Heavy metals in waste waters

Lester JN. 1983. Significance and behavior of heavy metals in waste water treatment processes 1. Sewage treatment and effluent discharge. Sci Total Environ 30 1-44. 

Mahanti HS. 1990. Concentration and spectrochemical determination of trace heavy metals in waste water. Res Indust 35 124-126. 

Schalscha, E. G., Marlaes, M., Vergara, I., and Chang, A. C. (1982). Chemical fractionation of heavy metals in waste-water affected soils. J. Water Pollut. Control Fed. 54, 175-180. 

It is highly water soluble and quickly eliminated with urine when ingested. It has a low acute toxicity, and no chronic effects have been shown for plausible doses. However, concern does exist over its interaction with heavy metals in waste treatment processes and in the environment. 

Sulffde Precipitants. The removal of heavy metals from waste waters using soluble sulfides has been studied extensively. Peters and Ku (13) showed that pH strongly affects the removal of heavy metal sulfides from waste water. Their data showed that the solubilities of most heavy metal sulfides, other than arsenic (HI) sulfide, decreases up to about pH 9. Since most phosphate fluid fertilizers, such as 10-34-0 and 11-37-0, have a pH in the range of 6 to 7, these data indicate that concentrations of several heavy metals in phosphate fluid fertilizers could be reduced to very low levels by precipitation with inorganic sulfide reagents. The use of soluble sulfides to precipitate heavy metals from WPA has also been reported. Both Maruyama (14) and Berglund (15) have... 

WI Starch Xanthate. Research by Wing and others (22, 27-29) has shown that water-soluble (WS) starch xanthates, in combination with cationic polymers to form polyelectrolyte complexes, can effectively remove heavy metals from waste water. To eliminate the expensive cationic polymer and give a more economical method of heavy metal removal, further research by Wing and others (12,30-33) showed that xanthation of a highly crosslinked starch yields a water-insoluble (WI) product that is effective in removing heavy metals from waste water without the need for a cationic polymer. In more recent work, Tare and Chaudhari (34) evaluated the effectiveness of the starch xanthate (WS and WI) process for removal of hexavalent chromium from synthetic waste waters. 

Despite concerns about Cd, Hg, and Cr in soils, the soil is still a far safer medium for the disposal of pollutant wastes than any other part of the environment. Soils are better able to oxidize (the oxidized state is generally the least toxic state), to retain pollutants safely, and to remove them from the food web, than air or water. For example, the increase in toxic metal concentration in plants is about one-half to one-tenth of the corresponding concentration increase in soils. Assuming a total dry matter crop production of 10 000 kg ha ] and a soil bulk density of 1.3, adding the high amount of 130 kg ha-1 of a heavy metal in wastes to the surface meter of soil (a mass of 1 300 000 kg ha-1 m-1) increases the element s concentration in the first crop by about 1 mg kg-1 or 10 g ha-1, and that concentration and amount decreases with time. The amount in the harvested portion of the plant is much less than that in the total plant. 

Heavy metal ions are perhaps the most common of all water pollutants. The heavy metals include such frequendy encountered elements as lead and mercury, as well as many less common ones like cadmium, chromium, nickel, and copper. These metals can, at times, be acutely toxic, causing immediate symptoms, but often they are chronically toxic in very small quantities. Chronic toxicity is characterized by nagging symptoms that lessen normal body functions. Inadequate disposal of wastes from mining or industrial activities causes these metals to find their way into water supplies. In addition, some farming activities and the disposal of household wastes can contribute to the presence of heavy metals in our water supplies. 

Guan et al. (2009) removed trivalent chromium ions from waste water using synthetic zeolites. It was observed that zeolite can selectively adsorb chromium even in the presence of other alkali and alkaline earth metal cations including sodium and potassium. Xie et al. (2012) stated that if zeolites are modified with chitosan by forming a monolayer of chitosan on zeolite surface their adsorption capacities increases and they can preferentially adsorb phosphorous along with many other heavy metals from waste water. It was attributed to the increased porous structure of zeolites and non-zeolite fraction of different oxides. Monolayer of chitosan acted as binding material for adsorption of different heavy metal ions. 

Interactions studies between some divalents metal ions and pectins from citms and sugar-beet revealed that the chemical structure of the latter, namely the presence of acetyl functions, induces differences of binding process whereas the scale of selectivity was not affected. Some further studies could be carried out on the correlation between the binding mode and the degree of acetylation. Lastly, pectins showed a clear scale of selectivity towards heavy metals with high capacities of binding which make them suitable to be used in waste-waters depollution. 

The zone elution method has been used for quantitative estimation or recovery of heavy metals in plants and vegetable juices [29], mercury (11) in river and waste waters [52], zinc in different environmental samples [46], nickel and copper in alloys [53], zirconium in Mg-Al alloys [22], cobalt, zinc, nickel, and copper in natural water and alloy samples [54], thiocyanate in spiked photogenic waste water [55], and aluminum in bauxite ores [42],... 

Chemical remediation refers to the application of various minerals or chemicals to adsorb, bind, precipitate or co-precipitate trace elements and heavy metals in soils and waters thereby reducing their bioavailability, toxicity, and mobility. In situ immobilization refers to the treatment of contaminants in place without having to excavate the soils or waste, often resulting in substantial cost savings. However, in situ immobilization or extraction by these physicochemical techniques can be expensive and are often only appropriate for small areas where rapid and complete decontamination is required. 

Clevenger T.E. Use of sequential extraction to evaluate the heavy metals in mining wastes. Water Air Soil Pollut 1990 50 241-254. 

Sorption can significantly diminish the mobility of certain dissolved components in solution, especially those present in minor amounts. Sorption, for example, may retard the spread of radionuclides near a radioactive waste repository or the migration of contaminants away from a polluting landfill (see Chapters 21 and 32). In acid mine drainages, ferric oxide sorbs heavy metals from surface water, helping limit their downstream movement (see Chapter 31). A geochemical model useful in investigating such cases must provide an accurate assessment of the effects of surface reactions. 

In the past twenty years many legal provisions have been created to regulate substance flows (recycling management systems, waste management, electrical and automotive recycling). In many instances these laws exphcitly contain threshold values for certain substances or even ban certain substances. They are thus very effective on the use of these substances in production processes. This is also tme for threshold values of chlorinated compounds in industrial waste, the ban on certain heavy metals in the automotive industry and substance-related requirements for waste water from the textile industry (Annexe 38 of Waste Water Ordinance ). 

The WES-PHix process is designed to chemically stabilize ash from municipal solid waste combustion. This technology reduces the solubility of certain heavy metals in ash through the addition of soluble phosphate, lime, and water. The addition of these reagents to ash promotes... 

The Unipnre Environmental, Unipnre process technology is a unique iron co-precipitation method for removal of heavy metals from waste streams or groundwater. It can act as a primary metal-removal system or as a polishing step to an existing treatment system. The reactor mod-nle replaces the nentrahzation tank in a conventional wastewater treatment system. The process prodnces solids that are extremely insolnble in water and mild acid solutions. 

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