环境工程毕业设计外文翻译

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1、 Catalytic strategies for industrial water re-use F.E. Hancock Synetix, Billingham, Cleveland, TS23 1LB, UK Abstract The use of catalytic processes in pollution abatement and resource recovery is widespread and of significant economic importance R.J. Farrauto, C.H. Bartholomew, Fundamentals of Indus

2、trial Catalytic Processes, Blackie Academic and Professional,1997. For water recovery and re-use chemo-catalysis is only just starting to make an impact although bio-catalysis is well established J.N. Horan, BiologicalWastewater Treatment Systems； Theory and Operation, Chichester, Wiley, 1990. This

3、paper will discuss some of the principles behind developing chemo-catalytic processes for water re-use. Within this context oxidative catalytic chemistry has many opportunities to underpin the development of successful processes and many emerging technologies based on this chemistry can be considere

4、d . Keywords: COD removal； Catalytic oxidation； Industrial water treatment 1.Introduction Industrial water re-use in Europe has not yet started on the large scale. However, with potential long term changes in European weather and the need for more water abstraction from boreholes and rivers, the ava

5、ilability of water at low prices will become increasingly rare. As water prices rise there will come a point when technologies that exist now (or are being developed) will make water recycle and re-use a viable commercial operation. As that future approaches, it is worth stating the most important f

6、act about wastewater improvement avoid it completely if at all possible! It is best to consider water not as a naturally available cheap solvent but rather, difficult to purify, easily contaminated material that if allowed into the environment will permeate all parts of the biosphere. A pollutant is

7、 just a material in the wrong place and therefore design your process to keep the material where it should be contained and safe. Avoidance and then minimisation are the two first steps in looking at any pollutant removal problem. Of course avoidance may not be an option on an existing plant where a

8、ny changes may have large consequences for plant items if major flowsheet revision were required. Also avoidance may mean simply transferring the issue from the aqueous phase to the gas phase. There are advantages and disadvantages to both water and gas pollutant abatement. However, it must be remem

9、bered that gas phase organic pollutant removal (VOC combustion etc.,) is much more advanced than the equivalent water COD removal and therefore worth consideration 1. Because these aspects cannot be over-emphasised， a third step would be to visit the first two steps again. Clean-up is expensive, rec

10、ycle and re-use even if you have a cost effective process is still more capital equipment that will lower your return on assets and make the process less financially attractive. At present the best technology for water recycle is membrane based. This is the only technology that will produce a suffic

11、iently clean permeate for chemical process use. However, the technology cannot be used in isolation and in many (all) cases will require filtration upstream and a technique for handling the downstream retentate containing the pollutants. Thus, hybrid technologies are required that together can handl

12、e the all aspects of the water improvement process6,7,8. Hence the general rules for wastewater improvement are: 1. Avoid if possible, consider all possible ways to minimise. 2. Keep contaminated streams separate. 3. Treat each stream at source for maximum concentration and minimum flow. 4. Measure

13、and identify contaminants over complete process cycle. Look for peaks, which will prove costly to manage and attempt to run the process as close to typical values as possible. This paper will consider the industries that are affected by wastewater issues and the technologies that are available to di

14、spose of the retentate which will contain the pollutants from the wastewater effluent. The paper will describe some of the problems to be overcome and how the technologies solve these problems to varying degrees. It will also discuss how the cost driver should influence developers of future technolo

15、gies. 2. The industries The process industries that have a significant wastewater effluent are shown in Fig. 1. These process industries can be involved in wastewater treatment in many areas and some illustrations of this are outlined below. Fig. 1. Process industries with wastewater issues. 2.1. Re

16、fineries The process of bringing oil to the refinery will often produce contaminated water. Oil pipelines from offshore rigs are cleaned with water； oil ships ballast with water and the result can be significant water improvement issues. 2.2. Chemicals The synthesis of intermediate and speciality ch

17、emicals often involve the use of a water wash step to remove impurities or wash out residual flammable solvents before drying. 2.3. Petrochemicals Ethylene plants need to remove acid gases (CO2, H2S) formed in the manufacture process. This situation can be exacerbated by the need to add sulphur comp

18、ounds before the pyrolysis stage to improve the process selectivity. Caustic scrubbing is the usual method and this produces a significant water effluent disposal problem. 2.4. Pharmaceuticals and agrochemicals These industries can have water wash steps in synthesis but in addition they are often fo

19、rmulated with water-based surfactants or wetting agents. 2.5. Foods and beverages Clearly use water in processing and COD and BOD issues will be the end result. 2.6. Pulp and paper This industry uses very large quantities of water for processing aqueous peroxide and enzymes for bleaching in addition

20、 to the standard Kraft type processing of the pulp. It is important to realise how much human society contributes to contaminated water and an investigation of the flow rates through municipal treatment plants soon shows the significance of non-process industry derived wastewater. 3. The technologie

21、s The technologies for recalcitrant COD and toxic pollutants in aqueous effluent are shown in Fig. 2. These examples of technologies 2,6,8 available or in development can be categorised according to the general principle underlying the mechanism of action. If in addition the adsorption (absorption)

22、processes are ignored for this catalysis discussion then the categories are: 1. Biocatalysis 2. Air/oxygen based catalytic (or non-catalytic). 3. Chemical oxidation 1. Without catalysis using chemical oxidants 2. With catalysis using either the generation of _OH or active oxygen transfer. Biocatalys

23、is is an excellent technology for Municipal wastewater treatment providing a very cost-effective route for the removal of organics from water. It is capable of much development via the use of different types of bacteria to increase the overall flexibility of the technology. One issue remains what to

24、 do with all the activated sludge even after mass reduction by de-watering. The quantities involved mean that this is not an easy problem to solve and re-use as a fertilizer can only use so much. The sludge can be toxic via absorption of heavy metals, recalcitrant toxic COD. In this case incineratio

25、n and safe disposal of the ash to acceptable landfill may be required. Air based oxidation 6,7 is very attractive because providing purer grades of oxygen are not required if the oxidant is free. Unfortunately, it is only slightly soluble in water, rather unreactive at low temperatures and, therefore, needs heat and pressure to deliver reasonable rates of reaction. These plants become capital intensive as pressures (from _10 to 100 bar) are used. Therefore, although the running costs maybe low the initial capital outlay on the plant has a very significant effect on the