Enrichment Culture Of Phosphorus Accumulating Biofilm And Enhancement Of Phosphorus Absorption And Release Performance

The recovery of phosphorus（P）via PAOs-biofilm has becoming one of the potential pathways of sewage resource utilization.In previous study,PAOs-biofilm reactor had been constructed under alternative anaerobic-aerobic conditions,and the P recovery performance had been investigated.However,the proper conditions for PAOs-biofilm culture are still unclear,and the P recovery performance is unsatisfactory.Focusing on these problems,this study explored the effects of dissolved oxygen（DO）levels,hydraulic conditions and particle size of inoculated sludge on the culture of PAOs-biofilm.Furthermore,the P recovery performance was intended to be improved via optimizing Vs:Vr（the volume ratio of synthetic sewage stream to recovery stream）and anaerobic p H.The results showed that in the range of 2-6 mg/L,higher DO was more favorable to facilitate the secretion of extracellular polymer（EPS）from the PAOs-biofilm,and PN/PS（protein/polysaccharide）amounting to 4.33.The final biofilm thicknesses of 222.43,295.6,and 666.89μm for the three reactors of DO₂,DO₄,and DO₆ respectively,indicated that the higher DO was beneficial to accelerate the growth rate of PAOs-biofilm.And there was no significant difference in the species of PAOs at different DO levels the relative abundance was significantly influenced by DO levels,among which the abundance of Ca.Accumulibacter and Xanthomonadales was significantly and positively correlated with DO.High influent P load（influent P concentration of 30 mg/L）under weak perturbation was more favorable to the rapid enrichment culture of PAOs-biofilm with better P uptake and release,which could shorten the culture period from 44 to 20 days.In summary,this study suggested that rapid enrichment culture of PAOs-biofilm can be achieved within 20 days with oxidation ditch sludge as sludge source,40%fill ratio,temperature of about 21°C,p H of 7.5,DO of6 mg/L,and high influent P concentration（30 mg/L）,and P uptake and release of up to 30 mg/L in one cycle.Further,the anaerobic COD/P could be changed by regulating Vs:Vr to effectively enhance the P recovery effect of PAOs-biofilm:when Vs:Vr was reduced from 3:1 to 1.5:1,the anaerobic COD/P was reduced from 20 to 5 mg-COD/mg-P,and the P concentration of the recovered solution could reach 85 mg/L,which was 45%higher than the previous study of the group;P_rel/HAc_upt ratio（amount of P released per unit mass of organic carbon consumed）reached 5.06 P-mmol/C-mmol,the highest P uptake/release rate was 1.60/2.67（mg-P/（g-VSS-h））,P removal rate reached 90-95%,effluent P concentration was less than 0.5 mg/L.Meanwhile,PAOs were enriched when Vs:Vr was1.5:1,and the relative abundance increased from 8%to 14.9%,mainly including Thiothrix,Rhodospirillales,Rhodobacter,Saprospiraceae.GAOs were screened out to some extent,and the relative abundance decreased from 38%to 22%.It was further found that the metabolic activity of PAOs-biofilm was regulated by anaerobic COD/P,when Vs:Vr was 1.5:1,anaerobic COD/P=5,PAOs-biofilm had higher P_rel/HAc_upt ratio and higher PHA_synt/HAc_upt with amount up to 1.23 C-mmol/C-mmol,and Gly_degrad/HAc_upt was 1.25-2 times higher than the other experimental groups.