Waste valorization through anaerobic co-digestion in coffee and swine farms: CH₄ yield optimization and farm-scale viability

Considering that the Brazilian southeast has several agricultural farms that produce coffee and raise swine, and that the waste generated in these farms has some complementary characteristics, the present study aimed to optimize the methane (CH₄) yield in the batch anaerobic co-digestion of liquid swine manure (LSM), coffee wastewater (CFW), and coffee husk and pulp. The optimization occurred through a two-factor central composite rotational design with a variation of CFW percentage (8 to 22 %) in the mixing liquid substrates and the organic matter concentration (0.3 to 12 gCOD L^-1). The optimized condition had an ideal nutritional condition (14 % of CFW, 86 % of LSM, 7.3 gCOD L^-1 and COD/N ratio of 35) to obtain high CH₄ production (971.7 mLCH₄), yield (160.9 mLCH₄ g^-1VS), maximum specific production rate (1.6 mL h^-1) and low lag phase (217.6 h).