Impacts of Marine Algal Blooms on Disinfection Byproduct Formation in Seawater Desalination

PI Name: Ning Dai

Funding Source: National Science Foundation (CAREER award)

Project period: 3/1/2017-2/28/2022

Reverse osmosis (RO)-based seawater desalination is one of the most important technologies for meeting the growing global water demand. At the intake of RO desalination plants, disinfectants (e.g., chlorine) are often added to suppress fouling of the treatment units, especially RO membranes, by microorganisms. These disinfectants can react with marine organic matter to form harmful disinfection byproducts (DBPs). Recently, marine algal blooms were shown to interrupt desalination operations by causing severe membrane fouling, as a result of the high concentration of algal organic matter (AOM) during algal blooms. While disinfectants are crucial for controlling fouling during algal blooms, the implications of high AOM concentrations on DBP formation in desalination have not been considered. This project investigates the formation of DBPs from algae species relevant to marine algal blooms and to develop DBP mitigation strategies accordingly for desalination operations. Education activities are an integral part of this project, aiming to promote professional competencies of environmental engineering students at all degree levels and to broaden participation of women and underrepresented racial/ethnic minorities in science, technology, engineering, and mathematics (STEM).

This project focuses on both the fundamentals of DBP formation from marine algae and the application of findings to desalination operations. The project encompasses four research objectives. First, the DBP formation potential of bloom-relevant marine algae species are evaluated under conditions simulating disinfection in seawater desalination during algal blooms. Representative species are selected based on their relevance to marine algal blooms along the U.S. coasts. The algae culture and the extracted intra- and extra-cellular AOM are subject to a suite of disinfectants, chlorine, chloramine, chlorine dioxide, ozone, permanganate, and their combinations. Second, DBP formation is evaluated for fresh AOM derived from different algae growth stages and aged AOM after biotic and abiotic transformation. The findings are indicative of the persistence of bloom impacts on DBP formation. Third, the mechanisms of DBP formation from marine algae cells and the important DBP precursors are identified. The fundamental knowledge of DBP formation under desalination scenario is the basis for designing DBP prevention strategies for desalination facilities. Lastly, the effects of AOM transformation upon disinfection on its membrane fouling potential are characterized to suggest strategies to achieve a balance between membrane fouling control and DBP prevention. Analytical tools such as gas, liquid, and size exclusion chromatography, mass spectrometry, and spectrophotometry are employed to monitor DBP formation and characterize AOM transformation. The integral educational activities include graduate student training in research and mentoring, providing research experience for undergraduates, incorporating cooperative design project-based learning in graduate and undergraduate environmental engineering courses, and K-12 outreach focusing on high school and middle school teacher development.