Functionalized Amphiphilic Block Copolymers and Complex Emulsions for Selective Sensing of Dissolved Metals at Liquid-Liquid Interfaces.

Increasing contamination in potable water supplies necessitates the development of sensing methods that provide the speed and selectivity necessary for safety. One promising method relies on recognition and detection at the liquid-liquid interface of dynamic complex emulsions. These all-liquid materials transduce changes in interfacial tensions into optical signals via the coupling of their chemical, physical, and optical properties. Thus, to introduce selectivity, it is necessary to modify the liquid-liquid interface with an interfacially stable and selective recognition unit. To this end, we report the synthesis and characterization of amphiphilic block copolymers modified with metal chelators to selectively measure the concentrations of dissolved metal ions. We find that significant reduction in interfacial tensions arises upon quantitative addition of metal ions with high affinity toward functionalized chelators. Furthermore, measurements from UV-vis spectroscopy reveal that complexation of the block copolymers with metal ions leads to an increase in surface excess and surfactant effectiveness. We also demonstrate selective detection of iron(III) cations (Fe3+) on the µM levels even through interference from other mono-, di-, or trivalent cations in complex matrices of synthetic groundwater. Our results provide a unique platform that couples selective recognition and modulation of interfacial behaviors and demonstrates a step forward in the development of the multiplexed sensing device needed to deconvolute the complicated array of contaminants that comprise real-world environmental samples.

Engineered Slippery Surface to Mitigate Gypsum Scaling in Membrane Distillation for Treatment of Hypersaline Industrial Wastewaters.

Membrane distillation (MD) is an emerging thermal desalination process, which can potentially treat high salinity industrial wastewaters, such as shale gas produced water and power plant blowdown. The performance of MD systems is hampered by inorganic scaling, particularly when treating hypersaline industrial wastewaters with high-scaling potential. In this study, we developed a scaling-resistant MD membrane with an engineered "slippery" surface for desalination of high-salinity industrial wastewaters at high water recovery. A polyvinylidene fluoride (PVDF) membrane was grafted with silica nanoparticles, followed by coating with fluoroalkylsilane to lower the membrane surface energy. Contact angle measurements revealed the "slippery" nature of the modified PVDF membrane. We evaluated the desalination performance of the surface-engineered PVDF membrane in direct contact membrane distillation using a synthetic wastewater with high gypsum scaling potential as well as a brine from a power plant blowdown. Results show that gypsum scaling is substantially delayed on the developed slippery surface. Compared to the pristine PVDF membrane, the modified PVDF membranes exhibited a stable MD performance with reduced scaling potential, demonstrating its potential to achieve high water recovery in treatment of high-salinity industrial wastewaters. We conclude with a discussion of the mechanism for gypsum scaling inhibition by the engineered slippery surface.

Solar membrane distillation: desalination for the Navajo Nation.

Provision of clean water is among the most serious, long-term challenges in the world. To an ever increasing degree, sustainable water supply depends on the utilization of water of impaired initial quality. This is particularly true in developing nations and in water-stressed areas such as the American Southwest. One clear example is the Navajo Nation. The reservation covers 27,000 square miles, mainly in northeastern Arizona. Low population density coupled with water scarcity and impairment makes provision of clean water particularly challenging. The Navajos rely primarily on ground water, which is often present in deep aquifers or of brackish quality. Commonly, reverse osmosis (RO) is chosen to desalinate brackish ground water, since RO costs are competitive with those of thermal desalination, even for seawater applications. However, both conventional thermal distillation and RO are energy intensive, complex processes that discourage decentralized or rural implementation. In addition, both technologies demand technical experience for operation and maintenance, and are susceptible to scaling and fouling unless extensive feed pretreatment is employed. Membrane distillation (MD), driven by vapor pressure gradients, can potentially overcome many of these drawbacks. MD can operate using low-grade, sub-boiling sources of heat and does not require extensive operational experience. This presentation discusses a project on the Navajo Nation, Arizona (Native American tribal lands) that is designed to investigate and deploy an autonomous (off-grid) system to pump and treat brackish groundwater using solar energy. Βench-scale, hollow fiber MD experiment results showed permeate water fluxes from 21 L/m2·d can be achieved with transmembrane temperature differences between 40 and 80˚C. Tests run with various feed salt concentrations indicate that the permeate flux decreases only about 25% as the concentration increases from 0 to 14% (w/w), which is four times seawater salt concentration. The quality of the permeate water remains constant at about 1 mg/L regardless of the changes in the influent salt concentration. A nine-month MD field trial, using hollow fiber membranes and completely off-the-shelf components demonstrated that a scaled-up solar-driven MD system was practical and economically viable. Based on these results, a pilot scale unit will be constructed and deployed on the tribal lands.

Plankton filtration with compressible crumb rubber packs.

The experiments described provide insight into the feasibility of using compressible particulate packs to filter live plankton. The pore constriction sizes are controlled by subjecting the filter pack to isotropic confinement, thereby allowing for: (1) enhanced filtration upon confinement and (2) enhanced unclogging upon relaxation. Results show that filtration efficiency increases with increasing confinement; however, complete plankton retention is difficult to attain due to the plankton's ability to pass through pore constrictions that are smaller than the plankton size. The results are anticipated to offer potential benefits to ballast treatment and aquatic filtration operations.