EFFECT OF RIVER SEDIMENT ON THE BIODEGRADATION KINETICS OF SURFACTANTAND NONSURFACTANT COMPOUNDS

The half-time of biodegradation of the surfactant sodium dodecylsulfat e (SDS) by Pseudomonas species C12B, was reduced two fold by the prese nce of a riverine sediment. The sediment alone gave comparatively negl igible biodegradation of SDS under otherwise equivalent conditions, Th e sediment had no effect on the kinetics of biodegradation of the non- surfactant pyruvate by Pseudomonas strain C12B. In the light of (i) th e known strong adsorption of the surfactant SDS, but not pyruvate, to river sediment and (ii) the SDS-stimulated attachment of Pseudomonas C 12B and other SDS-degraders to the sediment, the above observations in dicate that acceleration of biodegradation was the result of simultane ous attachment of both SDS and biodegradation competent bacteria to th e sediment. This interpretation was strengthened by analysis of the bi odegradation kinetics. The data obtained for biodegradation in the abs ence of sediment, were fitted best by a model involving logistic growt h on the added surfactant. The biodegradation data in the presence of sediment were fitted to variants of this model, including one allowing growth on material endogenous to the sediment. Of the several models tested, the data were fitted best by one which is consistent with accu mulation of both bacterial cells and substrate at the sediment surface . The enhancement of surfactant biodegradation by sediment is discusse d in the context of the design of biodegradability tests and environme ntal acceptability.