Biological Shock Effect Of Rural Sewage Outflow And Development Of Biological Enhanced Treatment Process

Based on the great fluctuations of water quantity and quality in rural domestic sewage and the frequent occurrence of off-flow,this study presented a sludge-secondary effluent co-fermentation integrated rural sewage treatment equipment.The as-constructed equipment realized the self-sufficiency of carbon in the internal system.Specifically,this equipment treated domestic sewage during the day time and replenished the secondary effluent and sludge fermentation liquid mixture at night（off-flow period）.Results show that the system is still efficient and stable in pollutant removal under the condition of night flow interruption.This study provided a realistic basis for future rural sewage treatment and a new idea of sludge resource reuse.With the traditional A²/O system as the research object,the pollutant removal,sludge activity and microbial structure of the system under the conditions of the off-flow at night were studied by field simulation.The study found that the outage problem had a significant inhibitory effect on the pollutant removal efficiency of the system and affected the microbial population.During the 35d operation,the COD,NH₄⁺-N,TN and TP concentrations in the effluent were increased（the wastewater quality was degraded from the initial level A to the final level B）;the SVI of activated sludge in the aerobic zone increased from 83.81 mL/g to175.19 mL/g and the MLVSS/MLSS decreased from 0.93 to 0.63,and the sludge sedimentation performance and activity decreased significantly;16S rRNA sequencing result show that the relative abundance of four typical heterotrophic bacteria in the system decreased from 4.20%to 1.83%;The relative abundance of Denitrifying Bacteria was dropped from 5.20%to 2.77%.In order to alleviate the impact of the current interruption on the activated sludge system,a sludge-secondary effluent co-fermentation integrated rural sewage treatment device was designed.This device is coupled with a sludge fermentation unit,and the fermentation liquid and tail water are mixed in a certain ratio as a preparatory water source during the outage period.In the 35d pilot study,the average concentration of COD,TN and TP in the effluent was respectively 24.34 mg/L,9.14 mg/L and 0.76 mg/L,which indicated high efficiency of pollutant removal.As for the microbial structure,the relative abundance of heterotrophic increased from 1.83%to 3.46%,the relative abundance of denitrifying bacteria increased from 2.77%to 4.48%,and the relative abundance of phosphorus-accumulating bacteria increased from 2.55%to 3.58%,indicating that such operating mode is helpful in the enrichment of related functional bacteria in the system.In order to further improve the output of high-quality carbon source in the fermentation unit,the activated sludge and excess sludge were used as seed sludge to study their anaerobic self-fermentation acid production characteristics.The results show that under the same fermentation conditions（30℃,64h,and 1500 r/min）,when the maximum acid production was reached,the production of SCOD and VFAs were 376.84 mg/L and 47.71 mg/L for activated sludge,and 249.82 mg/L,27.68 mg/L for excess sludge,respectively.With the activated sludge as inoculated sludge,there were higher VFAs production and it contained more acetic acid components.Therefore,in this study,activated sludge was selected as the seed sludge for anaerobic fermentation.