In order to identify hexavalent chromium (Cr6) sources, behavior, and treatability, this thesis has profiled Cr6 in seven full-scale drinking water treatment plants and six distribution systems. Bench-scale jar tests assessed the treatment efficacy of coagulation and developed strategies to remove ultra-low level (0.01- 1.0 ~tg/L) Cr6.
All water sources measured in this project contained dissolved Cr6 greater than or equal to the California Public Health Goal (0.02 ~g/L Cr6). The investigated coagulation plants did not remove Cr6; in fact, four of the seven treatment plants inadvertently added Cr6 to the treated waters. Thirteen types of drinking water treatment chemicals were evaluated as a potential non-water source of chromium. Amongst these, only iron-based coagulants contained trace levels of chromium sufficient to account for the observed increases at the full-scale plants. Other discussed non-water sources include leaching of chromium-bearing infrastructure or oxidation of Cr3. One of the treatment systems showed chlorine oxidized Cr3 to Cr6 and raised the finished concentration, in less than seven hours.
One suggested improvement strategy was to use ferrous iron to reduce and remove Cr6 during coagulation. Bench-scale tests showed ferrous iron and a cationic polymer improved removal of both Cr6 and Total Cr. Chlorine interfered with that reduction. The full-scale test of this reduction-coupled coagulation treatment successfully decreased the finished Cr6 concentration when 40% ferrous iron was used and the point of chlorination was moved downstream from the coagulation process.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-3793 |
| Date | 01 May 2014 |
| Creators | Olsen, Christel |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact Andrew Wesolek (andrew.wesolek@usu.edu). |
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