Construction And Operation Characteristics Of Single-pool Switching Biofilm System

As the consciousness of urban water environmental protection is increasing,the standards of sewage disposal are becoming more and more stringent.In the common sewage biological treatment methods,the biological method has the advantages of high efficiency and stable operation of the activated sludge process,so it has been paid attention to and popularized.The performance of biological filler is the key to determine the treatment effect and operation cost of biofilm,thus it is an important research direction in the field of environmental engineering to develop new wastewater treatment materials and develop reasonable treatment process.In this paper,soybean straw was used as the biological membrane carrier.In the same reactor,a single-pool switching biofilm system was constructed to realize the transformation of oxygen/aerobic mode of biological system.We studied the biological membrane capacity of straw load and the influencing factors of system operation,optimized the operating conditions of the system and analyzed the characteristics of microbial flora of biofilm system.The results have some reference value to broaden the utilization of agricultural straw resources and improve the application effect of wastewater treatment biofilm system.Selecting the woody part of the soybean straw root to pretreatment,different types of straw biomass fillers were prepared,and the ability of soybean straw hanging film was determined through the experiment of hanging membrane.The experimental results showed that the surface of soybean straw was rough and the hanging area was large.It has strong biocompatibility,good effect of hanging film and thick biofilm.Through the contrast of the material characteristics of the hanging film,the moisture content,the ash,the tensile strength and the fracture strength of the straw are increased.Static suspensions and dynamic suspensions were performed by means of non-continuous flow.Reaction system hanging film completed when the removal rate of COD and ammonia nitrogen was about 80%,the removal rate of ammonia nitrogen was stable at about 55%,and indicative organism of rotifers are found in the microscopic examination.The reactor was divided into two single pools with straw filler,and alternately aerated in two single cells in a period of one week,and the positions of inlet and outlet were exchanged simultaneously.The experimental conditions of the reactor were optimized by changing the time of water retention,pH and dissolved oxygen concentration.Considering the difference of environment in different seasons,the process was carried out in winter and summer separately,and the effect was compared in different seasons.The experimental results are as follows: the optimal operation parameters of the system during the summer operation are: HRT=8h,pH=7.0,DO=5.0mg/L,and the best operating parameters of winter operation are: HRT=12h,pH=7.0,DO=4.0mg/L.Due to the limitation of temperature,the reactor operation removal effect of summer is superior to winter.However,it shows that the system has good low temperature resistance in winter since the system can maintain stable operation,and can keep certain removal of various pollutants.In order to verify the removal ability of the biofilm system under the optimum operating conditions,we use the simulated domestic sewage as the influent,and making the reactor operate stably under the best operating condition.The results showed that the COD removal rate of the biofilm system can reach more than 85%,and removal rates of ammonia nitrogen and total nitrogen can reach about 78% and 59%,respectively,and the effluent can meet the Class A of Integrated Wastewater Discharge Standard.The mechanism of denitrification in single-pool switching biofilm system was analyzed,and it was found that the operation of alternating aeration mode not only made the reactor have obvious aerobic and anoxic regions,but also in the aerobic aeration reaction tank.Because of the uneven distribution of dissolved oxygen and nutrients,it was found that there existed a vertical partition in the aerobic reaction tank,indicating that there are environmental conditions for simultaneous nitrification and denitrification in the system.After the reactor was restarted,the performance analysis experiment showed that it was only 3 days to recover the removal capacity of the pollutant after the operation of the reactor was stopped for 31 days,indicating that the reactor had good tolerance of poor substrate and fatigue resistance.The microbial community composition in the process system was analyzed,and the results showed that the microbial community in the biofilm formed on the straw biomass filler was very rich by means of alternating aeration,and the dominant species were Proteobacteria,Bacteroidetes,Cholobi,Spirochaetae,and Firmicutes.