Enhanced copper removal and bioelectricity generation in sediment microbial fuel cells through biostimulation and bioaugmentation

Abstract

Unlike conventional sediment microbial fuel cell (SMFC), a single medium SMFC is a cathode embedded in an anoxic sediment environment to avoid electron competition from oxygen and to increase the chance of copper ions being removed by reduction as electron acceptors. The high concentration of copper ions in the sediment limits microbial activity, and therefore an effective method to be proposed to overcome this problem. The carboxymethyl cellulose (CMC) immobilized beads containing copper-tolerant bacteria have multiple functions, including adsorption of copper ions, protection of copper-tolerant bacteria from inhibition by high concentrations of copper ions, and promotion of copper-tolerant bacteria activity as a co-substrate. The results show that copper-tolerant Ochrobactrum oryzae had improved organic removal (85%) at high concentrations of copper ions, which was 1.48–1.65 times and 5 times more effective than those containing other strains and mixed bacteria. Immobilization of Ochrobactrum oryzae with CMC reduced the inhibition of Ochrobactrum oryzae by copper in the sediment and ensured the stable generation of electricity by the SMFC. When cell-immobilized beads were added to the anode zone of SMFC, the maximum output voltage (173.9 mV) and copper ion removal efficiency (74%) were 2.89 and 1.15 times higher than the output voltage and removal efficiency achieved without bead addition, respectively. The dominant bacteria in the anode zone on day 70 were electrochemically active species capable of degrading organic compounds. SMFC combining biosorption, biostimulation, and bioaugmentation technologies was developed in this study for the remediation of sediment containing high concentrations of copper ion.