Preliminary Studies On Enhanced Bioremediation Of Soil Contaminated By Heavy Oil With Biosurfactant

Crude oil continues to be used as the principle source of energy. Crude oil contains a complex mixture of compounds, and its major constituents are the saturated compounds, the aromatics, the resins, and the asphaltenes. The world demanding for fuel has led to the exploration and production of an increasing number of crude oil reserves. When not managed properly, wild scale production, transport, refining process, use and disposal of crude oil may have made it a significant hazards to human health and the earth's ecology. Crude oil spills into environment will often eventually end up on soil. Along with the advance of exploration and refining process technology, the world scale heavy oil exploration has been activity day by day. Nevertheless, the intrinsic bioremediation of heavy oil contaminated soil is a very long process as the indigenous population of hydrocarbon degrading bacteria is considerably low and the high viscosity and low bioavailability heavy oil that contains amount of asphalt and resin. Hence, soil contaminated by heavy oil at petroleum-related sites should be paid more and more attention, and some effectual measures should be taken to recover contaminated soil.Recently, there are four feasible groups of contaminated soil remediation technologies, including physical, chemical, biological and synthetical remediation. Although physical remediation can clean up mostly pollutant in soil rapidly, the soil construction and constituents could be destroyed, and these treatments are expensive. Chemical remediation also acquired better oil remove efficiency, but the second pollution induced by chemical reagents in these treatments is likely to limit their application. Botanical and microbial remediation technologies are both bioremediation. They are economic efficiencies technologies. However, Botanical remediation could be influenced by bioavailability of pollutants, and the low remediation rate of these treatments is another disadvantage. Microbial remediation is the method that petroleum hydrocarbons in soil can be devolve and remove at the microbial metabolic activities through utilizing physical, chemical and biological process of the system of soil- microbe-pollutant themselves, and has been regarded as promising environmentally friendly and economic efficiency treatment technology for such contamination. Nevertheless, the high viscosity and low bioavailability heavy oil that contains amount of resin and asphalt, which make them the most difficult to be biodegraded. Therefore, it is necessary to take some measures to enhance the bioremediation.In the process of microbial remediation, the control step of the biodegradation petroleum hydrocarbons is the rate that the pollutants transfer from soil particles into inside of cells. Some studies showed that surfactants are thought to improve the stability of the emulsion and desorbs a number of hydrophobic compounds adsorbed to soil. Therefore, the bioavailability of petroleum hydrocarbons could be improved by introduced surfactants. Because chemically synthesized surfactants are not biodegradable and can be toxic to the environment or can became a limit factor as priority carbon resources. However, many microorganisms produce extracellular or membrane-associated biosurfactants because of their ability to decrease surface tension, to stabilize emulsified liquid, biodegradability, low toxicity. Thus, Biosurfactants could be used to help enhance heavy crude oil contaminated soil bioremediation.Until now, there are some studies on the screening biosurfactants produced bacteria and applying biosurfactants to enhance composting, oil extraction, contaminated soil remediation. However most of these studies aimed at a single pollutant or some saturated hydrocarbon, few reports on remediation of heavy oil contaminated soil. In our country, the problem of heavy oil polluted soil of Liaohe oil field is more and more significant followed by heavy oil exploitation, refining process et al. Far beyond the critical value of 500mg/kg, the oil content is above 10000mg/kg in serious polluted soil of Liaohe oil field. Therefore, the contaminated farmland soil Liaohe oil field was selected as testee soil, and indigenous microbial strains of the soil were habituated. Then biosurfactants produced bacteria were screened, and the biosurfactants were extracted. In succession, biodegradation of heavy oil by bacterial consortium amended with biosurfactants was monitored in shake flask conditions. Heavy oil degrading rate, total amount bacteria, and dehydrogenase activity of soil were selected as the representations of the general chemistry index, bacteriology index and the toxicity index. The contaminated soil treatments were set up to investigate the effects of these additives on biodegradation. The research of this paper is helpful to guide the application of heavy polluted soil bioremediation technology, and provide heavy oil degrading bacterial consortium and biosurfatants in enhanced bioremediation of heavy polluted soil.In this paper, adding heavy oil intentionally firstly habituated indigenous microbial strains of the soil. Thirty-three bacterial strains were isolated with heavy oil as the carbon source alone. Two higher biosurfactant produced strains and nine higher heavy oil-degrading strains were screened from all the isolates. The biosurfactants produced by strain XJ1 and SJ4 in the fermentation broth could reduce the surface tension of water from 72.4 mN/m to 36.1 mN/m and 36.2 mN/m respectively. In the process of inoculating the two strains, the rates of heavy oil-degradation were 35.89% and 31.59% after treatment for 14 days. Infrared spectral analytic results show the biosurfactants are both kinds of glycolipid. For strains XJ1 and SJ4, the surface tension of fermentation broth is a cell-density-dependent phenomenon: that is, the greater the number of cells, the higher the concentration of biosurfactants and the lower value of surface tension. Biosurfactants produced by strain XJ1 and SJ4 contains are amphiphilic molecules consisting of a hydrophilic and a hydrophobic domain. Thus these compounds could be added to heavy oil polluted medium to enhance bioremediation processes. In that the lag phase of the bacterial consortium could be shortened by addition of the biosurfactant the biodegradation was promoted. The results in shake flask conditions showed a significant reduction of two heavy oil levels [1‰and 2‰(W/V)] of the liquid culture media compared with that of no addition of the biosurfactants at the end of 180 hours.During biodegradation process of 180 hours, the heavy oil biodegradation rates increased from 26.59±0.89% and 24.58±0.66% to 38.13±2.67% and 34.36±1.37% respectively compared with that of no addition of the biosurfactant. In addition, amount of bacteria has been on a steady level, the biosurfactant could be decomposed through metabolic activities of the bacterial consortium and the alkalescence liquid culture media turned to neutral.This result implied that the biosurfactant could be used to promote the bioremediation process of the soil contaminated with heavy oil. Then the series contaminated soil treatments were set up. All treatments incubated in the presence of inorganic nutrient (C: N: P: K=100:10:1:1), water content (15%), temperature (30 oC), and agitation frequencies. During biodegradation process of 60 days, heavy oil degradation, bacterial growth, dehydrogenase activity (DAH) and pH values of soils were measured. Maximum heavy oil degradation occurred in NS+BC+GBS with the concentration of treatment soils decreased from 39.9798±0.0250 mg/g to11.0781±0.7449 mg/g. Correspondingly, degradation rates approximately 72%, and the arguments of biodegradation were more pronounced than in NS+BC. Moreover in NS+BC+GBS, the microorganism population kept 108 CFU/g of soil higher than other treatments, the DAH increased significantly and the alkalescence soil turned to neutral during the treatment process. But the studies of this paper on biosurfactants enhanced heavy oil polluted soil bioremediation are still on Preliminary periods. All impact factors of the enhanced treatment only have been investigated at one level. Whether this impact factors level is the best or not, it will have to do some further researches in order to continue perfecting treatment condition. In addition, further research is needed how to improve the condition of production of bisurfactants. If the amount of produced bisurfactants has been increased, application of the biosurfactants will be feasible.