Role of Natural Organic Matter in Accelerating Bacterial Biodegradation of Sodium Dodecyl Sulfate in Rivers

The influence of natural organic matter (NOM) on the adsorption of sodium dodecyl sulfate (SDS) and bacteria to riverine sediment surfaces and the effects of these interactions on the rates of SDS biodegradation in river environments were investigated. SDS was adsorbed substantially to native sediment (containing 16% w/w NOM) but not to organic-free sediment or organic-free sediment coated with either a commercial (Aldrich) or natural humic acid. The presence of NOM on the sediment surface did not influence the overall distribution of the SDS-degrading bacteria, Pseudomonas C12B, between sediment-attached and free-living states. However, the attachment of bacteria to native sediment was stimulated by the addition of SDS, and attachment was maximal within the period of SDS degradation. The rate of SDS biodegradation in the presence of native sediment was faster than that observed in the absence of sediment, and this increase in rate could not be solely attributed to the presence of indigenous bacteria in the sediment. In contrast, the rates of biodegradation in the presence of organic-free and humic-coated sediments were found to be comparable to that observed in the absence of sediment. The results indicated that NOM on sediment surfaces substantially influences SDS biodegradation by localizing both the surfactant and thus, in turn, bacteria at the sediment surface, thereby increasing the likelihood of catalysis.