Analysis of mid-positioning BAC filter technology

BAC filter, placed in the end of process flow in the traditional O₃-BAC advanced treatment process, usually using the same filter type with sand filter, has adsorption effect, biochemical function and filtration function, so it can used to avoid secondary pollution. But problems were found in BAC filter placed after sand filter, such as hidden trouble from microorganism leak and low efficiency of biochemical effect. Placing BAC filter between sediment tank and sand filter, on one hand, most of the turbidity could be removed by coagulation-sediment treatment, which is good for particle activated carbon adsorbing. On the other hand, with sand filter behind it, turbidity in effluent of BAC filter was out of restriction, and it is possible to use the filter type of high up-flow biological aerated filter (HUBAF). A pilot was tested to choose the better flow way, filter media type and gradation, filtration rate , empty bed contact time, oxygen supplying way and backwash way for BAC filter, and a new technology, up-flow aerated biological activated carbon filter (UBACF), was developed, compared with post positioning BAC filter, it can well cope with the condition when the inlet turbidity was high. Meanwhile UBACF keeps the adsorption effect, and the backwash parameters and abrasion rate of activated carbon were almost the same, however, it greatly enhanced oxygen supplying ability and mass transferring efficiency, improved nitrification of NH₃-N and biodegradation of organic.