Upgrading Of An AO Process To Modified A~2O For Biological Nutrients Removal

Due to inefficient nutrients removal, Guodian Shenyang North Wastewater Treatment Plant is required upgrade and reconstruction to achieve efficient nutrients removal. Based on original construction, the reversed A2O and modified A2O processes were employed to upgrade and treat municipal wastewater with low C/N ratio. At the same time, landfill leachate was added into influent with the purpose of improving the pollutants removal performance. The reasons of incompetent nutrients removal in SDAO process were explained. The nutrients removal performances of upgrading processes were investigated when treating low C/N ratio municipal wastewater.By means of contrast test, pilot-scale SDAO process shown the similar pollutants removal performance with the project-scale SDAO process. Pilot-scale SDAO process could represent original wastewater treatment system and carry out the study on upgrading. Due to low C/N ratio and absent of the anaerobic zone, TN removal efficiency was only reached to 25.7%, and TP was hardly removed in SDAO process.After upgrading the SDAO process, the reversed A2O and modified A2O processes maintained efficient COD and NH4+-N removal performance as SDAO process. Meanwhile, the TN removal performance was obviously improved. Under the C/N ratio of 4.0-6.0, the TN removal efficiencies were increased from 25.7% to 48.1%(reversed A2O) and 53.8%(modified A2O), and the effluent TN concentration were decreased from 24.4 mg/L to 17.0 mg/L (reversed A2O) and 14.0 mg/L (modified A2O). The TN removal performance of modified A2O was superior to that of reversed A2O. Via adding sodium acetate (COD of 40 mg/L), the phenomenon of phosphorus release was occurred in anaerobic zone, and the TP removal performance of upgrading processes were obviously improved under the C/N ratio of 5.8. The TP concentration in the modified A2O process effluent was decreased from 1.35 mg/L to 0.11 mg/L with TP removal efficiency increasing from 23.4% to 93.6%. The effluent meet the discharge standard GB-18918-2002 one grade A.Landfill leachate (the proportion of 1.8‰) and sodium acetate (COD of 10 mg/L) adding into municipal wastewater, the modified A2O also could reach efficient nutrients removal performance with the C/N ratio of 4.8. The effluent meet the discharge standard GB-18918-2002 one grade A. The result indicated it was feasible that modified A2O could treat a suitable amount of landfill leachate with municipal wastewater in economic and technologic aspects.The dominant fluorescence materials were the tyrosine-like and the tryptophan-like materials, and the fulvic-like materials were secondary components in the influent of Guodian Shenyang North Wastewater Treatment Plant. Protein-like materials were more efficiently removed in biotreatment process than fulvic-like materials which were large molecular weight and biorefractory components. The result shown that the fluorescence materials removal performance of the upgrading processes were similar to that of SDAO process. Adding landfill leachate had hardly effect the fluorescence characteristics of modified A2O effluent.High-throughput sequencing result shown that the Alpha diversity of microbial community in reversed A2O and modified A2O processes were higher than that in SDAO process. However, the Alpha diversity of modified A2O system was decreased after adding landfill leachate. At phylum level, Proteobacteria, Bacteroidetes, Planctomycetes, Chlorojlexi, Firmicutes and Verrucomicrobia, which were important components of active sludge, were ubiquitous and widely existed in SDAO and upgrading processes. However, their relative abundances were affected by the types of processes and wastewater.