Document Type

Dissertation

Date of Award

8-31-2023

Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)

Department

Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Tamara M. Gund

Third Advisor

Edgardo Tabion Farinas

Fourth Advisor

Yuanwei Zhang

Fifth Advisor

N. M. Ravindra

Abstract

Membrane distillation (MD) has gained significant popularity as a separation and purification technique in diverse domains, such as saline/brackish water treatment, organic recovery, and wastewater treatment. The objective of this research is to advance MD by developing a novel air sparged membrane distillation in treating saline water, recovering solvents, and achieving preconcentration. To optimize the flux and selectivity in membrane distillation, the study also employed a response surface method based on a central composite rotatable design.

In this study, a novel air-sparged membrane distillation (ASMD) is introduced for the treatment of saline water, utilizing a nanocarbon immobilized membrane. The performance of this technique was compared with that of an unmodified PTFE (polytetrafluoroethylene) membrane. Both the feed and permeate sides of the membrane module are subjected to air sparging. The results demonstrate a significant improvement in the flux of the membrane distillation process with the incorporation of air sparging. Moreover, the presence of air sparging brought about a notable change in the fouling reduction as well as pattern of salt formation on the membrane surface. The deposition of salt is considerably reduced in the air-sparged membrane distillation setup, resulting in an extended membrane life. These findings highlight the potential of the air-sparged membrane distillation technique for efficient desalination of saline water, offering promising applications in various other fields.

The study also explored the application of ASMD for dealing with humic substances from an aqueous stream using direct contact membrane distillation. This innovative approach was employed to mitigate fouling issues. The incorporation of carbon nanotubes not only acted as a screening mechanism to hinder the presence of macro-sized humic acid molecules but also helped reduce fouling and improve evaporation efficiency.

In another related application, sweeping gas membrane distillation is employed to concentrate trace amounts of 1,4 dioxane from an aqueous solution. To assess the preconcentration performance, carbon nanotube and graphene oxide-modified membranes are utilized. The results reveal that the permeate concentration becomes enriched with 1,4 dioxane, effectively concentrating the target compound. Furthermore, the nanocarbon-modified membranes demonstrated superior performance in terms of both selectivity and flux when compared to a standard base PTFE membrane. This enhancement indicates the potential of these modified membranes for more efficient and effective trace concentration of 1,4 dioxane via membrane distillation processes. These findings open promising avenues for environmental and industrial applications, where the concentration of trace contaminants is of utmost importance.

In chapter six, the main objective was to concentrate the biofuel precursor, isoprenol, which is obtained from the fermentation process. To achieve this, a nanocarbon-modified membrane was utilized. Among the different nanocarbon membranes investigated, the graphene oxide immobilized membrane proves to have the most favorable separation index. The study also highlights the significant role of air sparging in altering the volatility of isoprenol. This technique successfully enriched a low percentage of isoprenol to a higher concentration within the mixture. This study contributes to the development of sustainable biofuel production in the renewable energy sector.

In chapter 7, the primary emphasis lies in the recovery of moderately soluble ethyl acetate from water through air-sparged membrane distillation. To achieve this, a central composite design was adopted, enabling the determination of the necessary number of experiments to develop a regression model for predicting both flux and selectivity. The response surfaces revealed interesting curvature effect concerning ethyl acetate selectivity. By optimizing the process parameters, the study demonstrates that air sparging proves to be an effective technique for significantly enhancing flux and selectivity in membrane distillation.

In conclusion, this dissertation demonstrates that air sparging can be used to modify membrane distillation, effectively increasing the permeate flux and reducing fouling propensity. Meanwhile, nanocarbon-modified membranes have been found to exhibit better performance than unmodified base PTFE membranes. Overall, this study has significant implications for the future development of membrane distillation techniques in various separation and purification fields with applications in desalination, biofuel recovery and solvent recycling

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