Research On Denitrification And Phosphorus Removal From Low C/N Effluent Strengthened By Iron-carbon Microelectrolysis Coupled Solid Carbon Source

Sufficient carbon source is the basic guarantee of microbial denitrification and phosphorus removal.However,in most of China's sewage treatment plants,the concentration of organic matter is relatively low.And in many regions,COD/N of sewage treatment plants is less than 3-5,resulting in poor effect of denitrification and phosphorus removal in the biological treatment process and difficulty in meeting the discharge requirements.Therefore,denitrification of low C/N sewage is a difficult problem to improve tail water quality of sewage treatment plant..This research mainly focused on low C/N municipal sewage.A composite denitrification and phosphorus removal system was constructed by combining iron-carbon micro-electrolysis autotrophic denitrification and solid carbon source heterotrophic denitrification.The iron-carbon micro-electrolysis fillers with different iron-carbon volume ratios was prepared and the best iron-carbon ratio was selected;the corn cob dosage was determined,iron-carbon micro-electrolysis coupling solid carbon source strengthening denitrification and dephosphorization system was constructed,and the optimal operating parameters were determined.And through high-throughput sequencing technology,the mechanism of its denitrification and dephosphorization was analyzed,which provided the foundation for the subsequent development and application.Based on the characteristics of multiple iron-carbon micro-electrolytic fillers,fillers with different iron-carbon ratios were prepared by a series of manufacturing processes included mixing,granulating,drying,calcined and cool.In the performance test of reduce nitrate by iron-carbon micro-electrolysis filler,the reduction effect of the fillers with different iron-carbon ratios was Fe:C=1:3>Fe:C=1:2>Fe:C=1:1>Fe:C=2:1>Fe:C=3:1.And the removal of NO3-is mainly the function of Fe2+ to convert it to NH4+.In the system of iron carbon micro-electrolysis combined with microorganism for nitrogen and phosphorus removal.The presence of DO is beneficial to the removal of NH4+ and improves the denitrification effect of the whole system,but is not significant for phosphorus removal.Under the condition of DO>0.5mg/L,Fe:C=1:2 was the optimal iron-carbon ratios of iron-carbon micro-electrolysis fillers.At this time,the effluent concentrations of ammonia nitrogen,nitrate nitrogen,total nitrogen and phosphorus were 0.77mg/1-3.12mg/L,4.23mg/1-6.16mg/L,6.79mg/1-8.51mg/L and 0.01 mg/1-0.06mg/L respectively,and the removal rates were about 96.02%,79.46%,89.46%and 99.10%,respectively.Nitrogen and phosphorus removal in low C/N wastewater was achieved.But the phenomenon of continuous accumulation of nitrous was present.For the system of Fe:C=1:2 iron carbon micro-electrolysis combined with microorganism,it was investigated the effect of C/N for nitrogen and phosphorus removal.The experiment showed that with the increase of C/N,the removal rate of nitrogen in the system gradually increased from 28.95%to 95.94%,while the removal of phosphorus was not affected by C/N and remained stable at more than 90%.In order to improve the system of denitrification effect and reduce the accumulation of nitrate,the composite system was constructed by combining iron-carbon micro-electrolysis and solid carbon source for nitrogen and phosphorus removal.Solid carbon source adopts com cob that has been pretreated by alkali.Considering the nitrogen removal effect and COD concentration of effluent,the amount of com cob added is determined,which is 5.0g/200ml,or 25.0g/L.In iron-carbon micro-electrolysis-solid carbon source biological nitrogen and phosphorus removal system,control inlet C/N=1.5,HRT=2.0h?5.0h,D0=1.0mg/L?3.0mg/L and pH=5.5-8.5,respectively,the optimal operating parameters are HRT=4h,DO=2.0mg/L,pH=7.0.At this time,ammonia,nitrate,total nitrogen removal rate is 95.63%,93.48%,94.72%,respectively.In the analysis of iron-carbon micro-electrolysis filler surface(FC),corncob surface(CC)and suspended(SS)microbial population in the system,Miseq high-throughput sequencing results showed that there were abundant heterotrophic denitrifying bacteria in the system,such as Gemmobacter Defluviimonas,Thauera and Dechloromonas,and there were also autotrophic denitrifying bacteria Arenimonas related to iron-carbon micro-electrolysis.At the same time,Actinotalea,Chryseolinea and Novosphingobium,which decompose cellulose,hemicellulose and lignin,also exist.It is proved that heterotrophic denitrification and autotrophic denitrification are combined in the system,and multiple microorganisms act together.