Date of Graduation

5-2015

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor

Julian Fairey

Committee Member

Norman Dennis

Second Committee Member

Wen Zhang

Abstract

In 2009, the United States Environmental Protection Agency (EPA) promulgated a national turbidity standard for runoff water leaving highway construction sites at 280 nephelometric turbidity units (NTU). Meeting this standard can be challenging as turbidities of runoff waters can exceed 15,000 NTU. The objective of this research was to assess polyacrylamide (PAM), a coagulant aid used in water treatment, to help meet the EPA turbidity regulation. Twelve commercially available PAM types were studied, selected on the basis of charge type (cationic, nonionic, anionic), charge density (0-100%), and molecular weight (0.1-28 Mg mol-1). Jar tests were conducted with runoff waters from AHTD construction sites and synthetically made formulations of tap water blended with bentonite, illite, kaolinite, and Arkansas Red Dirt. Jar tests were completed at PAM doses between 0.5-20 mg L-1 and the turbidity of the supernatant was measured following a quiescent settling period. Results showed that anionic PAMs with low charge densities were most effective at reducing supernatant turbidities, likely due to enhanced interparticle bridging. Hydraulic flocculation tests were done with two PAM types in lab-scale continuous flow reactors and at a controlled field site. It was concluded that anionic PAMs at a dose of 10 mg L-1 provided adequate turbidity reduction and that channel baffling induced hydraulic flocculation and further reduced effluent turbidities.

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