THE EFFECTS OF AQUATIC HUMIC SUBSTANCES AND OZONATION ON THE STABILITY OF PARTICLES (COAGULATION, FULVIC, OZONE, ALUMINA, IRON).

摘要

Ozone is widely used in drinking water treatment in Europe, and interest in this process is growing in the USA. Reports in the literature indicate that ozonation of raw water can lead to reductions in turbidity and particle concentrations, and reduced chemical requirements for particle coagulation. Little is known about the mechanisms and factors that contribute to these beneficial effects of pre-ozonation on the coagulation process. The majority of the evidence presented in the literature suggests that the reactions of ozone with natural organic substances present in solution, or adsorbed on particles, may play an important role in explaining these observations.; The objective of this research was to investigate, under well-defined and controlled experimental conditions, the effects of humic substances on particle stability, and the influence of ozonation on the stability of particles coated with humic material. The stability of the particles was assessed by estimating collision efficiency factors ((alpha) values) from coagulation rate experiments, by monitoring particle volume distribution during coagulation, and by electrophoretic mobility measurements. Alumina particles were exposed to fulvic and humic acids extracted from Bay Tree Lake (former Black Lake) in NC. Various organic carbon loadings and ozone doses were investigated. Some of the experiments were performed in the presence of iron.; Fulvic and humic acids were found to greatly reduce the coagulation rate and alter the electrophoretic mobility of the alumina particles, with the humic acid being more effective in stabilizing the particles. These effects were observed even at low organic carbon loadings (around 0.10 mg C/m('2) of Al(,2)O(,3)).; The stability of the alumina particles coated with fulvic and humic acids was not significantly affected by ozonation in the range of ozone doses commonly employed in water treatment plants. Thus, the beneficial effects of ozonation on coagulation do not seem to be associated with the disruption of organic coatings on particles by ozone. However, when the ozonations were performed in the presence of iron, ozone considerably reduced the stability of humic acid-coated particles.