Heavy-Metal Removal

Heavy Metals Removal. Heavy metals should be removed prior to biological treatment or use of other technologies which generate sludges to avoid comingling metal sludges with other, nonhazardous sludges. 

Table 12. Effluent Levels Achievable in Heavy Metal Removals...

Chemical Oxidation. Chemical oxidation can be appHed ia iadustrial wastewater pretreatment for reduction of toxicity, to oxidize metal complexes to enhance heavy metals removal from wastewaters, or as a posttreatment for toxicity reduction or priority pollutant removal. 

Effluents from both dye works and dyehouses are treated both before leaving the plant, eg, neutrali2ation of acidic and alkaline Hquors and heavy metal removal, and in municipal sewage works. Various treatments are used (34). 

O Heavy metal removal most treatment plants do not have special stages for metals but rely on oxygenation, coagulation and ion exchange in filters to remove them. Where metals persist, additional treatment would be needed. 

Biosorption is a process that utilizes biological materials as adsorbents [Volesky, 1994], and this method has been studied by several researchers as an alternative technique to conventional methods for heavy metal removal from wastewater. 

Granular bed filters are used in ten coil coating plants to remove residual solids from the clarifier effluent, and are considered to be tertiary or advanced wastewater treatment. Chemicals may be added upstream to enhance the solids removal. Pressure filtration is also used in this industry to reduce the solids concentration in clarifier effluent and to remove excess water from the clarifier sludge. Figure 7.4 shows a granular bed filter and Table 7.13 presents the heavy metal removal data of a lime clarification and filtration system. 

Miretzky, P., Saralegui, A., and Fernandez-Cirelli, P., Simultaneous heavy metal removal mechanism by dead macrophytes, Chemosphere, 62, 247-254, 2006. 

In a separate study, Igwe and Abia46 determined the equilibrium adsorption isotherms of Cd(II), Pb(II), and Zn(II) ions and detoxification of wastewater using unmodified and ethylenediamine tetraacetic acid (EDTA)-modified maize husks as a biosorbent. This study established that maize husks are excellent adsorbents for the removal of these metal ions, with the amount of metal ions adsorbed increasing as the initial concentrations increased. The study further established that EDTA modification of maize husks enhances the adsorption capacity of maize husks, which is attributed to the chelating ability of EDTA. Therefore, this study demonstrates that maize husks, which are generally considered as biomass waste, may be used as adsorbents for heavy metal removal from wastewater streams from various industries and would therefore find application in various parts of the world where development is closely tied to affordable cost as well as environmental cleanliness.46... 

Normally, treatment of coproduced groundwater during hydrocarbon recovery operations will include, as a minimum, oil-water separation and the removal of dissolved volatile hydrocarbon fractions (i.e., benzene, toluene, and total xylenes). In addition, removal of inorganic compounds and heavy metals (i.e., iron) is often required. Dissolved iron, a common dissolved constituent in groundwater, for example, may require treatment prior to downstream treatment processes to prevent fouling problems in air-stripping systems. Heavy metals removal is normally accomplished by chemical precipitation. 

Alternative 1 consists of preliminary treatment for heavy metals removal with the primary concern being iron removal (Figure 8.3). The levels of iron observed in the groundwater at this site would be very detrimental to the downstream treatment processes. This pretreated water would then be used for cooling tower makeup water followed by biological treatment. This approach would be the easiest and cheapest alternative. This combined process should provide effective removal of BTEX. 

Kempton S, Sterrit RM, Lester JN. 1987. Heavy metal removal in primary sedimentation. I. The influence of metal solubility. Sci Total Environ 63 231-247. 

T0235 Electrochemical Treatment of Contaminated Ground Water—General T0279 Environmental Research and Development, Inc., The Neutral Process for Heavy Metals Removal... 

T0207 Doe Run Company, TERRAMET Heavy-Metal Removal Technology... 

HPT Research, Inc., has developed the ionic state modification (ISM) process for the treatment of acid mine drainage (AMD). ISM is an ex situ treatment technology that uses magnets, electricity, and proprietary chemical to precipitate heavy metals, remove sulfate ions, and neutralize acidity from AMD and industrial wastewaters. The end products of the process are a metal hydroxide sludge, a calcium sulfate sludge, and treated liquid effluent. The vendor claims that the metal hydroxide sludge may have some value as an ore, the calcium sulfate may be used as an agricultural additive to soils, and the liquid effluent is free of metal contamination and has low sulfate concentrations. 

Nanofiltration membranes usually have good rejections of organic compounds having molecular weights above 200—500 (114,115). NF provides the possibility of selective separation of certain organics from concentrated monovalent salt solutions such as NaCl. The most important nanofiltration membranes are composite membranes made by interfacial polymerization. Polyamides made from piperazine and aromatic acyl chlorides are examples of widely used nanofiltration membrane. Nanofiltration has been used in several commercial applications, among which are demineralization, oiganic removal, heavy-metal removal, and color removal (116). 

Iron (III) hydroxide waste Especially for heavy metals removal from wastewater, iron (III) hydroxide waste and waste slurry from the fertilizer industry, xanthate, rice husk, carbon, and coconut shell have been studied and can be considered as alternatives. 

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