Study On The Synergy Mechanism Of ABR-MBR Combined Process For Denitrifying Phosphorus Removal

The ABR-MBR combined reactor based on combination of the anaerobic baffled reactor(ABR)with microbial phase separation and membrane bioreactor(MBR)with high-effect entrapment was constructed in this study,and the circulation and interactivity of combined process was realized by adding nitrate recycling and sludge reflux to enhance ABR providing enough high-quality carbon source for denitrifying phosphorus removal.After the functional units were constructed the denitrifying phosphorus coordination mechanism was studied.The main findings of this study are as follows:(1)High efficient carbon removal in ABR was an important guarantee for the effective nitrification of MBR.When the influent organic loads of the ABR were 1,1.5 and 2 kg·(m3·d)-1,the COD concentration of effluent was stable at 60 mg·L-1,and the average removal rate of NH4+-N in MBR was more than 95%,the low COD concentration of ABR effluent ensured the efficient removal of NH4+-N.The optimal organic load of the ABR for effective carbon removal and effective nitrification of the ABR-MBR combined reactor was 2.0 kg·(m3·d)-1,and the peak value of VFA under this load was located at the HRT of 2.4 h,the amount of VFA of in the second department of the the ABR was 54.88 mg·L-1,which was used for phosphorus release.(2)Under the conditions of organic load rate of 2.0 kg·(m3·d)-1 in ABR,total hydraulic retention time(HRT)of 9 h,the SRT of 15 d,sludge reflux ratio of 100%,and the nitrate recycling ratios increased from 100% to 350%,the effluent COD and NH4+-N concentrations of ABR-MBR combined reactor were within 50 mg·L-1 and 1 mg·L-1 respectively.Sufficient quality carbon can be provided by ABR for phosphate release,the average concentration of phosphorus released at the second chamber of ABR were 9.41,9.83,7.03 and 3.18 mg·L-1 respectively,and the amount of phosphorus uptake in the anoxic were 8.8,13.9,11.79,and 6.5 mg·L-1 respectively.If the nitrate recycling ratio is too high,the amount of phosphorus released would be reduced due to NOx--N from the nitrate recycling.What's more,low nitrate recycling ratio would inhibit phosphorus release due to lack of electron acceptor.Accordingly,the adequate amount of electron acceptor provided by MBR was the guarantee for high efficiency denitrifying phosphorus removal.The average effluent concentration for soluble phosphorus were 1.49?0.5?0.43 and 1.74 mg·L-1 separately,the aerobic stage ensured the further removal of phosphorus.(3)Under the conditions of total hydraulic retention time(HRT)of 9 h,the SRT of 15 d,sludge reflux ratio of 100%,and nitrate recycling ratios set at 300%,and the influent C/N ratios set at 3.6,4.2,4.8,6.0 and 7.2 respectively,the average effluent concentration for soluble phosphorus were 0.22,0.34,0.39,0.42 and 2.45 mg·L-1 separately,and the low influent C/N ratio was of benefit to phosphate removal.In addition,when the influent C/N ratio was 3.6~6.0,the removal of TN was linear with the anoxic phosphorus uptake of ABR,and it was conducive to the removal of TN after increasing the influent C/N ratio in this stage.(4)In this study,The ABR-MBR combined process which was based on a way of inner carbon supply and nitrate recycling ratios were adopted to treat low C/N ratio domestic sewage,and a stable and effective denitrification phosphorus removal efficiency was achieved.The results indicated that the optimized denitrifying phosphorus removal efficiency was achieved under the conditions of organic load rate of 2.0 kg·(m3·d)-1 in the ABR,total hydraulic retention time(HRT)of 9 h,the SRT of 15 d,sludge reflux ratio of 100%,and nitrate recycling ratios set at 300%,The average removal rates of TN and soluble PO43--P were 84% and 94%,the amount of phosphorus removed by denitrifying phosphorus removal accounted for 87% of the total phosphorus removed,and the average effluent concentration for TN and soluble phosphorus were 12.98 mg·L-1 and 0.43 mg·L-1 separately.