The overarching focus of this project was microorganism control in drinking water.  To accomplish this a two-pronged approach was taken: (1) virus attenuation by processes currently implemented in water treatment plants and novel promising technologies and (2) bacterial removal by microfiltration.

First, we considered two structural types of viruses: those that have an outer fortress, called an envelope, and those that do not since both are present in wastewater.  Using a coronavirus surrogate, we presented strong evidence that existing water treatment facilities can easily reduce vast quantities of enveloped viruses, thereby protecting household water from such contagions.  In particular, the water purification step called coagulation could alone get rid of 99.999% of the virus, markedly decontaminating water for consumption.  For these experiments, a known concentration of coronavirus surrogate was added to clean water.  Next, we tested the action of coagulants commonly used in water treatment plants.  After coagulation, we examined small samples of the virus-infused water under an electron microscope and found that the virus strain assembled on the coagulants, forming clusters.  We then checked the presence of infectious viruses in the water after removing the clumps and found a tremendous reduction.

Next, using sophisticated microscopy and computational analysis, we validated the merit of a water purification technology that uses electricity to remove and inactivate an assortment of waterborne viruses.  This novel water purification technology is called electrocoagulation, which could add another level of safety against pathogens that cause gastrointestinal ailments and other infections in humans.  Conventional coagulation methods use chemicals to trigger the clumping of particles and microbes within untreated water.  These aggregates can then be removed when they settle as sediments.  While effective, coagulation chemicals could be very acidic, making their transport to treatment plants and storage a challenge.  Instead of chemicals-based coagulation, we investigated if an up-and-coming coagulation method that uses electricity was as effective at removing microbes from water.

For these experiments, iron or aluminum electrodes were inserted in a sample of untreated water laden with viruses.  When electrical current was passed, the anode oxidized, releasing iron and aluminum ions into the solution.  In the process, as aluminum and iron precipitated, viruses attached to these clumps to form bigger aggregates, which were easily removed from the water.  Iron outperformed aluminum because it was able to combine with dissolved oxygen to produce hydroxyl radicals, which chemically reacted with viruses thereby inactivating them (a process that did not occur with aluminum).  An important contribution of our research was that we pictured viral inactivation using electron microscopy.

Clumping caused a tremendous challenge because there is no easy way to isolate the virus from the metal-rich aggregates, making it difficult to visualize viral damage and analyze if iron electrocoagulation was the cause of the viral damage or the virus extraction from the iron-rich clumps.  To address this problem, we developed a novel computational technique to directly image the viruses aggregated alongside iron/aluminum.  We found that iron electrocoagulated non-enveloped viruses were significantly damaged but not those isolated from conventional coagulation.  In contrast, both conventional coagulation and electrocoagulation and both iron and aluminum coagulants damaged enveloped viruses.  Iron electrocoagulation concurrently removed and inactivated viruses to achieve equivalent or higher total reductions with less charge consumption compared with aluminum suggesting its superiority as a water purification process.

Traditionally, water purification is a multistep process to ensure that even if one step fails, the subsequent ones can ensure safety - a multiple barrier approach, so to speak.  In this research, we presented evidence that process intensification with electrocoagulation, where coagulation and disinfection are combined within a single step before subsequent purification stages, ensured better protection against waterborne pathogens.

Finally, we investigated bacterial removal by microfiltration and the ability of bacteria to clog filters.  We selected a bacterium lacking cell walls, which rendered them deformable under typical filtration pressures.  Specifically, we evaluated the behavior of Acholeplasma laidlawii by microfiltration membranes.  This bacterium even passed through so-called ?sterile filters? (rated at 100 nanometers) thereby representing a new worst-case scenario to test membrane rejection and their ability to sterilize feed streams of biotechnological importance.  Additionally, in comparison with rigid silica particles of the same size under identical testing conditions, these ?squishy? bacteria clogged filters to a significantly greater extent by compressing against their surface and restricted flow.

Further, parallel to laboratory experiments and computational modeling, we designed several water purification lesson plans aimed at elementary and high school students.  Undergraduate students were trained to demonstrate these experiments on multiple occasions at local K-12 schools.  We also participated in "career days" at a rural school to convey the importance of pursuing a STEM education and the benefits of engineering careers.

Last Modified: 11/23/2022
Modified by: Shankar Chellam