Research On Biofilm Phosphorus Recovery Process Using Organic Carbon From Municipal Wastewater

The phosphorus（P）recovery from the municipal sewage in mainstream treatment is irresistible in development of technologies for wastewater treatment,and is also increasingly focused in international environmental engineering industry.In comparison with conventional EBPR process,the biofilm-based P recovery technology is designed to simplify the recovery process and improve recovery efficiency.However,in the existing studies,additional carbon sources（COD ranging from 200 mg/L to 1600mg/L）need to be added in the anaerobic stage to obtain the high-phosphorus recovery liquid.The COD concentration in urban sewage in China is generally in the range of 200-300mg/L.The study will simulate urban sewage quality and build a new operation model.the incoming water was firstly carried out in the anaerobic section,and the carbon source was used to release phosphorus,and then the phosphorus was absorbed in the aerobic section.In this study,an experiment was carried out for simultaneous removal of concentrated phosphorus by PAOs-biofilm with suspended filler,in which organic matter in water was used as carbon source.The device used in the experiment is a cylindrical reactor with an effective volume of5L.In the process of experiment,firstly,PAOs-biofilm was cultured and the influence of disturbance factors on membrane hanging was investigated in the culture;secondly,the study of phosphorus removal and enrichment was carried out with the film-forming suspension filler as the main functional body,and the influence of factors such as NH₄⁺-N,DO,HRT,V_S:V_rand the mixing state of the filler on the phosphorus removal and enrichment efficiency of the reactor was investigated in the operation.In the process of culture and operation,biofilm samples were collected for thickness EPS,SEM,high-throughput sequencing and other measurements.Through the experiment,the following conclusions are drawn:（1）The disturbance state is an important environmental factor for the cultivation of PAOs-biofilm.Weak disturbance condition is more favorable to the cultivation of PAOs-biofilm.Under this condition,organic load is 0.25kg（COD）/[kg（MLSS）·d],the anaerobic and aerobic conditions are controlled for 4 hours at the same time,and the water is changed every 48 hours,and the drainage volume ratio is 25%,the suspended filler can complete the PAOs-biofilm hanging within 30 days,the hanging rate is100%,the film thickness is up to 121.5μm,4 hours of PO₄^3--P release 2.6mg/L,4 hours of PO₄^3--P uptake 0.85mg/L.（2）It is feasible to use municipal wastewater organic carbon for phosphorus removal and enrichment.During the operation,the PAOs-biofilm was controlled under the condition of strong disturbance,the stirring speed is 170r/min,the relative ratio of anaerobic and aerobic HRT is 3,5h,Vs:Vr is 2:1,the influent p H value is 7,DO is6mg/L.In this case,the effluent COD is stable below 50mg/L,the removal rate is stable above 90%,the effluent PO₄^3--P is stable at about 0.5mg/L,the concentration of phosphorus recovery liquid is stable between 50-60mg/L,and the maximum is60mg/L,and the P_rel/C_uptis 0.23.（3）In operation,when DO is 6mg/L,the phosphorus uptake capacity was 1.38times that of DO at 3mg/L;Prolonging the aerobic HRT appropriately can increase the amount of phosphorus uptake in the aerobic section,and the effluent can be as low as0.5mg/L.which confirmed that increasing DO can enhance the phosphorus uptake performance of the PAOs-biofilm,and prolonging aerobic HRT can improve the phosphorus uptake effect of the system.（4）p H、anaerobic HRT are the important factors to improve the phosphorus release performance of the reactor.When the influent p H is 7,tthe concentration of phosphorus recovery liquid is nearly doubled compared with that of the influent p H is7.5,and stabilized to more than 50mg/L.However,when the p H in the reactor exceeds 8.3,there will be no phosphorus absorption and release effect.When the anaerobic HRT is 2h,the phosphorus release performance of the system is reduced,but when the anaerobic HRT is 4h,5h,the phosphorus release performance of the system is more stable.Longer anaerobic HRT can make the polymerization in the anaerobic section of the PAOs-biofilm more complete transformation.（5）In this study,controlling Vs:Vr is 2:1 and the relative ratio of anaerobic and aerobic HRT is 1:1-1:1.5,which can create a more suitable growth environment for PAOs-biofilm.In addition,the high concentration of influent NH₄⁺-N has a certain influence on the improvement of phosphorus uptake and release performance of the PAOs-biofilm system.When the concentration of NH₄⁺-N is 50mg/L,nitrification is obvious in the reactor,and the effluent contains about 13mg/L of NO₂^--N.（6）The strong disturbance and high stirring speed of the biofilm can make its fluidization state better and give full play to its efficiency.The strong perturbation state is more favorable to the renewal of PAOs-biofilm,so as to ensure its activity.When the stirring speed was 170r/min,the phosphorus absorption and release performance was stronger.The phosphorus uptake and release amount was 2 times and 1.5 times as much as that of 90r/min,and 1.5 times and 1.2 times as much as that of 130r/min。（7）In the process of cultivation and operation,the content of EPS in the PAOs-biofilm increased from 26.09mg/g·VSS to 216.28mg/g·VSS;the morphology of microorganism changed from spherical and short rod-shaped to filamentous bacteria.The species richness and diversity got lower and lower,while the proportion of dominant flora increased.The abundance of Proteobacteria at the phylum level increased from 28%to 66%.The abundance of Candidatus Competibacter at the genus level increased from 0.4%to 28.14%.The abundance of Defluviicoccus,Thiothrix,Sphaerotilus and Pseudomonasand etc.all increased to different degrees.