An Experimental Study On Nitrogen Removal Of Low C/n Wastewater By Ecological System

The COD and NH₄-N of effluent are usually effectively removed after sewage treatment plant,while the TN is often not removed and the main ingredient is NO₃-N. The sewage can lead to eutrophication and impact the ecological system of the river by discharging. Adopting biological method to remove nitrogen with such a low C/N wastewater, the denitrification process can not occurred effectively due to lack of organic matter and the electron donor is not sufficient.Based on the principles of ecological engineering, we designed an aerobic and anaerobic reactor with ecological system, and the sewage are forced to be two areas automatically(the ratio of volume is 1:2).Using the reactor to treat the secondary effluent of Taizhouwu treatment plant and investigating the removal efficiency of nitrogen with different hydraulic loading and NO₃-N concentration. The denitrification of factors such as pH and C/N is confirmed after the static and dynamic experiments and the results showed as follows:①The DO in the aerobic zone of the reactor is changed fluctuantly and the anaerobic zone is generally between 0.5² mg/L, thus, the anaerobic zone is suited for denitrification because of the low DO concentration.②When the flux of influent is 5 L/h, 10 L/h and 20 L/h, the NO₃-N concentration decreased to 11.8 mg/L, 13.7 mg/L and 16.9 mg/L from 19.4 mg/L, and the removal rate is 38.6%, 29.3% and 12.2% respectively.③When the reactor is added with glucose and the organic carbon source is sufficient, the effect of denitrification is best while the C/N is 1.82. The removal rate of TN and NO₃-N is 87.2% and 93.21%, and the effluent concentration dropped to 2.2 mg/L and 1.04mg/L, respectively.④All the four hydroponic macrophytes can remove nitrogen effectively and the efficiency is different. The removal rate of TN with Eichhornia crassipes and Agavaceea is better than the other plants, the concentration of TN dropped to 15.7 mg/L and 17.9 mg/L from 32.2 mg/L, and the removal rate is 51.2% and 56.8% respectively. Besides, the removal efficiency of NH₄-N with Eichhornia crassipes and Agavaceea can reach 90% above.⑤When the reactor is combined with Eichhornia crassipes, the exudation can enter in the anaerobic zone and denitrification can use the DOC, and the removal rate of NO₃-N is advanced 20.37% and 9.27% while the flux of influent is 10 L/h and 20 L/h respectively.⑥When the flux of influent is 20 L/h, the removal rate of NO₃-N is only 12.3% with heterotrophic denitrifying bacteria, and the rate can reach 37.7% while the sulfur-autotrophic denitrification is occurred, the quality of the effluent is stable and the effect is not affected by the organic carbon source.