Decarbonization of Sewage Sludge Processing Through Solar Thermal Energy Integration

Abstract Disposal of sewage sludge results in significant energy consumption and carbon emissions. Greenhouse-type drying methods have been investigated to reduce emissions; however, their use in high capacity plants is limited due to the large amount of space required and the dependence on climatic conditions. This study investigates the energy performance of high temperature hot oil production using concentrated solar power (CSP) systems installed on existing wastewater treatment plant (WWTP) pool areas, and utilizing it as a heat source in an indirect dryer. An annual energy balance was simulated using CSP and dryer models, analysing both a 95% dry matter (DM) condition at the dryer outlet and a 50% DM condition suitable for autothermal combustion. The energy analysis showed that about 28% of the total annual energy required for full drying and about 42% for partial drying could be provided by solar energy. In terms of CO₂ emissions, similar reductions were observed for partial drying and load shifting applications. Complete drying in the plants resulted in emission reductions of 1–3.5 million tonnes, while partial drying resulted in reductions of 2–8 million tonnes. As opposed to greenhouse-based drying systems, this method of integration allows the use of solar energy without requiring additional space. The integration of CSP energy systems into the sewage sludge drying process offers significant benefits in terms of energy savings and emission reductions. Through further optimization of the solar system and maximization of the use of the solar area, zero-emission sludge management could be achieved.