Effect of hydraulic residence time on nitrogen removal from a synthetic mariculture wastewater using a bench-scale recirculating bioreactor embedded with aerobic denitrifying bacteria Marinobacter alkaliphilus strain JY28

Beads loaded with tea dregs powder and immobilized aerobic denitrifying bacteria (Marinobacter alkaliphilus strain JY28) were prepared by cross-linking sodium alginate and polyvinyl alcohol. The beads were subsequently utilized for nitrogen removal in treatment of wastewater from a marine recirculating aquaculture system (MRAS). The effects of hydraulic residence time (HRT) on nitrogen removal efficiency, microbial community succession, and the physicochemical properties and kinetic behaviors of the immobilized bacterial beads were investigated. The results indicated that the highest NO₃^--N removal rate was 99.4 ± 0.6 % at an HRT of 10 h, while the cumulative NO₂^--N concentration remained at its lowest level (0.04 ± 0.05 mg L^-1). Furthermore, the peak maximum specific nitrogen removal rates (μ_max) for NO₃^--N and NO₂^--N were found to be 16.12 mg L^-1·h^-1 and 8.61 mg L^-1·h^-1, respectively. The surface of the immobilized bacterial beads was rough and effectively bound Marinobacter alkaliphilus strain JY28. The interior of the beads possessed an irregular honeycomb-like and porous structure, favorable for the immobilization and proliferation of Marinobacter alkaliphilus strain JY28. The presence of the ring structure in the functional bonds enhanced both the mechanical strength and the immobilized bacterial beads stability. Marinobacter alkaliphilus strain JY28 was retained in the bacterial beads and consistently maintained its dominance during the whole experimental process. The results lay a theoretical foundation for application of immobilized bacterial beads for highly efficient nitrogen removal in MRAS wastewater treatment.