Macrophyte-Assisted Vermifiltration for Wastewater Treatment

Fresh domestic wastewater was obtained from a household septic tank within the Oforikrom sub-metro in Kumasi Metropolitan Assembly (KMA) located in Ghana. Three different macrophytes and two different earthworm species (based on their availability) were used in the study. The macrophytes consisted of Water Hyacinth (Eichhornia crassopes), Water Lettuce (Pistia stratiotes) and Duckweed (Spirodela sp.) while the earthworm species consisted of Eudrilus eugeniae and Eisenia foetida. Six different MAV experimental treatment setups were then constructed. The setups were labelled HE, LE, DE, HF, LF and DF. Thus, HE had Water Hyacinth and Eudrilus eugeniae, LE had Water Lettuce and Eudrilus eugeniae, DE had Duckweed and Eudrilus eugeniae, HF had Water Hyacinth and Eisenia foetida, LF had Water Lettuce and Eisenia foetida and DF had Duckweed and Eisenia foetida. A setup consisting of an empty barrel, which only contained the wastewater to mimic the conditions in septic tanks, was labelled as the control. The macrophytes used were obtained from a stream and cultured in tap water for 24 hours following the procedure used in [22 (link)]. About 0.25m² patches of cultured macrophytes were stocked in the macrophyte chamber of the experimental treatment units following the stocking density described in [23 (link)]. The earthworm species used for the vermiculture were obtained from a breeding stock cultured in the laboratory at a temperature of 25°C. The macrophyte chamber and the vermifilter bed of each setup were constructed with 60.0 cm³ polyethylene terephthalate barrels following design specifications described in [17 (link)]. Schematic diagram of the setup is presented in Fig 1. The vermifilter bed had three layers. The top layer (50 cm thick) was made up of coconut coir (6–8 mm) as a bulking material with an empty space of 5 cm at the top for aeration purpose. The middle layer (55 cm thick) consisted of sand (1–2 mm, 10 cm thick), gravels (6–8 mm) and matured vermicompost as a substrate. This middle layer housed the earthworm packing bed where four hundred and fifty (live weight ~255–275 mg) clitellated earthworms species were added, following the stocking density used by [24 (link)]. The bottom was the supporting layer and consisted of coarse layer of lateritic hardpan gravels (12–14 mm, 15 cm thick). The experimental setups were allowed to acclimatize for seven days before the start of the experiments. The wastewater was pumped into the macrophyte chamber using a 0.5HP single stage laboratory vacuum pump at a hydraulic loading rate (HLR) of 0.339 m³ m^-2 d^-1. HRL is critical for the optimal treatment performance of MAVs and this HRL used was suitable to prevent clogging in the treatment setups. Infiltration of effluents from the macrophyte chamber through the vermibed occurs by gravitational flow in a vertical flow system (VFS) through a showerhead of 1–2mm perforations for its uniform distribution. Following the sampling procedures in [1 ,17 (link)], effluent samples after macrophyte chamber and vermifiltration were collected every 48hours for two weeks for physico-chemical, pathogen and helminth analysis.