Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

R. Scott Summers

Second Advisor

Fernando Rosario-Ortiz

Third Advisor

Karl Linden

Fourth Advisor

Joseph Ryan

Fifth Advisor

Detlef Knappe

Abstract

Stormwater is a major contributor of organic contaminants (OCs) in aquatic environments and there is growing interest in harvesting it as a new water supply. Biochar sorbents are a promising technology to control OCs in stormwater. Biochar physicochemical properties, which determine its performance, vary widely depending on its production conditions. Modeling OC sorption by biochar is challenging because of the heterogeneous-physicochemical properties of OCs and biochars that interact through different sorption mechanisms. In addition, stormwater contains dissolved organic matter (DOM) that fouls OC sorption. When DOM is present, the proportional removal of OCs is independent of their initial concentration until the OC initial concentration exceeds a concentration-threshold. The influence of sorbent type, compound type, and DOM concentration on the magnitude of the concentration-threshold has not been studied to-date. The objectives of this dissertation are: (i) determine how production conditions can be optimized to enhance the OC sorption capacity of biochar sorbents, (ii) elucidate OC sorption mechanisms, (iii) evaluate how stormwater character, OC properties, and biochar production conditions influence DOM’s competitive effect, and (iv) evaluate how OC and sorbent type influence concentration-thresholds.

Eight OCs were studied to probe the influence of OC physicochemical properties on sorption capacity and mechanisms with forty-two biochars produced by varying the pyrolysis highest treatment temperature (HTT), duration, precursor material, production system, and post pyrolysis air oxidation. Activated carbon was examined as benchmark sorbent and graphite served as a nonporous, unfunctionalized graphene-based reference sorbent. Batch tests were conducted to evaluate sorption capacities in deionized water, seven stormwaters, a surface water, a wastewater effluent, and two DOM size fractions. Greater HTTs corresponded to greater sorption capacities and a significant improvement in sorption capacity was observed when increasing pyrolysis durations above 4 hours. Steric hindrance, - electron donor acceptor interactions, electrostatic repulsion, O-H/ bonds, and anion/ bonds may play a role in overall sorption. The abundance of low-molecular weight DOM in stormwater, OC sorption mechanisms and sorbability, and biochar production conditions govern DOM competition. Concentration-thresholds correlate with the background-competing substances’ competitive effect and target-sorbate-Freundlich 1/n values.

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