PR Log - Aug 14, 2012 - "Innovative Environmental Technologies, Inc. has developed processes and methods based on the over 700 sites it has designed and implimented remedial solutions for since 1998.", says Michael Scalzi, President of IET. "Establishing an in-house collection of our own and licenced IP separates us from the industry as a technology leader and innovator. The development of a process in which chlorinated solvents with in high sulfate containing environments may be remediated offers a unique solution to a problem previously thought to prohibit traditional reductive technologies.
In our most recent advance, IET has identified a mechanism for addressing chlorinated solvent impacts in high sulfate environments, providing for the implementation of a variety of reductive processes. In combination with these technologies, or as a stand-alone approach, IET has again demonstrated that as a remedial contractor facing challenges placed on us by our customers we can offer unique and innovative solutions.
The induction of Ferric Ammonium Citrate (NH4FeC6H5O7) as a remedial compound for the degradation of chlorinated solvents in sulfate rich reducing conditions. The injection of soluble ferric ammonium citrate combines biotic and abiotic pathways to degrade Chlorinated Volatile Organic Compounds (CVOC’s; PCE, TCE, etc.) and alleviate the accumulation of harmful daughter products (Cis and Trans DCE and VC) associated with biotic dechlorination.
Ferric ammonium citrate is a water-soluble complex salt of undetermined structure, commercially available as a powder, granule, or crystal. The compound is a transparent solid, either reddish-brown or green in color depending on its chemical composition. Brown ferric ammonium citrate contains 16.5-18.5% Fe, 9% NH3, and 65% hydrated citric acid, where as green ferric ammonium citrate contains 14.5-16% Fe, 7.5% NH3, and 75% hydrated citric acid. Ferric ammonium citrate readily reduces in light and is most commonly known for its use in cyanotype printing, water purification, and as an acidity regulator in food additives. As a remedial compound, ferric ammonium citrate has a variety of chemical properties that are favorable to enhancing the degradation of chlorinated solvents.
Chlorinated solvents are the most common class of ground water contaminants detected in hazardous waste sites in the U.S. The Agency for Toxic Substances and Disease Registry (ATSDR) has repeatedly listed chlorinated solvents and their degradation products as the most frequently detected group of priority contaminants. Due to the unique characteristics of each site, the remediation of these compounds is often met with a variety of obstacles, inherent to both the target organics and environmental conditions. As a remedial compound ferric ammonium citrate offers a means to overcome such obstacles and apportion the degradation of CVOC’s chemically and biologically. This allows for an initial and prolonged means of removal; first via the production of iron bearing soil minerals (pyrite) and second by stimulating conditions for biologically mediated natural attenuation. Traditionally, sulfate bearing ground waters were thought not amiable for reductive dechlorination. The reduction of sulfate to sulfide, a compound toxic to microbes, inhibits biological activity thus preventing natural attenuation. However, unlike conventional remediation methods ferric ammonium citrate utilizes the reduction of sulfate, to promote the formation of pyrite as a remedial byproduct. The mechanism described herein combats the toxic effects of sulfide on dechlorinating bacteria, while also providing a means of removing target organics through soil mineral (pyrite) suspension.
The approach conceived utilizes the interaction between naturally occurring sulfate (the assumed environmental conditions) and ferric iron through subsequent injections of ferric ammonium citrate. Ferric iron (Fe+3) can reduce to ferrous iron (Fe+2); readily supplying electrons to exchange and react with sulfide. Together, sulfide and iron form pyrite, an iron bearing soil mineral with a favorable reductive capacity. Pyrite possesses a finite number of reactive sites that are directly proportional to both its reductive capacity and the rate of decay for the target organics. The reductive capacity of iron bearing soil minerals (like pyrite) initially results in a rapid removal of target organics by minimizing the competition between contaminants and sulfate as a terminal electron acceptor. Preventing these unfavorable interactions with ferric iron provides a continual source for electron exchange resulting in the timely removal of contaminants through pyrite suspension.
As described above, this reaction works to combine toxic sulfide with ferrous iron for target organic adsorption onto pyrite reactive sites. Once the reductive capacity of pyrite is met, the bound chlorinated solvents precipitate out, removing the contaminants rapidly and without the production of daughter products. Despite the substantial removal this abiotic reaction is often short lived and requires a slower reaction to remove remaining contaminants through biotic dechlorination.
Biotic degradation pathways use a series of slow sequential reactions to convert chlorinated solvents to harmless byproducts via electron exchange. Natural attenuation of these contaminants is enhanced in the presence of an electron donor, food source, electron acceptor, and/or substrate for the microbes. This two-part process integrates the actions of dechlorinating bacteria and the chemical reduction of chlorinated solvents by utilizing their byproducts as an electron acceptor for microbial metabolism. As a result, a sequential dechlorination of contaminants ensues (ex. chlorinated ethylenes) replacing contaminants with a harmless byproduct (ex. Ethylene). Ferric ammonium citrate offers all of the essential components necessary to achieve biotic degradation; ammonium and citrate respectively.
Ammonium and citrate are responsible for stimulating the conditions for microbial growth and initiating the process of biological reductive dechlorination. Citric acid has an essential role in maintaining the biochemistry of microbial metabolism during the krebs cycle and is therefore a key additive for the proliferation of dechlorinating microbes. Citric Acid readily loses its protons in acidic conditions. Thus citrate acts as a H+ donor for the microbes to proceed in a favorable exchange of electrons. This exchange promotes the degradation of the targeted organic contaminants, eventually resulting in the replacement of chlorine atoms with hydrogen atoms via a biotic degradation pathway (first order elimination reaction). In addition to citrate, Ammonium also aids to the pathway by supplying essential nutrients to fuel microbial anaerobic processes. Ammonium also acts as a buffer, stabilizing pH conditions and counteracting acids produced by-way of anaerobic dechloriniation. With an ample supply of nutrients and sustained source of electrons for microbial metabolism, ferric ammonium citrate can achieve a prolonged biotic degradation of remaining contaminants after pyrite suspension.
As a whole, ferric ammonium citrate offers a means to abiotically and biotically apportion the dechlorination process for immediate and prolonged degradation effects. When emplaced in groundwater and soils impacted by chlorinated solvents the ferric ammonium citrate offers all the necessary components for the effective and rapid remediation of compounds such as tetrachloroethane, tetrachloroethene, trichloroethane, trichloroethene, carbon tetrachloride and their anaerobic daughter products.