Trickling Filters

Trickling filters are either rectangular or circular in shape and about 2 m deep. They are filled either with coarse, crushed rock or large anth­racite coal or blast furnace slag or broken bricks or graded clinkers. The under drain system is provided in the bottom of bed to collect effluent. Sewage is delivered to the filters by means of a rotating distributor.

 

Operation : The sewage is allowed to trickle over the filtering medium by means of rotating arm distributor. As the trickled sewage strats percolating downwards through the filtering media, micro-organism (present in sewage) grow on the surface of aggre­gates, using organic material of the sewage as food. Aerobic con­ditions always prevail and purified sewage is removed from the bottom. The normal trickling filters remove 90% BOD.