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Bioremediation - 3 - 10 September 1993 <br /> In addition to slower degradation rates, under anaerobic conditions it is possible to generate <br /> phytotoxic compounds such as hydrogen sulfide. Hydrogen sulfide and methane may also create <br /> nuisance odors. Sulfates are not abundant in soil and are not commonly used as electron acceptors <br /> in controlled biodegradation of petroleum hydrocarhom. <br /> Because petroleum hydrocarbons are for the most part easily degraded aerobically, aerobic <br /> biodegradation is the most commonly used method in the field and has been studied in more detail <br /> than anaerobic biodegradation. However, if the organics are in the concentration range of 4,000 to <br /> 50,000 mg/l, anaerobic biodegradation may be more effective; aerobic biodegradation may be more <br /> effective for organic concentrations of less than 4,000 mg/l, <br /> Optimal bacterial growth and metabolism in aerobic environments have been shown to occur within <br /> the following parameters: <br /> Oxygen DO > 2 ppm (IL02 > 200 ppm may he toxic to microbes) <br /> Moisture - 20% - 80% of the water-holding capacity (in soil) <br /> Nitrogen - > 5 ppm (added as NH4') <br /> phosphorus - > 1 ppm (added as PO4') <br /> Temperature - 30° - 40° C (86° - 104° F) <br /> pH - 6 - 8 <br /> Salinity (FC) - upper limit 6 - 10 mmhoslem (saline soils EC > 4.0 rmnhoslcm) <br /> Fe'I - G 2 ppm (to avoid precipitation) <br /> Trace minerals - site specific <br /> The addition of micronutrients, such as nitrogen, phosphorus, and trace minerals, for field <br /> applications, has usually been judged to be uneconomical. Therefore, the potential merits of <br /> micronutrient addition are usually not assessed. <br /> Nitrates may be added as ammonium or urea. The presence of large amounts of nitrates may <br /> encourage denitrification under anaerobic conditions. The nilydtes in ammonium and urea may also <br /> pose leaching problems if too much ammonium is added. However, in well aerated soil of neutral <br /> pH, temperature > 50° F, ammonium is nitrified to nitrates in one to two weeks and teaching and <br /> denitrification should not occur. The positively charged ammonium ion binds to negatively charged <br /> soil particles. <br /> Bacteria rely on water to exchange everything through cell walls and provide mobility_ However, at <br /> 100% moisture, there is little available oxygen and at 10% moisture, osmotic and matrix farces <br /> reduce metabolic activity, Moisture content must be controlled in bioremediation of soil to maintain <br /> microbe metabolism_ <br /> There are three approaches to controlled bioremediation: <br /> 1. Above-ground bioreactors <br /> a. Aerated lagoons <br /> h- Activated sludge systems <br /> 80' d 800' oN 22,6 26- 91 dab ON 131 <br />