Removal of Diesel from Aqueous Solutions by a Combined Adsorption and Microbial Degradation Process

Diesel contamination in water bodies poses a significant environmental challenge due to the toxic effects of its water-soluble fraction (WSF) on aquatic ecosystems and human health. The aim of this work was the design of a new technological procedure for the purification of water contaminated with the WSF of diesel. The procedure is based on the adsorption of organic pollution on an organozeolite, after which the biodegradation of the adsorbed pollutant takes place. The material for obtaining organozeolite was a natural zeolite from the Zlatokop deposit (Vranje, Serbia). The zeolitic surface was modified with hexadecyltrimethylammonium bromide (HDTMA-Br), a cationic quaternary ammonium salt. The adsorption experiments, with initial WSF concentrations of 2.5–25 mg/L, at pH 6 and at 20 °C, were performed in a batch system using organozeolite, and the results showed that more than 90% of the WSF of diesel was removed, reaching equilibrium after 1 h. The maximum adsorbed capacity of organozeolite for the removal of the WSF of diesel fuel from water under the tested conditions was 22.2 mg/g. Equilibrium data were well fitted by a linear isotherm model, while a pseudo-second-order equation well fitted the kinetic data. After adsorption, a 15-day biodegradation experiment was carried out under batch conditions. The results showed that the examined consortium of microorganisms degraded 80% of the adsorbed contaminant. Additional respirometric analyses showed that, in parallel with the degradation of the contaminant, the degradation of the long-chain HDTMA ions at the surface of the organozeolite also occurred. To the best of our knowledge, this is the first study combining adsorption and biodegradation to remove the WSF of diesel from water.