Integrated waste-to-energy process for hazardous landfill leachate valorization: Economic profits related to sustainability and environmental assessment

While recent studies have presented hazardous landfill leachate (HLL) bio-digestion for biogas recovery, there is a research gap in enhancing the relative abundance of methanogens and managing the sludge digestate to avoid the risk of secondary pollution. This study represents the operation of an anaerobic digester amended with sawdust biochar to improve the HLL detoxification performance, followed by managing the sludge digestate to raise the project’s internal rate of return (IRR). This objective is justified by employing an integrated techno-financial and life cycle assessment (LCA) approach. Implementing the biochar-supplemented digester for HLL’s substrate conversion into biofuel achieved the shortest payback period (6.2 yr), considering biochar carbon credit (0.231 USD), biogenic gas selling (0.312 USD), biogas carbon marketing (0.118 USD), pollutant shadow price (0.064 USD), and digestate biochar selling (0.080 USD) per 1 m³. Increasing the Methanosaeta, Methylophilus, Paludibacter, Novosphingobium, and Pseudomonas relative abundances by 61.8 %, 529.3 %, 261.8 %, 25.9 %, and 100.0 %, respectively, enhanced the 2, 6-dichlorophenol dechlorination performance in the biochar-amendment digester. This project also maintained LCA endpoint impact categories of 6.05 × 10⁸ species·yr, 8.11 × 10⁵ DALYs, and 7.99 × 10² USD 2013 for ecosystem quality, human health, and natural resources, respectively. Because the proposed project would sustain an IRR of 9.7 %, and conserve terrestrial/aquatic ecosystems, future studies should focus on replacing fossil-based fuel with bio-CH₄ to mitigate the effects of human-induced climate change.