Leachate reactions

The most important leachate reactions are dissolution and precipitation of solids and minerals, redox (reduction/oxidation) reactions with organic matter, and ion exchange and sorption on clay minerals and organic matter. 

Good bed drainage characteristics are necessary to ensure that reaction products are easily transported out of the filter media. The leachate is generally recycled through the humidification process to reduce the wastewater stream. 

The harmful liquid that collects at the bottom of a landfill is known as leachate. The generation of leachate is a result of uncontrolled runoff, and percolation of precipitation and irrigation water into the landfill. Leachate can also include the moisture content initially contained in the waste, as well as infiltrating groundwater. Leachate contains a variety of chemical constituents derived from the solubilization of the materials deposited in the landfill and from the products of the chemical and biochemical reactions occurring within the landfill under the anaerobic conditions. 

Fortuitous or co-metabolic biodegradation may account for a significant portion of the removal of xenobiotics in the environment.24 Numerous examples of co-metabolic activity have been described for pure substrates,22 but co-metabolism has been very difficult to demonstrate in mixed-substrate, mixed-culture systems, because products of the co-metabolic reactions of one species may be degraded by another.24 To encourage co-metabolism, easily degradable co-substrates should be included in the leachate prior to biological treatment. Fatty acids, which often occur in landfill leachates, may fulfill this requirement. 

Understanding the basic hydraulic mechanisms for synthetic liners and clay liners is very important in appreciating the advantages of a composite liner. Clay liners are controlled by Darcy s law (Q = kiA). In clay liners, the factors that most influence liner performance are hydraulic head and soil permeability. Clay liners have a higher hydraulic conductivity and thickness than do synthetic liners. Additionally, leachate leaking through a clay liner will undergo chemical reactions that reduce the concentration of contaminants in the leachate. 

The most likely mineral phases to oxidize under the kinetic testing conditions are the sulfides. Acidity generated from their oxidation is likely to react with calcite and to a lesser extent magnesite. Talc minerals are unlikely to react with leachate. Expected reactions are therefore of the forms ... 

Reactions between Fe(ll) in contaminated groundwater (5.8 mg/L) and oxic sediment also affected As mobility. Ferrous iron was oxidized by manganese oxides to ferric iron which precipitated as hydrous ferric oxide, creating additional sorption sites. Evidence for this reaction included an increase in ferric oxide concentrations in reacted column sediments and manganese concentrations in leachate that were greater than in the initial eluent. 

Precipitation inhibitors, dispersants contrasted, 3 686 Precipitation leachate procedure, synthetic, 25 868-869 Precipitation reactions, for niobium and tantalum determination, 27 142-143 Precipitation reagents, protein, 22 133 Precipitation with compressed antisolvent (PCA) process, 24 17, 18 Precipitator dust, in phosphorus manufacture, 19 12 Precipitators, electrostatic, 23 180 Precision agriculture, 23 328 26 269-270 Precision measurement techniques, noble gases in, 27 370 Precision scales, 26 245 Preconcentration, of uranium ores, 25 401 Pre-crosslinked polychloroprene grades, 19 852... 

The processes controlling transfer and/or removal of pollutants at the aqueous-solid phase interface occur as a result of interactions between chemically reactive groups present in the principal pollutant constituents and other chemical, physical and biological interaction sites on solid surfaces [1]. Studies of these processes have been investigated by various groups (e.g., [6-14]). Several workers indicate that the interactions between the organic pollutants/ SWM leachates at the aqueous-solid phase surfaces involve chemical, electrochemical, and physico-chemical forces, and that these can be studied in detail using both chemical reaction kinetics and electrochemical models [15-28]. 

Aboul-Kassim [1] studied the characterization, chemodynamics, and environmental impact assessment of organic leachates from complex mixtures. He reported that an important factor in controlling the rate of solid phase adsorption reactions is the type and quantity of solid phase components as well as the time period (i. e., short vs long) over which the organic contaminant has been in contact with the solid phase. 

The relationship between the solution concentrations in the fly ash leachates and specific chemical reactions in waste/water system has been... 

Fig. 1. Schematic diagram showing major pathways, reactions and stable weathering products for CCB alteration. Heavy solid arrow indicates changes caused by progressive natural weathering of alkaline CCBs at high L/S (liquid/ solid) ratios. Heavy dashed arrow indicates changes caused by progressive alteration of CCBs by acidic leachate solutions at low L/S ratios.

Because you are more interested in groundwater contamination, you wonder how fast TMP would be transformed by chemical reactions at 10°C and pH 8.0 in a leachate from a waste disposal site containing 0.25 M Cl, 0.05 M Br", and 10-4 M CbT. Calculate the approximate half-life of TMP under these conditions by trusting your colleague s measurements and by assuming that all relevant reactions exhibit about the same activation energy of 95 kJ-mol"1. Also assume an s-value of 0.9 in the Swain-Scott relationship (Eq. 13-3). 

The next phase of the experiment was the determination of the kinetics involved in the metal-binding reactions within the CHEMFIX product matrix. Eight (8) samples of each SSM were treated by the CHEMFIX process at the optimum reagent ratio. A TCLP extraction was performed 0, 1, 3, 5, 8, 24, 48 and 72 hours after treatment. The TCLP leachate from each sample was analyzed for target metals concentration. 

Kaulbach R (1996) Ozone technology for waste water treatment AOX and COD removal from landfill leachates with ozone and Radical Reactions in Clausthaler Umwelt-Akademie Oxidation of Water and Wastewater, Vogelpohl A (Hrsg.), Goslar 20.-22. Mai. 

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