Adsorption of Linear Alkylbenzenesulfonates and Their Complexes with Cationic Surfactants on River Sediment, and Their Biodegradation in River Water

Abstract

In order to know the behavior of linear alkylbenznesulfonate (LAS) and their complexes (LAS-CS) with cationic surfactants (CS), alkyltrimethylammonium chloride (TM) and dialkyldimethylammonium chloride (DM), in the aquatic environment, the formation of LAS-CS, their adsorption on the river sediment and primary biodegradation in the river water were studied. The formation of LAS-CS reached to the equilibrium within thirty minutes, and no effects of pH and reaction temperature were observed. It was confirmed that LAS formed LAS-CS with TM and DM at molar ratios from 1 : 1 to 6 : 1 and from 1 : 1 to 2 : 1, respectively. The adsorption isotherms of LAS and LAS-CS with TM or DM at molar ratios of 1 : 1 and 2 : 1 followed to the Freundlich's equations. The adsorption capacities of LAS-CS were smaller than that of LAS. Their order was LAS>LAS-TM>2LAS-TM>LAS-DM>2LAS-DM. The adsorption capacities of LAS, LAS-TM and 2LAS-TM increased with increasing the alkyl chain length of LAS, whereas those of LAS-DM and 2LAS-DM showed little variation among the alkyl chain length homologues. The primary biodegradation rates of LAS-CS with TM or DM at molar ratios of 1 : 1 and 2 : 1 were slower than that of LAS. Their order of biodegradation (% decreased during 14 days) was LAS (100%)>2LAS-TM (56%)>LAS-TM (36%)>2LAS-DM (31%)>LAS-DM (29%). The biodegradation of LAS and LAS-CS also decreased with increasing the alkyl chain length of LAS.