Biodegradation of phthalate esters by immobilized microbial cells

Gordonia sp. strain 236 can grow with various phthalate esters as sole carbon sources. We studied on the biodegradation of di-2-ethylhexyle phthalate (DEHP) and di-n-butyl phthalate (DBP) by using an im mobilized strain 236. Spiral plastic supports (made of ABS resin, about 18 mm in diameter and about 250mg in weight) were used for the immobilization of the strain. When the strain 236 was cultivated in medium containing 5000μg/ml DEHP, the strain was adsorbed on supports quickly. The amount of adsorbed cells was about 150mg per 1 g supports on a dry basis. In the treatment tank model utilizing the immobilized strain 236, 88.3 % of 250μg/ml DEHP was degraded in 48h in the 1st test run, and 91.7% of 1000 μg/ml DEHP and 100 % of 1000μg/ml DBP were degraded in 48h in the 12th test run. In addition, about 95% of 2000μg/ml DEHP and 2000μg/ml DBP were degraded in 4h in 18th test run. The strain 236 hardly grows at pH5, and lyses and cannot grow at pH10. However, the immobilized strain 236 showed an initial rate for DEHP degradation at pH5 of 3.6 times that of pH7, and DEHP could be degraded even at pH10.