Research

I have a wide range of interests in environmental microbiology and the application of biotechnologies in engineering systems. Basically, I am fascinated by the questions of “why” and “how” of the amazing microbial world. Why are microbial communities so diversified while amazing patterns can still be detected? Why some microbes can withstand the attacks of antibiotics while others can not? More important, how can we inhibit the growth of pathogens while kill those beneficial bacteria? How can we develop cost-effective wastewater treatment systems and generate renewable biofuels to meet human needs in a sustainable way? All these questions are of great interest to me and I believe that they can only be answered through a combination of scientific disciplines. Some of my recent research projects are listed as follows:

Antibiotic Resistance/Emerging Contaminants/Biological Wastewater Treatment

  • Microbial  Source  Tracking  for  Gunpowder  Creek  Watershed  in  Kentucky, microbialsourcetrackingSanitation  District  No.  1  of  Northern  Kentucky and  Boone  County  Conservation District, 2015 – 2016
    Microbial source tracking (MST) is a technique to detect dominant sources of fecal contamination in environmental waters. Fecal pollution poses a health risk to humans via pathogens and MST has been developed during the last two decades to monitor fecal pollution. As it is unrealistic to monitor all pathogens in surface waters, cultivable fecal indicator bacteria (FIB), such as E. coli, have been traditionally used to evaluate fecal pollution. However, FIB are not always correlated well with pathogens, and cultivable microorganisms typical only represent less than 1% of microorganisms in the total microbial community, which could result in an inaccurate estimation of fecal pollution of surface waters. Instead, molecular culture-independent and library-independent method, such as real-time PCR, can be used to trace host-specific gene markers in humans and animals in total microbial community. The objective of this project is to identify the origin of potential fecal pollution for NKY watersheds to improve environmental quality and protect public health.
  • antibioticresistantbacteriaRapid and Accurate Quantification of Antibiotic Resistant Bacteria and Quantitative Risk Assessment for Water Security, Singapore National Research Foundation, 2013 – 2016
    Antibiotics have been widely used in humans and animals and bacterial resistance to antibiotics may pose a health risk to humans. The levels of antibiotic resistance in environmental samples will be measured. Molecular microbiology techniques will be further optimized for environmental samples, such as surface water, sediments, and soils. Prevalence of antibiotic resistance, antibiotic resistance genes, and biosynthetic genes will be quantified. Various factors on the development and persistence of antibiotic resistance will be evaluated. Quantitative risk assessment will be conducted to evaluate the risks of antibiotic resistance and to optimize strategies of minimizing antibiotic resistance in water bodies to improve water security.
  • Evaluation of Macrolide-lincosamide-streptogramin B Antimicrobial Resistance at Environmental Samples, antibioticresistanceSingapore Ministry of Education, 2010 – 2013
    Macrolide-lincosamide-streptogramin B (MLSB) antimicroibals are a group of three classes of chemically distinct but functionally similar inhibitors of bacterial protein synthesis. MLSB antimicrobials have been widely used in humans and animals to treat and prevent infections. Antimicrobials used in humans and agriculture are transferred to feces and animal wastes, and finally transferred into the environment. The extensive use of antimicrobials correlates with the development of antimicrobial resistant bacteria in the environment and threatens human health. The information on MLSB antimicrobials and MLSB antimicrobial resistance is important to evaluate the linkage between antimicrobial use and resistance levels and potential health risks posed to humans. Hence, quantification of antimicrobials, antimicrobial resistance, and persistence of antimicrobial resistant microorganisms and their resistance genes in environmental samples will provide important information for environmental risk assessment.
  • microconstituteMonitoring Microconstituents in an Advanced Wastewater Treatment (AWT) Facility and Modeling Discharge of Reclaimed Water to Surface Canals for Indirect Potable Use, U.S. WateReuse Research Foundation, 2007 – 2010
    The detection of various trace level organic pollutants in U.S. drinking water supplies recently has created substantial concern in the public and regulatory communities. Current research suggests that the trace organics, a.k.a., endocrine disrupting compounds (EDCs) and pharmaceuticals and personal care products (PPCPs), found in reverse osmosis permeate pose no human health risk, though public concern over these compounds remains a substantial hurdle. However, existing literature does indicate that some trace organic compounds at or above 1 ng/L will induce hormonal changes in aquatic life. This project was designed to demonstrate the removal of trace organics through various membrane processes (membrane bioreactors, ultrafiltration, and reverse osmosis); correlate trace organic concentration to toxicological response using tissue culture and live fish bioassays; and track the fate and transport of trace organics from a surface water injection point to groundwater supply wells.
  • MLSB Antimicrobial Resistance in Soil amended with Swine Wastes, National Pork Board, 2005 – 2007soil
    Antimicrobials are poorly adsorbed by animals and it is estimated that between 30% and 90% of the administered antimicrobials is excreted into feces. Therefore, animal manure could be a substantial reservoir of antimicrobials and antimicrobial resistant microorganisms through land application of swine manure in agriculture. If the antimicrobial resistant bacteria are pathogens, they can directly threaten human health. Even if the antimicrobial resistant bacteria are not pathogens, they can serve as reservoirs of resistance genes and these genes may spread through horizontal gene transfer to pathogenic organisms. Traditional culture-based methods focus on monitoring resistance in enteric bacteria or specific pathogens because of their direct impact on public health, but these bacteria are often present in low abundance (< 1%) and may not reflect the overall resistance level in the microbial community. PCR-based methods can be used to measure the prevalence of antibiotic resistance genes in total microbial communities, but still requires the choice of specific genes and cannot identify the resistant organisms. To overcome the shortcomings of culture-based methods and PCR, I have developed a variation of fluorescence in situ hybridization (FISH) probe to measure the methylation site of 23S rRNAs that encodes MLSB antimicrobial resistance. Combined with phylogenetic probes, the levels of antimicrobial resistance in particular microorganism were determined.
  • imageanalysisDevelopment of Image Analysis and Statistical Tools for Microbial Ecology Studies, University of Illinois at Urbana-Champaign, 2002 – 2007
    Image analysis is the basis for many molecular microbiology techniques, such as fluorescence in situ hybridization and microarray. However the quantification of fluorescence signals is difficult because of the large variability of all microbial communities. Commonly used quantification techniques such as fixed value thresholds or signal-to-noise ratio thresholds have intrinsic problems because these thresholds often vary between experiments. Accurate quantification needs both precise normalization and extraction of biological signals and robust post-processing of extracted information. I have developed a macro package for automated and quantitative analysis (AQUAN) of fluorescence in situ hybridization images, which can automatically separate and extract more than thirty features of each cell while keeping the interference of other cells and background at a minimal level. Statistical tools are necessary for the classification of signals. Fuzzy c-means (FCM) clustering was used to analyze the intrinsic data structure of extracted signals and the classification was much more robust than threshold-based techniques. As a result, I significantly increased the accuracy of fluorescence in situ hybridization image analysis through the combination of computational and statistical methods with molecular techniques and cut the analysis time by more than 80%.

Efficient Production of Biofuels from Carbon Dioxide

  • biofuelA New Type of Photosynthesis through Electrodedriven Anaerobic Respiration, Singapore Ministry of Education, 2012 – 2014
    A new type of photosynthesis through electrode-driven anaerobic respiration will be tested to convert carbon dioxide and water to biofuels. Compared to oxygenic photosynthesis, this new type of photosynthesis utilizes carbon dioxide and water to produce extracellular compounds instead of biomass. Therefore all the energy and efforts for processing biomass can be saved and the overall efficiency of biofuel production will be greatly enhanced. As a carbon-neutral and high-efficiency process, the technique proposed in this project could greatly enhance the production efficiency of biofuel.
  • Photoelectrochemical Water Splitting for the Production of Value-added Chemicals, Singapore, Peking and Oxford Research Enterprise, 2010 – 2013
    Solar energy will be used to split up water to hydrogen and oxygen. Then hydrogen or protons will be used to reduce carbon dioxide to produce value-added products, such as biofuels.  Anaerobic microorganisms will be used for carbon dioxide fixation and conversion. Molecular microbiology techniques will be utilized for microbial community characterization and performance enhancement.

Electrochemical Removal of Chemical and Biological Contaminants with NanomaterialsCNTfilter

  • Removal of Off-flavor Compounds by Electrochemical Carbon Nanotube Filters, Singapore National Research Foundation, 2013 – 2015
    The proliferation of cyanobacteria in surface water during algal blooms is a global issue that leads to the production of off-flavor compounds, which usually cause taste and odor issues. Conventional water treatment technologies can remove some of these contaminants, but usually result in high energy consumption. It is therefore important to develop cost-effective advanced water treatment technologies to remove contaminants and odors to improve water quality. Electrochemical carbon nanotube filters proposed in this study have great potential to remove chemical and biological contaminants with minimal energy consumption. The efficiency of CNT filters will be evaluated for the removal of off-flavor compounds for point-of-use water quality improvement.
  • Development of Electrochemical Graphene Filters to Treat Organic Contaminants, 2013 – 2015
    Development of cost-effective water treatment techniques is critical to tackle global water quality challenges. grapheneMembrane processes, such as microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are promising among state-of-the-art water treatment technologies. Graphene is an elemental carbon nanomaterial and could be used as membranes for water treatment. Graphene is a 2D one-atom-thick layer of graphite, and has attracted significant attention due to its high electrical and thermal conductivity, mechanical strength, optical and chemical properties, solution processability, and specific surface area up to 2630 m2 g-1. Although graphene has many advantageous properties, the current research on its environmental applications has mainly focused on material fabrication and chemical sorption. However, the short breakthrough time due to limited sorption sites on graphene membranes has limited its application. The objective of this study was to develop a novel graphene-based electrochemical filter to utilize both the high specific surface area and high conductivity of graphene to physically adsorb and electrochemically oxidize chemical contaminants.

Water Reuse

  • DPRGuidelines for Engineered Storage for Direct Potable Reuse Systems, U.S. WateReuse Research Foundation, 2013 – 2015
    As communities move towards more direct potable reuse (incorporation of highly purified recycled water into a drinking water source without an environmental buffer), it will be imperative to provide utilities with guidance on sizing, design, and response procedures for potential changes in water quality in engineered storage systems as they will become increasingly important in overall water management. The availability of an engineered storage buffer is a key element in direct potable reuse using current treatment and monitoring techniques. The engineered storage buffer must be of a sufficient capacity to allow for the protection of public health from inadequate treatment and for the measurement of specific constituents to be assured that the quality of the water provided meets all applicable public health standards. The project will develop recommendations for optimizing engineered storage systems for direct potable reuse through examining current practices and existing research to generate a guidance document and report.
  • waterreuseLow-cost Technologies for Small-scale Water Reclamation Plants, U.S. WateReuse Research Foundation, 2008 – 2010
    The shortage of fresh water is a severe problem for many areas of the world. Water reclamation and reuse provide promising opportunities to ease fresh water shortage problems. However, data and technical information for low-cost treatment technologies for small-scale water reuse projects are often unavailable, especially to communities with limited financial and technical resources in rural areas and in developing countries. In response to this need, the U.S. WateReuse Research Foundation funded this study to identify and evaluate established and innovative technologies that provide treatment of flows of less than one million gallons per day (mgd). A total of 26 treatment processes in 284 utilities were evaluated as part of this project. The primary value of this work is the extensive cost database, where the cost and operations data from existing small-scale wastewater treatment and water reuse facilities have been gathered and synthesized. From these data, the costs and maintenance issues for the various types of treatment technologies are compared and contrasted.
  • UVUltraviolet (UV) Disinfection Bioassay Tests and System Performance Evaluations, Carollo Engineers, 2007 – 2010
    As a consulting engineer at Carollo Engineers, which dominates the US UV validation market, I have conducted more than 30 UV disinfection system validations and performance evaluations for five major UV equipment manufacturers in the world. The performance of UV disinfection systems can be affected by many factors, such as reactor configuration, end-of-lamp life, fouling factor, flow rate, power, UVT, and turbidity. The comparison of the performance of UV reactors with multiple variables between different sites and tests is a challenge and statistical tools have to be used. Various statistical tools, such as multivariate linear regression, analysis of variance, and factorial design, can significantly improve the accuracy and cut the costs of engineering testing.

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