The Comparison Of Pre-denitrification And Post-denitrification In BAF Process On Nitrogen Removal

In past few years in China, the sewage treatment plants mainly use the traditional treatment processes like oxidation ditch and SBR process. These processes are effective in removing COD and ammonia nitrogen, but they are much less effective in reducing total nitrogen. Urban sewage discharge standards have been improved. It is urgent to promote the water treatment processes. Based on existing processes operated in the plants, pre-denitrification bio-filter or post-denitrification bio-filter is chosen for their small covers and low cost. In this study, the impact of hydraulic load, COD/TN and reflux ratio on the removal of the pollutants were explored and the comparison of pre-denitrification bio-filter and post-denitrification was conducted, which provided the references data with actual application in the plant.For the pre-denitrification bio-filter, when the reflux ratio was 100%(optimum), the hydraulic capacity was 1.5 m3/(m2·h), the concentrations of total nitrogen, COD and ammonia nitrogen were 35 mg/L,120 mg/L and 5 mg/L, the effluent concentration of above were 3.45 mg/L,20.04 mg/L, and 0.64 mg/L and the average removal rates were 90.14%,83%,95.73% respectively. The water quality met the discharge standard of GB18918-2002IA level.For the post-denitrification bio-filter,when the carbon source addition was COD/TN=7, hydraulic capacity was less than 1.5 m3/(m2·h) and the concentration of total nitrogen, COD and ammonia nitrogen in inlet were 35 mg/L,70 mg/L,15 mg/L, the effluent concentration of above were 4.48 mg/L,15.43 mg/L,0.44 mg/L, and the average removal rates were 87.32%,77.51%,97.07%, respectively.Through the analysis of the experimental data, it comes to the conclusion that the effluent treated by both kinds of process can achieve the IA level of GB 18918-2002 standard, but in financial prospective, pre-denitrification bio-filter is not cost effective in comparison of post-denitrification bio-filter because it not only needs to consume energy to return sludge, but also needs to add carbon resources for the COD in the effluents is difficult for the microorganism to utilize, the operating cost of post-denitrification is approximately RMB 0.1 costs less than that in pre-denitrification bio-filter.