Wen's Research Group
Wen Zhang, Ph.D., P.E., BCEE
Principal Investigator
Professor
Phone: (973) 596-5520
Fax: (973) 596-5790
Email: wen.zhang@njit.edu
Office Location: Colton Hall 211
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3. Control and mitigate harmful algal blooms by reactive nanobubbles.
Zhang’s group has published three journal articles related to nanobubble technology in Chemosphere, Environmental Engineering Science, and Journal of agricultural and food chemistry. Zhang has patented the NBs generation system (US20190083945A1). This research project was funded by Undergraduate Research and Innovation program (URI) Phase-2 in New Jersey Institute of Technology. The research project has also been funded by United States Environmental Protection Agency (USEPA) 2018 People, Prosperity and the Planet (P3) with $15000.
Bacterial contamination is one of the greatest global problems for drinking water security. Microorganisms can grow collectively in adhesive polymers on biologic or non-biologic surfaces to form a biofilm. Our research goal is to evaluate the biofilm prevention when the liquid media (e.g., water) contains air or other gaseous NBs. We hypothesize that hydrophobic NBs are thermodynamically inclined to adsorb on solid surfaces such as stainless steel. Moreover, the surface adsorption of NBs leads to a negatively charged bubble layer that will inhibit biofilm formation via electrostatic and steric repulsion against bacteria. Thus, it is imperative to undertake different approaches such as the interaction energy analysis using DLVO theories and electrochemical detection to 1) investigate the colloidal properties and interactions of NBs with bacteria; 2) evaluate biofilm formation and prevention mechanisms in the presence of NBs.
As one of the important environmental applications of ozonation, the potency of biofilm prevention by ozone NBs is characterized and evaluated in a customized microfluidic cell in Fig. 2, where bacteria were spiked in the buffer solution to flow into the cell via the light blue tubular port. The bacterial strain, E. coli purchased from American Type Culture Collection was used as the bacterial inoculum to simulate the biofilm formation on a substrate surface (a stainless-steel plate). Biofilm growth on the substrate surfaces induces a change in the electrical characteristics in both the surround medium and the interface of the solid substrate surface.5 To characterize these changes, the electrochemical impedance (EIS) measurements was conducted.
Persistent environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals (e.g., Cu, Fe, Pb, and Zn) accumulate in the depositional zone of rivers and lakes from current and past releases. They have wide environmental distribution in water and sediment and bioaccumulation in organisms, which pose serious ecological and human health impacts. Despite the implementation of stringent controls and regulation of waste disposal and release, considerable amounts of persistent environmental pollutants that accumulated in sediment may still release at the sediment-water interface. Particularly, bubble-facilitated contaminant transport is one of the most important processes or causes of pollutant release and resuspension. Microbubbles (MBs) are generally defined as gaseous bubbles with diameter typically between 10 and 100 μm. Microbubbles could form usually because of microbial metabolisms that lead to production of carbon dioxide (CO2), methane (CH4) and hydrogen (H2). Due to the disturbance from bubble ebullition, sediment pollutants may rise to the water-sediment interface and begin to partition to water phase. However, not many past studies to date systematically examined the MBs-facilitated organic and metal contaminant emission in benthic sediment environment. To address this knowledge gap, our group measured organic (PFOA) and metal (Pb) contaminant release due to the bubbling process in soil columns and determined the factors (e.g., bubble flux and bubble types) for the pollutant release. This study involved the experimental monitoring of the leached pollutants when nanobubbles were present in the purged fluid. Moreover, we conducted COMSOL simulation to examine the bubble flow characteristics and impacts on pollutant leaching or desorption from the polluted sediment soil.
Coastal (and estuarine) hypoxia is an environmental problem of major and growing global importance – oxygen-depleted conditions (hypoxia and anoxia) result from phytoplankton growth and decay fueled by nitrogen, phosphorus, and sediment inputs from watersheds and have major deleterious impacts on fish and other living resources. Zhang’s group aims to devise a green sustainable process based on reactive nanobubbles (NBs) technology to control and mitigate harmful algal blooms (HABs). NBs may potentially be produced with air, oxygen, ozone or other reactive gases that promote rapid oxidation and decomposition of algae and associated organic contaminants (e.g., cyanotoxin). Although there has been a growing number of NBs applications (e.g., detergent-free cleaning, water aeration, ultra-sound imaging and intracellular drug delivery, and mineral processing), its
2. Application of NBs towards biofilm prevention and removal.
potential as a water purification technology remains largely unexplored. The fundamental chemistry of NBs and antimicrobial mechanisms are also not well understood. Accordingly, this project aims to address knowledge gaps to better understand and utilize the unique characteristics of NBs (such as high colloidal stability) and high reactivity (e.g., radical formation) in water dispersion for environmental applications. Zhang’s group aims to devise a ground-breaking and green technology based on reactive NBs to tackle the challenges of harmful algal bloom and cyanotoxin removal. The central hypothesis is that (1) NBs have higher colloidal stability and longer residence time as opposed to regular bulk bubbles or microbubbles that usually float up and escape from water; (2) NBs could produce radicals, especially under external stimuli such as UV irradiation; (3) NBs, due to their ultrasmall sizes, have greater reactivity toward algae and algal pollutants, compared to regular bubbling or purging (e.g., ozonation). Some additional research questions deserve explorations include the algal cell damage kinetics and mechanisms, degradation kinetics and removal efficiency of cyanotoxin, ammonia and other relevant nutrients.
1. Effects of NBs on sediment pollutant resuspension.
Publications:
1. AKA Ahmed, Wen Zhang et al. "Generation of nanobubbles by ceramic membrane filters: The dependence of bubble size and zeta potential on surface coating, pore size and injected gas pressure." Chemosphere 203 (2018): 327-335.
2. AKA Ahmed, Wen Zhang, et al. "Colloidal Properties of Air, Oxygen, and Nitrogen Nanobubbles in Water: Effects of Ionic Strength, Natural Organic Matters, and Surfactants." Environmental Engineering Science 35.7 (2018): 720-727.
3. AKA Ahmed, Xiaonan Shi, Wen Zhang et al. "Influences of Air, Oxygen, Nitrogen, and Carbon Dioxide Nanobubbles on Seed Germination and Plant Growth." Journal of agricultural and food chemistry 66.20 (2018): 5117-5124.
Patent:
Zhang, Wen, Taha Marhaba, and Ahmed Khaled Abdella Ahmed. "System, device, and method to manufacture nanobubbles."
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