Water treatment requirements are steadily increasing globally, with higher demands on both the quality and quantity of water that systems must be able to deliver. These demands disproportionately impact small and rural water treatment systems, where economy of scale makes treating emerging contaminants and achieving higher water quality metrics significant concerns Systems such as reverse osmosis or traditional drinking water plants, may be inappropriate or impractical for these situations. One technology that may be applicable to these scenarios is membrane distillation (MD) as either a stand-alone treatment option or a polishing step. MD is an attractive technology for these small systems, with relatively simple operation and high documented rejection rates of metals, salts, and other non-volatile contaminants. The performance of MD with volatile and semi-volatile components is not as well understood, and the work discussed here seeks to develop an understanding of the factors that govern transport of these compounds within MD systems.
A novel, gas-tight direct contact membrane distillation (DCMD) system was developed to test a variety of non-volatile, semi-volatile, and volatile compounds in a closed-loop system. This bench scale system is the first of its kind, and allowed for more precise identification of contaminant transport than has been achieved in previous studies. A series of batch experiments were carried out using an array of salts and metals to test the transport of non-volatile substances that have been reported in the literature to be well rejected by MD. Further experiments were carried out with emerging contaminants of concern such as nitrogenous disinfection byproducts, pharmaceuticals and personal care products, and other volatile and semi-volatile constituents. Concentrations of these compounds in the feed and the distillate tanks were measured at intervals to quantify compound behavior, and the data obtained was then compared against physical and chemical parameters of the compounds in question, providing insight into the phenomena governing their transport in these systems.
As a result of this work, it was determined that compound rejection in MD systems is governed largely by compound volatility, as defined by Henry’s Constant. Furthermore, the interpretation of the results indicates that passage of compounds across the membrane is an equilibrium process, dominated by temperature and compound concentration on either side of the membrane. This confirms, and provides a theoretical basis, for the theoretically perfect rejection of non-volatile compounds by MD systems that has often been documented, and explains the behavior of volatile and semi-volatile compounds in these same systems.
|Advisor:||Hiibel, Sage R.|
|Commitee:||Fuchs, Alan, LaTourrette, Nancy, Yang, Yu|
|School:||University of Nevada, Reno|
|Department:||Civil and Environmental Engineering|
|School Location:||United States -- Nevada|
|Source:||MAI 56/05M(E), Masters Abstracts International|
|Keywords:||Contaminant transport, Henry's constant, Membrane distillation, Volatile contaminants|
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