Adsorption Kinetics and Equilibrium Studies of an Endocrine Disruptor,Di-(2-ethylhexyl) Phthalate,from Wastewater by Biofilms

Abstract

Abstract

An endocrine disrupting chemical, di-(2-ethylhexyl) phthalate (DEHP), can be removed from wastewater by biological aerated filters, but the removal mechanism is not clear. This original study focused on the adsorption isotherm and kinetics of DEHP on biofilms from a biological aerated filter at 4°C. This low temperature was selected to reduce interactions between the biological metabolism and adsorption as much as possible. The experimental data at 4°C fit with the Langmuir and Freundlich isotherm models. R² for the Langmuir and Freundlich isotherm is 0.969 and 0.949, respectively. For the Langmuir isotherm, q_max (Langmuir adsorption capacity) is 161.55 μg/g and k_L (Langmuir constant) is 0.186L/μg. For the Freundlich isotherm, n (Freundlich constant) is 1.68 and k (Freundlich adsorption capacity) is 29.46 μg/g. The adsorption capacity of 1g biofilm for DEHP is 34.67 μg as calculated from pseudo-second-order kinetics, which corresponds well with adsorption rate data. There was a dynamic balance of DEHP concentration between biofilms and wastewater. Without biological activity, DEHP would migrate from the biofilms back into the wastewater if the concentration of DEHP in biofilms becomes higher than that in the wastewater. These results are fundamental to understand DEHP removal mechanisms in a biological aerated filter.