Abstract
A two-sludge system is one of the wastewater treatment systems to utilize denitrifying phosphate accumulating organisms (DPAOs) which can simultaneously remove nitrogen and phosphorus under an anoxic condition. In the two-sludge system, DPAOs for denitrification-dephosphatation are separated from a nitrification process. The denitrification-dephosphatation process consists of anaerobic, anoxic and reaeration treatments. In this study, 4 sets of operational conditions of the denitrification-dephosphatation process were investigated using sequencing batch reactor (SBR), in terms of removal efficiencies and accumulation of DPAOs. In the SBR experiment, treated water in the nitrification process was replaced by KNO3 solution. In runs with only a 10-min reaeration or a limited aeration, SVI increased to 300 mL/g and some activated sludge was washed out. The run with a 60-min reaeration following 90-min anaerobic and 120-min anoxic treatments showed a good sedimentation property and the best nitrogen and phosphorus removal, so they were selected as the improved system conditions. From the calculations based on pumping rates and oxygen demands, it was found that the electricity consumption of the two-sludge system was about 30% less than the A2/O system, because no circulation pump was necessary and aeration time was shortened.
