Effects of sorption on the biodegradation of 2-methylpyridine in aqueous suspensions of reference clay minerals

The effects of sorption on the bioavailability of 2-methylpyridine (2-MP) were investigated by determining the biodegradation of 2-MP by an Arthrobacter sp. in aqueous suspensions of reference clay minerals and a synthetic cation exchange resin. Adsorption of 2-MP on kaolinite, illite, hectorite, montmorillonite, and Dowex® was determined by the batch equilibrium method. In general, adsorption of 2-MP was positively correlated with the cation exchange capacity of the sorbent, suggesting that sorption of 2-MP on clay minerals occurs through a cation exchange reaction via the 2-methylpyridinium ion. The biodegradation of 2-MP was most rapid in the kaolinite suspensions, followed by no clay > illite ≫ Dowex > hectorite/montmorillonite. With the exception of kaolinite, adsorption of 2-MP on clay minerals and Dowex reduced the rate of biodegradation. The degree of attenuation was positively correlated with the fraction of 2-MP sorbed, suggesting that sorbed 2-MP was not directly available for degradation. Desorption was not rate limiting in suspensions containing hectorite, montmorillonite, or Dowex; however, desorption may have become limiting in the kaolinite and illite suspensions. The results of this study clearly indicate that adsorption can directly affect the degradation of 2-MP in complex mineral systems.