Immobilization and in-situ biodegradation of microcystins using engineered biofiltration for drinking water production

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Harmful algal blooms (HABs) in surface waters are caused by massive growth of algae often with associated toxins called ‘cyanotoxins’ produced by cyanobacteria. HABs threaten the Nation’s water supplies and cost millions of dollars per year in responses and lost revenue. Microcystin is the most common cyanotoxin produced by cyanobacteria blooms in freshwater lakes. Microcystin is highly toxic to humans and animals, and large concentrations have resulted in the temporary shutdown of an entire municipal drinking water system. Despite large investments in HAB mitigation, cyanotoxins continue to be a great challenge for safe drinking water production. The goal of this project is to address this challenge through the development of novel engineered nanomaterials to remove microcystin from drinking water and break it down to non-toxic products. The engineered nanomaterials will be fabricated using biochar (charcoal produced from plants) with specific modified surfaces to trap microcystin and remove it from water. Special bacteria then degrade the toxins trapped on the surface in a microscale bioreactor. Successful development of this ‘trap and destroy’ technology has potential to transform our ability to remove cyanotoxins from drinking water. Additional societal benefits result from the training of graduate students in multidisciplinary science to enhance the Nation’s STEM workforce.The goal of this research project is to develop new three-dimensional net-like functional hydrogel-biochar composite materials to selectively capture and degrade microcystin in drinking water. This goal will be achieved through four specific objectives to: i) develop materials for selective microcystin adsorption through complementary pore size, ion exchange, and π-π electron donor-acceptor interactions; ii) optimize microcystin uptake kinetics through strong electrostatic interactions or ion exchange with positively charged quaternary ammonium groups; iii) encapsulate microcystin-degrading bacterial consortia into functional biomaterials to enable in situ biodegradation of microcystin; and iv) remove clogging and regenerate adsorbent binding sites in the biofiltration system through a chemically enhanced backwash. Novel advances in this research include the synthesis of a new cationic poly(diallyldimethylammonium-co-styrene)-grafted cellulose nanofibril and biochar composite, elucidation of microcystin adsorption/biodegradation mechanisms using Thomas, Adams-Bohart, and CXTFIT models, and sorption site characterization using density functional theory. The viability and function of microcystin-degrading bacteria encapsulated in biomaterial composites will be evaluated by coupling scanning electron microscope and culturing methods. Reverse transcriptase quantitative PCR, 16S rRNA gene sequencing, and metagenomics analysis will be used to develop genotypic insight into microcystin degradation mechanisms. Successful completion of this research will help advance water treatment technologies by integrating novel targeted biodegradation with new functional nanomaterials as an effective water treatment technology. Societal benefits will result from effective and low-cost treatment technology for microcystin removal to protect the Nation’s drinking water supplies from HABs.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.