Sorption of Polymeric Quaternary Ammonium Compounds to Humic Acid

Abstract

Polymeric quaternary ammonium salts or polyquaterniums are used not only in the water and wastewater industry but also in cosmetics. The former have been extensively studied with sorption to wastewater treatment plant (WWTP) biosolids an important factor in their fate, mitigating release to the environment. Compounds of cosmetic origin have not received the same scrutiny as those used in other applications despite differences in their structure, characteristics and properties such as toxicity. In this work, the sorption of selected polyquaterniums found in cosmetics to treated humic acid, employed as a surrogate for WWTP biosolids, is investigated. For comparison, the sorption of poly(diallyldimethylammonium chloride) (poly(DADMAC)), a polyquaternium commonly used as a flocculant, and cetyl pyridinium chloride, a monomeric quaternary ammonium compound, are also determined. The humic acid/water partition coefficients (KD) of cetyl pyridinium chloride (52,000 L kg−1) and poly(DADMAC) (2,200 L kg−1) were greater than those of the polyquaterniums found in cosmetics (200 to 1,200 L kg−1). Assumptions of partitioning mainly to biosolids and substantial removal relative to the influent concentration of WWTPs may therefore not be valid.