Recycling of coffee by-products by composting in context of climate-relevant emissions and products

Abstract

Coffee has become one of the most popular beverages and provides a livelihood for millions of people around the world. Coffee is one of Costa Rica's most important and emblematic exports (about one and a half million bags per year) and is closely linked to the country's national identity. However, climate change poses a challenge to the livelihoods of Costa Rican coffee farmers and the long-term viability of the crop. Thus, the environmental impact of coffee production must also be reduced and made more sustainable. Therefore, it is necessary to treat the residues from coffee production as climate-neutral and resource-saving as possible in the sense of a circular economy. This is of particular importance, not least because the consumption of coffee has increased worldwide. Agriculture and waste management are disconnected from each other worldwide. This leads to permanent nutrient depletion of soils and high greenhouse gas (GHG) emissions due to insufficient or excessive use of fertilizers. Coffee by-products, especially coffee pulp, are usually considered waste on coffee plantations and are mostly discarded or disposed of in rivers. In some cases, composting of residues also takes place, which usually results in high emissions due to improper rotting processes. In the context of global warming, inadequate composting and mineral fertilization contribute to greenhouse gas emissions. Composting emits greenhouse gases such as methane from the decomposition of organic material and carbon dioxide from fossil fuels from the equipment required to turn and process the waste. Fertilization of coffee plants, on the other hand, emits greenhouse gases such as nitrous oxide from the soil, especially when nitrogen fertilizers are used. This leads to serious consequences for the climate and the environment. The purpose of the present thesis was to investigate which methane emissions occur with the current treatment method of the residues and how an optimized composting process can significantly reduce these emissions and at the same time produce an organic fertilizer. In addition, nitrous oxide emissions from the use of composts compared to mineral fertilizers on coffee plantations should be investigated. This should contribute to making coffee production more sustainable.