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ENVR18 ELC C7
Chapter 7
| Question | Answer |
|---|---|
| It is the process of removal/inactivation of pathogenic organisms by chemical or physical means? | Disinfection |
| This step in the process includes any pre-disinfection treatment necessary to achieve the required level of removal or inactivation potentially present in the source water? | Primary disinfection |
| This step in the process involves the maintenance of a disinfectant residual in the distribution system? | Secondary disinfection |
| For which type of system(s) must there contain a disinfectant residual that persists throughout the distribution system? | For any system, because all waters entering a distribution system must have secondary disinfection |
| All waters entering a distribution system require what? | Disinfectant residual that persists throughout the distribution system (secondary disinfection) |
| This measure in water treatment is introduced to maintain a persistent disinfectant residual to protect the water from microbiological re-contamination? | Secondary disinfection |
| List three reasons for provision of secondary disinfection? | Reduce bacterial growth; controlled biofilm formation; serve as an indicator of distribution system integrity |
| How does secondary disinfection serve as an indicator of distribution system integrity? | If chlorine residual is far below expected quantity at various points throughout the distribution system, it means that the chlorine may be depleted by nuisance organisms. |
| Which three chemicals can be used to provide secondary disinfection? | Chlorine, chlorine dioxide and monochloramine |
| These commonly used secondary disinfectants provide a persistent disinfectant residual, and can be used for the maintenance of a residual in the distribution system? | chlorine, chlorine dioxide and monochloramine |
| Which three chemicals can be used for the maintenance of a residual in the distribution system? | Chlorine, chlorine dioxide and mono chloramine |
| Chemically assisted filtration followed by disinfection (or equivalent) is the minimum treatment for what type of system? | Surface water treatment system |
| Primary disinfection is the minimum treatment for what type of system? | Ground water treatment system |
| List the three forms in which chlorine is available? | Chlorine gas; calcium hypochlorite; sodium hypochlorite |
| How is combined chlorine residual calculated? | It is calculated by subtracting the free chlorine residual from the total chlorine residual. |
| Which type of impurities does chlorine react with? | Organic matter and inorganic matter |
| With which substances does chlorine react with when it is first added to water? | Organic matter and inorganic matter |
| This step in the treatment process involves the inactivation of harmful pathogens in the water before the water enters the distribution system, and it includes pathogen removal through pre-disinfection barriers or treatment processes? | Primary disinfection |
| Heavy incrustations, sediment accumulation and biofilm activity may cause what? | Rapid decay of a disinfectant residual |
| The process which destroys or impairs pathogens by interfering with cellular activity is? | Inactivation |
| This may occur through a chemical or physical means such as the application of chlorine, ozone, chlorine dioxide or the use of UV light? | Inactivation |
| It is the term used to represent the percentage of removal and/or inactivation of harmful pathogens in water, and used in place of many-digit numbers? | Log |
| It is a powerful oxidant that is highly corrosive, and it is by far the most common agent for inactivation? | Chlorine |
| It is the addition of chlorine to the water supply until the demand has been satisfied and a free chlorine residual is formed? | Breakpoint chlorination |
| List 2 common disadvantages of using chlorine? | The formation of iron precipitate (filtration problems); the formation of DBPs |
| Initially, any chlorine added to water will have little or no disinfecting action, and additional chlorine must be added. This is known as? | Chlorine demand |
| It is a concentration of chlorine species present in water after the chlorine demand has been satisfied? | Chlorine residual |
| It is the chlorine remaining after a given contact time under specific conditions? | Chlorine residual |
| This can take a number of forms in water, depending on the pH and temperature of the water, and whether there is ammonia in the water? | The chlorine residual |
| This disinfectant is formed when chlorine reacts with water to form hypochlorous acid (HOCL) and the hypochlorite ion (OCL negative)? | Free chlorine residual |
| In free chlorine residual, which of the 2 compounds is more powerful? | Hypochlorous acid (HOCL) |
| In the formation of free chlorine residual, the ratio of the 2 compounds formed depend on which 2 factors? | pH and temperature |
| As the pH increases, the amount of hypochlorous acid (HOCL) formed ____? | Decreases |
| In the formation of free chlorine residuals, in which the desired disinfectant is hypochlorous acid (HOCL), the pH objective range is? | 6.5 to 8.5 for drinking water |
| As the pH increases, the amount of hypochlorite ions___? | Increase |
| When chlorine readily reacts with ammonia that is in the water, the compounds formed make up the? | Combined chlorine residual |
| The sum of the free chlorine residual and the combined chlorine residual is reported as the? | Total chlorine residual |
| The application of chlorine and ammonia to form chloramines for the purpose of disinfection is called? | Chloramination |
| List the eight factors affecting disinfection? | Dosage and type of chemical; contact time; pH; temperature; turbidity; and microorganisms; reducing agents; injection point and mixing |
| In this disinfection method, the substance used comes in a solid or liquid form; it is safer to operate than chlorine gas systems; the solution it makes is very corrosive? | Hypochlorite |
| In this disinfection method, the substance used comes in a gaseous form; the solution is very corrosive, and the gas is very toxic? | Chlorine gas |
| In this disinfection method, the substance used comes in either a liquid or gas form; requires long contact time; and has no special handling requirements? | Chloramine |
| In this disinfection method, it comes in a gaseous form; it is expensive; it must be generated on-site? | Chlorine dioxide |
| In this disinfection method, it comes in a gaseous form; has a high energy cost; and must be generated on-site? | Ozone |
| With this disinfection method, it is a physical disinfection practice; does not produce DBPs, but is more effective with filtered water; quartz sleeves must be cleaned regularly? | UV light |
| With this disinfection method, it is a physical disinfection practice; very expensive for large-scale operations; only practical application is in the household in an emergency situation? | Heat/boil water advisories |
| It is the practice of removing all or specified fraction of the total chlorine residual? | Dechlorination |
| This practice may be used to reduce the residual chlorine to a specified level at the point where the water enters the distribution system? | Dechlorination |
| These are harmful chemical contaminants that are produced when a disinfectant reacts with natural organic matter present in water? | DBPs |
| Two examples of DBPs that are considered as carcinogens include? | Trihalomethanes and haloacetic acids |
| A 90% inactivation rate leaving 10% of live organisms is? | 1 Log |
| A 99% inactivation rate leaving 1% of live organisms is? | 2 Log |
| A 99.9% inactivation rate leaving 0.1% of live organisms is? | 3 Log |
| A 99.99% inactivation rate leaving 0.01% of live organisms is? | 4 Log |
| It is used to determine the appropriate dosage of chemical disinfectants in order to provide effective pathogen inactivation to the required level (log)? | Contact time |
| This concept involves operating conditions such as flow, temperature, pH and time? | Contact time of disinfectants |
| How is contact time calculated? | It is calculated by multiplying the disinfectant residual concentration (in mg/L) by the disinfectant contact time in minutes |
| This tool helps determine whether the log inactivation rate is being met? | CT tables |
| This substance is a gas that is greenish yellow in colour and 2.5 times heavier than air? | Chlorine gas |
| This disinfection agent provides a residual for secondary disinfection? | Chlorine gas |
| This disinfection agent is highly corrosive, precipitates iron and can create DBPs? | Chlorine gas |
| When chlorine is initially added to water, it immediately reacts with which substances? | Dissolved inorganic substances and/or organic substances |
| It is chlorine dosage minus chlorine residual? | Chlorine demand |
| Only after the chlorine demand is satisfied and the reaction with all the dissolved ammonia is complete is the chlorine available in the form of? | Free chlorine residual (or free available chlorine) |
| Chloramines are referred to as? | Combined chlorine |
| Free chlorine residual (or free available chlorine) consists of these two forms of chlorine? | Hypochlorite ion and hypochlorous acid |
| This form of chlorine is often the preferred form of drinking water disinfection? | Free chlorine |
| It is the form of chlorine that does not cause objectionable taste and odour issues? | Free chlorine |
| It is the form of chlorine that works faster than combined chlorine? | Free chlorine |
| This type of chlorine lasts longer and can maintain sanitary protection throughout the water distribution system? | Combined chlorine |
| Water must have a minimum free chlorine residual of ___ when leaving a water plant? | 0.2 mg/L |
| Water must have a minimum free chlorine residual of ___ at all points in the distribution system? | 0.05 mg/L |
| The maximum chlorine residual at any time and/or location should not exceed ___? | 4 mg/L |
| For a system that chlorinates with gas, the minimum and maximum chlorine residual limit for secondary disinfection is? | 0.05 mg/L and 4.0 mg/L |
| For a system that chlorinates with chlorine dioxide, the minimum and maximum chlorine residual limit for secondary disinfection is? | 0.05 mg/L and 0.8 mg/L |
| For a system that chloraminates, the minimum and maximum combined chlorine residual is? | 0.25 mg/L and 3.0 mg/L |
| The total amount of chlorine added to the water is known as? | Chlorine dosage |
| The chlorine dosage is equal to? | Chlorine demand plus chlorine residual |
| Further additions of chlorine after breakpoint is reached result in an increase in the? | Free chlorine residual |
| Breakpoint chlorination occurs in how many steps? | Four |
| In this step of breakpoint chlorination, chlorine reacts with organic/inorganic materials, disinfection does not occur and no chlorine residual is formed? | The first step of breakpoint chlorination |
| In this step of breakpoint chlorination, a combined chlorine residual begins to form? | The second step of breakpoint chlorination |
| In this step of breakpoint chlorination, chlorine demand is satisfied (breakpoint is reached), and some chloramines and chlororganics are destroyed? | The third step of breakpoint chlorination |
| In this step of breakpoint chlorination, the continued addition of chlorine will produce free chlorine residual (the best residual for disinfection)? | The fourth step of breakpoint chlorination |
| Selection of the appropriate inactivation process depends upon? | Raw water characteristics |
| Two important considerations when selecting the appropriate inactivation process include? | Inactivation of pathogens and minimizing production of DBPs |
| Sodium hypochlorite, calcium hypochlorite and chlorine gas are all considered as? | Chlorine |
| This disinfectant is available as 12% or 5% chlorine concentrations? | Sodium hypochlorite solutions |
| This disinfectant will increase the pH of water? | Sodium hypochlorite solution |
| The raw form of this disinfectant is powdered or granular, and prepared into a solution? | Calcium hypochlorite |
| This disinfectant is commonly used for post-construction disinfection (new water mains)? | Calcium hypochlorite |
| This disinfectant is fed under vacuum conditions through an injector to form a concentrated chlorine solution? | Chlorine gas |
| This disinfectant solution is introduced into the process through a diffuser or mixed with mechanical mixer? | Chlorine gas solution |
| It is a powerful disinfectant that is generally more rapidly effective than chlorine? | Chlorine dioxide |
| This disinfectant is very unstable and cannot be stored, and therefore must be generated on-site and directly injected into the water being treated? | Chlorine dioxide |
| This disinfectant is generated by mixing sodium chlorite and chlorine in controlled proportions? | Chlorine dioxide |
| Chloramines are produced by the application of ammonia and chlorine at a mass ratio of approximately? | A 4.5:1 ratio |
| The preferred chloramine used for secondary disinfection is in the form of? | Monochloramine |
| Substances present in the water which reduce effectiveness of UV disinfection include? | Hardness, iron and manganese concentrations |
| This disinfectant diffuses very fast through the microbe cell wall, and destroys organisms much quicker. Which free chlorine residual compound is this? | Hypochlorous acid |
| The lower the pH, the ___ hypochlorous acid is produced? | Greater (because the water is acidic) |
| Free chlorine residual is more easily maintained in ___ water? | Cold |
| Bromate as a DBP is generated when which disinfection method is used? | Ozone |
| Chloramines produced which DBPs? | They produce no known DBPs |
Created by:
ctherria