Nutrients, Fe and bacterial removal in sub surface flow constructed wetlands treating polluted mine water

Abstract

A study was carried out to compare the performance of a pilot scale subsurface flow constructed wetland system to treat polluted water in Ragama prison quarry, an abandoned mine pit Two cement sand tanks with the dimensions of 7.5 m * 0.75 m x 0.75 m were constructed. Both the tanks used a mixture of aggregates as the substrate, where 40-60 mm was used in the treatment zone and both 20-30 mm and 40- 60 mm was mixed in the ratio of 1:1 in the inlet and outlet zones. Typha Latifolia (T.Latifolia) was planted in one tank, while the other was kept unplanted as the control. The initial plant biomass density was 1.7 kg/m2. Each horizontal subsurface flow bed is fed continously with polluted water at 173 litres per day and the retention time was maintained as 8 days. Concentration of nitrate, nitrite, ammonia, total and ortho phosphate, Fe and faecal coliform in the influent and effluent of the wetland system were monitored daily and their removal rates were determined. Nitrites, nitrates, phosphorus and Fe removal.in planted tank varied between 45%-80% whereas it was between 40%-70% in the unplanted tank. Removal efficiency of free ammonia in planted system was 6 % less than that of unplanted tank .However, bacterial removal in both planted and unplanted tanks were similar being 51%.