Surface waters, heavy metals

E. Alonso, A. Santos, M. Callejon, and J.C. Jimenez. Speciation as a screening tool for the determination of heavy metal surface water pollution in the Guadiamar river basin. Chemo-... 

Muramoto S and Oki Y (1984) Influence of anionic surface-active agents on the uptake of heavy metals by water hyacinth (Eichomia crassipes). Bull Environ Contam Toxicol 33 444-450. 

The non-biodegradable water soluble heavy metals are either oxidized or reduced by the microorganisms and produce less soluble species. The less soluble form of these metals which are formed due to microbial reactions are adsorbed or precipitated/co-precipitated on the surface of the adsorbent and the extra cellular protein of the microorganisms in the biolayer (Srivastava and Majumder, 2008 Vails and Lorenzo, 2002). The methylation of metals is also another important route for bioremediation of heavy metals in water (White et al, 1997). Though the microbial action on metal ion transformation is still a matter of research, it is assumed that there are two paths. In one path oxidation or reduction of heavy metal ions takes place by extra cellular enzymes where the metal ions do not enter into the bacterial cell. In the other path the metal ions are transported into the microbial cells by trans-membrane proteins and are converted to other less soluble forms by metabolic actions of enzymes in the cells followed by subsequent excretion from the cells, yet both the paths are plasmid mediated (Vails and Lorenzo, 2002). Whether the microbial action on a metal ion is performed by only one path or by both the paths is a matter of research. 

Chelant Control. Chelants are the prime additives in a solubilizing boiler water treatment program. Chelants have the abihty to complex many cations (hardness and heavy metals under boiler water conditions). They accomplish this by locking metals into a soluble organic ring stmcture. The chelated cations do not deposit in the boiler. When apphed with a dispersant, chelants produce clean waterside surfaces. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Effective metal ion adsorbent has been prepai ed by the immobilization of propylthioethyleamine ligand onto the surface of silica gel (SN-SiO,).The effectiveness of this material to bind metal ions has been attributed to the complexation chemistry between the ligand and the metal. We are investigating properties of propylthioethyleamine grafted on the surface of silica and possibility of application of the obtained surface for preconcentration of heavy metals such as zinc, lead, cadmium, copper, etc. from water solutions. 

In natural conditions, Ceratophyllum demersum and Potamogeton pectinatus L. have been found to be effective adsorbents of Cd(II), Cu(II), and Pb(II). The adsorption percentage of the metals onto plant surfaces followed the pattern Pb(II) > Cu(II) > Cd(II). P. pectinatus biomass adsorbed a higher content of heavy metals than C. demersum. According to the results, both species are of interest in the phytoremediation and biomonitoring studies of polluted waters.122... 

In landfills, heavy metals have the potential to leach slowly into soil, groundwater, or surface water. Dry cell batteries contribute about 88% of the total mercury and 50% of the cadmium in the MSW stream. In the past, household batteries accounted for nearly half of the mercury used in the United States and over half of the mercury and cadmium in the MSW stream. When burned, some heavy metals such as mercury may vaporize and escape into the air, and cadmium and lead may end up in the ash. 

To summarize, the use of heavy water as a deuterium source has provided a wealth of experimental information. Evidence for the associative ir-adsorption of benzene [species (I) J is secure (2). Evidence for hydrogen exchange in the benzene ring by an abstraction-addition mechanism is less well established, partly because of uncertainties that surround the mode of chemisorption and reaction of water at metal surfaces. Nevertheless, it would be wrong to deny that Scheme 6 is consistent with a large body of experimental work. 

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