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Use of Ozone as an Aid to Coagulation/Filtration

American Water Works Association Research Foundation, 9/1/88-2/28/91

Students: Orren Schneider, Ashish Paralkar, Karin Franklin, James Walsh, Geoffrey Baldwin & Michael Fox

The purpose of this study was to ascertain which physical and chemical aspects of raw water quality determine a water's susceptibility to the coagulating effects of ozone; and to the extent possible determine the mechanisms by which ozone improves subsequent coagulation or filtration. The ultimate goal of this study and others like it was to develop a relationship between raw water quality and optimum conditions for ozone/coagulation/settling and ozone/direct filtration.

Proposal, Plans and Reports

  • Progress Reports: #1, #2

Project Data


Conference presentations based on this work

Theses/Dissertations based on this work


Additional Background: The use of ozone in U.S. drinking water treatment plants has grown rapidly in recent years. The stimulus for this growth is the need to comply with new and more stringent water quality regulations, along with a new appreciation for the beneficial effects of ozone treatment. One of these effects that often appears prominently in evalutions of ozone is its impact on subsequent coagulation and filtration. While many have reported improved performace in conventional and direct filtration plants, some studies have shown no significant effect or even a detrimental effect.

Both bench-scale and pilot-scale treatment studies were conducted in this research. Bench-scale experiments were performed on real waters and model systems (Phases I and II, respectively) with the goal of identifying those raw water constituents that are important in determining the coagulating effects of ozone. Once this was completed, some more fundamental studies aimed at further elucidating the mechanisms were initited (Phase III). The investigation of preozonation with direct filtration required that pilot scale studies be conducted (Phase IV). These were performed at the West River Filtration Plant (New Haven, CT), which has a low alkalinity surface water supply.
Phase I studies comprised conventional jar testing of raw and ozonated waters from four diverse sources. This work showed that the effects of preozonation on subsequent coagulation are highly specific to the coagulant used, the raw water quality and the criteria used to judge coagulation. In this phase and later phases of this research, preozonation was observed to improve coagulation with a cationic polyelectrolyte, but not with alum. Preozonation was also found to improve turbidity removals, but not removal of organic matter as measured by ultraviolet absorbance.

Phase II and III experiments were conducted on carefully prepared model waters containing turbidity in the form of either a clay suspension, or an algae suspension. The composition of these waters was modified systematically, and standard jar test procedures were used to assess ozone's effects on coagulation. Studies with the inorganic colloid (i.e., clay) water showed the importance of organic functionality and charge on requisite polymer dose. These experiments also demonstrated the importance of calcium and iron concentration on the coagulating effects of ozone. Work on the organic (i.e., algae) colloid system showed that ozone affects the stability of algal cells in a species-specific manner. Ozone caused a visible change in the reticulate layer in Scenedesmus which ultimately led to a higher rate of flocculation and greater removal in laboratory jar tests. In contrast, ozone had little apparent effect on Chlorella.

Phase IV comprised the direct filtration field studies. The 10 gpm dual train pilot plant at South Central Connecticut Regional Water Authority's West River Filtration Plant was used to test some of the findings of the earlier phases. Both a cationic polymer and alum were examined at varying doses, with and without ozone. In several experiments the raw water was amended with calcium. The train incorporating preozonation consistently showed lower filtered water turbidities than the no-ozone control. In most cases, the optimal polymer dose for turbidity removal was also lower for the ozone train than for the no-ozone control. Addition of calcium had a smaller effect on polymer dose as compared to the model water experiments.

Six graduate students were responsible for conducting all laboratory experiments in connection with this research. Their specific contributions are identified below:

  • Geoffrey Baldwin - Phase IV, inorganic colloid system
  • Michael Fox - Phase I
  • Karin Franklin - Phase I; Phase II & III, inorganic colloid system
  • Ashish Paralkar - Phase I; Phase II, III & IV, organic colloid system
  • Orren Schneider - Phase I
  • James Walsh - Phase IV, inorganic colloid system; Field Studies



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