Treatment Of Municipal Wastewater By Pilot-scale Anoxic/oxic Mbr

This experiment was carried out to treat municipal wastewater by pilot-Scale anoxic/oxic integrated membrane bioreactor with effluent intermittent discharging modes. The TMP and membrane specific flux were used to charaterize the situation of membrane fouling during the normal operation time of the reactor (from August 24 to December 23), whose effluent reached a stable level of 40L/h.In this thesis, three aspects were included in the main research contents as follows : The removal of organics, NH₄⁺-N ,TN, TP,turbidity and other indexes were analyzed in the first aspect; Influence of sludge concentration,sludge viscidity, run/off time of effluent, microorganism, aeration intensity, particle size of sludge, temperature and other factors on the membrane fouling was studied in the second aspect; The recovery of membrane specific flux of membrane module after the thydraulic cleaning and the chemical cleaning was studied in the third aspect.The average removal rate of COD, NH NH₄⁺-N , TN, TP and TOC reached 89.29%, 98.16%, 51.49%, 66.79% and 71.29% respectively during the normal operation time, and the effluent turbidity was up to 0.54NTU on average. Compared with larger fluctuation of the removal of TN and TP, The removal of organics and NH₄⁺-N was rather better.The quality of effluent could be good and membrane module could run well when the sludge concentration ranged from 3000 to 5000mg/L. The membrane specific flux could be expressed: J_b=k₁*J* exp(-k₂MLSS), k₁ and k₂ were coefficients correlated with process operating parameters, which could be recognized as constants when membrane specific flux and and other process operating parameters were constant. The increase of sludge concentration could cause higher sludge viscidity and more extracellular polymeric substances(EPS). The best run/off time of effluent was determined as 10min:3min when the membrane resistance was well controlled and the water yield was satisfied. The main influential factor of membrane fouling was EPS which mainly included protein and polysaccharide up to 52.67% totally in this experiment. Filamentous bacteria and other microbe, which could result in membrane pore size smaller and even blockage when the microbe was adsorbed on the membrane surface or inserted into membrane pores, was frame as flocculating and aggregating sludge. The aeration intensity could cause membrane fouling no matter strong or weak, and the stronger aeration intensity could cause the size of sludge particle smaller. The aeration intensity should be controlled at the critical level. The best aeration intensity was 1.3m³/h in this experiment. Low temperature could cause membrane fouling more easily. The sludge viscidity on average was 6.67Pa.s in low temperature time while 9.56Pa.s in medium temperature time.The membrane specific flux returned to 93.75% after the thydraulic cleaning and 100% after the chemical cleaning.