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;
124 Cards in this Set
- Front
- Back
|
What is the first step in the water treatment plant and how long does it last? |
-Coagulation in a flash mixer that lasts between 30-60 seconds
|
|
|
What is the first step after coagulation and how long does it last?
|
-Flocculation, lasts from 15-45 minutes
|
|
|
Describe the function of a flocculation basin
|
-Water is gently mixed to allow smaller floc particles to form larger floc particles.
|
|
|
Describe the handling difference between large floc particles and small floc particles and why
|
-Large floc particles are more fragile, so often flocculation basins are "segmented" into multiplecompartments, each with a lower G value as the flow progresses and particle sizes increase
|
|
|
What process comes after flocculation and how long does it take?
|
-Sedimentation, 4 hours detention time. Four zones: Inlet, Outlet, Settling, Sludge
|
|
|
What process comes after sedimentation?
|
-Filtration
|
|
|
Describe how filtration works
|
-A process of both microstraining and adsorption. Positively charged chemicals from coagulation penetrate to different levels of the filter bed. They then ‘catch’ any remaining negatively charged particulates
|
|
|
Define adsorption
|
-A gathering of something on the surface of another material
|
|
|
How does an operator determine when to backwash a filter?
|
-Three factors: head loss, increase in filter effluent turbidity, and time/gallons of water filtered.
|
|
|
What stage of the process comes after filtration and what purposes does it serve?
|
-The water is sent to a clearwell. Before it gets there, flouride/disinfectant/corrosion control is added. The clearwell provides the necessary contact time for the disinfectant to work.
|
|
|
Name three types of pathogens
|
-Virus, bacteria, protozoan
|
|
|
Give some examples of bacteria that could be found in the water
|
-Salmonella, shigella, Typhoid, Cholera
|
|
|
Give some examples of protozoans that could be found in the water
|
-Giardia, Cryptosporidium
|
|
|
What disinfection methods are effective against cryptosporidium?
|
-Ozone and UV only (NOT chlorine)
|
|
|
What are the safety limits for chlorine exposure?
|
-0.5ppm is the PEL
-The RMCL is 2.0ppm -The MCL is 4.0ppm -IDLH at 10ppm |
|
|
At what concentration can your nose detect chlorine?
|
-0.3-0.5ppm
|
|
|
What is the minimum chlorine residual in the distribution system?
|
-0.2ppm
|
|
|
How is liquid and gaseous chlorine fed?
|
-By a PD pump and a chlorinator, respectively
|
|
|
Describe the effect of chlorine on metals in the water
|
-Can help remove iron and manganese from raw water
|
|
|
What are two benefits of using chloramines over free chlorine in the finished water?
|
-Longer lasting (more stable), produces 80% less THMs
|
|
|
What are three disadvantages of using chloramines over free chlorine in the finished water?
|
-Can cause taste/odor problems, can lead to nitrification problems, patients on dialysis must be notified.
|
|
|
What are some properties of ozone as a disinfectant?
|
-100x stronger than chlorine and 30,000x faster. 20 min half life, no residual, no THMs
|
|
|
What is hard or soft water caused by?
|
-Calcium and magnesium levels
|
|
|
What are the ranges for soft and hard water?
|
-60-100 mg/l
|
|
|
What action does hard water have on pipes and equipment?
|
-Scaling
|
|
|
Why don’t we distribute soft water from a water plant?
|
-It has a low pH and is very corrosive
|
|
|
Define pH
|
-A measure of hydrogen ion concentration in a solution. Also, a measure of the intensity of the basic/acidic qualities of the water
|
|
|
Describe the lime softening method of removing calcium and magnesium
|
-Lime is added to a pH of 10.8 at which point magnesium precipitates and drops out, then CO2 is added (recarbonation) to a pH of 9.6 where calcium precipitates and drops out
|
|
|
Why are iron and manganese undesirable in the water?
|
-They cause discoloration of the water and staining of clothing and fixtures. Also, they are a nutrient source for some bacteria (crenothrix, gallionella, etc)
|
|
|
What is the MCL for iron?
|
-0.3 mg/l
|
|
|
What is the MCL for Manganese?
|
-0.05 mg/l
|
|
|
Define secondary standards
|
-Guidelines that are not enforceable. Not a threat to health but affect the aesthetic qualities of the water
|
|
|
What is the dissolved and particulate form of iron?
|
-Dissolved = Ferrous (+2)
-Particulate = Ferric (+3) |
|
|
What is the dissolved and particulate form of manganese?
|
-Dissolved = Manganous (+2)
-Particulate = Manganic (+4) |
|
|
Name three methods of controlling iron and manganese
|
-Sequestration, Oxidation, Ion Exchange
|
|
|
Describe the sequestration method of iron and manganese control
|
-Polyphosphates are added that coat I+M, bind their electrons, and keep them in a dissolved state
|
|
|
Describe the oxidation method of iron and manganese control
|
-The addition of oxygen and removal of an electron (oxidation). This changes the state of I+M from soluble to insoluble
|
|
|
What are three methods of oxidation of I+M?
|
-Aeration (slow)
-Chlorine (most common) -Permanganate (must be dosed exactly or pink water may occur) |
|
|
Why is the ion exchange method of iron and manganese control not used?
|
-Can create a water with zero hardness, which is very acidic. Not good for large scale operations
|
|
|
What is the MCL for nitrite?
|
-1 mg/l (measured as nitrogen)
|
|
|
What is the MCL for nitrate?
|
-10 mg/l (measured as nitrogen)
|
|
|
What is the MCL for coliform bacteria in a large water system?
|
-Since more than 40 samples are needed, no more than 5%
|
|
|
What does the SWTR say about turbidity limits?
|
-No more than 1.0 NTU leaving the plant, no more than 5.0 NTU in the system
|
|
|
What is the goal for an individual filter cell with respect to turbidity?
|
-Less that 0.3 NTU in 95% of samples
|
|
|
What things can trigger a Tier 1 violation?
|
-Fecal coliform
-Nitrite -Nitrate -Chlorine Dioxide -Turbidity -Perchlorate -(CNN-FTP) |
|
|
What does C-Value refer to?
|
-The smoothness inside of pipes. The higher the C value, the smoother the pipe
|
|
|
What is a coupon?
|
-Steel specimen inserted to remove corrosiveness
|
|
|
What is a typical velocity of water inside of mains?
|
-2-4 fps
|
|
|
What is a gate valve?
|
-A metal disk raised and lowered to stop flow in a main. Not for throttling
|
|
|
What is a foot valve?
|
-A special check valve installed at the bottom of a pump’s suction line. It keeps the line full when the pump has stopped, so the pump will not lose its prime
|
|
|
Give three definitions of alkalinity
|
-The capacity of water to resist a change in pH
-The capacity of water to neutralize acids -A measure of how much acid must be added to lower pH to 4.5 |
|
|
Why is a pH of 4.5 relative to alkalinity?
|
-4.5 is the point at which you have no alkalinity
|
|
|
What are the forms of alkalinity?
|
-Mainly carbonates and bicarbonates
|
|
|
How does calcium and magnesium contribute to alkalinity?
|
-Calcium carbonate and magnesium carbonate react with Hydrogen ions.
|
|
|
What is the convention for measuring alkalinity?
|
-It is measured in terms of carbonate hardness and expressed as mg/l of equivalent Calcium Carbonate
|
|
|
What happens when calcium or magnesium atoms are attached to a carbonate ion (CO3)?
|
-The alkalinity is a contributor to hard water
|
|
|
Define soft water and some of its chemical properties
|
-15-60 mg/l, low CaCO3, low alkalinity, low pH
|
|
|
Define the two types of alkalinity:
|
-Carbonate hardness: caused by carbonate and bicarbonate ions or Ca and Mg
-Non-Carbonate hardness: Ca and Mg that has bound with sulfates, chlorides, or nitrates |
|
|
Define Total Hardness
|
-The combination of carbonate and non-carbonate hardness
|
|
|
If Total Hardness is greater than alkalinity, then…
|
-then alkalinity = carbonate hardness and the remainder is non-carbonate hardness
|
|
|
If alkalinity is greater than Total Hardness, then…
|
-then all alkalinity is in carbonate form
|
|
|
Describe the effects of Calcium Carbonate Saturation
|
-Water is stable when it is at perfect saturation of calcium carbonate at a given pH. It is neither scale forming nor corrosive.
|
|
|
What is the effect of raising pH of a perfectly saturated water?
|
-The carbonate precipitates out and becomes scale forming
|
|
|
What is the effect of lowering the pH of a perfectly saturated water?
|
-It becomes corrosive
|
|
|
What is pHs?
|
-The convention Langolier developed for predicting the pH at which water is perfectly saturated with calcium carbonate
|
|
|
What is the equation for LSI?
|
-pH (measured) - pHs
|
|
|
What does a negative LSI imply?
|
-Limited scaling potential
|
|
|
What does a positive LSI imply?
|
-The water is supersaturated with CaCO3 and will form scale
|
|
|
If the pH and alkalinity of a marble test increase, what does this indicate?
|
-That the water is under saturated
|
|
|
If the pH and alkalinity of a marble test decrease, what does this indicate?
|
-That the water is super saturated
|
|
|
What happens to bicarbonate ions at 9.6 pH?
|
-They are converted to carbonate form and precipitate as calcium carbonate
|
|
|
In lime softening as the pH increases to 10.8, what occurs?
|
-hydroxide becomes present and combines with magnesium to precipitate magnesium hydroxide
|
|
|
After lime softening, what is the next step? Why?
|
-Recarbonation, in order to keep the Langolier Index Positive
|
|
|
What causes rotten egg odors?
|
-Anaerobic bacteria convert sulfate to sulfide
|
|
|
How can you remove odors from water?
|
-Activated carbon or oxidation
|
|
|
Where is granular activated carbon used?
|
-In the filter beds
|
|
|
Where is powdered activated carbon used?
|
-Flash mix, long before chlorine because they cancel each other out
|
|
|
How is oxidation performed?
|
-Mechanically (using an aerator)
-Chemically |
|
|
What chemicals are oxidizers?
|
-Chlorine
-Ozone -Potassium Permanganate (only oxidant that is not a disinfectant) |
|
|
Why is oxidation performed?
|
-Taste/odor control
-Corrosion control (iron and manganese are precipitated) |
|
|
Trihalomethane definition
|
-Derivative of methane in which three halogen atoms are substituted for three hydrogen atoms
|
|
|
Methods of THM suppression
|
-No predisinfection (or use ozone)
-GAC in filter beds -Aeration after chlorination |
|
|
Problems associated with corrosion
|
-Damage to pipes, causes leaks, replacement frequency increases of water heaters, valves, meters, etc
-Reduced flows, tuberculation -Leeching of lead and iron |
|
|
Factors influencing corrosion:
|
-Low pH = corrosive
-Low alkaline waters have fewer tendencies to resist a change in pH, may become acidic and corrosive -D.O. - reacts with hydrogen in water and removes protective barriers to corrosion. Also reacts with iron to form precipitate “ferric hydroxide” rust. This forms layers in pipes -> tubercle formation. -Erosion: Faster than 5 fps will erode. Turbidity over time will erode. -Sulfate reducing bacteria: eat sulfate, produce sulfide, leave black metal deposits, sulfide can react and create sulfuric acid (very corrosive) -Iron bacteria (crenothrix etc) convert ferrous iron to ferric precipitate, deposit rust particles on slime sheaths around cells. This deposited iron can be released during periods of high flows, causing red water and unpleasant odor. Underneath deposits, pitting and tuberculation. |
|
|
What is the effect of raising the pH of water on corrosion?
|
-Will make the water less corrosive and cause a deposition of calcium carbonate which will coat and protect the main
|
|
|
Define confined space |
A space that meets three factors: -Is large enough for bodily entry -Limited or restricted access and egress -Is not designed for continuous occupancy |
|
|
Permitting requirements for confined space:
|
-Contains the potential of containing a hazardous atmosphere
-Contains a material that has the potential for engulfing the entrant -Has an internal configuration such that an entrant could become trapped or asphyxiated by inwardly converging walls -Contains any other recognized serious safety or health hazard |
|
|
-Required positions for permitted confined space entry:
|
-Supervisor
-Authorized entrant -Attendants -Rescue and Emergency Services (First Aid/CPR) |
|
|
Things to cover before entering a confined space |
-Atmosphere monitoring
-ventilation -isolation (including lock out/tag out) -entry permit -PPE -Comms -Rescue Plan |
|
|
Potential hazards inside a confined space
|
-oxygen deficient atmosphere
-flammable atmospheres -toxic atmospheres -‘FOT’ -general physical hazards (temp, noise, slippery, falling objects) |
|
|
Properties of chlorine
|
-Strong oxidizer
-Non-flammable, but highly supports combustion -2.5x heavier than air -Expands from liquid to gas phase at 450:1 -IDLH at 10ppm -Highly corrosive in the presence of water |
|
|
HAZWOPR definitions
|
-IDLH - Could escape within 30 minutes w/o irreversible effects
-PEL/TLV - 8 hour time-weighted average -STEL - 15 minute time-weighted average |
|
|
Leaking container protocol
|
-SSS
-plus logic. Expl if isolated how does that effect all downstream processes |
|
|
Define SCADA and how it is used
|
-Supervisory Control and Data Acquisition
-information from sensors or manual inputs are sent to PLCs (programmable logic controllers) or RTUs (remote terminal units), which then send that information to computers with SCADA software. SCADA software analyzes and displays the data in order to help operators and other workers to reduce waste and improve efficiency in the manufacturing process. |
|
|
How does Alum function as a coagulant? |
Aluminum Sulfate (Al2(SO4)3.16H2O) is commonly used as a coagulant. The alum is dissolved in the water and the aluminium ions (Al3+) that form, have a high capacity to neutralise the negative charges which are carried by the colloidal particles and which contribute to their stability. The aluminium ions hydrolyse and form aluminium hydroxide (Al(OH)3), which precipitates as a solid. During flocculation when the water is slowly stirred, the aluminium hydroxide flocs “catch” or enmesh the small colloidal particles. The flocs settle readily and most of them can be removed in a sedimentation tank. |
|
|
How does lime function as a coagulant? |
Lime can also be used as coagulant, but its action is different from that of alum and ferric chloride. When lime is added to water the pH increases, resulting in the formation of carbonate ions from the natural alkalinity in the water. The increase in carbonate concentration together with calcium added in the lime results in the precipitation of calcium carbonate (CaCO3). The calcium carbonate crystals enmesh colloidal particles in the same way as alum or ferric flocs. When lime is used as a coagulant, the pH has to be lowered in order to stabilise the water chemically. Carbon dioxide is normally used for this purpose. |
|
|
How does Ferric Chloride function as a coagulant? |
(FeCl3) is commonly used as a coagulant. When added to water, the ion precipitates as ferric hydroxide (Fe(OH)3) and the hydroxide flocs enmesh the colloidal particles in the same way as the aluminium hydroxide flocs do. The optimum pH for precipitation of iron is not as critical as with aluminium and pH values of between 5 and 8 give good precipitation. |
|
|
How do polyelectrolytes give aid to coagulants? |
Polyelectrolytes are mostly used to assist the flocculation process and are often called flocculation aids. They are polymeric organic compounds of long polymer chains that act to enmesh particles in the water. Polyelectrolytes can be cationic (carrying a positive charge), anionic (carrying a negative charge) or non-ionic (carrying no net charge). |
|
|
Define log removal |
Basically, it's how many 9's the process has removed or inactivated of microorganisms 1-log reduction = 90% 2-log reduction = 99% 3-log reduction = 99.9% 4-log reduction = 99.99% |
|
|
Nitrification |
Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate first by nitrosomonas and then by nitrobacter, respectively. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. |
|
|
What are the mechanisms of coagulation |
The coagulant alters or destabilizes negatively charged particulate, dissolved, and colloidal contaminants. There are two primary destabilization mechanisms in drinking water treatment: charge neutralization and sweep flocculation. The mechanism is dependent upon the coagulant dose. Most drinking water treatment plants operate using sweep flocculation, which requires a higher coagulant dose, rather than charge neutralization. In charge neutralization, the positively charged metal coagulant is attracted to the negatively charged colloids via electrostatic interaction. Flocs start to form during the neutralization step as particle collisions occur. Adding excess coagulant beyond charge-neutralization results in the formation of metal coagulant precipitates. These metal hydroxide compounds (e.g., Al(OH)3 or Fe(OH)3) are heavy, sticky and larger in particle size. Sweep flocculation occurs when colloidal contaminants are entrained or swept down by the precipitates as they settle in the suspension. |
|
|
Optimal pH range of coagulation for alum |
6 to 7 |
|
|
Optimal pH range of coagulation for iron |
5.5-6.5, although a wider range of 5-8 (wider than alum) is still effective |
|
|
Effects of pH on coagualtion |
The pH during coagulation has a profound influence on the effectiveness during the destabilization process. The pH controls both the speciation of the coagulant as well as its solubility, and it also affects the speciation of the contaminants. For high alkalinity water, an excessive amount of coagulant may be required to lower the pH to the optimal pH ranges (alum pH 6 to 7, iron 5.5 to 6.5). Just remember speciation and solubility. |
|
|
Effects of temperature on coagualtion
|
it affects the viscosity of the water. Thus lower temperature waters can decrease the hydrolysis and precipitation kinetics.
|
|
|
How is flow measured in the sedimentation basin |
overflow rate is the process loading rate and is usually expressed in gpm/sf or gpd/sf |
|
|
Typical overflow rate in a sedimentation basin |
0.3 to 1 gpm/sf |
|
|
What is filter loading rate? |
a measure of the filter production per unit area and is typically expressed in gpm/sf. Typical filter loading rates range from 2 to 6 gpm/sf
|
|
|
When is ammonia typically added to form chloramines in the finished water? |
ammonia is most frequently added to the water after chlorine (after achieving primary disinfection) and prior entering the distribution system |
|
|
Preformed chloramination |
Where alternative primary disinfectants, such as ozone or chlorine dioxide, ammonia may be added before chlorine or chlorine and ammonia may be added simultaneously. Simultaneous application is sometimes referred to as preformed chloramination |
|
|
Where is an alternative point of application of chloramines and why? |
Chloramine residuals are common during filtration to inhibit microbial (biofilm) growth on filter media that could increase filter head loss (pressure) build up
|
|
|
What is the ratio of chlorine to ammonia and why? |
At chlorine-to-ammonia-nitrogen (Cl2:NH3-N) mass ratios less than 5:1, monochloramine (NH2Cl) is the predominant species. Monochloramine is also the preferred species, as it is a more powerful oxidant and is less likely to cause taste and odor problems in the distribution system than the other species. |
|
|
What is a desirable pH of chloraminated water and why? |
The pH of chloraminated water is oftentimes at 8 and above as monochloramine stability is enhanced in that range. |
|
|
What are the components of quantifying mixing in the flocculation basin? |
Mixing speed, mixing energy (G), and time. Gt is often a convention that is used. |
|
|
Disadvantages of chloramines to water quality and distribution sytems |
Chloramination has been demonstrated to form currently unregulated DBPs like cyanogen chloride and N-nitrosodimethylamine, and impact the stability of existing pipe scale in previously chlorinated distribution systems. |
|
|
What is the benefit of combining ozone with hydrogen peroxide? |
it enhances the formation of hydroxyl radicals (·OH). The hydroxyl radical is a stronger oxidant that molecular ozone alone |
|
|
What are the downsides of using ozone alone? |
reactions with some organic molecules (i.e. PCE, TCE, atrazine, taste and odor compounds such as MIB and Geosmin) are not readily oxidized by O3 or may require a higher ozone dose (which may not be cost effective); combining ozone with peroxide can make the process more economical |
|
|
Which comes first, hydrogen peroxide or ozone? |
H2O2 is applied ahead of ozone so that the H2O2-treated water is ozonated |
|
|
Peroxide to ozone ratios |
H2O2 to ozone ratios between 0.2 to 3.0. The optimal ratio for removing most compounds ranges from 0.3 to 0.6 |
|
|
Purpose of aeration treatment |
(1) oxidation of substances such as iron and manganese by air or oxygen addition, and (2) removal of carbon dioxide, taste and odor causing substances, VOCs and volatile SOCs, ammonia, trihalomethanes, pesticides, herbicides, and gases such as methane, hydrogen sulfide, and radon. |
|
|
Benefits of spray aeration |
iron oxidation and stripping VOCs and dissolved gases
|
|
|
G |
Mean velocity gradient, ie the power input per unit volume of fluid |
|
|
Zeta potential |
electrokinetic potential in colloidal dispersions; the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle |
|
|
Overview of zeta potential and charge ranges |
Zeta potential provides a measure of the overall surface charge of all the particles and colloids in a water sample. Most particles and colloids, including NOM, algal cells, microorganisms, clay and silt, that are found in natural water at normal pH conditions (pH 6 to 9) are negatively charged possessing a zeta potential in the range -14 to -30 mV (Jeffersonet al., 2004). These surface charges give rise to repulsive forces which prevents aggregation and results in a stable system. |
