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Questions and Answers
What is the main action of a trickling filter?
What is the main action of a trickling filter?
What is the purpose of passing settled effluent through a trickling filter?
What is the purpose of passing settled effluent through a trickling filter?
What forms on the surface of the support material in a filter bed?
What forms on the surface of the support material in a filter bed?
What is the most common packing material used in a trickling filter?
What is the most common packing material used in a trickling filter?
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Which organisms primarily remove the majority of the organic loading in the biological film?
Which organisms primarily remove the majority of the organic loading in the biological film?
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Why is it important for a trickling filter's packing material to have a voidage of 45-55%?
Why is it important for a trickling filter's packing material to have a voidage of 45-55%?
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What are nitrogenous matter and ammonia oxidized to in the filter bed?
What are nitrogenous matter and ammonia oxidized to in the filter bed?
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What role does the secondary sedimentation tank play after a trickling filter?
What role does the secondary sedimentation tank play after a trickling filter?
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How does a rotary system in some trickling filters improve performance?
How does a rotary system in some trickling filters improve performance?
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What role do higher organisms like protozoa play in the filter bed?
What role do higher organisms like protozoa play in the filter bed?
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What can poison the active slime in a filter bed?
What can poison the active slime in a filter bed?
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What is a primary drawback of operating a simple filter at abnormally high organic loading rates?
What is a primary drawback of operating a simple filter at abnormally high organic loading rates?
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Study Notes
Trickling Filter
- A trickling filter is not a true filtration process, but rather a fixed film bio-reactor.
- Settled effluent to be treated is passed down through a packed bed counter-current to a flow of air.
- Micro-organisms adhering to the packing matrix adsorb oxygen from upflowing air and organic matter from the downflowing effluent.
- The organic matter is then metabolized, and the stream's BOD (Biochemical Oxygen Demand) is reduced.
Design and Operation of a Trickling Filter
- A conventional trickling filter typically consists of a cylindrical concrete tank, 2 to 3 m in depth and 8 to 16 m in diameter.
- The tank is packed with a bed of stone (usually granite) or special plastic packings, underlaid with drains.
- The packing material should have a diameter of 50 to 100 mm to provide a specific surface area of around 100 m2/m3.
- The packing material should be packed to give a voidage of 45 to 55% to minimize the risk of blockages.
- Synthetic packing material has a higher surface area and voidage, allowing higher treatment rates per unit volume of bed and reducing the likelihood of blockages.
Importance of Secondary Sedimentation
- A trickling filter is always followed by a secondary sedimentation tank or humus tank to remove suspended matter (e.g. biofilm sloughed off the packing) from the treated effluent.
Effluent Treatment and Biological Film
- In conventionally loaded or low-rate filters, the effluent from which the suspended solids have been removed is fed onto the upper surface of the bed by spray nozzles or mechanical distributor arms.
- A slime layer of biologically active material (bacteria, fungi, algae, protozoa, and nematodes) forms on the surface of the support material.
- The bacteria in the biological film remove the majority of the organic loading, breaking down complex organic materials, and oxidizing nitrogenous matter, ammonia, and other compounds.
- Higher organisms (protozoa, etc.) control the accumulation of the biological film and improve the settling characteristics of the solids (humus) discharged with the filter effluent.
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Description
Learn about the concept of a trickling filter in the context of unit operations, where settled effluent is treated by passing down through a packed bed counter-current to a flow of air. Discover how micro-organisms adhere to the packing matrix, absorb oxygen, and metabolize organic matter to reduce BOD in the effluent.
