Superfund Research Program
Chloro-Organic Degradation by Polymer Membrane Immobilized Iron-Based Particle Systems
Project Leader: Dibakar Bhattacharyya
Grant Number: P42ES007380
Funding Period: 2000-2019
Dr. Dibakar Bhattacharyya’s research group has continued to make highly significant advancements in organic detoxification technologies. Toxic organic compounds, such as, trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) are persistent groundwater pollutants. The group has taken a unique, two-pronged approach, using both oxidative (hydroxyl radical based reactions) and reductive (bimetallic nanoparticles) techniques to degrade these toxic compounds. This allows them to deal with issues that neither technology can address by itself. For instance, PCB reduction by Fe/Pd nanoparticles yields biphenyl with lower toxicity than the parent compound. But further oxidation technique is required to produce chlorine free organic acid products with minimal toxicity.
Hydroxy radical generation via advanced oxidation processes (such as the Fenton reaction) has been widely used for the degradation of toxic organic compounds. Although much work has been done on the remediation of these compounds in the aqueous phase, organics such as TCE are present in both the aqueous and organic (in the form of droplets, DNAPL) phases. In order to effectively remediate groundwater, in-depth studies on the degradation of contaminants in both phases are needed. Experimentation proved that the chelate-modified Fenton reaction can effectively dechlorinate (complete DNAPL type droplet degradation) TCE in both the aqueous and organic phases at near-neutral pH. The researchers have also developed a highly novel technique (layer-by-layer assembly in membranes) for potential on-site synthesis of H2O2 (needed for oxidation reactions) with very high enzyme stability.
Earlier work of the preparation of Fe0 and bimetallic Fe/Pd nanoparticle in solution phase and its reactivity towards toxic chloroorganics has also been documented. Various attempts have been reported in the literature to stabilize the Fe-Pd nanoparticles and prevent them from agglomeration such as using additives. However, the use of additives, such as carboxymethyl cellulose, do lead to some drop in reactivity towards TCE. This approach does require optimization of additive concentration.
Dr. Bhattacharyya’s novel approach of immobilization of Fe(II) in a polymer domain allows for the greater control of these reactions. In-situ polymerization of polyacrylic acid (PAA) has been performed inside the pores of a polyvinylidene fluoride (PVDF) membrane for Fe(II) capture by ion exchange.
The researchers have also developed a new approach (green synthesis) to form nanosized iron without using any solvent. In their recent study, the membrane support was modified by aqueous phase in situ polymerization of acrylic acid, with ethylene glycol added as a cross-linking agent, followed by ion exchange with Fe2+. This was followed by brohydride reduction to Fe0 and subsequent Pd deposition. This resulted in the formation of bimetallic (Fe/Pd) nanoparticles with an average size of 20-30 nm inside of the membrane pores and 50-100 nm on the external membrane surface. The resulting particles showed high TCE degradation. Their recent studies have also demonstrated that Fe/Pd films can effectively dechlorinate various chloro-organics including 3,3',4,4'-tetrachlorobiphenyl (PCB-77). They have also developed a computer simulation model to optimize iron particle size and Pd coating effectiveness for complete dechlorination of PCBs.
The research group is continuing their collaborative work with the Kentucky Research Consortium for Energy and Environment (DOE-KRCEE) to implement the potential use of both routes of dechlorination for the removal of trichloroethylene (TCE) at the Paducah Gaseous Diffusion Plant Superfund site in Paducah, KY.