Low-cost onsite selection of suitable unplanted sand drying bed structure for faecal sludge treatment in less developed countries: A case study of Yaounde in Cameroon

Abstract

There are lots of drying bed structures in the literature that are planted or unplanted but few indicate reasons behind their choice. As this technology is widely spread in less developed countries, identification and analysis of selection criteria for appropriate unplanted faecal sludge drying beds are necessary. This article analyses a case study in Yaounde for domestic septage over three bed structures for which sludge and percolates parameters are analyzed and treatment performance assessed through 10 technical criteria using a low-cost infrastructure with a minimal footprint. These are related to mass and volume reduction, organic and mineral pollution, as well as drainage capacity. The bed structure used is constituted of gravel and sand with 20–30 cm thickness. These beds recorded more than 85% reduction in organic and suspended matter and a 70% reduction in nitrates and lead concentration with at least 38% of dissolved material and chemicals removed. Considering the suggested criteria, a bed with 20 cm of gravel and 20 cm of sand was found to be the most efficient for material and pathogens removal. This method provides an interesting selection option with low-cost infrastructure, material, and operation for popular selection of suitable faecal sludge treatment technology in less developed countries. HIGHLIGHTS Unplanted sand drying bed can remove 70–90% of organic and ion contaminants.; Drainage capacity of UFSDB ranges from 0.022 to 0.031 L/s m2.; The most suitable drying bed ensures drainage, contaminant removal, and dehydration.; 20-cm sand and gravel bed structure is the most suitable drying bed for low-concentration domestic septage.; Low-cost modules can be used to test drying bed structures in less developed countries.;

Keywords

• drying
• faecal sludge
• multicriteria
• selection
• treatment
• yaounde