Exploring the high-concentration powdered carrier bio-fluidized bed process nitrogen removal performance: Effect of...

High-concentration powdered carrier bio-fluidized bed (HPB) process has been demonstrated its ability to enhance nutrient removal in wastewater treatment. However, the HPB process still lacks theoretical support for the regulation of dissolved oxygen (DO). This study explored the mechanism of DO on nitrogen removal in the HPB process comparing inert carrier (diatomite) and functional carrier (Fe-C) under four different DO. The results showed an enhancement in total nitrogen removal efficiency for both diatomite and Fe-C HPB systems with DO decrease. When the DO decreased from 4-6 mg/L to 0.5-1.0 mg/L, the simultaneous nitrification-denitrification pathway increased by 13.33 % and 9.57 %, and the anammox pathway increased by 3.91 % and 1.97 % respectively. Analyses of sludge characteristics and EPS indicated that low DO is beneficial for carrier to promote sludge micro-granulation in two HPB systems. Microbial analysis indicated that the abundance of functional bacteria in micro-granules was significantly higher than that in floc sludge. Additionally, the relative abundance of denitrifying bacteria (DNB) was increased and anammox bacteria (AnAOB, Candidatus_Kuenenia) was significantly enriched in the micro-granules (2.901 % and 2.653 %) at low DO (0.5-1 mg/L). Further, DNB and AnAOB as an inner core and nitrifying bacteria mainly worked outside of the micro-granules, the above synergistic metabolism results in efficient nitrogen removal. Although the limited capacity of Fe-C to enrich functional bacteria, batch tests revealed that Fe-C increases the rate of microbial nitrogen metabolism through hydrolysis of macromolecules and micro-electrolysis effect. These results will provide theoretical support of the HPB process in practical engineering and potential exploration.