Coffee is perhaps one of the most vital ingredients in humans' daily life in modern world. However, this causes the production of million tons of relevant wastes, i.e., plastic cups, aluminum capsules, coffee chaff (silver skin), and spent coffee grounds (SCG), all thrown untreated into landfills. It is estimated that 1 kg of instant coffee generates around 2 kg of wet SCG; a relatively unique organic waste stream, with little to no contamination, separated directly in the source by the coffee shops. The produced waste has been under researchers' microscope as a useful feedstock for a number of promising applications. SCG is considered a valuable, nutrients rich source of bioactive compounds (e.g., phenolics, flavonoids, carotenoids, lipids, chlorogenic and protocatechuic acid, melanoidins, diterpenes, xanthines, vitamin precursors, etc.) and a useful resource material in other processes (e.g., soil improver and compost, heavy metals absorbent, biochar, biodiesel, pellets, cosmetics, food, and deodorization products). This paper aims to provide a holistic approach for the SCG waste management, highlighting a series of processes and applications in environmental solutions, food industry, and agricultural sector. Thus, the latest developments and approaches of SCG waste management are reviewed and discussed.

Advanced tertiary treatment and disinfection technologies have enabled the production of wastewater (WW) with quality complying with the established criteria for reuse in agriculture. This study assessed the impacts of tomato crop irrigation with two qualitatively distinct treated WW effluents, as compared to control tubewell water (TW) irrigation, on the soil geochemical properties, tomato fruit safety and crop productivity. The treated effluents reused for irrigation were produced in two Municipal Wastewater Treatment Plants (MWTPs) utilizing two discrete tertiary treatment and disinfection technologies, i.e. Slow Sand Filtration and chlorination (MWTP I), and Membrane Bioreactor and UV radiation (MWTP II), respectively. The impacts on soil pH, electrical conductivity, total organic C, Cl − , NO 3 − and heavy metal (Zn, Mn, Ni, Cu, Co) content were evaluated. In addition, the heavy metal content in tomato fruits and leaves, as well as the microbial load in fruit flesh and peel was determined. Crop productivity was measured by the mean fruit weight and maximum diameter, and by the number of fruits per harvest. Irrigation with either WW did not significantly affect the soil pH, organic C and heavy metal content, as well as crop productivity, in comparison to control TW irrigation. Furthermore, the heavy metal content of tomato fruits and leaves in all irrigation treatments was found to be below the maximum permissible levels set for fruit safety and the critical tissue concentration for phytotoxicity, respectively. Moreover, no microbiological contamination (total coliform, fecal coliform, Escherichia coli, Salmonella spp., Listeria spp.) of tomato fruits was found from any irrigation treatment. Overall, results obtained with regard to the parameters examined strongly suggest that advanced tertiary treated effluent of good quality might be safely reused, in terms of both environmental sustainability and public health safety, for vegetable irrigation, concurrently promoting water use efficiency in dry areas.

Water scarcity renders wastewater (WW) reuse for irrigation an increasingly common practice worldwide. Comprehensive guidelines and criteria have been established to secure the safety of WW irrigation, especially for food crops or crops that are eaten raw. The aim of this short-term study was to assess the impacts of strawberry crop irrigation with tertiary treated wastewater (WW) using common irrigation techniques (Drip, sprinkler, drip under plastic mulch), as compared to potable water (PW) irrigation, on strawberry fruits' quality and safety, and on crops' productivity. The impacts on fruits' weight and marketability, as well as on fruits' taste (soluble solids, titratable acidity and soluble solids/titratable acidity ratio), antioxidant capacity (ascorbic acid concentration, FRAP, total phenolics and total anthocyanin content), heavy metal content (Cu, Zn, Mn, Co, Ni) and microbial contamination (total coliform, E. coli, Salmonella spp., Listeria spp), were evaluated. The results revealed that WW irrigation did not significantly affect the fruits' marketability, taste and antioxidant capacity, as well as the heavy metal content, in comparison to controlled irrigation, regardless of the irrigation technique applied. Fruits heavy metal content was found to be below the maximum permissible levels (MPLs) set for fruit safety, whereas no microbiological contamination (total coliform, E. coli, Salmonella spp., Listeria spp.) of fruits was found in all irrigation water treatments. Overall, the results obtained with regard to the parameters examined highlight the potential for the reuse of the advanced tertiary treated effluent of good quality as a valid alternative for the irrigation of strawberry crops, even with sprinklers. However, further long-term studies are needed in order for such a practice to be regulated.