Immobilization of nitrifying bacteria in magnetic PVA–SA-diatomite carrier for efficient removal of NH 4 + -N from effluents

Magnetic polyvinyl alcohol–sodium alginate–diatomite (PVA–SA-diatomite) composite carriers for immobilized microorganisms were prepared for removal of NH4+-N from effluents. The mass transfer efficiency, chemical stability, and NH4+-N removal efficiency of the carriers were investigated. The amount of each ingredient added significantly affected the performance of the carriers. The optimal concentrations of PVA, SA, diatomite, and Fe3O4 were 10%, 1%, 1%, and 2%, respectively. The obtained carrier achieved a NH4+-N removal efficiency of 72.5% after reaction for 12 h, which was 31.8% higher than that with the non-magnetic carrier. The removal of NH4+-N was attributed to the cooperative action among non-magnetic ingredients, magnetic ingredients, and microorganisms. The adsorptions of NH4+-N by non-magnetic ingredients and Fe3O4 contributed 21.2% and 25.5%, respectively, and microorganism metabolism contributed 53.2% to NH4+-N removal. The novel texture structure of the carrier leads to improved mass transfer of nutrients and stable activity of microorganisms. Nitrification followed the first-order reaction for low concentration of effluents and zero-order reaction for high concentration of effluents. The reaction rate increased with increasing initial NH4+-N concentration. The magnetic carrier was applicable for a long time. These results show the great potential of the developed carrier for industrial applications.