The rationale for using constructed wetlands for treating wastewater is that wetlands are naturally among the most biological active ecosystem on earth. The aim of the study was to determine the impact of shorter retention time on the performance of constructed wetland in terms of Chemical Oxygen Demand (COD) and other elements removal. The application of wastewater with retention time of seven days as well as the evaluation of water quality after treatment at Goudini experimental wetland was carried out throughout the year. The results had shown an overall average COD removal of 60% throughout the year. Results also showed reasonable removal of other elements namely; potassium, pH, nitrogen, electrical conductivity, calcium, sodium, magnesium and boron from the wastewater by constructed wetlands. The results showed low COD removal during July until September after which it improved tremendously. The reason for low COD removal during first three months could be attributed to the fact that there was no gradual increase of wastewater application to the wetlands i.e. from 4,050 litres per day to 8,100 litres per day. The results had showed that constructed wetland as a secondary treatment system is effective in terms of COD and other elements removal from winery and distillery wastewater. COD removal throughout the year was 60% with seven days retention time. When compared with previous studies that showed 80% COD removal within 14 days retention time, therefore the 60% removal is very critical to wine industries as more wastewater will be applied to the system.
Keywords: COD, constructed wetlands, plants, retention time, wastewater