Less than 10% of the plastics generated globally are recycled, while the rest are incinerated, accumulated in landfills, or leach into the environment. New technologies are emerging to chemically recycle...

Management responses to prion diseases of cattle, deer, and elk create a significant need for safe and effective disposal of infected carcasses and other materials. Furthermore, soil may contribute to the horizontal transmission of sheep scrapie and cervid chronic wasting disease by serving as an environmental reservoir for the infectious agent. As an initial step toward understanding prion mobility in porous materials such as soil and landfilled waste, the influence of pH and ionic strength (I) on pathogenic prion protein (PrP Sc ) properties (viz. aggregation state and ζ-potential) and adsorption to quartz sand was investigated. The apparent average isoelectric point of PrP Sc aggregates was 4.6. PrP Sc aggregate size was largest between pH 4 and 6, and increased with increasing I at pH 7. Adsorption to quartz sand was maximal near the apparent isoelectric point of PrP Sc aggregates and decreased as pH either declined or increased. PrP Sc adsorption increased as suspension I increased, and reached an apparent plateau at I ∼ 0.1 M. While trends with pH and I in PrP Sc attachment to quartz surfaces were consistent with predictions based on Born-DLVO theory, non-DLVO forces appeared to contribute to adsorption at pH 7 and 9 (I ) 10 mM). Our findings suggest that disposal strategies that elevate pH (e.g., burial in lime or fly ash), may increase PrP Sc mobility. Similarly, PrP Sc mobility may increase as a landfill ages, due to increases in pH and decreases in I of the leachate.

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This paper describes reactive transport simulations conducted to assess the impact of mineral fouling on the hydraulic behavior of continuous-wall permeable reactive barriers (PRBs) employing granular zero-valent iron (ZVI) in carbonate-rich alluvial aquifers. The reactive transport model included a geochemical algorithm for simulating corrosion and mineral precipitation reactions that have been observed in ZVI PRBs. Results of simulations show that porosity and hydraulic conductivity of the ZVI decrease over time and that flows are redistributed throughout the PRB in response to fouling of the pore space. Under typical conditions, only subtle changes occur within the first 10 years (i.e., duration of the current field experience record with PRBs), and the most significant changes do not occur until the PRB has operated for at least 30 years. However, changes can occur sooner (or later) if the rate at which mineral-forming ions are delivered to the PRB is higher (or lower) than that expected under typical conditions (i.e., due to higher/lower flow rate or inflowing ground water that has higher/lower ionic strength). When the PRB is more permeable than the aquifer, the median Darcy flux in the PRB does not change appreciably over time because the aquifer controls the rate of flow through the PRB. However, seepage velocities in the PRB increase, and residence times decrease, due to porosity reductions caused by accumulation of minerals in the pore space. When fouling becomes extensive, bypassing and reductions in flow rate in the PRB occur.