Water Well Journal

July 2016

Water Well Journal

Issue link: https://read.dmtmag.com/i/692787

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Page 28 of 87

dioxide, hydrogen peroxide, potassium permanganate, bromine, and chlorine. Chlorine dioxide has actually been used in water treatment in the United States since the mid-1940s and provides a much stronger oxidation than the more common chlorine. However, chlorine dioxide must be generated at the point of demand and most conventionally performed in a vessel or generator requir- ing a controlled chemical reaction. Although chlorine dioxide does not produce disinfection byproducts and shows superior biofilm penetration, its use throughout the industry has been limited potentially from the site generation requirement and the chemical's short half-life. Hydrogen peroxide is the strongest oxidizer used in water disinfection when in its acid form of peracetic acid. However, it is not a strong biocide and is not approved as a stand-alone disinfectant in the U.S. and therefore is commonly found in mixed oxidation technologies. Additionally, the release of nas- cent oxygen into the well environment is a detriment to its use in well disinfection. Potassium permanganate is considered a strong oxidizer and is most effective on iron and manganese, creating an in- soluble particulate. Although there are no disinfection byprod- uct issues with potassium permanganate, it is not considered an effective biocide, and with the strong staining potential of the resulting solution when mixed with water, it is not normally used in well disinfection. Bromine is a halogen chemistry like chlorine but is found to be more effective as a disinfectant at higher temperatures where chlorine compounds are less stable. Bromine is not used for disinfection of water wells, but is used in the drilling process to create high density drilling fluids. Chlorine, the most available and cost effective oxidation chemistry used for water disinfection, is available in many forms. The initial use back in the early 1900s was chloride of lime or calcium hypochlorite, with liquid sodium hypochlorite being used more in groundwater today. Of course, gas chlo- rine is still used in many water treatment plants with the addi- tion of ammonia forming chloramines to reduce the creation of unwanted disinfection byproducts. Regardless of what type of chlorine used when added to water, they all form hypochlorous acid and hypochlorite ions. The hypochlorous acid is the most biocidal form and is highly dependent on pH values near neutral to maintain its existence. In our industry today, there are a variety of chlorine enhancing chemistries designed to buffer the pH to the desired values and providing the most effective disinfection activities. An additional oxidation chemical used in groundwater, but one that is not a disinfectant, is persulfate. This oxidant is most effective in degrading chlorinated solvents and petro- leum products, even the difficult carbon tetrachloride. Persul- fates have been used for remediation of contaminated soils through the process of in situ chemical oxidation. Although the measurement and evaluation of disinfection potential within our industry has been accomplished by the value of "free total chlorine," the value can be compromised with changes in pH value and reaction with amines, contribut- ing to chlorine values but with little oxidizing capacity. To this point the water industry has accepted the value of oxidation reduction potential (ORP) for assessment of bioci- dal capabilities. The ORP value is an equilibrium between the various forms of chlorine and is regardless of the pH value. The World Health Organization recognized in 1972 an ORP value of 650 mV provided instantaneous disinfection of viral bacteria. The ORP value in current water technologies is used for monitoring and controlling many aspects of water treat- ment and corrosion control processes, providing a valuable tool to our industry. Summary The oxidation reaction is a friend to the groundwater industry—most prominently with the process of disinfection and residual benefits of general corrosion providing some metal passivation, effervescences of the reaction providing agitation during disinfection, and the contaminant removal process using persulfates. On the other hand, the oxidation reaction is a foe to the industry in the degrading of well systems through corrosion, the accumulation of iron oxides in well fouling, the potential encrusting of biofilm from excess oxidation, and the potential formation of disinfection byproducts. Roger Miller serves as a senior consultant for Water Systems Engineering Inc. His work over the past 30 years has involved research and development, analytical procedures, site assessment, and project oversight in the groundwater industry. DACUM Codes To help meet your professional needs, this article covers skills and competencies found in DACUM charts for drillers and pump installers. DO refers to the drilling chart and PI represents the pumps chart. The letter and number immediately following is the skill on the chart covered by the article. This article covers: DOB-2; DOF-2; DOG-10; PIC-1, 5, 6; PIE-20; PIF-1, 8 More information on DACUM and the charts are available at www.NGWA.org. Take in NGWA Webinar on Oxidation The author will present a webinar on this topic, "The Oxidation Reaction—Friend or Foe to the Groundwater Industry," from 1-2 p.m. ET on August 23. To learn more, click on "NGWA Events and Education" under the Events/Education tab at www.NGWA.org. WWJ WWJ July 2016 27 Twitter @WaterWellJournl

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