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Gdańsk University of Technology

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Valorization of paper-mill sludge laden with 2-chlorotoluene using hydroxyapatite@biochar nanocomposite to enrich methanogenic community: A techno-economic approach

While several studies have investigated the anaerobic digestion of paper-mill sludge (PMS), this technology suffers from nutrient insufficiency, inhibition by aromatic compounds, and low bio-CH4 yield. Hence, PMS was anaerobically co-digested with chicken manure (CM) and supplemented by hydroxyapatite@biochar (HAP@BC) nanocomposite for enhancing 2-chlorotoluene degradation and enriching the methanogenic archaea. Multiple continuous stirred tank reactors (CSTRs) were operated at 12.6 h hydraulic retention time (HRT), using PMS (R1), CM (R2), PMS + CM (R3), PMS + CM+100 mg HAP/L (R4), and PMS + CM+100 mg HAP@BC/L (R5). The maximum bio-CH4 yield of 147.5 ± 9.1 mL/g COD and 2-chlorotoluene removal of 91.2 ± 6.8 % were obtained from R5, experiencing a sufficient C/N ratio of 14.7 and the highest activities of acidogenesis (42.0 %), aceto- genesis (37.9 %), and methanogenesis (42.1 %). The abundances of Euryarchaeota, Bacteroidota, and Chloroflexi at the phylum level, and Pseudomonas, and Bacillus at the genus level could highly contribute to the dechlori- nation mechanism and acetate transformation into CH4. This biomass-to-bioenergy project (10 m3/d capacity) could benefit from pollution reduction, biogas recovery, and carbon credit, giving 5.6 yr payback-period, 3503 USD net present value, and 12.1 % internal rate of return. Because R5 exhibited an efficient techno-economic anaerobic biodegradation performance, future studies are required to optimize its HRT condition and HAP@BC dosage.

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