Abstract:

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 1.31mL/mg 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.

Key words: potato starch wastewater, anaerobic digestion, microbial electrochemical system, methane, carbon dioxide, in-situ purification, cathode electro-fermentation

摘要：

马铃薯淀粉废水的良好可生化性使其非常适合通过厌氧消化来产甲烷，但是其高的化学需氧量（chemical oxygen demand，COD）容易使传统厌氧消化系统“酸败”，从而造成产甲烷性能降低和系统稳定性差的问题。电发酵产甲烷系统可有效解决传统厌氧消化的“酸败”问题，但针对高浓度马铃薯淀粉废水的研究还未见报道，且外加电位对系统的性能影响还有待探索。本文采用双室套筒微生物电化学反应器作为电发酵系统处理溶解性COD（SCOD）为6400mg/L的高浓度马铃薯淀粉废水，考察了不同阴极电位（-1.0V、-1.2V、-1.4V vs. Ag/AgCl）对电发酵体系产甲烷性能的影响，并揭示了阴极电发酵抑制系统酸败和提高产甲烷速率的机制。实验结果表明，电发酵系统通过阴极原位供氢将厌氧消化产生的CO₂转化为甲烷，从而提高了甲烷的产量和纯度。将阴极电位从-1.0V降低到-1.2V时，施加的电流从-0.05mA增加到-0.15mA，甲烷产量从1.03mL/mg SCOD增加到1.31mL/mg SCOD，甲烷含量从88%增加到95%。进一步降低阴极电位至-1.4V时，产生的氢气超过了反应体系内将CO₂转化为甲烷所需的氢气，高氢气分压抑制了丙酸盐和丁酸盐向乙酸盐的转化，故系统的甲烷产量没有改善反而受到了抑制。因此，-1.2V是该电发酵体系的最佳电位。这些结果表明，电发酵体系可以用于从高浓度马铃薯淀粉废水中直接进行厌氧消化产甲烷，电发酵通过原位供氢和嗜氢产甲烷途径来增强系统甲烷产量，而氢气的供应速率是电发酵成功的关键。

关键词: 马铃薯淀粉废水, 厌氧消化, 微生物电化学, 甲烷, 二氧化碳, 原位提纯, 阴极电发酵