Vertical-flow constructed wetlands as an emerging solution for faecal sludge dewatering in developing countries

Yard-scale experiments aiming at assessing the suitability of vertical-flow constructed wetlands to dewater faecal sludge (FS) were conducted in Yaoundé (Cameroon). During 6 months, beds vegetated either with Cyperus papyrus L. or Echinochloa pyramidalis (Lam.) Hitchc. & Chase were fed under constant solids loading rates (SLR) of 100, 200 and 300 kg TS (total solids) m2/year. Physicochemical parameters of raw FS and percolate as well as the dewatering efficiency of each bed unit were monitored weekly. Results showed that, despite the high loading rates, the beds’ pollutant removal efficiencies were more than 78% for the parameters considered and were not affected by the SLR or the macrophyte types. Beds loaded at 100 kg TS m2/year rarely clogged with an average dry matter content ≥ 30%. However at SLR ≥ 200 kg TS m2/year, the occurrence of clogging was higher in the papyrus beds than those of E. pyramidalis. Approximately 30–40 cm/year of sludge will be accumulated in beds loaded at the lowest SLR against 50–70 cm/year at 200 kg TS m2/year and more than 80 cm/year at 300 kg TS m2/year. These promising findings suggest the system as adequate for further investigation at real scale for FS dewatering in the context of developing countries. [authors abstract]