Simultaneous biological nitrogen and phosphorus removal with a sequencing batch reactor–biofilm system

• A pilot-scale sequencing batch reactor–biofilm (SBR–BF) hybrid system was explored.
• Nitrogen and phosphorus were simultaneously removed in SBR–BF system.
• DNPAOs play an important role for phosphate uptake and denitrification.
• Activated sludge and biofilm provided good living conditions for different bacteria.

To achieve simultaneous biological nitrogen and phosphorus removal, a pilot-scale sequencing batch reactor–biofilm (SBR–BF) system was explored. SBR–BF system was started up with two phases, which were anaerobic/aerobic and anaerobic/aerobic/anoxic, to enrich phosphate accumulating organisms (PAOs) and denitrifying phosphate accumulating organisms (DNPAOs), and to form system of suspended activated sludge and attached biofilm. Operation cycle of SBR–BF system was adjusted as fill 5 min, anaerobic 90 min, aerobic 210 min, anoxic 90 min, settle 30 min, draw 15 min and idle 40 min, and average removal of chemical oxygen demand, total nitrogen and total phosphorus respectively reached 95%, 94%, and 97% during stable operation for 3 months. Analysis of a typical wastewater treatment cycle testified that DNPAOs played an important role for phosphate uptake and denitrification under aerobic and anoxic conditions. The SBR–BF system not only provided good living conditions for PAOs, DNPAOs, nitrifying bacteria and denitrifying bacteria which had different generation times, but also prevented the competition for carbon source between different bacteria.