- Selections of publications (with links on the images) from several themes of my research group are presented below.
- A full list of my publications can be accessed from the following links:Google Scholar | Research Gate
- Developing flow cytometry tools for monitoring viruses in recycled water
- Protecting human health in resource-oriented fecal sludge management through commercialization of the Viscous Heater for black soldier fly larvae growth
- Quantitative microbial risk assessment of the sanitation value chain: The case of urine collection and struvite fertilizer production in Durban, South Africa
- Microbial Health Risks for sanitation service workers: a comparison of fecal sludge emptying techniques
Water for Ecosystems
- Assessment of woodchip bioreactors for pesticide removal in agricultural tile drainage
- Associations of poly- and per-fluoroalkyl substances in aqueous fire-fighting foam and associations with proteins
- Evaluation of pesticde bioaccumulation in black soldier fly larvae
Enhancing Health and Hygiene in Resource Recovery
for more Sustainable Sanitation
An important theme of my recent work has been the protection of human health in the development of innovative resource recovery operations. This work has evaluated microbial inactivation processes during the extraction of nutrients from human urine to produce marketable fertilizers. We are also evaluating the microbial safety of products derived from fecal sludge — specifically focusing on the inactivation of microorganisms during heat treatment of sludge and the growth of black soldier fly larvae.
Urine is often falsely considered sterile, or nearly-so. Our work showed consistent cross-contamination of urine with pathogen-containing feces in a urine-diverting dry toilet system located in Durban, South Africa. The results emphasized the need to consider the health risks in handling urine and processing the material into valuable fertilizers.
Subsequently, we evaluated the inactivation of pathogen surrogates during the production of (solid) struvite fertilizers or (liquid) nitrified fertilizers from urine. We recommended simple design strategies to improve inactivation of microbial contaminants in urine to make a safer struvite endproduct. We found limited inactivation during nitrification requires further treatment following this process.
I have also worked to quantify health risks throughout the entire sanitation value chain, from urine collection through fertilizer production. The objective of this work is to identify critical control points to protect individuals involved in resource recovery and to improve endproduct safety. The research applies videography as a tool to evaluate human-environment interactions for modeling disease transmission, as described in the video publication below:
Water Reuse for Ecosystem Enhancement
This work explored opportunities to directly benefit ecosystems through the application of recycled water for environmental restoration projects. The overarching goals of the work are to identify design strategies that improve water quality and generate valuable ecosystem services.
I led a review with researchers from four universities and industry to evaluate case studies and research concerning the management, water quality, hydrology, and ecosystem services changes that occur when using recycled water for streamflow augmentation. We deemed these projects as “Stream Renewal” — seeking to revitalize degraded urban streams and provide ecosystem benefit. We then launched a case study of the costs and benefits of streamflow augmentation with recycled water at Calera Creek in Pacifica, Ca. While the biological changes observed do not support the same, pristine environment observed in natural systems, water provided for instream flows and public access to waterways can provide important economic value to communities.
Perfluoroalkyl Acids, Proteins, Bioaccumulation
This work has sought to evaluate exposure to and bioaccumulation mechanisms of per- and polyfluoroalkyl substances (PFASs) by understanding PFAS-protein interactions. Unlike many persistent organic pollutants, PFASs do not typically partition into fatty tissues. It was hypothesized that binding to proteins may instead be an important mechanism for observed bioaccumulation of these chemicals.
Perfluorooctanoate (PFOA) is the most notorious of the PFAS class of persistent chemicals of concern and was used in many commercial and industrial applications since the 1950s. Human exposure to PFOA is linked to cancer, elevated cholesterol, and immune suppression, among others. We found that PFOA binds strongly to human serum albumin (Bischel et al., 2010). Binding of such long-chain PFASs to proteins has now been included in bioaccumulation models for these compounds (Ng and Hungerbühler, 2014, 2013). As a result of health concerns, PFOA and other long-chain perfluorinated compounds were phased out of production in the United States in the early 2000s. However, production of so-called “short-chain” PFASs has greatly expanded, serving as replacement compounds for existing applications of long-chain PFASs. Production of long-chain PFASs also continues elsewhere in the world, notably in Asia. Many of the replacement compounds and their metabolites are expected to be as persistent in the environment as their long-chain homologues, but little is known regarding their exposure pathways, bioaccumulation potential and mechanisms, and toxicity. More work is needed on these compounds to understand their changing production, environmental fate and transport processes, and routes of human exposure.