Potable Water Treatment Plant Research Articles

Improvement of Ozone Oxidation and Disinfection Design

For a long timei the aim of ozonation has been the improvement of the organoleptic qualities of treated water. Disinfection! and particularly virus inactivationi also has been a reason for introducing ozonation steps in the treatment line of a potable water treatment plant. Other purposes of ozonation then have been developed in different fields of application, such as iron and manganese removal, micropollutants oxidation, urban wastewater disinfection! coagulant and flocculant aids, and improvement of biological treatment. During the last few years, numerous studies have been concerned either with the kinetics of ozonation reactions, or the modelling of contact systems. A better fit between these two factors should be found.

Changes in Particle Size Distributions on a Fixed Bed of Granular Activated Carbon

The particle size distribution at different bed depths of a fixed bed of granular activated carbon (GAC) has been monitored during 50 weeks of a pilot column run at the Waterford, New York potable water treatment plant. Initial backwashing resulted in significant stratification of GAC in the column: larger particles (average diameter 1.18 mm) settled in the bottom of the column (105 cm), and smaller particles (average diameter 0.97 mm) were concentrated near the top (24 cm), compared to samples of unstratified virgin Calgon F400 (average diameter 1.09 mm). During column loading and initial backwashing, more fines were created than were present in the virgin GAC (average 6.5% of GAC fines in the > 40 mesh fraction, compared to only 0.3% in the > 40 mesh fraction for virgin Calgon F400). After 50 weeks of service there was an overall trend toward a smaller average particle size (0.9 mm) with development of a more regular pattern of bed stratification (1.08 mm at the bottom and 0.75 mm at the top). These changes are attributed to breaking of large particles (12-20 mesh) and creation of intermediate size particles (20-30 and 30-40 mesh).

Detection and Inhibition of an Organic Interference in the Indigo Method for Ozone

Abstract Aqueous samples of organic solutes often exhibit a delayed reaction in the indigo test for dissolved ozone which is similar to the reaction of ozone itself. This phenomenon has made timing critical in aqueous ozone measurements and has been observed in both laboratory situations with high organic carbon:ozone ratios and in a potable water treatment plant with low organic carbon:ozone ratios. Organic hydroperoxides, singlet oxygen, and Fenton's reagent but not triplet oxygen, hydrogen peroxide, nor p-benzoquinone were found to interfere. Addition of phenolic antioxidants was found to inhibit the interference. These results extend the utility of the indigo method to solutions of high organic carbon concentration.

Influence of Preozohation on Clarification by Flotation for Drinking Water Treatment

Abstract A preozonation study has been done at the potable water treatment plant of Moulle, in the North of France. The water is particularly rich in organic matter, with also algal blooms every, year, so the coagulan t treatmen t dose which is necessary for an optimal treatment, is very high. Previous laboratory tests have shown the importance of a preoxidation step, before the coagulation–flocculation–sedimentation industrial treatment line. It is also well known that flotation permits a significant reduction of coagulant dose. In addition, prechlorination of a water containing a large amount of organic matter induces the formation of a relatively high concentration of haloforms.