A Tubular Bio-reactor Device Used For Enhancing Denitrification Of The Effluent From Rural Wastewater Treatment Facilities And The Demonstration Project

Excessive nitrogen discharge from the effluent of rural wastewater treatment facilities is one of the important reasons for inducing eutrophication in Tiaoxi Basin.As such,a new type of Tubular Bio-reactor Device?TBD?was initiated based on solid-phase slow-release carbon source and ecological floating bed process,which can enhance the nitrogen removal of the effluent from the rural wastewater treatment facilities.In this research,the optimizations of the TBD system were done in terms of filling substrates,structural styles and technological parameters,and its corresponding N-removal microbial mechanism of nitrogen removal was also analyzed with the help of the high-through biological techniques.A pilot-scale trial and a demonstration project were also launched based on the above experimental results.The objective of this research was to provide relevant basis for reducing the nitrogen discharge load in effluent of rural wastewater treatment facilities and thus promoting the improvement of water environment quality in watershed.The main results of this research are as follows:?1?In the study of optimization of TBD Filling Substrate,nitrogen removal performance of TBDs filled with different substrates,including retinervus luffae fructus,hemp fiber,bagasse and chemical fiber material,were compared.The results showed that TBD filled with bagasse demonstrated the best N-removal performance and its removal efficiency of NH₄⁺-N,NO₃^--N and TN were up to 72%,64%and 82%,respectively.The hemp fiber was proved to be relatively stable after 150 days of operation and could be used as the biofilm carrier of TBD.The carbon release performance of bagasse was preferable and could be used as the solid-phase carbon source of TBD;?2?In the study of optimization of TBD Structural Style,nitrogen removal performance of TBDs of different structural styles were compared.The results showed that the optimal structure form of TBD was the bagasse filling rate of 8.3%,no hole and plant planted outside the tube.The effluent from rural wastewater treatment facilities could meet the Class V of Environmental Quality Standard for Surface Water?GB3838-2002?after the treatment of TBD.The removal of NH₄⁺-N by TBD mainly depended on the absorption of plants and the nitrification of microorganisms in roots,while the removal of NO₃^--N mainly depended on the denitrification process in the tubular reactor.The results of high-throughput sequencing of microorganism showed that the aerobic denitrifying bacteria?Acinetobacter,Citrobacter and Pseudomonas etc.?and the anoxic denitrifying bacteria?Steroidobacter,Thermomonas and Azospira etc.?were the dominant bacteria in the middle and terminal of TBD,respectively.The relative abundance of these bacteria were up to 42%and 22%,indicating that the optimal structure style of TBD could promote the forming of microenvironment of"aerobic denitrification-anoxic denitrification"bacteria distributed sequentially along the reactor.This unique distribution of denitrifying bacteria could be an important reason of the sound denitrification performance of TBD;?3?In the study of optimization of TBD technological parameter,nitrogen removal performance of TBDs of different technological parameters were compared.The results showed that the optimal technological parameters of TBD were the flow velocity of 1.5 m/h,circulating flow of 5.5 L/h and its removal efficiency of NH₄⁺-N,NO₃^--N and TN were up to 62%,81%and 79%respectively.In addition,higher dissolved oxygen in the inlet was favorable for the NH₄⁺-N removal?up to 73%?while lower dissolved oxygen was propitious for the NO₃^--N removal?up to 92%?.The results of high-throughput sequencing of microorganism showed that the denitrification-related bacteria occupied dominantly?29%?,which meant it could be beneficial to the enrichment and growth of the denitrifying functional bacteria in the TBD with optimal technological parameters.This provided a guarantee for the nitrogen removal enhancement of the effluent from the rural wastewater treatment facilities;?4?In the pilot-scale trial based on systematical optimization parameters,the nitrogen removal and over-all performance of TBD on effluent from rural wastewater treatment facilities was evaluated,and the results showed that the removal efficiency of NH₄⁺-N,NO₃^--N and TN was up to 95%,89%and 90%,respectively.The water quality of the effluent met the Class-V of Environmental Quality Standard for Surface Water?GB3838-2002?and the problem of over-proof organic pollutant concentration was not found either.The analysis of the along-path physical-chemical factors of TBD showed that the C/N ratio increased while the dissolved oxygen concentration decreased along the path in the TBD.Thus,a unique distribution characteristic of abundant carbon source was and the coexistence of"Oxic-Anoxic"?O-A?segments were formed in the TBD,which promoted the sequential distribution of"aerobic denitrification-anoxic denitrification"bacteria and could improve the denitrification performance of TBD;?5?In the Demonstration Project,a project-scale TBD based on the results of system optimization and pilot-scale trial was established and the nitrogen removal and over-all performance,on the effluent from No one rural wastewater treatment facility in Yujiatian Village,Huzhou,Zhejiang Province,was evaluated.The results showed that the removal efficiency of NH₄⁺-N,NO₃^--N and TN was up to 85%,60%and 78%respectively,and the effluent met the Class-V of Environmental Quality Standard for Surface Water?GB3838-2002?.Through the analysis of the contribution of plant absorption to nitrogen removal,it was found that the plant uptake was not the main approach to nitrogen removal in TBD and it mainly relied on the microbial activities for the enhanced nitrogen removal of the effluent from the rural wastewater treatment facility.Technical and economical analyses showed that TBD has a good application prospect in the field of enhanced nitrogen removal from the effluent of rural wastewater treatment facilities due to its good nitrogen removal performance?removal rate up to 73%⁹6%?and low costs?the treatment cost was only 0.3yuan/m³ effluent?.