Immobilization of nitrifying bacteria in magnetic PVA–SA-diatomite carrier for efficient removal of NH[formula omitted]-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.