EFFECT OF ALUM COAGULATION ON IRON REMOVAL IN AERATED GROUNDWATER USING RAPID SAND FILTERS

Abstract

The oxidation process of dissolved iron particles in water changes the iron into red-brown solid particles (particulate), which settle down in the water. Those large particles that settle down in the water can be handled. Nevertheless, iron that does not procedure large enough particles to settle down remains suspended (colloidal iron) and thus leaves the water with red tint. Unfortunately, these particles threat the industry and the municipal of water supplies. This is due to formation of scales as well as blockage of water pipes that lead to economic problems. Numerous studies have been conducted to study the effect of using oxidation processes followed by the filtration process only for the removal of iron from water. This study introduces a comparison of filtration of aerated raw water though a filter of sand bed with and without Alum as a coagulant prior to filter. A synthetic iron dozes are added to tap water to represent a predetermined different concentrations of iron as 2 and 3 mg/L which result in 14 and 32 NTU, respectively, after aeration of raw water. The effluent of water was taken at regular time intervals to monitor the progressive rate of removal of these elements for different values of filtration rates 120, 180 and 240 m 3 /m 2 /day. A single layer gravity rapid sand filter was used with sand bed of 70 cm thickness, effective diameter of 0.7 mm and uniformity coefficient of 1.57. During the experiments, the iron concentration and turbidity in the effluent were recorded at all the used filtration rates. The results show that the low limit of the removal efficiency of iron is 89% and the high limit is 97% without coagulation and 78% to 97% with coagulation. Also, the higher the concentration of iron and turbidity, in the influent, the higher the efficiency removal of filter for all filtration rates takes place. For all tested parameters of influent iron concentrations and filtration rates, the effluent iron concentrations and effluent turbidities within the allowable limits of Egyptian drinking water specifications (0.3mg/l for iron and 1.0 NTU for turbidity), except for filtration rates exceeds the 180m3/m2/day the turbidity was above these allowable limits for both cases using coagulant or not. It obvious, also, from experiments that at low concentration of influent iron (below 3 mg/l) and filtration rates up to 180m3/m2/day there is no need to coagulation process.