In this post, I am going to discuss the trickling filter and types of trickling filter and its disadvantages. The effluent from primary settling tank which contains unstable organic matter should be converted into stable forms like nitrates and sulphates by oxidation ( aerobic process)
Filtration: Influent should be sprinkled over the open beds of coarse aggregate. Effluent from filers again settled in the secondary settling tank.
Sludge in secondary clarifiers of sedimentation tank is digested in the sludge digestion process
Types of trickling filters in wastewater treatment
- Intermittent sand filters
- Contact beds
- Low rate trickling filters
- High rate trickling filters
1.Intermittent sand filters
Intermittent sand filters are used in special cases for treating sewage from tuberculosis hospitals.
The BOD removal in intermittent sand filters is 90 % to 95%.
2. Contact beds ( Contact filters)
Filter media consists of gravel, broken bricks or stone are used in contact beds. BOD will be removed to an extent of 60% to 75%
3. Tickling filters
Trickling filters work on the principle of the attached growth process.
a) Conventional or low rate trickling filters
The purification of sewage is brought about mainly by aerobic bacteria which forms a bacterial film around the particles of filtering media.
Size of filter media 25mm to 75mm stone aggregate, depth of filter is 2 to 3 m. Provided with open top and there will be free circulation of air through the medium. BOD removal efficiency is 75% to 80%.
The conventional trickling filter is very useful to medium town and industrial cities requiring full treatment of sewage.
OPERATIONAL TROUBLES IN TRICKLING FILTERS ( Disadvantages)
1. Fly nuisance: Psychoda (Fly)
2. Odour nuisance: The remedy is chlorination of sewage.
3. Ponding troubles: Filers media gets clogged due to the growth of algae and fungs and this is called ponding.
Adding Chlorine or copper sulphate to the sewage kills algae thereby ponding can be avoided.
Efficiency = (BOD removed/ BOD APPLIED ) × 100
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