|dc.description.abstract||This research investigates the utilization of aluminum coagulation (electrocoagulation (EC) and conventional chemical coagulation) and membrane-based separation processes (microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO)) for treatment of various impaired water sources. The first and major part of this research emphasizes the evaluation and optimization of aluminum (electro)coagulation combined with MF as pretreatment to NF and RO for surface water purification and water reclamation. The second part of this work focuses on mechanisms of boron removal by aluminum EC during hydraulic fracturing wastewater treatment. The overall hypothesis of the research is that aluminum EC, which generates Al(OH)3 precipitates in situ partially removes dissolved, macromolecular, and colloidal contaminants including natural organic matter (NOM), boron, and turbidity, which can significantly improve water quality and reduce fouling in downstream membrane-based water treatment operations.
In the first part of this research, coupling of electrocoagulation/electroflotation (EC/EF) with MF was shown to provide multiple barriers against contaminants such as NOM, microorganisms, and inorganics (e.g. silica) while reducing MF fouling. Furthermore, coupled EC-MF was also shown to control NF fouling during non-saline and brackish surface water treatment. This was attributed to fractional removal of both hydrophobic and hydrophilic NOM fractions along with “nanocolloids” which consequently reduced pressure requirement for NF. Since NF fouling mechanisms depend on membrane solute rejection characteristics, this study also demonstrated the need to balance product water quality with the need to minimize NF membrane fouling through appropriate membrane selection. Potential mechanisms and effectiveness of pretreatment were evaluated by conducting forensic post-analysis of NF/RO membrane surfaces via various surface characterization techniques (e.g. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and atomic force microscopy). The effect of added chemicals (i.e. coagulant and anti-scalant) during operation of real-world pilot-scale RO plant for wastewater reclamation was also investigated by extensive membrane autopsy.
Investigations on the feasibility of aluminum EC for treatment of hydraulic fracturing wastewater (particularly for boron removal) was also conducted. This work emphasized mechanistic understandings of the boron uptake by freshly precipitated amorphous Al(OH)3 generated during EC. The hypothesized ligand-exchange mechanism governing boron uptake by Al(OH)3 precipitates was confirmed via extensive surface characterization.||en