Trichloroethylene, stripping

Trichloroethylene use has declined as a result of environmental concerns. However, trichloroethylene may replace some 1,1,1-trichloroethane appHcations. Perchloroethylene used in small businesses for dry cleaning will be regulated for emissions under the same guidelines as those that govern the large chemical producers. This will cause replacement of perchloroethylene for those appHcations where recovery is uneconomical. Methylene chloride has been classified as a suspected carcinogen and its use will decline in aerosol and paint stripping appHcations because of health concerns. 

There has been an emphasis on recovery and recycling of trichloroethylene to reduce emissions of this photoreactive chemical to the atmosphere (CMR 1986 McNeill 1979). Photooxidative destruction has been successfully used in conjunction with air-stripping techniques to volatilize trichloroethylene from water and degrade it to nontoxic products (Bhowmick and Semmens 1994). If possible, recycling should be used instead of disposal. 

Release of trichloroethylene also occurs at treatment and disposal sites. Water treatment facilities may release trichloroethylene from contaminated water through volatilization and air-stripping procedures (EPA 1985e). Trichloroethylene is also released to the atmosphere through gaseous emissions from landfills. The compound may occur as either an original contaminant or as a result of the decomposition of tetrachloroethylene. Trichloroethylene has also been detected in stack emissions from the incineration of municipal and hazardous waste (James et al. 1985 Oppelt 1987). 

Okouchi S. 1986. Volatilization coefficient for stripping trichloroethylene, 1,1,1-trichloroethane and tetrachloroethylene from water. Water Sci Technol 18 137-138. 

Goltz MN, RK gandhi, SM Gorelick, GD Hopkins, LH Smith, BH Timmins, PL McCarthy (2005) Field evaluation of in situ source reduction of trichloroethylene in groundwater using bioenhanced in-situ vapor stripping. Environ Sci Technol 39 8963-8970. 

An emulsion, formed during extraction of a strongly alkaline liquor with trichloroethylene, decomposed with evolution of the spontaneously flammable gas, dichloro-acetylene [1]. This reaction could also occur if alkaline metal-stripping preparations were used in conjunction with trichloroethylene degreasing preparations, some of which also contain amines as inhibitors, which could also cause the same reaction [2], Apparently accidental contact of the solvent with potassium hydroxide solution led to generation of flames in the charging port of a stirred reactor [3], See Tetrachloroethylene Sodium hydroxide... 

The Perox-Pure system is most effective in treating water with contaminant concentrations less than about 500 mg/liter. Removal efficiencies are high for organic compounds with double bonds (e.g., trichloroethylene, perchloroethylene, and vinyl chloride) and for aromatic compounds (e.g., phenol, benzene, and toluene). These compounds are easily oxidized. The Perox-Pure system can be used alone or in combination with other remedial technologies, such as air stripping. 

The air-stripping tower, illustrated in Figure E6.10.1, provides the air-water contact area, either through a porous medium that is unsaturated with water, through bubbles rising through the water or both. The polluted water comes in at the top (Co), and cleaner water comes out of the bottom of the stripping tower, while clean air comes in at the bottom, and air with trichloroethylene in it comes out the top of the tower. This... 

The plug flow reactor model predicts that there will be 1 % of the trichloroethylene remaining at the bottom of the stripping tower. 

Now, we need a solution to the plug flow with dispersion model for steady-state operation of an air-stripping tower. The mass transport equation for this situation, assuming minimal trichloroethylene builds up in the bubble, is... 

Storage stability studies indicate that badge samples can be stored up to two weeks either refrigerated or at ambient temperatures. However, for volatile compounds such as acetone and trichloroethylene migration does occur and separation of the charcoal strips immediately after exposure is recommended. 

Trichloroethylene (TCE) is the most prevalent organic contaminant of drinking water supplies in the United States. Air stripping, the once conventional treatment method, is now largely disallowed. Extensive efforts have been made to develop bacterial systems to remove TCE from water. Efforts to obtain bacteria that... 

A 1-1. three-necked flask is equipped with a mercury-sealed stirrer, an inlet tube, and a reflux condenser which is connected through a soda-lime tube to a gas-absorption trap.1 The apparatus is dried in an oven and assembled rapidly to exclude moisture it is advisable to set up the apparatus in a hood to vent ammonia which may escape by accident. The flask is cooled in a Dry Ice-trichloroethylene bath, and 200 ml. of anhydrous (refrigeration grade) ammonia is introduced through the inlet tube from an ammonia cylinder which is either inverted or equipped with a siphon tube. Just before the apparatus is assembled, 8.1 g. (0.35 gram atom) of sodium is cut, weighed, and kept under kerosene in a small beaker. The Dry Ice bath is removed, the inlet tube is replaced by a rubber stopper, and a crystal of hydrated ferric nitrate (about 0.2 g.) is added. A small (about 5-mm.) cube of the sodium is cut, blotted rapidly with filter paper, and added quickly to the liquid ammonia. The solution is stirred until the blue color disappears, after which the remainder of the sodium is added in narrow, thin strips about as rapidly as... 

For example, fixed-film bioreactors (using sand as the biofilm matrix, and methane or natural gas as the primary substrate) can remove up to 60% of trichloroethylene (TCE) from polluted water. They can also remove more than 90% of TCE and trichloroacetic acid (TCA) from vapor streams generated by the air stripping of polluted ground-water. 

Design a PTA for stripping trichloroethylene at 60°F and above for a water flow rate of 750 gpm, influent concentration of 0.05 mg/L. Assume that treatment of the discharge gas is not required. Use a 6-ft-diameter column. The packing MSF equals 12. 

It is the overall mass transfer coefficient, however, that ultimately controls the rate of removal of a substance by air stripping. For example, dichloroethane, which has a lower Henry s constant than trichloroethylene, has been found easier to remove by air stripping, owing to its higher mass transfer coefficient (10). The mass transfer coefficient for a specific substance in a specific air-stripping system may be calculated by (9) ... 

Kosusko et al. [160, 161] reviewed studies for the destruction of groundwater air-stripping emissions. The catalyst consisted of a precious metal deposited on a ceramic honeycomb. Typical organic compounds in air stripping overhead are pentane, cyclohexane, trichloroethylene, benzene, cumene, etc. Catalyst deactivation occurs when H2S is present in the ground water or when aerosols are stripped. Figure 31 shows an example of a system used for the purification of stripped air. Air is treated countercurrently with a contaminated water stream. Downstream from the demister the contaminated gas is heated by an external source such as the combustion of natural gas. Part of the contaminants will be oxidized. 

For dilute mixtures where the majority component is not being absorbed or stripped, the mixture components usually can be considered to behave as individual entities subject to their individual solubilities. Thus, for a mixture of 1000 ppm-vol trichloroethylene and 500 ppm-vol perchloroet-hylene, the solubility for each can be determined as if the other is absent. In general, for several components of varying solubility, the relative solubility is... 

Example 22.4 Water containing 6 ppm trichloroethylene (TCE) is to be purified by stripping with air at 20°C. The product must contain less than 4.5 ppb TCE to meet emission standards. Caleulate the minimum air rate in standard cubic meters of air per cubic meter of water and the number of transfer units if the air rate is 1.5 to 5 times the minimum value. 

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