In this “APHA Method”, the chlorine demand is calculated by subtracting the residual chlorine concentration from the concentration of chlorine dosed, after correction for blanks. The chlorine demand obtained in this way must be quoted for a given chlorine dose, contact time, temperature and sample pH.
What is the formula for chlorine demand?
chlorine residual. Dose, mg/L = Demand, mg/L + Residual, mg/L The chlorine demand is the amount of chlorine used in reacting with various components of the water such as harmful organisms and other organic and inorganic substances. When the chlorine demand has been satisfied, these reactions stop. In some cases, such as perhaps during the initial phase of treatment, chlorinating just to meet the chlorine demand is sufficient. In other cases, however, such as at the end of the treatment
Is there a chlorine demand standard?
concentration Chlorine Standard Solution, 50–75 mg/L as Cl2 is also available for testing low chlorine demand waters. • High chlorine demand waters require larger chlorine doses. Add 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, 1.0 mL and 1.2 mL Chlorine Dosing Solution in the test procedure for high chlorine demand waters.
How to calculate chlorine dose?
demand is 3.1 mg/L and a chlorine residual of 0.8 mg/L is desired? First calculate the chlorine dose in mg/L: Chlorine Dose = Chlorine Demand + Chlorine Residual Chlorine Dose = 3.1 mg/L + 0.8 mg/L Chlorine Dose = 3.9 mg/L Then calculate the chlorine dosage (feed rate) in lbs/day: (mg/L Cl 2) (MGD flow) (8.34 lbs/gal) = lbs/day Cl 2
What is a chlorine demand?
What is Chlorine Demand? Chlorine demand is defined as the inability to maintain a chlorine residual in a pool or spa even after repeated application of a chlorinating product. There are a great number of substances that can contribute to chlorine demand.
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What is the chlorine demand?
Chlorine demand is the difference between the amount of chlorine added to water or wastewater and the amount of residual chlorine remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of the impurities in the water.
How do you calculate chlorine feed rate?
For example, if 20 oz. (2.5 cups) of 12.5% NaOCl (w/w) with a specific gravity (SG) of 1.2 is added to 10 gallons of water, the percent strength (w/v) is 0.2307% (table). To determine the amount of liquid chlorine (12.5%) added to 25 gallons of water, multiply the results for a 10 gallon solution by 2.5 (2.5 x 20 oz.
How do you calculate chlorine residual in water?
0:263:23Water Distribution Math | Chlorine Demand - YouTubeYouTubeStart of suggested clipEnd of suggested clipWell we know that the demand is equal to the dose. Minus the residual. So looking at this formula.MoreWell we know that the demand is equal to the dose. Minus the residual. So looking at this formula. We know that the residual is 1 point 5 milligrams per liter so that's this term.
What instrument determines chlorine demand?
Chloroscope is an instrument used to check the residual chlorine in drinking water. In this test, a chlorinated water sample is taken in a glass tube after the required contact period. To this, a stipulated quantity of chemical reagent is added. The color formed is observed after 5 minutes.
What is chlorine feed rate?
Use the following equation to determine lbs/day of chlorine (feed rate): (mg/L Chlorine)(MGD flow)(8.34 lbs/gal) = lbs/day Chlorine. (2.5 mg/L)(0.75 MGD)(8.34 lbs/gal) = 15 lbs/day.
How much chlorine do I need for 1000 Litres?
To dose water in a tank with 5 mg/L chlorine use: 40 millilitres of liquid pool chlorine or 170 millilitres of bleach, for every 1000 litres in the tank.
How do you calculate the ppm of chlorine in water?
Parts per million (ppm) is calculated by weight. One ppm is equal to 1 pound of chlorine in 1 million pounds of water. One million pounds of water is approximately 120,000 gallons. Converting to ounces, (1 pound = 16 ounces) 1 ounce of chlorine in 7,500 gallons equals 1 ppm.
How do you size a chlorine pump?
Multiply the Flow Rate (in gallons per minute) times the Applied Dosage in Parts Per Million Desired times 1440. Then divide by the Solution Strength being used. Household bleach is approximately 5% chlorine, pool chlorine is 10 to 12%.
Which methods is used for determination of chlorine?
There are three main methods to test free chlorine residual in drinking water in the field in developing countries: 1) Pool test kits, 2) Color-wheel test kits, and 3) Digital colorimeters.
What is a good chlorine residual?
The minimum recommended WHO value for free chlorine residual in treated drinking water is 0.2 mg/L. CDC recommends not exceeding 2.0 mg/L due to taste concerns, and chlorine residual decays over time in stored water.
What is the DPD method?
DPD Method means an analytical method for determining chlorine residual utilizing the reagent DPD (n-diethyl-p-phenylenylenediamine).
How is chlorine contact time calculated?
This value is commonly referred to as “CT”. To calculate CT, multiply the free chlorine residual concentration (C) measured at the end of the contact time by the time (T) the water is in contact with free chlorine. To get the required CT value of 6, adjust the free chlorine residual concentration or the contact time.
How do you size a chlorine dosing pump?
Multiply the Flow Rate (in gallons per minute) times the Applied Dosage in Parts Per Million Desired times 1440. Then divide by the Solution Strength being used. Household bleach is approximately 5% chlorine, pool chlorine is 10 to 12%.
What is the ratio of chlorine to water?
To disinfect water, add one part of the chlorine solution to each 100 parts of water you are treating.
How do you calculate chlorine to ammonia ratio?
NH3. * Chlorine weighs 5 times more than Nitrogen (70/14), hence a perfect ratio is 5:1.
How to determine chlorine demand?
It can be determined by adding the desired residual for the finished water to the chlorine demand of the untreated water. Chlorine Demand - amount of chlorine used by iron, manganese, turbidity, algae, and microorganisms in the water. Since chlorine doesn't kill the microbes instantly, demand is relative to time. Chlorine Residual - amount of chlorine (determine by testing) remaining after the demand is satisfied. Residual, like demand, is based on time. The longer the time period after the dosage, the lower the residual will be, untill all of the demand has been satisfied. To produce a free chlorine residual, enough chlorine must be added to the water to produce what is referred to as breakpoint chlorination. This is the point at which near complete oxidation of nitrogen compounds is reached. Any residual beyond breakpoint is mostly free chlorine. The most commonly used dry hypochlorite, calcium hypochlorite, contains about 65 to 70% available chlorine, depending on the brand. Because hypochlorites are not 100% pure chlorine, more pounds per day must be fed into the system to obtain the same amount of chlorine for disinfection. Liquid hypochlorite (sodium hypochlorite) is supplied as a clear, greenish-yellow liquid in strengths from 5.25 to 16% available chlorine. Often referred to as "bleach", it is, in fact, used for bleaching. Common household bleach is a solution of sodium hypochlorite containing 5.25% available chlorine. The typical concentration (density) of sodium hypochlorite is 144 mg/mL.
How to determine breakpoint chlorine?
When determining breakpoint chlorination, compare the expected increase in residual with the actual increase in residual. Expected increase in residual is reflected directly by the increase in chlorine dose, lb/day. If the water is being chlorinated beyond the breakpoint, then any increase in chlorine dose will result in a corresponding increase in chlorine residual. Use the mg/L to lb/day equation to determine the expected increase in residual that would result from an increase in the chlorine dose:
Why is chlorine added to water?
The main objective of adding chlorine is to disinfect the water and maintain enough chlorine in the treated water as it travels through the distribution system (chlorine residual). At times, distribution systems can be a fair distance from the storage tanks and in dead end sections where water is not used, pathogens may re-grow if a proper chlorine residual isn't maintained in the treated water sent out for consumption. This results in poor water quality as well as slime and biofilm growth in the distribution system that will end up contaminating the clean, treated water being distributed.
How much chlorine is in a dry hypochlorite?
The most commonly used dry hypochlorite, calcium hypochlorite, contains about 65 to 70% available chlorine, depending on the brand. Because hypochlorites are not 100% pure chlorine, more pounds per day must be fed into the system to obtain the same amount of chlorine for disinfection. The equation below allows you to determine the pounds per day of hypochlorite required:
How much calcium hypochlorite is used in a day?
A total of 37 lbs of calcium hypochlorite (66% available chlorine) is used in a day. If the flow rate treated is 2,400,000 gpd, what is the chlorine dosage, in mg/L?
How much chlorine is needed to disinfect a flow of 1.8 MGD?
A chlorine dose of 7.3 mg/L is required to disinfect a flow of 1.8 MGD. If the calcium hypochlorite to be used contains 67% available chlorine, how many pounds per day hypochlorite will be required for disinfection?
What is pre chlorine?
Pre-chlorination is when chlorine is applied to the water almost immediately after it enters the treatment facility. In this step the chlorine is usually added directly to the raw water, or added in the flash mixer. It is added at this stage to eliminate algae and other forms of aquatic life from the water so they won't cause problems later on in the treatment process. Pre-chlorination is found to remove taste and odors as well as oxidize any iron, manganese or hydrogen sulfide that might be present.
Abstract
Conventional methods of calculating chlorine demand are dose dependent, making intercomparison of samples difficult, especially in cases where the samples contain substantially different concentrations of dissolved organic carbon (DOC), or other chlorine-consuming species.
1. Introduction
Microbiological safety of drinking water is generally achieved by treating the water with a chemical disinfectant, usually a powerful oxidising agent such as chlorine, chlorine dioxide or ozone.
2. Materials and methods
Water samples were taken from locations throughout the Wanneroo groundwater treatment plant (GWTP), Perth, Western Australia, and from a separate bore drawing from an artesian aquifer near this treatment plant.
3. Results and discussion
To demonstrate the procedure for calculation of chlorine demand, as described in Section 2, the results for a typical water sample are presented.
4. Conclusions
This method of chlorine demand calculation has a number of advantages over the widely used APHA method, and other similar methods: • Conventional methods of calculating chlorine demand are dose dependent, making intercomparison of samples difficult, especially in cases where the samples contain substantially different concentrations of chlorine-consuming species (e.g.
Acknowledgements
We thank Water Corporation (Western Australia) and the Australian Research Council (ARC SPIRT Grant) for financial support. We also thank Water Corporation and Orica Australia Pty. Ltd., for provision of samples from the Wanneroo GWTP and for their valuable expertise on many aspects of water treatment operations.
Why is chlorine demand so bad?
Chlorine demand occurs when something throws a wrench in your pool’s chemical balance. Ultimately, your swimming pool isn’t getting the chlorine it needs to sustain its quality.
How to keep chlorine in pool?
Make sure you have a rigorous maintenance schedule to add chlorine regularly and test your pool water often. Sometimes, a proper schedule isn’t enough to combat chlorine demand. If your pool is highly susceptible to leaves and dirt, adding a pool cover to place over the water when it’s not in use is a fantastic idea.
What is Chlorine Lock?
Chlorine lock is a supposed condition that occurs when your pool has too much cyanuric acid in the water. The confusion surrounding this event comes from the use of the term “lock”. Essentially, adding too much cyanuric acid ( chlorine stabilizer) is believed to “lock up” the functionality of your chlorine.
Why is chlorine so high in spring?
Chlorine demand is more prevalent in the spring when pools begin to open. The reason being is that the water has remained stagnant throughout the winter. During this time, a buildup of contaminants would have likely occurred. That requires additional chlorine to create a balance.
Why is chlorine needed in a pool?
For example, if your pool placement is susceptible to organic contaminants or debris such as tree branches, additional chlorine is needed to stabilize the water quality. So, the demand of chlorine in your pool is higher. If you don’t add more, the chlorine will become less effective overall.
Can you break a chlorine lock?
For obvious reasons, this seems like a real concern. How do you break chlorine lock? The last thing a pool owner wants is bacteria running rampant in their pool water. Don’t fret though – there is no such thing as unusable or “locked” chlorine – there is no evidence proving the claim! What occurs most of the time is a lack of chlorine, leading to a test that fails to register chlorine effectiveness.
Does chlorine lock up your pool?
Essentially, adding too much cyanuric acid ( chlorine stabilizer) is believed to “lock up” the functionality of your chlorine. Chlorine acts as a sanitizing agent that keeps your pool clean. Through a chemical reaction, chlorine kills bacteria found in pools. Chlorine lock claims that the chemical reaction is locked, ...
What is the amount of chlorine added to water called?
The amount of chlorine added to the water is known as the chlorine dose . This is a measured quantity chosen by the operator and introduced into the water using a chlorinator or hypochlorinator.
What is the amount of chlorine used up by reacting with substances in the water?
The amount of chlorine used up by reacting with substances in the water is known as the chlorine demand. If nothing reacts with the chlorine (as would be the case in distilled water), then the chlorine demand is zero.
How to test for chlorine residual?
The DPD Colorimetric Method introduced in this lab is one of several procedures which can be used to test for chlorine residual. This method requires compensation for color and turbidity and can detect chlorine concentrations only as low as 10 ug as Cl2/L. Standard Methodsintroduces several other procedures and explains which procedures are most effective under a variety of circumstances. In every case, remember that chlorine is a relatively volatile substance and that samples should be tested as soon as possible after the water is collected.
What is the equivalent chlorine level for potassium permanganate?
b. Prepare a series of potassium permanganate standards covering the equivalent chlorine range of 0.05 to 4 mg/L. (The procedure for producing the standards is explained in Standard Methods on page 4-64.)
How much DPD to add to a test tube?
b. Add 0.5 mL of DPD indicator solution to the test tube.
What color does iodine change to?
When free iodine becomes present in the water, the indicator makes the solution change to a red color, with the intensity of the color equivalent to the amount of chlorine found in the solution. Equipment. This procedure requires a piece of colorimetric equipment, some glassware, and titration equipment.
How to set 100%T on a spectrophotometer?
a. Set 100%T on the spectrophotometer or filter photometer using a distilled water blank, in accordance with manufacturer's instructions. (Prepare the distilled water blank in the same manner as you prepare the sample for testing.)
What is chlorine demand?
Every now and then, your pool can develop an insatiable appetite for chlorine. An intense and unexpected hunger that seems impossible to satisfy. These sudden chlorine demands usually result from an imbalance in the pool chemistry. And in this post, we’ll be covering what causes those imbalances, and showing you how to cure chlorine demand.
What causes chlorine demand?
We know, you want to cure chlorine demand right now. But remember, that in war, knowing your enemy makes all the difference.
How to cure chlorine demand
Although it may seem counter-intuitive, the best way to fight chlorine demand is to feed into it. To be clear, you need to supply your pool with as much chlorine as possible in order to make your water normal again.
How to prevent chlorine demand in the future
So now you know to cure chlorine demand, but what about preventing it? The answer is simpler than you think. Here’s why:
Closing thoughts
After reading this article, you can rest easy knowing that there is, in fact, life after chlorine demand. All jokes aside, we firmly believe you can cure chlorine demand without a problem. Simply testing your water and treating it accordingly is 90% of the job. The rest is following up with good pool and chemical maintenance.