Iron and carbon granules added to anode enhanced the sludge decrement and electrical performance of sludge microbial fuel cell

Sludge microbial fuel cell (SMFC) can utilize the organics in sludge to generate power, and has attracted widespread attention. However, the low efficiency of organics utilization and limited power-output are the main challenges that need to be addressed. This study proposed an in situ method without additional energy to enhance the performance of SMFC by adding the package of iron and carbon granules (FeC). In the reactors including FeC-SMFC (the FeC package placed under the carbon felt anode and separated from the closed-circuit), FeC-OSMFC (FeC-SMFC in open-circuit), and FeCSMFC (the FeC package attached to the anodic bottom and closed-circuit), the degradation of refractory organics especially humic acid-like substances was significantly promoted, due to the FeC micro-electrolysis at neutral pH. More organics were beneficial for the enrichment of typical exoelectrogens belonging to Proteobacteria and Firmicutes, thereby improving the electrical performance of FeC-SMFC and FeCSMFC, compared with normal SMFC without FeC package (NSMFC). In FeCSMFC, the soluble and total chemical oxygen demand removal efficiencies were 65.60% and 52.64%. The removal efficiency of volatile suspended solids in FeCSMFC was 69.26%, which was 30.05%, 14.97%, 9.87% and 6.62% higher than that in open-circuit SMFC, NSMFC, FeC-OSMFC and FeC-SMFC, respectively. The power output of FeCSMFC was 37.28 W m⁻³, 6.06 and 1.76 times higher than that of NSMFC and FeC-SMFC, respectively. The addition of FeC package to anode is a cost-saving and effective method to enhance electricity generation and sludge decrement of SMFC.