Piggery wastewater (PW) containing high concentrations of COD, nitrogen and phosphorus can pose severe environmental impacts and ecology crisis. In Taiwan, the daily discharge of PW was over 110,000 m<sup>3</sup>. To solve this issue, anaerobic digestion (AD) is one of conventional approaches for converting organic portions in wastewater to green biogas or biochemicals. A few studies have demonstrated that not only the renewable energy (e.g., methane and hydrogen) can be generated but also the organic waste can be degraded. In fact, various types of organic wastes (e.g., rice husk (RH)) can be introduced in the AD process to enhance the performance, known as co-digestion. However, several process hurdles, such as a long residence time and the acidification of digestate, still inhibit the performance of biogas production and the stability of AD processes. In this study, an innovative AD system with an external electric field (i.e., electrically-assisted anaerobic co-digestion, EAAD) was developed for enhancing the biogas production. A nominal current was introduced in the EAAD process to stimulate the activity of microorganisms, which can significantly improve the productivity of bioproducts. In this study, the performance of EAAD was evaluated using a real PW produced in Chiayi, Taiwan. The results indicated that the electroactive bacteria can be rapidly stimulated with the electric field, thereby improving the rate of biogas production. For the effect of co-digestion, the results showed that the biomethane production per volatile solid was significantly increased with RS. In addition, the kinetic models were established for EAAD to describe the behavior of microorganisms under different stages. The key biological design parameters were identified according the kinetic models. Moreover, the life cycle assessment (LCA) was conducted to balance the process energy consumption and the biogas production in different operating conditions. The results from both reaction kinetics and LCA demonstrated the advantages for biogas production and energy recovery using EAAD. It was thus concluded that the developed EAAD process exhibited a great potential on converting organic wastes to bioenergy, compared with the conventional AD. The future research directions include the elucidation of reaction pathways for microorganisms in EAAD, as well as the large-scale demonstration in the existing AD plant.

Performance evaluation of electrically-assisted anaerobic co-digestion for biogas production using Piggery Wastewater and Rice Husk

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