A Review on Sludge Management Options in Small Communities Based on Different Wastewater Treatment Alternatives

Sludge management represents a critical challenge in wastewater treatment, particularly for small communities in developing countries where technical and economic limitations hinder the implementation of conventional treatment systems. This review aimed to evaluate sludge management options in small communities based on different wastewater treatment alternatives, addressing environmental and health implications. Wastewater treatment methods in small communities were categorized into three groups based on sludge production: sludge-less (including subsurface constructed wetlands, trickling filters, and intermittent sand filters), low-sludge (including septic tanks, biogas settlers, anaerobic baffled reactors, and anaerobic filters), and high-sludge (including conventional activated sludge-based systems, rotating biological contactors, and membrane bioreactors). The findings revealed substantial variations in sludge quantity across different treatment processes, with conventional activated sludge systems producing the highest sludge volumes while constructed wetlands and trickling filters generate minimal sludge. Two main sludge management approaches—centralized and on-site—were identified, with on-site methods such as planted sludge drying beds and sludge treatment wetlands offering more suitable options for small communities due to their lower operational and energy requirements. However, health and environmental concerns, including pathogen content, heavy metals, nutrients, and potential groundwater contamination, necessitate proper sludge stabilization before agricultural reuse. This review provides essential criteria for sludge management in small communities that support decision-makers in selecting appropriate options based on local characteristics and emphasizes the critical influence of wastewater treatment method selection on sludge management outcomes in rural areas.