Theme: 01. Remediation Technology Innovations

Topic Area: 01b. Bioremediation: Advances in Amendment Formulations

Formatted Title:

Sustainable Remediation via Bioelectrochemical System for a Petroleum Site

Background/Objectives:

At a municipally-owned public works facility in southern Florida, BTEX, cumene, and semi-volatile compounds (SVOCs), including naphthalene and methylnaphthalene, were detected above Florida’s Groundwater Cleanup Target Levels (GCTLs) in the surficial groundwater aquifer. The source of the groundwater impacts is a discharge discovered in 1987 from historical underground storage tanks, before they were replaced. The site remediation goal is to reduce all contaminant concentrations to the GCTL without interfering with the daily operations of the municipality and/or damaging the tanks. Langan was awarded a contract to complete environmental assessments for the city, including the public works facility, in their effort to redevelop their facilities into public spaces, in an environmentally conscious manner.

Approach/Activities:

A pre-design site investigation was conducted to evaluate the natural attenuation of the petroleum-related contaminants at the site. Two treatability studies were conducted to evaluate treatment effectiveness via in-situ chemical oxidation (ISCO) and a sustainable bioelectrochemical degradation technology, E-Redox^®. E-Redox^® is an electrochemically induced oxidation-reduction technology patented by Advanced Environmental Technologies, LLC (AET). The ISCO study using alkaline activated persulfate was conducted at Langan’s Treatability Facility at the New Jersey Institute of Technology (NJIT) and the bioelectrochemical degradation study was conducted at AETs facility in Fort Collins, Colorado. Bioelectrochemical devices enhance aerobic biodegradation by transferring excess electrons to the electrodes, where the electrons react with oxygen to complete the respiratory electron transfer cycle for microbes in an environment with depleted terminal electron acceptors. Based on the results of these two studies, bioelectrochemical degradation using AET’s E-Redox® Units was selected as the superior remediation technology.

The pilot study of this innovative technology began in June 2021. E-Redox® units provided by AET, consisting of electrodes and connection wire for the bioelectrochemical process, were placed into two dedicated wells and were operated for one year. The full-scale application was implemented in June 2022, and included the addition of four additional E-Redox® wells. One additional E-Redox® well was installed at a deeper interval to target cumene concentrations at another source area well.

Results/Lessons Learned:

The treatability study results indicated that bioelectrochemical degradation using E-Redox® technology achieved complete degradation of all site contaminants without mobilizing metals. The life-cycle analysis showed that this technology has a fraction of the carbon footprint of other technologies applicable to this site. This site is the first field implementation of this sustainable remediation technology on the East Coast.

Based on quarterly groundwater monitoring data, a decreasing trend for benzene in the source area monitoring well has been observed since the implementation of the remedial system. Fluctuations in other contaminant concentrations were observed and may be attributed to an upgradient source. We have observed that the limiting factor for the system operation was likely the depletion of essential nutrients. This could cause the decrease of biodegradation activity, which correlates with the declining voltage profiles measured in the E-Redox® Units. To resume and increase the effectiveness of the system following modifications were implemented during the full-scale remediation:

Addition of diammonium phosphate (DAP) supplemented with potassium chloride to replenish nutrient levels in the treatment area. The first quarterly nutrient injection was conducted in October 2023.
Replacement of cathodes in the E-Redox® units on quarterly basis to maintain unit effectiveness.

Quarterly groundwater sampling is currently ongoing to evaluate remedial effectiveness.

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David Deacon