Superfund Research Program
PAH Bioremediation and Monitoring in Biowalls
Project Leader: Paul L. Bishop
Grant Number: R01ES015446
Funding Period: 2006-2009
In the progress of the research, "PAH Bioremediation and Monitoring in Biowalls," researchers are integrating Micro Electro Mechanical Systems (MEMS) technology with the square-wave anodic stripping voltammetry (SWASV) sensing method to measure heavy metals. Mercury-based stripping voltammetric or potentiometric techniques are well known as very powerful techniques for multi-element trace heavy metal determination in environmental, biological and industrial samples. Dr. Bishop's research team developed a miniaturized heavy metal sensor with a more environmentally friendly bismuth (Bi) on-chip planar electrode and microfluidic channels by using standard MEMS fabrication technology with the goal of developing a portable instrument. The team adapted the sensor for analysis of cadmium ions in an in-situ mulch permeable reactive barrier (PRB) system operated in the lab. In order to characterize the potential windows of the proposed sensor, researchers conducted some preliminary experiments using cyclic voltammetry (CV) in different buffer solutions. Dr. Bishop's team performed CV with the integrated Ag/AgCl reference electrode using the PalmSens, at a scan rate of 100 mV/s. The team found that the proposed sensor with integrated planar Bi working electrode and Ag/AgCl reference electrode could be used for in situ heavy metal detection, such as for Zn (II), Cd (II), and Pb (II), using ASV in both phosphate buffered saline and acetate buffer solutions.
The team used the miniaturized Bi-based sensor in conjunction with SWASV to determine trace cadmium in the mulch PRB system. Researchers relied on passive flow of groundwater under a natural hydraulic gradient through the mulch PRB to promote contact with pollutant compounds. Because the mulch PRB is relatively narrow and there is not any significant channeling, researchers assumed that the flow rate of a groundwater plume contaminated with Cd(II) across the mulch PRB is the same as outside the mulch PRB. The team found that sorption capacity is an important factor when designing PRB systems. Accordingly researchers found the breakthrough curve: where the normalized concentration of Cd(II), defined as the effluent concentration divided by the inlet concentration, is plotted against the pore volume of the Cd(II) solution. In these curves, common position of the breakthrough curve along the pore volume axis relates to the Cd(II) removal capacity of the mulch or bio-mulch PRB (both were tested). The team observed that after 20 pore volumes, in case of the mulch PRB, breakthrough occurred. However, for the bio-mulch PRB, they found that as the pore volumes increase to 40, the breakthrough curves became steeper. After 50 pore volumes, the mulch PRB reached its saturation value in the effluent. The bio-mulch PRB on the other hand shifted the breakthrough curve to the right, occurring late, and thus slowly saturating with Cd(II) due to bio-sorption.