Living Filters for Sustainable and Selective Treatment of Drinking Water and Beverages

Many communities in the U.S. and globally suffer because of a lack of access to safe drinking water. Cleaning water, however, using conventional technology is a dirty business that is expensive as well as material and energy intensive. There is a need to broaden access as well as provide more sustainable solutions that can improve people’s water and their health. Living filters are cultures of living microbes that are engineered to both sense and treat contaminants at the very low concentrations relevant for drinking water. Here we demonstrate a system that targets the removal of arsenic from drinking water and beverages such as fruit juice and wine. Conventional remediation based on chemical sorption is challenging because of interferences from phosphates, silicates, flavor compounds, and organic matter; membrane-based separations also can be impacted by these species and more critically will remove all compounds including those that should be preserved for flavor in the case of beverages. Here, we exploit the extraordinary selectivity of biological recognition to solve this problem. Microbial engineering is applied to generate <i>E. Coli</i> that contain multiple copies of arsenic-binding proteins that are highly selective for arsenic and effectively no binding to smaller anions. When protein expression is induced, bacteria remain healthy and produce thousands of copies of Ars-R and when exposed to arsenic, the organisms within 30 minutes will reduce arsenic to sub-ppb levels. Sorption isotherms reveal at low concentrations (&lt;50 ppb) sorption is defined by cellular transport while at higher concentrations the intracellular protein-arsenic interaction is limiting. The sorption behavior of these bacteria is insensitive to millimolar concentrations of phosphates, silicates, and many salts and is unaffected by the components of wines or fruit juices. Conventional microfiltration systems can be applied to remove all microbes down to levels suitable for meeting stringent EPA standards for drinking water. The integration of magnetic separation allows the capture of arsenic-laden microbes attached to magnetic nanoparticles which can be reused for future separations. Flavor compounds as measured by mass spectrometry in beverages remain unaffected by these treatment processes. Most recently we have incorporated bioluminescent reporters into the living filters which permit the detection of arsenic to optimize the treatment system. These engineered materials can be freeze-dried with modest impact on performance. Dry powders can be shipped easily under ambient conditions and then cultivated at the site prior to their integration into the treatment system. An important benefit of these materials is that the sorbent is in effect living, allowing for sustainable and low-cost manufacturing.