Glucose-driven uncoupling of methanogenesis from acidogenesis to generate carboxylates in anaerobic digestion: Insights into microbial dynamics and operational parameters

Anaerobic digestion is a process for resource recovery used to produce biogas. However, research focus has shifted toward producing valuable carboxylates due to low natural gas costs. This study uncoupled methanogenesis from acidogenesis by adding glucose as an external carbon source to maintain low pH and enable stable carboxylate production in bioreactors inoculated with beef cattle waste. The central pattern observed involves glucose utilization converted predominantly to lactate or acetate inhibiting methanogenesis. Shorter retention times (5 vs. 20 days) increased total acid production (53.5 vs. 49.7 g/L), especially lactate and butyrate, while recirculation changed acid profiles toward acetate (about 30–60 % increases). Adjustment of pH from acidic (pH 4.0) to neutral (pH 6.5) enhanced total acid accumulation (up to 58.0 g/L) with acetate as a dominant product, whereas lactate production significantly decreased by about 80 %. Chemical oxygen demand analysis also showed improved carbon conversion with recirculation and pH adjustment, which highlights their role in enhancing carboxylate yields. Microbial community analysis revealed Bacillota (49.4–63.8 %) – Bacilli (33.9–64.7 %) – Bacillus (4.3–35.8 %) as the predominant taxa. Lactic acid bacteria played an important role in early lactate production. Methanogens were detected early, indicating successful inhibition of methanogenesis in later phases. Network analysis further identified Clostridia and Dysgonomonas as major contributors to acetate production and linked Lactiplantibacillus to lactate accumulation. These findings highlight operational parameters in carboxylate profiles and microbial dynamics during anaerobic fermentation with glucose as an external carbon source. We suggest that this mechanism would also apply to any other soluble, rapidly fermented carbohydrate substrate source. • This study aims to uncouple methanogenesis and improve carboxylate yields instead. • Shorter retention time increased total acid production, favoring lactate and butyrate. • Recirculation shifted acid profiles towards increased acetate production by 30–60 %. • pH from acidic to neutral enhanced total acid accumulation with increased acetate and decreased lactate. • Network analysis identified Clostridia and Dysgonomonas as key acetate producers, linking Lactiplantibacillus to lactate.