Our research covers a wide spectrum of topics related to the transport, characterization, and removal of environmental colloids. We collaborate synergistically with microbiologists, chemical engineers, mathematicians, medical doctors, geologists, and other environmental engineers and scientists. In particular, we investigate two seemingly disparate topics; water purification (treatment of drinking water, industrial and municipal wastewater including hydraulic fracturing water, etc.) and tropospheric aerosols:
(1) Membrane technologies for water purification. We investigate bacteria and virus removal by microfiltration or ultrafiltration. MF/UF are also being used as pretreatment to reduce fouling of higher-pressure membranes (i.e. nanofiltration and reverse osmosis) in integrated membrane systems. MF/UF fouling control and increasing contaminant removal by these low-pressure membranes following pretreatment by chemical- or electrocoagulation or by periodic backwashing is also being studied. We are actively researching desalination of brackish water by nanofiltration and reverse osmosis. NF is particularly attractive as an energy efficient alternative to RO for desalination of surface and ground water dominated by divalent ions such as sulfate. Our group published some of the early work quantifying the temperature effects and activation energies for water and solute transport across nanofilters. We are also interested in trace contaminant control (e.g. amino acids) and controlling fouling of NF and RO membranes. This aspect of our work has applications to water reuse as well.
(2) Electrocoagulation. This is an increasingly popular alternative to conventional chemical coagulation. We have pioneered the use of aluminum and iron electrocoagulation as pretreatment technique for micro- and ultrafiltration. Their ability to enhance virus removal/inactivation and NOM/DBP control during surface water treatment is also of interest. Boron removal from saline wastewater generated by fracking is also being evaluated.
(3) Aerosols. Our research focuses on the elemental characterization and source apportionment of primary inhalable particulate matter. We developed novel microwave digestion and inductively coupled plasma – mass spectrometry techniques for rare earths (lanthanoids) and platinum group elements in PM2.5 and PM10 including the use of a collision cell. We also perform positive matrix factorization and chemical mass balancing using a wide suite of metals to identify primary PM sources and estimate their contributions to PM mass. We were amongst the first to link rare earth metals to establish the contributions of catalytic cracking catalysts employed in petroleum refining. We use lanthanoids as crustal markers to apportion long-range transported North African dust from the Sahara-Sahel region to the Houston area. Similar work is also being performed in the Middle-East region in Qatar. Additionally, we are working to link rhodium, palladium, and platinum to light-duty gasoline-driven vehicles (i.e. mobile sources) by making measurements in tunnels and surface roads.
(4) Environmental nanotechnology. Our principal interest in this subject is towards photoactivation of fullerene nanoparticles and the associated inactivation of viruses through reactive oxygen species as intermediates. We also demonstrate the use of bismuth nanoparticles to reduce bacterial production of extracellular polymeric substances and its impacts on controlling biofilm formation in a variety of technological surfaces.