Adsorption of benzalkonium chlorides (BACs) by powdered activated carbon (PAC)

Abstract

Quaternary ammonium compounds (QACs) are cationic surfactants and are widely used for industrial products such as cosmetic and cleaning products. The most commonly used QACs are benzalkonium chlorides (BACs). Among BACs, benzyl dimethyl dodecyl ammonium chloride (BAC12) that has 12 alkyl chain, benzyl dimethyl tetradecyl ammonium chloride (BAC14) that has 14 alkyl chain, Benzyl dimethyl hexadecyl ammonium chloride (BAC16) that has 16 alkyl chain are the most commonly used BACs. They have been utilized in many industries (food industries, textile industries, paper industries, oil and gas industries, plastic industries, etc.) also to prevent biofouling in the pipelines and product deterioration. BACs are detected in the environment and are highly toxic even in small amounts. However, conventional water treatments are not being removed BACs well. Although it has been studied to reduce BACs by advanced oxidation processes or adsorption, some studies have been difficult to apply in real treatment plant. Therefore, in this study, we investigated the fundamental mechanism of major BACs adsorption to better understand the removal of major BACs in water treatment by using powdered activated carbon (PAC) that is commercial adsorbent in actual treatment plants and easy to apply. Adsorption experiments were carried out in batch form, and BACs were analysed by using HPLC-DAD. To investigate the adsorption characteristics of BACs using PAC, experiments were conducted at different concentrations, pH, temperature and dissolved organic matter. The adsorption difference between mixture of BACs and single BACs adsorption were also examined. BAC12, BAC14 and BAC16 were adsorbed well on PAC and removal rates were more than 90 % within 20 minutes. The adsorption kinetic of BACs followed the pseudo-second order (qe of 144.93-161.29 mg g-1 and k2 of 3.18  10-3 -9.16  10-3 g mg-1 min-1) and the isotherm was more suited to the Langmuir isotherm model (qmax = 188.68 -206.19 mg g-1, KL: 4.89-8.10 L mg-1). Results of the adsorption experiments at various pH ranges, BACs removal from neutral and basic had more adsorption capacities than acid condition. Thermodynamic analyses examined that the adsorption BACs between PAC was spontaneous and endothermic reaction. In presence of dissolved organic matter in solution, BACs were complexed with humic acids and this complexed humic acids was adsorbed to PAC, resulting in increased BACs removal rate. Binary BACs experiments showed different characteristics compare to single BACs because their competed their adsorption with each other. The adsorption capacities were reduced to 2.1-66.7 % compared to the BACs single adsorption. As a result of the adsorption of binary BACs, adsorption was increased in the order from BAC16, BAC14, BAC12. The reason for the better adsorption of BAC16 was because van der Waals force is stronger due to more carbon chains than BAC12 and BAC14. Our results imply that activated carbon can be a promising prospect in terms of removal efficiency of BACs.