Study On Optimized Operation And Performance Of CLR-A~2O-MBR Coupling Process For Leachate Treatment From Municipal Solid Waste Incineration Plant

Due to rapid urbanization and continuous improvement of people's living standard,the amount of municipal solid waste?MSW?in China sharply increases with time.In recent years,incineration technology has been widely used for municipal solid waste treatment due to its high degree of waste reduction and efficient energy recovery.However,the storage of MSW usually generates large amounts of leachate in incineration plants.The high-strength wastewater contains various kinds of organic matters,high ammonium concentration and other toxic matters?e.g.heavy metal ions?,and its efficient treatment is still challenging now.In this study,a full-scale high-efficiency anaerobic reactor was firstly adopted to treat actual leachate wastewater,with aerobic residual sludge as inoculum.During the anaerobic treatment process,the sludge granulation was intensively investigated.Meanwile,microbial community structure was studied by molecular ecology techniques.Moreover,according to the low C/N ratio of anaerobic effluent,an A²O-MBR coupling process was developed in this study.By optimizing its operational parameters,a short-cut nitrification and denitrification was successfully established to treat leachate anaerobic effluent,which efficiently removed organic matter and total nitrogen.The final effluent could meet the the discharge standard.The main research results were as follows:?1?The operation process of CLR anaerobic reactor could be divided into four stages:sludge acclimation stage,organic loading rate?OLR?improvement stage,system recovery stage and stable operation stage.The initial reactor OLR was 3.14-4.61 kg COD/?m³·d?.After83 days operation,anaerobic granular sludge was successfully formed.When reactor was stably operated,VFAs/alkalinity ratio and VFAs concentration were respectively below 0.1and 1 000 mg/L.Meanwhile,COD removal efficiency and biogas yield reached 89.4-93.4%and 0.42-0.50 m³/kg COD_removal,respectively.The up-flow velocity was further improved by increasing external circulation.Sludge wash-out was observed under high up-flow velocity of4.0 m/h,which caused water quality deterioration.The optimal operational performance was achieved when up-flow velocity was controlled at 1.5-3.0 m/h,with recirculating ratio of2.6-6.24.Based on the above experiments,the substrate degradation kinetics model was established,which could well described the CLR reactor operation.?2?During the CLR reactor operation,anaerobic granular sludge was successfully formed from aerobic residual sludge.The whole granulation process covered acclimation phase,rapid granulation phase and mature phase,where the sludge concentration at the bottom was gradually increased and stable expanded sludge bed was formed.The contents of protein and polysaccharide in sludge EPS were respectively increased by 362%and 64%.Besides,the zeta potential and cell hydrophobicity of sludge were increased to-10.6 mV and78.67%,respectively.It also was found that they were both positively correlated with the protein/polysaccharides ratio in EPS,with coefficients of 0.963 and 0.945.The 3D-EEM and FT-IR technology were used to analyze the EPS variation,which further verified the crucial importance of protein-like EPS on sludge granulation.?3?The dehydrogenase activity of inoculum was only 4.5 mg/?g·h?,which was gradually increased to 6.7 mg/?g·h?during sludge acclimatization stage.By elevating organic loading rate,the activity was finally reached about 12.8 mg/?g·h?.In addition,the CoF₄₂₀ content in inoculum was only 0.026?mol/g,which was remarkly increased by around 6.1 times and finally reached 0.158?mol/g when reactor was steadily operated.The results demonstrated that the formation of anaerobic granular sludge contributed to the efficient active biomass immobilization.The obvious succession of microbial community structure was observed with the reactor operation.Bacterial community structure had more changes than methanogenic community structure.At the stable operation stage,the genus Clostridium played a dominnat role in hydrolytic acidification,and hydrogen-production acetogenisis was primarily catalyzed by the genus Syntrophobacter and Desulfovibrio.Besides,the genus Methanosaeta and Methanoculleus were the dominnat microflora for CH₄ generation.?4?The leachate after anaerobic digestion was the typical of high ammonia nitrogen and low carbon/nitrogen ratio.Experimental results show that when the dissolved oxygen concentration was maintained at 0.5-1.0 mg/L,the concentration of nitrite could be increased rapidly with the nitrosation rate over 90%,which showed the obvious accumulation of nitrite.In the appropriate pH condition of?8.0±0.5?,the"ammonia valley"appeared with the nitrosation rate and ammonia oxidation rate increased to 94%and 95%respectively.The nitrite concentration reached the maximum value.When the pH rose to?9.0±0.5?,the concentration of nitrite and nitrate were decreased,indicating that the activity of ammonia oxidizing bacteria and nitrite oxidizing bacteria was inhibited.Meanwhile,the C/N ratio also affected the operation effect of nitrosation significantly with the concentration of nitrite nitrogen reached 740 mg/L at C/N ratio of 3.While the nitrite concentration was only 30mg/L when the C/N ratio was increased to 7.?5?The A²O-MBR process was adopted for the treatment of leachate with low carbon and nitrogen ratio by short-cut nitrification and denitrification technology.Based on the effect of biodegradation and membrane interception,the COD and ammonia nitrogen removal could be efficient and stable during the operation of aerobic segment.The UASB reactor was used in the denitrification segment.In allusion to the carbon source insufficient and low total nitrogen removal rate,the efficiency of coupling process was studied through the methanol and raw leachate wastewater compared as the denitrification carbon source.Experimental results show that when the methanol and raw leachate added by 4 g COD/L and 2.5%respectively,the total nitrogen removal rate of coupling process could be reached 94%and95.4%respectively,and the total nitrogen of effluent less than 70 mg/L,which met the requirements of sewage discharge standards?CJ343-2010?.The results of the above study confirmed that the A²O-MBR process could achieved the standards of leachate treatment with no carbon source added.