Effectiveness of natural wetland in waste water treatment: a case study of tibia wetland, Limuru Municipality, Kenya.
Gitau, James Kinyua
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Information on wetland function in waste water treatment is very important as the information can be used to detect undesirable qualities of water. The aim of the study was to assess the effectiveness of natural wetlands in the treatment of waste water. The study was carried out for a period of four months (November 2012 to February 2013). The objectives of the study was to find out the physico-chemical parameters of water from Limuru water and Sewerage Company and Bata Shoes Company before entering the wetland and after passing through the wetland, and whether there was a significant difference between the physico-chemical characteristics of water before and after passing through the wetland. Sampling was done during the day and samples analyzed within four hours after sample collection. The parameters whose concentrations were determined included pH, electrical conductivity, temperature, BOD, TDS, TS, TSS, DO, phosphate, chromium and nitrate. Data was analyzed using Anova, Microsoft excel program, T-Test (2 tailed). The study revealed that for most of the parameters understudy there was a decrease in their concentration after the water passed through the wetland except for DO and pH. From T-Test (2-tailed) analysis, it was noted that there was a significant difference between the levels of BOD, TSS, TS, TDS, conductivity, Nitrate-Nitrogen, phosphate and chromium before entering the wetland and after passing through the wetland. DO and pH improved after the water passed through the wetland. The study revealed that the wetland played a role in the removal of pollutants where the best performance was obtained at TSS removal efficiency of 97.67%. BOD, Chromium, Nitrate, Total Solids, and Phosphate ranged between 50-96% while conductivity and Total Dissolved Solids were less than 50%. DO increased by 23.4% and pH changed by -0.79% hence the effluent water was less acidic as compared with influent water. BOD failed to meet the required NEMA and General standards even after passing through the wetland. The study concluded that Tibia wetland was effective and had potential in treatment of the waste water from the discharging facilities. It is recommended that wetlands can be conserved and used as waste water treatment facility instead of regarding them as waste land. Measures should be put in place to improve the final effluent quality to ensure that the levels of the parameters in the effluent are within the permissible limits. For further research, the plants dominating the study site be studied so as to find out how they reduce the physico-chemical parameters in waste water and to see if they can be recommended for use in other treatment sites.