Use of coffee mucilage as a new substrate for hydrogen production in anaerobic co-digestion with swine manure

• Biohydrogen production using coffee mucilage and swine manure was achieved.
• C/N ratio around 50 could support the increase in organic load keeping stability.
• Repetitive batch cultivation is useful to detect changes in the pathway.
• Butyric and acetic pathways are the main routes in biohydrogen production.

Coffee mucilage (CM), a novel substrate produced as waste from agricultural activity in Colombia, the largest fourth coffee producer in the world, was used for hydrogen production. The study evaluated three ratios (C1–3) for co-digestion of CM and swine manure (SM), and an increase in organic load to improve hydrogen production (C4). The hydrogen production was improved by a C/N ratio of 53.4 used in C2 and C4. The average hydrogen production rate in C4 was 7.6 NL H2/LCMd, which indicates a high hydrogen potential compare to substrates such as POME and wheat starch. In this condition, the biogas composition was 0.1%, 50.6% and 39.0% of methane, carbon dioxide and hydrogen, respectively. The butyric and acetic fermentation pathways were the main routes identified during hydrogen production which kept a Bu/Ac ratio at around 1.0. A direct relationship between coffee mucilage, biogas and cumulative hydrogen volume was established.