Design and simulation of a constructed wetland to treat the tail water runoff from Mubuku irrigation scheme.

Abstract

Tail water is the excess water that runs off the field at the low end of furrows, boarder strips, basins and flooded areas during surface irrigation. Tail water is loaded with agrochemicals like fertilizers, pesticides, herbicides and insecticides. Farmers apply fertilizers to boost crop yields, but not all the fertilizer applied is utilized by plants. Some of the excess chemicals are washed to irrigation canals during irrigation or rainfall and conveyed downstream. Mubuku irrigation scheme tail water is discharged into river Sebwe which has posed a health threat to the community that draws river Sebwe water for domestic use. For example, the presence of' nitrate (from fertilizer) in drinking water at concentrations greater than 50 mg/l could cause methaemoglobinaemia in babies aged less than 6 months (WHO, 1998). In addition, nitrate in the alimentary canals of humans may react with amines to form carcinogenic nitrosamines, which could contribute to the development of gastric cancer. The tail water from Mubuku irrigation scheme. was quantified and characterized to aid in the designing the constructed wetland treatment system. Design and simulation of various components of the constructed wetland like filter media, inlet and outlet pipes, drainage system, vegetation and liner was done using the given relevant formulas. From the research 319.68m 3 of tail water are being discharged from Mubuku irrigation scheme to river Sebwe per day with chemical and biological characteristics of BOD[248mg/l], TN[248mg/1], TP[248mg/l], COD[248mg/l] hence need for treatment before discharging to river Sebwe.