Electricity generation from cassava wastewater by a single chamber microbial fuel cell

Abstract

This study examined the effects of the organic loading rate (OLR), pH and the temperature in cassava wastewater treatment and the power generated by a single microbial fuel cell. The study was divided into two parts under temperature of 45 ℃ and 30 ℃. The first part was examined the effect of OLR of 0.56, 1.44, 2.79, 4.14 to 6.25 kg-COD/m³-d at pH 7.0 to remove COD and generate electricity. The second part was examined the effect of pH at 5.0, 5.5, 6.0, 6.5, 7.5, 8.0, 8.5 and 9.0 on OLR of 0.56 kg-COD/m³-d to remove COD and generate electricity. When controlled pH 7.0, the efficiency of COD removal was achieved at maximum from the OLR of 0.56 kg-COD/m³-d at both temperatures. The efficiency of COD removal was 91.44 ± 0.72% and 90.72± 0.87% at 30 ℃ and 45 ๐C respectively. The maximum of power density was obtained from OLR of 6.25 kg-COD/m³-d, which the value was 28.68 W/m3 at 30 ๐C and 27.85 W/m3 at 45 ℃. The maximum of coulombic efficiency was obtained from the OLR of 0.56 kg-COD/m³-d which was 30.2% at 30 ℃ and 28.5% at 45 ℃. The temperature affected on the electron transferring from anode to cathode. At the lower temperature, electron was able to transfer from anode to cathode more effectively than at higher temperature. High temperature caused high electrical resistant, so the power output decreased when temperature increased. At OLR of 0.56 kg-COD/m³-d, the maximum efficiency of COD removal was achieved at a pH of 7.5 at both temperatures. The efficiency of COD removal was as 96.77 ± 0.93% and 95.93± 1.44% at 30 ℃ and 45 ℃ respectively. The maximum of power density obtained from pH 8.5 which the values were 30.30 W/m³ at 30 ℃ and 26.06 W/m³ at 45 ℃. The maximum of coulombic efficiency was obtained from pH 8.5 which was 52.9% at 30 ℃ and 50.6% at 45 ℃. The microbial communities in the anode of a single chamber microbial fuel cell under 30 ℃ could be divided into four groups as Gammaproteobacteria, Betaprotobacteria, Bacteroidetes and Firmicutes. While under 45 ℃ operation, the microbial communities could be divided into three groups as Gammaproteobacteria, Betaprotobacteria and Firmicutes. The microbial communities included several fermentative bacteria, exocellular electron-transfer, methane oxidizers, sulfate-reducing bacteria and groups of facultative bacteria.