Enhanced Removal Of The Organic Matter And Ammonia Nitrogen In A Receiving River Of Wastewater Treatment Plants’ Tail Water By Biological Aerated Filter

The ecological base flow of Xinhe River passing through Xi Xian New Area is deficient,of which the tailwater of sewage treatment plant is the main supplementary water source.Targeted water quality assurance technologies are urgently needed to meet the water quality requirements of the Yellow River Basin and ecological protection and high-quality development.Compared with the activated sludge,biofilm has strong impact resistance,long microbial generation period and long biological chain,which is suitable for the Purification of water quality with low pollution intensity,such as the tail water of sewage treatment plants and the polluted rivers.In this study,Biological aerated filter with 0.86 cubic meter Effective volume is adopted to be the biological treatment unit.Hydraulic load and air-water ratio were selected as the key parameters.The main contents including:(i)The characteristics of organic compounds were characterized by gel chromatography,three dimensional fluorescence,Fourier transform infrared(FTIR)and equilibrium chromatography,and then the biodegradation characteristics of different molecular weights and different kinds of organic compounds are studied;(ii)The treatment efficiency and influencing factors of BAF on ammonia nitrite and nitrite under different working conditions were studied and a calculation method of water head loss of BAF based on Kozeny-Carman equation was proposed;(iii)The main microbial population structures and their differences in BAF were verified by high throughput sequencing.The main contents and results of the experiment are as follows:(1)The main organic compounds in Xin river are humus,soluble microbial products and proteins.Fluorescence parameter analysis showed that:Organic matter in rivers originates from the metabolic process of aquatic plankton and microorganisms,and has strong biogenic characteristics.(2)Organic compounds are mainly aromatic compounds.Calculated by total organic compounds,more than 70%of the organic molecular is distributed in 7000-14000Da,When HL=0.13m/h and g/w=6:1,BAF can remove 97%aromatic compounds with molecular weight less than 1000Da.In the reactor,the conversion process of organic compounds with a molecular weight of more than 1000Da is mainly SMP with small molecular weight and protein to SMP with large molecular weight.The structure of organic compounds in the reactor is obviously complicated.BAF has limited effect on removal of macromolecular organics in tailwater and new river,so it needs to be combined with other pretreatment facilities.(3)BAF can remove ammonia nitrogen effectively,the treatment effect is affected by hydraulic loading(HL)and the ratio of gas and water(g/w).Under operating condition of HL=0.13,g/w=2:1,the effluent NH4+-N is lower than 1.50mg/L,which complied with standard Ⅳ of surface water.When g/w=1:1,the accumulation trend of nitrite is obvious.Under higher g/w,the nitrite concentration is under 0.1mg/L at the first sample site.The treatment effect of BAF to nitrate is strongly affected by HL,it achieves best effect under the working condition of HL=0.13m/h,g/w=4:1.The simultaneous nitrification and denitrification(SND)process is affected by HL and g/w,which is also affected by COD/NH4+-N.Under the condition of COD/NH4+-N=67-70,HL=0.13m/h,g/w=4:1,SND achieves the highest efficiency.(4)In this study,based on Kozeny-Carman equation,take the Microbial and physical retention synergies as a core,a computing method of water head loss is established as follows:H=k(u0(1-φ0)2/φ03+un(1-φn)2/φn3)(5)The changes of microbial population structure were similar in BAF.The main microbe are Chloroflexi,proteobacteria,Acidobacteria,Actinobacteria,Firmicutes,Gemmatimonadetes,planctomycetes,and Nitrospirae.The relative abundance of Nitrospirae decrease with the height.On the contrary,The relative abundance of proteobacteria and Acidobacteria rises with the height.Lower filter of the BAF has the most amount of species.The treatment effect of biological aerated filter on ammonia nitrogen in river is good,and the effluent concentration conforms to the standard of surface water.For organic compounds with a relative molecular weight less than 1000Da,BAF has a good degradation effect,but the organic matter of>1000Da does not appear obvious degradation in the reactor.Besides,there is a transformation process from small molecules to organics with molecular weight of 7000-14000da.The aerated biofilter has limited ability to treat the organic matter in tail water receiving river and it needs to be combined with coagulation,advanced oxide,film filter or anaerobic biological treatment.