Evaluating the performance of faecal sludge dewatering technologies in urban settings of developing African countries: a review.

Inadequate dewatering technologies are reported as the dominant challenge in handling faecal sludge (FS) within urban settings of most African countries. Studies have been carried out to evaluate the efficiencies of unplanted sand drying beds (USDBs), decentralized wastewater treatment systems (DEWATS), and geo-tubes. However, limited information is available on comparative capabilities in dewatering the FS. This work reviewed treatment efficiencies by assessing the reported actual waste removal capacities and ascertaining if they align with the design removal provisions. Peer-reviewed papers, books, and technical reports from trusted sources were examined. The results show that all the technologies perform best in dewatering the FS; however, USDBs are widely adopted for city-wide treatment, and the other two are suited for decentralized communities. The USDB is challenged by frequent clogging and poor quality of dewatered sludge when reused or recycled in the production of solid fuel and compost due to sticking sand after sludge harvesting. The DEWATS and geo-tubes increase operational costs when used to treat the FS at a large scale. More studies should be conducted to explore locally made, cost-effective filter media and technologies to enhance the dewatering quality and quantity of the FS and increase the quality of recycled by-products. HIGHLIGHTS: This paper reviewed the capabilities of sand drying beds, decentralized wastewater treatment systems (DEWATS) and geo-tubes in dewatering the faecal sludge (FS). All reviewed dewatering technologies significantly reduce the solid concentration of faecal sludge, so they perform best in dewatering the FS. Sand drying beds are considered a suitable technology for city-wide sanitation management, the other two are best suited for decentralized communities. Although sand drying beds are viewed as the most promoted and adopted city-wide dewatering technology, they face clogging and poor quality of harvested dry solids for reuse and recycling purposes. More studies on alternative filter media and/or technologies are urgently needed. If the filter media is in contact and or is removed together with dry sludge during harvesting, then the media should be organic so that it enhances the quality of reused or recycled byproducts. [ABSTRACT FROM AUTHOR]