Marco Schiavon

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.

Despite their key role in integrated waste management, direct (incineration) and indirect (gasification/pyrolysis) waste combustion processes are still opposed by some of the general public due to the past emission levels of air pollutants. In fact, although the release of air pollutants (especially dioxin) to the atmosphere from waste combustion processes has gradually decreased over the years, thanks to the introduction of stricter regulations and more advanced removal technologies, there is still an unsolved problem regarding the public acceptance of waste-to-energy facilities. The aim of this paper is to provide an overview of the state-of-the-art air pollution control (APC) technologies used in waste combustion facilities. Air pollution control technologies are designed to reduce or eliminate the emissions of harmful pollutants into the atmosphere. These technologies are important for safeguarding public health, protecting ecosystems, complying with regulations, and promoting a more sustainable and resilient future for both local and global communities. This paper will highlight the complexity behind emission control and the efforts made by this sector over the years. This paper will also propose suggested configurations based on the interactions/complementarity between different APC technologies and recent findings to improve their performance.

A pilot-scale experiment was implemented in a waste bioreactor with an inner capacity of 1 m³ in order to simulate a real-scale composting process. The waste underwent composting conditions that are typical of the initial bio-oxidation phase, characterised by a high production of volatile organic compounds (VOCs), hydrogen sulphide (H₂S) and odorants. The waste bioreactor was fed with an intermittent airflow rate of 6 Nm³/h. The target of this study was to investigate the air treatment performance of three biofilters with the same size, but filled with different filtering media: (1) wood chips, (2) a two-layer combination of lava rock (50%) and peat (50%), and (3) peat only. The analyses on air samples taken upstream and downstream of the biofilters showed that the combination of lava rock and peat presents the best performance in terms of mean removal efficiency of odour (96%), total VOCs (95%) and H₂S (77%) concentrations. Wood chips showed the worst abatement performance, with respective mean removal efficiencies of 90%, 88% and 62%. From the results obtained, it is possible to conclude that the combination of lava rock and peat can be considered as a promising choice for air pollution control in waste composting facilities. GRAPHICAL ABSTRACT