A methodological approach to investigate the pH effect on biosorption process: experimental and modeling procedures

A methodological approach to study and model equilibrium of heavy metals in biosorption processes has been proposed and discussed. Four cases of copper biosorption are here reported and discussed as examples of application: biosorption of copper onto Sphaerotilus natans, Rhizopus oligosporus, calcium alginate and olive mill residues (OMR) have been here described and discussed. Several empirical and semi-empirical models have been proposed and summarised, to consider the pH effect on the heavy metal up-take. The proposed models, originated from Langmuir isotherm, may be useful to fit experimental data avoiding pH control during biosorption tests and simply monitoring its equilibrium value. The adsorption isotherms were built considering experimental procedures at constant pH (in standard manner) and in pH edge conditions. Both empirical and semi-empirical models were able to fit these experimental results. The pH-edge experimental procedure coupled with the proposed pH-related models is proposed as useful tools to investigate and model biosorption processes with single heavy metals in solution.