Effect Of Reflux Ratio On Pollutant Removal And The Mechanism In Two Microaerobic Processes Treating Manure-free Piggery Wastewater

Manure-free piggery wastewater(MFPW)has the characteristics of high ammonium(NH4~+-N)and low chemical oxygen demand to total nitrogen ratio(C/N).Biological nitrogen removal is the key and difficult problem in its treatment.In the previous study,upflow microaerobic sludge reactor(UMSR)and upflow microaerobic biofilm reactor(UMBR)had been developed,in which the ANAMMOX was the main nitrogen removal approach.However,the enrichment and cultivation of the ANAMMOX population is difficult.High reflux ratio takes the increase in management costs of UMSR and UMBR treating wastewater.To achieve efficiency nitrogen removal in treating,The microbial community and main pollutant removal of the two microaerobic treatment processes were studied by restarting up and reducing the reflux ratio.This work would be helpful in the startup and management of the microaerobic treatment process.UMSR and UMBR could recover from the idle state and a new steady state was reached within 55 and 53 days,respectively.Within the steady phase,the removal rates of NH4~+-N anf TN in UMSR averaged 95.6%and 88.1%,respectively.And NH4~+-N and TN removal could achieve respectively 96.5%and 91.7%in UMBR.Through high-throughput sequencing analysis,Various of ammonia nitrogen oxidizing bacteria(AOB),nitrite oxidizing bacteria(NOB),denitrifying bacteria,and ANAMMOX bacteria were found in both UMSR and UMBR processes.It was suggested that there were different nitrogen removal approaches in two reactors.Using the calculation and analysis of the relevant biochemical reactions,it was found that the contribution of ANAMMOX to remove nitrogen from the UMSR and UMBR was 66.67%and 64.33%,respectively.Through this,UMSR and UMBR have recovered and ANAMMOX was the dominant approach to nitrogen removal from the wastewater By the reflux ratio decreasing from 20:1 stage to 5:1,the UMSR system has the best NH4~+-N and TN removal at the reflux ratio of 15:1,reaching 98.1%and 93.4%,respectively.The denitrification performance of the UMBR system shows a gradual decline in the process of the reflux ratio decreasing from the 25:1 stage to the 15:1stage.In the stable operation stage with a reflux ratio of 15:1,the UMBR system maintained a good denitrification efficiency,and the removal rates of NH4~+-N and TN were 89.4%and 82.4%,respectively.Contrastive analysis of two reactors,the UMSR has better processing performance under the same operating conditions.The analysis results of microbial community and functional population showed that the Alpha diversity in UMSR and UMBR systems changed significantly with the decrease of reflux ratio.Heterotrophic denitrification,autotrophic denitrification,nitrification,and ANAMMOX were changed with different operation.Under the condition of the reflux ratio of 15:1 in UMSR.The ANAMMOX and AOB have the strongest metabolic activity and the reactor has the best denitrification efficiency.With the gradual decreasing of the reflux ratio,the contribution of ANAMMOX approach in UMBR was reduced.Meanwhile,the metabolic activities of ANAMMOX and AOB were suppressed.