Examination of the release of lead and bacteria from activated carbon point-of-use filters
Advisor: Professor Thanh H. (Helen) Nguyen
Zoom Meeting ID: 812 7903 6280, password 697448
Abstract
Drinking water distribution system infrastructure in the United States is aging and degrading, contributing to numerous public health crises and a rise in concern over chemical and microbiological water quality. Point-of-use (POU) filters certified to remove Pb, many of which are composed of porous solid block activated carbon media, have become increasingly popular as a temporary solution to address drinking water quality problems. Unfortunately, these filters can release high concentrations of bacteria and fail to effectively remove particulate Pb. For their rapid rise in usage, these POU filters are understudied, and some unintended consequences go overlooked in the pursuit of an inexpensive and convenient solution to decrease Pb exposure in drinking water. The goal of this work was to capture a holistic view of the contributions activated carbon POU filters make to drinking water quality.
First, we examined the impacts of the common corrosion inhibitor phosphate on biofilm characteristics and the relationship between biofilm structure and bacterial release from POU filters. This knowledge is essential for understanding where these filters fit in a system where other lead contamination prevention measures may be in place. We measured the bacterial release from activated carbon POU filters fed with groundwater - a common source of drinking water - with and without phosphate. Phosphate filters released lower concentrations of bacteria than groundwater filters, and phosphate biofilms grew to be thicker and rougher than groundwater biofilms.
Second, we quantified the risk posed by the bacterium Legionella pneumophila (L. pneumophila) in homes supplied by private wells with a quantitative microbial risk assessment (QMRA). This study provides important insights into the prevalence of L. pneumophila in private wells, the risks it poses, and measures homeowners can take to mitigate their risk most effectively. We measured L. pneumophila concentrations from rural homes drawing water from private wells and modeled the risk of illness for handwashing, dishwashing, and showering. L. pneumophila was detected in about 30% of samples, and the risk was most sensitive to the concentrations of L. pneumophila and aerosols.
Third, we built another QMRA model for L. pneumophila to understand the role POU filters play on the microbial risk of drinking water. This study is important for understanding how POU filters impact microbial risk and for determining the factors one can target to most effectively mitigate their microbial risk from using these filters. We modeled scenarios without filters (with and without chlorine) and with filters (new and ripe filters) for common water usage activities where POU filters may be used: drinking from a drinking fountain, handwashing, dishwashing, and showering. Systems without filters and without chlorine had the highest risk, followed by those with ripe filters, those without filters and with chlorine, and finally, those with new filters.
Fourth, we examined the impacts of water hardness and biofilm in the filters on the Pb removal efficiency of activated carbon POU filters. This study provides important insights into how well filters will remove Pb as bacteria accumulate and grow, the contribution of aggregation to this Pb removal efficiency, and to what extent additional measures need to be taken to minimize bacterial growth. We challenged filters with and without biofilm growing inside with Pb phosphate nanoparticles with varying concentrations of calcium. Adding calcium and dissolved biomass diminished the repulsion of negatively charged Pb phosphate nanoparticles, increasing aggregation and improving POU filter performance.