An Innovative Process to Improve Turbidity and Organics Removal by BAC Filters

The turbidity criterion for the product water of a WTP according to the State Project ‘863＇ on the safeguard technology of drinking water in the southern areas of China is 0.1 NTU. The turbidity removal in the activated carbon filter was analyzed in a pilot-scale test and an innovative technology to improve the turbidity removal in a biologically activated carbon （BAC） filter was put forward in order to meet the criterion. Experimental results showed that the enhanced filtration by adding polymerized aluminium chloride （PAC） into the BAC filter was quite effective in turbidity control. The effluent turbidity was kept at a stable level （mean） of 0.033 NTU with a high removal of about 80% for influent turbidity of 0.110- 0240 NTU with an addition of PAC at 0.05 mg L^-1, meeting the requirement for filtrate turbidity equal to or less than 0.1NTUC totally. In addition, the larger the PAC dosage was, the lower the effluent turbidity was. However, further improvement of turbidity removal was not obvious for PAC dosages beyond 0.10 mg L^- 1, and an optimal PAC dosage in the range of 0.05 - 0.10 mg L^- 1 was proposed.