Effect of feeding frequency on the performance of Compact Vertical Flow Constructed Wetland treating faecal sludge leachate under high hydraulic load

Abstract

The poor management of faecal sludge remains a crucial health and environmental concern in sub-Saharan Africa. The use of Vertical Flow Constructed Wetland (VFCW) as low-cost solution for the treatment of this special waste is possible if the hydraulic load and feeding operation are appropriate. This work investigates at a pilot-scale on the effect of fractioning the application of faecal sludge leachate from planted drying beds at the hydraulic loading rate of 150 mm/d into one, two and three batches per day once a week on the treatment efficiency of VFCW. Results showed no significant differences (P > 0.05) in performance between one, two and three batches per day for all the monitored parameters with the exception of faecal coliforms. Three batches at 5 hours’ intervals permitted to reach the Cameroonian guidelines for faecal coliforms discharge of effluent compared to two and one application daily, but not the overall nitrogen requirements. An effective treatment of faecal sludge can be envisaged: raw faecal sludge applied in batches on planted drying beds at 200 kg TS/m2/yr. followed by a subsequent treatment on VFCW planted with Echinochloa pyramidalis at a loading rate of 150 mm/d applied in three batches with at least 5 hours resting time between two feedings.

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Keywords: Faecal sludge, hydraulic loading rate, feeding frequency, Vertical Flow Constructed Wetlands, Echinochloa pyramidalis