Separation in Waste Treatment

In addition to distillation, several other kinds of separation procedures are used for waste treatment. These are mentioned here as examples of separation processes. 

Distillation is an example of a separation in which one of the constituents being separated undergoes a phase transitioii from one phase to another, and then back to the same phase. In distillation, for example, a liquid is converted to the vapor state, and then lecondraised as a liquid. Sev other kinds of separations by phase transition as applied to waste treatment are the following  

Evaporadon is usually employed to remove water from an aqueous waste to concentrate it A special case of this technique is thin-film evs ration, in which volatile constituents are removed by heating a thin layer of liquid or sludge waste spread on a heated surface. 

Drying— removal of solvent or water from a solid or semisolid (sludge) or the removal of solvent from a liquid or suspension— is a very important operation, because water is often the major constituent of waste products, such as sludges. In freeze drying, the solvent usually water, is sublimed from a frozen material. Hazardous-waste solids and sludges are dried to reduce the quantity of waste, to remove solvent or water that might interfere with subsequent treatment processes, and to remove hazardous volatile constituents. 

Physical precipitation is used here as a term to describe processes in which a dissolved solute comes out of solution as a solid as a result of a physical change in the solution. The major changes that can cause physical precipitation are cooling the solution, evaporation of solvent, or alteration of solvent composition. The most common type of physical precipitation by alteration of solvent composition occurs when a water-miscible organic solvent is added to an aqueous (water) solution of a salt, so that the solubility of the salt is lowered below its concentration in the solution. 

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Separation Techniques, Academic, New York, 1972 Lemhch, Adsub-ble Methods, in li (ed.). Recent Developments in Separation Science, vol. 1, CRC Press, Cleveland, 1972, chap. 5 Grieves, Chem. Eng. J., 9, 93 (1975) Valdes-Krieg King, and Sephton, Sep. Purif Methods, 6,221 (1977) Clarke and Wilson, Foam Flotation, Marcel Deldcer, New York, 1983 and Wilson and Clarke, Bubble and Foam Separations in Waste Treatment, in Rousseau (ed.). Handbook of Separation Processes, Wiley, New York, 1987. 

Wilson DJ, Clark AN (1987) Bubble foam separation in waste treatment In Rousseau RW (ed) Handbook of separation process technology. Wiley, New York, chap 17... 

Among the basic fields of applications, the major use of acrylamide polymers is liquid-solid separation in water treatment and waste treatment. Smaller quantities are used in the manufacturing of paper and in the processing of minerals in mining. Relatively nonlarge quantities are use as additives for enhanced oil recovery. 

Flotation is a solid-liquid separation process, that transfers solids to the liquid surface through attachment of gas bubbles to solid particles. Flotation processes are used in the processing of crushed ores, whereby a desired mineral is separated from the gangue or non-mineral containing material. Various applications in solid separation processes are also in use in waste treatment. 

Atom economy is high. As a reagent, no compounds are needed and consequently none are produced as the electron is immaterial. This results in a greater advantage of electrochemical reactions compared to chemical conversions, namely, an effective contribution to pollution control. The direct ET from the electrode to the substrate avoids the problem of separation and waste treatment of the, frequently, toxic end products of chemical reductions or oxidations. Furthermore, by electrodialysis, organic acids or bases can be regenerated from their salts without the use of, for example, sulfuric acid or... 

The reactor is the nucleus of the process. Getting the fluid dynamics right in the reactor means improved safety, productivity, and selectivity, which in turn influences upstream (reduced raw material costs) and downstream (reduced separation and waste treatment costs) see Figure 1. 

An example of a solid-liquid phase separation - often referred to as a mechanical separation - is filtration. Filters are also used in gas-sohd separation. Filtration may be used to recover liquid or sohd or both. Also, it can be used in waste-treatment processes. Walas [6] describes many solid-hquid separators, but we will only consider the rotary-drum filter. Reliable sizing of rotary-drum filters requires bench and pilot-scale testing with the slurry. Nevertheless, a model of the filtering process will show some of the physical factors that influence filtration and will give a preliminary estimate of the filter size in those cases where data are available. 

A variant envisages the use of aqueous methanol for both the extraction of hydrogen peroxide and the epoxidation of propene as shown, in a simplified form, by Figure 18.3. Thus, no extra water is added to the epoxidation reactor, which decreases separation and waste-treatment costs. On the laboratory scale, the quantity of methanol dissolving into the working solution is small and apparently does not interfere with the AO cycle of reactions [154, 161]. 

The conclusion which should emerge in the light of the situation outlined is that the process of digestion should not be used as an unrelated and separate operation in waste treatment. The inputs to and products of digestion should only be considered in design as part of a dynamic system in which each of the many elements comprising the whole is considered as having a cause and effect relationship in the total system response. 

Nevertheless, as noted by Douglas (1988), the reactor system is often the heart of the chemical process, as it dictates the downstream processes (e.g., separation and waste treatment) and strongly influences both the recycle and separation structures as well as the energy network. Despite this, the general approach is to design the reactor system in isolation and then to design the... 

Future problems associated with separations and waste treatment processes, will be the result of two major changes in reactor development. These are the use of new materials of construction for fuel cladding or fuels themselves, and the increase in specific activity of processed fuels. 

It is clear that metal-free aerobic oxidations have the advantage over metal-catalyzed aerobic oxidations, in terms of downstream separation and waste treatment. 

This chapter summarizes the applications of LMs, particularly for the separation of radiotoxic actinides and shows their potential in waste treatment and partitioning. For decontamination of the waste solutions which are generated in nuclear facilities, one must seek a process which is both technically efficient in removing the contaminants and also economically attractive for large-scale operation. 

The capital cost of most aqueous waste treatment operations is proportional to the total flow of wastewater, and the operating cost increases with decreasing concentration for a given mass of contaminant to be removed. Thus, if two streams require different treatment operations, it makes no sense to mix them and treat both streams in both treatment operations. This will increase both capital and operating costs. Rather, the streams should be segregated and treated separately in a distributed effluent treatment system. Indeed, effective primary treatment might mean that some streams do not need biological treatment at all. 

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