Performance Analysis Of Nitrogen And Phosphorus Removal In MUCT-MBR

Excess nitrogen and phosphorus discharged in the environment were the major pollutants of eutrophication.In order to reduce such pollution,the permitted requirements for nutrient discharges are becoming more stringent.The research and development of enhanced nitrogen and phosphorus removal technology has been a focus issue.Because both denitrifiers and phosphorus-accumulating organisms(PAO) require carbon resources,the availability of COD in municipal wastewater is often an essential factor.Denitrifying phosphorus-accumulating organisms(DPAO) can accomplish denitrification and phosphorus removal using the same carbon resource.The use of DPAOs was beneficial to reduced COD consumption,lower aeration cost and less sludge production and has been obtained widespread attention.Biological nutrient removal(BNR) was investigated in a combined modified University of Cape Town and membrane bioreactor(MUCT-MBR) system.Through increase influent load,demand of COD,nitrogen and phosphorus removal,resistance to load,sludge yield, characteristic of PAO and membrane fouling were investigated.1.The removal performance of MUCT-MBR was studyed through reducing the ratio of C/N gradually and increasing nitrogen load(0.088 kg·m^-3·d^-1 to 0.137 kg·m^-3·d^-1).The steady removal performance exhibited with average removal efficiencies of COD,TN and TP were 90%,81.6%,75.2%.Obvious denitrifying phosphorus removal occurred with C/N ratio 3.98.When nitrite was the main electron acceptor,the ratio of denitrifying phosphate uptake to the total phosphate uptake were 99.8%and the sludge yield was 0.28 kgVSS/kgCOD;when nitrate was the main electron acceptor,the ratio was 92%and the yield was 0.32 kgVSS/kgCOD.In case of nitrite,the system not only kept TP and TN removal at 89.1%and 82.2%,but also ensured less sludge production.The excellent TP removal performance could be obtained if electron acceptors were enough to satisfy denitrifying phosphorus uptake.2.MUCT-MBR was started up under high nitrogen load.The average COD,TN and TP removal efficiencies of 89.3%,75.4%,79.2%were obtained in short time.The effluent TP removal of MUCT-MBR was mainly depended on denitrifying phosphorus removal under anoxic condition.3.Batch experiments of anaerobic phosphorus release showed that phosphorus release changed into uptake under deficient COD conditions and obvious phosphorus uptake occurred with sucrose as carbon resource.It was presumed that PAO enriched under MUCT-MBR mode has a little capability of anaerobic phosphorus uptake,but the phenomenon occurred occasionally without clear explanation.Given enough electron acceptors,if initial loading amount increased,the amount of anoxic phosphorus uptake per NO₃^--N denitritied increased, but phosphorus uptake ratio(SPUR) has no change;the amount of anoxic phosphorus uptake and SPUR per NO₂^--N denitritied decreased.SPUR with NO₂^--N as electron acceptors was higher than with NO₃^--N as electron acceptors,but SPUR with NO₃^--N+NO₂^--N as electron acceptors was highest.At the end of anaerobic,the TP content of sludge and glycogen in PAO were lowest and PHB was highest;under anoxic and aerobic condition,PHB reduced along with the TP content of sludge and glycogen in PAO,which validated denitrifying phosphorus removal phenomenon.Sludge bulking occurred because MUCT-MBR was operated under lower carbon resource,but membrane filtration ensured effluent clarification.