Removal and degradation of β-lactam antibiotics in water using didodecyldimethylammonium bromide-modified montmorillonite organoclay.

β-Lactam antibiotics including penicillin G, nafcillin, cefazolin, cefotaxime, and oxacilline in water were rapidly removed and degraded by using didodecyldimethylammonium bromide (DDAB)-montmorillonite (MT) organoclay. Removal of antibiotics increased with increasing the amount of organoclay added and the amount of DDAB sorbed on MT. Extents of organoclay sorption of antibiotics were represented by the binding constants to DDAB molecules and correlated to the aqueous-octanol distribution coefficients. The degradation rate of β-lactam antibiotics was found to significantly increase by the organoclay sorption. Even under the mild conditions (25°C and pH 7), penicillin G (m/z=335) nearly completely (>98%) degraded into penicilloic acid (m/z=353) missing β-lactam ring within 2h. The first-order reaction rate of the primary degradation increased with increasing in temperature. The activation energy estimated from the Arrhenius plot was 49kJmol(-1) and lower than the value (83.5kJmol(-1)) in water, strongly suggesting catalytic activity of DDAB-MT organoclay. The applicability to wastewater treatment was demonstrated by using secondary effluents of municipal sewage treatment plants and synthesized hospital wastewaters.