Removal of emerging pollutants in water treatment plants: adsorption of methyl and propylparaben onto powdered activated carbon

Abstract

Methylparaben (MeP) and Propylparaben (PrP) are widely used in consumer products and their presence in surface, ground and waste water is a source of concern. They belong to category 1 of the Endocrine Disrupter Priority List for wildlife and human health and hence, these compounds should be completely removed from drinking water in Water Treatment Plants (WTP). Adsorption with powdered activated carbon (PAC) is a solution to eliminate emerging pollutants (ECs), as occurs in Benidorm WTP; however, it is necessary to know the conditions for the removal of these compounds and to optimize its application achieving lower economic costs. With this aim, the process has been characterized studying the adsorption equilibrium and kinetics in single and bicomponent batch experiments, using the commercial carbon Pulsorb PWX HA. The individual adsorption of MeP and PrP by PAC suits an “L” isotherm, according to Giles’ classification. The Langmuir and Freundlich models properly described the adsorption of MeP and PrP in monocomponent experiments. On the other hand, the results from bicomponent experiments suggested the existence of competitive adsorption with lower adsorption capacities for MeP. The multicomponent model Ideal Adsorbed Solution (IAS)-Freundlich predicted with more accuracy the competitive adsorption. For both compounds, the kinetic studies fit the pseudo-second order model. Differences between the removal efficiencies of similar compounds, MeP and PrP, were observed with ultrapure and real water, regarding the PAC dose and the contact time. The removal by adsorption in WTP could be optimized considering the parameters determined in this research.