Comparative study of 17β-estradiol removal from aqueous solutions using pine bark and almond shell as adsorbents

We have investigated the adsorption of the endocrine disruptor 17 beta-estradiol (E2) on pine bark and almond shell. These traditional Portuguese agro-forestry by-products were milled, sieved into different particle size fractions and submitted to two different kinds of treatment. Adsorption experiments were conducted in batch system at room temperature and at pH 4.75 and 6.80, respectively, for pine bark and almond shell. E2 was more effectively adsorbed on 100 to 150 mu m particles of both sorbents. Pine bark washed with hot water and pine bark treated with formaldehyde showed higher percentage of adsorption than any other material tested at doses of 5.0 gL(-1). The adsorption was of comparable efficiency in case of almond shells at doses of around 20 gL(-1). In this case, the percentage of adsorption was found to be 88 and 90% for the sorbents treated with formaldehyde or washed with hot water. The adsorption isotherms were found to fit a Freundlich equation, with correlation coefficients (R-2) between 0.904 and 0.998. The sorption coefficient (K-F) ranged from 0.03 to 29.9 (mg(1-1/n) L-1/n g(-1)). The differences observed among the adsorption capacities are discussed in terms of physico-chemical characterization of the materials.