A Techno-Economic Evaluation of Potential Routes for Industrial Biosolids Conversion

Renewable sources of energy have been widely investigated to reduce the reliance on fossil fuel energy sources that are depleting and have their adverse impacts on the climate and environment. Biosolid, a form of biomass holds the potential of a renewable energy source due to their carbon content. These solids are removed as waste residues from municipal and Industrial wastewater treatment plants. The most dominant biosolids management method has been landfilling for decades, a practice that can be seen as a waste of a valuable resource. In addition, recent research findings proved that this practice has unfavourable impacts on the food chain. This has been an additional motivation to research the possibilities of unlocking the potential of these solids. Published research work investigated different types of biomass waste but limited literature is available on biosolids in general and on industrial biosolids in specific. This paper evaluates the potential of converting industrial biosolids into value added products that can be used as feedstocks in chemical production or can be utilized for heat and power co-generation. The study focuses on well-established thermal conversion technologies mainly pyrolysis, gasification anaerobic digestion and the developing hydrothermal technology. A MILP model is developed to provide a techno economic assessment of the treatment routes using these technologies. The model assists in deciding on the optimal treatment route with the objective of minimum cost. The model was executed using a case study of industrial biosolids stream with a flowrate of 50 ton/d and water moisture of 30% The results show that for the given biosolid stream anaerobic digestion treatment route will provide the optimal minimum cost route. The model demonstrates that the selection of the suitable route highly depends on technology limitation and biosolids stream characteristics.