Maximizing biogas production from expired dairy products: A two-stage anaerobic digestion approach

This study investigated expired dairy product (EDP) removals in a two-stage system in anaerobic batch reactors co-digested with synthetic domestic wastewater (SDW) to evaluate H2 and CH4 production. Acidogenesis was performed in anaerobic batch reactors with 10%, 15%, and 20% EDP (v/v) mixed with SDW, and the effluents were the substrate for methanogenic reactors. During acidogenesis, reactors with 10%, 15%, and 20% EDP achieved 86.8%, 90.1%, and 92.3% carbohydrate removal, producing 1.5, 1.9, and 1.7 mol H₂ per mol carbohydrate removed, respectively. Paraclostridium was the dominant genus (55.7–82.7%) involved in hydrogen, volatile fatty acid (VFA) and alcohol generation. Methanogenesis assays with 10% and 15% EDP achieved high methane yields (323.0 and 225.1 mL CH₄ gVSadd⁻1) and COD removals (91.8% and 94.7%), while 20% EDPs led to inhibition due to VFA accumulation. Methanosaeta was prevalent in high-yield reactors, correlating with effective COD removal. This study highlights the potential for EDP recovery through biogas production.