Hybrid agricultural waste valorization through machine learning-optimized hydrothermal carbonization and sustainability: A review
Elendu Collins, Fan Yang, Shuzhi Wang, Yunfei Liu, Xuyang Wang, Jia Duo, Peigao Duan, Oluwadamilola Oluwatoyin Hazzan
Abstract
As societies increasingly seek sustainable solutions to combat climate change and environmental pollution, valorizing agricultural waste through hydrothermal carbonization (HTC) offers innovative solutions but also presents significant challenges. A primary concern is the variability of agricultural feedstocks, which exhibit diverse chemical and morphological characteristics, including lignin, cellulose, hemicellulose, and amino acid contents, all of which influence the quality of hydrochar (HC) produced. This review examines the optimization and modeling of the HTC process through hybrid statistical and machine learning (ML) models aimed at addressing this heterogeneity and improving HC quality. Integrating ML and statistical techniques into the HTC process via reactions such as Maillard, depolymerization, and decarboxylation provides innovative strategies for effective agro-waste management. This effort also explores the synergistic combination of agricultural waste streams in promoting beneficial microorganisms vital for soil health, including Rhizobia and Mycorrhizal fungi. Additionally, life cycle assessment (LCA) emphasizes the sustainability of the HTC approach, ensuring that carbon sequestration and greenhouse gas reduction are considered. Compared with pyrolysis, HTC of agro-waste results in a lower environmental burden, with 30 % and 24 % reductions in global warming and ecotoxicity potential. This study highlights the critical role of hybrid-optimized HTC in advancing climate-smart agriculture and sustainable agro-waste management. • Optimized HTC using hybrid statistical/ML models enhances hydrochar quality and addresses feedstock variability. • Synergistic use of diverse agricultural waste streams promotes beneficial microorganisms essential for soil health. • LCA confirms HTC sustainability, highlighting carbon sequestration, greenhouse gas reduction potential for a greener future. • HTC of agro-waste showed a reduced environmental burden, with 30 % less GWP and 24 % less ETP compared to pyrolysis.