Zhiyong Huang

Hydrocarbon degradation and bioemulsifier production by thermophilic Geobacillus pallidus strains

Geobacillus pallidus XS2 and XS3 were isolated from oil contaminated soil samples in Yumen oilfield, China, and were able to produce bioemulsifiers on different hydrocarbons. Biodegradation assays exhibited that approximately 70% of PAH (250 mg/L) or 85% of crude oil (500 mg/L) was removed by the thermophilic bacteria after 20 days. The bioemulsifiers of the two strains were isolated and obtained a productive yield of 4.24±0.08 and 3.82±0.11g/L, respectively. GPC analysis revealed that the number-average molecular weights (M(n)) of the two bioemulsifiers were 271,785 Da and 526,369 Da, with PDI values of 1.104 and 1.027, respectively. Chemical composition studies exhibited that the bioemulsifier XS2 consisted of carbohydrates (68.6%), lipids (22.7%) and proteins (8.7%) while the bioemulsifier XS3 was composed by carbohydrates (41.1%), lipids (47.6%) and proteins (11.3%). Emulsification assays approved the effectiveness of bioemulsifiers over a wide range of temperature, pH and salinity.

Optimization of biosurfactant-mediated oil extraction from oil sludge.

Oil extraction from oil sludge with biosurfactant formulas was optimized by a Taguchi orthogonal array design of L16 (4(5)) with five main factors, including biosurfactant type (surfactin, lichenysin, rhamnolipid and emulsan), biosurfactant concentration, pH, salinity and solvent. Oil recoveries obtained with the sixteen batch washing experiments with the selected levels of each factor were processed with Design Expert/SPSS and a specific combination of factors with a predicted oil recovery of 76.81% was obtained. The predicted optimal biosurfactant formula of 2.0g/L rhamnolipid, pH 12.0, 10g/L NaCl, and 5.0g/L n-butanol were validated by a washing experiment that yielded an oil recovery of 74.55%, which was 27.28% higher than the grand average oil recovery of the whole experiment design. Based on the optimum biosurfactant formula, the oil extraction process followed first-order kinetics as the washing rate constant and final oil recovery increased with temperature. These results will be informative and meaningful for the design of oil sludge treatment in industrial application.

The Removal of Crude Oil in Waste Drilling Muds by a Constructed Microbial Consortium

Waste drilling muds (WDMs) contain serious pollutants produced by crude oil and gas well drilling. Bioremediation has been known as a useful and cost-effective method for disposal of contaminants in various environments. In this study, an efficient and stable microbial consortium was constructed successfully by successive enrichment of indigenous microorganisms, which can remove oil contaminants from waste drilling muds. Denaturing gradient gel electrophoresis analysis (DGGE) and 16S rRNA gene clone library analysis were used to evaluate the dynamic changes in the microbial consortium in the process. After 7 days’ treatment, the main contaminants were removed mostly by constructed microbial consortium than control treatment, which showed that the constructed consortium was of great potential to remediate polluted drilling fields.

Partial Purification and Chemical Characterization of a Bioemulsifier and Its Application in MEOR

The bioemulsifier secreted by strain XS2, which was isolated from oil-contaminated soil samples in Yumen oil field, China, was partially purified and analyzed. Protease hydrolysis and heat treatment results showed that the protein composition of the bioemulsifier played a significant role in emulsification activity. High-performance liquid chromatography (HPLC) study suggested that the protein composition may exist as glycoprotein. Monosaccharide analysis by gas chromatograph–mass spectrometer (GC–MS) showed that galactose, glucose, xylose, and mannose presented in the bioemulsifier. The emulsification activity of this bioemulsifier was relatively high due to different carbohydrates (n-hexadecane 61 %, liquid paraffin 60 %, Toluene 77 %). Furthermore, single well stimulation trial in Changqing oil field, was done to explore the potential application in Microbial-enhanced oil recovery (MEOR). Up to September 2014, the cumulative increased crude oil production was about 88 T in total 240 days, and the water content of the well-produced liquid decreased from 85 to 25 %. These data illustrated that the bioemulsifier performed a high potential in applications and had important economic values.

Study on Process Optimization for Bioemulsifier Production

A useful bioemulsifier was secreted by Geobacillus sp. XS2 isolated from an oil-contaminated soil sample from Yumen oil field in northern China. The extracellular bioemulsifier was able to form a stable oil/water emulsion. The effects of different bioemulsifier concentrations on cell growth and activity of fermentation broth with water-soluble and water-insoluble carbon sources were studied. Various carbon sources, nitrogen sources, and C/N ratios were screened, and the culture conditions such as pH and ventilation were optimized through the fermentation progress. After a series of steps of optimization, the maximum bioemulsifier production reached to 21.1 g/L ± 1.15 g/L and more than four times higher than that observed in the initial experiment. And the bacterial strain XS2 showed a good performance to adapt to the environment and strong potential for industrial applications.