Abstract:Over ten million tonnes of solid residues are generated yearly from coffee agro-industry worldwide, along with larger amounts of wastewaters and cultivation residues. Both wastewaters and solid residues, such as defective coffee beans and spent coffee grounds, along with coffee husks (pulp and mucilage) that constitute around 60% of the wet weight of the fresh fruit, represent a relevant source of pollution and environmental threat, particularly from the widely adopted wet processing of coffee berries. Several attempts have been done to re-use the coffee processing solid residues, which include direct use as fuel in farms, animal feed, fermentation studies, adsorption studies, biodiesel production, briquetting, pelletizing, tannin extraction and production of specialty commodities. For the re-use of wastewaters, biogas production and direct delivery on plantations have been proposed or adopted, along with the treatment through infiltration, irrigation or (anaerobic) lagooning, reed bed and aerobic lagooning. In this study, the possible alternatives for the re-use and valorisation of the coffee processing and plantation are critically reviewed, taking into account the experiences with other agro-industrial residues and wastewaters, in the frame of a sustainable agro-industrial development.

There are two problematic solid residues from agriculture and agro-industry, produced in vast amounts in rural areas: those from coffee bean production and processing and those deriving from the extraction process of olive oil. Notwithstanding these residues originating in different geographical areas, they have striking similarities. They both derive from traditional, conventional and organic agriculture; they have a high content in lignins, celluloses and (poly)phenols; they are produced in million tonnes annually; they pose relevant environmental problems for disposal; they contain bioactive compounds; and the approach for their re-use is often similar, sometimes overlapping. The most promising re-uses in rural areas are for agriculture, as animal feed and for energy production. There are also minor uses, suitable for the production of added-value commodities. The re-use will be dependent on a variety of factors according to the diversity of (a) pedoclimatic areas that include altitude and latitude, soil texture and organic matter content, water regime and availability, (b) level of expertise of the small farmers, (c) social environment that includes training opportunities and availability to create associative forms among producers, (d) access to trade and communication networks and (e) easy access to community-level processing installations. The perspectives of agronomic management and valorization are compatible with the objectives of a regenerative, sustainable agriculture.