Award Date

12-15-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Jacimaria Batista

Second Committee Member

Daniel Gerrity

Third Committee Member

Erica Marti

Fourth Committee Member

David James

Fifth Committee Member

Spencer Steinberg

Number of Pages

263

Abstract

Groundwater contamination with oxyanions is an issue that must be addressed for environmental, ecological and societal reasons. Chemical and biological treatment methods of reduction are already known and practiced, but the simultaneous presence of multiple oxyanions can add complicating effects to treatment sequence and efficacy. This research was concerned with the investigation of the chemical reductive treatment of Cr(VI) using both calcium polysulfide (CaSx) and ferrous sulfate (FeSO4), and the biological reductive treatment of chlorate, Cr(VI), nitrate and perchlorate using multiple organic substrates. The chemical treatment phase consisted of initial jar tests, using CaSx and FeSO4, followed by a laboratory column study using CaSx. The biological treatment phase first implemented microcosm testing, using EOS-PRO, Industrial Sugar Wastewater (ISW) and Molasses as organic substrates, followed by laboratory column testing utilizing EOS-PRO and ISW.

The chemical jar tests showed that high doses (around 10 mg Cr(VI)/L) could be treated, to a great extent, by 2-3 times stoichiometric doses of CaSx and 10-20 times stoichiometric doses of FeSO4, (perhaps even lower for one groundwater/soil). Treatment was improved in the presence of solids, and the type of solids was also found to have importance. Treatment of low Cr(VI) concentrations (about 0.5 mg Cr(VI)/L) was seen to be less effective. It is thought that at lower Cr(VI) concentrations, dissolved oxygen competes with Cr(VI) for reduction and thereby reduces the efficacy of the reductant. The in-situ-simulating column tests resulted in very strong and reliable removal of Cr(VI) and total dissolved chromium from the column effluent water, regardless of initial Cr(VI) concentration (~1 mg Cr(VI)/L or ~10 mg Cr(VI)/L).

Biological treatment testing was not thoroughly isolated from the possible chemical effects of the organic substrate additions. The microcosm testing showed that reduction of all the oxyanions was possible, except for perchlorate which was only found to reduce minimally. However, different substrates were observed to greatly affect the treatment efficacy. For example, Cr(VI) was found to have low detection after just 7 days with ISW use (thought to be partially a chemical process) in one groundwater, while EOS-PRO resulted in higher Cr(VI) concentration after 36 days. On the other hand, EOS-PRO greatly reduced nitrate in one groundwater after 26 days, while nitrate concentrations were still higher after 99 days when ISW was used. Different contaminants were noted to have very different reactions to substrates. ISW treated Cr(VI) very quickly, but was very ineffective at reducing chlorate. Overall, Cr(VI) reduction kinetics were found to be first-order, but the reduction reaction orders of other oxyanions were thought to be affected by the presence of the co-occurring oxyanions. The groundwater/soil also had dramatic impacts on treatment. Biological column reduction testing indicated reduction of all oxyanions was possible, but treatment effectiveness varied noticeably between different groundwater/soils.

In general, the order of treatment from easiest to most difficult seemed to be Cr(VI), nitrate, chlorate and perchlorate, although the groundwater/soil and substrate had dramatic effects on the results.

Keywords

Biodegradation; Chlorate competition; Groundwater remediation; Hexavalent chromium reduction; In Situ chromium treatment; Perchlorate

Disciplines

Environmental Engineering

File Format

pdf

File Size

3.9 MB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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