Hydrogen, alcohols and volatile fatty acids from the co-digestion of coffee waste (coffee pulp, husk, and manufacturing wastewater) by applying autochthonous microorganisms. Coffee waste

Hydrogen production from coffee waste (pulp, husk, and manufacturing wastewater) is an attractive topic due to the potential for energy reuse in the sector (drying and roasting grains). However, the lack of information on co-digestion of coffee waste with autochthonous microorganisms (bacteria and fungus) limits its application. The objective of this study was to screen the factors that affect H2 production with coffee waste pretreated in a hydrothermal reactor and autochthonous microbial consortium, and the potential synthesis of intermediated products with commercial value. The effects of pH factors (4.0, 5.5 and 7.0), temperature (30-50 °C), agitation velocity (0-180 rpm), headspace (50-70%), bioaugmentation (0-20%), coffee pulp and husk (2-6 g/L), coffee manufacturing wastewater (7-30 gCOD/L) and yeast extract concentration (0-2 g/L) were evaluated using a Plackett-Burman design approach. The highest H2 production potential (82 ml H2) was obtained under the following conditions: 30 °C, 180 rpm, 50% headspace, without bioaugmentation, 2 g/L pulp and husk coffee, 30 gCOD/L coffee manufacturing wastewater and 2 g/L yeast extract. The main soluble metabolite products were acetic acid (1956 mg/L), lactic acid (7294 mg/L) and ethanol (1816 mg/L). Lactobacillus sp., Clostridium sp., Saccharomyces sp. and Kazachstania sp. were the primary autochthonous microorganisms identified in the batch reactors. By means of metagenome functional analysis the enzymes related to lignin, phenol, cellulose, lignocellulose, and pectin degradation were identified, as well as acidogenesis, acetogenesis, and hydrogen production.