Abstract

This study proposes a novel and sustainable composting system that integrates solar energy with circular water management through a humidification–dehumidification (HDH) approach. Three composting reactors containing fresh organic waste from household sources were established. In two of the reactors, heated air was supplied via a solar air heater. In one of these, the humidified air generated during composting was directed to a heat exchanger, where condensation occurred, and the recovered water was recirculated to maintain compost moisture. The second reactor received heated air but no water recovery. The third reactor served as a control, where natural evaporation was allowed, and no additional heat or water was supplied. After 90 days, compost moisture decreased from 50.1 % to 27.3 %, 24.7 %, and 10.3 % in the reactors with water recovery, control, and no water recovery, respectively. Maximum composting temperatures were 70.1 °C, 61.0 °C, and 37.2 °C for the respective systems. Integrating the solar HDH unit significantly improved compost hydration, enhanced microbial activity, accelerated compost maturation, and reduced water and energy requirements. These results demonstrate the system's potential to enhance compost quality and process efficiency while conserving resources. This integrated approach offers a scalable, low-cost, and resource-efficient solution for composting in water-scarce environments, supporting circular economy goals. © 2025 Elsevier Ltd