Research On Treatment Of Rural Domestic Sewage By PVA-EM Bacteria Strengthen Bioreactor Combined With Bioretention

Southern rural domestic sewage is more dispersed,and it is difficult to be adopt measures on centralized sewage treatment.At present,a single biological or ecological treatment method can not meet the requirements of nitrogen and phosphorus removal from rural domestic sewage.The PVA-EM carrier strenghten bioreactor combined with bioretention was purposefully developed for the treatment of rural domestic sewage.In this study,PVA was used to immobilize EM bacteria and applied in bioreactor to improve the removal efficiencies of pollutants.The combined process design was carried out from the perspective of bioreactor structure and parameters,and bioretention of plant selection,media structure and structural layer design;the treatment effect of rural domestic sewage was measured through the start and stable operation phase of combination process.The conclusions were as follows:?1?The single-factor and orthogonal experimental design were carried out to determine the preparation conditions of the PVA-EM carrier,physical properties of the carrier and the treatment effect of the sewage were used as evaluation index;the immobilized microbial activity and the carrier structure were determined by OUR and SEM,respectively.The results showed:the removal efficiencies of COD,TN and TP were 58.71%,59.81%and 32.42%,when the concentrations of PVA,SA and CaCl₂were 6%,1.2%and 2.5%,respectively.The OUR,up to 0.42mg/?L·min?,indicated that PVA-EM carrier had high activity.SEM showed that PVA-EM carrier had uniform holes on the surface and interior,which was favorable for the exchange with the outside of microorganisms.?2?The treatment process of PVA-EM carrier was studied by 3 factors of aerobic/anaerobic,carrier input ratio,HRT,and comparison of EM biomembrane process.The results suggested that the removal efficiencies of TP,COD and TN were40.59%,70.97%and 85.12%,respectively,when the carrier input ratio and HRT were1/50 and 12h under aerobic conditions.Through comparative studies,the results suggested that the removal efficiencies of COD and TN were 88.71%and 81.24%,respectively,and the treatment effect was better than that of EM biomembrane process,but the TP removal rate was all about 30%,without obvious difference.?3?The design of the bioreactor-bioretention combination process was carried out,the bioreactor was treated with intermittent aerobic treatment.Optimization design of bioretention chose Canna as the plant,structure from top to bottom was a plant?Canna?,water layer?15cm?,bark layer?bark,5cm?,filler layer?red soil:compost:zeolite=35:10:55,35cm?,sand filter?river sand,15cm?and the gravel drainage layer?gravel,15cm?,and the diameter was 20cm.?4?The bioreactor and the bioretention start-up studies showed that the bioreactor of the PVA-EM carrier start time was about 5-7 days,which was significantly higher than that of other methods.The bioretention removal rate of TP and COD was more than 90%and 80%respectively,but TN removal efficiency was poor and unstable.The concentration of TN,TP and COD in the effluent of the stable operation system could reach the secondary standard of the urban sewage treatment industry?GB 18918-2002?.The COD removal rate was above 90%,and the TN removal rate was stable at 85-90%,and the TP removal rate could reach more than90%.The bioreactor-bioretention combination system has the advantages of simple structure,good treatment effect,easy maintenance and low cost,which can provide reference for rural domestic sewage treatment.