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117 Cards in this Set
- Front
- Back
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What are pathogenic organisms? |
Disease producing organisms |
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What is disinfection? |
The selective destruction or inactivation of pathogenic organisms |
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Drinking water standards are established by what agency of the federal government? |
The EPA |
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What does MCL stand for? |
Maximum contaminant level |
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List the major parts of a typical hypochlorinator system |
1. A chemical solution tank( for the hypochlorite) 2. Diaphragm type pump 3. Power supply 4. Pressure switch 5. Water storage tank |
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What are the benefits of prechlorination? |
Control of algal and slime growths Control of mudball formation Improved coagulation Reduction of tastes and odors Increased chlorine contact time |
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List 2 inorganic reducing chemicals with which chlorine reacts rapidly |
Hydrogen sulfide and ammonia |
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List the physical and chemical agents that have been used for disinfection |
Physical: ultraviolet rays, heat, ultrasonic waves Chemical: (other than chlorine) iodine, bromine, bases (sodium hydroxide and lime), ozone |
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What are the three types of electrode type lamps used to produce UV radiation? What is a ballast? |
Low pressure, low intensity Low pressure, high intensity Medium pressure, high intensity A ballast is a type of transformer that is used to limit the current to a UV light |
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What properties make chlorine gas so hazardous? What type of breathing apparatus is recommended when repairing chlorine leaks? |
Chlorine is extremely toxic and corrosive in moist atmospheres A self contained type of breathing apparatus, positive pressure/demand breathing equipment, or rebreather kits |
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What three methods are used to measure chlorine residual in treated water? |
1. Amperometric Titration 2. DPD colorimetric method 3. ORP (oxidation reduction potential) probes |
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What hazards are associated with the handling of sodium chlorite? |
Spills must be neutralized immediately Sodium chlorite is very combustible around organic compounds If it comes into contact with clothing, remove clothes immediately to soak them in water or burn them |
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Why should chlorinators be located in a separate room? |
Chlorine gas leaks can damage equipment and are hazardous to operators |
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What are possible chlorinator abnormal conditions? |
Chlorine leaks, chlorine gas pressure too low, injector vacuum too low, chlorine residual too low |
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What abnormal conditions could be encountered when operating a evaporator? |
Too low a water level, Low water temperatures, no chlorine gas flow to chlorinator |
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Why would frost appear on valves and flex connectors? |
High flow rates of gas will remove gas from container faster than it can change from liquid to gas. When frost appears, the chlorine gas may condense to liquid chlorine and plug the supply lines |
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What is the primary advantage of vacuum system chlorinators? |
Safety: if failure occurs in the vacuum system, the chlorinator either stops the flow of chlorine in the equipment or allows air to enter the vacuum system rather than allowing chlorine to escape into the atmosphere |
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How is the rate of gas flow in a chlorinator measured? |
The rotameter |
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What are the two common methods of feeding hypochlorite into the water being disinfected? |
Pumping directly into the water Pumping through and ejector, which draws in additional water for dilution of the hypochlorite solution |
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Incomplete nitrification causes the production of nitrate, which produces what problems in the disinfection of water? |
-Rapidly reduces free chlorine and can interfere with the measurement of free chlorine. -A loss of total chlorine and ammonia -an increase in the concentration of heterotrophic plate count bacteria |
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Why is ozone generator on site? |
It is unstable and decomposes to elemental oxygen in a short amount of time |
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What kinds of safety hazards are associated with UV lamps? |
The UV light can burn skin and eyes The lamps contain mercury vapor that could be released if lamp is broken |
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What maintenance is required on ORP probes? |
Clean the units sensor once a month |
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What does an ORP probe measure in a disinfection system? |
The effectiveness of a chlorine residual in disinfecting the water |
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How often should treated water residual chlorine measurements be made? |
Three times per day with small systems Every two hours on large systems |
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When and how often should the weights of chlorine containers be recorded? |
Every day, at the same time |
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If chlorine is escaping from a cylinder, what should you do? |
Turn the cylinder so that the leak is on top and the chlorine will escape as a gas |
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How would you determine if you were chlorinating at the breakpoint? |
Increase the chlorinator feed rate. If the increase in the free chlorine residual is the same as the increased dosage, then you were chlorinating at or past the breakpoint |
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What is the suggested free chlorine residual for treated water (measured at a point just beyond post chlorination)? |
0.5 mg/L |
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How can you determine if the chlorine residual analyzer is working properly? |
By measuring the actual chlorine residual and comparing this result with the results of the analyzer |
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What is the purpose of evaporators? |
Used to convert liquid chlorine to gaseous chlorine for use by gas chlorinators |
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When starting a gas chlorinator, how is the system checked for chlorine gas leaks? |
By placing an ammonia-soaked rag near each valve and joint The formation of a white cloud of vapor will indicate a chlorine leak |
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Why should a hypochlorite feed pump be operated in the upper end of its range (at 6 or 7 in a range of 0 to 10)? |
The frequency of the strokes or pulses of the pump will be close together and the chlorine will be fed continuously to the water |
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What should be the chlorine residual in the most remote part of the distribution system? |
0.2 mg/L |
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What is removed by the upper and lower valves of ton chlorine tanks? |
The upper valve discharges chlorine gas The lower valve discharges liquid chlorine |
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What is a fusible plug? |
A safety device that melts to prevent buildup of excessive pressures and the possibility of rupture due to fire or high temperatures |
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What type of container is commonly used to store hypochlorite? |
Plastic containers |
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How large a supply of hypochlorite should be available? |
One week supply |
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Under what conditions should waters not be pre-chlorinated? |
When the raw waters contain organic compounds. It could lead to the formation of THMs and taste and odor problems |
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List the two most common locations of chlorination in a treatment plant |
1. Pre-chlorination ahead of any other treatment processes 2. Post chlorination after the water has been treated and before it enters the distribution system |
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How is the efficiency of a disinfectant measured? |
By its CT value By the contact time (T) in minutes being multiplied by the concentration (C) of the disinfectant residual in mg/L measured at the end of the contact time. CxT= Measure of the degree of pathogenic inactivation |
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What is a major limitation of using chloramine residuals? |
Chloramines are less effective as a disinfectant then free chlorine residuals |
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How would you preevent short circuiting in a UV system? |
By maintaining the water level over the lamps at the appropriate level |
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What actions should an operator take when there is a sudden absence of chlorine residual in the distribution system? |
Retest for chlorine residual Check chlorination equipment Search for a source of contamination that could cause an increase in chlorine demand |
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Why is the applied chlorine to ammonia-nitrogen ratio usually greater than the actual chlorine to nitrogen ratio leaving the plant? |
Because of the chlorine demand of the water |
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What are the three primary methods by which chloramines are produced? |
Pre-ammoniation followed by chlorination Concurrent ammoniation and chlorination Pre-chlorination/postammoniation |
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What is breakpoint chlorination? |
The addition of chlorine to water until the chlorine demand has been satisfied |
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How does pH influence the relationship between hypochlorous acid (HOCl) and hypochlorite ion (OCl-)? |
The higher the pH level, the greater the percent of OCl- |
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How do chlorine gas and hypochlorite influence pH? |
Chlorine gas lowers pH Hypochlorite increases pH |
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How is the chlorine dosage determined? How is the chlorine demand determined? |
1. Chlorine dose, mg/L= chlorine demand + chlorine residual 2. Chlorine demand, mg/L= Chlorine dose - chlorine residual |
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What is a major limitation to the use of ozone? |
The inability of ozone to provide a residual in the distribution system |
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What two factors influence the effectiveness of disinfection on microorganisms? |
The number and type of organisms present in the water |
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How does the temperature of the water influence disinfection |
Higher temperature is better Colder water requires longer disinfection time or greater quantities of disinfectants |
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How does pH influence the effectiveness of disinfection? |
Most disinfectants are more effective in water with a pH around 7.0 then at a pH over 8.0 |
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What happens when a microorganism loses an electron? |
It becomes an activated and can no longer transmit a disease or reproduce Chlorine steals electrons from microorganisms |
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At what turbidity level have most of the bacteria been removed from the water? |
1 NTU or less |
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List five reducing agents |
Hydrogen sulfide Ferrous ion Manganous ion Ammonia Nitrite ion |
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What must be satisfied before chlorine becomes available to accomplish disinfection? |
The demand for chlorine by reducing agents |
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What percentage should chlorine containers be filled to? |
No more than 85% of their capacity |
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List 4 characteristics of chlorine dioxide |
1. Does not form carcinogenic compounds 2. Not affected by ammonia 3. Effective disinfectant at higher pH levels 4. Does not react with organics in water |
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What is the maximum chlorine to ammonia-nitrogen ratio? |
5:1 |
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At what chlorine to ammonia nitrogen ratio should no free chlorine be present? |
3:1 to 5:1 |
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What is the danger in allowing nitrification episodes to occur? |
You may be left with very low or no total chlorine residual |
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What is the immediately dangerous to life or health level for chlorine? |
10 ppm |
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What is the maximum permissible exposure limit for chlorine? |
0.5 ppm |
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What is the maximum permissible exposure limit for chlorine? |
0.5 ppm |
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At what level may chlorine gas be fatal after a few breaths? |
1000 ppm |
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What is used to generate chlorine dioxide and where is it generated? |
Chlorine dioxide is generated on site Sodium chlorite and chlorine are used to generate chlorine dioxide |
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How does turbidity effect disinfection? |
Turbidity will reduce the efficiency of disinfecting chemicals |
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How does turbidity effect disinfection? |
Turbidity will reduce the efficiency of disinfecting chemicals |
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How does temperature affect disinfection? |
Higher temperature=More efficient disinfection |
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What six factors influence disinfection? |
pH Temperature Turbidity Organic matter Inorganic matter Reducing agents |
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How much does chlorine gas weigh relative to air? |
Chlorine gas is 2.5 times heavier than air |
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How does chlorine react with the reducing agent hydrogen sulfide? |
Produces odor of rotten eggs Forms sulfuric acid and elemental sulfur |
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How does chlorine react with the reducing agent ammonia? |
Forms chloramines, which means that less chlorine is available to act as a disinfectant |
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What is nitrification? |
A microbial process in the oxidation of ammonia Ammonia-oxidizing bacteria and nitrite-oxidizing bacteria are involved |
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What is rechlorination? |
The practice of adding chlorine in the distribution system |
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Chlorine gas cylinders should never be stored near what 5 materials? |
Turpentine, ether, anhydrous ammonia, finely divided metals, hydrocarbons |
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What are evaporators? |
They are used to convert liquid chlorine to gaseous chlorine for use by gas chlorinators |
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Your sense of smell can detect chlorine concentrations as low as what? |
3 ppm |
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What three chemicals could you use to absorb a chlorine spill? |
Solutions of caustic soda, soda ash, or agitated hydrated lime slurries |
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What will happen if chlorine comes into contact with the sweat on your body? |
It will form hydrochloric acid |
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What are the five uses of chloramines? |
-reducing the formation of THM's and DBP's -having a residual in the furthest parts of the system -penetrating the biofilm -killing HPC bacteria -reducing taste and odor problems |
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What is the Safe Drinking Water Act (SDWA)? |
Establishes primary and secondary drinking water regulations Developed by the EPA Originally enacted in 1974 1996 Amendments: DBP Rule, Enhanced surface water treatment rule, ground water disinfection rule |
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What is the Safe Drinking Water Act (SDWA)? |
Establishes primary and secondary drinking water regulations Developed by the EPA Originally enacted in 1974 1996 Amendments: DBP Rule, Enhanced surface water treatment rule, ground water disinfection rule |
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Total Coliform MCL Giardia MCL Enteric Viruses MCL |
Total Coliform MCL: less than 40 samples per month, no more than 1 positive. More than 40 samples per month, no more than 5% positive Giardia MCL: 3-log removal (99.9%) Enteric Viruses MCL: 4-log removal (99.99%) |
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What type of bacteria is MORE resistant to disinfection? |
Spore-forming bacteria |
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The removal process has four stages. Describe the removal rates of each stage |
Coagulation: Alum usage can increase virus removal up to 99% Sedimentation: remove 20 to 70% of microorganisms Filtration: 20 to 99% Disinfection: whatever remains |
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What is the most commonly used distribution system disinfectant? |
FREE (uncombined) chlorine is most common Monochloramine is second |
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List three forms of chlorine commonly used for disinfection |
Chlorine gas Calcium hypochlorite Sodium hypochlorite |
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When should chloramines be removed from water prior to use? |
Prior to any contact with fish Prior to use in dialysis treatment |
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Before a main is disinfected, the main should be flushed for how long and at what velocity? |
30 minutes at 2.5 ft./s |
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When shutting down a gas chlorinator, why should the discharge line be left open? |
To prevent chlorine gas from expanding and causing high pressures in the line |
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Why should the chlorine injection point never be located on the intake side of pumps? |
It will cause corrosion in the pump |
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What two water quality lab tests are run on samples of water from a water supply system? |
Chlorine residual tests Bacteriological tests |
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What two water quality lab tests are run on samples of water from a water supply system? |
Chlorine residual tests Bacteriological tests |
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Which five strategies can be used for preventing nitrification? |
Breakpoint chlorinate Decrease detention times Decrease free ammonia A flushing program Increase disinfectant dosage ratio |
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Chloramines are either monochloramine, dichloramine, or trichloramine. Which is best? |
Monochloramine is best. Dichloramine causes taste and odor problems and is a poor disinfectant |
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Any free chlorine added to water will immediately form either HOCl or OCl- depending on the pH. Describe this |
The lower the pH, the more HOCl; The lower the pH, the better the disinfection; HOCl is a better disinfectant than OCl- The higher the pH, the greater percent of OCl- |
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Any free chlorine added to water will immediately form either HOCl or OCl- depending on the pH. Describe this |
The lower the pH, the more HOCl; The lower the pH, the better the disinfection; HOCl is a better disinfectant than OCl- The higher the pH, the greater percent of OCl- |
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1 L of liquid chlorine can evaporate and produce how many liters of chlorine gas? |
450 liters |
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On-site generated chlorine systems produce what percentage sodium hypochlorite? |
0.8% |
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What is the pH range usually found in distribution systems? |
6.5 to 9.5 |
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What are the two warning signs for nitrification? |
-Decreases in ammonia level, total chlorine level, and pH -Increases in nitrate level and heterotrophic plate count bacteria |
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How do you disinfect Wells and pumps? |
When a new well is completed, disinfect the well, pump, screen, and piping as well as the gravel in the gravel envelope 50 mg/L chlorine does with 24 hours of contact time |
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How do you disinfect Wells and pumps? |
When a new well is completed, disinfect the well, pump, screen, and piping as well as the gravel in the gravel envelope 50 mg/L chlorine does with 24 hours of contact time |
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How do you disinfect mains? |
Methods: continuous, slug, tablet Disinfect the main with the slug method using 500 mg/L dosage and 30 minute minimum contact time |
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How do you disinfect Wells and pumps? |
When a new well is completed, disinfect the well, pump, screen, and piping as well as the gravel in the gravel envelope 50 mg/L chlorine does with 24 hours of contact time |
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How do you disinfect mains? |
Methods: continuous, slug, tablet Disinfect the main with the slug method using 500 mg/L dosage and 30 minute minimum contact time |
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How do you disinfect a tank? |
Maintain a chlorine residual of at least 50 mg/L for at least 6 hours, but preferably 24 hours Or you can spray the walls with a 200 mg/L solution, but wear a self-contained breathing apparatus |
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What should never be used to extinguish fires if chlorine is involved? |
Chemical or carbon dioxide extinguishers |
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How should chlorine cylinders be moved? |
Use hand truck with clamp supports Use a lifting clamp, cradle, or carrier Never lift with chains, rope slings, or magnetic hoists |
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How should chlorine cylinders be moved? |
Use hand truck with clamp supports Use a lifting clamp, cradle, or carrier Never lift with chains, rope slings, or magnetic hoists |
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How are chlorine cylinders tested? |
Tested at 800 psi every 5 years |
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What is the strength of commercial/industrial hypochlorite? |
12-15% chlorine |
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When measuring the disinfection and a distribution system, what other test is measured at the same time and location? |
Total coliforms |
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Are canister type gas masks adequate in situations where chlorine leaks occur? |
No |
