Powder Activated Carbon Strengthening SBR For Simultaneous Nitrogen And Phosphorus Removal Under Limited Aeration

In order to control the increasingly serious problem of water eutrophication，themunicipal sewage treatment plant put forward higher requirements for the discharge standardsof the nitrogen and phosphorus in the effluent. In the same time, many biological nitrogen andphosphorus removal procedure also come into being. As we know, the biological nitrogen andphosphorus removal process both need organic carbon, but the domestic sewage of partialarea in China has a low organic carbon, so the problem of treating low carbon sewage needsto be solved. To solve this problem, this research was carried in a sequencing batch reactor(SBR) treating simulated domestic sewage. The simultaneous nitrogen and phosphorusremoval efficiency between the powdered activated carbon-sequencing batch reactor(PAC-SBR) and SBR for the best process condition were compared under the limited aeration.In addition, the effect of different C/N ratio for the nitrogen and phosphorus removal inPAC-SBR was studied. What’s more, the operating characteristics and the superiority ofPAC-SBR under the limited aeration were analyzed.The operation condition of SBR was determined by the culture of the activated sludge.And the final cycle was set to be6h, which included1h flow stage–1h agitation stage–3haeration stage–30min agitation stage–30min sedimentation and decanting stage. When theSBR was run under different aeration rates, the COD、ammonia nitrogen and TP removalefficiency was reduced with the decrease of aeration rate. Too high or too low aeration ratewould both reduce the TN removal efficiency. The results showed that the average removalefficiency of COD、TN and TP in SBR achieved90.02%、81.13%and88.12%, respectively atthe aeration rate of24L/h.The PAC-SBR showed obvious advantages for its average removal efficiency of COD、TN and TP was higher than SBR. The effluent of PAC-SBR was improved evidently, becauseits quality reached the A kind of the first Class standard requirements for―Discharge standardof pollutants for municipal sewage treatment plants‖(GB18918-2002). Compared with theSVI value higher than150mL/g of SBR, the value of PAC-SBR was finally fluctuatedbetween90~118mL/g and it had a higher sludge concentration. When the PAC-SBR wasoperated with the increase of C/N(5、7.5、10) ratios, the influence for ammonia nitrogenremoval efficiency was little and the TN removal efficiency was gradually increased. The TPremoval efficiency was stably higher95%while the C/N ratio was equal or higher than7.5.The results explained that the increase of organic carbon in influent was favorable to the denitrification by the denitrifying bacteria which enable the nitrogen removal efficiency ineffluent to be the best.During the operation of PAC-SBR under the limited aeration, the powder activatedcarbon with the porous structure and the large specific surface can adsorb the dissolvedoxygen、microbial cells、the enzyme and the biodegradable organic matter on its surface. Forthat reason, the DO concentration in the PAC-SBR was decreased, which increased the DOtransfer rate. The activated sludge using PAC as the biological carrier, which combined theexcellent adsorption of PAC and the oxidizing ability of microorganisms, could improve theflocculate structure and increase the concentration of substrates around the microbial floc. Asa result, the ammonia oxidizing bacteria and the aerobic polyphosphate accumulatingorganism adsorbed by PAC could quickly use the DO and substrates for biodegradation,which increased the activity of the corresponding functional bacteria. That procedure led tothe successive anoxic-anaerobic-low aerobic/anoxic-anoxic environment in the PAC-SBR,which was available to the simultaneous nitrification-denitrification and the denitrifyingphosphorus removal. In the end, the simultaneous nitrification and denitrification rateachieved55.4%and the ratio of denitrifying phosphorus accumulating bacteria (DPAO) to thetotal polyphosphate accumulating bacteria reached55.57%in the PAC-SBR. The two datahelped save the carbon source and enhanced the simultaneous nitrogen and phosphorusremoval efficiency for low-carbon domestic sewage in the PAC-SBR under limited aeration.