Date of Award

January 2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Feng Xiao

Abstract

As bioretention systems are becoming an increasingly popular low impact development (LID) application for stormwater mitigation, they lack mechanisms that demobilize phosphorus (P) especially dissolved phosphorus (DP). In many cases, these LIDs release more P than is input due to a high P index derived from the plant material inherent within bioretention systems. The objectives of this project are to utilize low-cost water treatment residuals (WTR) as bioretention amendments to capture P. The adsorption characteristics are observed by means of batch level experiments to observe the P adsorption potential without the influence of hydraulic parameters, and column experiments to observe P adsorption capacities more applicable to that in a bioretention column. Langmuir and Freundlich isotherm models were fit to the composite isotherms to determine the equation parameters and discover peak adsorption capacities. The Freundlich model better fit the FeOH3 floc isotherms while the Langmuir model was more suitable for the AlOH3 floc isotherms. The models output 7.114 mg- P/g and 1.390 mg-P/g for the FeOH3 and AlOH3 flocs respectively. The Thomas model was employed to the column experiment residual P data to discover peak adsorption capacities, were it computed 2.315 mg-P/g and 1.845 mg-P/g for the FeOH3 and AlOH3 flocs respectively. These adsorption values are similar to that of Geolithe and Hematite as indicated in literature.

The adsorption mechanisms primarily transpired by means of outer-sphere complexation. This mechanism rendered loosely bound P to the amendments permitting rapid, liable adsorption, but also left the adsorbed P susceptible to mild/moderate desorption. Adsorption capacities were further inhibited by high pH levels and the presence of polymers in conjunction with the WTR. Overall, the WTR were successful in capturing DP in a wide variety of scenarios, validating their usage as an effective, low-cost, innovative solution in reducing phosphorus loading within bioretention systems

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