Anaerobic digestion of untreated and treated process water from the hydrothermal carbonisation of spent coffee grounds. (April 2022)

• Record Type: Journal Article
• Authors: Campbell, B.S.; Thorpe, R.B.; Peus, D.; Lee, J.
• Is Part Of: Chemosphere. Volume 293(2022)
• Publication Date: 2022-04
• Subjects: Hydrothermal carbonisation -- Anaerobic digestion -- Biogas -- Process stability -- Spent coffee grounds; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2022.133529
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: This study investigates the long-term performance of the mesophilic (35 °C) anaerobic mono-digestion of process waters (PW) from the hydrothermal carbonisation (HTC) of spent coffee grounds. At an organic loading rate (OLR) of 0.4 gCOD L −1 d −1, initial instability was seen, but after 40 days and supplementary alkalinity, the digestion stabilised with the chemical oxygen demand (COD) in the untreated PW degraded with 37.8–64.6% efficiency and the yield of methane at 0.16 L gCOD −1 . An increase in OLR to 0.8 gCOD L −1 d −1 caused a collapse in biogas production, and resulted in severe instability in the reactor, characterised by falling pH and an increasing volatile fatty acid concentration. Comparatively, the digestion of a treated PW (concentrated in nanofiltration and reverse osmosis after removal of the fouling fraction), at OLR between 0.4 and 0.8 gCOD L −1 d −1, was stable over the entire 117 days of treated PW addition, yielded methane at 0.21 L gCOD −1 and the COD was degraded with an average efficiency of 93.5% - the highest efficiency the authors have seen for HTC PW. Further anaerobic digestion of untreated PW at an average OLR of 0.95 gCOD L −1 d −1 was stable for 38 days, with an average COD degradation of 69.6%, and methane production between 0.15 and 0.19 L gCOD −1 . The digestion of treated PW produced significantly higher COD degradation and methane yield than untreated PW, which is likely to be related to the removal of refractory and inhibitory organic material in the post-HTC treatment by adsorption of hydrophobic material. Graphical abstract: Image 1 Highlights: Process waters from the HTC of spent coffee grounds anaerobically digested. Novel pre-treatment of process water for P-recovery enhanced digestion performance. Adsorption of hydrophobic organics removes recalcitrant compounds before AD. COD degradation efficiencies of 69.6% (untreated PW) and 93.5% (treated PW). Specific CH4 yields of 0.16 L gCOD −1 (untreated PW) and 0.21 L gCOD −1 (treated PW).