Effects of COD/TN and HRTS on Nutrients Removal by an Alternating Anoxic/Oxic CAST
碳氮比及HRTS对交替缺氧/好氧CAST去除营养物的影响

The effects of different COD/TN and HRTS (hydraulic retention time of select) on nutrients removal were investigated by using an alternating anoxic/oxic CAST (cyclic activated sludge technology) fed with municipal wastewater. The results showed that various COD/TN and HRTS had a bigger influence on the nitrogen removal efficiency rather than the COD removal efficiency. As the influent C/N ratios were about 2.6 and 3.5, ammonia was removed by 98% and TN removal efficiency was increased from 62.9% to 76.2% and 72.1% to 84.6%, respectively, by increasing the HRTS from 1.8 h to 5 h. When the COD/TN ratio was increased to about 4.4, TN removal efficiency was decreased from 86.3% to 58.2% by enlarging the HRTS, which was due to the incomplete nitrification of ammonia. It was also observed that both of increasing the COD/TN and HRTS could improve the phosphorus removal performance of the system. Furthermore, effluent of CAST reached the demanded A of integrated wastewater discharge standards (GB 18918-2002) when the COD/TN and HRTS were 4.4 and 1.8 h, respectively.