Adsorption of stable and labile emerging pollutants on activated carbon: degradation and mass transfer kinetic study

The design of adsorption processes for pharmaceuticals removal depends not only on the adsorption equilibrium but also on the mass transfer and adsorbate stability, being a problem still not solved the case of degradation products. By selecting different stable (amoxicillin, ciprofloxacin, carbamazepine and ibuprofen) and labile micropollutants (omeprazole) as case studies emerging pollutants, we have quantitatively analysed these effects on activated carbon. For stable compounds, the experimental data were fitted to equilibrium models to obtain information about the different adsorption mechanism depending on the characteristics of the molecules. Mass transfer effects were analysed for all the adsorbates, observing the control of intraparticle pore diffusion mechanism, since the effective pore diffusion coefficient is in the range from 10–8 to 10–10 cm2 h−1. As far as omeprazole is concerned, a kinetic model is proposed for predicting its degradation, identifying the reversibility of several degradation steps. The overall adsorption of OMP and derivates is calculated, observing the pore diffusion is considered as the rate-limiting step. For the first time, a combined model considering the chemical degradation and the adsorption of the degradation products is proposed and experimentally validated. This represents an important step in the modelling of processes leading to the purification of water from this type of pollutant.