Sorption and biodegradation of 2,4-dichlorophenol in the presence of organoclays

Abstract

The influence of sorption on the biodegradation of 2,4-dichlorophenol (DCP) by Ralstonia eutropha was investigated using organoclays. The aim was to examine the suitability of organoclays combined with biodegradation in remediation techniques. Two types of organoclays were used: a dodecyltrimethylammonium montmorillonite, where 89% of the former sodium ions were exchanged by the cationic surfactant (C 12-MM), and a dioctadecyldimethylammonium montmorillonite complex (35% exchange of the sodium-ions) (2C 18-MM). The organoclays showed high sorption affinity to DCP resulting in the intercalation of DCP into the interlayers of the organoclay. The sorption processes were reversible and completed within minutes. Neither organoclay was inhibitory to R. eutropha degrading fructose. This was different with DCP as sole energy and carbon source. In the presence of DCP C 12-MM led to a decrease in cell numbers caused by a coupled effect of DCP and small amounts of free C 12 in solution. This was not observed with 2C 18-MM, as the concentration of 2C 18 in solution was lower because of the lesser degree of exchange (35% compared to 89%). The addition of 2C 18-MM enabled complete biodegradation of DCP in initially toxic DCP concentration ranges. Adsorption lowered the DCP concentration to a non-toxic level. Because the sorption process was reversible, DCP was desorbed when R. eutropha reduced the DCP concentration in the liquid phase by biodegradation. The whole amount of DCP—dissolved and initially adsorbed—was degraded as confirmed by oxygen consumption and cell concentration measurements. Organoclays can be very helpful tools in remediation when the exchanged amount of surfactant remains low. They even allow bioremediation under toxic circumstances, as was shown with 2C 18-MM.