In another publication, Stephenson and Duff reported significant reduction in the toxicity of wastewaters subsequent to the chemical coagulation process. ![]() They observed removal of 88% of total carbon and 90-98% of color and turbidity from mechanical pulping effluents using Fe3+/Al3+ salts. Dissolved organics are also removed by physical adsorption to flocs.Ĭhemical precipitation of mill effluents from CTMP, BKME (bleached Kraft mill effluent), NSSC, E & C bleach discharges have been extensively studied by Stephenson and Duff using alum, lime, ferric chloride, ferrous sulfate, magnesium hydroxide, polyimine, polymers, and alum in combination with lime. Hydrogen bonding, electrostatic and surface interactions (adsorption) between the metal hydroxides and organic anions (containing hydroxyl and carboxyl groups) lead to the formation of metal hydroxide-organic compound precipitates. Typically, these trivalent cations remain in solution at acidic pH and form metal hydroxides that aggregate rapidly at higher pH conditions. Almost all of these toxic compounds can be effectively removed through coagulation using chloride and sulfate salts of Fe3+ and Al3+. The not-so-easily biodegradable fraction of pulping and bleaching effluents consists of polar and hydrophobic compounds, notably resin acids, long-chain fatty acids, aromatic acids and phenols, lignin, and terpenes. The effectiveness of this process is dependent upon the nature of coagulating agent, coagulant dosage, pH, ionic strength, and the nature and concentration of compounds present in wastewaters. ![]() This method relies on the addition of metal salts to cause agglomeration of small particles into larger flocs that can be easily removed by settling.
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