The interplay of active energy harvesting and wastewater organic loading regulates fermentation products and microbiomes in microbial fuel cells

Fruit juice wastewater (FJW) contains high strength and acidic organics that are difficult to remove. We developed microbial fuel cells (MFCs) to treat FJW and employed new energy harvesting methods to investigate how different operation conditions influence system performance and microbial community assembly. Specifically, we found both energy harvesting regime and organic loading affected current production, organic matter decomposition, product distribution, and microbial community. The power output under maximum power harvesting (MFC-MPP) condition showed the most stable output of 300 mW/m2 under different organic loadings. The MFC reactors maintained good organic removal (82.10-94.65%) at low loading of 1500-3000 mg/L, but the removal decreased with high loadings (7500-15,000 mg/L), presumably due to insufficient retention time, acid accumulation, and reduced degradability. Accordingly, higher VFA concentrations were observed in high loading reactors with the dominant products, formic acid and acetic acid. Electrofermentation coefficients (0.02-23.85%) of MFCs suggested that microaerobic electrofermentation (MEF) occurred in all reactors. MFCs under active harvesting demonstrated lower community diversity of anode biofilms at high organic loadings. The majority of dominant populations in the anode biofilm was affiliated with Lactococcus, Veillonella, and Bacteroides. This work demonstrates active energy harvesting and organic loading had interplay effects on system performance and microbiome, and system operation should consider such impacts to improve performance. AEH also provides a new alternative to a poised potential strategy for electrofermentation controlling.