Analyses of particles in raw waters containing iron and organic carbon

Many impurities in water supplies exist in the form of particles, which are removed in the water treatment process. In this study, the size of particles in raw water containing iron and organic carbon was measured. Methods for the separation of these particles from suspension were suggested based on the measured particle sizes. Samples from a groundwater and a surface water supply were analysed. The sizes of the particulates were measured with microscopes and particle counters. The groundwater studied contained about 7 mg L(-1) of iron and particles with a mean size of 7.8 microm. The particles in the surface water, with an iron content of 0.45 mg L(-1), were smaller with a mean size of 1.5 microm. The size of particles in surface water increased about eight times during quiescent settling; this increase of the particle size was not observed in the groundwater. The large size of the particles identified in the groundwater suggested direct filtration as the optimal method for their removal. Batch tests were completed with three types of filter media, preceded by oxidation with ozone. The effective size of the filter media used varied from 0.3 to 0.8 mm. In the filtration, 99-95% of the iron was removed, confirming that the particles formed in the groundwater after oxidation were large enough to be removed by direct filtration.