Solar Drying of Biosolids – Recent Experiences in Large Installations

The conversion of raw sewage sludge into valuable biosolids for beneficial reuse requires a suitable pre-treatment process. However, traditional technologies are causing high investment costs, operation costs, and energy demand; or are not fully meeting the demands of the market. As recent experiences from the world's largest solar drying and solar-assisted drying plants in Palma de Mallorca, Spain and Oldenburg, Germany show, solar drying is an effective alternative for large facilities. Drying costs and energy consumption are less than half, maintenance is low, and operation is simple and safe at these facilities when compared to traditional thermal dryers. Also, carbon dioxide (CO2) emissions are reduced by a factor of seven when compared to conventional dryers. By using waste heat from other processes, the area requirement can be reduced by a factor of three to five. The final product is suitable as fuel for Waste-to-Energy (WTE) plants, coal power plants, or cement kilns. It can also be used as a Class-A fertilizer for agricultural use, or land application.