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Flocculation Effects of Ozone (OVERVIEW) 

Received for Review: 22 February 1993

Accepted for Publication: 5 November 1993

Study Synopsis

This paper was derived from other studies done by the author of this study, combined with results and conclusions from other literature and studies. The author noted, “There are numerous reports on coagulation/flocculation effects of preozonation, which cannot be interpreted by one single mechanism. About 7 basic processes are presently discussed.” Thus, this study was compiled in order to make some sense of the various studies by comparing like-findings.

Positive Findings from the Study

  • “Preozonation effects can be explained with algae flocculation, with the destabilization of particles, and with polymerization of the dissolved organics.”


  • When ozone was added to raw water, the following effects were observed:
    • “A direct aggregation of particles, measurable as a shift in the particle size distribution to larger diameters and by increases or decreases in turbidity.”
    • “Formation of colloidal or suspended particles from dissolved material.”

        NOTE: These effects are the same effects seen in soil when ozone is added to irrigation water: flocculation in the soil, and thus increased percolation.


  • “There are various reports that seasonal benefits of preozonation are most dominant in raw waters with elevated algae content, indicating either ozone action on algae cells or on their dissolved organic products.” NOTE: Ozone has the ability to get rid of algae, and in this study was especially effective at elevated levels of algae.


  • “Ozone can cause the lysis and destruction of algae cell walls.” NOTE: A definitive statement of ozone’s destruction of algae.


Negative Findings from the Study

The following statements suggest that there are many unknowns in the study that have caused either inconclusive or confusing results. None of the below statements affect the positive statements above, but they are informative regarding the difficulty of the study of ozonation.


  • “The major problem of all investigations has been the very limited knowledge about the chemical characteristics of the DOC (dissolved organic matter), often being of the fulvic and humic acid type or caused by algae products, and by the unknown types of particles.” NOTE: The study sees this as a problem because, for further filtration the chemical characteristics of the DOC need to be known. The positive fact the ozone eliminated algae in great amounts outweighs this unknown factor for use in irrigation water.


  • “The complexity of the systems studied (natural and model waters] and the present lack of methods to characterize the broad spectrum of polar, high molecular weight organics before and after ozonation, will limit our understanding of the mechanisms in natural waters. These problems lead to the necessity that time and money-consuming tests will be required in studying the effects of ozone on particle and organics removal, especially as predictions for optimal conditions are fairly difficult to make.”NOTE: This comment refers to the difficulty in understanding the exact mechanism at-play. It does not refute the results seen (and noted in the section above).

Thoughts and Comments

Please note that the flocculation effects as discussed in the article are related to flocculation in water for the purpose of further filtration.  The findings above pulled from the study mostly cover general comments regarding preozonation effects that would apply to use in irrigation water. With drinking water, the filtration steps that follow ozonation are in some cases adversely affected by the preozonation because of the chemical properties necessary for some of these advanced filtration processes to work. As these continued processes are not necessary for irrigation water, the information in the study specifically related to further filtration after ozonation was not included in this overview.

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