Dechlorination cleaning

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Keywords Additional discharge streams Antisealants Chemical treatment Coagulation/flocculation Concentration factor Dechlorination Filtration High recovery Membrane cleaning Pretreatment Recovery rate... 

Photochemical decomposition can also be carried out in the presence of a suspension of photoactive material such as Ti02 where substrate absorption onto the uv activated surface can initiate chemical reactions e. g. the oxidation of sulphides to sul-phones and sulphoxides [37]. This technology has been adapted to the destruction of polychlorobiphenyls (PCB s) in wastewater and is of considerable interest in environmental protection. Using pentachlorophenol as a model substrate in the presence of 0.2 % TiOj uv irradiation is relatively efficient in dechlorination (Tab. 4.5) [38]. When ultrasound is used in conjunction with photolysis, dechlorination is dramatically improved. This improvement is the result of three mechanical effects of sonochemistry namely surface cleaning, particle size reduction and increased mass transport to the powder surface. 

Under conventional dechlorination conditions (20 equiv of zinc dust, acetic acid, 25°C or 50°C) the reduction of 4,4-dichlorocyclobutenones affords complex mixtures of products which include the desired cyclobutenones as well as significant amounts of partially reduced byproducts. He have found that the desired transformation can be accomplished cleanly provided that the reduction is carried out at room temperature in alcoholic solvents (preferably ethanol) in the presence of 5 equiv each of acetic acid and a tertiary amine (preferably tetramethylethylenediamine). Zinc dust has proven to be somewhat superior to zinc-copper couple for this reduction. The desired cyclobutenones are obtained in somewhat higher yield using this procedure as compared to the related conditions reported by Dreiding [Zn(Cu), 4 1 AcOH-pyridine, 50-60 C] for the same transformation. ... 

T0237 ElectrokineticaUy Enhanced Bioremediation—General T0238 Electrokinetics, Inc., Electrokinetic Soil Cleaning T0239 Electro-Petroleum, Inc., Electrokinetic Treatment T0248 ENERGIA, Inc., Reductive Photo-Dechlorination (RPD)... 

The available surface area of the iron has the greatest effect on the reaction rate (Johnson et al., 1996). The iron is commonly treated with hydrochloric acid prior to the experiment to accelerate dechlorination and improve reproducibility. By cleaning the metal surface, the passive oxide layer is broken off, the surface area is increased by etching and pitting, and the density of highly reactive sites is increased (Agrawal and Tratnyek, 1996). Because of... 

Many groundwaters are contaminated with the cleaning solvents trichloroethylene (TCE) and perchloroethylene (PCE). They are two of the most common organochlorine compounds found in Superfund sites. Radiation-induced decomposition of TCE in aqueous solutions has been the subject of several recent studies [15-20]. In most of the referenced studies, the complete destruction of TCE was observed. Dechlorination by a combination of oxidative and reductive radiolysis was stoichiometric. Gehringer et al. [15] and Proksch et al. [18] have characterized the kinetics and mechanism of OH radical attack on TCE and PCE in y-ray-irradiated aqueous solution. Trichloroethylene was readily decomposed in exponential fashion, with a reported G value of 0.54 pmol J-1. A 10 ppm (76 pM) solution was decontaminated with an absorbed dose of less than 600 Gy. For each OH captured, one C02 molecule, one formic acid molecule and three Cl- ions were generated. These products were created by a series of reactions initiated by OH addition to the unsaturated TCE carbon, which is shown in Eq. (45) ... 

The graded and cleaned particles of waste plastic are then introduced into a melt-ing/preheating system with an extruder feeder. The hard metal, clay and sand, glass, etc. are separated here by sedimentation, and then the waste plastic is charged in the dechlorination section. The solid metal, glass, etc. is removed from the melting/preheating section periodically. 

The major thrust of this work has, in particular, concerned the electrolytic dechlorination of polychlorinated biphenyls and similar species for environmental control of pollutants. However, there is a wider potential for this technology in the use of aqueous solvent systems for syntheses involving otherwise water-immiscible organic compounds. Water is of course the cheapest, most widely available and environmentally friendly solvent and with modem concerns over ecology and the search for clean technologies there is considerable opportunity for this particular application of ultrasound in electrochemistry. 

The derivative (31c), however, undergoes a clean photoreaction to afford the oxetan (32c). The chloroketone (3Id) affords, on irradiation, many products among which are the oxetan (32d) and the dechlorinated compound (31e). The homolysis of (3Id) to the radical (33) is a facile process and occurs in competition with cyclization to the oxetan. 

The main reaction products were ethane (from TTCE) and benzene (from CBZ) (i.e. total dechlorination), in both cases with selectivities higher than 99 %. This result is very important considering that the final aim of this work is the development of a clean technology for the treatment of wastes. Very little amount of trichloroethylene were foimd in the hydrodechlorination of TTCE, whereas in the case of CBZ hydrodechlorination neither chlorocyclohexane nor cyclohexane were found. Likewise, the solvent (toluene) did not react in appreciable extension, being observed only small amounts of methyl-cyclohexane. TTCE was found to be more reactive than CBZ. 

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