ABSTRACT
Four screening methods, colorimetric assay, blood-plate hemolysis method, surface tension activ- ity and oil spreading technique were introduced to isolate strains producing bio-demulsifiers from 6 different bacteria source samples. The results of various screening methods were evaluated in this paper. Seventeen demulsifying strains were obtained, which are qualified in demulsification test of kerosene model emulsions. Among them, 5 strains showed high demulsifying ability, achieving 70% plus demulsifying ratio within 24 hours. Petroleum-contaminated soil, excess sludge from biological process treating oilfield produced water and sludge from municipal wastewater treatment plant were the best among all tested sources. Due to the determination limit, the colorimetric assay and blood-plate hemolysis method are not competent to screen bio-demulsifiers strains. The measurement of surface tension and oil spreading method were easy but accu- rate methods to isolate bio-demulsifiers strains. Although demulsification test of model emulsion is an effec- tive technique to target strains with the capability of breaking emulsions, it is sophisticated and time-con- suming. Thus it is recommended to use surface tension and oil spreading methods in pre-screening and vali- date the results in demulsification test with kerosene model emulsions.