Aquatic Pollution and Coastal Management

Unit 2 : Sewage and domestic wastes, treatment and reuse

a) Trickling Filters

A trickling filter consists of a bed of graded media such as stones, gravel, clinker, slag or even synthetic plastic material, with drains at the bottom to collect the treated waste. The waste is evenly distributed over the top surface of the bed with the help of a rotating arm or nozzles, from where it percolates down in the filter to the collecting drains. A film of microbial growth develops on the filtering medium, which may be of 0.2-2.0mm thick. The film consists of bacteria, fungi, protozoa and algae and commonly called as ‘Zoological film’ due to predominance of a bacterium, Zoogloea.
As the waste trickles down over these microbial surfaces, the organic constituents of the waste are metabolized into more stable products.