Experimental Study On Optimization Of Biological Phosphorus Removal Via Side-stream Fermentation Tank

At present,the poor water environment makes many China’s wastewater treatment plants face nitrogen and phosphorus removal process upgrading and reconstruction.The nitrogen removal process often choose a variety of way to optimize the biological treatment,however,the phosphorus removal process is limited by lacking of carbon source,the second pond spate separation difficulties and the effect of nitrate in the return sludge,less enhanced biological phosphorus removal measures,generally use more depth processing and chemical phosphorus removal,it brings large investment cost,high sludge yield and increased indirect carbon emission.Side-stream enhanced biological phosphorus removal（S2EBPR）process,which is popular in the United States and Denmark,has been proved to be able to achieve a good phosphorus removal effect under the condition of less planned land and lower influent organic matter,and has a good application prospect.However,S2EBPR has the disadvantages of side-stream flow ratio and side-stream tank HRT parameters and long side-stream tank HRT,which limits the practical application of this process.In view of the deficiencies and shortcomings of S2EBPR,this topic takes S2EBPR process as the research object,through experiments to explore the optimal HRT of side-stream tank and the influence of fixed packing on fermentation effect and activity.Based on this,the overall performance of S2EBPR process and the change rule of microbial population characteristics in the start-up and stable stages of S2EBPR process were investigated.Several feasible schemes for further strengthening phosphorus removal were also discussed.First,shake flask batch reactor respectively explores the fermentation time and add the effects of the packing on the side-stream tank operation results showed that the fermentation time significantly affect phosphorus bacteria and denitrifying bacteria activity,when the fermentation time is 48 h phosphorus bacteria aerobic phosphorus absorption significantly enhanced activity,is not fermented sludge 4.83 times,when the fermentation time is greater than 48 h,The activity of nitrifying bacteria decreased significantly,after 96 h fermentation,the sludge degradation rate of NH₄⁺-N decreased by 38.5%,and the optimal HRT of side-stream tank was 48 h.The experiment of adding fixed fillers to fermentation sludge showed that the fillers could enhance sludge fermentation and inhibit the activity of functional bacteria.When HRT=24 h,the gas production,NH₄⁺-N and PO₄^3--P dissolution rate in the filler group were1.67,1.6 and 1.22 times higher than those in the non-filler group.Under different fermentation time,the activity of functional bacteria in the filler group decreased by 0%to 15%compared with that those in the non-filler group.It was found that the longer the fermentation time of the sludge supernatant was,the higher the phosphorus uptake of the sludge was.The maximum phosphorus uptake of the aerobic phase of the sludge was 48.2 mg·L^-1 when HRT=72 h.According to the batch test results,the S2EBPR pilot device was established,and it was found that the side-stream tank could significantly enhance the biological phosphorus removal effect,and the effluent PO₄^3--P concentration decreased from 5 mg·L^-1 to 0.8 mg·L^-1 after the addition of the side-stream tank.The side-stream tank will increase the main NH₄⁺-N load and reduce the treatment efficiency,and the effluent NH₄⁺-N concentration increases from 0.57mg·L^-1 to 1.59 mg·L^-1.Microbial community analysis showed that there were no conventional phosphorus bacteria in the pilot system,but only atypical phosphorus bacteria such as Acinetobacter,Pseudomonas and Aeromonas.The abundance of Candidatus decreased from29.7%to 3.3%with the increase of the side-stream tank,which may be the main reason for the intensive phosphorus removal in the side-stream tank.Finally,the study adjusted the main/side flow tank HRT,cancelled the main anaerobic segment/adjusted reflux site and added polyurethane filler to enhance the phosphorus removal effect.The extension of 48 h to 72 h in the side-stream fermentation tank improved the main phosphorus removal efficiency,and the effluent PO₄^3--P concentration decreased from 0.9 mg L^-1 to 0.3 mg·L^-1.However,the improvement of the fermentation level in the side-stream fermentation tank would lead to the main NH₄⁺-N load,and then lead to the increase of NO₃^--N concentration in the side-stream fermentation tank and reduce the fermentation level.After adjusting the sludge reflux site at the same time in the main anaerobic segment of S2EBPR device,it was found that the phosphorus removal efficiency decreased rapidly in the absence of anaerobic segment,and the effluent PO₄^3--P concentration increased from 0.3 mg·L^-1 to 8.0mg·L^-1,indicating that it could not be achieved without the main anaerobic segment.In the pilot experiment,adding fixed fillers in the side-stream fermentation tank did not enhance anaerobic fermentation,and the main fillers had no effect on the removal rates of PO₄^3--P,TN and COD.The presumed reason is that the ambient temperature of the experiment is only 20℃,the number of acid-producing fermentation bacteria in the side flow fermentation tank is small,and the enrichment effect cannot be achieved by adding fillers.Therefore,the presence or absence of fillers has little influence on the operation effect of the device.This study investigated the overall efficiency and mechanism of S2EBPR process in the process of start-up and stable operation,and tried to use a variety of means to strengthen the actual efficiency of S2EBPR process,the results are conducive to a deeper understanding of S2EBPR mechanism of action,optimization of process operation parameters.To provide technical support and data basis for solving the problem of poor biological phosphorus removal under the current situation of low carbon sources in China.