Study On Nitrogen And Phosphorus Removal Of A/O-BAF With Composite Filler At Low Temperature

The sewage treatment technology in rural areas of northern China lags behind especially during the low temperature period.Biological Aerated Filter?BAF?is a kind of efficient biofilm wastewater treatment technology which is suitable for rural sewage treatment because of its advantages of low investment costs,small occupied area and good treatment effect,etc.However,influenced by various conditions,the nitrogen removal efficiency of BAF is unstable,and the effluent of traditional biological phosphorus removal is still difficult to meet the discharge standard.This paper aims at the study of nitrogen and phosphorus removal efficiency and microbial diversity by comparing at low temperature?10¹5 ??,the medium of the BAF-A reactor is composite filler system?zeolites and ceramic?while BAF-B reactor with iron rich media.This experiment investigated the start-up process of two sets of reactor and pollutant removal efficiency as well as its influencing factors under low temperature in order to optimize the process parameters.In addition,the variation law of pollutants along the BAF-B reactor was also studied,and then analyzed the pollutant removal performance and microbial community diversity at low temperature.The COD removal rate of the two reactors are stabilized up to more than 80% and NH₄⁺-N removal rate are kept about 60% after 37 d operation at low temperature.It is considered that the start-up process has basically finished.Selected iron rich media height?40,60,80,100cm?,hydraulic loading?0.25,0.50,0.75,1.00,1.25m3/?m2·h??,the reflux ratio?0,100%?to conduct pollutant removal efficiency contrast,and then the optimal process parameters are determined: hydraulic loading 0.50 m3/?m2·h?,reflux ratio 100%,gas water ratio 10:1 and iron rich media height 80 cm.The removal rate of BAF-B rates on COD?NH₄⁺-N ? TN ? TP and SS can reach 84.08%,96.84%,45.97%,97.52% and 98.14% respectively when the water temperature was 14.0 ?,and the effluent concentration of COD,NH₄⁺-N,TP and SS can reach the standard level 1A,especially the removal efficiency of TN and TP was significantly improved compared with BAF-A reactor,which was increased by 10.86% and 51.70%,respectively.Along the direction of flow,the removal of SS occurs mainly at a media height of 0.0⁰.3 m in anaerobic column while 2.0².3m in anaerobic column;the removal efficiency of COD in upper media layer and the front of the aerobic column is obvious;The concentration of TN?NO3-N and NO₂-N decreased in anoxic column While the concentration of NH₄⁺-N have no obvious changes.In aerobic column,however,a small amount of TN can be removed,the concentration of NH₄⁺-N and NO₂-N are on a declining curve,yet the concentration of NO3-N is increased gradually;The concentration of TP decrease most obviously in the filter column with iron-rich media;The pH value in the BAF-B reactor show a trend of increasing first and then decreasing.Research on the reducing in temperature 14 ? to 10 ?,the removal efficiency of COD,NH₄⁺-N,TN,TP and SS for the BAF-A reactor is decreased by 6.72%,10.60%,1.33%,13.92% and 1.44%,respectively;The corresponding indicators are decreased by 7.35%,11.60%,9.49%,9.20% and 4.55%,respectively,although the treatment effect of BAF-B reactor is better.The diversity of nitrifying bacteria in four samples of AL14,BL14,AL12 and BL12 at the temperature of 14 ? and 12 ? are analyzed,and 2 phylums,3 classes,4 orders,4 families,6 genuses,12 specieses,25 OTU are obtained.The OTU abundance of the samples are BL14>AL12>AL14>BL12;community diversity are AL14 > AL12 > BL14 > BL12.The results show that iron rich media has little effect on the total number of species,but the diversity decrease,and the total number and diversity of species decrease with the decrease of temperature.As a whole,28 phylums,59 class,110 orders,196 families,334 genuses,502 specieses and 794 OTU of the bacteria,archaea community are obtained from 8 samples.Methanosaeta of Euryarchaeota is only detected of archaea in the AM14,BM14 and AM12.The abundance of samples from high to low order are AM12,BM12,BU14,AU14,AL14,BM14,AM14 and BL14.The bacterial diversity from high to low order are AM12,AU14,BM14,BL14,BU14,AM14,BM12 and AL14.The results show that the microbial community structure and diversity have a variety along the flow direction,and the total number of species and diversity of bacterial community are increased with iron rich filler,while the total number of species have a reduce,and diversity of bacterial community have a increase during the decrease of temperature.Through the OTU cluster and different levels of taxonomic analysis,that the upper column of aerobic column of two sets of reactors to remove organic substances with more microorganisms,while the lower part of the number of species involved in nitrification is more;using iron rich media mainly to nitrification and denitrification removal increased the abundance of nitrogen of microorganisms,and the positive and negative two the direction of abundance based on Organic matter degradation microorganism;degradation of organic matter to reduce the temperature,abundance changes are the pros and cons of microbial nitrification and denitrification and denitrification microbes in two directions,generally the opposite direction still accounts for the majority of.The effect of temperature changes and the use of iron rich media on the functioning microorganisms is similar to that of the aforementioned analysis.In addition,there are a significantly positive correlation with environmental factors at the level of phylum by RDA: SHA-109 and TP;Gracilibacteria and TN,TP;Microgenomates and NH₄⁺-N,COD,TN;Actinobacteria and TN,TP;Verrucomicrobia and TN,TP;Firmicutes and SS;Hydrogenedentes and TP.In addition,Nitrospirae and TN,TP;Chlamydiae and NH₄⁺-N show an obviously negative correlation with environmental factors.