| The General Office of the State Council issued a guideline on promoting high-quality development of animal husbandry in 2020,pointing out that the comprehensive production capacity of animal husbandry has been enhanced,but the development quality is not high.At the same time,it proposed to vigorously promote the recycling and green breeding of livestock and poultry wastes.But livestock and poultry aquaculture wastewater discharge,complex composition,high pollutant concentration,has become one of the key factors restricting the high-quality development of aquaculture industry.At present,livestock and poultry breeding wastewater is mostly treated by anaerobic and aerobic biological treatment mode,which forms a large amount of anaerobic digestion liquid after anaerobic digestion.Anaerobic digestion solution has complex water quality,low carbon/nitrogen ratio（C/N）,and needs to consume a large amount of organic carbon sources and energy in the conventional treatment process,resulting in low economic benefits.Therefore,the study of energy saving,low carbon and consumption of anaerobic digestion liquid treatment technology is helpful to promote the high-quality development of livestock and poultry industry.In this paper,a sequential batch biofilm reactor（SBBR）with hydrophilic sponge as filler was constructed for the purpose of achieving the degradation of organic and nitrogen pollutants in the digestive fluid.Based on the water quality characteristics of the anaerobic digestion liquid of livestock and poultry breeding wastewater,the water quality conditions of the experimental influent were determined as follows:chemical oxygen demand（COD）concentration was 500mg/L,ammonia nitrogen（NH4+-N）concentration was 260 mg/L,and total phosphorus（TP）concentration was 18 mg/L.The anaerobic-aerobic（A-O）mode was adopted to realize the start-up and stable operation of SBBR system,and the influence of aeration intensity and aeration mode on the removal efficiency of nitrogen-containing pollutants and other pollutants was explored.In addition,the pollutant degradation law and microbial community composition in the reactor during the typical cycle of each operation stage were investigated,and the influence of different operating conditions on the reactor efficiency was analyzed from the biological perspective.After two weeks of operation,the SBBR reactor achieved stable pollutant removal.Macroscopically,the microbial aggregates were spread in the macropore and micropore structures in the hydrophilic sponge,and the growth state was good.SBBR reactor effluent ammonia nitrogen concentration is 107.76 mg/L,the average removal rate is 58.21%.The average accumulation of nitrite nitrogen reached 22.37 mg/L,the accumulation of nitrite nitrogen remained below 2 mg/L,and the accumulation rate of nitrite nitrogen remained above80%.The mean total nitrogen concentration of effluent was 133.44 mg/L,and the average total nitrogen removal rate was 48.40%.The average COD concentration of effluent is 110.86 mg/L,and the average removal rate is 76.37%.The microbial community in the reactor was analyzed after start-up.The main microbial populations in the reactor were Firmicutes,Proteobacteria,Bacteroidota,Actinobacteriota and superphyla.Under different aeration conditions,SBBR system has great difference in pollutant removal efficiency.In general,with the increase of aeration rate,the removal capacity of ammonia nitrogen and total nitrogen of SBBR system increases.When aeration rate increased from 0.4 L/min to 1.0 L/min,the average ammonia nitrogen removal rate increased from 58.38%to 81.31%.The mean nitrogen removal rate increased from 47.71%to 78.33%.However,when the aeration rate was 0.8 L/min,the effluent nitrite nitrogen concentration was the highest and the accumulation effect of nitrite nitrogen was the best.Under different aeration rates,the variation regularity of pollutant concentration in the reactor and the variation trend of dissolved oxygen（DO）concentration were similar in each typical period.However,when the aeration rate was 1.0 L/min,the DO concentration in the reaction system increased to 2.4 mg/L,and a large amount of nitrate nitrogen was accumulated.Under the three aeration conditions,the COD removal effect is good.The average COD concentration of effluent is 113.67,114.56 and 80.11mg/L,respectively,and the average COD removal rate is 74.96%,77.37%and 83.44%,respectively.Under different aeration conditions,the removal rate of phosphorus by SBBR system is only about 10%.High-throughput analysis of microbial community structure in the reactor under different aeration rates showed that the composition of bacteria with high abundance in the community was similar under different aeration conditions,but the abundance of various groups was significantly different.From the door level,The dominant groups in the reactor were Proteobacteria,Patescibacteria,Actinobacteriota,Bacteroidota,Firmicutes and Chloroflexi.Compared with continuous aeration and intermittent aeration,there is little difference in the removal rate of ammonia nitrogen between the two aeration modes.However,intermittent aeration further improves the removal rate of total nitrogen in SBBR reactor and alleviates the accumulation of nitrate nitrogen in continuous aeration stage when the aeration rate is L.0L/min.The average concentration of nitrate nitrogen in effluent is 0.85 mg/L.The removal rate of ammonia nitrogen was 80.24%,and the total nitrogen removal rate increased to 79.08%.There is little difference in COD removal effect between the two aeration modes.However,the intermittent aeration mode improved the phosphorus removal effect of the reactor.During the intermittent aeration,the reactor showed a relatively stable phosphorus removal ability.The average concentration of total phosphorus in effluent was 12.18 mg/L,and the average removal rate of total phosphorus was 25.13%.In the case of intermittent aeration,DO concentration fluctuation in the reactor is more stable,and DO concentration is generally stable below 0.8mg/L.From the perspective of community composition,species diversity and richness decreased when continuous aeration operation was changed to intermittent aeration operation.At phylum level,species composition is similar,but species abundance differs greatly.In both aeration modes,The dominant groups were Bacteroidota,Proteobacteria,Patescibacteria,Chloroflexi,Actinobacteriota and Firmicute,Myxococcota,and Verrucomicrobiota.However,when intermittent aeration mode was adopted,the percentages of Sphinomonas,A4b,Chitinophagales and Rhizobacter increased obviously,while the percentages of propioniclava and TM7a decreased obviously. |
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