How to accurately assess surfactant biodegradation-impact of sorption on the validity of results

Surfactants not only are widely used in biotechnological processes but also constitute significant contaminants of the modern world. Among many reports, there is a shortage of works which summarize the issue of surfactant sorption to biomass in a way that would elucidate the biological factors for analysts and analytical factors for microbiologists. The main factor, which is not as obvious as one would expect, is associated with the susceptibility of analytical approaches to errors resulting from incorrect handling of biomass. In case of several publications reviewed in the framework of this study, it was not possible to establish whether the decrease of the analytical signal observed by the authors actually resulted from biodegradation of the surfactant. This review emphasizes the necessity to consider the possibility of surfactant sorption to microbial cells, which may result in significant detection errors as well as conceptual inconsistency. In addition, a reference study regarding representative surfactants (cationic, anionic and non-ionic) as well as yeast, Gram-negative, Gram-positive bacteria, and activated sludge was provided to highlight the possible errors which may arise from disregarding sorption processes when determining degradation of surfactants. This particularly applies to systems which include ionic surfactants and activated sludge as sorption may account for 90% of the observed depletion of the surfactant. Therefore, a systematic approach was proposed in order to improve the credibility of the obtained results. Finally, the need to employ additional procedures was highlighted which may be required in order to verify that the decrease of surfactant concentration results from biodegradation processes.

Study of Organic Surfactant Sorption in Organophilic Clays

Bentonite clays, due to an immense variety of applications, are widely studied. Yet currently, organically modified bentonite clays studies have been increasing. The methods most studied involve addition of ionic or non-ionic surfactants to synthesize organophilic clays. The synthesis can be performed in two ways: by ion exchange (double replacement reaction chemistry), or by ion-dipole interaction where organic molecules are adsorbed on the surface of clay. The present work studies the sorption mechanisms of ionic and non-ionic surfactants to the surface of bentonite clays, thus making them organophilic. The results for the sorption experiments were obtained by adjusting the parameters of known mathematical models to the experimental data, the linear, and Freundlich models gave the best results for the sorption isotherms.