On the reason why acid treatment of biomass enhances the biosorption capacity of cationic pollutants

The present work is aimed at understanding the effect of acid treatment and demonstrating the reason for its effect. For this, Corynebacterium glutamicum biomass was used as a model biomass. Two cationic (cadmium and Methylene Blue) and one anionic (Reactive Red 4) pollutants were used to evaluate the sorption capacity by the biomass. Isotherm experiments showed that acid treatment of the biomass increased the uptake of the cationic pollutants, but decreased that of the anionic pollutant. Through the results of FTIR and potentiometric titrations, it was found that carboxyl groups on the biomass increased after acid treatment. The carboxyl groups seem to be generated likely through hydrolysis of esters in the biomass under the acidic condition. Therefore, increase of the carboxyl groups provided the binding sites for cationic pollutants, whereas it may interfere with the binding of anionic pollutants.