Trickling Filters

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