Nitrogen removal from sewage by continuous flow SBR system with intermittent aeration

A continuous-flow sequential batch reactor system with intermittent aeration known as the intermittent cycle extended aeration system was used to investigate the efficiencies of nitrogen removal for sewage. In the conventional intermittent cycle extend aeration system with continuous aeration process to treat the synthetic sewage wastewater under 3 cycles per day (cycle time = 8 hours), high COD removal efficiencies were achieved, but high levels of nitrate (22.3-23.6 mg l-1) and decreased pH values were also found in the effluent. In the intermittent aeration, the dissolved oxygen in the reactor was reduced from the range of 3.5-5.0 mg l-1 to 0.5-1.2 mg l-1, the nitrogen in the influent was partially oxidized to nitrite-nitrogen, although nitrate-nitrogen was also present in the effluent. In detailed cyclic study of the reactor with relatively low D.O. (0.3-1.0 mg l-1) and high MLSS (3200 mg l-1 at half full water level), the experimental results of intermittent aeration processes showed higher oxidation rates of ammonia to nitrite (1.44-3.55 mg N g-1 MLSS hr-1) than the conversion rates of nitrite to nitrate (0.00-1.22 mg N g-1 MLSS hr-1). It was thus, concluded that denitrification rates were not affected by the limited supplement of soluble organic carbon in the system. In addition, NOx(-)-N could be removed with a total nitrogen removal rate up to 94.9% when the MLSS was controlled in concentrations of 3200 mg l-1 at half full water level with low D.O. The process of intermittent aeration of ICEAS could provide an economic and effective means for nitrogen removal in treating sewage.