Chlorine with ozone

Today in addition to Paris, many other cities use ozone in production of potable water. Zurich, Switzerland, Florence, Italy, Brussels, Belgium, Marseille, France, Singapore and Moscow, Russia all have ozone water treatment plants. In Europe many swimming pools, both public and private use ozone in place of chlorine. With ozone, no salts are added to the water, so that in addition to a high level of sterility, the acidity (pH) is easier to control. In the United States, ozone s use is limited, but LaSalle, Illinois has a relatively new ozone water treatment facility. ... 

Compare chlorine with ozone. Let x denote the density of ozone. Then, by Graham s law,... 

Chlorite ion is oxidized rapidly to chlorine dioxide by ozone at pH 4, yielding one mol CIO2 per mol O3 when chlorite is in excess (k > lO" (39). The oxidation of bromite to bromate by ozone is too rapid to measure. Chlorine dioxide is oxidized rapidly to chlorate. Chlorate, bromate, and iodate ions do not react with ozone. 

Ozone can be used to completely oxidize low concentrations of organics in aqueous streams or partially degrade compounds that are refractory or difficult to treat by other methods. Compounds that can be treated with ozone include alkanes, alcohols, ketones, aldehydes, phenols, benzene and its derivatives, and cyanide. Ozone readHy oxidizes cyanide to cyanate, however, further oxidation of the cyanate by ozone proceeds rather slowly and may require other oxidation treatment like alkaline chlorination to complete the degradation process. 

Prepai ative isolation of nonvolatile and semivolatile organic compounds fractions (hydrophobic weak acids, hydrophobic weak bases, hydrophobic neutrals, humic and fulvic acids) from natural and drinking waters in optimal conditions was systematically investigated by solid-phase extraction method with porous polymer sorbents followed by isolation from general concentrate of antropogenic and/or toxic semivolatile compounds produced in chlorination and ozonation processes. 

The chlorine atoms in the upper atmosphere come from the breakdown of CF2 CI2 and other similar chlorofluorocarbons (CFCs), known commercially as Freons. Production of these compounds was more than one million tons in 1988, largely for use in relrigerators and air conditioners. Once released into the atmosphere, CFCs diffuse slowly upward in the atmosphere until they reach the ozone layer. There, ultraviolet light Irom the sun splits off chlorine atoms. These react with ozone, with dramatic results. Annual ozone decreases have exceeded 50% above Antarctica. The background photo shows the Antarctic hole (red-violet) on September 24, 2003. 

The reaction of volatile chlorinated hydrocarbons with hydroxyl radicals is temperature dependent and thus varies with the seasons, although such variation in the atmospheric concentration of trichloroethylene may be minimal because of its brief residence time (EPA 1985c). The degradation products of this reaction include phosgene, dichloroacetyl chloride, and formyl chloride (Atkinson 1985 Gay et al. 1976 Kirchner et al. 1990). Reaction of trichloroethylene with ozone in the atmosphere is too slow to be an effective agent in trichloroethylene removal (Atkinson and Carter 1984). 

Oxidant Removal The presence of oxidizers such as chlorine or ozone can degrade polyamide RO membranes, causing a drop in salt retention. Cellulosic membranes are less sensitive to attack. Addition of 1.5 to 6 mg sodium bisulfite/ppm chlorine or contacting with activated carbon will remove oxidizers. Vacuum degassing with a hydrophobic filter module is also used. 

Ozonation treatment can be used to oxidize cyanide, thereby reducing the concentration of cyanide in wastewater. Ozone, with an electrode potential of +1.24 V in alkaline solutions, is one of the most powerful oxidizing agents known. Cyanide oxidation with ozone is a two-step reaction similar to alkaline chlorination.22 Cyanide is oxidized to cyanate, with ozone reduced to oxygen as per the following equation ... 

Single-stage chlorine refrigeration system (ammonia/carbon dioxide/chlorine) with no use of ozone-depleting chemicals. 

Only metabolites leached from the cell were affected. Elford and van den Ende reported that ozone at 20 ppm had a lethal effect on some bacteria deposited from aerosol mists on various surfaces. Relative humidity is an important factor, particularly when ozone concentration is low. They found little death at a humidity below 45%, at concentrations of 1 ppm, as opposed to a 90% kill in 30 min at 0.025 ppm with a humidity of around 70%. A 5-min exposure of Bacillus cereus to ozone at 0.12 mg/liter was the minimal lethal dose, whereas 0.10 mg/liter was effective for B. megaterium and E. coli. Spores of the Bacillus sp. were killed by ozone at 2.29 mg/liter. These responses were of the all-or-none type with ozone between 0.4 and 0.5 mg/liter of water. Time of exposure, from 1 to 32 min, was not important. Chlorine was effective at 0.27-0.30 mg/liter, with time an important consideration. These two gases did not affect E. coli in the same way. 

Photolytic. Anticipated products from the reaction of allyl chloride with ozone or OH radicals in the atmosphere are formaldehyde, formic acid, chloroacetaldehyde, chloroacetic acid, and chlorinated hydroxy carbonyls (Cupitt, 1980). 

Chemical/Physical. Anticipated products from the reaction of 1,2-dichlorobenzene with ozone or OH radicals in the atmosphere are chlorinated phenols, ring cleavage products, and nitro compounds (Cupitt, 1980). Based on an assumed base-mediated 1% disappearance after 16 d at 85 °C and pH 9.70 (pH 11.26 at 25 °C), the hydrolysis half-life was estimated to be >900 yr (Ellington et al, 1988). 

Irradiation of gaseous formaldehyde containing an excess of nitrogen dioxide over chlorine yielded ozone, carbon monoxide, nitrogen pentoxide, nitryl chloride, nitric and hydrochloric acids. Peroxynitric acid was the major photolysis product when chlorine concentration exceeded the nitrogen dioxide concentration (Hanst and Gay, 1977). Formaldehyde also reacts with NO3 in the atmosphere at a rate of 3.2 x 10 cmVmolecule-sec (Atkinson and Lloyd, 1984). 

When CFCs slowly rise in the atmosphere and reach the ozone layer, they are broken down into component molecular compounds and atoms by the UV rays of the sun. Some of these chemicals then react with ozone to break it down, thus reducing the amount of O3. Further, some chlorine (also from the oceans) and some other elements combine with the O and to form other chemicals. This also contributes to the reduction of ozone faster than natural processes can reform it. Ozone is a renewable resource. The issue is this can a balance be obtained between the destruction of ozone in the atmosphere, by both natural and man-made causes, and its natural regeneration ... 

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