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What is filtration?
Removal of particulates or dissolved materials.
What is the purpose of disinfection?
To kill unwanted organisms entering the system.
What methods are used for disinfection?
Ozone (O3), Ultraviolet (UV) light, or chlorination.
What is degassing?
Removal of nitrogen (N2).
What is a simple screen?
Removes particulates by being placed at the pump inlet.
What is a rotary filter?
Water is passed through a rotating screen.
What happens as water passes through a rotary filter?
As part of the screen is filtering, the other part is being cleaned by a backwash.
What are the two rotary filter types?
Axial and vertical.
What are bag filters used for?
To remove fine materials.
What are bag filters made of?
Nylon or other synthetic materials.
Where are bag filters used?
Inlets of raceways and tanks.
Where are cartridge filters typically utilized?
Laboratory or hatchery systems.
What are particle filters?
Filters where water runs through bedding material, catching suspended materials.
What happens to the water flow when the bed material of particle filters gets smaller?
Smaller suspended materials can be removed, but the flow becomes slower.
What is backwashing in filtering?
Cleaning process to remove trapped particles.
Why is backwashing important?
Essential to maintain the efficiency and lifespan of the filter.
What is the process of backwashing?
Flow of water is reversed to fluidize bed material, allowing trapped particles to be removed.
What effect does having multiple housing in filters have?
Greater efficiency, but requires more management.
What are diatomaceous earth filters?
Fine powder that traps contaminants and particles in water.
What kind of material are diatomaceous earth filters used for?
Very fine particles.
What is another name for filter material in diatomaceous earth filters?
Celite.
What are the steps of DE filters?
Pre-coat cycle establishes a uniform cake of DE; service cycle terminated when pressure loss is reached.
What are gravitational filters?
Filters that use gravity to separate insoluble materials with a density greater than water’s.
What is the relationship between density increase and efficiency of gravitational filters?
Positive relationship; as density difference increases, efficiency increases.
What is simple sedimentation?
Water is held still for hours to weeks to allow sediment to settle.
What should be added to simple sedimentation tanks to increase efficiency?
A coagulant, for example, aluminum sulfate.
What do coagulants do for simple sedimentation?
Cause clumping, increasing the sinking rate of sediment.
What is chitosan?
A coagulant used for harvesting microalgae, which is non-toxic.
What kinds of coagulants are there?
Aluminum sulfate (alum) and chitosan.
What is centrifugation for filtering?
A process that increases the pull on heavy particles to separate them from liquid.
What is efficiency in centrifugation a function of?
Rotational speed, centrifuge radius, flow rate, and the density of suspended material.
What is a hydroclone?
A device that uses centrifugal force to separate particles from liquid.
What are the two major parameters of hydrocyclones?
Characteristics of the feed stream and the geometry of the cyclone.
What happens to liquid and sediment in a hydrocyclone?
Lighter material (water) moves upward, heavier material moves downward.
What are biological filters used for?
To use bacteria to remove nutrients or convert ammonia into a more oxidized state.
What is an under-gravel filter?
A filter where the material is always underwater, sucking water through gravel inhabited by bacteria.
What type of reactions occur with under-gravel filters?
Oxidation reactions, requiring high dissolved oxygen levels in water.
What is a trickling filter?
A filter where water is trickled over small stones.
What is the dissolved oxygen (DO) level in a trickling filter?
DO is never limiting.
What is a drum in filtering systems?
A system consisting of a series of rotating disks partially submerged in water.
What are fluidized bed filters?
Filters that use suspended media to promote healthy bacteria growth.
What type of current do fluidized bed filters use?
Upwelling current that passes through a medium, with particles moving constantly.
What is nitrification?
The conversion of toxic ammonia into less harmful nitrogen compounds.
What do nitrification reactions require?
Dissolved oxygen (DO) and consideration of ammonia toxicity.
What happens to ammonium at higher pH values?
Ammonium shifts to ammonia.
What does nitrosomonas do?
Oxidizes ammonia into nitrite and uses energy to fix carbon dioxide into organic molecules.
What does nitrobacter do?
Oxidizes nitrite into nitrate.
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