This study investigated the efficacy of bioaugmentation in enhancing biomethane yield from the anaerobic co-digestion of carbohydrate- and lipid-protein-rich wastes with sewage sludge. Four microbial treatments were evaluated: two novel strains isolated from anaerobic sludge (Bacillus sp. MH1 and Serratia sp. MH2) and two reference strains (Lactobacillus casei and Saccharomyces cerevisiae). These were tested individually and as two defined consortia (L. casei-MH1 and S. cerevisiae-MH2) in batch reactors under mesophilic conditions (35 °C) over 150 days. The MH1 treatment, both as a pure culture and in a consortium, demonstrated superior performance. Its success is mechanistically linked to proficient enzymatic hydrolysis of proteins via serine proteases, leading to a diverse profile of fermentation intermediates and the establishment of lactate-driven syntrophic partnerships. Conversely, the MH2 treatment significantly enhanced methane yields by facilitating the breakdown of recalcitrant lignocellulosic compounds, generating key precursors like acetate and propionate, and promoting alcohol-based syntrophy. The inclusion of reference strains, however, was correlated with a reduced hydrolysis rate. Kinetic analyses revealed that bioaugmentation with the isolated strains altered the fermentation dynamics, shifting the cumulative biogas production from a sigmoidal to a stepped profile. This was characterized by two distinct lag and logarithmic phases, indicating a more complex microbial succession that challenges conventional kinetic modeling. The MH1 treatment achieved the highest cumulative biomethane volume (12,244 mL), specific yield (0.608 m3/kg-VSdegraded), and volatile solids reduction (68%). Kinetic parameters confirmed its superiority, exhibiting the maximum hydrolysis rate constant (k = 0.022 d-1) and daily biogas production rate (Rm = 6.6 m3/kg-VSdegraded.d).

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