Date of Award

8-2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Hydrogeology

Advisor

Castle, James W

Committee Member

Rodgers Jr. , John H

Committee Member

Snider , Eric

Abstract

ABSTRACT
In a year-long study, pilot-scale constructed wetland treatment systems (CWTSs) targeted removal of selenium (Se) from a simulated impaired water through dissimilatory Se reduction. Effects of temperature and precipitation on the treatment of Se in the CWTSs were investigated. The experimental design consisted of CWTSs amended with a fermented yeast product (AquaSmartTM, Diamond V¨, Cedar Rapids, IA), which served as a nutrient source for Se-reducing bacteria, at mass loadings of 1.75, 3.5, 5.25, 7, and 8.75 mg/min. The 5 µg/L treatment goal for CWTS outflow concentration was measured in 69 of 378 samples taken from all CWTSs. Of the 69 samples that met the treatment goal, 7.2, 7.2, 10.1, 10.1, 31.9 and 33.3% of the samples occurred in the control, 1.75, 3.5, 5.25, 7, and 8.75 mg AquaSmart/min treatment groups, respectively. CWTSs amended with AquaSmartTM mass loading rates of 8.75 and 7 mg/min consistently reduced aqueous concentrations of Se from 50 μg/L to less than 5 μg/L, meeting the USEPA chronic water criterion for Se (USEPA, 2002; 2004). Se removal efficiency correlated positively with nutrient amendment loading. Nutrient amendment addition provided nutrients and energy to Se-reducing bacteria allowing for Se reduction, and therefore Se removal, to continue through the winter months. The influence of seasonal temperature change on Se removal efficiency in CWTSs decreased with increased nutrient mass loading. Seasonal temperature decrease greatly impacted Se removal in the control, 1.75, 3.5, and 5.25 mg/min treatment groups. CWTSs amended with AquaSmartTM at mass loadings of 8.75 and 7 mg/min achieved greater Se removal efficiency than the control CWTSs as temperature decreased. R2 values determined from comparison of mean removal efficiency and temperature ranged from 0.18 for the 8.75, and 7 mg/min loading to 0.67 for a control group with no amendment added. Dissolved oxygen (DO) concentration of 2 mg/L or less and negative oxidation-reduction potential influenced Se removal. Measured precipitation did not correlate strongly to Se removal. Results from this study indicate that Se removal to less than 5 µg/L can be achieved in CWTSs and is aided by the addition of AquaSmartTM. Nutrient-amended CWTSs may provide industry with a viable technology to treat waters containing elevated levels of Se.

Included in

Geology Commons

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