Feedstock Characterization for Enhanced Heat Recovery from Composting Processes: A Review

Compost Heat Recovery Systems (CHRS) sustainably capture heat from composting waste biomass, helping reduce greenhouse gas emissions and fossil fuel reliance. The choice of feedstock affects the performance of CHRSs as it controls the microbial activities and the amount of heat generated. This review evaluates plant-based, animal-derived, and non-agricultural feedstocks to optimize CHRS energy recovery. A systematic review of 244 studies, published from 1996 to 2023 and available on Scopus, Web of Science, and external databases, categorized feedstocks based on properties like carbon-nitrogen ratio (C/N), moisture content, bulk density, and heating value to assess their impact on energy recovery and compost quality. The review followed the PRISMA guidelines, excluding irrelevant documents and those that lacked quantitative data. Animal-based materials, which have high levels of moisture and nutrients, such as nitrogen (14.50–32.20 g/kg TS) and phosphorus (13.0–13.5 g/kg TS), promote rapid growth of microbes and consistent heat production supported by their stable carbon content (353.8–450.0 g/kg TS) and optimal C/N ratios (5.90–28.90). On the other hand, plant-based materials that are rich in volatile solids (327.2–960.0 g/kg TS) and lignin (36.7–290.0 g/kg TS) offer a steady and prolonged release of heat but decompose more slowly.