Impact of cathode potentials on methane production from high-concentration potato starch wastewater in electro-fermentation systems
The good biodegradability of potato starch wastewater makes it very suitable for methane production through anaerobic digestion(AD).However,its high chemical oxygen demand(COD)can easily cause"acid shock"to traditional AD,thereby inhibiting methane production and reducing the stability of the system.The electro-fermentation(EF)system can effectively alleviate the"acid shock"of traditional AD,but it has not been reported for the treatment of high-concentration potato starch wastewater,and the impact of the cathode potential on the system's performance still needs to be investigated.Herein,we used a dual-chamber tubular electrochemical cell as the EF system to study the impact of the cathodic potentials(-1.0V,-1.2V,-1.4V vs.Ag/AgCl)on methane production from high-concentration potato starch wastewater(SCOD,6400mg/L).The mechanisms of how the EF system alleviates the"acid shock"and enhances methane production were also elucidated.The results demonstrated that the cathode enhanced the methane production by in situ supplying of hydrogen to upgrade the CO2 in the biogas into methane.Decreasing the cathode potential from-1.0V to-1.2V,the applied current(i.e.hydrogen)increased from-0.05mA to-0.15mA.Consequently,the methane production increased from 1.03mL/mg SCOD to 1.31mUmg SCOD,and the methane purity increased from 88％to 95％.Further decreasing the cathode potential to-1.4V,the hydrogen produced was higher than the hydrogen needed for the CO2 methanogenesis,and the high hydrogen pressure inhibited the conversion of propionate and butyrate to acetate.Hence,methane production at-1.4V was not improved but inhibited.Therefore,-1.2V was the optimized potential for the EF system.These results demonstrated that the EF system could be used for methane production from high-concentration potato starch wastewater.The EF enhanced the methane production by in situ hydrogen supply and biogas upgrading.The amount of hydrogen supplied was the key to the success of the EF system.
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