ENHANCED TEX BIODEGRADATION IN NUTRIENT BRIQUET-PEAT BARRIER SYSTEM

A two-layer barrier system has been developed to remediate gasoline-co ntaminated ground water. This system consists of a nutrient briquet la yer to continuously supply nitrate as the electron acceptor for contam inant biodegradation and a peat layer to remove residual nitrate via b iological denitrification and residual contaminants by sorption. Nitra te release rates from three different sizes of concrete briquets were used to estimate parameters for modeling solute diffusion in aggregate d porous media with mobile and stagnant porewater regions. Toluene, et hylbenzene, and xylene (TEX) biodegradation rates in denitrifying micr ocosms at pH 8 and 9 were lower than in microcosms at pH 7.4. No degra dation was observed at pH 10 under denitrifying conditions. A laborato ry-scale, permeable barrier system was developed to evaluate TEX remov al and to identify any operational problems. Average removal efficienc ies were 86% for toluene, 71% for ethylbenzene, 43% for m-xylene, and 28% for o-xylene in the nutrient briquet and downstream soil column ov er a 45-day operating period. There was no evidence of benzene biodegr adation under denitrifying conditions in the batch microcosms or conti nuous-flow columns.