Bioremediation Of Crude Oil Contaminated Soil With Immobilized Microorganism

In oil exploration and exploitation,during the storage and transportation and refining processes,inevitably there will be a lot of crude oil and oil products spilled or leaked onto the ground, causing a large area of oil contaminated soil,soil and ecological environment on a range of hazards.As petroleum hydrocarbons have high biological toxicity,residue in the environment for long periods and cause great harm,how to rehabilitate the contaminated environment becomes increasingly concerned by the community. Bioremediation, be able to be used for in-situ treatment with low-cost, and minimize the negative effects of pollutant concentrations and environmental and other advantages, is very suitable for our present practical needs.To enhance the breeding efficiency of hydrocarbon degrading bacteria in the soil and to facilitate the enlargement of production, preservation, and transportation of the cultures, it will make great sense to make them into immobilized form.Efficient biodegrading microorganism consortium of crude oil of the Yellow River Delta were acclimated and enriched from oil contaminated soil.Their tolerance and biodegradability was tested by liquid culture medium which contains high concentrations of crude oil.Three dominant species were obtained through isolation and purifying culture, and were identified as Microbacterium foliorum, Gordonia alkanivorans and Mesorhizobium.Four kinds of natural polysaccharide were chosen for carrier materials to make the consortium into immobilized beads.The handling difficulty, mechanical strength, and mass transfer abilities of bead were examined, and sodium alginate was selected as carrier, for its simple handling, strong mechanical strength and mass transfer ability.And then diatomite particles were added to sodium alginate to enhance the mechanical strength and mass transfer of the immobilized beads,and the impact of immobilization time on microorganism's activity was tested as well. Finally the preparation conditions of the immobilized beads were set as follows: carrier solution consists of 6% sodium alginate-2% diatomite (w/v),mixed with an equal volume of degrading bacteria saline suspension, and then be dropped into 0.1M CaCl2 solution with acid buret and incubated for 12h. The immobilization efficiency of this method is 92.25%.Scanning electron microscopy microstructures of the immobilized beads were observed,showing a cellular network structure within the particles.Most of the bacteria were embedded in the pores or adhered on the walls of the pores.Particle porosity inside bead is abundant, which is beneficial for oxygen, water and substrate transfer, and can provide sufficient space for the embedded cells'growth. There for, favorable conditions were provided for microorganism cells'growth and multiplication inside the carrier.The immobilized hydrocarbon degrading bacteria in three inoculums were added to the crude oil contaminated soil for biodegradation experiment, and soil moisture and N, P levels were controlled to the desired level.the same amount of free bacteria were inoculated respectively as control.The immobilized consortium achieved much higher reproductive rate TPH degradation efficiency in soil, especially in the initial period of the experiment. After inoculated for 20 days,the immobilized consortium inoculated groups achieved high TPH degradation rate of 27.29%,29.83% and 27.56%, respectively, higher than that of free bacteria at 12.43%,10.10% and 6.43% respectively. And the populations of biodegrading bacteria in soils inoculated immobilized consortium were higher than that of free consortium at 1.20～1.53 magnitude.Finally the storage conditions for the immobilized beads were tested.When the beads are kept in sterilized water at 4℃, they can maintain better biological activity for at least there weeks. The results of this study provides new theoretical basis for the application of immobilized microorganisms in bioremediation of large areas of contaminated soil.