Cadmium wastewater pollutants

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

The pollutants of concern are the same as in wet basic oxygen furnaces, but the concentration of metals (primarily lead and zinc, but also arsenic, cadmium, copper, chromium, and selenium) in wastewater is higher because of the higher percentage of scrap charged. Wastewater treatment operations are similar to those for the wet basic oxygen furnaces, including sedimentation in clarifiers or thickeners and recycle of the water.14... 

Wastewater is generated in the primary zinc and primary cadmium recovery subcategories by acid plant blowdown, which results from sulfuric acid recovery, air pollution control, leaching, anode/ cathode washing, and contact cooling. The streams may contain significant concentrations of lead, arsenic, cadmium, and zinc. Tables 3.26 and 3.27 present classical and toxic pollutant data for the primary zinc and primary cadmium subcategories. 

Concentrations of Classical Pollutants in the Raw Wastewater of the Primary Zinc and Cadmium Subcategories... 

Many toxic pollutants were detected in the process wastewaters from metal molding and casting processes. The toxic pollutants detected most frequently in concentrations at or above 0.1 mg/L were phenolic compounds and heavy metals. The pollutants include 2,4,6-trichlorophenol, 2,4-dimethyl-phenol, phenol, 2-ethylhexyl, cadmium, chromium, copper, lead, nickel, and zinc. Each type of operation in the foundry industry can produce different types of pollutants in the wastewater stream. Also, because each subcategory operation often involves different processes, pollutant concentrations per casting metals may vary. 

Prominent among the heavy metals found in the wastewater generated in the copper sulfate industry are copper, arsenic, cadmium, nickel, antimony, lead, chromium, and zinc (Table 22.11). They are traced to the copper and acids sources used as raw materials. These pollutants are generally removed by precipitation, clarification, gravity separation, centrifugation, and filtration. Alkaline precipitation at pH values between 7 and 10 can eradicate copper, nickel, cadmium, and zinc in the wastewater, while the quantity of arsenic can be reduced through the same process at a higher pH value. 

As was indicated in the previous section, the concentration of iron in the mixed wastewaters ranged from 5980 to 6100 mg/L its pH was 0.7 and zinc concentration was 15 pg/L. Since these wastewaters come only from acid baths and not from other processes of the plant, parameters such as cadmium and fluoride are not encountered. The discharge standards for the metal industry effluents set by the Turkish Water Pollution Control Regulation (Official Gazette, Table 15.7, September 4, 1988) are shown in Table 28.10.1... 

Lee K.W., Keeney D.R. Cadmium and zinc additions to Wisconsin soils by commercial fertilizers and wastewater sludge application. Water Air Soil Pollut 1975 5 109-112. 

In the pesticide industry, metals are used principally as catalysts or as raw materials that are incorporated into the active ingredients, for example, metallo-organic pesticides. Priority pollutant metals commonly incorporated into metallo-organic pesticides include arsenic, cadmium, copper, and mercury. For metals not incorporated into the active ingredients, copper is found or suspected in wastewaters from at least eight pesticides, where it is used as a raw material or catalyst zinc becomes part of the technical grade pesticide in seven processes and mercury is used as a catalyst in one pesticide process. Nonpriority pollutant metals such as manganese and tin are also used in pesticide processes. 

The USEPA is responsible for creating and enforcing the NESHAPs for all hazardous air pollutant sources. The CAA states that new or existing major sources must have emission standards based on the maximum available control technology (M ACT) to reduce hazardous air pollutant emissions. The MACT standards are based on the performance of the best 12% of the control devices in the same source category. These MACT emissions requirements were extended in 1997 to cover wastewater biosolid incinerators at publicly owned treatment works (POTWs) that have the potential to discharge cadmium, lead, and mercury (Richman, 1997). 

Gas and liquid emissions and mine tailing are the principal pollution sources sulfur dioxide release, particulate, diffused dust, cooling wastewater, ash production, fluorine, lead, cadmium and zinc emissions. 

Legislative directives are becoming the primary drivers of industrial and municipal water treatments, for example the implementation of the Integrated Pollution and Preventative Control Directive. This has placed an increased pressure on the industry in order to improve the wastewater treatments. The European Union is forcing tighter standards, whilst the USA introduces new ambient standards limiting particulate less than 2.5 microns in diameter. There are also standards around the world which require reduction of mercury, cadmium, lead, and other toxic metals. It is noted that fabric filters are superior to other air pollution devices in removing these compounds. "... 

Sudha, P.N., Celine, S., and Jayapriya, S. 2008. Removal of heavy metal cadmium from industrial wastewater using chitosan coated coconut charcoal. Nat. Environ. Pollut. Technol. 6(3) 421 24. 

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