Degradation characteristics of secondary effluent of domestic wastewater by combined process of ozonation and biofiltration

The performance of the combined process of ozonation and biofiltration was studied for treating the secondary effluent from sewage treatment plant. It was found that COD, NH₃-N, and TOC were removed from 40-52, 10-19, and 9-13 mg/L in the raw water to 18-23, 0.5-1.5, and 7-8.5 mg/L in the effluent water (removal efficiency were 58, 89, and 25%, respectively), respectively, with an ozone dose of 10 mg/L (0.7-1.1 mg O₃/(mg TOC) and 0.2-0.25 mg O₃/(mg COD)), and contacting time of 4 min. Under the operation conditions, ozonation enhanced the biodegradability of the organics in the secondary effluent, as illustrated by increasing biodegradable dissolved organic carbon (BDOC) value from 0.8-1.1 mg/L in the raw water to the 2.0-2.7 mg/L in the effluent water. Meanwhile, the percentage of the organics with molecular size less than 1 k Da in the secondary effluent increased from 52.9 to 72.6%. The experimental results supported the expectation that the combined process of O₃/Biofiltration might enhance the overall treatment efficiency of secondary effluent treatment.