Use of Biologically Active Barriers for in situ Treatment of Contaminated Groundwater

Abstract

Aerobic biodegradation has been shown to be effective for many fuel spills. However, success is often limited by the inability to provide sufficient oxygen to the contaminated intervals due to the low solubility of oxygen. Nitrate can serve as an electron acceptor in place of oxygen and results in anaerobic biodegradation of organics via denitrification. Since nitrate is less expensive and more soluble than oxygen, it may be more economical to restore fuel-contaminated aquifers using nitrate rather than oxygen. The aim of this study is to design a two layer trench system to offer an alternative of treating groundwater contaminated with low levels of organics which will be less expensive than the biological and physical processes currently in use. The proposed barrier includes a cement-nutrient(nitrate and phosphate)-briquet layer and a peat layer. Denitrifiers growing on the briquets in the first layer will use the nutrients released from cement-nutrient briquets and degrade BTEX transported into the surface of an attached biofilm. The peat layer will be used to adsorb the residual organics and remove excess nitrate. Laboratory studies are being conducted to evaluate BTEX biotransformation and assess the potential to remediate contaminated aquifers using a nutrient briquet-peat barrier system. Batch equilibrium experiments were conducted to estimate the nutrient release rate and parameters for transport models. Simulated transport results were then compared with results from a one dimensional column test. Microcosm experiments were performed to evaluate BTEX degradation rate under aerobic, anaerobic, and denitrifying conditions. The microbial transformation of BTEX was also studied in a series of columns: a cement-nutrient briquet column, followed by a peat column and a soil column. This system was used to simulate biodegradation in a saturated-flow barrier. A feed solution containing anoxic synthetic groundwater amended with BTEX was pumped through the column. The column influent and effluent were monitored for dissolved oxygen, BTEX, nitrate, nitrite, ammonia, phosphate, pH, and other relevant parameters.