Effectivity of Vertical Sub-Surface Downflow Constructed Wetland System with Varying Composition in Reducing Chromium and Color in Synthetic Textile Wastewater

Abstract

Abstract-Textile and leather tannery wastewater pollute water bodies with their content of chromium metal (Cr) and synthetic dyes which are highly toxic. The use of constructed wetland systems is an approach to treat such wastewater before being discharged directly into the environment. This study was conducted to examine the effectiveness of vertical sub-surface downflow constructed wetlands with varying composition in decreasing Cr concentration and color thickness (value) in synthetic textile wastewater. Systems were varied by substrate composition and presence of the plant Leersia hexandra. Synthetic textile wastewater containing K 2 Cr 2 O 7 and reactive dye were flowed downward into five systems: (1) soil-sandgravel substrate, without plants; (2) soil-sand-wood chips substrate, without plants; (3) soil-sand-gravel substrate, and L.hexandra plants; (4) soil-sand-wood chips substrate, and L. hexandra plants; and (5) a system without substrate or plants as control. Chromium concentration and color thickness were measured at 8, 16, 24, 32 and 40 hours after treatment. Measurements at 8 hours showed that systems no. 1, 2, 3, and 4 decreased Cr concentration in effluent as much as 87,6%; 79,1%; 81,4%; and 89,2% respectively. Meanwhile Cr concentration in the control system's effluent remained relatively constant. Systems no. 1, 2, 3, and 4 decolorized the effluent up to 94,6%; 89,6%; 93,4%; and 86,0% respectively; meanwhile, color in the control system was unchanged. All four treatment systems could effectively reduce Cr concentration and color thickness in synthetic textile wastewater. However, results did not support the hypothesis that the presence of plants would significantly affect Cr removal, or that the addition of wood chips to substrate would enhance decolorization effects.