Presentation on theme: "WQT 134 Environmental Chemistry II"— Presentation transcript:
1WQT 134 Environmental Chemistry II Chlorine DemandWQT 134Environmental Chemistry II
2Lab 9 ObjectivesReading assignment:AWWA Water Treatment, Principles and Practices of Water Supply Operation, Third Edition, American Waterworks Association, ISBNChapter 7 DisinfectionUnderstand/Review Chlorination in the disinfection Process
4Chlorine Chemistry in Water Start with chlorine gas Cl2 + H2O HOCl + HCl2. If the pH of the water is greater than 8, the hypochlorus acid (HOCl-) will dissociate (break) to yield hypochlorite ion.HOCl H+ + OCl– @pH>83. pH is less than 7, HOCl will not dissociate.HOClHOCl@pH<7Free residual hypochlorous acid (HOCl) is more 1000 times more effective than combined residual monchloramine
5Which of the following is true about chlorine chemistry? pH < 7 favors hypochlorous acidpH >8 hypochlorite ions form which can still disinfectantHOCL is 100 times more powerful then OCL-All of the above
6HOCL is 1,000 times more powerful then monochloramine? TrueFalse
8Cl:NH3 and pH Impact in Water If ammonia (NH3) is present in water, the hypochlorus acid (HOCL) will react to form one kind of chloramine depending on the pH, temperature, and reaction time.2. Monochloramine and dichloramine are formed at pH3. Monochloramine is most Cl2:NH3 <5:14. pH , Cl:NH3 > 5:1 -Monochloramine converts to dichloramines5. pH < 4.5, Cl2:NH3 ~15:1 -Trichloramine which produces a very foul odor.
9Chlorine-Ammonia (chloramines) Chlorine- Ammonia reactions are governed by:Rates of formation of mono and dichloramine.pHTemperatureTimeCl:NH3 ratioFact: High Cl:NH3 ratio, low temp & pH favor dichloramineCombined Available Chlorine- chlorine existing in the water in chemical combination with ammonia-nitrogen or organic nitrogen
10Chloramines in Water 3. pH 4.5-8.5; pH 8.0-8.5 Monochloramine: NH3 + HOCl NH2Cl + H2O2. pH ; pHDichloramine: NH2Cl + 2HOCl NHCl2 + 2H2O4. pH <4.5Trichloramine: NHCl2 + 3HOCl NHCl3 + 3H2OChloramines are an effective disinfectant against bacteria but not against viruses.Add more chlorine to the wastewater to prevent the formation of chloramines and form stronger disinfectants.
11Add the Extra Free Chlorine (HOCL) 5. Additional free chlorine (HOCL or OCL-) reacts with chloramine to produce hydrogen ion, water , and nitrogen gas which will come out of solution.In the case of the monochloramine, the following reaction occurs:2NH2Cl + HOCl N2 + 6HCl + H2OAdded free chlorine reduces the concentration of chloramines in the disinfection process. Instead the chlorine that is added is allowed to form the stronger disinfectant, hypochlorus acid.
12If abundant (15 times) Cl is around and the pH < 4 If abundant (15 times) Cl is around and the pH < 4.5 Trichloramine is the most likely chloramine to form?TrueFalse
13Which of the following impact chloramine disinfection? pHTemperatureTimeAll of the above
17Chlorine Residual Analysis Starch Iodide Titration: common in wastewaterAmperometric Titration: common in wastewater with cloudy or turbidity problemsDPD colorometric- common in water and wastewater. Measures free residual or combined residual.
18Breakpoint Chlorination Breakpoint chlorination: The point at which near complete oxidation of nitrogen compounds are reached . Any point beyond breakpoint is mostly free chlorine (HOCL and OCL-)A. Amount of chlorine requiredTheory: 7.6 to 15 times the ammonia nitrogen content of the waterPractice: up to 25 times the ammonia nitrogen contentB. Beyond breakpoint90% free residual chlorine (HOCL and OCL-)10% combined chlorineC. Why must breakpoint chlorination be reached?Necessary for the production of free residual chlorine (HOCL and OCL-)Reduces taste and odorsReduces chloramines
20Breakpoint Chlorination Zone I: Chlorine is destroyed by reducing agents such as iron, manganese, clay and silt. Chlorine reduced to chlorideZone II: Chlorine comes into contact with organics and ammonia. Chloroorganics and chloramines are formed.Zone III: Chloroorganics and chloramines are partially destroyed. Chloramines are broken down and converted to nitrogen gas which leaves the systemZone IV: Breakpoint. Beyond this point, free available residual is formed. Some chloroorganics still remain as combined residual.Chlorine demand is difference between applied chlorine and the free chlorine residual at any two points on the breakpoint curve.
21In Zone 1 most of the chlorine dose gets used by chlorine demand ? TrueFalse
22In Zone II chlorine reacts with ammonia to form combined chlorine ? TrueFalse
23In Zone III some combined chlorine gets broken down to nitrogen gas ? TrueFalse
24At Breakpoint chlorine added becomes free available chlorine? TrueFalse
25Application of Chlorine in Water Treatment Distribution Free Chlorine Residual- chlorine dosed in excess of the demand and beyond the breakpoint will produce free chlorine residualHOC (hypochlorous acid) and OCL- (hypochlorite ion).Free chlorine – 10 to 100 times more effective then combined residualOxidizes certain taste and odor compounds like H2SOxidizes Fe+2, Mn+2Controls biofilms on filters and mains
26Which of the following waters would have the highest concentration of hypochlorous acid? a. pH of 7b. pH of 8c. pH of 9d. pH of 10
27Which of the following compounds is considered to be "free" chlorine in its present state? HClCa(OCl)2NaOClHOCl
28The amount of chlorine used by organic matter in water is a portion of the: chlorine demandchlorine dioxidefree available chlorinechlorine residual
29When feeding chlorine gas and ammonia, it is noticed that you have gone over the "hump", this means that you could befeeding "free" chlorinepast the breakpoint toward the "free" point on the curveforming chloraminesdestroying chloramines and building DBP's
30Chlorine can react with nitrogen in several ways to form chloramine products. Which of the following is the trichloramine (nitrogen trichloride) compound mostly responsible for taste & odor development, when using ammonia and chlorine as a disinfectant?NCl3NHCl2NH2ClN3HCl2
31Breakpoint chlorination is achieved when no chlorine residual is detectedthe strong chlorine taste at the plant is not found in the distribution systemthe ammonia level in the water decreasesa chlorine dose increase results in an increase of chlorine residual
32The chlorine curve has three locations where a measurable residual can be detected. The strongest, most aggressive form of chlorine is found on the _______ portion of the curve.disinfection-by-product (DBP)chloramine destructionfree-chlorinemonochloramine buildup
33In water disinfection, hypochlorination refers to the use of _________ hypochlorite SodiumCalciumMagnesiumPotassium
34Chlorine residual may be determined using the reagent: Diethyl-p-phenylene diamineEthylene diamine tetraacetic acidPolychlorinated biphenylsSodium thiosulfate
35A chlorine demand test will show the: Safe amount of chlorine that may be fed without killing peopleNumber of lbs required to kill 100% of coliformsAmount of chlorine required to give a desired residual after a given timeAmount of chlorine required to satisfy the biochemical oxygen demand
36Which of the following methods is not used to determine chlorine residual? PhotometricIodometricTitrimetricAmperometric
37Today's Lecture Objectives: To understand basic chlorine demand chemistry has been met? Strongly AgreeAgreeNeutralDisagreeStrongly Disagree