Alternating electric field enables hyperthermophilic composting of organic solid wastes

Hyperthermophilic composting (HTC) achieves compost temperatures above 80 °C, usually depending on the inoculated hyperthermophilic bacteria, which has been well used in full-scale plants. However, the scarcity of hyperthermophilic bacteria and the high cultivation cost hinder the development of HTC. Recently, a direct-current electric field applied on conventional aerobic composting raised compost temperature to 70-75 °C, but gradient moisture distribution under the action of the direct-current electric field affected microbial metabolic heat and limited the temperature rise. Herein the effects of alternating electric field (AEF) promoting a uniform water distribution and further raising the temperature to achieve HTC were investigated. Our results demonstrated that AEF raised the compost temperature to 90 °C, and the period with temperatures above 80 °C lasted 4 days. The physicochemical properties and maturity index showed that the AEF improved the biodegradation and humification of organic matter due to the generation of metabolic heat. The AEF enriched thermophilic bacteria (Ureibacillus: by 52.36% on day 3; Navibacillus: by 46.54% on day 41). A techno-economic analysis indicated that the proposed approach with the AEF had a cost advantage over HTC with the inoculation of hyperthermophilic bacteria. Therefore, the AEF composting system represents a novel and applicable strategy for HTC.