Enhanced removal of the endocrine disruptor compound Bisphenol A by adsorption onto green-carbon materials. Effect of real effluents on the adsorption process.

The high exposure to the endocrine disrupting compounds (EDC) in water represents a relevant issue for the health of living beings. The xenoestrogen Bisphenol A (BPA), a suspected EDC, is an industrial additive broadly used for manufacturing polycarbonate and epoxy resins. Due to its harmful effect in humans and the aquatic environment, an efficient method to remove BPA from wastewater is urgently required. The present work aims to study the adsorption of BPA from aqueous solutions onto carbonaceous materials, e.g., a synthesized carbon xerogel (RFX), a chemical-activated carbon from Kraft lignin (KLP) and a commercial activated carbon (F400) for comparative purposes. Batch kinetic and adsorption tests of BPA in ultrapure water were accomplished, finding higher adsorption capacities of BPA onto both F400 activated carbon (qsat = 407 mg g-1) and the biochar KLP (qsat = 220 mg g-1), versus to that obtained for the xerogel (qsat = 78 mg g-1). Furthermore, kinetic experiments revealed faster kinetic adsorption for RFX and KLP materials, achieving the equilibrium time within 24 h, attributed to their more-opened porous structure. Pseudo-first order, pseudo-second order, Elovich, intra-particle diffusion and film diffusion models were used to fit the experimental data. Thus, the BPA adsorption isotherms were analysed by Langmuir, Freundlich, Sips, Redlich-Peterson and Dual-site Langmuir (DLS) isotherm models.In addition, the influence of different aqueous matrices, such as a hospital wastewater, a wastewater treatment plant (WWTP) effluent and a river water, on BPA removal efficiency has been explored. These adsorption tests revealed a clear competitive effect between the target compound (BPA) and the natural organic matter content (NOM) present in the matrices for the active sites, resulting in a high decreasing of BPA adsorption removal.

New insights from modelling and estimation of mass transfer parameters in fixed-bed adsorption of Bisphenol A onto carbon materials.

The removal of Bisphenol A, 2,2-bis (4-hydroxyphenyl) propane (BPA) in fixed-bed columns was investigated by breakthrough adsorption tests at different operation conditions and further prediction by a mathematical model to describe the adsorption-diffusion process onto two synthesized carbon porous materials. In this study, a xerogel (RFX) prepared by an optimized conventional sol-gel method and a lignin-based activated carbon (KLP) obtained via chemical activation were used in batch and fixed-bed adsorption experiments. The materials were fully characterized and their adsorptive properties were compared to those obtained with a commercial activated carbon (F400). RFX and KLP materials reached the equilibrium adsorption in only 24 h, whereas F400 activated carbon required 48 h. In addition, F400 and KLP adsorbents showed higher equilibrium adsorption capacity values (qe = 0.40 and 0.22 kg/kg, for F400 and KLP, respectively) than that obtained for the xerogel (qe = 0.08 kg/kg). Both synthesized carbon-adsorbents were studied in fixed-bed adsorption tests, exploring the effect of the operation conditions, e.g., initial BPA concentration (0.005-0.04 kg/m3), weight of adsorbent (0.01-0.05 g) and volumetric flow rate (0.2 to 1.0 mL/min), on the adsorption performance of the column. All the tested adsorption columns reached the equilibrium in a very short time, due to the efficient dimensionless of the bed. Additionally, the regeneration of the exhausted adsorbent was studied, achieving the total reuse of the solids after three consecutive cycles using methanol as regeneration agent. Finally, a mathematical model based on mass conservation equations was proposed, allowing to efficiently fit the experimental BPA breakthrough curves and estimate the external and adsorbed-phase mass transfer coefficients with a high accuracy.