Stabilization of Anaerobic Co-Digestion Process via Constant the Digestate Solids Content

• Main Authors: Risu Na, Keisuke Uchitani, Kazuto Yoshida, Naoto Shimizu
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Processes
• Subjects: anaerobic digestion; solid content; biogas; mass balance; specific methane yield
• Online Access: https://www.mdpi.com/2227-9717/9/2/197

The process instability of anaerobic digestion (AD) is a common issue and may result in underperformance or short-term process failure. Extensive research has shown that total solids (TS) content in AD has a significant impact on system stability and performance. However, no study has examined the feasibility of stabilizing the AD process by maintaining constant TS content in the digestate. In this study, an innovative control approach based on constant TS content in the digestate during AD was developed using a mass balance equation. Two levels of TS content (desired values of 4% wet basis (w.b.) and 6% w.b.) were compared with conventional control. The process stability was examined by monitoring digestate components and pH. Substrate-specific methane yield (m³ CH₄/kg VS) was used to assess the effectiveness of the controlled conditions. The results showed that the digestate TS content during AD can be controlled and that the digestion process can be stabilized by controlled conditions. In addition, constant TS in the digestate (within 1% w.b. of the desired level) gave increased levels of biogas production (10.2%), methane (13.5%), and substrate-specific methane yield (43.3%) at 4% TS, and respective increases of 16.6%, 21.2%, and 20.8% at 6% TS when compared with standard operation.