System Level and Microfluidic Devices to Lower Energy Requires For Selective Desalination

Abstract

Desalination of seawater, wastewater, and impaired groundwater is becoming essential to meet global water demands. In Saudi Arabia alone, desalination will meet 70% of the country’s water sources by 2050. Three selective desalination processes are presented in this dissertation including i) pressure-driven membrane using reverse osmosis (RO), ii) thermal-driven process by membrane distillation (MD), and iii) electro-potential driven of electrocatalytic for selective ion conversion. Modern RO membranes have reached their theoretical performance limits, resulting in minimal need to innovate at membrane material level. Bulk salt removal is not always needed, however, selective removal of problematic salt may provide lower cost strategies. Therefore, the overarching goal of this dissertation involves i) evaluating wastewater desalination at system level to reduce energy required to enable wastewater reuse, and ii) exploring micro level reactor architectures to identify low-energy strategies for selective ion treatment in impaired waters. System level strategies at wastewater facilities by leveraging local co-located cool water source enabled MD system to treat warm wastewater RO brine resulting in enhanced water recovery, decreased brine volume, and minimized energy requirements. A temperature differential of (ΔT= 10 ͦ C) between brine and surface water was adequate for membrane distillation process leading to 25% less energy than normal MD. Two micro-sized reactor designs were considered for selective salt removal. First, microfluidic testing platforms were successfully designed and fabricated using natural and engineered nanotubes as potential new architectures for salts separation. Tobacco mosaic virus (TMV) was gown and purified along with carbon nanotubes (CNTs) and were deposited on silicon wafers as part of the microfluidic devices. Progress was terminated after two years, due to complications associated with alignment of the nanotubes on wafers. Specifically, the separation issues and straight alignment of nanotubes as a key parameter for microfluidic device fabrication. The innovation I made provided a platform for further research through micro-sized devices. I pivoted to study selective ion destruction rather than separation, using an electrochemical microfluidic device. The electrochemical microfluidic device allowed probing of energy consumption in microchannel and showed one order of magnitude lower energy for nitrite removal when compared to a conventional electrochemical reactor.