【文章內(nèi)容簡介】 d 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 and identify contaminants over plete 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 dispose of the retentate which will contain the pollutants from the wastewater effluent. The paper will describe some of the problems to be overe and how the technologies solve these problems to varying degrees. It will also discuss how the cost driver should influence developers of future technologies. 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. . Refineries 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. . Chemicals The synthesis of intermediate and speciality chemicals often involve the use of a water wash step to remove impurities or wash out residual flammable solvents before drying. . 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 pounds before the pyrolysis stage to improve the process selectivity. Caustic scrubbing is the usual method and this produces a significant water effluent disposal problem. . Pharmaceuticals and agrochemicals These industries can have water wash steps in synthesis but in addition they are often formulated with waterbased surfactants or wetting agents. . Foods and beverages Clearly use water in processing and COD and BOD issues will be the end result. . Pulp and paper This industry uses very large quantities of water for processing – aqueous peroxide and enzymes for bleaching in addition 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 nonprocess industry derived wastewater. 3. The technologies 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) processes are ignored for this catalysis discussion then the categories are: 1. Biocatalysis 2. Air/oxygen based catalytic (or noncatalytic). 3. Chemical oxidation 1. Without catalysis using chemical oxidants 2. With catalysis using either the generation of _OH or active oxygen transfer. Biocatalysis is an excellent technology for Municipal wastewater treatment providing a very costeffective route for the removal of anics 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 do with all the activated sludge even after mass reduction by dewatering. The quantities involved mean that this is not an easy problem to solve and reuse as a fertilizer can only use so much. The sludge can be toxic via absorption of heavy metals, recalcitrant toxic COD. In this case incineration 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 bee 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 costs of the process. Catalysis improves the rates of reaction and hence lowers the temperature and pressure but is not able to avoid them and hence does not offer a plete solution. 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