Plants metal removal

Soil. The first reported field trial of the use of hyperaccumulating plants to remove metals from a soil contaminated by sludge appHcations has been reported (103). The results were positive, but the rates of metal uptake suggest a time scale of decades for complete cleanup. Trials with higher biomass plants, such as B.juncea, are underway at several chromium and lead contaminated sites (88), but data are not yet available. 

The total emissions of hazardous air pollutants from a CGCC plant having wet cleanup are expected to be at least an order of magnitude lower than those achievable from a modem coal-fired steam plant (41). Metals removal in hot-gas cleanup systems is still under development. 

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. 

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. 

The phytofiltration of Pb(II) and Cd(II) has been also studied using species of Salvinia. S. minima Baker is a small free-floating aquatic fern native to Mexico, Central America and South America. It has been proved to be an excellent aquatic phytoremediator and hyperaccumulator of Cd(II) and Pb(II).72,76 The relevance of using a compartmentalization analysis (CA) complementary to the use of BCFs and metal removal kinetics by plants has been demonstrated using S. minima... 

A discussion of the use of floating aquatic plants for metal removal at large scale in surface flow constructed wetlands (SFCWs) is provided below. 

Metal removal in SSFCWs has been recently focused on metal elimination from synthetic water and different wastewaters,66-86 on the evaluation of the effects of season, temperature, plant species, and chemical oxygen demand (COD) loading on metals removal,87 and on the accumulation of metals in wetland plant species and sediments.88-89 Recent reviews on heavy metal phytoremediation wetlands are also available.48... 

Dushenkov, V., Kumar, N.P.B. A., Motto, H., and Raskin, I., Rhizofiltration The use of plants to remove heavy metals from aqueous streams, Environmental Science and Technology, 29, 1239-1245, 1995. 

Removal rates have been consistent over the five-year period showing that removal is not concentration dependent (Tables 1 2). The overall percentages of metals removed remain high at close to 99% for all years. The system design allows sampling of two distinct compartments (ABRs) and the plant based treatment cells. Examining metal removal, it is apparent that much of the As, Cd and Zn are removed in the ABR cells (Table 2). Arsenic and Cd are removed at better than 95% in the two ARB cells, but Zn removal achieves only 88.7%. This table also shows occasional release of Zn and Cd from plant cells. 

Ozone has many industrial applications. It is a sterilizing and deodorizing agent. It is used for disinfection of filtered drinking water and to purify waste-waters. It also is used in water treatment plants for removal of metal impurities by oxidizing them into insoluble compounds. This removes undesired taste, odor, and color from the water. Ozone also is used for odor control. 

Table 1 presents a detailed breakont of the costs for the hypothetical treatment of 22,000 tons of contaminated soil using the soil recycle treatment train (D10059U, p. 21). The hypothetical case cost estimate is based on a fines content of 16.5%. The estimated cost per ton is sensitive to the percent of fines present. This occnrs becanse the metals removal and/or biological treatment capacity can limit the utilization rate of the wash plant (D10059U, p. 21). 

Microbial mat formation may also stimulate metal removal through sulfate reduction. Barnes, Scheeren Buisman (1994) have developed a process that specifically uses sulfate-reducing bacteria to treat metal-contaminated groundwater. In this process, as groundwater is pumped through the water treatment plant, sulfide produced by sulfate-reducing bacteria precipitates the metals in the water. Metal concentrations in the treated water were reportedly reduced to fig/l quantities and the water was suitable for release into the environment. 

Abatement by the California Regional Water Quality Control Board, Central Valley Region, has included ditches to divert surface water from the mine workings, a seal at the mine adit, and operation of a pilot mine wastewater treatment plant to remove residual toxic heavy metals as part of contingency planning. 

Solids separation in the settlement basin controlled the removal of metals in the pilot plant, because removal efficiency varied Inversely with flow rate at the roughly constant level of neutralization attained, e.s., Table 2 shows a 72% mean copper removal for the 28 gpm mean high flow, versus 93% mean removal at the mean 1.6 gpm swan low flow. On this basis, effluent copper varies with flow rate raised to the 0.33 power, because ... 

Vlyssides, A., Barampouti, E.M. and Mai, S. (2005) Heavy metal removal from water resources using the aquatic plant Apium nodiflorum. Communications in Soil Science and Plant Analysis, 36(7-8), 1075-81. 

One TOF supplier has found that pulp and paper mills are the most profitable (i.e., purchase the most expensive type of TDF) type of customer, followed by cement plants and utility boilers.8 Pulp and paper mills pay a higher price for TDF for several reasons. First, the pulp and paper mills demand a higher quality of shredded tire that is, tires that are clean and have all the metal removed.8 Second, they do not have the fuel-buying power that a utility might have thus, tires provide a proportionally larger economic incentive for them.8 One pulp and paper mill was paying approximately 39 and 43/ton for TDF in 1990 and in part of 1991, respectively.9... 

The test was in response to problems resulting from TDF burning in a FBC boiler retrofitted from a spreader/stoker design, and located at a Wisconsin power plant.16 Problems during the commercial test indicated that better tramp metal removal was necessary, combustion was not adequate, and that the particulate control device, an electrified filter bed, was not commensurate with the ash levels generated.16... 

Wetlands have the potential to remove metals from AD by metal adsorption on ferric oxyhydroxides, metal uptake by plant and algae, metal complexation by organic materials, and metal precipitation as oxides, oxyhydroxides, or sulfides. However, only metal precipitation as either oxides or sulfides has long-term metal-removal potential (Evangelou, 1995b). 

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