AWWA B300 ADD A-2011 Hypochlorites.pdf

1、B300a-11 Addendum to ANSI/AWWA B300-10 Standard forHypochloritesApproved by AWWA Board of Directors Jan. 23, 2011.Approved by American National Standards Institute April 11, 2011.APPENDIX ARecommendations for the Handling and Storage of Hypochlorite Solutions*This appendix is for information only an

2、d is not a part of ANSI/AWWA B300.Several key factors have been identified that impact the formation of perchlo-rate, bromate, and other contaminants in hypochlorite solutions. The major factors impacting perchlorate formation parallel those that also affect the decomposition of hypochlorite: temper

3、ature, ionic strength, concentration, and pH. By using the information gathered in the study referenced below and by applying the “Predictive Model” to hypothetical liquid hypochlorite storage scenarios, several quantitative and qualitative recommendations can be made:Dilute stored hypochlorite solu

4、tions upon delivery.1. The decomposition of hypochlorite and subsequent formation of chlorate and perchlorate is dependent upon hypochlorite concentration and ionic strength. Higher ionic strength and hypochlorite concentration will drive the reaction towards a greater production of * HypochloriteAn

5、 Assessment of Factors That lnfluence the Formation of Perchlorate and Other Contaminants. 2009. Water Research Foundation, Denver, Colo.Copyright 2011 American Water Works Association. All Rights Reserved.2chlorate and perchlorate while also increasing the rate of decomposition of hypochlo-rite. By

6、 diluting a 2M hypochlorite solution by a factor of 2, the rate of perchlorate formation decreases by a factor of 7 because of the combination of concentration and ionic strength effects. A fourfold dilution of a hypochlorite solution will decrease the rate of formation by a factor of 36. A tenfold

7、dilution of a hypochlorite solution will decrease the rate of perchlorate formation by a factor of 270.Store the hypochlorite solutions at lower temperatures.2. Higher temperatures speed up the chemical decomposition of hypochlorite and the subsequent formation of chlorate and perchlorate. Every 5C

8、(9F) reduction in storage temperature will reduce the rate of perchlorate formation by a factor of approximately 2. To mini-mize temperature increases, the product should be stored out of direct sunlight.Control the pH of stored hypochlorite solutions at pH 1113 even after dilu-3. tion. Storage of c

9、oncentrated hypochlorite solutions at pH values lower than 11 is not recommended because of rapid decomposition of hypochlorite ion/hypochlo-rous acid and the consequent formation of chlorate, even though this reduces the amount of perchlorate formed. When the pH is higher than 13, perchlorate for-m

10、ation is enhanced because of the ionic strength effect. As such, utilities should continue to insist that manufacturer specifications include pH control in the range of 1113. Given the typical pH range of on-site generation (OSG) hypochlorite (pH 910), such solutions should be used as soon as possib

11、le after manufacture and should not be stored for more than 12 days.Control the removal of transition metal ions by purchasing filtered 4. hypochlorite solutions and by using low-metal ion concentration feedwater for the OSG systems and dilution water. The presence of transition metal ions results i

12、n an increased degradation rate of hypochlorite. While this degradation is concomitant with reduced perchlorate formation, the free available chlorine concentration is also reduced, forcing a utility to use a higher volume of a hypochlorite solution, which results in higher mass loading of contamina

13、nts such as perchlorate, chlorate, and bromate.Use fresh hypochlorite solutions when possible.5. Hypochlorites will naturally decompose to produce oxygen, chlorate, and perchlorate. Less storage time will minimize the formation of these contaminants in the hypochlorite solution. Rotate stock and min

14、imize the quantity of aged product in storage tanks prior to the delivery of new product. A fresh hypochlorite solution will also contain a higher concentration of hypochlorite, thereby reducing the amount of solution required to obtain the target chlorine residual. Again, higher hypochlorite concen

15、tration in Copyright 2011 American Water Works Association. All Rights Reserved.3a fresh hypochlorite solution will correspond to lower concentrations of contami-nants dosed.For utilities using OSG hypochlorite, use a low-bromide salt to minimize 6. the amount of bromide present in the brine. Bromate formation will occur rapidly in hypochlorite solutions in the presence of bromide. By controlling the amount of bromide in the salt and source water used for on-site generation, bromate formation can be minimized.Copyright 2011 American Water Works Association. All Rights Reserved.