BOD5 dynamics in three vertical layers in free-water surface wetlands

Abstract

This paper introduces a first-order variable residence time (VART) model, the so-called BOD-VART model, to estimate the biochemical oxygen demand (BOD) in built wetlands with a free-water surface. The BOD-VART model mathematically designs a free-water surface wetland into three vertical layers: the vegetated water column layer, the upper root layer dominated by advection, and the lower root layer dominated by diffusion. It also biogeochemically simulates various processes and mechanisms of BOD removal, including mass transfer between the layers through advection, dispersion, and diffusion. The inclusion of a dynamic diffusion-dominated root zone is a unique feature of the BOD-VART model. In this study, the BOD-VART model was tested using data obtained from the Lake Manzala Engineering Wetland, Egypt. The test results showed that the determination coefficient and root mean square error values were 0.74 and 1.97 mg/l, respectively. The BOD-VART model is a reliable and efficient instrument for modeling designed wetlands and determining the effect of different mass transfer processes on the treatment elements in developed wetlands.

Keywords

• BOD5 removal processes
• Constructed wetland
• Residence time