Compost Heat Recovery Systems: An alternative to produce renewable heat and promoting ecosystem services

Aerobic biodegradation of biomass can release considerable heat, reaching temperatures of up to 65 °C. This heat can be recovered and used for domestic purposes through the implementation of Compost Heat Recovery System (CHRS). In this study, data were collected from a full-scale CHRS, fed with tree-pruning residues, installed in a farmhouse located in Northern Italy. The CHRS (2.75 kW average heating power) worked in conjunction with a pellet combustor for one year. Energy and carbon balances were analyzed and compared (over a 15-year life-time) with combinations of alternative heating systems (both traditional and green ones). The real case study provided a heat supply at a competitive cost (0.087 € kWh−1). A scenario with two CHRSs would further decrease costs (0.074 € kWh−1). In terms of the carbon balance, a CHRS can save up to 0.252 kgCO2-eq kWh−1 of energy produced, compared to a fossil-fuel alternative (natural-gas), while promoting carbon storage for around 0.05 kgCO2-eq kWh−1 in agricultural soils by compost amendment. Over a 15-year period, each module can potentially substitute fossil-derived heat for around 264 MgCO2-eq, while increasing soil carbon pool by around 20 MgCO2-eq, as C-stock calculated on a medium-term scenario (100-years). CHRSs have great potential to furnish renewable heat at competitive prices, while providing other ecosystem services, such as carbon storage and nutrients cycling to soil. Economic valorization of tree-pruning residues could also be an incentive for the implementation of agroforestry practices and landscape features. Further studies are needed in this relatively unexplored field, which might be of interest in the context of EU regulatory frameworks such as the EU Directive 2018/2001 and the upcoming Common Agricultural Policy (CAP) 2021 – 2027.