Approach to the circular economy through agro-livestock waste composting with heat recovery and agricultural use of the resulting compost

In this work, plant waste and cow manure were co-composted to recover the heat generated during the thermophilic stage of composting by heating water through conducting heat exchangers buried in the pile. The parameters associated with the degradation and humification of organic matter during composting and the agronomic and economic value of the final compost were also determined. Furthermore, the effects of adding the obtained compost on soil agronomic characteristics and alfalfa yield and production profitability were compared with those of mineral fertilisation, cow manure and a control without amendment. The total energy recovered from composting was 14,528W or 0.105 MJ kg−1 dry matter of the initial waste mixture. Extracting heat from composting did not negatively affect the quality of the compost since this material had an adequate level of organic matter stability and maturity, notable nutrient content, low concentrations of potentially toxic elements and an absence of phytotoxicity. Moreover, applying compost to the soil increased its organic matter and nutrient content, contributing to greater alfalfa production. Increased alfalfa production led to a higher net income from using compost as an organic fertiliser (16,488 USD ha−1). Therefore, composting agricultural and livestock wastes is a viable method for managing these wastes, obtaining sustainable thermal energy and producing compost with adequate agricultural quality. This contributes to closing agricultural and livestock production cycles with notable economic benefits within a circular economy framework.