Enhancement Of Organic Pollutant Removal And Electricity Production In Sludge Microbial Fuel Cell By Dosing Zero Valent Iron

With the widespread application of wastewater treatment technology,a large amount of excess sludge is produced annually.Because of the widespread use of activated sludge technology,excess sludge is becoming a severe environmental problem.Sludge recycling and the enhancement of organic pollutant removal has become a hot issue recently.This study combined sludge microbial fuel cell?MFC?with anaerobic zero-valent iron?ZVI?enhancement technology and constructed a sludge MFC system enhanced by ZVI dosing.Through the setting up of gradient ZVI dosage and selecting three different ZVI forms including iron powder,iron scrap and nano-iron powder,in combination with pollutants removal performance,electrochemical properties and anodic microbial community structure analysis was carried out to study this system.Results show that dosing with ZVI can effectively enhance electricity production and organic pollutant removal of sludge MFC.Dosing with 10g/L ZVI had a maximum power density of 33.34mW/m²,increased by 78.77% compared with the control group.ZVI also facilitated the sludge hydrolysis process and released SCOD rapidly during the 0¹0d.After 60 days' operation,the maximum TCOD and VS removal rate were obtained by dosing 20g/L ZVI,which increased by 19.54% and 11.00% respectively compared to the control group but only had a little difference with dosing with 10g/L ZVI.Hence,10g/L is the best ZVI dosage.Moreover,ZVI contributed to the adjustment of sludge p H,ORP and the enrichment of electricigens.Furthermore,this study compared the difference of enhancement by dosing with iron powder,iron scrap and nano-iron powder under 10g/L ZVI dosage.Nano-iron powder increased the maximum power density from 32.03mW/m² of iron powder to 37.20mW/m² and reduced the electron transfer resistance to 2.014? improving the anodic electron transfer ability.However,the promoting effect of nano-iron powder was only distinct during the early operation stage of the MFC while the addition of scrap iron had a 41.03% increase in the electricity production of MFC with a maximum power of 25.95mW/m² compared to the control group.By dosing with iron powder,the anodic electron transfer resistance was reduced and the double layer capacitance reached the highest representing the best electrochemical performance.In addition,dosing with different forms of ZVI had a similar promoting effect compared to the control group on organic removal and sludge reduction.The reason for this promoting effect is that the ZVI dosing enhanced the removal of sludge protein.Through the microbiology analysis of the sludge MFC enhanced by dosing ZVI,ZVI facilitated the enrichment of electricigens and lead to the community differences of anodic microbial film and sludge microorganisms.At the functional gene level,ZVI increased the abundance of functional genes related to protein and amino acid degradation promoting the degradation process of protein in sludge.The abundance of cytochrome C functional gene accelerated the direct electron transfer of anodic electricigens.The dissolution of Fe²⁺ by the anaerobic corrosion process of ZVI may have promoted the indirect electron transfer process.Moreover,TCOD removal rate and MFC power output had a good liner relation,indicating the correlation of MFC electrogenesis and organic pollutant removal.This study showed that through exogenous dosing with ZVI,the performance of electricity generation and sludge organic pollutant removal in MFC was significantly enhanced.This method is convenient and effective in providing a new approach to the disposal of excess sludge and the promotion of MFC power output.