Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Laurie S. McNeill

Committee

Laurie S. McNeill

Committee

Joan E. McLean

Committee

William J. Doucette

Abstract

This project investigated the behavior of hexavalent chromium (Cr(VI), a potential carcinogen) in drinking water. While Cr(VI) can exist naturally, it can also be oxidized from Cr(III), a known trace nutrient. Recently, the State of California implemented a water regulation specifically for Cr(VI) at 10 parts per billion (ppb). This project completed a comprehensive evaluation of chromium behavior when in contact with common drinking water treatment chemicals including chlorine, monochloramine, chlorine dioxide, potassium permanganate, and ozone.

The results of these oxidation experiments are highly applicable to water treatment facilities. If a treatment plant is using monochloramine, there is no indication that Cr(III) oxidation would occur. When using chlorine, around 80% of Cr(III) will oxidize to Cr(VI) within 12 hours under typical treatment conditions. If chlorine dioxide is used in treatment at pH 7, complete Cr(III) oxidation can be expected within 6 hours of addition. Similarly at all pH values, potassium permanganate will cause complete Cr(III) oxidation in 4 hours. Ozone will oxidize all available Cr(III) within minutes of contact.

This information on chromium behavior when in contact with different treatment chemicals allows water utilities and regulators to make more informed decisions to protect public health and limit exposure to this potentially harmful metal species.

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