High temperature slagging gasification demonstration-scale trial of sewage sludge: Feasibility analysis towards mono treatment, operational challenges and life-cycle assessment

The application of high temperature slagging gasification was investigated for treatment of sewage sludge aiming to reduce landfill dependency and create high quality by-product, slag, with excellent heavy metal encapsulation. A demonstration scale facility designed for treatment of municipal solid waste (MSW), with a capacity of 11.5 tonnes a day is applied to assess the operation of the first-of-its-kind mono sewage sludge gasification. This study aims to explore the operational conditions, engineering controls and technical challenges associated with sewage sludge slagging gasification, while assessing the properties of the by-products generated for recycling and reutilization. During mono sludge gasification, higher amounts of biomass charcoal and limestone (CaCO₃) are required to improve the melting of slag and maintain the stability of the gasifier as compared to the usual MSW gasification. Typically used sorbent, slaked lime (Ca(OH)₂), is replaced by sodium bicarbonate (NaHCO₃) to ensure effective removal of acidic gasses from flue gas such as sulfur oxides. Slag generated from sludge demonstrates low leaching of heavy metals, meeting inert waste requirements based on EU landfill standards and shows comparable properties to the MSW slag. The amount of gasification fly ash (GFA) generated for disposal is minimized to only 5.1% of the mass of initial feedstock and is classified as non-hazardous waste acceptable for direct landfill. Life cycle assessment (LCA) provides useful information and critical insights on the competitive advantages and deficiencies of mono sludge slagging gasification, highlight the potential areas for improvement to further enhance the overall environmental performance.