Ecotoxicological Assessment of Coffee Waste As Component of Organic Fertilizers

About 6 million tons of coffee waste are generated annually in the world, which is largely left unrecycled, accumulate, and have a negative impact on the environment due to the caffeine, tannin, polyphenols, and other toxic substances in it. The use of coffee waste as organic fertilizer is limited by the presence of these toxic compounds. A possible way to mitigate the negative impact of coffee waste on soil biota could be by composting, including vermicomposting. In this study, ecotoxicological assessment of coffee waste was carried out before and after vermicomposting using earthworms Eisenia andrei. Fresh waste showed high toxicity: spent coffee grounds were classified as hazard class II and coffee chaff as hazard class III. After vermicomposting, toxicity decreased: samples with 25−50% waste content became low hazardous (class IV), and those with 100%, moderately hazardous (class III). The study confirmed that vermicomposting is an effective method of coffee waste detoxification to obtain safe organic fertilizers. For practical application, dosages of no more than 50% of waste in compost are recommended.