Formatted Title
Laboratory Evaluations of ZVI and EVO in Combination with Sulfidation and Added Sulfur Containing Amendments
Background/Objectives
Laboratory batch and column studies were conducted to compare the ability of several different sulfidated zero valent iron (ZVI) particles to react with halogenated solvents at different loadings, incubation times, contaminants, and bioaugmentation culture. The impact of several iron and sulfur containing compounds including ferrous gluconate, ferrous lactate, ferrous sulfate, and ferrous sulfide (mackinawite) alone and in combination with emulsified vegetable oil (EVO) were also evaluated. Sulfate additions can promote sulfidation of ZVI and formation of ferrous sulfides in situ that increase abiotic reactions.
Approach/Activities
Laboratory batch studies were completed across a diverse range of conditions – particle sizes, ZVI loadings of 1 to 11 g/L, with and without sulfidation, with and without soluble sulfate, and organic substrate electron donors. Contaminants included chlorinated ethenes (CEs) such as tetrachlorethene (PCE), trichloroethene (TCE); chlorinated methanes (CMs) such as carbon tetrachloride (CT), chloroform (CF); chlorinated ethanes (CAs) such as 1,2-dichloroethane (2DCA), 1,1,1-trichloroethane (1,1,1-TCA); bromoform (BF), and ethylene dibromide (EDB). Incubation times ranged from 21 to 91 days at room temperature under static conditions. Some studies used only water and other amendments and other studies incorporated soil. Column tests were conducted with four ZVI particles at 4% loadings in sand and a sulfidated ZVI particle or combinations of 10 g/kg of a small ZVI particle, EVO, and a ferrous sulfide solution (FSS). Other batch studies evaluated the impact of the FSS alone and in combination with EVO as well as the addition of soluble sulfate.
Results/Lessons Learned
The addition of sulfide with sodium dithionite, calcium polysulfide, sulfur, and FSS to the ZVIs generally increased the extent and rate of dechlorination for PCE, 1TCA, and EDB over the corresponding untreated ZVIs. CT or BF generally were degraded almost to completion with and without sulfide. In the first column studies, the 4% by weight ZVI loading resulted in average CE removals from the influent of 79% (larger ZVI) to a maximum of 98% (smaller ZVI). With the same size ZVI particle, the addition of sulfide increased the average CE removal from 79% to 93% in the sulfide treated column. Another comparative column study showed greater removals of the parent and daughter products with the combinations of ZVI and FSS than ZVI alone. The combinations of SRS, ZVI, and FSS resulted in 97% or greater of TCE, 1,1,1-TCA, and CF from the influent concentrations. ZVI loadings > 4 g/L and in combination with sulfidation and organic substrates, was shown to be very effective in degrading many solvents.
Variable impact of FSS alone was observed. FSS alone requires quite high loadings to be effective. Combinations of FSS and SRS showed some improvement in the degradation of CE, CA, and CM The combination of FSS, SRS, and bioaugmentation culture achieved the maximum removals of CE, CA, and CM. In many of the FSS treatments, there was rapid degradation but little improvement over the next one to two months.