Efficiency of constructed wetland systems cultivated with black oats treatment of domestic sewage

Abstract

The objective of the present work was to evaluate the efficiency of a constructed wetland system cultivated with black oat (Avena strigosa Schreb) for the treatment of domestic sewage effluent from a septic tank, with emphasis on removal of carbonaceous matter, nutrients (N, P and K) and sodium. The experiment was conducted in four constructed wetland system (CWS) with horizontal subsurface flow for secondary/tertiary treatment domestic sewage. The CWS 1, 2, 3 and 4 received, respectively, organic load rates (OLR) of 100, 200, 400 and 600 kg ha -1 day -1 of BOD. Average efficiencies for removal of BOD, COD, total nitrogen, phosphorus, sodium and potassium were, respectively, 69.5, 70.2, 17.8, 26.2, 14.9 and 16.6%. Low efficiency in the removal of nutrients (N, P and K) was due a high OLR applied which provided also a large input of nutrients to the system. Sodium removal efficiency was low because it is a highly soluble ion and is poorly absorbed by plants. In general, lower OLR result in greater pollutant removals from the domestic sewage.