Pilot-study On The Treatment Of Micro-polluted Water Using Biologically Enhanced Filtration

In these days, the use of conventional drinking water treatment processes becomes increasingly challenged with the deterioration of surface water quality and the enaction of more stringent drinking water regulations. Therefore, removing pollutants from raw water is becoming one research focus. This paper investigated the application of biologically enhanced filtration for drinking water treatment. The new process can remove organics and turbidity in the same filter, and is a feasible way to treat micro-polluted source water.Further study was conducted to evaluate the performance of biologically enhanced filtration removing organis, NH₄⁺ —N and turbidity through pilot-plant experiments which was conducted with raw water from a sedimentation tank in Nanjing Chengbei Waterworks. Furthermore, several influencing factors were examined, including: empty bed contact time (EBCT), water temperature, flocs and backwash of biofilters. The Results of experiment on biofiltration performance show that biofiltration can remove organics, NH₄⁺ — N as well as turbidity in the same filter effectively. When water temperature is 8℃, filtration rate is 7.5m/h, the removal of TOC, COD_Mn and UV₂₅₄ in bio-active filters are 12.2%～38.5%,13.2%～30.5% and 17.6%～55.6% respectively, and the NH₄⁺ —N removal rate reaches 58%～97%, when the concentration in raw water is 0.41 mg/L. Biologically enhanced filtration has also superior characteristic of tubidity removal. When the influent turbidity is bellow 5NTU, the effluent turbidity can maintain less than 0.2NTU for a long time.The removal effects of the process are affected by EBCT, water temperature, flocs and filter backwash. In the rage of 4.8min～20min, increasing EBCT will improve the performance of biofilters but less than proportionally; the removal rate is better in higher temperature; the accumulation of flocs in bio-active filter maybe act as a diffusion barrier for biodegradable compounds, thus bring some disadvantage for biofiltration; backwash with chlorinated water has great impact on biologically enhanced filtration.