Removal of pollutants (COD, TSS, and NO3−) from textile effluent using Gambusia fish and Phragmites australis in constructed wetlands

Abstract

In developing countries, the discharge of polluted effluents into the environment has caused environmental problems. For this purpose, constructed wetlands are attracting great concern owing to their low cost and less operation and maintenance requirements. The main aim of this work was to study the effectiveness of constructed wetlands utilizing Phragmites australis plants and Gambusia fish in the treatment of textile effluent. The constructed wetlands are located in the eastern part of a wastewater treatment plant near a grit chamber unit. This research was carried out in four polyethene rectangular tanks with a capacity of 80 L. The tanks were filled to about 20% with sand with a porosity of 48% and the diameter of the gravel bed used in the horizontal sub-surface flow unit varied between 5 and 25 mm. The results of different tanks showed the highest and lowest removal efficiencies of chemical oxygen demand (COD) were in the tanks containing Phragmites australis/Gambusia fish and Phragmites australis, respectively. The best tank for the removal of total suspended solids (TSS) was the tank containing the Phragmites australis and the Gambusia fish. In the tank containing the Phragmites australis plants, the removal efficiency of NO3−, COD, and TSS was in the range of 40–70, 68–72, and 49–71%, respectively. The maximum increase of nitrate, approximately 78%, was observed in tank 2, which contained only fish. In the control tank, the removal efficiency of NO3−, COD, and TSS was in the range of 0–10, 10–18, and 15–25%, respectively. The results of this study showed that if these systems were properly designed and operated, they could be used to treat various wastewaters, especially in developing countries.