Phytoremediation of Primary Sewage in Vertical Flow Constructed Wetlands
The study examined the performance of pilot scale vertical flow constructed wetland in phytoremediation of primary sewage lagoon effluent generated from a tertiary institution. The experimental layout consists of four units, with each unit composed of three cells connected in series. Three of the units were vegetated while non-vegetated units serve as control. The cells are rectangular plastic beds of 1.2m x, 0.9m x 0.4m. Treatment areas were packed with gravel of 40, 10 - 25 and 2-10mm diameter respectively. Three cells were each planted with Rhynchospora corymbosa (RC) and, Coix lacryma-jobi (CL) while the third cell contains a mixture of the two plants. The fourth cell was left unplanted and serves as a control. All the cells were operated at hydraulic retention times of 4, 7, and 10 days. High reduction of COD, NH3, NH3-N and NH4 were observed in all the units. The unit with the lowest removal efficiency for these parameters was the control thus demonstrating the effectiveness of phytoremediation. Removal efficiency for the parameters considered range from 40 to 50% for RC and 50 - 53% for Coix. A TSS influent concentration of 6800 mg/1 was reduced by 86.1% to 268 mg/1 for HRT of 7 days and a further reduction of 96.3% for HRT of 10 days. Treatment efficiency as high as 76 to 100% was observed with increase in HRT from 4 to 10 days, for particulate phosphorus, PO4, NH4-N, NH4 and COD. The removal rate for most parameters increased with longer HRT. Results indicate that the combination of the two plants in the same reactor was not as effective as single plant in individual cells. Rhynchospora corymbosa and Coix lacryma-jobi plants reduced the pollutants in sewage, hence these could be effectively used in wetlands for the treatment of primary sewage.