Use of Soybean Oil and Soybean Products for Groundwater Bioremediation
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Date
2004-07-07
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Recent laboratory and field studies have shown that injection of soybean oil and related materials into the subsurface can provide an effective, low-cost alternative for enhanced anaerobic bioremediation. The purpose of this laboratory study is to further evaluate the effectiveness of emulsified soybean products for the reduction and immobilization of nitrate, chromate, and acid mine drainage.
Batch microcosm screening studies were first conducted to evaluate the potential of several different substrates to enhance in-situ anaerobic biodegradation of nitrate. The substrates evaluated were food-grade materials, including molasses, liquid soybean oil, fully hydrogenated soybean wax, blown soybean oil, soy methyl ester, and mineral oil. With the exception of mineral oil, the tested substrates were all able to support nitrate degradation with the slowest degradation rates occurring for fully hydrogenated soybean wax.
Intermittent flow through soil column studies were also conducted to evaluate the substrate degradation rate, nitrate removal efficiency, and lifespan of different soybean treatments. The soybean oil treatment stimulated denitrification removed nitrate and nitrite concentrations below detection in the liquid and fully hydrogenated soybean wax treated columns without the addition of a denitrifying bacterial inoculum. No apparent benefits or disadvantages were observed for either treatment.
An identical study was conducted for chromate. Microcosm results were favorable, showing aqueous chromium (VI) removal even in no added carbon control microcosms. However, soil column experiments yielded mixed results. No removal of influent chromium was observed in columns treated with liquid or fully hydrogenated soybean oil at high influent chromate concentrations. A second set of columns were tested with lower concentrations of chromate, and resulted in complete removal of effluent chromium to below detection.
Batch microcosms were also constructed with acid mine drainage (AMD) generating spoils from a former coal mine in Sequatchie Valley, TN. The bottles were amended with simulated acid mine drainage and a small liquid inoculum from an anaerobic treatment wetland. Several combinations of treatments were evaluated including easily degradable sugars (molasses), more slowly degradable oils (soybean), yeast extract, and partially neutralized with sodium bicarbonate buffer. Despite the low pH and presence of toxic metals, in-situ reduction of AMD was significantly enhanced with a soybean oil substrate. Sulfate declined from 1,800 mg/L to 10 mg/L, pH increased from 2.6 to 6.4 and iron was precipitated in a 2:1 molar ratio with sulfate removal. Lesser removal of some iron and sulfate also occurred in bottles amended with only molasses and yeast extract. These results demonstrate that soybean oil addition can be very effective in treating AMD and the initial pH of the AMD is not a significant problem if an appropriate microbial inoculum is provided.
Laboratory soil columns packed with mine spoils were also studied for AMD degradation. Treated columns received a one time amendment of the commercially available soybean emulsion EOS® (Edible Oil Substrate) and were bioaugmented with the bacterial consortia developed from the microcosm studies. Simulated AMD was then pumped through the columns with a six to seven-day hydraulic retention time (HRT). During passage through the EOS® treated columns, pH increased from <3 to ~6, SO₄ was reduced by 75%, and aluminum, copper and zinc were reduced to below the analytical detection limit. Amendments were later made to the influents to include greater concentrations of manganese, zinc, aluminum, copper, and sulfate with less iron. The effect of the added sulfate increased electron donor usage and effectively shortened the potential lifespan of the treatment.
Changes in permeability were monitored for all the column experiments to evaluate the potential for fouling of an edible oil barrier with biomass and/or inorganic precipitates. Significant loss in permeability was observed in most of the treated columns. A mass balance of the carbon added through soybean treatment and potential carbon use due to biological redox reactions is also evaluated for all columns. The rate of carbon use appears heavily reliant on the electron acceptor loading rate, but only gross estimates of treatment lifespan are possible due to high mass balance error.
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Keywords
anaerobic respiration, chromate, acid mine drainage, nitrate
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Degree
MS
Discipline
Civil Engineering
