Study On Phosphorus Removal And Strengthen Of A/O Biological Denitrification With Iron-rich Media

Denitrification and phosphorus removal of urban sewage is one main task for current environmental protection work. It's common to use A/O process to treat urban sewage, but A/O process exist two typical problems: DO contradiction and low phosphorus removal performance, which tried to be solved at the same time under conditions of feasible technology and reasonable cost. Firstly, operation parameters of A/O reactor are optimized,and then compare denitrification and phosphorus removal efficiency of ROP-A/O reactor and A/O reactor by setting oxygen and phosphorus removal filter column; finally, research mechanism of iron-rich media in chemical phosphorus removal and strengthening biological denitrification of ROP-A/O reactor, and influence of iron-rich media on activated sludge microbial community diversity.The optimum parameters of A/O reactor as follows: RS is 50%, SRT for 16 d, RW of 200%;under these conditions, SV30, MLSS, SVI is 20.6%, 2562mg/L, 80.7 respectively; the corresponding effluent is 28.8 mg/L, 0.63 mg/L, 25.50 mg/L and 3.18 mg/L when the concentration of COD, NH4+-N, TN and TP of influent is 371.2 mg/L, 60.93 mg/L, 59.53mg/L, 4.76 mg/L respectively, removal rate is 92.2%, 99.0%, 57.1%, 32.9% respectively.Fe³⁺ is produced thorough electrochemical effect of iron-rich media, and it can improve the coagulation sedimentation performance of activated sludge, reduce sludge specific resistance and improve sludge dewatering performance. Iron-rich media can increase removal efficiency of COD, NH4+-N, TN, TP at the same time. When RW is 100%-300%, the removal efficiency of COD, TN, TP increase,but NH4+-N change litter as RW increasing for ROP-A/O reactor;when RW is 300%,removal efficient of pollutants reach its best; removal efficiency is 93.8%, 99.9%, 61.6%, 74.4% respectively when influent concentration is 281.8mg/L,59.53mg/L, 51.97mg/L, 7.42mg/L, and COD, NH4+-N of effluent reach the standard level 1A,so level 1B to TN and level 2 to TP.Phosphorus removal of ROP-A/O reactor depend on microorganism and chemical;chemical phosphorus removal is principal, which occurs mainly in oxygen and phosphorus removal filter column. When RW is 100% and 200%, TFe concentration is rise firstly, then reduce and then rise along oxygen and phosphorus removal filter column; when RW is 300%,TFe concentration is rise firstly, and then reduce, no rise again is mainly affected by high TP concentration of influent. Electrochemical reaction is also deoxidation reaction that can remove DO within reflux nitrifying liquid, which make for strengthen the anoxic environment;when RW is 100%-300%, deoxidation effect become better as RW increasing. When RW is different, TP concentration reduce and TP removal rate rise along ROP-A/O reactor.When concentration of Fe³⁺ is 0.5mg/L, changes of activated sludge microbial community diversity as follows: number of species of activated sludge reduce 1, but microbial community diversity increase, litter influence on uniformity of species distribution. Fe³⁺maybe is principal component that cause deviation in microorganism of CG and EG sample.Besides, Fe³⁺ can promote growth of Nitrosomonadales and Nitrospirae, and diversity of microbial of Nitrosomonadales and Nitrospirae increase.Influences of Fe³⁺ on OTU of organisms of activated sludge as follows: make OTU56,OTU82, OTU106, OTU203, OTU251, OTU255, OTU341, OTU355 vanish, and newly born OTU39, OTU69, OTU236, OTU270, OTU307, OTU321, OTU360. The highest three OTU of abundance of CG sample from more to less in turn is OTU233, OTU406, OTU343, and so OTU406, OTU354, OTU94 to EG sample. After adding Fe³⁺, the most remarkable three OTU increase in abundance from more to less in turn is OTU354, OTU159, OTU221, and so decrease is OTU233, OTU343, OTU191. Fe³⁺ have no influence on species of main OTU, but significantly affect abundance of main OTU.In terms of phylum level, Including Proteobacteria, Bacteroidetes and Firmicutes, the highest three phylum of relative abundance of CG and EG sample are same. Fe³⁺ has a distinct promoting effect for Proteobacteria and Firmicutes, but don't for Cyanobacteria and Bacteroidetes. At the genus level, the highest four genus of relative abundance of CG sample is Saprospiraceae, Chloroplast, Clostridium and NS9, and so Saprospiraceae, Clostridium,Acinetobacter, Epulopiscium to EG sample. Fe³⁺ promote growth of Acinetobacter and Epulopiscium obviously, but don't for Chloroplast and Saprospiraceae.