Search

Biodegradation of two amphiphilic "soft" antimicrobially active derivatives of lauric (dodecanoic) acid, a quaternary ammonium salt and an amine oxide bearing an amide or ester group, was followed using microorganisms from activated sludge. Primary biodegradation was determined by ion-selective electrodes, total biodegradation as the chemical oxygen demand. Though organic ammonium salts quickly undergo primary biodegradation, the rest of the molecule is difficult to destroy. In contrast, amine oxides are easily biodegradable.

Bacterial strains with a high biodegradation potential were isolated from activated sludge. Their ability to decompose the hard bis-quaternary ammonium salt FB was determined by the method of chemical oxygen demand (COD) in a mineral medium, where the compound FB was the only source of carbon. The COD values were very low after 21 d and in the course of this period they reached zero level twice. The contribution of adsorption to decrease the COD value was small. The maximum COD decrease was accompanied by an increase of cell respiration. It is suggested that FB is effectively decomposed in spite of the fact that according to its structure it is a typical hard detergent.