Three identical membrane bioreactors （MBRs） were operated over 2 years at different sludge retention time （SRT） of 10 d, 40 d and no sludge withdrawal （NS）, to elucidate and quantify the effect of SRT on the slu...Three identical membrane bioreactors （MBRs） were operated over 2 years at different sludge retention time （SRT） of 10 d, 40 d and no sludge withdrawal （NS）, to elucidate and quantify the effect of SRT on the sludge characteristics and membrane fouling. The hydraulic retention times of these MBRs were controlled at 12 h. With increasing SRT, the sludge concentrations in the MBRs increased, whereas the ratio of volatile suspended solid to the total solid decreased, and the size of sludge granule diminished in the meantime. A higher sludge concentration at long SRT could maintain a better organic removal efficiency, and a longer SRT was propitious to the growth of nitrifiers. The performance of these MBRs for the removal of COD and NH4^＋-N did not change much with different SRTs. However, the bioactivity decreased as SRT increase. The measurement of specific oxygen uptake rates （SOUR） and fluorescence in situ hybridization （FISH） with rRNA-targeted oligonucleotide probes testified that SOUR and the proportion of the bacteria-specific probe EUB338 in all DAPI-stainable bacteria decreased with increasing SRT. The concentrations of total organic carbon, protein, polysaccharides and soluble extracellular polymeric substance （EPS） in the mixed liquor supernatant also decreased with increasing SRT. The membrane fouling rate was higher at shorter SRT, and the highest fouling rate appeared at a SRT of 10 d. Both the sludge cake layer and gel layer had contribution to the fouling resistance, but the relative contribution of the gel layer decreased as SRT increase.展开更多
In this study,four sequencing batch reactors(SBR),with the sludge retention time(SRT)of 5,10,20 and 40 d,were used to treat domestic wastewater,and the effect of SRT on nitrite accumulation in the biological nitrogen ...In this study,four sequencing batch reactors(SBR),with the sludge retention time(SRT)of 5,10,20 and 40 d,were used to treat domestic wastewater,and the effect of SRT on nitrite accumulation in the biological nitrogen removal SBR was investigated.The real-time control strategy based on online parameters,such as pH,dissolved oxygen(DO)and oxidation reduction potential(ORP),was used to regulate the nitrite accumulation in SBR. The model-based simulation and experimental results showed that with the increase of SRT,longer time was needed to achieve high level of nitritation.In addition,the nitrite accumulation rate(NAR)was higher when the SRT was relatively shorter during a 112-day operation.When the SRT was 5 d,the system was unstable with the mixed liquor suspended solids(MLSS)decreased day after day.When the SRT was 40 d,the nitrification process was significantly inhibited.SRT of 10 to 20 d was more suitable in this study.The real-time control strategy combined with SRT control in SBR is an effective method for biological nitrogen removal via nitrite from wastewater.展开更多
Effect of sludge retention time( SRT) on the removal of potential and polysaccharides in an anaerobic / anoxic / aerobic( AAO) process was investigated. The Lowry method and anthrone method were used to detect protein...Effect of sludge retention time( SRT) on the removal of potential and polysaccharides in an anaerobic / anoxic / aerobic( AAO) process was investigated. The Lowry method and anthrone method were used to detect proteins and polysaccharides. Total removal efficiency of proteins at SRT of 10 to 25 d in the AAO system was higher than 90%. Polysaccharides removal efficiencies were above 80% when SRT was increased from 15 to 25 d,whereas only 81% of polysaccharides was removed at SRT of 10 d. The biodegradation part of proteins and polysaccharides increased from87. 40% to 93% and from 74. 22% to 86. 94% with increasing SRTs.The ratios of polysaccharides and proteins in extracellular polymer substances( EPSs) were around 1. 5-3 in different SRTs. As SRT increasing,polysaccharides and proteins discharged with residual sludge decreased gradually. The amount of EPSs decreased with increasing SRTs.展开更多
A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobi...A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.展开更多
基金supported by the National Natural Science Foundation of China (No 50678170)
文摘Three identical membrane bioreactors （MBRs） were operated over 2 years at different sludge retention time （SRT） of 10 d, 40 d and no sludge withdrawal （NS）, to elucidate and quantify the effect of SRT on the sludge characteristics and membrane fouling. The hydraulic retention times of these MBRs were controlled at 12 h. With increasing SRT, the sludge concentrations in the MBRs increased, whereas the ratio of volatile suspended solid to the total solid decreased, and the size of sludge granule diminished in the meantime. A higher sludge concentration at long SRT could maintain a better organic removal efficiency, and a longer SRT was propitious to the growth of nitrifiers. The performance of these MBRs for the removal of COD and NH4^＋-N did not change much with different SRTs. However, the bioactivity decreased as SRT increase. The measurement of specific oxygen uptake rates （SOUR） and fluorescence in situ hybridization （FISH） with rRNA-targeted oligonucleotide probes testified that SOUR and the proportion of the bacteria-specific probe EUB338 in all DAPI-stainable bacteria decreased with increasing SRT. The concentrations of total organic carbon, protein, polysaccharides and soluble extracellular polymeric substance （EPS） in the mixed liquor supernatant also decreased with increasing SRT. The membrane fouling rate was higher at shorter SRT, and the highest fouling rate appeared at a SRT of 10 d. Both the sludge cake layer and gel layer had contribution to the fouling resistance, but the relative contribution of the gel layer decreased as SRT increase.
基金Supported by the National Key Technologies Research and Development Program of China during the Eleventh Five-year Plan Period(2006BAC19B03)the Project of Scientific Research Base and Scientific Innovation Platform of Beijing Municipal Education Commission(PXM2008_014204_050843the State Key Laboratory of Urban Water Resource and Environment(HIT)(QAK201006)
文摘In this study,four sequencing batch reactors(SBR),with the sludge retention time(SRT)of 5,10,20 and 40 d,were used to treat domestic wastewater,and the effect of SRT on nitrite accumulation in the biological nitrogen removal SBR was investigated.The real-time control strategy based on online parameters,such as pH,dissolved oxygen(DO)and oxidation reduction potential(ORP),was used to regulate the nitrite accumulation in SBR. The model-based simulation and experimental results showed that with the increase of SRT,longer time was needed to achieve high level of nitritation.In addition,the nitrite accumulation rate(NAR)was higher when the SRT was relatively shorter during a 112-day operation.When the SRT was 5 d,the system was unstable with the mixed liquor suspended solids(MLSS)decreased day after day.When the SRT was 40 d,the nitrification process was significantly inhibited.SRT of 10 to 20 d was more suitable in this study.The real-time control strategy combined with SRT control in SBR is an effective method for biological nitrogen removal via nitrite from wastewater.
基金National Natural Science Foundations of China(Nos.21477018,21007010)Hunan Province Ministry of Transportation Scientific Research Projects,China(Nos.200908,201105)Ministry of Transport Science and Technology Program,China(No.2010353343290)
文摘Effect of sludge retention time( SRT) on the removal of potential and polysaccharides in an anaerobic / anoxic / aerobic( AAO) process was investigated. The Lowry method and anthrone method were used to detect proteins and polysaccharides. Total removal efficiency of proteins at SRT of 10 to 25 d in the AAO system was higher than 90%. Polysaccharides removal efficiencies were above 80% when SRT was increased from 15 to 25 d,whereas only 81% of polysaccharides was removed at SRT of 10 d. The biodegradation part of proteins and polysaccharides increased from87. 40% to 93% and from 74. 22% to 86. 94% with increasing SRTs.The ratios of polysaccharides and proteins in extracellular polymer substances( EPSs) were around 1. 5-3 in different SRTs. As SRT increasing,polysaccharides and proteins discharged with residual sludge decreased gradually. The amount of EPSs decreased with increasing SRTs.
文摘A bench-scale anaerobic/anoxic/aerobic process-biological aerated filter （A^2/O-BAF） combined system was carded out to treat wastewater with lower C/N and C/P ratios. The A^2/O process was operated in a short aerobic sludge retention time （SRT） for organic pollutants and phosphorus removal, and denitrification. The subsequent BAF process was mainly used for nitrification. The BAF effluent was partially returned to anoxic zone of the A^2/O process to provide electron acceptors for denitrification and anoxic P uptake. This unique system formed an environment for reproducing the denitdfying phosphate-accumulating organisms （DPAOs）. The ratio of DPAOs to phosphorus accumulating organisms （PAOs） could be maintained at 28% by optimizing the organic loads in the anaerobic zone and the nitrate loads into the anoxic zone in the A^2/O process. The aerobic phosphorus over-uptake and discharge of excess activated sludge was the main mechanism of phosphorus removal in the combined system. The aerobic SRT of the A^2/O process should meet the demands for the development of aerobic PAOs and the restraint on the nitrifiers growth, and the contact time in the aerobic zone of the A^2/O process should be longer than 30 min, which ensured efficient phosphorus removal in the combined system. The adequate BAF effluent return rates should be controlled with 1--4 mg/L nitrate nitrogen in the anoxic zone effluent of A^2/O process to achieve the optimal nitrogen and phosphorus removal efficiencies.
