Abstract:

Immobilization of the bacterium Rhodococcus erythropolis DS-3 cells, which was isolated from the oil-soaked soil of Gudao oilfield and could decompose dibenzothiophene (DBT) by 4S pathway, was studied.The effects of immobilization conditions on the bacterium’s bio-desulfurization characteristics and on desulfurization of diesel fuel were investigated.The results showed that the immobilized cells with sodium alginate and polyvinyl alcohol as the immobilized carrier and 1 mmol·L^-1 dimethyl sulfoxide as the culture medium showed good bio-desulfurization characteristics and long natural life.The optimum immobilized condition was 4℃ crosslinking temperature with the concentrations of sodium alginate 2%, polyvinyl alcohol 8%,cells to mixed carrier ratio 0.1 g·ml^-1 and calcium chloride content 2%.After three cycles of circulated desulfurization, the content of DBT decreased from 0.5 to 0.011 mmol·L^-1, the overall rate of desulfurization was 93%, and the average desulfurization efficiency was about 0.225 mg DBT ·(g DCW)^-1·h^-1.The refined diesel fuel with sulfur content 340 mg·L^-1 could be desulfurized by immobilized cells to a low sulfur content of 42 mg·L^-1.Furthermore, the reuse and life periods of immobilized cells were much better than unimmobilized cells.The life periods of the reactivated immobilized cells reached more than 250 h.DS-3 could utilize alcohol, saturated aliphatic alkane which has a C₈—C₁₅ carbon chain as its sole carbon source, but could not utilize cycloalkane, aromatic hydrocarbon and saturated aliphatic alkane which has a carbon chain shorter than hexane or longer than hexadecane.The preference of carbon source was in the order of ethanol, glucose and alkane.GC-FID analysis of refined diesel fuel before and after bio-desulfurization showed that the composition of alkane had little change during bio-desulfurization.It was indicated that the desulfurization of DS-3 specifically cut carbon sulfur bond but had no effect on alkane.