Use of vegetable oil in a pilot-scale denitrifying barrier

Nitrate in drinking water is a hazard to both humans and animals. Contamina ted water can cause methemoglobinemia and may pose a cancer risk. Permeable barriers containing innocuous oils, which stimulate denitrification, can r emove nitrate from flowing groundwater. For this study, a sand tank (1.1 x 2.0 x 0.085 to in size) containing sand was used as a one-dimensional open- top scale model of an aquifer. A meter-long area near the center of the tan k contained sand coated with soybean oil. This region served as a permeable denitrifying barrier. Water containing 20 mg l(-1) nitrate-N was pumped th rough the barrier at a high flow rate, 11121 week(-1), for 30 weeks. During the 30-week study, the barrier removed 39% of the total nitrate-N present in the water. The barrier was most efficient during the first 10 weeks of t he study when almost all of the nitrate and nitrogen was removed. Efficienc y declined with time so that by week 30 almost no nitrate was removed by th e system. Nitrite levels in the effluent water remained low throughout the study. Barriers could be used to protect groundwater from nitrate contamina tion or for the in situ treatment of contaminated water. At the low flow ra tes that exist in most aquifers, such barriers should be effective at remov ing nitrate from groundwater for a much longer period of time. Published by Elsevier Science B.V.