Civil Engineering ETDs

Publication Date

Summer 6-5-2017

Abstract

Cooling towers, integrated circuit (IC) manufacture and reverse osmosis (RO) generate copious amounts of wastewater high in colloidal and reactive silica inhibiting on-site or synergistic reuse. Silica present in cooling water can reach solubility limits via evaporation and form impervious scale on heat transfer surfaces that decreases efficiency. When water is treated by RO operating at high rejection, silica forms difficult-to-remove scale on the membrane feed side in the form of glassy patches and communities of aggregate particles, inhibiting aspirations for zero liquid discharge. Current methods for silica scale mitigation include abundant dosing with chemical antiscalents or complex operating schemes. This work evaluates the implementation of the common chemical coagulant ferric chloride (FeCl3) and highly insoluble ferric hydroxide (Fe(OH)3) in the removal of silica by coagulation and adsorption mechanisms, respectively. Ferric chloride was optimized for silica colloid coagulation in IC wastewater via charge neutralization resulting in 97.2% turbidity removal. Adsorption of reactive silica on ferric hydroxide using a sequencing batch reactor approach exhibited 94.6% silica removal for the first adsorption cycle in under 60 minutes. Silica adsorption was found to fit the Langmuir isotherm relationship and was further modeled with surface complexation reactions using PHREEQC. Analytical characterization provided evidence of silica polymerization on the iron surface. This work serves to provide a benchmark of ferric chloride and ferric hydroxide application in silica removal for real industrial wastewater streams. Marrying these compounds together has proven to be an effective approach for comprehensive silica removal.

Keywords

water reuse, silica, coagulation, adsorption, IC, RO

Sponsors

National Science Foundation CREST and EAPSI programs

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Dr. Kerry J. Howe

Second Committee Member

Dr. Patrick V. Brady

Third Committee Member

Dr. Jr-Lin Lin

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