Certification Action Line – Answers – October 2013

Oct. 1, 2013

Answers from the October 2013 edition of Certification Action Line.

1. True. Elemental oxygen exists naturally as two atoms of oxygen which are combined to form the O2 molecule. Ozone O3 is an unstable allotropic form of gaseous oxygen that is formed when energy from ultraviolet rays or electrical discharges strike oxygen O2 molecules and disrupt or break the O2 bonds, thereby forming single oxygen radicals (O1). These O1 radicals recombine with other O2 molecules to form ozone (O3).

2. c. The oxidation potential of ozone is 17 percent greater than hydrogen peroxide, 24 percent greater than potassium permanganate, and 40 percent greater than hypochlorous acid from free chlorine in water.

3. b. When ozonation is coupled with hydrogen peroxide (H2O2) and/or ultraviolet (UV) radiation, hydroxyl free radicals (HO·) are produced rapidly over a wide pH range. The hydroxyl free radical, with available hydrogen (H+) ions, is a 33 percent stronger oxidizing agent than is ozone alone. This coupled ozone technology whereby HO· is deliberately produced from ozone decomposition is called ozone "Advanced Oxidation" or the "Peroxone Process."

4. True. Corona discharge generated ozone can produce concentrations sufficient for one mg/L or ppm residuals after five minutes contact time. In clarified water, such ozone dosages will inactivate 99.9 percent of protozoan cysts. 

5. a. Some of the VOC compounds are reactive with ozone, while others are nonreactive, or are so slowly reactive as to be essentially unreactive. All volatile organic compounds can be removed from water by air stripping, which occurs at least to some degree in ozone contacting chambers. Off gases should be properly vented or treated.

6. b. Dry feed gas is important to consistent ozone output in both ultraviolet and corona discharge ozone generation. However, in corona discharge generators, the production of nitrogen oxides increases exponentially with feed gas moisture above -40° C dew point. The nitrogen oxides create nitric acid when dissolving in water, which is very corrosive to the corona discharge glass/ceramic dielectric material and the downstream process equipment. Moisture with UV generators does not produce significant levels of nitric acid as it does with corona discharge generators.

7. c. When ozone is generated from air using UV-based generators, the concentrations of ozone in the gases exiting the generator are much lower than levels achievable by corona discharge, on the order of 0.1 percent to 0.01 percent by weight, compared to 1 percent to 4 percent by eight typical of corona discharge generators.

8. d. Because ozone is the strongest oxidizing agent currently available for potable water treatment, special care must be taken to ensure that piping, valves, gaskets, and other materials carrying ozone are resistant to ozone's reactive characteristics. Carbon steels and nonferrous metals such as copper and aluminum will be corroded by ozone. Natural rubber and many plastics and synthetic rubbers cannot be used as gaskets, seals, or O-rings, as upon exposure to ozone these products will quickly become brittle and crack. Materials such as stainless steel, Teflon, PVDF (Kynar®), Gortex, Hypalon®, glass, and ceramic can be used with ozone in gas phase. In water, up to six parts per million (ppm) of ozone is acceptable in polyvinyl chloride (PVC), chlorinated polyvinyl-chloride (CPVC), and high density polyethylene (HDPE) materials.

9. True. Ozone is very effective in oxidizing hydrogen sulfide (H2S). In fact the reaction of ozone with the sulfide (S2-) ion is found to be so rapid, that the sulfide is converted completely to sulfate, which is innocuous in the water. At least 2.0 to 4.0 milligrams per liter (mg/L) of ozone for each mg/L of sulfide ion are necessary.

10. a. In waters containing organic compounds such as humic substances, tannins, and synthetic organic chemical (SOCs), and ozonation by-product is assimilable organic carbon (AOC) compounds such as aldehydes, ketones, carboxylic acids, and combinations thereof. AOC compounds are more easily metabolized by and thereby supportive of microbial growths. Where control of AOC and microbial regrowths is an objective, it is recommended that ozonation be followed by biofiltration on sand, anthracite, activated carbon (i.e., biologically activated carbon (BAC)) or combinations of such filter media in order to biomineralize the AOC compounds and to provide biological stabilization in the treated water supply. This is particularly important when the water being treated is high in dissolved organic carbon (DOC) levels.

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