Question Answer
Other than water temperature (density and viscosity) list three other factors that may hinder the settling of a particle in a clarifier? Turbulence, flow currents, and sludge buildup
What are the three most important factors to be considered when sizing a clarifier? Detention time, rise rate, and weir overflow rate
This term means the average length of time the water is in the clarifier? Detention time
Detention time calculation depends on which two factors? Clarifier volume and flow rate
This term is defined as the upward velocity of the water in the clarifier? Rise rate (also known as overflow rate)
Rise rate calculation depends on which two factors? Water flow and the surface area of the clarifier
List two ways in which detention times are commonly expressed? m3/hour or m3/day
This concept is expressed as the flow per unit surface area of the clarifier? Rise rate
The volume of the clarifier divided by the flow is? Detention time (in hours)
The flow rate divided by the surface area of the clarifier is? Rise rate
This concept is expressed as m3/day per m2? Rise rate
If the rise rate is greater than the settling rate of a certain particle, then that particle will ____? not be removed
Most clarifiers are designed with rise rates in the range of _____ meters per day? 25 to 75
The weir loading rate calculation uses which two factors? Length of the effluent weir and flow rate
How is weir loading rate calculated? Flow rate divided by the weir length
How are weir loading rates typically expressed? m3/day per m of weir length
These are known as high-rate settlers, and were developed to increase the efficiency of solids removal in clarifiers? Tube settlers
These are used in sedimentation tanks (clarifiers) and provide better effluent quality because they allow increased surface loading rates? Tube settlers
Tube settlers can increase surface loading rates by as much as ___ the conventional loading rate? Double
Tube settlers are placed ____ of the clarifier, and are inclined at a ____ angle? Just below the surface/60° angle
With this type of clarifier, the influent line usually runs underneath the tank and rises vertically to the surface in the centre of the clarifier? Circular clarifier
With a circular clarifier, what is used to reduce short-circuiting in the clarifier? Cylindrical inlet baffle
It is the part of the circular clarifier that is used to move floating material to the outside of the tank surface? Skimmer arms
In a rectangular clarifier the influent usually enters along? The short side of the clarifier
In a rectangular clarifier, what is one of the most important parts? Inlet baffle
In a rectangular clarifier, this component is used to distribute the flow as evenly as possible across the clarifier, and it is considered as one of the most important parts of a rectangular clarifier? Inlet baffle
List three types of currents which occur in a clarifier? Surface, density, and hydraulic currents
These are the types of currents, which occur in a clarifier, that are caused by wind? Surface currents
These types of clarifier currents are caused by differences in floc concentration or water temperature? Density currents
These currents are caused by characteristics of the clarifier such as inlet and outlet arrangements, the sludge removal system, the shape of the clarifier, among other factors? Hydraulic currents
These types of currents are undesirable because they result in higher velocities in an irregular pattern throughout the clarifier? Hydraulic currents
These types currents are the most significant of the three major types of currents because they decrease the solids removal efficiency? Hydraulic currents
These types currents cannot be controlled? Density currents
Which type of weir, v-notch or rectangular, provide a more even flow? V-notch weir
Water treatment plant sludges usually consist of ____ and _____? Aluminum hydroxide floc/original suspended particles
The solids concentration of sludge removed from a clarifier can vary greatly from _____? less than 0.25% to more than 10%
Sludge greater than ____ solids concentration require removal by pumping? 3%
Interference with settling process (re-suspension of settled solids); sludge becoming septic (taste and odour problems); and excessive reduction of clarifier volume are all problems that are caused by? Accumulation of sludge
This is a common method of determining the amount of sludge to be removed from a clarifier? Measure sludge blanket depth
What is the most important single factor influencing clarifier performance? Water flow
Clarifiers should be shut down and thoroughly inspected at least once? Annually
The two processes that take place in a solids contact system are? Flocculation and sedimentation
This process sometimes takes place in a solids contact system? Coagulation
This treatment process operates on the principle of recycling settled sludge or slurry into coagulation and flocculation processes to form a “seed” or coagulent aid? Solids contact system
This treatment process is used for both turbidity removal and for water softening? Solids contact system
This treatment process tends to be more sensitive to rapid changes in raw water flow, quality, and temperature? Solids contact system
This treatment process has internal mechanisms that are usually more expensive and difficult to maintain? Solids contact system
As raw water enters a solids contact unit, it is mixed with ____ in the central mixing zone? Previously-formed solids (sludge)
What is one of the most important aspects of the operation of a solids contact system? Control of solids
What are the two zones of a solids contact unit in which maintaining a substantial sludge content is most critical? Flocculation zone and separation zone
What are the three fundamental principles that must be understood in order to properly operate a solids contact system? Chemical dosage; recirculation; solids control
This fundamental principle in the operation of a solids contact system is one of the most difficult factors to assess? Recirculation
The recirculation rate in a solids contact system is determined by? Speed of the mixing device (impeller, turbine, pumping unit, etc.)
What is the first step to determine the effectiveness of recirculation in a solids contact system? Determine percentage of solids in the reaction zone
How is the percentage of solids in the reaction zone of a solids contact system determined? 10 minute settling test in a 100 mL graduated cylinder
What is the recommended guideline for percent solids (by volume) in the reaction zone of a solids contact system? 10 to 30%
In the operation of a solids contact system, which is preferable: maintain too much sludge or maintain too little sludge? It is considered better to maintain too much sludge
In the operation of a solids contact system, during periods of increasing flow the main thing to watch for is? Depth of sludge and floc carryover in the effluent
In the operation of a solids contact system, for each rise rate there will be an optimum _____ to be maintained? Slurry quantity
In the operation of a solids contact system, higher flow rates typically require ____ to maintain control over solids level? High recirculation rates
In the operation of a solids contact system, changes in flow rate should be made? As gradually as possible
In the operation of a solids contact system, changes in raw water turbidity usually require adjustment to the? Coagulent dosage
If the raw water is clear enough whereby the pre-treatment step (coagulation/flocculation/sedimentation) can be omitted, the process is called? Direct filtration
List the four basic chemical and physical filtration mechanisms? Physical straining; sedimentation; adsorption; biological activity
This basic filtration mechanism entraps particles by pores in the filter medium which are smaller than the particles themselves? Physical straining
This basic filtration mechanism is the process whereby particles settle out by gravity onto the surface of the media? Sedimentation
This basic filtration mechanism is the process in which one substance becomes bonded to the surface of another (solid) substance? Adsorption
This basic filtration mechanism involves a variety of biological reactions caused by living organisms trapped in the media beds, but it is not usually a significant factor? Biological activity
This main component of the filter must be deep enough to accommodate the underdrain system, filter media, and the head (pressure) of water needed to force the water through the media beds? Filter chamber
This main component of the filter supports the filter media, collects the filtered water, and distributes water evenly over the entire filter area during backwashing? Underdrain system
This main component of the filter is comprised of one or more materials? Filter media
Particles of this medium are relatively large, so that large turbidity particles can be removed from the water without the bed clogging up too quickly? Coal
This medium has smaller particle size and is responsible for removing smaller turbidity particles giving a high quality filtered water? Sand
This term is commonly used when discussing dual media filtration? Anthrafilt
Sand as a medium commonly has an effective particle size of about? 0.5 mm
This main component of the filter is located above the media beds, and the purpose is to collect backwash water and convey it to a holding tank? Wash troughs
If media particles are small and more closely packed together the spaces between them will also be smaller and result in? Head loss
The depth of media beds increases this operational parameter? Head loss
What are the two ways of operating a filter system which compensate for the change in resistance to flow during a filter run? Constant rate and declining rate filtration
This filter system operation requires an important item of equipment known as? Constant rate filration/A rate controller
This consists of some type of flow control valve on the effluent line, which is governed by the output signal from a flow sensing device on the same line? A rate controller
For this filter system operation, the purpose of this piece of equipment is to hold the flow through the filter constant, at a preselected rate, regardless of the degree of bed plugging (two answers)? Constant rate/Rate controller
When the beds are clean, the flow will tend to be too high, so the valve will be partly closed to restrict the flow to the desired value. As the beds plug, the valve gradually opens to compensate for the increased resistance to flow in order to maintain consistent flow throughout the entire run. What type of filter system operation is this? Constant rate filtration
During constant rate filtration, the loss of head gauge reading will ______ during the filter run as the beds plug? Increase steadily
For this filter system operation, because flow through the filter is constant, changes in plant throughput are made by changing the number of filters online? Constant rate filtration
For constant rate filtration, adjusting the setting on the rate controller to control plant production rate is typically ____? not practised
For this filter system operation there is no rate controller? Declining rate filtration
For this filter system operation, flow through the filter is simply allowed to decrease as the beds plug up during the run? Declining rate filtration
For this filter system operation, negative head and air binding is prevented with each filter having an effluent weir set at the? Same elevation
For this filter system operation, a valve on the effluent line is used to shut off effluent during backwashing and to limit the initial flow through the filter when beds are clean (to prevent breakthrough)? Declining rate filtration
For this filter system operation, the main advantage of the system is that the complexity and expense of specialized equipment is eliminated, and what piece of equipment is eliminated? Declining rate filtration/rate controllers
What is one of the most important factors in filter operation? Filter loading rate
This concept is defined as the flow per unit area of filter surface (similar to rise rate in a clarifier)? Filter loading rate
This concept calculation requires the water flow rate and the surface area of the filter? Filter loading rate
The filter loading rate calculation requires which two factors? Flow rate and surface area of the filter
The filter loading rate is represented with the letter? R

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