Study Of Oxic/anoxic Two-stage Integrated Wastewater Technology For Advanced Ammonia Nitrogen Removal

In developing countries such as China,the rural population is dispersed and the economic level is low in rural areas,which is not suitable for the establishment of the large-scale centralized wastewater treatment plants.Therefore,compared to the centralized wastewater treatment,the decentralized treatment systems in rural areas have more broad development prospects and promotion space due to many advantages such as small footprint,low investment,low noise and convenient management.The characteristics and challenges of rural domestic sewage in China are mainly for these aspects:random distribution of emission point source,remote location,inconvenient power intervention,large fluctuations of wastewater quality and quantity,and increasing ammonia nitrogen concentration in wastewater.According above features,reliable,simple,and cost-effective oxic/anoxic two-stage integrated wastewater technology for advanced ammonia nitrogen removal was proposed in this project.In this research,an integrated two-stage packed-bed treatment device was designed and developed,with the design idea of two-stage treatment:nitrification in the inner layer and joint denitrification process in the outer layer.With the low C/N ratio sewage as the object,the changes of nitrogen(ammonia,nitrate and nitrite)in the oxic zone and anoxic zone of the reactor were detected and studied,as well as the effects of temperature,COD and pH on the denitrification.Finally,the combined denitrification system was established in this process.Moreover,the biofilm samples at different locations in the reactor were carried out by high-throughput sequencing analysis.Further,the combined denitrification system was certificated by the microbial analysis;meanwhile,the coupling mechanism of autotrophic and heterotrophic denitrifiers was established.The conclusions are as follows:(1)The design of an integrated two-stage packed-bed reactor was reasonable with the "O/A" structure:Carriers composited with carbon fiber composite and polyurethane were filled in oxic zone;iron-carbon micro-electrolysis carriers and carriers coupling with iron-carbon and biomass were filled in anoxic zone.Compared to the conventional"A/O"process,the reflux and agitation were needless in the reactor,which can reduce the power consumption significantly and save the energy efficiently.(2)When the influent condition was as follows:NH4+-N = 40.0 mg/L,pH = 8.0-8.5,DO(oxic zone)= 3.5 ± 0.3 mg/L,HRT(oxic zone)= 12.0 h,HRT(anoxic zone)= 20.7 h and T(anoxic zone)= 30 ± 1 ?,the TN removal can reach above 98%with the NO3--N and NO2--N in effluent approached 0.0 mg/L,NH4+-N below 0.5 mg/L and COD approached 20.0 mg/L.These data in effluent fully achieved the advanced ammonia nitrogen removal and reached A standard(discharge standard of pollutants for municipal wastewater treatment plant(GB18918-2002)).(3)The combined denitrification system was established and the three denitrification pathways(autotrophic denitrification,heterotrophic denitrification and chemical reduction)were proved to be existed in the process.The three pathways co-existed,coordinated and promoted each other,which can provide excellent guarantee for the nitrogen removal efficiency of the reactor.(4)The analysis of the microbial population in each biofilm sample showed that abundant nitrifying bacteria(oxic zone)and denitrifying bacteria(anoxic zone)were existed in the system,and microbes in the carriers can breed well and maintain stability,which can offered the excellent nitrogen removal.The microbial analysis in the anoxic zone proved that heterotrophic and autotrophic denitrifiers can couple well,and the abundant microorganisms acted together to support the efficient operation of the process.Finally,the denitrification mechanism of autotrophic and heterotrophic denitrifiers was established.Oxic/anoxic two-stage integrated wastewater technology for advanced ammonia nitrogen removal showed many advantages(efficient,stable and cost-low advanced removal for ammonia nitrogen,no need of sludge reflux,small footprint and low sludge yield),which can provide technical support and theoretical basis for the advanced denitrification of low C/N sewage in rural areas of China.