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Using Filamentous Bacteria and Membrane Sepration Technology to Treating Domestic Wastewater under Low Load

Author: YiZhiRun
Tutor: WangZengChang
School: Taiyuan University of Technology
Course: Environmental Engineering
Keywords: sludge bulking membrane - bioreactor filamentous bacteria membrane fouling
CLC: X703
Type: Master's thesis
Year: 2009
Downloads: 31
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Abstract

The water crisis have become important factor constrained Chinese social and economic development in 21st century, treatment and reuse of the wastewater are important measure to resolve the water crisis, membrane technology are an important tool for sewage treatment and reuse, and it is the fist technology of choice for tertiary or advanced wastewater treatment and reuse. Membrane bioreactor(MBR) is a new technology of the combination of membrane technolgy and bioreators for wastewater biology treatment with the character of removing organic pollutants with high efficiency,excellent effluent water quality, and easy flow, compact structure, etc. It has an extremely broad application prospects in wastewater reuse and resources of the area. Activated sludge process is an effective and widely used practice of biological wastewater treatment technologies, however, regardless of which improved activated sludge process, membrane bioreactor are not, sludge bulking phenomenon is one of the main problems hard to be solved .The purpose of this study is to investigate the removal efficiency of the reactor for the COD and NH3-N and other pollutants, to investigate the process and characters of sludge bulking, as well as the impact of membrane fouling under low organic load condition when the submerged membrane bioreactor occurs sludge bulking;and studying the operation of factors for the impact on membrane fouling, such as membrane flux, aeration intensity, suction time and take the time to stop; in order to make results comparable, while engaged in a submerged membrane bioreactor check experiment as a contrast.Submerged membrane bioreactor sludge bulking trial andcheck trial use the same equipment. The submerged membrane - bioreactor of this study is the long rectangular plexiglass container and using a perforated pipe to aeration at the bottom of the reactor , which is equipped with hollow fiber membrane module above. Through aeration, one hand the activated sludge mixture in the membrane - bioreactor can maintain certain circulation speed in order to reduce the deposition of the activated sludge on the surface of the membrane,on the other hand,it can supply the needed oxygen in the process of microbial decomposition of organic sewage . Raw water enters into the reactor from the top of the reactor and is extracted at the role of self-priming pump through membrane filtration by the suction after treated adequately.The main conclusions are shown as follows:1.Activated sludge occurs sludge bulking easily under low load . In this experiment, when the load reachs 0.05 kgCOD / kgMLSS?d, sludge bulking happen. Check experiment is normal. 2. The change of sludge concentration in different periods .In sludge bulking ,sludge concentration phase of the general trend is downward, decrease is not too obvious. It is down to 2000mg / L at the time of 2600mg / L starting from the installation of new membrane after 31 days of running. Normal status, the sludge concentration of the general trend is upward, begin rising more rapidly, to the late, response is relatively flat in the past few days. It is up to 3750mg / L at the time of 2600mg / L starting from the installation of new membrane after 31 days running3. The change of sludge volume index (SVI). At the beginning of the sludge bulking experiment, the COD concentration of tank / L gradually reduce from 400mg, SVI value increase gradually, but the beginning stages of the experiment, because of bacteria micelles dominance, SVI value is slow growing;when COD concentration reduced to 100mg / L, only 0.05kgCOD/kgMLSS ? d, in the experiment later; at this stage, wastewater SVI is increasing quite rapidly, and soon reached a 200mL / g or more the pool. Stable operation of the control test period ,SVI value always maintained at 100mL / g around.4. At different stages, the cases of MBR removal efficiency of COD. At 25 days of trial begining, the supernatant COD concentration and the effluent COD concentration in sludge bulking test be lower than the supernatant COD concentration and the effluent COD concentration in the controls. At this point, extracted water is considerable clean, COD concentration reached a minimum 25mg / L in the sludge bulking test. But the last two samples, sludge bulking phase COD concentrations is higher than the control test period.COD removal rate in sludge bulking phase system is significantly better than it in the control trial period system at 25 days of the trial begining, COD removal rates is up to 97% in sludge bulking phase system. COD removal rate has been growing in controlled trial period system at beginning of the experment , the other two experment sample, is higher than it in sludge bulking experment ,at last reached 96%.5. About NH3-N. NH3-N removal rate trend are firstly increased and then decreased in both sludge bulking trial phase and the control test period. not at the relative lack of nutrients, no serious outbreaks of filamentous ago, NH3-N removal rate in sludge bulking period system is higher than it in the control adaptation period; in sludge bulking period NH3-N removal rate from 84% is up to 96% of the largest, while NH3-N removal rate in the control trial period increased from 80% to the biggest 97%; at last , NH3-N removal rate dropped to 88% in sludge bulking period, NH3-N removal rate decreased to 93% in controlled trial phase.6. At the beginning of both sludge bulking trial phase and the control test period ,the suction pressure slowly grows , after about 13d ,the pressure increases rapidly, to the 28d ,to the most. That is, during reactor start-up phase membrane fouling is slow, during reactor stable operation phase, membrane fouling is faster, but the former was significantly higher than the latter, during sludge bulking phase it requires a larger pressure to meet the flux requirements. This is mainly because of that in the stable operational phase a large number of filamentous bacteria grow, the result indirectly reflects the degree of membrane fouling during the sludge bulking and shows that filamentous bacteriathat have greater influence for membrane fouling,which is caused by large surface and the physiological and biochemical characteristic that secreting mucus of filamentous bacteria.Therefore, even though ,MLSS during controlled trial phase is much higher than it during sludge bulking phase, but shows better membrane flux, membrane fouling of controlled trial phase is smaller than it of the sludge bulking phase.7. The results of sludge bulking test and controlled trial: when filamentous bacteria is in micro-expansion, COD, NH3-N removal effect in sludge bulking are better than it in controlled trial; When filamentous bacteria fully expand, its removal effect is worse then controlled trial simultaneously, and membrane fouling is seriouser than controlled trial.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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