Determination of treatment and hydraulic efficiency of the ‘Gravel-Vermiculite-Bagasse’’ composite horizontal subsurface flow constructed wetlands

Performance of ‘Gravel-Vermiculite-Bagasse’’ substrate medium was investigated. This was done by investigating treatment and hydraulic performance of this substrate composition, in polishing maturation Waste Stabilisation Ponds effluent. In this study, pilot scale subsurface constructed wetlands consisting of four units each of size 0.35 by 1m by 0.45 were used. The four cells were packed with gravel, vermiculite and bagasse in different ratios. Cattails were then planted in all the cells. The influent water quality varied slightly over the sampling period. Suspended solids varied from 44 to 260 mg/l, BOD5, varied from 65 to 196mg/l; dissolved oxygen varied from 11.24 to 5.76 mg/l, pH from 7.37 to 9.35 and temperature from 28.1 to 38.40C. with the exception of a few days of heavily rainfall, influent water quality parameters were consistently lowered. The study indicated that addition of vermiculite and bagasse resulted in increased removals of the pollutants under study. A mathematical model for Bod5 was developed to help predict the expected performance of constructed wetland units with similar characteristics as the set-up used in this research. The study also indicated that addition of vermiculite to gravel slightly lowered the hydraulic conductivity of the substrate used.