Co–digestion of coffee residues and sugarcane vinasse for biohythane generation

Three abundant coffee residues (green coffee powder, parchment and defatted cake) and sugarcane vinasse were co-digested under thermophilic anaerobic conditions. A pilot plant was set-up and operated under optimized conditions using mesophilic sludge seed to produce biohydrogen. The initial conditions were acidogenic regimes (pH 5.0–6.5) followed by methanogenic conditions (pH 6.5–8.0). Results indicated the concomitant generation of biohydrogen and biomethane (termed biohythane) from the coffee residues. The green coffee powder bioreactor produced a hydrogen-rich biohythane for the first 15 days with a maximum yield on day four (31.45% hydrogen). Results also suggested that start-up of the biosystem reached the methanogenic stage in only 20–25 days and produced methane yields as high as 0.14mlCH4/gVSadded. For the co-digestion of defatted cake and vinasse, the only gas of interest produced was biohydrogen 32% vol./vol. between the 9th and 32nd day. Anaerobic co-digestion of parchment and vinasse produced biohythane at an average yield of 0.21mlCH4/gVSadded.