Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
78 Cards in this Set
- Front
- Back
|
What is the difference between conventional filtration and direct filtration? |
Direct filtration is not preceded by sedimentation, and flocculation facilities are reduced in size or omitted |
|
|
List the five particle removal mechanisms involved in filtration |
1. Sedimentation on media (very important) 2. Adsorption (very important) 3. Biological action 4. Absorption (not too important after initial wetting) 5. Straining (SABAS) |
|
|
List the four specific classes of filters |
Gravity filters (Sand, dual media, mixed media) Pressure filters (mixed media) Diatomaceous Earth (Precoat) Slow sand filters |
|
|
What is Garnet? |
A group of hard, reddish, glassy mineral sands made up of silicates and base metals |
|
|
What material is used for precoat and body feed operations? |
Diatomaceous Earth |
|
|
What is most often used to support granular filter materials? |
Gravel |
|
|
Filtration rate is commonly expressed in what units? |
Gallons per minute per square foot of filter surface area Liters per second per square meter of surface area |
|
|
What is the major operational difference between sand and dual media filters? |
Sand filters require more frequent backwashing Dual media filters permit a higher filtration rate without a high head loss |
|
|
What two main factors influence the time period before a filter becomes clogged? |
The amount of suspended solids Filtration rate |
|
|
When would a filter be taken out of service for cleaning or backwashing? |
Just before clogging or breakthrough have occurred A specific time period has passed A specific head loss is reached Effluent turbidity |
|
|
List for types of surface wash (supplemental scour) systems for filters |
Baylis, air scour, rotary, fixed grid, (BARF) |
|
|
What does a filter control system provide? |
Control of flow rates through filter To maintain an adequate head above the filter media |
|
|
What is the primary purpose of using activated carbon (granular form) as filter media? |
To remove taste and odor causing compounds, as well as other trace organics |
|
|
What is in-line filtration? |
The addition of filter aid chemicals immediately prior to filtration Coagulant chemicals are added directly to the filter inlet pipe and are mixed by the flowing water |
|
|
When and where our filter aid chemicals used? |
During periods of pre-treatment process upset, or when operating at a high filtration rates Just prior to filtration |
|
|
When is direct filtration used? |
When source waters are low in: turbidity, color, plankton, coliform organisms |
|
|
If both head loss and turbidity breakthrough are constantly a problem due to improperly sized media, what should be done? |
A deeper filter bed with a larger media size should be considered |
|
|
What problems can develop if backwash rates are either too high or too low? |
Too low: won't completely remove trap solids from filter media Too high: cause excessive loss of filter media and media disturbance such as mounding |
|
|
What is the most important water quality indicator used to monitor the filtration process? |
Effluent turbidity |
|
|
How can filter effluent turbidity be measured on a continuous basis? |
By an online turbidimeter |
|
|
What could cause a sudden increase in head loss through a filter? |
Surface sealing of the filter media (lack of depth penetration) |
|
|
How would you change the operation of a filter if there was a sudden increase in head loss through the filter? |
Adjust the filter aid chemical feed rate Reduce the filtration rate |
|
|
How could you make a quick determination of filtration removal efficiency? |
By comparing filter influent and effluent turbidity levels with those of recent record |
|
|
When are filters routinely taken off-line? |
Backwashing, turbidity breakthrough occurs, demands for water are reduced |
|
|
Why should the surface wash system be activated just before the backwash cycle starts? |
To aid in breaking up solids on the filter media and to prevent the development of mudballs |
|
|
What should be done if a filter will be out of service for a prolonged period? |
Drain water from filter to avoid algal growth |
|
|
What is the SWTR definition of surface water? |
All water open to the atmosphere and subject to surface runoff |
|
|
Particle counters can be used as a substitute for indicating the potential removal of what 2 microorganisms that are a threat to public health? |
Giardia: SWTR requires a 99.9% (3-log) removal Cryptosporidium |
|
|
Particle counters can be used to enhance the performance of which two water treatment processes? |
Sedimentation and filtration |
|
|
What is the difference between turbidimeter and particle counter measurements? |
Turbiditmeters Measure the average amount of particulate matter in a slowly changing volume of water Particle counters count and size the particles individually in a constant flow stream |
|
|
How does the rate-of-flow filter control system work? |
Each filter effluent control valve is connected to a flow meter and, as the filter run continues and the media begins to clog, the control valve slowly opens to maintain a constant flow of water through the filter |
|
|
What is the best way to compare filter runs |
Unit filter run volume UFRV |
|
|
Why is the appropriate feed rate for a filter aid chemical important? |
Overdosing can cause sealing of the filter media resulting in shortened filter runs |
|
|
Operators may encounter which types of filter backwash problems? |
Failure of the filter to become clean Media boils Media loss |
|
|
Particle counting, when used along with other measurement techniques, can be a valuable tool to diagnose what kinds of filtration problems? |
Disrupted media, improperly graded media, insufficient media, short circuiting, mudballs |
|
|
With grab samplers and particle counters, why do operators often use short lengths of Tygon tubing for the sample tubing? |
Easy to see the sample flow, easy to work with, flexible, inexpensive, |
|
|
What could cause the particle concentration to appear high? |
Air bubbles, contamination, increased flow rate through the sensor |
|
|
What is the length of normal filter runs before cleaning? |
30 to100 hours |
|
|
What is the maximum filtration rate for gravity filtration? |
2 to 10 GPM/sq ft |
|
|
What is the filtration rate for slow sand filtration? |
0.015 to 0.15 GMP/ sq ft |
|
|
How is filtration rate measured? |
Gallons per minute per square foot |
|
|
How is filtration rate measured? |
Gallons per minute per square foot |
|
|
What percentage of processed water does the backwashing process use? |
2 to 4% |
|
|
What might suddenly increases in head loss during filtration indicate? |
Surface sealing of the filter media |
|
|
What are the turbidity requirements for conventional filtration? |
Monitor every 4 hours Turbidity less than 0.5 NTU |
|
|
What are the turbidity requirements for conventional filtration? |
Monitor every 4 hours Turbidity less than 0.5 NTU |
|
|
What are the turbidity requirements for direct filtration? |
Monitor every 4 hours Turbidity less than 0.5 NTU (same as conventional filtration) |
|
|
What are the turbidity requirements for diatomaceous earth filtration? |
Monitor every 4 hours Turbidity less than 1.0 NTU |
|
|
What are the turbidity requirements for diatomaceous earth filtration? |
Monitor every 4 hours Turbidity less than 1.0 NTU |
|
|
What are the turbidity requirements for slow sand filtration? |
Monitor once per day Turbidity less than 1.0 NTU |
|
|
What is the maximum turbidity level? |
5 NTU (Nephelometric turbidity units) |
|
|
What is the main difference between particle counters and turbiditmeters? |
Turbidimeters provide no indication of the number or size of particles, while particle counters do measures the number and size of particles |
|
|
What kind of process is filtration? |
Physical and chemical |
|
|
How does gravity filtration work? |
The water level or pressure (head) above the media forces the water through the filter media |
|
|
What are the 3 types of gravity filters? |
1. Single media (sand) 2. Dual media (Sand and anthracite coal) 3. Mixed media (Sand, anthracite coal, and Garnet) |
|
|
What is pressure filtration? |
The same as gravity filtration, except the filter is completely enclosed in a pressure vessel such as a steel tank -less reliable than gravity filters |
|
|
What is Diatomaceous Earth filtration? |
The filter media is added to the water as a slurry. It then collects on a septum (A pipe or conduit with porous walls) Also called precoat filtration |
|
|
What type of filtration is popular for small systems? |
Slow sand filtration |
|
|
Filter media are classified by what 4 aspects? |
Effective size, uniformity coefficient, specific gravity, and hardness |
|
|
What is the effective size of filter media? |
The size of sieve opening that permits 10% by weight of the particles (sand) to pass through |
|
|
The uniformity coefficient of a filter refers to what? |
The ratio of particle diameters (based on sieve sizes) comprising 60% and 10% of media weight. The more uniform the media, the slower the head loss build up. Media with uniformity coefficients of less than 1.5 are readily available |
|
|
What is another name for duel media filters? |
Depth filters |
|
|
What is another name for sand filters? |
Surface filters |
|
|
What is the definition of clogging? |
A buildup of head loss (pressure drop). Clogging leads to break through |
|
|
What is the split-flow control system? |
The flow to each filter influent is split or divided by a weir |
|
|
What is the rate-of-flow control system? |
Each filter effluent control valve is connected to a flowmeter |
|
|
What is a declining-rate control system? |
Flow rate varies with head loss |
|
|
What is a declining-rate control system? |
Flow rate varies with head loss |
|
|
What is a self-backwash system? |
Influent flow to each filter is divided by a weir |
|
|
What is the filter "ripening period"? |
After the initial coating of floc is deposited on the media surfaces, additional floc will build up on the previous floc |
|
|
What is another name for a turbidimeter? |
A Nephelometer |
|
|
It is best to calculate when the filtration cycle will be completed on the basis of what? |
1. Head loss 2. Effluent turbidity 3. Elapsed run time |
|
|
What is the unit filter run volume (UFRV)? |
The volume of water produced by the filter divided by the surface area of the filter |
|
|
When does turbidity breakthrough pose a problem? |
The initial few hours after a filter is placed in service Filters should be eased into service to avoid hydraulic shock loads |
|
|
To what water systems does the surface water treatment rule (SWTR) apply? |
All water systems using surface water and those using ground water that is under the influence of surface water |
|
|
What microorganisms can be indirectly measured by particle counters? |
Giardia and cryptosporidium, by monitoring the removal efficiencies of particles in the same size ranges |
|
|
How does filter ripening affect particle counters? |
During filter ripening, the number of particles will increase. Particle counts should then rapidly decrease within a few minutes |
|
|
How does lengthening filter run time affect the size of particles passing through the filter? |
With lengthening filter run time, The percentage of large particles passing through the filter increases while small particles decrease |
