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Increasing water demand coupled with projected climate change puts the Southwestern United States at the highest risk of water sustainability by 2050. Membrane distillation offers a unique opportunity to utilize the substantial, but largely untapped geothermal brackish groundwater for desalination to lessen the stress. Two types of hydrophobic, microporous hollow fiber membranes (HFMs), including polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), were evaluated for their effectiveness in direct contact membrane distillation (DCMD). Water flux and salt rejection were measured as a function of module packing density and length in lab-scale systems. The PVDF HFMs generally exhibited higher water flux than the PTFE HFMs possibly due to thinner membrane wall and higher porosity. As the packing density or module length increased, water flux declined. The water production rate per module, however, increased due to the larger membrane surface area. A pilot-scale DCMD system was deployed to the 2nd largest geothermally-heated greenhouse in the United States for field testing over a duration of about 22 days. The results demonstrated the robustness of the DCMD system in the face of environmental fluctuation at the facility. 

One of the biggest challenges for direct contact membrane distillation (DCMD) in treating wastewater from flue gas desulfurization (FGD) is the rapid deterioration of membrane performance resulting from precipitate fouling. Chemical pretreatment, such as lime-soda ash softening, has been used to mitigate the issue, however, with significant operating costs. In this study, mechanical vibration of 42.5 Hz was applied to lab-scale DCMD systems to determine its effectiveness of fouling control for simulated FGD water. Liquid entry pressure and mass transfer limit of the fabricated hollow fiber membranes were determined and used as the operational constraints in the fouling experiments so that the observed membrane performance was influenced solely by precipitate fouling. Minimal improvement of water flux was observed when applying vibration after significant (~16%) water-flux decline. Initiating vibration at the onset of the experiments prior to the exposure of foulants, however, was promising for the reduction of membrane fouling. The water-flux decline rate was reduced by about 50% when compared to the rate observed without vibration. Increasing the module packing density from 16% to 50% resulted in a similar rate of water-flux decline, indicating that the fouling propensity was not increased with packing density in the presence of vibration. 

Recent efforts to develop biocompatible and environmentally-friendly nanomaterials have yielded many biosynthetic methods for producing metallic nanoparticles which employ organisms from almost every branch of life. However, little progress has yet been made regarding the underlying mechanisms of most of these biosynthetic methods. In an attempt to address this gap in a knowledge, we have investigated the nanoparticle-producing ability of the ubiquitous biomolecule nicotinamide adenine dinucleotide (NADH), and have found that this coenzyme alone is sufficient to reduce Au3+ ion to gold nanoparticles (GNPs) in vitro. Synthesis using this method occurs nearly instantaneously at room temperature and produces uniformly spherical plasmonic nanoparticles with small sizes (<10 nm diameter). Both the speed of synthesis and the monodispersity of the produced GNPs are advantages over many other biosynthetic methods. As NADH is a universal component of all living things, our finding also suggests that this coenzyme may contribute to - or be wholly responsible for - some of the many previously- reported syntheses of GNPs by biological systems.