Waste management by making compost from industrial food by-products: coffee husk, and brewers’ grain

This study was conducted to develop the best composting system for the management of coffee husk from the coffee roasting industry, brewers’ grain from beer industry, and cow manure. Coffee and beer are among the most consumed beverages in the world. In 2014, the globally consumption of coffee was 149 million bags of coffee, and approximately 17.8 billion packages of coffee bought in common food stores. In 2016, the World beer production was about 195 million tons, with the production of considerable amounts of brewers’ spent grain (BSG). Coffee husk (a by-product of roasting) generated from coffee processing station and BSG are mostly disposed in landfills or into arable land, usually with no care of its fate. Results of raw materials analysis indicated that coffee husk has a C:N ratio of 14, brewers’ grain a C:N ratio of 13, and cow manure a C:N ratio of 14, hence with an adequate potential for compost production. Component analysis showed that coffee husk is rich in organic matter (cellulose, hemicelluloses, pectins, and lignins), chemical nutrients such as N and K, and secondary compounds such as caffeine, tannins, and polyphenols. BSG is a lignocellulosic material containing about 17% cellulose, 28% non-cellulosic polysaccharides, and 28% lignin. BSG is available in large quantities throughout the year, but its main application has been limited to animal feeding or energy production. An environmental friendly method is needed to re-use the food by-products that may give good agronomic replies. The treatment of coffee husk and BSG by oxygen-driven biological methods such as composting, would serve a dual purpose: fertilizer production and environmental protection. The topic of this study was producing efficient composts with lone coffee husk (Pile 1), coffee husk and BSG in proportion 2:1 (Pile 2), coffee husk and cow manure in proportion 4:1 (Pile 3), and a mixture of coffee husk, BSG, and cow manure in proportion 5:3:2 (Pile 4). Every pile was around 300 kg. All piles were covered with a plastic film in order to prevent excessive moisture loss and preserved in greenhouse. The composting method is aerated static pile composting, and the humidity of the materials is around 60%. Samples from each pile (about 500 g each) were collected separately every 10 days, and immediately stored at -20oC upon arrival at the laboratory for molecular analyses, and at 4oC for all the other analyses. The chemical parameters checked during 90 days composting were C, N, and biomass C content, total hydrolase activity (FDA test), and the content of several organic acids and alkaloids.