Trickling Filters & Advantages

Trickling Filters

What Are Trickling Filters?

•Fixed media treatment system
•Waste water is distributed over media colonised by micro-organisms
•Consists of a  bed of highly permeable media
•An under drainage system important both as a  collection unit  &  as  porous structure
•Biological community:

Trickling Filters
Trickling Filters


Organic material from liquid is adsorbed onto the slime layer whose outer portions degraded by aerobic micro-organisms. As they grow thickness of slime layer increases & oxygen is consumed before it penetrates full depth. Hence micro-organisms enter into an endogenous phase of growth & lose ability to cling to the media surface. Liquid then washes the slime off the media  & a new slime layer begins to grow. Losing of slime layer is known as  “sloughing”

Factors Considered In Design

•Dosing Characteristics Of The Distribution System
•Choosing The Right Packing / Media
•Configuration Of The Underdrain System
•Provision  For Adequate Ventilation

Distribution System

  • Consists of distributor arms mounted on a pivot in the centre,
  • These are hollow through which water is discharged over the filter bed
  • For uniform distribution the flowrate per unit of length should be proportional to the radius from the center
  • Head loss is in the range of  (0.6 –1.5 m)
  • Dosing tanks must ensure that minimum flow is sufficient  to rotate the distributor  & discharge all waters from nozzles

Filter Media

  • A material having high surface area per unit volume , does not clog easily
  • Media can be rock , plastic , pvc
  • Stones less than 25mm not be used as they do not provide sufficient pore space
  • Calculation of media depth

Underdrains & Airflow

These are waste water collection systems that collects the filtered waste water & solids discharged from the filter packing. They ventilate the filter by aproviding air for the micro-organisms by being open atleast to a circumferential channel. Should be designed such that forced air vibrations can be added later

Air flow:

  • Natural draft
  • Forced air ventilator


  • Because of their large air-water interface can remove co2,h2s, n2 & other gases
  • A portion of liquid in underdrain system is recycled:
  • It improves the treatment efficiency
  • To dilute strength of incoming wastewater
  • To maintain enough wetting of slime layer
  • Prevents ponding in filter
  • Suitable for shock loads
  • Low running cost