Constructed Wetland Microbial Fuel Cells Enhanced By Pyrite For Wastewater That Contained Chromium Treatment

The exposure of heavy metal chromium(Cr)in soil,water and other environmental media has a high risk of ecological toxicity.In this study,chromium containing wastewater was take as the treatment object.Three constructed wetland-microbial fuels(CW-MFC)were constructed:CW-MFC based on gravel and ceramsite(GC),CW-MFC based on gravel,ceramsite and pyrite(PS)and CW-MFC with iron scraps as the anodic filling material and gravel,ceramsite and pyrite as the substrate(Is Ano-PS).The effects of pyrite and pyrite combined with iron scraps on the treatment of chromium containing wastewater and synchronous power generation performance of CW-MFC system were studied.The removal effects of heavy metal Cr and its co-pollutants by pyrite and combined iron scraps were systematically investigated.At the same time,the influence of pyrite on the power generation performance of CW-MFC system was analyzed by monitoring the voltage change continuously.High-throughput sequencing technology and q-PCR quantitative analysis were used to explore the changes of microbial community structure and chromium reduction gene(chr R),so as to reveal the purification and synchronous electricity generation mechanism of chromium-containing wastewater treated by CW-MFC coupled pyrite.The main conclusions are as follows:(1)The removal efficiencies of total chromium,ammonia nitrogen and total phosphorus in PS group and Is Ano-PS group were significantly higher than those in GC group(p < 0.05),and the removal efficiencies of total nitrogen,Cr(Ⅵ)and COD were not negatively affected and the fluctuation was more stable.The results show that the application of pyrite coupled iron scraps in CW-MFC system can help to reduce the environmental risk of heavy metal chromium,and has better anti-pollution load capacity and long-term operation potential for chromium-containing wastewater.(2)The power generation performance of PS group and Is Ano-PS group was significantly higher than that of GC group(p < 0.05).The average voltage output of PS group was 20.7%higher than that of GC group,and the average voltage output of Is Ano-PS group was 40.2%higher than that of GC group.The internal resistance of Is Ano-PS group was 295.71Ω,and PS group was 326.13 Ω,which was significantly lower than GC group(453.16 Ω).The results show that the application of pyrite coupled iron scraps can effectively reduce the internal resistance and enhance the power generation performance of CW-MFC system.(3)The addition of pyrite in the substrate had no significant effect on the microbial community diversity in CW-MFC system,and the addition of iron scraps significantly reduced the microbial community diversity in anode.The results showed that the addition of iron scraps in the anode and pyrite in the substrate had a synergistic effect on the overall structure of anode microbial community(p < 0.05).(4)The anode microbial community structure of different CW-MFC systems was significantly different.At the phylum level,Proteobacteria and Firmicutes were the dominant phylum in PS.Firmicutes was the dominant phylum in Is Ano-PS.At the genus level,Paenisporosarcina and Geobacter were enriched in PS group.Paenisporosarcina,Geobacter and Aquabacterium were enriched in Is Ano-PS group,among which Aquabacterium was the characteristic bacteria of Is Ano-PS group.The cathode microbial community structure of different CW-MFC systems was significantly different.At the phylum level,Proteobacteria were the dominant phylum in GC,PS,Is Ano-PS.At the genus level,Pseudomonas and Noviherbaspirillum were enriched in PS group,Pseudomonas and Flavobacterium were enriched in Is Ano-PS group.These results show that pyrite and iron scraps can significantly change the anode and cathode microenvironment conditions and selectively enrich some functional bacteria conducive to the removal and denitrification of heavy metal Cr,so as to improve the efficiency of heavy metal chromium removal and denitrification.(5)Microbial co-occurrence network analysis of anode microbial community in Is Ano-PS group showed that Clostridia and Bacilli were positively correlated(Spearman > 0.6,p < 0.05),and the reduction of Cr(Ⅵ)was dominated by Clostridia and Bacilli.Saccharimonadia and Alphaproteobacteria are positively correlated,and these two microbial groups have synergistic effects with nitrogen cycling related genes.Patescibacteria,Chloroflexi and Proteobacteria played a key role in community,and the Patescibacteria belong to the low aboudance group,which is involved in nitrogen,sulfur and iron cycling,suggested that the low abundance group may played a key role in the microbial community.(6)The copy numbers of chr R in GC,PS,and Is Ano-PS were different significantly(p<0.05).The copy numbers in the anode and cathode of Is Ano-PS was the lowest,followed by the PS.These results indicate that the presence of iron scraps in the anode can provide electrons to promote the reduction of Cr(Ⅵ)and reduce the stress of Cr(Ⅵ)in the solution,thus the burden of Cr(Ⅵ)reduction functional microorganisms was reduced and the transcription level of chr R was affected.