|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Conference Paper|
|Title||Limitations of Urea as the Nutrient Source in Bioremediation of Petroleum Wastes|
S. Jin, P.H. Fallgren, and M. Li, Western Research Inst.
SPE Annual Technical Conference and Exhibition, 9-12 October 2005, Dallas, Texas
|Copyright||2005. Society of Petroleum Engineers|
Nutrient addition is important to achieving the carbon/nitrogen balance and successful biodegradation of petroleum contaminants. Urea has been considered as a preferred nitrogen source in enhancing biodegradation, because of its high nitrogen content and availability. This study investigated urea in the biodegradation of petroleum-contaminated soils collected from an arid and sandy location in Egypt. Ammonium nitrate served as the nitrogen amendment control in this study. Biodegradation of petroleum-contaminated soils from Wyoming was monitored as a comparison. Performance of urea was poor in the enhancement of biodegradation of petroleum-impacted soil from the Egyptian site, in addition, urea demonstrates an adverse effect on the biodegradation rates. Results indicate that urea may inhibit the microorganisms involved in petroleum degradation. Data from this study suggest that the application of urea in the enhancement of biodegradation of petroleum compounds may not be applicable in geological areas or soils structures similar to those in this study.
Key Words: Bioremediation, petroleum biodegradation, urea, nitrogen amendments
Petroleum exploration, transport, refining, and storage activities generate large amounts of wastes that have adverse impacts on soil and groundwater quality. Aerobic bioremediation of petroleum-contaminated soils has been widely applied in the restoration of polluted sites[1-3]. Aerobic bacteria convert petroleum hydrocarbons into carbon dioxide, water, microbial biomass and metabolites. Parameters that may affect the rate and efficiency of biodegradation include temperature, moisture, salinity, nutrient availability, microbial species, and type and concentration of contaminants[4-5]. Nutrient availability, such as nitrogen and phosphorus, is often limited in petroleum-contaminated soils due to the excessive carbon input from the hydrocarbons. Therefore, nitrogen and phosphorus are usually identified as the limiting factors for biodegradation in soils[6-7]. Optimal carbon to nitrogen to phosphorus (C:N:P) ratios are required to achieve the maximal hydrocarbon biodegradation[8-11].
A C:N:P ratio of 100:10:3 was used in our studies based on the previous data. This study only focused on the role of nitrogen source in biodegradation of petroleum compounds in soil. Nitrogen compounds were added to soils in the forms of ammonium salts and urea. Ammonium salts, such as ammonium chloride (NH4Cl) and ammonium nitrate (NH4NO 3), rapidly release ammonium into soils after application. Ammonium is in a reduced state, which makes it energetically favorable for amino acid formation and other metabolisms[2, 11]. Urea is becoming a popular nitrogen source for enhanced biodegradation, because of its high nitrogen content and relatively slow nitrogen-releasing characteristics. Urea’s slow release mechanism is attributed to the pathway of urease-catalyzed hydrolysis before ammonium is released. Urea has been demonstrated as an adequate and effective source of nitrogen in the enhanced bioremediation of petroleum contaminants in soils, [12-15]. Since large amounts of ammonium were observed increasing biodegradation rates, the potential amounts of ammonium that can be released by urea therefore appear to be beneficial to biodegradation.
However, soil nitrogen can be lost through nitrate leaching, ammonia volatilization, and denitrification into gaseous species, including nitrous oxide (N2O) and dinitrogen gas (N2 ). Xu et al. found that soils containing petroleum hydrocarbons tend to lose nitrogen at greater rates than uncontaminated soils. In addition, landfarm data indicate that urea may play a limited role in enhancing the biodegradation of petroleum wastes in sandy locations.
|File Size||102 KB||7|