Dr. Fayaz Lakhwala, Ph.D.

Increasing Contaminant Destruction During Application of Activated Carbon Reagents for Reductive Groundwater Remediation 

Dr. Fayaz Lakhwala, Ph.D., Key Accounts Manager -Soil & Groundwater Remediation, Evonik Corporation

Background/Objectives: 

It is well-established that activated carbon reagents used for groundwater remediation are effective for removal of many dissolved phase organic contaminants by adsorption. Recently, there has been an increased recognition that some contaminants can be degraded even after they have been adsorbed by these reagents. The relative rates of contaminant adsorption and contaminant degradation will determine the effective longevity of reagents that include activated carbon. Long-term monitoring at some sites has indicated that adsorption sites of activated carbon cam become saturated and the rate of biodegradation of adsorbed contaminants is not sufficient to overcome the continued mass loading. The objective of this presentation is to highlight the benefits associated with activated carbon reagents that are designed to promote strong degradation of organic contaminants after their adsorption and thereby enable greater longevity of treatment.    

Approach/Activities: 

The authors will review and the major classes of activated carbon reagents available for reductive remediation of groundwater including their composition including physical and chemical characteristics as well as potential for delivery of reducing equivalents to chlorinated organic compounds after their adsorption on/in activated carbon. Evonik has developed an in situ chemical reduction (ISCR) reagent composed of microscale zero valent iron + extended-release organic carbon + activated carbon to enable both adsorptive removal of dissolved contaminants and strong reductive dechlorination of both contaminants in the aqueous phase and those adsorbed to the activated carbon. The composition of the reagent is designed to ensure strong reductive dechlorination of contaminants both before and after they have been adsorbed by the activated carbon. The results from two completed in situ remediation projects where this reagent (EHC® Plus) was applied will be presented and discussed from the perspective of performance and cost.      

Results/Lessons Learned: 

Results from a long-term column study indicated that a column packed with aquifer solids and treated with the activated carbon-enhanced ISCR reagent removed PCE, TCE, cis-1,2-DCE, 1,2-DCA, CT, CF, and DCM to below method detection limits until the testing was terminated after 481 days of continuous flow representing more than 200 pore volumes. The total chlorinated VOC concentration in the groundwater entering the column was approximately 4,000 µg/L. Injection of the activated carbon-enhanced ISCR reagent at a former industrial stie generated strong reducing conditions, rapid reduction of native sulfate, an increase in Dehalococcoides sp. cell count of more than three orders of magnitude, and extensive reductive dechlorination of chlorinated ethenes with very little accumulation of partial degradation products.  Detailed results from this site and a second site will be presented.    

Fayaz currently serves as the Key Accounts Manager within Evonik’s Soil and Groundwater group. He holds M.S. and Ph.D. degrees in Chemical Engineering with a minor in Environmental Science. He has 30 years of experience in site remediation with roles in technology development, remediation, site investigation, project management and business development. In the past 20 years, his focus has been on the design and application of in situ chemical oxidation (ISCO), in situ chemical reduction (ISCR), enhanced reductive dechlorination (ERD), NAPL stabilization and treatment of heavy metals in soil and groundwater. Besides the US, he has worked on projects in several Asia Pacific and European countries.