Coagulation and Ozonation for Control of Natural Organic Matter and Disinfection Byproducts

Compagnie Generale des Eaux & Syndicat des Eaux d'Ile de France, 6/25/84-6/21/85

PIs: Bourbigot & Reckhow

The objectives of this research were to identify the most Important inorganic components of raw waters with respect to alum coagulation, and to assess their qualitative, and when possible, quantitative impacts on coagulation. Lab work was conducted at CGE's research affiliate, Anjou Recherche, in Maisons Laffitte, and at the Edmond Pepin WTP in Choisy-le-Roi.

Proposal, Plans and Reports

Project Data

  • Notebook
  • file with tables and figures


Presentations based on this work

  • Reckhow, D.A., "Aluminum Residuals Following Alum Coagulation, University of Massachusetts, September 20, 1985

Other UMass Projects Supported by CGE


Additional Background: In recent years many water treatment processes have been shown to or are suspected of producing potentially harmful byproducts. These concerns are associated with nearly all forms of oxidation and many adsorption and/or catalytic processes. Coagulation by aluminum salts has remained relatively unscathed by this controversy. This is still one of the most effective means of removing particles and dissolved organic matter. The only recognized health concern with Al coagulation is the possibility of elevated aluminum levels in the finished water. This, however, is easily measured and can be corrected if one knows the factors which control aluminum solubility.
Ideally one would prefer to have a more fundamental knowledge of the chemical factors involved in coagulation. That is those factors which make one raw water behave differently from another with respect to removability of particles, organics and aluminum. Given such a theoretical
framework, jar-tests might serve as a verification of treatability rather than a primary test. This could both reduce the uncertainty inherent in jar-tests as commonly practiced and alleviate the need to perform them on as regular a basis.

The major components of raw waters deemed to be important in aluminum coagulation of organics are inorganic ions, inorganic cations, algae and the nature of the dissolved or colloidal organics. While the nature of the clay particles are important with respect to their own removal, they seem to have little impact on the removal of natural organic material by trivalent metal ions.

Sulfate has been found to significantly lower the minimum pH of effective coagulation with aluminum while having little or no effect on the maximum pH of coagulation. These effects have been observed for suspensions of E coli, kaolin and aquatic fulvic acid solutions. Similarly, bicarbonate seemed to have the same benefical effect of widening the zone of coagulation toward the acid side. In contrast, phosphate and silicate effected a shift in both the upper and lower boundaries such that the zone of good coagulation was shifted into the more acidic range withouth widening. Based on concentrations commonly found in nature, Letterman proposed that sulfate, bicarbonate and silicate are the anions with the greatest impact on aluminum coagulation. Using a similar means of assessment one might expect calcium to be the most important cation in organics removal by aluminum. Recent studies have shown that calcium can have significant effects on the charge and adsorbability of aquatic fulvic acids.



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