites.Furthermore,we assess their catalytic performance,operational mechanisms,and future research directions to find effective,long-term solutions to water purification and ammonia synthesis.Electro-catalysis technology shows the potential in mitigating nitrate pollution and has strategic importance in sustainable environmental management.As to the application,challenges regarding complexity of the real water,the scale-up of the commerical catalysts,and the efficient collection of produced NH3 are still exist.Following reseraches of catalyst specially on long term stability and in situ mechanisms are proposed.
基金supported by the National Key Research and Development Program of China(No.2017YFC0505303)the China Major Science and Technology Project of Water Pollution Control and Management,China(No.2017ZX07202003)the National Natural Science Foundation of China(Nos.51478041 and 51678053)
文摘Excessive nitrate(NO3-)is among the most problematic surface water and groundwater pollutants.In this study,a type of magnetic cationic hydrogel(MCH)is employed for NO3-adsorption and well characterized herein.Its adsorption capacity is considerably pHdependent and achieves the optimal adsorption(maximum NO3--adsorption capacity is95.88±1.24 mg/g)when the pH level is 5.2-8.8.The fitting result using the homogeneous surface diffusion model indicates that the surface/film diffusion controls the adsorption rate,and NO3-approaches the center of MCH particles within 30 min.The diffusion coefficient(Ds)and external mass transfer coefficient(kF)in the liquid phase are1.15×10-6 cm2/min and 4.5×10-6 cm/min,respectively.The MCH is employed to treat surface water that contains 10 mg/L of NO3-,and it is found that the optimal magnetic separation time is 1.6 min.The high-efficiency mass transfer and magnetic separation of MCH during the adsorption-regeneration process favors its application in surface water treatment.Furthermore,the study of the mechanism involved reveals that both-N+(CH3)3 groups and NO3-are convoluted in adsorption via electrostatic interactions.It is further found that ion exchange between NO3-and chlorine occurs.
基金supported by the Natural Science Foundation of Zhejiang Province (nos. LY17E080001 and LQ18E080005)the China Scholarship Council (no. iCET 2017)。
文摘Bioaugmentation of denitrifying bacteria can serve as a promising technique to improve nutrient removal during wastewater treatment. While denitrification inhibition by bacterial quorum sensing(QS) in Pseudomonas aeruginosa has been indicated, the application of bacterial QS disruption to improve nitrate removal from wastewater has not been investigated. In this study, the effect of bioaugmentation of P. aeruginosa SD-1 on nitrate removal in sequencing batch reactors that treat nitrate rich wastewater was assessed. Additionally, the potential of a quorum sensing inhibitor(QSI) to improve denitrification following bacterial bioaugmentation was evaluated. Curcumin, a natural plant extract, was used as a QSI. The chemical oxygen demand(COD) and initial nitrate concentration of the influent were 700 ±20 mg/L and 200 ±10 mg/L respectively, and their respective concentrations in the effluent were 56.9 ±3.2 mg/L and 9.0 ±3.2 mg/L. Thus, the results revealed that bioaugmentation of P. aeruginosa SD-1 resulted in an increased nitrate removal to 82% ±1%. Further, nitrate was almost completely removed following the addition of the QSI, and activities of nitrate reductase and nitrite reductase increased by 88% ±2% and 74% ±2% respectively. The nitrogen mass balance indicated that aerobic denitrification was employed as the main pathway for nitrogen removal in the reactors. The results imply that bioaugmentation and modulation of QS in denitrifying bacteria, through the use of a QSI, can enhance nitrate removal during wastewater treatment.
基金supported by the Integrated Innovation Academic Center Chulalongkorn University Centenary Academic Development Project (CU56-FW14)support from the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission and the Ratchadaphiseksomphot Endowment Fund (FW1017A)support was obtained from the Graduate School, Chulalongkorn University and the National Research Council of Thailand
文摘A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank （0.04 m2 tank surface area）, packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions （e.g. 〉 2 mg/L） while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested （soil, sand, pumice stone and vermiculite）, pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD：N ratio of 5：1, a nitrate removal rate of 4591 ± 133 mg-N/m2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD：N ratio of 5：1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 ± 945 mg-N/m2 tank bottom area/day or 126 ± 18 mg-N/L of pumice packing volume/day.
基金We are grateful for the project grants supported by the Major Science and Technology Programs for Water Pollution Control and Management of China(Nos.2012ZX07205-001 and 2017ZX7103-007).
文摘This study focuses on identifying the factors under which mixed microbial seeds assist bio-chemical denitrification when Scrap Iron Filings(SIF)are used as electron donors and adsorbents in low C/N ratio waters.Batch studies were conducted in abiotic and biotic reactors containing fresh and aged SIF under different dissolved oxygen concentrations with NO_(3)^(-)−N and/or PO_(4)^(3−)influent(s)and their nitrate/phosphate removal and by-product formations were studied.Batch reactors were seeded with a homogenized mixed microbial inoculum procured from natural sludges which were enriched over 6 months under denitrifying conditions in the presence of SIF.Results indicated that when influent containing 40 mg/L of NO_(3)^(-)−N was treated with 5 g SIF,79.9%nitrate reduction was observed in 8 days abiotically and 100%removal was accomplished in 20 days when the reactor was seeded.Both abiotic and seeded reactors removed more than 92%PO_(4)^(3−)under high DO conditions in 12 days.Abiotic and biochemical removal of NO_(3)^(-)−N and abiotic removal of PO_(4)^(3−)were higher under independent NO_(3)^(-)−N/PO_(4)^(3−)loading,while 99%PO_(4)^(3−)was removed biochemically under combined NO_(3)^(-)−N and PO_(4)^(3−)loading.This study furthers the understandings of nitrate and phosphate removal in Zero Valent Iron(ZVI)assisted mixed microbial systems to encourage the application of SIF-supported bio-chemical processes in the simultaneous removals of these pollutants.
基金financial support from the Ministry of Science and Technology of the Republic of China(No.102-2221-E-009-010-MY3)
文摘In recent years there has been an increasing interest in the use of autohydrogenotrophic bacteria to treat nitrate from wastewater. However, our knowledge about the characteristics of extracellular polymeric substances（EPS） releasing by these activities is not yet very advanced. This study aimed to investigate the change in EPS compositions under various p H values and hydrogen flow rates, taking into consideration nitrogen removal. Results showed that p H 7.5 and a hydrogen flow rate of 90 m L/min were the optimal operating conditions, resulting in 100% nitrogen removal after 6 hr of operation. Soluble and bound polysaccharides decreased, while bound proteins increased with increasing p H. Polysaccharides increased with increasing hydrogen flow rate. No significant change of bound proteins was observed at various hydrogen flow rates.
基金This work was financially supported by the National Key R&D Program of China(Grant No.2016YFC0400706)the National Natural Science Foundation of China(Grant Nos.41671481 and 41977340)+1 种基金the Science&Technology Plan Project of Guangdong(No.2016B020240003)Key-Area Research and Development Program of Guangdong Province(No.2019B110205004).We would like to thank Professor Hong YG and Dr.Wu JP(Guangzhou University)for their warmful help on 15N labeling test and analysis.
文摘The problem of nitrate accumulation in aerobic tank and total nitrogen excessive discharge in effluent was very common in traditional livestock and poultry farming wastewater treatment systems owing to the lengthy process flow and low process control level.A strain LYX of aerobic bacterium was isolated from the activated sludge of a wastewater treatment system in a pig farm,which could remove nitrate effectively in aerobic tank and was identified Pseudomonas mendocina by 16S rRNA sequencing.Under the condition of nitrate as the sole nitrogen source,this strain removed over 90%of NO_(3)^(−)-N with an initial concentration of 110 mg/L under aerobic conditions within 48 hours.Among them,37.9%of NO_(3)^(−)-N was assimilated into Bio-N,about 51.9%was reduced to gaseous nitrogen and less than 0.5%of nitrogen was replaced by NO_(3)^(−)-N and NH_(4)^(+)-N,9.7%NO_(3)^(−)-N remained in the effluent at the end.At the same time,four key genes(napA,nirK,norB and nosZ)related to nitrate nitrogen removal were expressed during the denitrification process of P.mendocina LYX,in which the transcription level of the indicator genes of this aerobic denitrifying bacterium(napA)was the highest.In addition,it was found with the 15N tracer technique that inoculation of this strain on sludge increased the amount of nitrogen loss from 9.26 nmol N/(g·h)to 23.835 nmol N/(g·h).Therefore,P.medocina LYX is a potential bioagent for advanced nitrogen removal by assimilating and reducing nitrate simultaneously in aerobic tanks.
基金the support & contributions of the Singapore-Delft Water Alliance (SDWA)
文摘Effective control of eutrophication is generally established through the reduction of nutrient loading into waterways and water bodies. An economically viable and ecologically sustainable approach to nutrient pollution control could involve the integration of retention ponds, wetlands and greenways into water management systems. Plants not only play an invaluable role in the assimilation and removal of nutrients, but they also support fauna richness and can be aesthetically pleasing. Pandanus amaryllifolius, a tropical terrestrial plant, was found to establish well in hydrophytic conditions and was highly effective in remediating high nutrient levels in an aquatic environment showing 100% removal of NO^-N up to 200 mg/L in 14 days. Phosphate uptake by the plant was less efficient with 64% of the PO4-P removed at the maximum concentration of 100 mg/L at the end of 6 weeks. With its high NO^-N and PO43--P removal efficiency, P. amaryllifolius depleted the nutrient-rich media and markedly contained the natural colonization of algae. The impediment of algal growth led to improvements in the water quality with significant decreases in turbidity, pH and electrical conductivity. In addition, the plants did not show stress symptoms when grown in high nutrient levels as shown by the changes in their biomass, total soluble proteins and chlorophyll accumulation as well as photochemical efficiency. Thus, P. amaryUifolius is a potential candidate for the mitigation of nutrient pollution in phytoremediation systems in the tropics as the plant requires low maintenance, is tolerant to the natural variability of weather conditions and fluctuating hydro-periods, and exhibit good nutrient removal capabilities.
