Systematic Evaluation Of Nitrate And Perchlorate Bioreduction Kinetics In Groundwater Using A Hydrogen-based Membrane Biofilm Reactor

摘要

To evaluate the simultaneous reduction kinetics of the oxidized compounds, we treated nitrate-contaminated groundwater (～9.4mg-N/L) containing low concentrations of perchlorate (～12.5μg/L) and saturated with dissolved oxygen (～8mg/L) in a hydrogen-based membrane biofilm reactor (MBfR). We systematically increased the hydrogen availability and simultaneously varied the surface loading of the oxidized compounds on the biofilm in order to provide a comprehensive, quantitative data set with which to evaluate the relationship between electron donor (H_2) availability, surface loading of the electron acceptors (oxidized compounds), and simultaneous bioreduction of the electron acceptors. Increasing the H_2 pressure delivered more H_2 gas, and the total H_2 flux increased linearly from ～0.04mg/cm~2-d for 0.5psig (0.034 atm) to 0.13mg/cm~2-d for 9.5psig (0.65 atm). This increased rate of H_2 delivery allowed for continued reduction of the acceptors as their surface loading increased. The electron acceptors had a clear hydrogen-utilization order when the availability of hydrogen was limited: oxygen, nitrate, nitrite, and then perchlorate. Spiking the influent with perchlorate or nitrate allowed us to identify the maximum surface loadings that still achieved more than 99.5% reduction of both oxidized contaminants: 0.21 mg NO_3-N/cm~2-d and 3.4 μg ClO_4/cm~2-d. Both maximum values appear to be controlled by factors other than hydrogen availability.