Malynda A. Cappelle

Nanofiltration treatment options for thermoelectric power plant water treatment demands.

.......................................................................................................................................3 ACKNOWLEDGEMENTS ......................................................................................................................5 TABLE OF CONTENTS ........................................................................................................................7 LIST OF TABLES ................................................................................................................................9 List of Figures ................................................................................................................................11

Joint physical and numerical modeling of water distribution networks.

This report summarizes the experimental and modeling effort undertaken to understand solute mixing in a water distribution network conducted during the last year of a 3-year project. The experimental effort involves measurement of extent of mixing within different configurations of pipe networks, measurement of dynamic mixing in a single mixing tank, and measurement of dynamic solute mixing in a combined network-tank configuration. High resolution analysis of turbulence mixing is carried out via high speed photography as well as 3D finite-volume based Large Eddy Simulation turbulence models. Macroscopic mixing rules based on flow momentum balance are also explored, and in some cases, implemented in EPANET. A new version EPANET code was developed to yield better mixing predictions. The impact of a storage tank on pipe mixing in a combined pipe-tank network during diurnal fill-and-drain cycles is assessed. Preliminary comparison between dynamic pilot data and EPANET-BAM is also reported.

Analysis of micromixers and biocidal coatings on water-treatment membranes to minimize biofouling.

Biofouling, the unwanted growth of biofilms on a surface, of water-treatment membranes negatively impacts in desalination and water treatment. With biofouling there is a decrease in permeate production, degradation of permeate water quality, and an increase in energy expenditure due to increased cross-flow pressure needed. To date, a universal successful and cost-effect method for controlling biofouling has not been implemented. The overall goal of the work described in this report was to use high-performance computing to direct polymer, material, and biological research to create the next generation of water-treatment membranes. Both physical (micromixers - UV-curable epoxy traces printed on the surface of a water-treatment membrane that promote chaotic mixing) and chemical (quaternary ammonium groups) modifications of the membranes for the purpose of increasing resistance to biofouling were evaluated. Creation of low-cost, efficient water-treatment membranes helps assure the availability of fresh water for human use, a growing need in both the U. S. and the world.

Ion Exchange Membranes for Water Softening and High-Recovery Desalination

Water softening is typically performed by contacting hard water with cation exchange beads that are originally in the sodium ion form. When the ion exchange capacity of the beads is exhausted, they are regenerated by soaking them with a concentrated solution of NaCl, a cyclic and rather inefficient process that contributes considerable salt to the environment. The same cation exchange material can be made into a membrane and used to achieve water softening in a continuous process called Donnan dialysis. The regenerant NaCl solution (called the stripper) flows across one surface of the cation exchange membrane, and the hard water flows across the other. Diffusion of Na + ions from the concentrated stripper causes counter-diffusion of Ca 2+ ions out of the hard water into the stripper solution where their concentration reaches much higher levels than in the feed.