Performance Assessment and Operational Evaluation of a Ternary Anaerobic Co-Digestion System

One of the most challenging yet promising technologies combining waste management with waste utilization for the production of a renewable fuel (biogas) is anaerobic co-digestion. This study investigated the anaerobic co-digestion of three organic waste streams: cheese whey wastewater (CWWW), pig slurry (PS), and food waste leachate (FWL). FWL and CWWW were combined to form a base mixture of constant composition (BM), which was subsequently blended with diluted PS at three BM/PS mass ratios: 25/75, 50/50, and 75/25 (% v/v). The mixtures were evaluated under mesophilic conditions through laboratory-scale batch experiments to assess the influence of substrate composition on biomethane production and organic matter removal. Physicochemical characterization of the individual substrates and mixtures included pH, volatile fatty acids, alkalinity, chemical oxygen demand (COD), and volatile solids (VS). Biochemical methane potential (BMP) assays were conducted, with daily and cumulative methane production systematically monitored throughout the experimental period. Methane production kinetics were evaluated by fitting the modified Gompertz model to the experimental data, enabling estimation of maximum methane production potential, maximum production rate, and lag-phase duration. Experimental results demonstrated that the 75/25 BM/PS mixture achieved the highest specific biomethane yield (525.9 CH4 Nml/g VSadded) and maximum production rate (μm = 36.3 CH4 Nml/g VSadded/d), alongside the highest removal efficiencies for COD (83.0%), TOC (87.9%), and VS (63.7%), compared with the 50/50 (309.9 CH4 Nml/g VSadded) and 25/75 (156.5 CH4 Nml/g VSadded) mixtures. The integrated assessment of methane yield, kinetic parameters, and organic matter removal enables comparative evaluation of the three mixtures and identifies the 75/25 BM/PS formulation as the most favorable mixing ratio for efficient co-digestion of these waste streams.