Perchlorate is used as an oxidizer in rocket fuel, fireworks, batteries, and automobile airbags and also occurs in nitrate deposits that are used in fertilizers. It is a persistent environmental contaminant that has shown carcinogenic, neurodevelopmental, reproductive, and immunotoxic effects. Perchlorate contamination is a growing concern at Department of Defense (DoD) facilities nationwide, particularly with respect to groundwater contamination. Ion exchange resins have been used for perchlorate remediation of water; however, the selectivity of these resins is often poor. This leads to low capacity before regeneration of the resin and high salt concentrations needed for regeneration. Traditional membrane-based processes such as reverse osmosis and nanofiltration are not very effective at recovering perchlorate from contaminated water. More cost-effective and environmentally acceptable technologies that could reduce perchlorate from drinking water to below 2 parts per billion (ppb) are needed.
The objective of this project was to develop a scalable dendritic polymer-based filtration material with high capacity for the selective extraction of perchlorate from groundwater.
Branched dendrigrafts with perchlorate binding sites were synthesized. Crosslinking was performed with polyethylene glycol (PEG) to strengthen the resin and reduce biofouling. Synthesis and purification were optimized for scale-up and cost reduction. Total capacities of the resins were characterized, and initial operating parameters were obtained.
This technology is expected to be implemented as a fixed bed system with sodium chloride (NaCl) regeneration. Brine containing perchlorate and other ions such as nitrate and sulfate from the regeneration process could be disposed of in liquid form, if not inhibited by regulation, or in evaporated form as salt.
In this project, both uncrosslinked, water-soluble dendrigrafts and PEG-crosslinked, water insoluble dendrigrafts were investigated and all showed perchlorate binding. Resins also were tested with high perchlorate concentrations to ensure that they would have a high affinity toward perchlorate even in the presence of high nitrate and sulfate concentrations. With these large capacities, the resin is expected to be effective for the removal of low or high concentrations of perchlorate. The highest perchlorate capacities, up to 325 meq/g, were found in the soluble dendrigrafts. It was also determined that these dendrigrafts are regenerable with lower concentration NaCl brine. In further experiments, these dendrigrafts did not show significant leakage of perchlorate, sulfate, or nitrate ions when the column was washed with a large amount of water.
This project provided DoD with the potential for an effective way to produce high perchlorate capacity, regenerable resins with selectivity towards perchlorate. Optimized operational data in a pilot test setting would be required to further develop the technology. (Project Completed - 2009)