BAC filtration - disinfection - sand filtration combination technology for handling risk of microorganism leak in O3-BAC process

The traditional ozone-biological activated carbon (O
₃
-BAC) water purification process, applied in the marsh and heated areas in the south of China, introduces a problem of microorganism leak which was observed in the effluent of BAC filter. A pilot plant of a new self-developed style "BAC filter-disinfection - sand filter" O
₃
-BAC process technology, with a flow rate of 5-12 m
³
/h, was compared with the traditional process. The results showed: in new process, BAC filter was placed in the middle of sediment tank and sand filter(mid-positioning BAC filter). It was suitable to choose up-flow dual medium aerated BAC filter, and it continued to have the ability to adsorb dissolved micro-pollutants. There was no obvious difference between BAC filter and traditional process in the operation indices such as backwashing parameters and activated carbon abrasion rate, while the ability of offering oxygen and mass transfer rate and the function of nitrification and biodegradation were greatly enhanced. New process kills the leaked microorganism by ozone united with chlorine or only with chlorine , well solving the problem of microorganism leak in the traditional process. With two-stage filtration and influent turbidity of below 0.6 NTU, choosing micro-flocculation contact filtration process for the sand filtration, the turbidity of effluent can be controlled in a level of below 0.15 NTU, furthermore, it was still possible to lower the effluent turbidity by using smaller sand as filter media, enhancing the ability of withholding microorganism in sand filter.