Research On The Characteristics Of Self-cleaning Activated Bio-filter For Tertiary Treatment Of Municipal Sewage

The difficult problems which usually seen in traditional filter such as the filter layer clogging, difficulty cleaning and running break for backwashing could be solved by Self-cleaning activated bio-filter—an improved biological sand filter we invented. Self-cleaning activated bio-filter can regulate water level through controlling water level regulator, while continuous sand lifting and cleaning can ensure top filter layer keep clean, and this equipment is characteristic of low cost, good filter effects, and easy operation and management.The design principles and operation parameters of Self-cleaning activated bio-filter were discussed, the water distribution system, central air-lifting pipe, sand-water separator and water level regulator all had their unique innovations. Water distribution system consisted of a main pipe and six branch pipes, extension cords of branch pipes was90degree of conical hopper. Central air-lifting pipe’s diameter was32mm, and the end of the intake pipe vertically extended into1～2cm of the bottom of the central air-lifting pipe, which could prevent sucking in filter material effectively. In sand-water separator, sand was washed cleanly rely on the use of friction and collision by multi-stage baffles, there were some orifices on the outer cylinder above the first level baffle, the sewage flowed into sludge discharge pipe through the orifices after cleaning and then discharge outside. The water level regulator could adjust the level of the discharging water level through rotating the sleeve.In this paper, the operating parameters of Self-cleaning activated bio-filter were studied, and got the best operating parameters of it:optimum filter thickness was40cm, the best of influent flow was1.1～1.6m3/h and it was better less than7m/h. The filter velocity, air flow and sand circulation rate were4.31～6.27m/h,0.4～0.6mg/L,5～9mm/min respectively. The backwash water should be1.5～2.0times of the sand-lifting amount.In this paper, the different decontamination effects in batch and continuous cleaning type of Self-cleaning activated bio-filter were studied. In the stationary filter process, Self-cleaning activated bio-filter had a good SS removal efficiency, the average removal rate of SS could achieve more than40%, the average removal rate of COD was15%, the average removal rate of TP was8%, the average removal rate of NH3-N was18%and the average removal rate of TN was8%. When opened the cleaning system in the "leak point" of stationary filtration, the SS of effluent would be normal after130min cleaning, when opened the cleaning system in the "removal efficiency of SS dropped points " of stationary filtration, the SS of effluent would be normal after70min cleaning. In continuous cleaning state, Self-cleaning activated bio-filter had a good decontamination effect. The average removal rate of SS could achieve more than50%, the average removal rate of COD was15%, the average removal rate of TP was8%, the average removal rate of NH3-N was20%and the average removal rate of TN was9%. In current research, the action of Self-cleaning activated bio-filter was simple physical filtration dominatly, so the average removal rate of SS could achieve more than50%, but the removal of COD, TP, NH3-N, TN were limited.Through comparing intermittent and continuous cleaning, it was found that continuous cleaning not only could obtain stable and efficient filtering effect, but also the operation is simple and convenient. For the aspects of energy saving, developing a stable and efficient automatic intermittent cleaning device was also a good idea.