Beneficial reuse of water treatment sludge in the context of circular economy

Water treatment processes produce large volumes of drinking water that must meet regulatory quality requirements. In the process of so doing, the treatment of water generates large volumes of ‘alum sludge’; a by-product typically considered a waste and disposed to landfill. However, reductions in access to landfill sites, increased disposal costs, and concepts of achieving zero-waste are spurring different approaches to sludge management and disposal. Principles of Circular Economy that seek to promote regenerative design, eliminating waste and continual use of resources, are becoming increasingly important for water authorities. This paper comprehensively reviews the general properties of water treatment sludge, contemporary disposal practices, and its sustainable resource management, including sludge reuse, recycling, and recovery options. The paper also discusses potential social, economic and environmental benefits and barriers of implementing sustainable resource management with water treatment sludge in the context of the Circular Economy. Future research opportunities are discussed with a focus on promoting sustainable management practices where water treatment sludge is considered a value-add resource.