Trickling filter

Trickling filter

Trickling filters are known for process stability, operating economy, and low energy consumption as opposed to activated sludge processes which depend greatly on the operator skill to achieve high removal efficiency and stability of treatment.

Designing of Trickling Filter

Trickling filters with depths under 10 ft require a much larger amount of media to produce an effluent equivalent to that produced by a deep filter. A 20-ft filter would require half as much volume of media to provide the same SOD5 removal as a 10-ft-deep filter. Thus, the depth of a filter has a significant effect on the volume required. Although plastic media filters are much deeper than conventional filters, very little recirculation of filter effluent is required. Consequently, energy consumption is not high. Random fill media such as Actifed or Flex rings have the added advantage that no special placement pattern or cutting is necessary. The media are randomly dumped, so they can be easily installed in any size or shape of tank.

Factors Considered in Design

  1. Dosing Characteristics of The Distribution System

  2. Choosing the Right Packing / Media

  3. Configuration of The Underdrain System

  4. Provision for Adequate Ventilation


In summary, the main advantages of media trickling filters are:

  1. Low energy consumption & reliable performance results in lower running cost

  2. Because of their large air-water interface can remove CO2, H2S, N2 & other gases

  3. A portion of liquid in underdrain system is recycled, It improves the treatment efficiency

  4. To dilute strength of incoming wastewater

  5. To maintain enough wetting of slime layer

  6. Prevents ponding in filter

  7. Suitable for shock loads.

  8. Proven more than 100-year-old technology

  9. Rugged system with simple and silent operation.

  10. Less monitoring required than Activated sludge process.

  11. Consistent effluent quality, Stand-alone treatment process for sewage if operated at low rates.

  12. To be used in combination with ASP for efficient performance.

  13. Low pathogen removal

  14. Bacteria, 20‐90%

  15. Viruses 50‐90%

  16. Giardia cysts 70‐90%

A trickling filter is a type of wastewater treatment system. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime to grow, covering the bed of media.


  1. Additional treatment may be needed to meet more stringent discharge standards.

  2. Possible accumulation of excess biomass that cannot retain an aerobic condition and can impair TF performance (maximum biomass thickness is controlled by hydraulic dosage rate, type of media, type of organic matter, temperature and nature of the biological growth).

  3. Requires regular operator attention.

  4. Incidence of clogging is relatively high.

  5. Requires low loadings depending on the medium.

  6. Flexibility and control are limited in comparison with activated-sludge processes.

  7. Vector and odour problems.

  8. Snail problems.

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