Mixed sulfate-reducing bacteria-enriched microbial fuel cells for the treatment of wastewater containing copper

Microbial fuel cells (MFCs) have been widely investigated for organic-based waste/substrate conversion to electricity. However, toxic compounds such as heavy metals are ubiquitous in organic waste and wastewater. In this work, a sulfate reducing bacteria (SRB)-enriched anode is used to study the impact of Cu²⁺ on MFC performance. This study demonstrates that MFC performance is slightly enhanced at concentrations of up to 20 mg/L of Cu²⁺, owing to the stimulating effect of metals on biological reactions. Cu²⁺ removal involves the precipitation of metalloids out of the solution, as metal sulfide, after they react with the sulfide produced by SRB. Simultaneous power generation of 224.1 mW/m² at lactate COD/SO₄²⁻ mass ratio of 2.0 and Cu²⁺ of 20 mg/L, and high Cu²⁺ removal efficiency, at >98%, are demonstrated in the anodic chamber of a dual-chamber MFC. Consistent MFC performance at 20 mg/L of Cu²⁺ for ten successive cycles shows the excellent reproducibility of this system. In addition, total organic content and sulfate removal efficiencies greater than 85% and 70%, respectively, are achieved up to 20 mg/L of Cu²⁺ in 48 h batches. However, higher metal concentration and very low pH at <4.0 inhibit the SRB MFC system. Microbial community analysis reveals that Desulfovibrio is the most abundant SRB in anode biofilm at the genus level, at 38.1%. The experimental results demonstrate that biological treatment of low-concentration metal-containing wastewater with SRB in MFCs can be an attractive technique for the bioremediation of this type of medium with simultaneous energy generation.