Pretreatment processes

Primary or pretreatment methods. Primary or pretreatment processes serve two purposes ... 

The pretreatment processes may be most effective when applied to individual waste streams from particular processes or process steps before effluent streams are combined for biological treatment. 

Cake dewatering is related to cake formation in a filter cake, the final moisture content is dependent on many variables that also control cake formation. Pretreatment processes, for example, affect both cake formation and cake dewatering. Cake dewatering is achieved by compacting the soHds ... 

Aluminum. Eor aluminum alloys such as 1100 and 3003 only a cleaning operation is necessary before apphcation of enamel. Eor ahoy 6061, deoxidation and alkaline-chromate pretreatment processes may also be used to improve both the cleanliness of the surface and the development of enamel adherence. The spent chromium-containing solutions can present disposal problems and should be handled in accordance with existing regulations (19). 

Liquid-liquid extraction is used primarily when distillation is imprac-tic or too costly to use. It may be more practical than distillation when the relative volatility for two components falls between 1.0 and 1.2. Likewise, liquid-liquid extraction may be more economical than distillation or steam-stripping a dissolved impurity from wastewater when the relative volatility or the solute to water is less than 4. In one case discussed by Robbins [Chem. Eng. Prog., 76 (10), 58 (1980)], liquid-liquid extraction was economically more attractive than carbon-bed or resin-bed adsorption as a pretreatment process for wastewater detoxification before biotreatment. 

Table 16.5 Examples of hazardous gases generation from waste pretreatment processes ...

He concluded that for aluminium and titanium certain etching or anodization pretreatment processes produce oxide films on the metal surfaces, which because of their porosity and microscopic roughness, mechanically interlock with the polymer forming much stronger bonds than if the surface were smooth . 

Thermal aging is another simple pretreatment process that can effectively improve adhesion properties of polymers. Polyethylene becomes wettable and bondable by exposing to a blast of hot ( 500°C) air [47]. Melt-extruded polyethylene gets oxidized and as a result, carbonyl, carboxyl, and hydroperoxide groups are introduced onto the surface [48]. 

The study of corrosion is essentially the study of the nature of the metal reaction products (corrosion products) and of their influence on the reaction rate. It is evident that the behaviour of metals and alloys in most practical environments is highly dependent on the solubility, structure, thickness, adhesion, etc. of the solid metal compounds that form during a corrosion reaction. These may be formed naturally by reaction with their environment (during processing of the metal and/or during subsequent exposure) or as a result of some deliberate pretreatment process that is used to produce thicker films or to modify the nature of existing films. The importance of these solid reaction products is due to the fact that they frequently form a kinetic barrier that isolates the metal from its environment and thus controls the rate of the reaction the protection afforded to the metal will, of course, depend on the physical and chemical properties outlined above. 

Before steel strip or rod can be cold rolled, tinned, galvanised, or enamelled, etc. any scale formed on it by previous heat treatment must be removed. This can be done by mechanical and other special methods, but if a perfectly clean surface is to be produced, acid pickling is preferred, either alone or in conjunction with other pretreatment processes. 

The metal pretreatment process requires ceneful selection, particularly with the cathodic process. BS4479 1990, Part 3, Recommendations for Conversion Coatings should be consulted. 

Under alkaline BW conditions, if magnesium bicarbonate is not removed by softening or other pretreatment processes, it forms brucite, an insoluble flocculant sludge of magnesium hydroxide [Mg(OH)2],... 

Today, in an era of water reuse and higher costs for premium-quality water, condensate line corrosion may be an inevitable and serious drawback when using naturally high-alkalinity water as a MU supply source. Some form of dealkalization pretreatment process generally is provided to high MU demand boiler plants but unfortunately not so often to smaller facilities. 

In larger HP boiler plants, excess alkalinity in the MU water is generally removed by means of (ion-exchange) dealkalization, demineralization, or other pretreatment processes, so that the bicarbonate and C02 potential is lost at source. 

Pretreatment processes should not be regarded as impurity-specific, stand-alone methodologies because, typically, each form of water impurity may be removed by more than one type of process and individual technologies can be modified to deal with particular RW chemistries. 

Notes on some common pretreatment processes are provided in the following sections. 

Pretreat process water to reduce the natural contaminants that contribute to the sludge volume. 

To facilitate biodegradation, the leachate may require modification through pH adjustment, removal or addition of oxygen, amendment with nutrients, or dilution or removal of toxic species. Microbial nutrition is complex and is better understood for aerobes than for anaerobes.34 Biological processes typically favor a pH near 7. Pretreatment processes to remove inhibitory components include coagulation and precipitation, carbon adsorption, and possibly ozonation. 

Energy production and consumption pose nature into pressure and make the energy sector becomes the largest contributor of greenhouse gas (GHG) emission in Vietnam since 2010, accounting for 67%. Several emission sources of GHG could be found in a waste treatment facilities it came from (1) emission of methane (CH4, GWP 25) at landfill of mixed waste, (2) from emission of fossil carbon dioxide through the combustion of plastics and composites or supported fuels (auxiliary), and (3) from emission of nitrous oxide (NOx) during incineration/ pretreatment process, etc. 

Data for the calculation of N20 emission in pretreatment process was taken from references. The N20 emissions are converted to C02 equivalents by following formula (5). The average emission of N20 in RDF plant applying DSP method is considered 5.6 g/ton MSW, which result to the increasing of GHGs emission by 1.62 kg C02 eq./ton MSW [15],... 

In the same way, N20 emission in pretreatment process was calculated, whereas N2O emission in this combustion step was taken from references for German waste, it is estimated to be 3.41 kg C02 eq./ton RDF (GWPN20 = 298) [15]. 

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