Adsorption mechanism of bacteria onto a Na-montmorillonite surface with organic and inorganic calcium

The adsorption of bacteria onto the Na-montmorillonite (Na-MMT) was studied as a function of time, bacterial concentration, temperature and pH with the introduction of the organic and inorganic calcium sources. The results indicated that albeit revealing the same adsorption mechanism, the organic calcium (i.e., Ca(CH3COO)2) proposed in this study is more beneficial and environmentally friendly than the inorganic calcium (i.e., CaCl2) in terms of the adsorption of bacteria onto the Na-MMT surface, which can be ascribed to the formation of the denser aggregates in the Na-MMT with Ca(CH3COO)2. Meanwhile, the adsorption kinetics and isotherms followed the pseudo-second-order kinetic model and Langmuir Equation for both two calcium sources. Meanwhile, the adsorption bands of the water molecules on the minerals were observed to shift significantly after the bacterial adsorption, showing that the hydrogen bonding on the Na-MMT surface played an important role during this process. A value of {Delta}H0 > 0 indicated that the bacterial adsorption was affected by van der Waals force and hydrophobic interaction. Finally, the negative zeta potentials of the Na-MMT increased with the addition of Ca2+ ions, and the experimental data also showed that the adsorption of bacteria onto the Na-MMT was mainly determined by the electrostatic and non-electrostatic forces.