Online

Shen, Yuxiang

Civil and Environmental Engineering

2022

Ph. D.

Membrane processes have been a promising purification and separation technique as it can potentially remove any ions, particles, and colloids by size selection. Membrane processes are still limitedly used in the real-world industrial application due to its relatively cost prohibitive maintenance and operation, which is attributed to membrane fouling and concentration polarization under pressurized conditions. To improve the efficiency of membrane filtration, alternatives to the traditional cleaning methods have been investigated to mitigate the fouling and concentration polarization problems. Among the alternatives, application of an external field, e.g., electric field or acoustic field, to the mitigate fouling during membrane filtration has been gaining increased attention in recent years. However, simultaneous application electric and acoustic fields to mitigate membrane are limited or lacking. This research focuses on the investigation of simultaneous application of electric and acoustic fields as a means to further enhance the fouling mitigation by providing additional foulant-foulant, and foulant-membrane interactions under combined fields conditions. There is a critical need for in situ characterization methods that could reveal effects of external fields on foulants during membrane filtration. In this dissertation the author presents (1) an apparatus designed and customized for simultaneous application of electric field and acoustic field during membrane filtration experiments; (2) experiment results based on microfiltration that confirm the synergistic effect under the given setup of combined fields; (3) mapping methods and results of enhanced darkfield hyperspectral microscopy (ED-HSI) applied to various foulants common in water and wastewater environment, including (i) pharmaceutical and personal care products (PPCP) molecular foulants and their adsorption to different types of carbon nanotubes (CNT), and (ii) Gram-negative and Gram-positive bacteria in planktonic conditions and in biofilms. The research in this dissertation investigates the application of electric field and acoustic field both individually and simultaneously to mitigate fouling during microfiltration. Under simultaneous application of fields: (1) the rate of fouling mitigation was larger than the numerical sum of each field when applied solely for synthetic wastewater matrix containing colloidal foulants, and (2) 25.1% of initial flux was recovered. The results suggest that electric field and acoustic fields can synergistically act to mitigate fouling while enhancing the flux recovery. A protocol based on ED-HSI was developed to characterize aqueous foulants relevant to membrane filtration. The mapping results revealed (i) adsorption mechanism of PPCP molecular foulant onto CNTs, and (ii) identification of different bacteria species in planktonic conditions and in biofilms.