Washed hydrochar from spent coffee grounds: A second generation of coffee residues. Evaluation as organic amendment

Soil Amendments and Biostimulants from the Hydrothermal Processing of Spent Coffee Grounds

“…Excluding hydrochars produced from the most severe HTC regime, 260 PE and 260 RAW, all untreated hydrochars exerted a deleterious effect on seed germination (S1, supplementary data). This result corroborates with previous studies, where the presence of polyphenolic allelochemicals are attributed to the inhibitory effect of SCG bio-amendments on plant biomass growth [16][17][18]33]. It is thought that polyphenolic components such as chlorogenic acid (CGA) are phytotoxic through mechanisms including interference with plant metabolic pathways, membrane cell oxidation and immobilisation of soil N and P [34].…”

“…These chars were produced under milder HTC settings (T = 175 and 185 °C, t = 1 h), and results corroborated with those obtained for 217 PE and 217 RAW PCs in this study. Despite stunted growth, crops exhibited enhanced mineral and polyphenolic content, mirroring previous investigations [18].…”

“…Changing extraction solvents to methanol or methanol: water (50:50 v/v) increased retention of total phenolic content in liquid extracts of the hydrochars due to increased solubility of alkaloids and polyphenols in organic solvents [47]. This likely contributed to the discrepancy between the results of this study (SCG PCs extracted using acetone: methanol (50:50, v/v)) and those reported by Cervera-Mata et al (SCG hydrochars washed with deionised water) as organic extraction of secondary chars further reduced the phenolic content of the solids [18]. A similar trend in the biocharization of SCG was also reported in a related study by Cervera-Mata et al where increasing destruction of phenolic content with temperature was attributed to removal of phytotoxicity and higher biomass yields [17].…”

“…The authors recommend development of mixtures of fresh or pre-treated SCG with NPK fertilisers to maximise crop yield and nutritional quality. A subsequent study by the same group, working within the circular economy framework, found that an enriched presence of polyphenols in hydrochar products from the HTC of SCG replicated inhibitory behaviour observed for fresh SCG-with greater potential for mobilization of mineral elements [17,18].…”

Determination of Relationship between Higher Heating Value and Atomic Ratio of Hydrogen to Carbon in Spent Coffee Grounds by Hydrothermal Carbonization

“…The biochar of HHV of different biomasses is shown in Table 5. Previous HHV studies were compared with the HHV of this study to assess the potential for biochar through HTC, and SCGs were found to have a higher HHV than the other biomass samples, indicating their potential as a valuable fuel source through HTC conversion [32][33][34]. The producing biochar using SCGs has been carried out in a variety of ways, and as a result, the possibility of biochar is fully demonstrated not only in this research's results but also in previous research.…”