Towards Sustainable Energy from Food Industry Sludges: Biogas Potential Assessment and Calcium-Based Additive Strategies

This study evaluated the biogas potential of industrial sludges from three food processing factories—chicken, dairy, and pig slaughterhouse—using Biochemical Methane Potential (BMP) tests. The effects of calcium-based additives (Ca(OH)? and CaCOs) and commercial microbial consortia (B1, B2, B3) on anaerobic digestion performance were investigated. Sludge samples from grease traps were tested in 10-L batch reactors at a 1:1 (v/v) substrate-to-inoculum ratio under mesophilic conditions for 35 days. Calcium-based additives significantly enhanced biogas production, although optimal dosages varied by sludge type. The highest improvements were observed at 0.5% (w/v) Ca for chicken sludge (+45.6%), 0.7% for dairy sludge (+14.3%), and 0.3% for pig sludge (+26.3%) compared to controls. Higher calcium concentrations led to inhibition across all substrates. In contrast, commercial microbial additives showed consistently poor performance, producing low biogas yields, suggesting limited effectiveness in complex industrial sludge matrices. Kinetic models (first-order, modified Gompertz, and modified logistic) accurately described biogas production in successful treatments but failed under inhibited conditions. Overall, the findings emphasise the need for sludge-specific optimisation of calcium dosing and caution against the indiscriminate use of commercial microbial products in industrial anaerobic digestion systems.