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.