THE FATE OF DETERGENT SURFACTANTS IN SEWER SYSTEMS

The fate of detergent surfactants in the sewer can be studied both in laboratory tests and in field experiments. The laboratory studies our be used to determine the rate of disappearance of a test molecule as a function of residence time and estimate its half-life in a given habi tat. In addition, important information can be obtained on the mechani sm of degradation. Field studies can determine the actual environmenta l concentrations of surfactants in raw sewage which can then be compar ed with the expected concentration based on consumption volumes. The d ifference between the measured and predicted concentration provides an estimate for the disappearance of the test chemical during its travel in the sewer and confirms the results of the laboratory tests. This p aper focuses on the fate of a number of important representative anion ic, nonionic and cationic surfactants, in the sewer. The results of la boratory die-away studies showed that, in general, the half-life for d isappearance in the sewer was in the order of hours for Fatty Alcohol Ethoxylate (AE), Fatty Alcohol Ethoxy Sulphate (AES) and Di-Ethyl-Este r Di-methyl-Ammonium Chloride (DEEDMAC). These laboratory findings for AES were confirmed by monitoring actual raw sewage reaching municipal sewage treatment plane. In addition, a field study demonstrated that the concentration of glucose amides (GA) is considerably reduced durin g its travel in the sewer. These complementary laboratory and field st udies provide key information for the safety assessment of surfactants . They demonstrate that the concentration of surfactants can be signif icantly reduced in the sewer resulting in a rapid reduction of the env ironmental loading, which is particularly important in environmental s ituations where inadequate or no sewage treatment exists.