Construction And Performance Research Of An Integrated High-Efficiency Biofilm Reactor With Self-Cleaning

With the new countryside policy developing in our country,the rural living standards have been greatly improved,Thus,the treatment of rural wastewater is more urgent than before.Rural wastewater has the characteristics of great variations in water quality and quantity,strong biodegradability,difficulty in collection,and large seasonal changes.At present,the common treatment methods mainly include activated sludge method,biofilm method and natural ecological method.Among them,the biofilm method has become a research hotspot due to its high active biomass,good denitrification effect,and flexible process.At present,the biofilm reactor is mainly investigated in treating urban wastewater,and there are not many studies on its applications in rural wastewater treatment.Therefore,it is of great significance to apply the biofilm method to rural wastewater treatment.Based on the current situations and characteristics of rural wastewater treatment,this study combines the advantages of biological aerated filter and moving bed biofilm reactor into a lab-scale integrated high-efficiency biofilm reactor with cycle cleaning which combined the biological treatment and biological filtration.In this study,the real wastewater was used to investigate the system treatment performance of chemical oxygen demand（COD）,ammonia（NH₄⁺-N）,total inorganic nitrogen（TIN）and total suspended solids（TSS）under different temperatures and influent organic loading conditions,and the microbial community structure was analyzed.The different functions of the aerobic section and the filtration section were clarified,the microbial community structure and significant difference species of the two function sections were analyzed.And analyzed the characteristics of the biofilm before and after cycle cleaning,the pollutants removal performance,the changes of the microbial community.This study investigates and analyzes the treatment capacity of the bioreactor from both macro and micro perspectives,and provides a theory for the integrated self-cleaning high-efficiency biofilm reactor and its application in rural wastewater treatment in the future.The maintained results are as follows:（1）The removal efficiency of COD and TSS is less affected by temperatures and influent loadings,and the removal loading of COD and TSS increases with the increase of influent organic loadings;while the removal efficiencies of NH₄⁺-N and TIN had an obvious plunge under low temperature.Adding iron salt immediately can effectively strengthen the removal performance under low temperature conditions.Under the conditions of influent concentrations of COD,NH₄⁺-N,TIN,and TSS were 242.5±87.7mg/L,43.0±13.4 mg/L,44.4±13.3 mg/L,and 186.1±92.2 mg/L;the effluent concentrations were 56.3±18.0 mg/L,9.8±7.4 mg/L,20.5±12.0 mg/L,and 16.7±8.5mg/L;the average removal rates of COD,NH₄⁺-N,TIN,and TSS were 75.49±6.90%,79.43±12.71%,55.61±17.99%,and 89.49±6.89%;the surface removal loadings were 3.35±1.78 g COD/m²/d,0.58±0.21 g NH₄⁺-N/m²/d,0.43±0.20 g TIN/m²/d,and 2.98±1.59 g TSS/m²/d,respectively.The effluent quality was relatively stable and met the secondary standard for rural wastewater discharge in Shandong Province.During the operation of the system,the microbial community abundance and the number of rare species gradually increased,and the relatively high abundance of JG30-KF-CM45,Acinetobacter,Pseudoxanthomonas and Hydrogenophaga and other genus with heterotrophic nitrification and aerobic denitrification functions were founded,which effectively promoted the simultaneous nitrification and denitrification process.（2）The biofilm thickness and biomass of the aeration section are greater than those of the filtration section,while the removal contribution rates of COD,NH₄⁺-N,TIN,TSS in aeration section were 60.56±10.96%,67.06±13.45%,30.96±15.71%,and64.34±16.76%,respectively.Aeration section is the main reaction zone for the biological treatment of the system.Meanwhile,the main function of the filtration section is to complete the post-enhancement treatment as an auxiliary reaction zone,intercept most of the TSS and further biodegrade the pollutants.There are significant differences in the microbial community structure at genus level between aeration section and filtration section under different temperature conditions.Under constant temperature of 20℃,the relative abundance of JG30-KF-CM45,Acinetobacter,Caldilineaceae,Rhodobacter,IMCC26207,Gemmatimonadaceae in the aeration section were significantly higher than the filtration section;under low temperature of10℃,the relative abundance of Acinetobacter,Trichococcus,Pseudorhodobacter,Comamonadaceae in the aeration section were significantly higher than the filtration section.（3）The average biofilm thickness and biomass of the system are significantly reduced from 284.33±89.99μm and 23.22±4.94 g MLSS/m² before cycle cleaning to124.57±20.40μm and 15.44±2.71 g MLSS/m² after cycle cleaning,respectively,which confirmed the significance of cycle cleaning.The changes in biofilm thickness and biomass before and after cycle cleaning indicate that the process can effectively renew the biofilm and remove redundant suspended solids.The average specific SCOD degradation rate increased from 5.7±2.63 g SCOD/m²/d before cycle cleaning to 7.08±2.71 g SCOD/m²/d after cycle cleaning,and the average specific nitrification rate increased from 0.82±0.27 g NH₄⁺before cycle cleaning to 1.01±0.32 g NH₄⁺-N/m²/d after cycle cleaning.After cycle cleaning under various working conditions,the system has significantly improved the removal performance of various pollutants.The cycle cleaning process significantly increased the status of the dominant populations in the community.In particular,the relative abundance of bacteria with heterotrophic nitrification and aerobic denitrification functions increased significantly,and the rising trend was also significant under low temperature conditions.（4）Based on the overall research results of the integrated self-cleaning high-efficiency biofilm reactor,preliminary loading design parameters and system maintenance methods for future reference are proposed:the COD loading is 3.35±1.78g COD/m²/d,and the ammonia nitrogen loading is 0.58±0.21 g NH₄⁺-N/m²/d,TIN loading is 0.43±0.20 g TIN/m²/d,TSS loading is 2.98±1.59 g TSS/m²/d,and HRT can be adjusted according to the concentration of influent pollutants to maintain a certain system loading.The system maintains a good treatment capacity;the system operation must ensure a regular cyclic self-cleaning process to complete the renewal of the biofilm and the elution of suspended particles and other impurities,and the regular self-cleaning process can effectively improve the packing blockage;Maintain stable microbial activity by adding a certain amount of iron salt.