Study On Advanced Treatment Of Municipal Wastewater By Using Modified Two-Stage Biological Contact Oxidation

The characteristics and trend of pollutants were characterized by monitoring the water quality of effluent from wangtang wastewater treatment plant in a long-term. Since the tail water of wastewater treatment plant could not achieve the water quality standard for scenic environment use stably, modified two-stage biological contact oxidation was used to treat the effluent of wastewater treatment plant .Continuous-flow biofilm formation method was used in the experiment. Results showed that the period of biofilm formation was about 20 days when temperature varied between 9.6℃and 17.3℃.The effect of the dosage of external carbon source on the removal of total nitrogen (TN) was investigated. The effect of the removal of TN was compared when the concentration of sodium acetate was 40mg/L, 50mg/L and 60mg/L respectively. Results showed that the optimum concentration was 50mg/L. The average removal rates of TN was 73.4% in the first stage. The excessive sodium acetate was removed in the second stage to avoid the effluent of COD exceeded the disposal limitation owing to the excessive external carbon sources. The average COD value of the effluent in the second stage was 26.91mg/L as the concentration of sodium acetate added was 50mg/L.The effect of hydraulic retention time on the removal rate of pollutants are analyzed in the experiment. When temperature was varied from 9.6℃to 17.3℃, water gas ratio was set as 1:1, and hydraulic retention time was 1h, The effect of the removal of TN was much lower than 1.5h and 2.5h. When hydraulic retention time was 1.5h, the concentration of suspended solids(SS), COD, TN of tail water decreased from 4.57mg/L, 21.69mg/L, 17.24mg/L to 3.49mg/L, 15.88mg/L, 4.8mg/L respectively after the advanced treatment. Correspondingly, the removal rates were 23.63%, 26.79%, 72.16%. When hydraulic retention time was changed into 2.5h, the removal rate of SS,COD, TN were increased 11.16%,8.56%,3.64% respectively. The effect was not very notable. In consideration of the all factors above, the optimum hydraulic retention time was 1.5h.The water quality of tail water could achieve the water quality standard for scenic environment use stably by use of modified two-stage biological contact oxidation. This research provided experiment study and data support for the advanced treatment of effluent of wastewater treatment plant.