SLUDGE FROM A WATER TREATMENT PLANT AS AN ADSORBENT OF ENDOCRINE DISRUPTORS Sludge from a water treatment plant as an adsorbent of endocrine disruptors

Abstract

Water Treatment Sludge (WTS) is a solid residue generated in large volumes. This material (in raw or modified form) was never evaluated for endocrine disruptors removal. Thus, the novelty of this work is to evaluate the removal of 17β Estradiol (E2) and 17α Ethinylestradiol (EE2) using adsorbents manufactured from WTS. The WTS underwent heat treatment, resulting in the Physically Modified Sludge (PMS). Then, PMS was chemically activated, giving rise to the sludge activated with phosphoric acid (PAS) or with potassium hydroxide (PHS). The adsorbents were characterized by TGA, ASAP, SEM, FTIR, XRD, XRF, and pH-PZC. The adsorption process was evaluated regarding the adsorbent dosage, kinetic, and isotherms. The modifications imposed on WTS were effective, increasing 1.6 times the surface area and pore volume. The adsorbents presented silica, quartz, and kaolinite in their compositions, and a pH-PZC around 6. The conditions that favor the removal of both endocrine disruptors were: 0.5 g of adsorbent, 100 μg.L-1 of initial concentration, pH of 5.5, and 240 min of stirring. PHS was the most promising adsorbent for E2 (with an adsorption capacity of 10.86 μg.g-1) and PMS for EE2 (removing 6.48 μg.g-1 of contaminant). The equilibrium time and fits kinetic models varied in function of the adsorbate concentration. The interaction between adsorbents-adsorbates occurs by chemisorption at the active sites and similar fits to Langmuir and Freundlich isotherm models were obtained. From the results obtained, a promising application for WTS residues and an alternative for E2 and EE2 removal from the aqueous solution was proposed.