Formatted Title
Development and Demonstration of Solid-Phase Colloidal Remediation Amendments for Use in Permeable Reactive Barriers
Background/Objectives
Background/Objectives. Utilizing direct push technology (DPT) injections for the installation of permeable reactive barriers (PRBs) can provide cost and flexibility advantages when compared to trenching and similar methods. Small particle size amendments are advantageous in that they can be injected using low pressure and promote uniform product distribution but also are known for their rapid reactivity caused by their high surface area with a premature consumption of the amendment and a lessened effective lifetime. This study describes the results of research efforts to develop and evaluate colloidal amendments engineered to maintain their functionality for several years after product application.
Approach/Activities
Approach/Activities. The development of a colloidal bioamendment with a particle size of less than 0.5 micrometers will be described. Treatability studies were performed to evaluate the colloidal bioamendment’s ability to degrade chlorinated ethenes. Persistence was evaluated by adding the bioamendment to a bottle and replacing 10 percent of the liquid volume every two weeks for 500 days. The research activities were followed by a pilot demonstration where colloidal activated carbon (CAC) and the colloidal bioamendment were co-applied using DPT.
Zero-valent iron is used to accomplish the abiotic reduction of groundwater contaminants. The development of a small particle size sulfidated zero-valent iron product (SZVI) engineered for in situ remediation will be described. SZVI contains a core-shell configuration with a surface layer of reduced iron sulfide and an iron core. This configuration inhibits unproductive hydrolysis reactions that consume iron and lessen its reactive lifetime. Reactivity was evaluated using closed bottle treatability studies and column studies. Persistence was evaluated using a multi-year column study where an oxygenated TCE solution was continuously passed through a sand column containing a representative in situ dose of SZVI. A remediation program was then performed using a series of five PRBs containing a mixture of SZVI and CAC applied using DPT.
Results/Lessons Learned
Results/Lessons Learned. Laboratory studies indicated the bioremediation amendment could accomplish and sustain the biodegradation of a 10 mg/L TCE solution. For the initial dose, elimination of TCE and daughter products was accomplished in about 30 days. Biodegradation continued over a longer period including several TCE re-spikes. The persistence experiment showed that a steady and continued supply of total organic carbon was provided (TOC) for 500 days. The results of the pilot study were successful with a complete degradation to ethene; elevated microbial counts and elevated TOC concentrations were maintained for over two years.
Laboratory studies with the SZVI product showed a rapid elimination of TCE, with a half-life of about three days or 30 times faster than bare ZVI. About 90% of the SZVI’s TCE degradation occurred via beta-elimination with a cis-1,2-dichloroethene (cDCE) yield of about 10%; cDCE degraded more slowly than the parent compounds. The column study showed that ZVI reactivity was maintained for over four years indicating that hydrolysis was inactive. The field application using SZVI and CAC was also successful, with the elimination of greater than 95% of contaminants in performance wells and allowing for the property redevelopment to move forward.