IRON REMOVAL FROM GROUNDWATER BY GRAVEL BASED AERATION: THE CASE OF BONGA TOWN, ETHIOPIA

Abstract

Iron is present naturally in groundwater that its metallic ions at excessive amounts contribute to a rusty taste and reddish color to the water. The concentration of iron in groundwater is a serious problem in Bonga Town, which is usually greater than the WHO limits set for human health of 0.3mg/l. The main aim of this research was to investigate the removal of iron from groundwater by gravel-based aeration techniques. To study the removal efficiency the effects of gravel size, gravel-bed depth, initial iron concentration, and detention time were varied. The synthetic water sample containing iron ions were prepared and oxidized by oxygen with a form of distributing over the gravel bed. The mean physicochemical parameters of the Bonga Town borehole water sample were found within the range of acceptable limits set by the WHO recommended standard except for the DO, turbidity, color and iron concentration. The result showed that the initial iron concentration in the sample water was 2.2 mg/l and the final concentration of iron after aeration was 1.28 mg/l, 1.18 mg/l, 1.04 mg/l and 0.78mg/l with a removal efficiency of 41.88%, 46.33%, 52.92%, and 64.60% for gravel size 2-5, 5-8, 8-12, and 12-18mm respectively at 60cm gravel depth. Based on the result obtained this method of iron removal is effective as the removal efficiency increased with larger gravel size, thicker gravel bed, higher detention time, and lower influent concentration of iron. A maximum iron removal efficiency of more than 85% was achieved at the optimum gravel size of 12-18mm and bed depth of 60cm at 60min detention time while the optimum concentration was found to be 1.0mg/L with average filtration rate of 0.12m 3 /m 2 /min. As a result, the system performed relatively well on reducing iron from water and the evaluation of aerated water quality shows overall improvement on water quality. Thus, since gravel is cheap and easily available in locally, it can be concluded that the gravel-based aeration, is an efficient and cost-effective approach which has the potential for removing iron from groundwater