环境工程毕业设计外文翻译--工业废水回用的接触反应策略(编辑修改稿)

环境工程毕业设计外文翻译--工业废水回用的接触反应策略(编辑修改稿)内容摘要：

The catalysts used are generally Group VIII metals such as cobalt or copper. The leaching of these metals into the aqueous phase is a difficulty that inhibits the general use of heterogeneous catalysts [7]. Chemical oxidation with cheap oxidants has been well practised on integrated chemical plants. The usual example is waste sodium hypochlorite generated in chloralkali units that can be utilised to oxidise COD streams from other plants within the plex. Hydrogen peroxide, chlorine dioxide, potassium permanganate are all possible oxidants in this type of process. The choice is primarily determined by which is the cheapest at the point of use. A secondary consideration is how effective is the oxidant. Possibly the most researched catalytic area is the generation and use of _OH as a very active oxidant (advanced oxidation processes) [8]. There are a variety of ways of doing this but the most usual is with photons and a photocatalyst. The photocatalyst is normally TiO2 but other materials with a suitable band gap can be used [9,10]. The processes can be very active however the engineering difficulties of getting light, a catalyst and the effluent efficiently contacted is not easy. In fact the poor efficiency of light usage by the catalyst (either through contacting problems or inherent to the catalyst) make this process only suitable for light from solar sources. Photons derived from electrical power that es from fossil fuels are not acceptable because the carbon dioxide emission this implies far outweighs and COD abatement. Hydroelectric power (and nuclear power) are possible sources but the basic inefficiency is not being avoided. Hydrogen peroxide and ozone have been used with photocatalysis but they can be used separately or together with catalysts to effect COD oxidation. For ozone there is the problem of the manufacturing route, corona discharge, which is a capital intensive process often limits its application and better route to ozone would be very useful. It is important to note at this point that the oxidants discussed do not have sufficient inherent reactivity to be use without promotion. Thus, catalysis is central to their effective use against both simple organics (often solvents) or plex recalcitrant COD. Hence, the use of Fenton’s catalyst (Fe) for hydrogen peroxide [11]. In terms of catalysis these oxidants together with hypochlorite form a set of materials that can act has ‘active oxygen transfer (AOT) oxidants’ in the presence of a suitable catalyst. If the AOT oxidant is hypochlorite or hydrogen peroxide then three phase reactions are avoided which greatly simplifies the flowsheet. Cheap, catalytically promoted oxidants with environmentally acceptable products of oxidation that do not require plex chemical engineering and can be produced efficiently would appear to offer one of the best solutions to the general difficulties often observed. . Redox catalysis and active oxygen transfer The mechanism of catalytically promoted oxidation with hydrogen peroxide or sodium hypochlorite cannot be enpassed within one concept, however there are general similarities between the two oxidants that allows one to write a series of reactions for both (Fig. 3) [5]. This type of mechanism could be used to describe a broad range of reactions for either oxidant from catalytic epoxidation to COD oxidation. The inherent usefulness of the reactions is that。 1. The reactions take place in a twophase system. 2. High pressure and temperature are not required. 3. The catalytic surface can act as an adsorbent of the COD to be oxidised effectively increasing the concentration and hence the rate of oxidation. The simple mechanism shows the selectivity issue with this type of processes. The oxidant can simply be deposed by the catalyst to oxygen gas – this reaction must be avoided because dioxygen will play no role in COD removal. Its formation is an expensive waste of reagent with oxygen gas ($20/Te) pared to the oxidant ($400–600/Te). To be cost petitive with alt。