Effect of river sediment on the biodegradation kinetics of surfactant and non‐surfactant compounds

The half‐time of biodegradation of the surfactant sodium dodecylsulfate (SDS) by Pseudomonas species C12B, was reduced two fold by the presence of a riverine sediment. The sediment alone gave comparatively negligible biodegradation of SDS under otherwise equivalent conditions. The sediment had no effect on the kinetics of biodegradation of the non‐surfactant pyruvate by Pseudomonas strain C12B. In the light of (i) the known strong adsorption of the surfactant SDS, but not pyruvate, to river sediment and (ii) the SDS‐stimulated attachment of Pseudomonas C12B and other SDS‐degraders to the sediment, the above observations indicate that acceleration of biodegradation was the result of simultaneous attachment of both SDS and biodegradation competent bacteria to the sediment. This interpretation was strengthened by analysis of the biodegradation kinetics. The data obtained for biodegradation in the absence of sediment, were fitted best by a model involving logistic growth 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 accumulation of both bacterial cells and substrate at the sediment surface. The enhancement of surfactant biodegradation by sediment is discussed in the context of the design of biodegradability tests and environmental acceptability.