Integrating anaerobic digestion with hydrothermal pretreatment for bioenergy production: Waste valorization of plastic containing food waste and rice husk

Combining hydrothermal treatment with anaerobic digestion (AD) can achieve significant potential as climate change mitigation tools and waste management strategies. A mixture of plastic sheets containing food residues and rice husk was subjected to hydrothermal carbonization of approximately 204.4 °C for 30 min (hydrothermal30) and 60 min (hydrothermal60). The hydrothermally generated products (hydrolysates), either solid fractions (hydrochar60 and hydrochar30), liquid fractions (liquid60 and liquid30), and a mixture of thereof (solid-liquid-mix60 and solid-liquid-mix30) were further utilized via AD batch experiments alongside a control non-treated digester. The lignocellulosic biomass was effectively solubilized in solid- and liquid-fraction after hydrothermal30 by 1.04 and 1.50 times tCOD and by 1.72 and 1.47 times TVFAs than the corresponding hydrothermal60, respectively. Additionally, the hemicellulose contents in the solid hydrochar fractions were significantly reduced (p < 0.05) by 86.10–93.47% over non-thermally treated biomass. The cumulative CH4 harvest improved by 1.4, 2.5, 2.1, 3.4, 6.6, and 10.0 times for hydrochar60, hydrochar30, solid-liquid-mix60, solid-liquid-mix30, liquid60, and liquid30 over the untreated control digester, respectively. Consequently, the recovery of two wastes to precious byproducts was affected by the hydrothermal carbonization times with the optimum condition at hydrothermal30 that exhibits a promising waste management option.