Experimental Study On Nitrogen And Phosphorus Removal By BAF Strengthened With Limestone/Iron-Rich Filler

Under the influence of low temperature in winter,the microbial activity in the wastewater treatment process of villages and towns in northern China decreases,resulting in the weakening of the treatment capacity,leading to the phenomenon that the effluent pollutants do not meet the standards.Biological aerated filter?BAF?has the advantages of small area and good effluent quality,and it is an optimal process for rural sewage treatment.However,there are many shortcomings in this process,such as the nitrification performance is susceptible to the influence of organic loading,and the phosphorus removal effect is not good.In this experiment,the efficiency of nitrogen and phosphorus removal and the diversity of microbial community were studied by using composite filler systems such as ceramsite,zeolite,limestone and iron-rich filler at low temperature.Firstly,the start-up process of bio-aerated filter consisting of ceramsite in anaerobic column and zeolite in aerobic column was investigated under the condition of temperature change.Secondly,the effects of limestone and iron-rich filler on pollutant removal efficiency at low temperature were analyzed.Finally,the effects of limestone and temperature on microbial community diversity in the reactor were analyzed.The reactor was operated for 23 days at 15?and 41 days at 11?for a total of 64 days,the removal rate of COD was more than 80%,the removal rate of NH⁺₄-N was more than60%,and the film-forming process was basically completed.The removal rates of COD,NH₄⁺-N,TN,TP and SS in the reactor were 89.49%?97.95%?46.33%?49.82%?97.73%respectively under the operating conditions of 15?,hydraulic load 0.5m³/?m².h?and gas-water ratio 10:1 under the action of limestone,when the reflux ratio of nitrate was100%.The effluent COD,NH₄⁺-N and SS could meet first-grade A standard emission requirements.Compared with the control group,the removal rates of TP and TN increased by 6.4%and 2.2%respectively,while the removal rates of COD,NH₄⁺-N and SS almost remained unchanged.The removal rates of COD,NH₄⁺-N,TN,TP and SS reached 85.63%?96.16%?88.79%?47.39%?95.55%respectively when the reflux ratio of nitrate was 100%.The effluent COD,NH₄⁺-N,TP and SS all met first-grade A standard emission requirements.Compared with the control group,the removal rates of TP and TN increased by 45.2%and 2.47%,NH₄⁺-N decreased by 1.93%,COD decreased by 2.1%,and SS almost unchanged.The results of temperature dependence on the reactor showed that the removal rates of COD,NH₄⁺-N,TP and TN were higher than those of zeolite columns when the temperature was 11°C,13°C,15°C and 20°C,respectively.However,the removal rate of SS is lower than that of the zeolite column.When the temperature is 11°C,13°C,and 15°C,the limestone zeolite mixed packing column does not significantly enhance the treatment effect of the reactor,but at 20°C,the removal rate of TP is compared.The zeolite column increased by 23.3%because of the endothermic reaction of limestone to the adsorption of phosphorus.The higher the temperature,the better the adsorption;The effects of limestone on bacterial community diversity in aerobic column of biological aerated filter were investigated at room temperature of 15?.The results showed that at the taxonomic level of phylum,class,order,family,genera and species,the number of bacterial populations in CO15 samples was higher than RO15.Among them,Nitrospirales,Flavobacterium,Candidatus Nitrotoga,Dokdonella,Isospospa and Halomonas were the most abundant species.Dominant strainLimestone increased 111species of bacteria at genus taxonomic level.There were 420 OTUs in the two samples.The total OTUs of CO15 and RO15 were 1161 and 917 respectively.Under the condition of limestone as filler,the effects of temperature on the diversity of microbial community were investigated at 11 C and 13 C,respectively.The total OTUs of CO11 and CO13 in the two samples were 904,1102 and 1099 respectively.The total OTUs of CO11 and CO13 in the two samples were 1102 and 1099 respectively.At the generic classification level,the top six species in the two samples were OLB17,Paludisphaera,Thermomonas,Singulisphaera,Luteimonas and Thauera.The abundance of OLB17 and Singulisphaera increased while that of Paludisphaera and Thermomonas decreased when the temperature decreased from 13 to 11,suggesting that low temperature promoted the growth of some dominant strains and inhibited the growth of some dominant strains.