Efficiency of ozonation followed by filtration through a biologi-cally active adsorption bed at removing biogenic organic substances from surface water

Abstract

Water entering the plant varies significantly in the content of total organic carbon and its fractions. The treatment train includes coagulation, sedimentation, rapid sand filtration, ozonation, biofiltration, disinfection and alkalization. The study aimed at assessing the applicability of ozonation, followed by biological filtration, to remove organic substances from surface water. Upon coagulation, sand filtration, ozonation, adsorption onto a biological activated carbon filter (BAF), and disinfection with chlorine and chlorine dioxide, water samples differed considerably in organic matter content before ozonation, as well as before and after biofiltration. The ozonation process brought about a reduction in total organic carbon and dissolved organic carbon concentrations, which was concomitant with a significant increase in the concentrations of biodegradable dissolved organic carbon fractions and in assimilable organic carbon. This may be attributed to the transformation of non-biodegradable substances to lower molecular weight compounds that are easier to assimilate by the microorganisms normally colonizing an adsorption bed. Even though the substances that originated from the ozonation process were effectively removed during biofiltration, the extent of removal was still insufficiently high to provide desired biological stability of the water. A benefit of biofiltration was efficient removal of refractory substances as a result of adsorption. The efficiency of the ozonation and biofiltration processes at removing organic substances increased in proportion with the increase in their concentrations in the water being treated.