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

Abstract

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) m−2/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 m−2/year rarely clogged with an average dry matter content ≥ 30%. However at SLR ≥ 200 kg TS m−2/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 m−2/year and more than 80 cm/year at 300 kg TS m−2/year. These promising findings suggest the system as adequate for further investigation at real scale for FS dewatering in the context of developing countries.

Treatment of Septic Tank Sludge in a Vertical Flow Constructed Wetland System

“…The solids loading rate obtained is lower than those reported in the literature, 125 to 250 kgTS/m².year (Koottatep et al, 2004) and 100 kgTS/m².year (Kengne et al, 2011), and can influence the quality of the percolated and post-treated liquid, as well as in the dewatering of accumulated sludge.…”

“…Such increase in solids content indicates that the dewatering step occurred expressively in the CW. In tropical regions, according to Kengne et al (2011), it is possible to achieve a percentage of dry solids of at least 30% in the treatment of sludge from septic tanks in CW. The application of the sludge in the CW was carried out weekly, there was no withdrawal of the accumulated material and the energy consumption was minimal.…”

Dewatering and Treatment of Septage Using Vertical Flow Constructed Wetlands

“…However, the relatively poor dewatering through drainage implies that a longer period may be required to eliminate water content through evapotranspiration, which highly relies on the local climate of the treatment plant. This explains why the SLR in tropical regions [12,23,24] could be higher than those in the temperate region [9,10,17]. As the duration of resting period is determined by the time needed to dry up the sludge deposit, a longer resting period actually reduces the overall productivity of the system.…”

The Improvement of Anaerobic Wastewater Treatment With Structured Media Growth System

“…In the WWTP of type B, the subsurface constructed wetland or dewatering performance depends on a variety of factors related substrate type, plants type, the maturity of beds, the climatic factors, the sludge characteristic as well as operational factors (hydraulic loading rates, solids loading rates, frequency of beds feeding, etc.) (Kengne, 2011). The effluent quality of type B can meet USEPA standard for water reuse of fish pond or agriculture irrigation that BOD should less than 30 mg/L, turbidity less than 2 NTU and TSS less than 30 mg/L.…”