Role of Temperature in Sludge Composting and Hyperthermophilic Systems: a Review

The utilization of nutrients in sewage sludge partly alleviates the economic and environmental constraints, and the composting process has been proved a cost-efficient and simple approach for the recycling of sewage sludge. During the bio-oxidative process, the thermophilic phase is considered to be the most effective stage for the biodegradation of organic matter in sewage sludge composting systems. However, the maximum temperatures of conventional thermophilic composting systems only reach approximately 55–60 °C because of the activity limitations of thermophiles at higher temperatures. Notably, increasing temperatures can accelerate the humification process and shorten the composting cycle. Therefore, the effect of rising temperature on sewage sludge composting was examined as a specific mechanism. Further, the consequent hyperthermophilic composting (HTC) system created by rising temperatures was reviewed. Moreover, the potential techno-economic advantages and future challenges of HTC systems were discussed. Finally, the microbial communities necessary to ensure the efficiency of HTC systems were analyzed and suitable hyperthermophiles for sludge HTC systems were proposed.