Influence of Stepwise Increased Organic Loading on Anaerobic Mono-digestion of Dead Fish in Sequencing Batch Reactor Process

Highly nutrient content dead fish (DF) waste can be considered a potentially valuable substrate for the anaerobic digestion (AD) to produce biogas. The effects of stepwise increased organic loading rate (OLR) on the process performance were investigated during mono-digestion of DF waste in anaerobic sequencing batch reactor mode. Two different sets of experiments have been conducted using whole dead fish (R DF ) and boneless dead fish (R BDF ) and OLR increased in five steps (1.95, 2.39, 2.73, 3.19, and 3.64 g VS/L/days) during the operational period. With the increasing of OLR, the biogas production rate increased by 79.07% and 58.20% at the end of the operation of R DF and R BDF , respectively. Higher alkalinity values throughout the experiment maintained stable pH values in between 7.87 to 8.01 for both R DF and R BDF . Total volatile fatty acids kept accumulating with the increasing OLR and the final concentrations were 7.69 ± 0.16 and 8.33 ± 0.19 g/L in R DF and R BDF, respectively. Overall, decreasing COD and VS removal efficiencies resulted in decreasing methane yields. The energy recovery rate was maintained at > 60% with the maximum OLR of 3.64 g VS/L/d of DF waste demonstrating its feasibility in the AD process as the only carbon source. Graphical Abstract