Pathogen detection and removal
Waterborne pathogens are an important cause of human morbidity and mortality in the world. Rapid pathogen monitoring protects public from exposure to contaminated water. Evaluation of removal efficiencies through various natural and engineered water treatment processes provides the information necessary to improve design for more effective treatments. Among all microbial pathogens, we have placed special focus on the human viruses due to their small size, low dose of infection and resistance to degradation.
Human virus removal is investigated in laboratory-scale stormwater biofiltration columns as well as natural and engineered wetlands as part of the project supported by the NSF Partnership for International Research and Education (NSF-PIRE). In collaboration with Australian colleagues, we are carrying out multi-year investigations of pathogen removal using low energy treatment options to harvest stormwater.
Another engineered water treatment method that has gained attention for the sanitary applications in the developing world is the use of electrochemical reactions driven by solar panels to oxidize pathogens and organics in human waste. A project funded by the Bill and Melinda Gates Foundation Reinvent the Toilet Challenge through a subcontract from California Institute of Technology is to understand the virus removal efficiency during the electrochemical treatment process in order to optimize the reaction time and to minimize the disinfection byproducts. A directly related project, also funded by the Gates Foundation, is to develop a low cost pathogen detection chip technology for rapid monitoring of water quality in the developing nations.
At the local level, municipal wastewater reuse has been implemented throughout Southern California to meet the ever-increasing water demand. However, the bacterial and viral removal efficiencies using different wastewater treatment processes have not been fully investigated. Toward this end, we are carrying out several sampling efforts at three local water reclamation plants that supply wastewater effluents for non-potable reuse. We are applying rapid fluorescence total bacteria and virus counting methods using flow cytometry to evaluate the log removal efficiency of each unit process during engineering treatment. This project has the potential to contribute to and possibly update the current statewide water reuse policy and improve public health protection from water reuse practices.
Graduate students involved in this area of study include Xiao (Eric) Huang, Edgar Gomez and Zheng (Sarah) Zhao. A senior undergraduate student Dana Hernandez is also an important team member for this particular project.
Quantitative Microbial Risk Assessment
Public health protection is the ultimate goal of pathogen monitoring during water and wastewater treatment. The Quantitative Microbial Risk Assessment (QMRA) provides a valuable tool to evaluate the health risk from different water use scenarios. The outcomes of this risk assessment have a great potential to influence policies concerning sustainable water practices and to further develop human health risk benchmarks.
Current risk assessment efforts in the group include evaluation of stormwater harvesting for household non-potable applications and de facto water reuse of drinking water sources containing a large portion of wastewater effluent. A recently completed project assessed the roof-top harvested rainwater for home grown food crop irrigation. A similar project studying the recreational health risk associated with coastal water contact (impacted by storm drain runoff during wet and dry weather conditions) is currently under development. NSF-PIRE provides the major funding support for these projects. Two graduate students, Keah-Ying Lim and Yiwen (Ian) Wu are currently leading the effort in this area.
Desalination membrane fouling study
Biofouling remains an important challenge for reverse osmosis (RO) membrane processes in drinking water purification. In the past few years, we have identified that bacterial quorum sensing (QS) pathways play an important role in biofilm formation and subsequent membrane fouling. We have successfully reduced biofilm formation on membrane surfaces through addition of quorum-sensing inhibitors (QSI) to treatment water. In the next step of this investigation, we will incorporate QSI onto a RO membrane surface thin film composite and investigate the incorporation stability, membrane properties with the hope of developing the next generation of anti-fouling RO membranes. Leda Katebian, a senior Ph.D. student within the group, is currently carrying out this project (funded by Dow-Resnick Bridge Program through California Institute of Technology). A closely related project focuses on understanding the relationship between chlorination pretreatment of seawater in desalination practice and identification of chlorine-tolerant, biofilm forming marine bacteria. A senior undergraduate student, Lynze Cheung, is currently conducting this study.
Degradation of Microcystins
Microcystins, also known as cyanoginosins, are a class of toxins produced by certain freshwater cyanobacteria. The presence of these toxins in drinking water presents a negative health effect for humans. Thus, a better understanding of the factors that contribute to toxin dynamics, and practical treatment methods for mediating cyanobacterial toxicity are needed. This project investigates the biodegradation of microcystins (i.e., MC-LR, MC-LA) incorporating a natural bacteria community. In collaboration with Metropolitan Water District of Southern California, we have isolated individual bacteria as well as the bacterial consortia that are capable of growing in minimal medium containing these toxins. We are investigating the degradation rate of the natural bacteria and applying this rate in the design and optimization of a theoretical biofiltration system. These efforts are aiming to advance full-scale biofiltration as a reliable, cost-effective and energy-efficient microcystin removal strategy in drinking water supplies during cyanobacteria blooms. Yuen (Ming) Cheung and Derek Manheim are two current graduate students leading research efforts on this project.
Algae and Bacteria Interaction
Harmful algal bloom has a significant impact on costal economy and public health. This project, funded by the National Science Foundation Biological Oceanography program, investigated the interaction of bacteria with bloom forming diatom Pseudo-nitzschia. Our research has shown that each individual species of Pseudo-nizschia has its own unique bacterial community associated with it. These communities improve the fitness of the host diatom species. On the contrary, addition of “foreign bacteria” to the Pseudo-nitzschia culture retards the growth and sometimes stimulates the production of algal toxin domoic acid. Bacteria are attracted to the exudates produced by Pseudo-nitzschia and migrate towards the algal exudates in the presence or absence of other complex organic nutrients. More information on the project can be found in our recent publications. This project has supported the career development of Dr. Marilou Sison-Mangus, who is now an assistant professor at UC Santa Cruz, and Dr. Janet Rowe. Several undergraduate students have gained research experience through this project as part of Undergraduate Research Program supported by UC Undergraduate Education Office. The background and outcome of this project have also been used in Back Bay Science Program public education lectures.