Oxygen transfer rate and BOD removal efficiency of constructed wetlands with dependence on construction

Abstract

Most cases of wastewater treatment involve three main types of constructed wetlands (CW). They are freewater surface wetlands (FWF) and subsurface flow CW including filters of vertical flow (SVF) and horizontal flow (SHF). The objectives of the article deal with the summarization of the data received from the investigations in Lithuania and the evaluation of constructed wetlands performance of different construction. The analysis of the filters’ efficiency was performed due to the estimation of the filter load for analysed pollutants and their removed amount for an area unit. According to the removal efficiency of organic pollutants (BOD5) filters could be put into the following order: SVF – SHF – FWF. At the load of all filters, according to BOD5 4.0 g m-2 d-1 the following treatment efficiency 93.5, 77.5 and 42.2%, respectively was reached. This directly correlates with the oxygen transfer rate according to which filters are ranged at the following ratio: SVF : SHF : FWF – 1.0 : 0.6 : 0.3.