Building Better Bio-Beads: Engineering Modulation of pH and Metabolite Diffusive Flux in Hydrogels

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Chlorinated organic solvents are the most common pollutants in groundwater in the U.S. Pollution of water supplies by these compounds represent a significant risk to public health, as several are known carcinogens that can result in exposure through drinking water. While engineers have developed treatment technology that uses the ability of microbes to consume these pollutants as food, the process can result in the production of harmful acids that eventually halts activity. The proposed research will shield these beneficial microbes in protective capsules called biobeads. These capsules will allow the beneficial microbes to continue to consume chlorinated organic solvents while producing clean water. These biobeads can be used with different microbes to address many environmental problems, with applications in many other fields including drug delivery, pharmaceuticals, food processing, and wastewater treatment. This project will augment undergraduate learning opportunities by incorporating the research into traditional undergraduate laboratory courses. If successful, this project will help protect the Nation's water security and ensure safe drinking water availability to the U.S. public. Chlorinated organic solvents like tri- and per-chloroethene (TCE and PCE) are the most common pollutants in groundwater in the U.S. Pollution of water supplies by these compounds represent a significant risk to public health, as several are known carcinogens that can result in exposure through drinking water. While compounds like PCE can be destroyed through low cost, anaerobic reductive dichlorination, this process can lower pH, resulting in the accumulation of more soluble, volatile, and hazardous degradation products. Microorganisms resist pH change through a variety of internal means, including proton efflux and control of membrane permeability to restrict transport. Unfortunately, these pH control methods come at the cost of metabolic energy and optimal growth of the microorganism. The objective of this proposal is to address the current deficiency of pH control in bioremediation of chlorinated solvents by leveraging existing fundamental concepts from biological microencapsulation, hybrid organic-inorganic material science, and mass transport theory. The research will involve building a biobead with the goal of self-regulated pH control. The biobead environment will be designed to emulate and improve on pH and transport control mechanisms naturally employed by microorganisms. The ultimate goal of biobead encapsulation is to extend the range of active metabolism for the encapsulated organism in non-ideal external pH gradients. This biobead design will be accomplished through incorporation of bioinspired mechanisms into a layered capsule design via addition of buffer groups to control internal pH, adjustment of electrostatic structural charges to restrict charged species transport, and deployment of catalytic layers designed to efflux or react with protons driven by external photic stimuli. The research will be leveraged by the combinatorial power of hundreds of first-year undergraduate student scientists engaged in relevant, active learning to provide valuable data to achieve project objectives.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.