Municipal sewage sludge management in a changing world: Trends and safe resource recovery

Abstract

In this review, we examine municipal sewage sludge management and resource recovery in relation to United Nations Sustainable Development Goal 6 (SDG 6: Clean Water and Sanitation), circular economy goals and public health protection. Major management alternatives, including agricultural land application, energy recovery, use in construction materials, land reclamation and biofuel production are assessed, along with their technical, regulatory, environmental and social constraints. Based on studies and case examples from diverse global regions, in this review we facilitate comparison of sludge management options and identify context-appropriate strategies amid rapid changes in current regulatory requirements and climatic conditions. The reviewed literature indicates that there is no single optimal pathway for sludge management; rather, the most suitable options are dependent upon sludge characteristics, treatment infrastructure, costs, monitoring capacity, local environmental conditions and relevant legal requirements. Resource recovery pathways can reduce environmental burdens and generate value by recovering energy, nutrients or useful materials, but in many cases they require pre-treatment, reliable process control and adequate monitoring. Although land application can improve soil fertility and organic matter content, it requires careful control of pathogens, heavy metals and other contaminants, in order to protect ecosystems and human health. In this study, we conclude that decision-making processes should take into account life-cycle assessments of sludge management alternatives, comprehensive comparisons of technical, environmental, economic and social aspects, environmental justice considerations, sustainability, governance, and integrated water resources management (IWRM). Such an integrated approach can support safer and more locally appropriate resource recovery pathways, while taking into account factors associated with regional conditions and regulatory frameworks.