Hemoglobin immobilized on mesoporous silica as effective material for the removal of polycyclic aromatic hydrocarbons pollutants from water

Abstract

Free hemoglobin (Hb) in water at pH 5 is able to oxidize 11 polycyclic aromatic hydrocarbons (PAH) (300 nM each) in the presence of H₂O₂ amounting to 75% PAH removal. PAH are carcinogenic, mutagenic and xenobiotic pollutants found in wastewaters of oil refineries. However Hb is pH sensitive and is effective only at pH 5. In order to use Hb for real wastewater treatment (6.5 < pH < 8.5), Hb was immobilized by simple adsorption in selected large pore mesoporous silicas at a loading of 300 mg Hb per g silica. The reaction of Hb with PAH is pseudo-catalytic because an excess of H₂O₂ ([H₂O₂]/[PAH] > 2500) and of Hb ([Hb]/[PAH] > 2) is necessary to reach an optimal PAH removal. The excess of Hb depends on the PAH physico-chemical characteristics. At pH = 7, the activity of free Hb decreased to 47% of PAH removal, whereas the Hb-immobilized silica allowed 82% of PAH removal. Immobilization of Hb in silicas leads to a protection of Hb towards pH, solvent, temperature and inactivation by H₂O₂. These results open the perspective for a new biotechnology process aimed at cleaning contaminated wastewaters by a reactive adsorption process followed by filtration.