| Water pollution and eutrophication are becoming increasingly serious. A2/O process is mostly used in simultaneous removal of nitrogen and phosphorus in wastewater in our country.As the competition between denitrifying bacteria and phosphate accumulating organisms for carbon source affects simultaneous removal of nitrogen and phosphorus,it can be removed if the anoxic tand is put to the front in inverted A2/O process. Membrane bioreactor which combines membrane separation and biological wastewater treatment,increases the pollutant removal efficiency and effluent quality. However,the high cost of membrane fouling and the high membrane limits its application.As dynamic membrane bioreactor uses cheap membrane materials,it can reduce the membrane cost and mitigate the membrane fouling. Fly ash is a by-product resulting from coal burning processes. It is solid waste with porous structure and higher specific surface area.After being acid modified,its surface area increases and adsorption performance is improved. Fly ash particles have rigid structure,and the skeleton function in the membrane fouling layer can help to control and mitigate membrane fouling. This subject adopted inverted A2/O and submerged dynamic membrane bioreactor process to treat the simulated domestic sewage,and determine the process operation conditions and parameters, and then based on this,modified fly ash was added to realize the goal of enhancing the removal of nitrogen and phosphorus and increasing the effluent quality.Experiments were performed to study the domestication, startup and operation of sludge as the performance of activated sludge determined the degradation efficiency of microbial of pollutants in wastewater. The results showed MLSS and particle size of sludge(d50) increased from 3460mg/L to 6100mg/L,27.8μm to 59.8μm in sludge domestication and startup stage respectively. The removal rate of COD、NH3-N and TP of effluent reached the level of A standard of discharge standard of pollutants for municipal wastewater treatment plant(GB 18918-2002) after the stable operation. Comparison experiments were done to investigate the effect of hydraulic retention time(HRT)and membrane materials on the removal of nitrogen and phosphorus of inverted A2/O-dynamic membrane bioreactor. The total hydraulic retention time of two groups of experiments was 12 h,and the proportion of hydraulic retention time of anoxic tank,anaerobic tank and aerobic tank was 1:1:2 and 1:2:3,respectively; membrane materials was stainless steel wire mesh and nylon fabric,respectively. The results showed the proportion of hydraulic retention time of anoxic tank, anaerobic tank and aerobic tank was 1:2:3;the average removal rate of COD、NH3-N 、 TN and TP of effluent were 94.98% 、 98.87% 、 73.18% and 88.68% respectively when the proportion of hydraulic retention time of anoxic tank,anaerobic tank,aerobic tank was 1:2:3,which was increasd by 1.57%,0.39%,8.72% and 18.08% respectively. The longer of anaerobic tank,the better of the biological phosphorus removal. Compared with the dynamic membrane materials of stainless steel wire mesh,the average removal rates of COD、NH3-N、TN and TP increased by 2.85%、4.11%、4.97% and 2.87% respectively when dynamic membrane materials was nylon fabric, and the form-film time of dynamic membrane materials of nylon fabric was shorter,the microorganism in mud cake layer was richer,the membrane fouling interval and run time were longer.The optimum dosage of modified fly ash was determined by static experiment,and the results of which showed when the dosage of modified fly ash was 1.0g/L,the removal rate of COD、NH3-N、NO3-N、TN and TP were highest. Particle size of sludge increased from 41.7μm to 65.1μm,SV30 decreased to 23% with good sedimentation performance. Microscopy showed rotifers and vorticellae in activated sludge biofacies were stable and active with reduced filamentous bacteria. With the above optimized experimental conditions, modified fly ash additive comparison experiments were done. The results showed when 1.0g/L modified fly ash were added to the inverted A2/O-DMBR,the average removal rate of TN and TP increased to 7.41% and 19.67% respectively, and the overall run time increased from 27 d to 35 d. The modified fly ash could effectively reduce the effluent concentration of pollutants, extend the running time and mitigate the membrane fouling. |
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