Study On Treatment Of Low Carbon-nitrogen Ratio Wastewater By Double Sludge Process System Of AAO-FBBR

Due to the characteristics of low carbon-nitrogen ratio of sewage,it is difficult to further improve the effluent quality of sewage plants in China,and the contradictions of carbon source competition among bacterial species are prominent,a technology that saves carbon sources and consumes less energy is needed.The experiment is based on the principle of denitrifying phosphorus removal,using anaerobic-anoxic-aerobic coupled fixed bed reactor(AAO-FBBR)double sludge process system to treat low-carbon-nitrogen sewage.The FBBR unit mainly performs the nitrification reaction,which converts ammonia nitrogen(NH3-N)into nitrate nitrogen(NO3--N),providing electron acceptors for denitrifying phosphorus accumulating bacteria(DPAOs)for phosphorus removal,while the AAO unit mainly performs denitrifying phosphorus removal.DPAOs consume the carbon source of sewage to synthesize the energy substances such as polyβ-hydroxybutyric acid(PHB)and glycogen(GLY)in the anaerobic region,and consume these energy substances for nitrogen and phosphorus removal in the anoxic region.At the same time,polyphosphate(Poly-P)is synthesized to realize efficient treatment of low-carbon-nitrogen sewage The main conclusions are as follows.(1)AAO-FBBR double sludge process system was successfully started and operated in 60 days in two stages in a continuous flow mode.After stable operation,the average effluent concentrations of COD,NH3-N,TN and TP were 10.67 mg/L,2.14 mg/L,10.85 mg/L and 0.24 mg/L,respectively,which all met the first class A standard;Material balance analysis in anoxic stage and cell staining showed that nitrogen and phosphorus removal were obvious.(2)Three different carbon-nitrogen ratios(4.90,3.47 and 2.92)were used to study the influence of AAO-FBBR double sludge process system.The removal effect of TN was better when the carbon-nitrogen ratio was 4.90,and the average concentration of effluent was 10.13 mg/L.The removal effect of TP was better when the carbon-nitrogen ratio was 3.47,and the average concentration of effluent was 0.20 mg/L.:While the the carbon-nitrogen ratio was 2.92,the average effluent concentrations of TN and TP slightly exceeded the standard,which were 15.28mg/L and 0.56mg/L respectively.Meanwhile,ΔPO43--P/ΔNO3--N was 2.02,1.52 and 1.94,respectively,and the average aeration saving was about 34.66%.(3)Under the condition of COD concentration of 40～160 mg/L,the anaerobic phosphorus release and anoxic phosphorus removal characteristics of AAO-FBBR double sludge process system were studied.Anaerobic phosphorus release experiment showed that phosphorus release was positively correlated with COD concentration;The anoxic phosphorus removal experiment showed that the anoxic nitrogen removal rate was positively correlated with COD concentration,while the anoxic phosphorus removal rate was negatively correlated with COD concentration.(4)The recovery of AAO-FBBR double sludge process system under the condition of low carbon-nitrogen ratio under abnormal condition was studied.The massive reproduction of earthworm was successfully inhibited,the AAO-FBBR double sludge process system gradually returned to normal,and the effluent water quality basically reached the standard,by stopping the aeration for 3 days and adjusting the aeration rates of different reactors,and operating for 7 days,under the influence of earthworm.The system gradually returned to normal and the removal rate of various pollutants was improved,by adding 100 mg/L powdered activated carbon(PAC),and operating for 11 days,under the condition that the AAO-FBBR double sludge process system could not operate normally due to the low carbon-nitrogen ratio.(5)Microbial diversity analysis showed that the system-related strains were domesticated and the dominant functional strains were screened.Inoculated sludge,AAO unit and FBBR unit formed distinct microbial populations due to their unique environments,and the differences of each sludge sample were obviously related to the connection sequence of their reactors and sludge reflux.The analysis of microbial community structure showed that the structure of sludge flora in the system changed obviously,and at the level of phylum,the main bacteria includes Proteobacteria,Chloroflexi,Bacteroidota,Acidobacteriota and Firmicutes.At the level of genus,DPAOs bacteria include Dechloromonas,Pseudomonas,Flavobacterium,Hyphomicrobium and Terrimonas.Based on the successful start-up of AAO-FBBR double sludge process system,the influence of influent carbon-nitrogen ratio on the system was studied,and the characteristics of anaerobic phosphorus release and anoxic phosphorus removal were studied,and the recovery of the system under abnormal conditions was studied.Finally,the pollutant removal mechanism of the system was discussed from the microbial point of view by high-throughput sequencing method,which is of great significance to the efficient treatment of sewage with low carbon-nitrogen ratio.