Research On Combined Process Of Enhanced Anaerobic And Composite Medium Ecological Filter Bed To Treat Rural Sewage

With the development of the rural economy and the improvement of people's living standards,the amount of rural sewage generated is increasing.The pollution of rural sewage to the environment has become one of the key issues that need to be solved urgently.Rural sewage treatment technologies include biological,ecological and combined treatment technologies.The anaerobic biological-ecological combined treatment technology has been widely used in rural sewage treatment because of its characteristics such as good pollutant removal effect,stable operation,and convenient operation and management.However,in the conventional rural sewage anaerobic biological-ecological combined treatment technology,the anaerobic unit often only uses simple anaerobic process,and the anaerobic hydrolysis effect is poor.The structure and function of the ecological unit are single,the design load of which is high,and the area is large.The overall removal effect of pollutants is limited in the conventional combined treatment technology.In view of the problems of conventional anaerobic biological-ecological combined process for treating low-concentration rural sewage,a new type of enhanced anaerobic-composite medium ecological filter bed process for treating rural sewage was studied in this paper.The enhanced anaerobic unit used an improved filler-type ABR process to enhance the hydrolysis effect on pollutants.The composite medium ecological filter bed unit utilized the synergy of biology and ecology to improve the removal effect of N and P pollutants in sewage,by planting functional plants and filling multiple layers of fillers with adsorption propertiy.The new-type of enhanced anaerobic-composite medium ecological filter bed combined system was constructed in this paper.Taking rural sewage as the treatment object,the start-up operation characteristics of the combined system was investigated.At stable operation period,the effect of combined system on the removal of pollutants such as COD,NH₄⁺-N,TN and TP was studied,and the variation of C,N and P in the combined system was analyzed.Based on high-throughput microbial sequencing,the change of characteristics of microbial community in different HRT and different zones in the enhanced anaerobic unit was studied,.The enhanced anaerobic unit and the composite medium ecological filter bed unit of the combined system were simultaneously started by gradually decreasing the enhanced anaerobic unit HRT and increasing the HLR.The enhanced anaerobic unit and the composite medium ecological filter bed unit were synchronized and successfully started within 34 days.At the end of the start-up period,the COD removal rate of the enhanced anaerobic unit reached 73.78%,and the packing condition of the biofilm was good.The removal rates of COD and NH₄⁺-N of the composite medium ecological filter bed unit reached 44.87%and61.50%,respectively,and the calamus in the composite medium ecological filter bed unit growed well.During the stable operation period of the combination system,the HRT of the enhanced anaerobic unit reduced from 8 hours to 3 hours,and the HLR of the composite medium ecological filter bed unit increased from 0.47 m³/?m²·d?to 1.25 m³/?m²·d?at the same time.The removal rate of COD by the combined system increased first and then decreased.Under the condition of the enhanced anaerobic unit HRT of 5 hours,COD removal rate was as high as 87.20%,in which the enhanced anaerobic unit contributed 38.08%,and the composite medium ecological filter bed unit contributed 49.12%.The DOM of different units of the combined system showed a gradual downward trend.The removal of DOM mainly occurred in the composite medium ecological filter bed unit.At the same time,the DOM removal effect of the enhanced anaerobic unit weakened with the shrinkage of HRT.Under the condition of HRT of 3 hours,the enhanced anaerobic unit showed a good hydrolysis effect,the proportion of COD_S increased from 75.19%to 82.14%,and the B/C increased from 0.29 to 0.51.During the stable operation period,the removal rate of NH₄⁺-N and TN by the combined system increased firstly and then decreased.Under the condition that the HRT of the enhanced anaerobic unit was 5 hours,the removal rates of NH₄⁺-N and TN were the highest,reached79.69%and 44.93%,respectively.The influent and the anaerobic unit effluent were mainly NH₄⁺-N,accounting for 80.96%-89.62%,96.76%-98.56%,respectively.The effluent was dominated by NO₃^--N and NH₄⁺-N,accounting for 21.18%-59.28%and 31.8%-72.94%,respectively.The removal rate of TP by the combined system gradually decreased.Under the condition that the HRT of the enhanced anaerobic unit was 8 hours,the removal rate of TP was the highest,reached 87.98%.The removal of TP by the combined system mainly occurred in the composite medium ecological filter bed unit.EEM analysis results showed that,there were mainly three types of humic acid,SMP and tryptophan-like protein substances in the EPS of each compartment of the enhanced anaerobic unit,among which the SMP content was the highest.The presence of humic acids was related to the content of humic acid in the influent sewage and the hydrolysis of the enhanced anaerobic unit.The gradual decrease of humic acid along the course indicated that the hydrolysis effect basically weakened along the way.Under the condition that the HRT of the enhanced anaerobic unit reduced from 8 hours to5 hours and 3 hours,high-throughput sequencing results showed that the Bacteria diversity in sludge was the lowest when the HRT was 8 hours while the relative abundance of methanogenic bacteria?Methanothrix?reached 22.93%.At the phylum level of Bacteria,the relative abundance of Chloroflexi and Firmicutes increased,the relative abundance of Proteobacteria decreased,while the relative abundance of Euryarchaeota increased first and then decreased.At the genus level of Bacteria,Longilinea,Levilinea,Ornatilinea,Clostridium sensu stricto,and Thermogutta all had hydrolytic acidification function.As HRT decreases,the relative abundance of these functional genus bacteria increased,which could enhance the hydrolytic acidification effect of enhanced anaerobic unit.At the phylum level of Archaea,Euryarchaeota was the absolute dominant phylum at the phylum level.When the HRT was 8 hours,the relative abundance was the highest?99.57%?.At the genus level of Archaea,the dominant genus were Methanothrix,Methanoregula and Methanospirillum.With the HRT of the enhanced anaerobic unit decreased,the substrate used for CH₄ production changed from mainly acetic acid to acetic acid and H₂.Under the same HRT condition?3 hours?of the enhanced anaerobic unit,the abundance of Bacteria increased firstly and then decreased along the way,with the highest abundance in the third compartment.The diversity of Bacteria gradually increased along the way,with the highest diversity in the fourth compartment.The dominant phylums at the phylum level were Chloroflexi,Proteobacteria,Firmicutes and Bacteroidetes.The dominant genus at the genus level were Ornatilinea,Levilinea,Longilinea,Clostridium sensu stricto and Thermogutta,which were representative acid-producing bacteria.The sum of the relative abundances of these bacteria in the first to third compartments was higher than that in the fourth compartment,indicating that the hydrolytic acidification effect of the first to third compartments was better than the fourth compartment.