Anaerobic digestion of coffee pulp. A pilot-scale study in Mexico

he coffee processing industry produces large amounts of coffee pulp which are not used and pose a problem for the environment. Anaerobic digestion of this organic waste was tested in a pilot-scale unit set up in Mexico. The composition and low pH of coffee pulp usually result in excess acid production during anaerobic digestion using completely mixed reactors. The TRANSPAILLE plug flow digester solved this problem of acidification for medium volatile solids (VS) loading rates of below 3.6 kg VS.m-3.day-1. The methane yield reached 0.315 m3.kg VS eliminated-1 with 44% VS reduction (w/w). After 50 days in a maturating pit, the final compost mass represented only 24% of the initial mass of coffee pulp. Energy-saving calculations show that biogas from coffee pulp can contribute 25-30% of the heat needed to dry coffee beans. The end compost can be used as an organic fertilizer for coffee plantations. (Résumé d'auteur