Award Date

December 2023

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

Eakalak Khan

Fourth Committee Member

David James

Fifth Committee Member

Brian Hedlund

Number of Pages

280

Abstract

Brine waste streams are a current environmental issue given their high concentrations of contaminants and total dissolved solids (TDS), specifically sodium and chloride. Developing technologies that address brine treatment challenges is an essential need for water and wastewater industries. In addition to high salinity industrial wastes, there are several water treatment technologies producing brine waste streams in high volumes including reverse osmosis (RO), membranes, and Ion-exchange. With rising water demands and decreasing water supply, RO membranes will be extensively employed for potable water reuse and water desalination. Reusable ion exchange resins are also widely used to remove oxyanions contaminants from waters (e.g., nitrate, perchlorate, chromate, arsenate), for water softening, for metal separation in mining and in many other industrial applications. Direct discharge of brines to surface water bodies and soils decreases the water quality in the long term since they contain high levels of contaminants (e.g., oxyanions, nutrients, heavy metals, and trace organics) and TDS. The ecotoxicity of high TDS on agriculture, seawater species, and on soil bacteria, has been well documented and includes increased mortality rate in seagrass and reduced leaf abundance, reduce activity of microbialcommunities in soils, etc. The current research aims at contributing to the knowledge gap in the treatment of waste brines contaminated with oxyanions. The research investigates the potential for biological reduction of nitrate, chromate, and perchlorate under high TDS conditions, similar to those conditions found in waste brines, using Haloferax mediterranei and Halomonas elongata.

Hfx. mediterranei indicated an excellent performance in reducing NO3-, ClO4-, and Cr+6 in brines containing 16% to 25% NaCl (20% to 29% (w/v) total salts) under anaerobic conditions. Hfx. mediterranei grew better and reduced nitrate and perchlorate faster at higher salt levels of 20-25%, compared to 16% NaCl emphasizing the importance of the optimum NaCl level for the growth of this archaeon. The kinetic modeling results demonstrate that a first-order reaction occurred at all nitrate and perchlorate concentrations for 16% NaCl, while a zero-order reaction took place for 20-25% NaCl across all perchlorate concentrations. Cr+6 reduction by Hfx. mediterranei was found to be very effective. As seen for nitrate and perchlorate reduction, the best Cr+6 reductions were incurred at 20-25% salt content compared to 16%. An over-90% reduction was observed after 3 and 12 days for Cr+6 concentrations of 5-10 mg. L-1 and of 25 mg. L-1, respectively. Hfx. meditteranei can reduce Cr+6 much faster than nitrate and perchlorate reductions. In the testing containing concomitant nitrate and perchlorate, the sequence of degradation in the current study follows the order of NO3-→ClO4- using Hfx. mediterranei with faster kinetic rates at the optimum salt concentrations of 20 and 25%.

H. elongata demonstrated a great performance in removing NO3- (92%-100%) and Cr+6 (66%-89%) in brines containing 8% to 12% NaCl under anaerobic conditions. The optimum removal of both contaminants occurred at 8% NaCl. Increasing the NaCl level resulted in a 7% to 27% decrease and a less than 10% decrease for Cr+6 and NO3- removal. When Cr+6 and NO3- occurred together, the reduction of both was also best at 8% NaCl. The reaction order for NO3- (zero order) and Cr+6 (first order) stayed the same when the contaminants occurred co-currently.

Keywords

Biodegradation; Brine Management; Halophilic Microorganisms; Oxyanions Removal; Water Treatment

Disciplines

Environmental Engineering

File Format

pdf

File Size

8780 KB

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/

Download

Available for download on Sunday, December 15, 2024


Share

COinS