Electrochemical Removal And Kinetics In The Removal Of Fluoride From Underground Water In Kenya
Maganga, Justin Kambale (1); Ulrike, Feistel (2); Stuede, Grit (2); Matata, Koti (1); Kasomo, Ricahrd (1)
1: Taita Taveta University, Kenya; 2: HTW Dresden University, Germany
The geology of Kenya makes it one of the countries in the World where fluoride (F) occurs in high concentrations, not only in rocks and soil, but also in surface and groundwater. The highest water F concentrations occur in certain springs, boreholes, and some lakes in the Rift Valley. With the rapid growth of Kenya’s population that stands at 38 million, it has become increasingly difficult to find sufficient fresh water supplies that are fit for human consumption. It is estimated that 19.5% of groundwater contain F concentrations above 5 mg/L. Fluoride levels above 1.5 mg/L leads to skeletal and dental fluorosis, cases which are common in parts of Western Kenya, Rift Valley and Central Provinces. Batch tests were conducted using standard NaF solution to investigate the electrode distance, electrode area, initial pH of the treatment solution, conductivity of the treatment solution, time, initial F concentration, current, influence of filtering during the process and the electrode performance. The optimum inter electrode distance obtained was between 12 mm and 25 mm. An electrode surface area of 20 cm2 and 60 cm2 and 100 mA direct current, had no significant change in F removal. The optimum pH was between of 4 and 6 due to the amphoteric character of Al (OH)3. Addition of 50 mg/L NaCl supporting electrolyte led to 43.3 % more F removal than the control and reduced specific energy by 44.6%. Results proved that the adsorption process of F and Al (OH)3 obeys a second order reaction. The applied Lagegren model confirms that the rate constant increases with increasing initial fluoride concentration. Between 4.5 mg/L and 44.0 mg/L initial F concentration, which is about tenfold higher, the rate constant increases by 24. The amount of F removed increases with increasing current. This correlation is only linear for short treatment duration and small cell area-to-volume-ratios (C/V). The filtration of the precipitate after 30 min increased F removal efficiency of a 60 min treatment process by 19 %. However, electrode performance reduced by 6 % within 20 h of operation due to increased electrode surface caused by pitting. The optimum results have been used to fabricate a prototype flow reactor that uses solar photovoltaic energy that will be used in the rural communities in Kenya. This technology is reliable as it uses renewable solar energy which is friendly and cost effective.