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Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Civil Engineering

Year Degree Awarded

2016

Month Degree Awarded

September

First Advisor

David A. Reckhow

Second Advisor

John E. Tobiason

Subject Categories

Environmental Engineering

Abstract

Ferrate has been proposed as an alternative pre-oxidant in drinking water treatment for many years. Despite extensive studies that examined ferrate oxidation of specific contaminants, little research has been done on the impacts of ferrate in raw waters that include natural organic matter (NOM) and bromide, and that are also treated with coagulants and chlorine. The future of ferrate as a potable water treatment chemical depends on its ability to achieve adequate disinfection while minimizing the formation of disinfection byproducts (DBPs) under these realistic scenarios.

In this work, laboratory-scale treatment studies were conducted to (1) clarify the stability of ferrate in natural waters under various conditions, (2) re-examine the ability of ferrate to oxidize bromine species, (3) explore the interactions of ferrate and coagulants in controlling DBP precursors, and (4) compare ferrate with ozone as alternative pre-oxidants.

Results showed that ferrate decay was catalyzed by ferrate decomposition products. Solutes capable of forming complexes with iron hydroxides retarded ferrate decay. In natural waters, NOM and bicarbonate inhibited the catalytic effects of ferrate decomposition products and stabilized ferrate.

Ferrate can oxidize bromide forming bromine and bromate, and in natural waters total organic bromine (TOBr) was also detected. The highest levels of bromine and bromate were formed at lower pH and in the absence of phosphate. Nevertheless, under environmentally relevant conditions, the formation of bromate and TOBr would not be a problem for ferrate application as their concentration levels are quite low.

The effectiveness of ferrate oxidation in combination with conventional treatment on DBP precursor removal was investigated. Results showed that intermediate-ferrate treatment (i.e., conventional treatment followed by ferrate oxidation) was most effective followed by pre-ferrate treatment (i.e., ferrate oxidation followed by conventional treatment) or conventional treatment alone, and the least effective was ferrate oxidation alone.

The effects of ferrate and ozone pre-oxidation on DBP formation from subsequent chlorination or chloramination were comparable at equivalent doses for most DBP species. Ozone led to higher haloketone and chloropicrin formation potentials than ferrate. The relative performance of ferrate versus ozone for DBP precursor removal was affected by water quality, DBP species, and oxidant dose.

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