Encapsulation of microorganisms for simultaneous nitrification and denitrification in aerobic reactors

Abstract

A special denitrifying capsule that was designed according to the theory of maldistribution of DO (dissolved oxygen) for simultaneous nitrification and denitrification (SND) in an aerobic reactor was prepared by an encapsulation technique. The morphology of the denitrifying capsule and its SND performance in an aerobic reactor used for treating synthetic low C/N wastewater were systematically investigated. The spherical capsule comprised a porous membrane, denitrifying active sludge and semen litchi powder, which were cohered together by a physical method. Well-shaped pores were distributed in the membrane and the average pore diameter was approximately 0.25 µm. Circular pores were present in the cross section of the membrane, and the thickness of the membrane ranged from 95.0 µm to 120.0 µm. After 7 days of acclimation, the denitrifying capsule showed good SND performance in an aerobic reactor with a DO concentration of 5.09 mg/L. The NH4+-N concentration of 51.09 mg/L was removed completely after 8 h, the effluent dissolved inorganic nitrogen (DIN) concentration decreased to 6.11 mg/L, the SND ratio reached to 91.6% at 6 h, and finally decreased to 2.09 mg/L at 15 h and could also reach 98.91%. The influent of NH4+-N loading had little effect on the nitrogen removal performance. And decreased of air input induced lower hydraulic shearing force compared to reactors with higher DO had a little effect on the diffusion and mass transfer of NO3--N. With this core shell structure denitrifying capsule, it was easy to achieve SND without controlling the DO concentrations at low levels or using intermittent aeration.