Co-digestion of Sludge with Food Waste to Recover Valuable Products: Exploring Inoculum Substrate Ratios and pH Influences

This study investigates the feasibility of lactic acid production from potato and rice-derived food waste, aiming to optimize conditions for enhanced bioprocessing. The experimental setup involves batch fermentation in a 10 L continuous stirred-tank reactor, examining the impact of different Inoculum-to-Substrate Ratios (ISRs) and pH conditions on lactic acid production. Experimental results reveal that potato fermentation at ISR 1:8 achieves rapid organic matter conversion within 48 h, while rice fermentation performs optimally at ISR 1:4, reaching maximum Soluble Chemical Oxygen Demand (sCOD) after 72 h. Lactic acid production is influenced by both ISRs and pH, with ISR 1:6 exhibiting the highest L-lactic acid concentration (87.7 g/L) in potato-based fermentation after 48 h and (74.04 g/L) at 72 h for rice. Moreover, maintaining pH 6 proves to be optimal for lactic acid accumulation in both potato and rice-based substrates, emphasizing the critical role of pH control in enhancing lactic acid fermentation efficiency.