UCLA

Water treatment processes using membrane technology, electrochemistry and nanomaterials have shown tremendous promise in the last several years. While pressure driven membrane treatment processes are capable of treating water sources containing a wide variety of contaminants, they suffer from several challenges such as osmotic pressure limitations and surface scaling and fouling. Membrane distillation is a vapor pressure driven process that does not suffer from osmotic pressure limitations, and hence can be used for the treatment of high salinity sources. However, fouling is still a major concern, along with the added high energy requirements. In this work, we look at a membrane distillation system that successfully separated non-volatile contaminants from a dairy farm waste stream, resulting in a concentrated stream of nutrients to be used as fertilizer, and a dilute stream of volatile compounds that can be used as the feed in fermentation processes. We also looked at treatment of high salinity brines by membrane distillation. Due to the excellent heat and electrically conductive properties of carbon nanotubes, an electrically conducting membrane fabricated by coating a polymeric membrane with a carbon nanotube suspension proved successful in mitigating inorganic scaling to a large extent. The externally applied electric potential reduced scale deposition by electrostatic repulsion and electrokinetic mixing. In another aspect of our research activities, we studied the degradation of perfluoroalkyl substances, a class of contaminants of emerging concern that are highly recalcitrant carcinogenic compounds. Typical remediation of these compounds takes place through adsorption on activated carbon followed by incineration. Studies have shown that they can be degraded by electrochemical oxidation. We utilized the excellent sorption and electrically conductive properties of carbon nanotubes to develop a novel degradation mechanism, where an externally applied potential weakened the C-F bonds, and hydrated electrons generated by UV light resulted in defluorination. We extended this study to linear perfluoroalkyl substances having different chain lengths and headgroups, studied the feasibility of this mechanism on dechlorination of chlorinated solvents commonly co-occurring in groundwater, studied the impact of mixtures of perfluoroalkyl substances and verified the two-electron mechanism by evaluating degradation rates of isotopically labeled and unlabeled compounds.