Study On Enanced Denitrifying Phosphorus Removal In The A-(O/A)~n -SMBR Process Treating Domestic Wastewater

With the growing concern on the problem of water eutrophication and the implementation of new Urban Sewage Discharge Standard (GB18918-2002). Developing stable and cost-effective technology, to improve nitrogen and phosphorus removal from domestic wastewate (especially low-carbon source wastewater) and to control eutrophication effectively, has become one of the hot areas in environmental engineering research.The aim of this study was to improve the nitrogen and phosphorus removal simultaneously from low-carbon source domestic wastewater in a sequencing membrane reactor (SMBR). Denitrifying phosphorus removal was enhanced by controlling some key operational parameters in a sequencing membrane reactor (SMBR). Performance of pollutants removal, as well as characteristics of the sludge and membrane fouling, was investigated under different conditions of SRT, alternating aerobic/anoxic time and dissolved oxygen (DO). Major conclusions obtained from this study were as following.Performance of the SMBR system (T=3h) under different SRT conditions was investigated when the system was operated in A/O mode. Results showed that, when SRT increased from 20d to 40d, no obvious differences in COD,NH3-N and TN removal was detected and the average removal efficiency was 92.95,96.81% and 71.94%, correspondingly. But SRT showed great effect on TP removal, when SRT was set at 20-30d, above 80% TP removal was achieved at stable state. When SRT was increased to 40d, the average TP removal efficiency was only 66.8%. However, the phosphorus content and the DPAO ratio in sludge increased with the increase of SRT.By adjusting the operation mode in the aerobic period, SMBR was modified to anaerobic-alternating anoxic/oxic (O/A) mode [A-(O/A)n-SMBR]. Studies demonstrated that high nutrient removal could be achieved in the A-(O/A)n-SMBR system (T=3h). When the alternating aerobic/anoxic time was set at 30/30min,15/15min,10/10min and 5/5min, the removal efficiencies of COD,NH3-N,TN and TP was kept at 92.97~94.82%,91.9~97.8%,86.57~90.13% and 88.68%~94.86%, respectively. And the denitrifying P-uptake ratio and the sludge production rate was 32.18%,41.75%,53.63%,50.06% and 0.45,0.33,0.27,0.29 kgVSS/kgCOD, correspondingly. The alternating O/A operation mode allowed the multi-nitrification/denitrification (phosphorus removal) occurred in series in the A-(O/A)n-SMBR system. As a result, performance of pollutants removal was improved in the A-(O/A)n-SMBR system. Meanwhile, denitrifying phosphorus removal was enhanced, leading to the decrease of the sludge production rateEnhance denitrifying phosphorus removal was studied by controling dissolved oxygen (DO) levels in the A-(O/A)n-SMBR system treating low-carbon source domestic wastewater. Results showed that NO2- accumulation and denitrifying phosphorus removal using NO2-as electron acceptor were achieved under lower DO levels. When DO was set at 0.5~0.8mg/L, no obvious prohibition of NO2-(20mg/L) on anoxic denitrifying phosphorus removal occurred. Studies also showed that DO had great effect on the composition of the PAOs. When DO was decreased from 2.0~2.5mg/L to 0.5~0.8mg/L, the facultative PAOs (PONn,PON和POn) ratio increased from 40.30% to 75.10%, while the PO ratio decreased from 59.70% to 24.9%.Characteristics of fouling control showed that, On-line oxidant (3‰NaClO)+HCl (pH=1~2) cleaning procedure was effective to restore the filtration ability of the membrane when the TMP was lower than30 kPa. Analysis of SEM demonstrated that gel layer could be removed efficiently by chemical cleaning, while HCl could remove inorganic particles formed by Ca,Mg, Al, etc. In addition, analysis of particle size distribution showed that small particles, especially those whose size were below 10μm, were the main contributor to the membrane fouling. Furthermore, the contribution ratio of cake layer, organic gel layer and inorganic particle layer to the total resistance was 60~70%, 20~30% and 5~10%, respectively.Based on the Monod kinetic equation, a series of dynamic models of each composition in the A-(O/A)n-SMBR system were established and computed, and some kinetic parameters (Ks,Vmax) in the system were obtained. Simulation and analysis by Matlab and SPSS program indicated the dynamic models were suitable for simulating the variation of each composition in the system.This paper includes 82 figures, 33 tables and 175 references.