Question Answer
The filter loading rate is expressed as? m3/h.m2
The filter loading rate expression m3/h.m2 is the same as? Metres per hour
Most dual media rapid gravity filters are designed to operate at a loading rate between? 5 and 10 m/h
If a filter system is operating at a higher loading rate, list three operating factors that have to be considered? Shorter runs; higher head losses; increased effluent turbidity
For this filter system operation, the loading rates are averages over a complete run? Declining rate filters
List four media conditions that an operator looks for during an inspection? Depth, cleanliness, cracking, or shrinkage
List five conditions an operator should look for during a backwash? Media expansion; evenness of backwash; media carryover; media boiling; and clarity of backwash wastewater
From a water quality standpoint, the _____ is the best indicator of proper filter operation? Effluent turbidity
This water quality parameter helps in determining the optimum operating conditions for upstream processes such as coagulation and flocculation? Filter effluent turbidity
This water quality parameter is monitored down stream as part of the coagulation/flocculation/clarification operating procedure? Filter influent turbidity
List the three factors used to determine if a backwash is required? Filter effluent turbidity; excessive media clogging; length of run
Operating a filter in this manner will result in the accumulation of organic matter in the beds that can turn septic and impart bad tastes and odours to the water? Excessive filter runs
Operating a filter in this manner will cause trapped particulate matter in the beds to compact and adhere to the media grains making backwash more difficult? Excessive filter runs
List the first three valves that should be changed over before a backwash? Influent and effluent valves closed; backwash waste drain valve opened
When should a backwash be terminated during manual operation? When the backwash water is clear
It is considered as an important factor in achieving an efficient backwash? Backwash rate (flow)
To remove the trapped solids from the beds effectively, the media must be ___ and ___? Expanded/fluidized
During a backwash, once the entire bed is expanded it takes on the properties of a ___ rather than acting as a ____? fluid/mass of solid particles
If the backwash flow rate is too high solids removal efficiency is reduced because individual grains are too far apart for the desired? Self scouring action
It is the uneven resettlement of the media when the backwash flow is stopped? Media mounding
Media mounding is caused by? Excessive backwash rates
Backwash rates are expressed in the same units as? Filter loading rates
These physical characteristics of the water supply help to determine the best backwash rate and the settling rate of particles? Temperature and viscosity
List three filter media characteristics that will help determine the best backwash rate? Size; specific gravity; and shape of particle
It is defined as the apparent depth of the expanded bed during backwashing divided by its depth during filtration? Bed expansion
Backwashing typically uses between ___ and ___ percent of the plant production, depending on the frequency of backwashing? 2% to 5%
Backwash rates are usually in the range of____, with typical values being around ____ for most types of dual media filters? 35 to 60 m/h; 40 to 45 m/h
This can be calculated from a knowledge of the filter bed area and the backwash rate? Backwash flow rate
List three of the most common causes of high effluent turbidity during filtration? Improper coagulant dosage/agitator speed; hydraulic overloading; filter breakthrough
This operating problem is usually the result of a filter being run for too long between backwashes? Filter cracking
This filtration system design problem results in excessively long backwash periods because the backwash has to be continued until all areas of the bed have been cleared? Uneven backwash water distribution
This operating problem occurs when the interfaces between different layers of filter media are uneven? Media mounding
This operating problem can be caused by excessively high backwash rates, failure to increase the flow gradually at the start of backwashing, or uneven backwash water distribution? Media mounding
This operating problem is caused by the release of dissolved air in saturated cold water because of negative pressures developed in the beds, or an increase in water temperature? Air binding
This operating problem that contributes to air binding will develop when a filter is operated at a head loss greater than the head of water over the media? Negative pressure
This operating problem is objectionable because it reduces the effective filter area and causes excessively high backwash rates in areas of the filter that are not affected by this problem? Air binding (air pockets)
List two pieces of equipment an operator should check if a filter shows excessive head loss even after a thorough backwash? Underdrain system and loss of head gauge
It is a term used to describe certain properties of water which result from the presence of dissolved mineral substances, mainly salts of calcium and magnesium? Hardness
This chemical characteristic of water tends to shorten the life of fabrics when washed? Hardness
It is expressed as milligrams per litre of calcium carbonate equivalent? Hardness
List two other compounds (non-carbonate) that are also responsible for water hardness? Calcium sulphate and magnesium sulphate
Calcium hardness is caused by? Calcium ions
Magnesium hardness is caused by? Magnesium ions
This term is used to define the sum of the hardness caused by calcium and magnesium ions, including other minerals such as iron and manganese if present? Total hardness
This is the term used to define hardness caused by calcium and magnesium bicarbonates? Carbonate hardness
This is the term used to define hardness caused by calcium and magnesium sulfates, including other minerals such as chlorides and nitrates if present? Non-carbonate hardness
It is defined as the capacity of water to neutralize acids, and is a measure of how much acid can be added to the water without causing a great change in pH? Alkalinity
What are the three types of alkalinity? Bicarbonate, carbonate, and hydroxide
What laboratory methods is used to measure alkalinity? Titration using indicator solutions
The phenolphthalein endpoint occurs at a pH of ___, and a pH above this value indicates that P alkalinity is present? 8.3
This chemical compound is not present when the pH is above 8.3 as a result of P alkalinity? Carbon dioxide
Hydroxide alkalinity is not present when the pH is below ___, and when all the alkalinity is in the carbonate and/or bicarbonate form? 8.3
P alkalinity is? Phenolphthalein alkalinity
What laboratory method is used to test for total alkalinity? Methyl Orange titration
The methyl Orange titration endpoint occurs at a pH of? 4.5
What are the two main types of softening processes in common use? Chemical precipitation and ion exchange
This type of softening process involves the addition of lime or soda ash to water to remove the hardness-producing components out of solution? Chemical precipitation
This type of softening process requires the use of specially-formulated resin and sodium? Ion exchange
Which of the two main types of softening processes are typically used in very small systems? Ion exchange
The lime soda ash softening process converts bicarbonates and sulfates into ____ and ____ in order to precipitate the calcium and magnesium from solution? Carbonates and hydroxides
The conversion of soluble calcium and magnesium salts to less soluble forms is the principle of this treatment method? Chemical precipitation softening
Calcium hydroxide is? Lime
Sodium carbonate is? Soda-ash
Which of the two compounds requires twice as much lime in order to be effectively removed: calcium bicarbonate or magnesium bicarbonate? Magnesium bicarbonate
Which of the two compounds is less soluble: magnesium carbonate or magnesium hydroxide? Magnesium hydroxide
Which chemical addition is required in order to remove non-carbonate hardness (to react with sulfates)? Soda-ash
Which chemical compound does not produce hardness but it is taken into account in the softening reactions because it consumes lime? Carbon dioxide
Water which has been treated by the lime or lime/soda-ash softening process can sometimes be? Unstable (chemical components out of balance)
Following the chemical softening process, the stability of water can be improved by removing the excess? Calcium hydroxide
Excess calcium hydroxide is removed with this process? Re-carbonation
This chemical process lowers the pH by neutralizing the excess hydroxide in water (the calcium hydroxide after softening)? Re-carbonation
Excess calcium hydroxide is precipitated out of solution using this process? Re-carbonation
Which chemical compound is used in the re-carbonation process? Carbon dioxide
What can happen to the water chemistry if too much carbon dioxide is used in the re-carbonation process? Lower pH
Calcium carbonate may re-dissolve and increase the hardness of water if the ____during the re-carbonation process? pH gets too low
This chemical compound can be used instead of soda-ash in the chemical softening process, but it is not often used because it is more expensive and is a very dangerous chemical to handle? Caustic soda
This coagulant is considered as acidic which lowers raw water pH, and reduces raw water alkalinity? Alum
If coagulation precedes lime-soda ash water softening, what adjustment is required in order to have effective softening, and why? More lime-soda ash required because coagulant decreases pH
What is considered as the optimum pH for coagulation? 6 to 7
Efficient colour removal in the coagulation process requires a pH of? 6
Coagulant and softening chemicals are typically added at ____ in a small plant? The same point
When coagulation and lime-soda ash softening occur in the same facility, what will typically follow coagulant dosage adjustments? Lime-soda ash dosage adjustment
Lime reacts with calcium bicarbonate at a pH range of ___, and forms which reaction product? 10 to 11, calcium carbonate
Lime reacts with magnesium bicarbonate at a pH range of ___, and forms which reaction byproduct? 10 to 11, Magnesium carbonate
Magnesium carbonate: precipitates out or remains in solution after lime treatment? Remains in solution
Calcium carbonate: precipitates out or remains in solution after lime treatment? Precipitates out
What is known as partial lime softening often occurs when this chemical compound is not removed? Magnesium carbonate
With full lime treatment, magnesium carbonate will be converted to _____ at a pH above ____? magnesium hydroxide, 11
What is known as full lime softening is performed in order to remove this chemical compound? Magnesium carbonate
Magnesium hydroxide: precipitates out or remains in solution after lime treatment? Remains in solution
If re-carbonation is required, this takes place at which stage of the treatment process? Clarifier effluent (carbon dioxide addition)
Which chemical compound is produced by the re-carbonation reaction? Calcium carbonate (precipitate)
This softening process treats only some of the water, and softened water is then blended with non-softened water after the first clarifier? Split treatment
This softening process is used to eliminate the need for re-carbonation? Split treatment
This softening process has the added benefit of using two rapid mixers and two clarifiers, which also provides the advantage of allowing softening and coagulation reactions to be separate processes? Split treatment
The most commonly used softening chemical is? Hydrated lime – Ca(OH)2
Large quantities of ___are produced during the softening process? Solids (sludge)

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