The Performance Of Bioelectrochemical Systems Using Food Wastes As Substrate With Energy Recovery

Large volume of food wastes (FWs) are produced all over the world every year.Meanwhile, FWs are valuable resources due to the high Carbon/Nitrogen ratio,biodegradability and inexhaustibility. Considering the remarkable proportion ofbioenergy embedded in FWs, it is economic beneficial to develop method toachieve these environmental friendly energy recovery from FWs. Recently, asone kind of newly emerging renewable and environment-friendly technology,bio-electrochemical system (BES) has drawn increasingly attention in theacademic world. Microbial fuel cells (MFCs) and microbial electrolysis cells(MECs) are two classical technologies of BES. This study has discussed thefeasibility of using FWs as the substrate of BES to obtain simultaneous pollutantremoval and bioenergy recovery. The performance of MFCs fed with FWs interm of electricity generation was investigated. To enhance current generation inMFCs fed with FWs, alkaline pretreated sludge (AS) was added to FWs and themixture of FWs and AS was utilized as the substrate of MFCs. The improvementof electricity generation of MFCs fed with the mixture of FWs and AS wasdiscussed. On the other hand, MECs were studied as an alternate and a novel wayto dispose food wastes (FWs) and realize bio-hydrogen production at the sametime.The feasibility of using FWs as the substrate of MFCs was proven in our study.To obtain optimal electricity generation and pollutant removal, three differentorganic loading rates were compared, which was DF-10(COD=4900±350mg/L),DF-15(COD=3200±400mg/L) and DF-25(COD=2000±100mg/L). Themaximum power density of~18W/m3(~556mW/m2) was obtained at DF-15andthe maximum removal of COD was~86.4%. Total carbohydrate (TC), solubleprotein and total nitrogen (TN) removals were~86.4%,~95.9%,~67.1%and~16.1%respectively at DF-15. Microbial community analysis using454pyrosequencing of16S rRNA gene demonstrated the combination of thedominant genera of the exoelectrogenic Geobacter and fermentative Bacteroideseffectively drove highly efficient and reliable MFC systems with functions oforganic matters degradation and electricity generation.To enhance current generation in MFCs fed with FWs, the improvement of theperformance of MFCs by the addition of AS to FWs was studied. Four differentmix ratios of FWs and AS on COD basis were discussed, which were10/0，8/2，7/3and5/5respectively. At the mix ratio of FWs/AS=7/3, maximum powerdensity of~30W/m3was obtained, which was43%higher than that of MFCs fed with sole FWs. The TCOD removal efficiencies at mix ratio of FWs/AS=7/3was76.3±1.2%.Significant hydrogen production was achieved by using FWs as the substrateof MECs. Different applied voltages, which were0,0.6V,0.9V and1.1V,obviously affected the performance of MECs. The optimal applied voltage ofMECs fed with FWs was0.9, with the hydrogen yield of35.7±1.9mgH2/g-CODand average hydrogen production rate of0.36±0.09m3H2/m3-Reactor/d. Thecoulombic efficiency was82.6±5.3%and the hydrogen recovery efficiency ofthe cathode was53.2±6.1%. Meanwhile, the organic components of FWs wereeffectivley removed. The TCOD, total carbonhydrate (TC) and soluble proteinremoval efficiencies were80.4±4.8%,95.4±0.7%and86.4±3.9%. Comparedto significant propionic acid accumulation in the open circuit control, no obviouspropionic acid accumulation was observed in MECs with extra voltages applied.BES has been proven to be an renewable and environment-friendly technologyto realize FWs disposal and clean energy recovery simultaneously, which hasvast potential for future development.