Date of Award:

5-2014

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Laurie McNeill

Committee

Laurie McNeill

Committee

Joan McLean

Committee

Eva Nieminski

Abstract

This project provides insight for drinking water utilities to better understand chromium behavior in their own waters. Seven full-scale treatment plants developed a snapshot profile of chromium behavior and treatability. If ultra-low level Cr6 is to be controlled, the key treatment processes in need of further investigation are lime softening, oxidation by chlorine, chloramines, or permanganate, and reduction-coupled coagulation using ferrous iron.

Chlorine was shown to oxidize ultra-low levels of Cr3 to Cr6 in less than seven hours. The distribution system investigations showed the concentration of Cr6 could change between the point of entry and the tap. It is therefore stressed that Cr3 must also be removed during treatment; otherwise it may be oxidized and generate additional Cr6 during distribution.

Other non-water sources of chromium including leaching of chromium-bearing infrastructure and trace contamination of treatment chemicals. Thirteen types of drinking water treatment chemicals were investigated. Twelve of the 13 chemicals contained negligible amounts of chromium, but iron-based coagulants contained significant levels of chromium that were inadvertently added to some treated waters.

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