The effect of pyrite on Escherichia coli in water: proof-of-concept for the elimination of waterborne bacteria by reactive minerals.

We present proof-of-concept results for the elimination of waterborne bacteria by reactive minerals. We exposed Escherichia coli MG1655 suspended in water to the reactive mineral pyrite (FeS2) at room temperature and ambient light. This slurry eliminates 99.9% of bacteria in fewer than 4 hours. We also exposed Escherichia coli to pyrite leachate (supernatant liquid from slurry after 24 hours), which eliminates 99.99% of bacteria over the same time-scale. Unlike SOlar water DISinfection (SODIS), our results do not depend on the presence of ultraviolet (UV) light. We confirmed this by testing proposed SODIS additive and known photo-catalyst anatase (TiO2) for antibacterial properties and found that, in contrast to pyrite, it does not eliminate E. coli under our experimental conditions. Previous investigations of naturally antibiotic minerals have focused on the medical applications of antibiotic clays, and thus have not been conducted under experimental conditions resembling those found in water purification. In our examination of the relevant literature, we have not found previously reported evidence for the use of reactive minerals in water sanitization. The results from this proof-of-concept experiment may have important implications for future directions in household water purification research.

Climatic and soil-mineralogical controls on the mobility of trace metal contamination released by informal electronic waste (e-waste) processing.

Informal e-waste processing is a growing global problem. Local climate and mineralogical factors strongly control the chemical lability and dispersal of trace metals from informal e-waste processing. Previous work on e-waste contamination primarily focused on well-known sites in similar climates. Our exploratory analysis of a long-term (since 2008) e-waste incineration site in East Jerusalem demonstrated the ways in which local factors combined to uniquely control trace metal contaminant mobility. Our results suggest that the combination of e-waste processing methods, climate, and mineralogy at this site generated a geopolymer-like material combining ash from e-waste incineration and mountain rendzina soil. This material strongly sorbs trace metal contaminants. We measured the concentrations of: Cu, Fe, Mn, Pb, and Zn at 29 locations around and within the burn site. Samples collected less than 10 m from the edge of the incineration area had trace metal concentrations below the United States Environmental Protection Agency (U.S. E.P.A.) screening levels for residential soil. Sequential extraction showed that ∼50-80% of the total mobilized Pb was released from the residual solid fraction, suggesting strong sorption or incorporation into soil components. Large differences in the measured average specific surface areas (SSA) of uncontaminated (26.18 m2/g) and contaminated (4.48 m2/g) samples, despite comparable mineralogy by XRD, suggested the production of a geopolymer-like material. This was supported by close similarities between the SSA values of contaminated samples and those measured for geopolymer materials synthesized in the lab using kaolinite clay and fly ash (e.g., 4.9 m2/g).