Treatability evaluation of in situ biodegradation of chlorinated solvents in groundwater

Chlorinated solvents can be completely degraded by bacteria to carbon dioxide and water. Remediation of chlorinated solvents on an industrial scale has classically been performed using physical methods such as air stripping. These techniques tend to take many years because of the tendency of the compounds to sorb to soil particles. Bioremediation of these compounds is a relatively new approach on an industrial scale and the rate and extent of degradation is a function of the bacterial populations present as well as the physical/chemical nature of the site. Because bacterial degradation of chlorinated solvents usually involves co-metabolic processes, treatability studies that relate to what can be achieved in the field need to be performed in order to target the appropriate nutrient delivery regimen. This paper describes results of two treatability evaluations of groundwater contaminated with chlorinated solvents. One site was a landfill with PCE, TCE and cis-1,2-dichloroethylene as the major constituents of concern and the other site was an industrial facility where 1,1,1-trichloroethane and carbon tetrachloride were the primary constituents of concern. Addition of nutrients, methane, and oxygen was tested at the landfill site and addition of acetate and chemical oxygen was evaluated at the industrial site. Results demonstrated thatmore » bacteria capable of degrading the chlorinated compounds were present in both systems. The bacterial numbers increased along with decreases in dissolved oxygen and contaminants. Zeroth order degradation rates from the landfill site were 6 ppb TCE/day and 10 ppb c-1,2-DCE/day. Zeroth order degradation rates for the industrial site were much higher at > 100 ppb 1,1,1-TCA/day and > 28 ppb carbon tetrachloride/day.« less