Conversion of spent coffee grounds into vermicompost

The Potential of Spent Coffee Grounds in Functional Food Development

Coffee is a popular and widely consumed beverage worldwide, with epidemiological studies showing reduced risk of cardiovascular disease, cancers and non-alcoholic fatty liver disease. However, few studies have investigated the health effects of the post-brewing coffee product, spent coffee grounds (SCG), from either hot- or cold-brew coffee. SCG from hot-brew coffee improved metabolic parameters in rats with diet-induced metabolic syndrome and improved gut microbiome in these rats and in humans; further, SCG reduced energy consumption in humans. SCG contains similar bioactive compounds as the beverage including caffeine, chlorogenic acids, trigonelline, polyphenols and melanoidins, with established health benefits and safety for human consumption. Further, SCG utilisation could reduce the estimated 6-8 million tonnes of waste each year worldwide from production of coffee as a beverage. In this article, we explore SCG as a major by-product of coffee production and consumption, together with the potential economic impacts of health and non-health applications of SCG. The known bioactive compounds present in hot- and cold-brew coffee and SCG show potential effects in cardiovascular disease, cancer, liver disease and metabolic disorders. Based on these potential health benefits of SCG, it is expected that foods including SCG may moderate chronic human disease while reducing the environmental impact of waste otherwise dumped in landfill.

Towards the sustainable and circular bioeconomy: Insights on spent coffee grounds valorization

Discovered in Ethiopia, coffee became a popular beverage in Asia, Europe, Latin America, Australia, Africa and the North America as a drink after water and the largest goods after petroleum. However, the coffee industry generates a huge biomass as its byproducts of which the spent coffee grounds (SCG) is concerning, especially in the production chain away from the farm. Therefore, the valorization and revalorization of the SCG has a huge impact on the socioeconomic and environmental sustainability of the industry, up to the realization of the circular bioeconomy. With the advancing biorefinery concept, even an almost complete recovery of the SCG is reported at an experimental level. Such kind of studies increased with time following the action of the Sustainable Development Goals by the United Nations Development Program promulgated in 2015. The current review highlights on the background, socioeconomic, environmental contexts of coffee production and the SCG valorization and revalorization studies. Refereeing to 154 screened articles published in over 30 years' time, the SCG revalorization efforts and its integrated biorefinery as a green management approach are uniquely addressed. Plenty of studies have reported the production of bio-products from the SCG, such as the derivation of adsorbents, biochar, bioethanol, biogas, biodiesel, bio-oil, compost, construction material aggregates, cosmetics, electricity and food ingredients. In conclusion, the recovery potential of the SCG is promising and can substantially contribute to a sustainable and green bioeconomy. Nevertheless, the recovery of bioactive materials through SCG fermentation is still lacking. Most studies are conducted on a lab scale, which needs to be piloted and commissioned. Furthermore, the link between climate change and variability vis-à-vis the sustainable management of the SCG remains unaddressed.

Potential Uses of Spent Coffee Grounds in the Food Industry

Current estimates place the amount of spent coffee grounds annually generated worldwide in the 6 million ton figure, with the sources of spent coffee grounds being classified as domestic (i.e., household), commercial (i.e., coffee houses, cafeterias and restaurants), and industrial (i.e., soluble and instant coffee industries). The majority of the produced spent coffee grounds are currently being inappropriately destined for landfills or to a form of energy recovery (e.g., incineration) as a refuse-derived fuel. The disposal of spent coffee in landfills allows for its anaerobic degradation with consequent generation and emission of aggressive greenhouse gases such as methane and CO₂, and energy recovery processes must be considered an end-of-life stage in the lifecycle of spent coffee grounds, as a way of delaying CO₂ emissions and of avoiding emissions of toxic organic volatile compounds generated during combustion of this type of waste. Aside from these environmental issues, an aspect that should be considered is the inappropriate disposal of a product (SCG) that presents unique thermo-mechanical properties and textural characteristics and that is rich in a diversity of classes of compounds, such as polysaccharides, proteins, phenolics, lipids and alkaloids, which could be recovered and used in a diversity of applications, including food-related ones. Therefore, researchers worldwide are invested in studying a variety of possible applications for spent coffee grounds and products thereof, including (but not limited to) biofuels, catalysts, cosmetics, composite materials, feed and food ingredients. Hence, the aim of this essay was to present a comprehensive review of the recent literature on the proposals for utilization of spent coffee grounds in food-related applications, with focus on chemical composition of spent coffee, recovery of bioactive compounds, use as food ingredients and as components in the manufacture of composite materials that can be used in food applications, such as packaging.

Decentralized Composting of Food Waste: A Perspective on Scientific Knowledge

Composting has been demonstrated to be an effective and sustainable technology to treat a wide variety of organic wastes. A particular aspect of composting is the number of technological options that can be used, from full-scale plants to small composters. In this sense, the interest in composting at home or on a community scale is exponentially growing in recent years, as it permits the self-management of organic wastes and obtaining compost that can be used by the same producer. However, some questions about the quality of the obtained compost or the environmental impact of home composting are still in an early stage of development and provide little knowledge. In this review, the main points related to home and community composting are analysed in detail according to the current scientific knowledge by highlighting their advantages and possible drawbacks. Particularly, the composting process performance is analysed, with temperature stratification being one of the main problems related to small amounts of organic matter. Simultaneously, compost quality is determined using parameters such as stability and/or maturity, concluding that home compost can be similar to industrial compost in both aspects. However, sanitisation of home compost is not always achieved. Regarding its environmental impact, gaseous emissions, especially greenhouse emissions, are the most studied category and are generally low. Finally, the effects of pandemics on home composting are also preliminary commented, concluding that this strategy can be a good alternative to have cities that are more resilient.

Differences of Enzymatic Activity During Composting and Vermicomposting of Sewage Sludge Mixed With Straw Pellets

The study aims were focused on profiling eight hydrolytic enzymes by fluorescence method using a multifunctional modular reader and studying the proportion of basic microorganism groups during composting and vermicomposting of sewage sludge mixed with straw pellets in several proportions (0, 25, 50, 75, and 100%). The greatest decrease in enzymatic activity occurred in the first half of composting and vermicomposting. After 4 months of these processes, the least enzymatic activity was observed in the sludge with 50% and also 25% straw addition, indicating that straw is an important means for the rapid production of mature compost from sewage sludge. Enzymatic activity was usually less in the presence of earthworms than in the control treatment because some processes took place in the digestive tract of the earthworm. For the same reason, we observed reduced enzyme activity during fresh feedstock vermicomposting than precomposted material. The final vermicompost from fresh feedstocks exhibited less microbial biomass, and few fungi and G- bacteria compared to precomposted feedstock. The enzymatic activity during composting and vermicomposting of sewage sludge and their mixtures stabilized at the following values: β-D-glucosidase-50 μmol MUFG/h/g dw, acid phosphatase-200 μmol MUFP/h/g dw, arylsulphatase-10 μmol MUFS/h/g dw, lipase-1,000 μmol MUFY/h/g dw, chitinase-50 μmol MUFN/h/g dw, cellobiohydrolase-20 μmol MUFC/h/g dw, alanine aminopeptidase-50 μmol AMCA/h/g dw, and leucine aminopeptidase-50 μmol AMCL/h/g dw. At these and lesser values, these final products can be considered mature and stable.