Research On Micro-aerobic Active Sludge Cultivation Process And Control Of Membrane Fouling

Membrane bio-reactor?MBR?has been applied more and more in wastewater treatment,because of its promising water quality and low land space.However,high energy cost and membrane fouling as shortcomings hinder the practical application of MBR.This thesis studied the performance of pollutants removal when dissolved oxygen?DO?in MBR decreased gradually.High-throughput genic method was used to explore bacterial community structures during MBR operation.The foulant composition was analyzed including colloid particles and organic matters.H₂O₂ and NaClO were compared to better control membrane fouling,and their influence on microbial activity and filtration performance were characterized.A pilot-scale MBR with a capacity of 100t/d was operated for 260 days during experiments,related DO concentrations were modified following three different stages: the first is aerobic stage for 160 days with DO>2.0 mg/L,then low DO stage for 40 days with DO between 0.5 mg/L and 2.0 mg/L,final is micro-DO stages for 60 days with DO<0.5 mg/L.It was found that,during transition from aerobic to micro-DO stages,MLSS increased gradually,and the removal to N and P got improved.The effluent concentrations of COD,ammonia-nitrogen,total-nitrogen for MBR at micro-DO condition were 24.3 mg/L,2.8 mg/L,7.5 mg/L,respectively,reached to the standard of municipal wastewater treatment.DO modification resulted in the changes of microbial community in both composition and activity.At micro-DO stage,no NOB bacteria were detected.Thus micro-DO condition did strengthened the processes of shortcut denitrification,which is good to TN removal.It was found that there were some protein compounds existed in active sludge,which can deposit on gel-layer on the surface of membrane,thus worsen the membrane fouling.The active sludge at micro-DO condition was characterized with small floc and poor compression resistance,in which the macro-molecular proteins can migrate into the gel layer,may lead to serious membrane fouling.It was indicated that both sludge colloid and organics influence to the membrane fouling significantly.It was showed that H₂O₂ can improve the collection of sludge in ultra-filtration at the dosage of <200 mg/L.Functional microorganisms can be inhibited by H₂O₂ under following sequence: nitrifying bacteria > phosphate accumulation organismsbacteria >denitrifying bacteria.It was recommended that addition of 10 mg/L H₂O₂ was the best to ameliorate sludge performance.Addition of 10 mg/L NaClO can strengthen the filtration performance of sludge,resulting in formation of dense and tough particles.However,higher dosage of NaClO deteriorated the membrane fouling probably due to sludge disintegration.