Effect Of P/N Ratio On The Treatment Efficiency And Microbial Population Communities Of Short-cut Nitrification-denitrification Treating High Ammonia Nitrogen Wastewater

High ammonia nitrogen wastewater is harmful to the water environment.Therefore,the research on the treatment of high ammonia nitrogen wastewater has gradually increased in recent years.It is very common currently for the application of short-cut nitrification and denitrification in the treatment of high ammonia nitrogen wastewater,it can effectively solve the problems of insufficient carbon source and insufficient alkalinity.In the treatment of high ammonia nitrogen wastewater,lots of industrial wastewater with high concentration of ammonia nitrogen,such as coking wastewater,fertilizer industry wastewater,etc.,have the demand for phosphorus removal.To the contrary,some industrial wastewater,such as printing and dyeing wastewater,etc.,require for additional phosphorus because of their own deficiency of phosphorus.In the process of adding or removing phosphorus,there is the problem of matching of nitrogen and phosphorus,however the appropriate ratio of phosphorus to nitrogen is still unknown.Besides,there is no literature report about the ratio of phosphorus to nitrogen in the process of short-cut nitrification and denitrification.Therefore,the issue of ratio of phosphorus to nitrogen is worth studying.The paper involves the membrane bioreactor,and studies the effect of different ratio of phosphorus to nitrogen on denitrification efficiency in the process of short-cut nitrification and denitrification of high ammonia nitrogen wastewater.At the same time,the paper reviews the changes in soluble microbial products(SMP)in the effluent water and the dynamic changes of nitrification functional micro-organisms and microbial community structure in the reactor by the way of molecular biology,such as fluorescence in situ hybridization and high-throughput sequencing.The main results are as follows:(1)The optimum ratio of phosphorus to nitrogen obtained under the experimental condition is 0.008.At this time,the removal rate of ammonia nitrogen and total nitrogen is over 98%and 93%respectively,both of the sludge activity and the sludge yield coefficient are reaching the maximum.The lowest ratio of phosphorus to nitrogen that does not affect the denitrification effect is 0.006.At this time,the ratio of phosphorus to nitrogen continues to decline,the denitrification process of nitrite begins to be inhibited,and the denitrification effect is significantly reduced.(2)It would be better to control the ratio of phosphorus to nitrogen to 0.01,0.008,0.006,0.004 respectively.With the decrease of the ratio of phosphorus to nitrogen,the concentration of SMP in water continuously reduces.The relative molecular weight distribution of SMP features a distinct single peak,and all of them are mainly small molecules,with the molecular weight up to around 300 Da.SMP is mainly humic acid.It features that the composition of fluorescent functional group is significantly related to the change of the ratio of phosphorus to nitrogen.When the ratio of phosphorus to nitrogen is 0.008,the concentration of humic acid is the maximum.When the ratio of phosphorus to nitrogen gets down to 0.006,there are obvious changes in the humic acid species,with reduction of concentration level.(3)Under the different phosphorus-nitrogen ratios,the species richness and diversity of microbial population are basically similar.While,if there are changes in the composition of microbial population,the richness of microorganisms at the gate level and genera level are both obviously changed.Besides,if there is a great change in the microbial population structure,the structure of microbial population is quite similar between 0.006 ratio and 0.004 ratio of phosphorus to nitrogen.(4)The Ammonia oxidizing bacteria involved in the process of nitrification is Nitrosomonas,whose growth metabolism has no correlation with the ratio of phosphorus to nitrogen.Besides,no nitrite-oxidizing bacteria is detected under the condition of four different ratios of phosphorus to nitrogen.The microorganisms involved in the process of denitrification are Hyphomicrobium and Ottowia.With the decrease of the ratio of phosphorus to nitrogen,the richness of Hyphomicrobiumde and Ottowia tends to decline.The decrease of denitrification effect when the ratio of phosphorus to nitrogen is 0.004 may be related to the inhibition of these two microorganisms.