Long-term chemical and biological stability of surfactant modified zeolite

We determined the chemical and biological stability of surfactant-modified zeolite (SMZ) in laboratory batch and column experiments. SMZ prepared using hexadecyltrimethylammonium (HDTMA)-Br or -Cl was stable in high ionic strength and high- and low-pH environments, with more than 90% of HDTMA remaining bound to the zeolite surface after washing with 100 pore volumes. However, up to 20% of the HDTMA washed off in low ionic strength solutions (I < 5 mM) and up to 50% washed off in a 1.0 mM Cs+ solution. HDTMA bound to the zeolite surface was resistant to microbial degradation, with more than 98% of the original HDTMA remaining after 12-17 weeks of incubation under aerobic or anaerobic conditions. While aqueous HDTMA was biocidal, HDTMA bound on SMZ did not inhibit microbial growth. On the basis of the results of this study, SMZ appears suitable as a sorbent for longterm in situ applications and as a substrate for enhanced bioremediation.