As freshwater resources are limited and stressed, and as the cost of conventional drinking water treatment continues to increase, interest in the development of non-traditional water resources such as desalination and water reuse increases. Reverse osmosis (RO) is the predominant technology employed in inland brackish groundwater desalination in the United States, but the potential for membrane fouling and scaling generally limits the system recovery. The general hypothesis of this research is that electrodialysis (ED) technology can be employed to minimize the volume of concentrate waste from RO treatment of brackish water (BW) and thereby improve the environmental and economic feasibility of inland brackish water desalination. The objective of this research was to investigate the performance sensitivity and limitations of ED for treating BWRO concentrate waste through careful experimental and mathematical analysis of selected electrical, hydraulic, and chemical ED variables. Experimental evaluation was performed using a laboratory-scale batch-recycle ED system in which the effects of electrical, hydraulic, and chemical variations were observed. The ED stack voltage showed the greatest control over the rate of ionic separation, and the specific energy invested in the separation was approximately proportional to the applied voltage and equivalent concentration separated. An increase in the superficial velocity showed marginal improvements in the rate of separation by decreasing the thickness of the membrane diffusion boundary layers. A small decrease in the nominal recovery was observed because of water transport by osmosis and electroosmosis. Successive concentration of the concentrate by multiple ED stages demonstrated that the recovery of BWRO concentrate could significantly improve the overall recovery of inland BWRO systems. A mathematical model for the steady-state performance of an ED stack was developed to simulate the treatment of BWRO concentrates by accounting for variation of supersaturated multicomponent solution properties. A time-dependent model was developed that incorporated the steady-state ED model to simulate the batch-recycle experimentation. Comparison of the electrical losses revealed that the electrical resistance of the ion exchange membranes becomes more significant with increasing solution salinity. Also, a simple economic model demonstrated that ED could feasibly be employed, especially for zero-liquid discharge. / text

Cette thèse de doctorat concerne l’étude de la distillation membranaire sous vide pour l’élimination de l’arsenic contenu dans les eaux souterraines. En effet, la contamination des nappes phréatiques par l’arsenic est une problématique majeure dans de nombreux pays, et en particulier au Vietnam. Dans ce pays, choisi comme cas d’étude pour ce travail, environ 13% de la population est empoisonnée par des eaux souterraines contaminées par l’arsenic. De plus, ces eaux souterraines présentent des salinités élevées (5-10 g.L-1) dues à des infiltrations d’eau de mer dans les nappes. Ce travail de thèse a permis de démontrer la faisabilité de la distillation membranaire sous vide (DMV) pour éliminer l’arsenic contenu dans ces eaux et réduire leur salinité afin de les rendre propres à la consommation humaine. Les concentrations en As(III) dans le perméat de DMV sont toujours inférieures aux limites de la norme en eau potable (10 μg.L-1), même pour de très fortes concentrations en As(III) dans l’alimentation (jusqu’à 2000 μg.L-1). La DMV ne nécessite pas de pré-oxydation de l’As(III) en As(V), étape nécessaire dans de nombreux procédés conventionnels de traitement. De plus, un couplage entre l’osmose inverse (OI) et la DMV a été étudié : l’étape d’OI permet une pré-concentration en NaCl et As(III), puis ce rétentat est alors sur-concentré grâce à laDMV. La DMV a montré de très bonnes performances pour traiter un concentrat contenant de très fortes concentrations en As(III) (7000 μg/L). La DMV permet toujours de limiter les teneurs en arsenic dans le perméat à des valeurs en-dessous de la norme. Enfin, unesimulation d’un procédé global, incluant OI et DMV, et fonctionnant à un taux de conversion global de 96%, a été effectuée. Ce couplage ouvre la voie vers un traitement global de l’arsenic permettant de générer de très faibles quantités d’effluents finaux / This PhD work deals with vacuum membrane distillation (VMD) for arsenic removal from groundwaters. Contamination of water resources with arsenic was identified in 105 countries. Approximately 150 million people are being exposed to arsenic contamination, and 147 million of these people live in Asia. In Vietnam, chosen as the case study of this work, 13% of the population is being in risk of arsenic poisoning. Drinking water resources present not only high arsenic concentration (1 – 3050 ppb) but also high salinity (5 – 15 g/L). This work allowed demonstrating the feasibility of VMD to remove arsenic and also salts contained in groundwaters. As(III) concentration in the permeate of VMD was always lower than the standard level for drinking water (10 μg.L-1), even for high As(III) concentrations in the feed (up to 2000 μg.L-1). With VMD, a pre-oxidation step was not necessary to convert As(III) into As(V), as it is the case for other conventional treatment processes. Moreover, a coupling between reverse osmosis (RO) and VMD was studied. RO was considered as a first step to concentrate NaCl and As(III) before this retentate stream was further concentrated by the VMD. VMD could work efficiently with 99.9% of As(III) andNaCl rejections at a very high RO retentate concentrations ([NaCl] = 300 g/L and [As(III)] = 7000 ppb). Arsenic in the permeate was still lower than the required standard for drinking water. Finally, a simulation of the coupling was performed. By coupling of RO and VMD, ahigh global recovery of 96% could be achieved