Combining planted drying beds to maturation ponds at pilot scale for a comprehensive treatment of faecal sludge in Sub-Saharan Africa

Abstract

Hight birth rate in developing countries generates huge amounts of faecal sludge to treat at a given time. In sub-Saharan Africa, it is estimated that 95% of households are not connected to a sewerage system for excreta disposal and faecal sludge treatment plant almost absent, thus the necessity of developing cost-effective technologies to contain their harmful effect. In response to this preoccupation, pilot scale experiments combining drying beds to maturation ponds were conducted in Yaounde (Cameroon) for the treatment of faecal sludge. Raw faecal sludge was applied once a week at the load of 200 kg DM/m2/yr. on a 1 m2 section drying bed planted with Echinocloa pyramidalis plant for dehydration. The leachate obtained was subsequently polished in two shallow maturation ponds (50 cm depth) in series, following a varying hydraulic retention time (HRT) of 4, 7 and 10 days. Results showed the set-up to be effective at 10 days HRT in reducing significantly (p<0.05) nutrient and organic pollutants as well as faecal coliforms in the final effluent compared to 4 and 7 days. However, suspended solids removal remained inefficient due to high algal biomass. The performance of the system enabled the treatment to meet the requirements of the Cameroonian guidelines for discharge and reuse in non-restricted agriculture. These results constitute advancement towards a comprehensive treatment of faecal sludge with the perspective of reuse of the effluent. Validation of this treatment scheme at full scale is ongoing for its adoption and implementation in the Cameroon national sanitation strategy.