Review of the Integration of Drying and Thermal Treatment Processes for Energy Efficient Reduction of Contaminants and Beneficial Reuse of Wastewater Treatment Plant Biosolids

Biosolids have been traditionally used as a beneficial resource in the agricultural industry. However, contaminants of emerging concern (CECs) threaten their reuse due to concerns of toxicity, bioaccumulation, and increased regulations on acceptable CEC concentrations in biosolids. The thermal treatment of biosolids has the potential to destroy/mineralize these contaminants as well as transform the biosolids into valuable biochar. However, the thermal processing of biosolids is highly energy intensive due to the energy costs associated with drying biosolids to the required moisture content for thermal processing. This article performs a brief review of the drying of biosolids from a physical and theoretical viewpoint. It also provides an overview of pyrolysis and gasification. It explains the impact that moisture can have on both the degradation of CECs and the products that can be obtained through the thermal treatment of biosolids. Additionally, model-based, lab-based, and pilot-scale examples of integrated drying and thermal treatment processes are reviewed. Key challenges, such as the need for co-pyrolysis and co-gasification, as well as the impact of biosolids composition on energetic viability, are identified.