Potential of ecological water treatment elements to reduce pollution of river water used for urban agriculture in Addis Ababa, Ethiopia

Abstract

Cities in developing countries, such as Addis Ababa, face enormous challenges as a result of high demand for food and clean water, as well as the generation of large amounts of urban waste that is discharged into natural water bodies, contaminating rivers, lakes, and other freshwater bodies used in urban agriculture. Farmers in Addis Ababa and nearby areas use polluted irrigation water diverted from the highly contaminated Little and Great Akaki rivers. The study aimed to assess how well a floating treatment wetland with vetiver grass could reduce irrigation water pollution at the Mekanisa-Gofa-Lafto Cooperative (MGLC) farm in Addis Ababa, Ethiopia. Additionally, the study sought to provide design recommendations that could be implemented at the farmer level. The irrigation water underwent a 7-day treatment using a Vetiver grass floating treatment wetland. A field test was also conducted to evaluate the effectiveness of the floating treatment wetland in reducing pollutants at the study site. The results showed that the floating treatment wetland was able to reduce the Biochemical Oxygen Demand (BOD) (73.68%), Chemical Oxygen Demand (COD) (73.92%), Acidity/Basicity (pH) (0.39%), Chloride (Cl−) (43.12%), Total Hardness (66.56%) and Total Suspended Solid (TSS) (96.21%) values, approaching the recommended irrigation water quality guideline values within 3 days. In contrast, there was an increase in Electro Conductivity (EC) (22.2%) and Sodium (Na) (15.2%) concentrations, which exceeded the recommended values, due to evapotranspiration or the entry of the surrounding soil into the irrigation water of the study site.