Thermophilic co-digestion feasibility of distillers grains and swine manure: effect of C/N ratio and organic loading rate during high solid anaerobic digestion (HSAD)

Abstract

Anaerobic co-digestion of high solids containing distillers grains and swine manure (total solids, 27±2% and 18±2%, respectively) was evaluated in this study to assess the effect of C/N ratio and organic loading rate (OLR). Feed mixture was balanced to achieve a C/N ratio of 30/1 by mixing distillers grains and swine manure. Pilot-scale co-digestion of distillers grains and swine manure was carried out under thermophilic conditions in the continuous mode for seven different OLRs from R1 to R7 (3.5, 5, 6, 8, 10, 12 and 14 kg VS/m³ day) under high solid anaerobic digestion. The methane yield and volatile solid (VS) removal were consistent; ranging from 0.33 to 0.34 m³CH₄/kg VS day and 50–53%, respectively, until OLR 8 kg VS/m³ day. After which methane yield and VS removal significantly decreased to 0.26 m³ CH₄/kg VS day and 42%, respectively, when OLR was increased to 14 kg VS/m³ day. However, during operation, at OLR of 10 kg VS/m³ day, the methane yield and VS removal increased after the 19th day to 0.33 m³CH₄/kg VS day and 46%, respectively, indicating that a longer acclimatization period is required by methanogens at a higher loading rate.

Keywords:

• high solid anaerobic digestion
• distillers grains
• swine manure
• thermophilic co-digestion
• C/N ratio
• OLR
• VS removal
• methane yield