Cattle manure biochar as an additive to improve methane production from cheese whey in rural areas

Cheese production in the Puno region generates cheese whey (CW) as an organic waste while requiring substantial energy inputs, making anaerobic digestion (AD) a promising solution. Unlike previous studies focused on single-substrate systems, this study evaluated AD integration using CW from five cheese factories, with and without manure-derived biochar (BM-BC). CW mono-digestion showed rapid acid accumulation and methanogenesis inhibition (13.57–50.48 mL CH₄ g−1 VS). In contrast, BM-BC addition significantly increased methane yields to 270.94–352.08 mL CH₄ g−1 VS. BM-BC stabilized digestion through volatile fatty acid buffering, promoted microbial growth, and increased methane concentration to 63.4% v/v. Energy integration analysis showed that two factories could fully replace conventional fuels with biogas, while the others achieved approximately 80% substitution. Economic assessments indicated annual savings of USD 1885.0–6074.6 and payback periods of 1.6–5 years. Additionally, GHG emission offsets averaged 15.5 t CO₂-eq yr−1 across the evaluated factories. These findings demonstrate the technical, economic, and environmental viability of BM-BC-enhanced AD in the regional cheese industry, supporting renewable energy development and sustainability goals.