1.Simple, reliable, biological process.

2.Suitable in areas where large tracts of land are not available for land intensive  treatment systems.

3.May qualify for equivalent secondary discharge standards.

4.Effective in treating high concentrations of organics depending on the type of medium used.

5.Resistant to Shock Loads and Toxins. Not a mixed system, toxin affects localized. Recycle averages out shock loads.

6.Appropriate for small to medium sized communities.

7.Rapidly reduce soluble BOD5  in applied wastewater.

8.Waste sludge easy to dewater, primarily sloughed off bio layer. Settles and dewaters better than activated sludge.

9.Efficient nitrification units.

10.Durable process elements.

11.Low Energy requirements, do not typically require blowers.

12.Low maintenance, few moving parts.

13.Moderate level of skill and technical expertise needed to manage and operate the system.


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 unless regular flush is incorporated.

5.Loadings levels dependent on the medium.

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

7.Vector and odor problems unless regular flush is incorporated.

8.Snail problems unless regular flush is incorporated.

9.Cold weather can cause freezing, especially with associated low flow.


Trickling Filter

Trickling Filters • Trickling filters are artificial beds of crashed stones or other porous media through which the settled sewage is allowed to percolate. • It is widely used for biological treatment of wastewater in order to remove organic matter • The liquid waste is applied intermittently over the top surface of the filters by means of a distributor. Filtered liquid is collected at the bottom through filter box and under drain system

Trickling Filter Tension Rods Sprinkler Effluent Influent Under Drainage System Sectional Elevation Plan

Trickling Filters • Filtering Media: • Filter Material: Crushed stones, brick khoa, etc. • Depth of filtering media: Minimum of 3ft., Maximum of 10ft • Particle Size: ranges from 1 ~ 4inch in diameter. • Under drain system: • It is a network of tiny channels which rapidly discharge their flow into the main collection channel which normally runs along the middle of the filter. • Normally vitrify clay-block or porous brick construction. • Final sedimentation tank is an integral part of the trickling filter. The function of this tank is to remove the large masses of biological growth which flow with the effluent from the filter media.

Trickling Filter: General Layout Recirculation Trickling Filter Primary Clarifier Secondary Clarifier Influent Effluent General layout of a trickling filter

Organic Matter Removal • Removal of organic matter isn’t accomplished through filtering action • The liquid waste is brought into contact with air and with biological growth. • Organic removal is the result of an adsorption process which occurs at the surface of the biological film covering the filtering media. • Subsequent to their adsorption, the organic matter is utilized by the bacterial slimes for growth and energy. • Removal of organic matter is the function of: • Microorganism presents • Organic concentration applied • Stone size or microbial surface area • Time of retention of liquid in the filter • Temperature

Trickling Filter: Organic Removal Crushed Stone/Brick Bacterial Growth Sewage Organic Removal Process

Microorganisms • Trickling filter is considered as facultative system • At the beginning the process is aerobic. • The microorganisms create an anaerobic layer at the stone interface • Predominant microorganisms are: • Bacteria: anaerobic, facultative, aerobic • Fungi: aerobic (live where DO exists) • Algae: Live at the upper surface of the filtering media. It does not contribute to the overall stabilization of the sewage. • Higher animals: Worm, snail, insect larvae • Live at the upper aerobic area • Feed on microorganisms • Do not contribute to the filtering action

Recirculation is the return of a portion of the treated or partially treated sewage to the treatment process. Usually the return is from the effluent of the 2nd clarification to the influent of the primary clarifier. The effluent from the final clarifier may also be re-circulated to dilute the influent to the filter. Main purposes of recirculation: • It provides longer contact time in the filter and the load is reduced since the sewage is diluted • The rate of flow through filters can be kept constant by varying the amount of sewage that is re-circulated • The effluent quality is much improved • The seeding of filters is done continuously with active organisms and enzymes • It removes worn out films and reduce the film thickness • It improves the filter efficiency

Design Consideration for T.F. • Composition and characteristics of waste material • Organic and hydraulic loading to be applied on the filter • Pretreatment by sedimentation • Recirculation ratio and system • Filter beds: volume, area, and depth • Aeration • Temperature


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