Chemical treatment, wastewater

Primary or pretreatment of wastewater prior to biological treatment involves both physical and chemical treatment depending on the nature of the emission. 

Models typically range from 10 to over 1000 square feet of effective flotation area for raw wastewater flows to over 1000 gallons per minute. Complete systems often include chemical treatment processes. A dissolved air... 

Conventional wastewater treatment techniques consist of physical/chemical treatments, including oil separation, dissolved gas flotation, and ammonia distillation (for removal of free cyanides, free sulfides, and ammonia) followed by biological treatment (for organics removal) and residual ammonia nitrification. Almost all residuals from coke-making operations are either recovered as crude byproducts (e.g., as crude coal tar, crude light oil, ammonium sulfate, or other sulfur compounds)... 

Various treatment technologies are used at the iron and steel plant for recycle system water treatment prior to recycle and reuse, or end-of-pipe wastewater treatment prior to discharge to surface water or a POTW. The physical/chemical treatment technologies extensively used include equalization, tar removal, free and fixed ammonia stripping, cooling technologies, cyanide treatment technologies,... 

Thirty plants in the aluminum forming industry use etch or cleaning lines. Rinsing is usually required following successive chemical treatments within these etch or cleaning lines. Wastewater discharge values tend to increase as the number of rinses increase. Table 5.11 summarizes the classical and toxic pollutant data for etch line rinses. 

Chemical treatment of chromium wastewater is usually conducted in two steps. In the first step hexavalent chromium is reduced to trivalent chromium by the use of a chemical reducing agent. The trivalent chromium is precipitated during the second stage of treatment.15... 

This treatment process involves the use of chemical compounds to initiate a chemical reaction in the wastewater stream, which ends up neutralizing negatively charged colloids and thus, causing changes that would alter the nature of the wastewater, particularly to conform to the standard of wastewater discharge.4 The treatment process possesses an inherent disadvantage, especially net increase in the dissolved constituents of the wastewater, which can hinder reuse of the wastewater.2 Common chemical treatment processes are discussed below. 

Toxic pollutants found in the mercury cell wastewater stream include mercury and some heavy metals like chromium and others stated in Table 22.8, some of them are corrosion products of reactions between chlorine and the plant materials of construction. Virtually, most of these pollutants are generally removed by sulfide precipitation followed by settling or filtration. Prior to treatment, sodium hydrosulfide is used to precipitate mercury sulfide, which is removed through filtration process in the wastewater stream. The tail gas scrubber water is often recycled as brine make-up water. Reduction, adsorption on activated carbon, ion exchange, and some chemical treatments are some of the processes employed in the treatment of wastewater in this cell. Sodium salts such as sodium bisulfite, sodium hydrosulfite, sodium sulfide, and sodium borohydride are also employed in the treatment of the wastewater in this cell28 (Figure 22.5). 

With respect to physical/chemical treatment processes for industrial wastewater we can expect the following innovative developments11,16 17,19,20,... 

In many production processes the process water is used at a relatively high temperature. Also the wastewater which comes free may have an elevated temperature. To treat this wastewater with standard physical/chemical treatment processes at present this wastewater is cooled down to ambient temperatures. In case the treated water can be reused as process water it would be more efficient if the wastewater could be treated at higher temperatures, for example at 60 to 80 °C. However experience with the use of physical/chemical processes in this temperature range is lacking. It can be expected that in future more attention will be paid to this knowledge... 

Very often the use of process water and/or the treatment of wastewater requires the use of inorganic or organic additives. Sometimes these additives have to be considered later on as pollutants, sometimes as compounds of which the concentration in the process water should not be too high. It is therefor not allowed that the concentration of these additives exceeds a maximal admissible value. This means that in case of a continuous closed loop system, the physical/chemical treatment step has to remove an amount of these compounds corresponding to the amount of these compounds added elsewhere in the closed loop water system, minus the amount consumed in the production process. Often the consequence is that only relatively low removal efficiency in the treatment step is necessary. 

Sineero, AP Sincere, GA. Physical-Chemical Treatment of Water and Wastewater. New York CRC Press, IWA Publishing 2003. 

In any case the wastewater will finally be fed into rivers, lakes, or the sea thus some wastewater treatments have to be performed before the textile effluents are released either to the communal wastewater treatment plant (CWWT) or into the rivers, lakes, and so on. Normally physical and (bio-) chemical treatments (e.g., adjustment of pH, temperature, sedimentation, flocculation) are performed in the textile plant, while the following biological treatment (aerobic, anaerobic degradation) is performed either in the textile plant or in a CWWT. The site of the biological treatment is dependent on the location of the textile plant however, a biological treatment of textile effluents preceding release into surface water is state of the art. 

Met-Chem (formerly Metal Kleen, L.L.C.) is the U.S. hcensee of Metal Kleen A (MCA), a patented chemical treatment for removal of heavy metals from wastewater, flue gas, soils, and... 

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