Giorgio Cassani

Determination, aerobic biodegradation and environmental occurrence of aliphatic alcohol polyethoxylate sulfates (AES)

A new analytical method was developed for the routine specific determination of the anionic surfactant Alcohol polyEthoxylate Sulfate (AES) in environmental aqueous samples. An enrichment/fractionation of the target analytes in water samples was performed by solid-phase extraction (SPE) on graphitized carbon black (GCB) (recoveries: 90–103%), followed by hydrolysis/derivatization with fluorescent reagents and separation/detection by reversed-phase high performance liquid chromatography coupled with fluorescence (HPLC-FLD). The developed procedure was applied to the study of the aerobic biodegradation of AES under laboratory conditions and to a ten-month monitoring of AES, as well as of linear alkylbenzene sulfonates (LAS), nonylphenol polyethoxylates (NPE) and alcohol polyethoxylates (AE) surfactants, in the Po river (Northern Italy). The residual concentrations found in the river waters were compared and used for a preliminary estimation of the annual average loads of monitored surfactants in the Adriatic Sea.

Ring testing of the AnBUSDiC test; a new screening method for the anaerobic degradability of surfactants

BackgroundSurfactants are widely used across the globe both in industrial and consumer products; their biodegradation characteristics are therefore of high importance. Upon entering a wastewater treatment plant (WWTP), the majority of surfactants are aerobically mineralized to CO2 and H2O. However, a small fraction is inevitably left non-degraded and adheres to the remaining sludge. This sludge is usually further treated in anaerobic digester tanks. Assessment of existing methods for determining anaerobic biodegradability has led to the development of a new test method, which is in principle based on the method DIN 38414 part 8. This new test, named the anaerobic biodegradation under sludge digester conditions test (abbreviated to AnBUSDiC test) allows for a quantification of the degradation of surfactants under conditions encountered in the anaerobic digester tank of municipal WWTPs. The AnBUSDiC test has several advantages over existing methods. The main advantage is that it is particularly suitable for surfactants, because the two-step design minimizes possible unspecific digester gas formation caused by the surface activity of the test substances, therefore avoiding false positive results.ResultsIn order to further standardize the AnBUSDiC test and gain regulatory acceptance, a ring test was organized involving seven laboratories, and five model surfactants from different surfactant classes (anionic, non-ionic (branched and linear) and amphoteric) plus a positive control, glucose. The AnBUSDiC test produced reliable repeatable results between laboratories; however, some additional modifications were suggested. It was identified that the original test method did not identify a clear endpoint from which a biodegradation value should be taken. It was proposed that a new more concise endpoint be defined in combination with the AnBUSDiC test to allow better comparability between test results.ConclusionsThe inclusion of a second addition of test substance is a major step forward in the elimination of the variability produced by non-specific gas production. With the exception of one anomalous result for linear alkylbenzene sulfonates, for which an explanation can be provided, the AnBUSDiC method appears to provide overall robust and interpretable results.