Pollutant and method
Efficiency (percentage of pollutant removed)
Oil and grease API-type separation
Carbon adsorption Flotation
Coagulation/sedimentation with iron, alum, or solid phase (bentonite, etc.) Suspended solids Mixed-media filtration Coagulation/sedimentation BOD and COD
Bioconversions (with final clarifier) Carbon adsorption Residual suspended solids
Up to 90% of free oils and greases. Variable on emulsified oil. Up to 95% of both free and emulsified oils. Without the addition of solid phase, alum, or iron, 7080% of both free and emulsified oil. With the addition of chemicals, 90%.
Up to 95% of free oils. Efficiency in removing emulsified oils unknown.
Up to 95% of free oil. Up to 90% of emulsified oil.
Sand or mixed-media filtration 50-95%
Ion exchange or reverse osmosis_Up to 90%_
flocculants was shown to overcome this problem. However, chemical coagulation and flocculation for settling may not prove to be very efficient for such wastewaters. Wastes containing emulsified oils can be clarified by coagulation, if the emulsion is broken through the addition of salts such as CaCl2, the coagulant of choice for soap and detergent manufacture wastewaters . Also, lime or other calcium chemicals have been used in the treatment of such wastes whose soapy constituents are precipitated as insoluble calcium soaps of fairly satisfactory flocculating ("hardness" scales) and settling properties. Treatment with CaCl2 can be used to remove practically all grease and suspended solids and a major part of the suspended BOD . Using carbon dioxide (carbonation) as an auxiliary precipitant reduces the amount of calcium chloride required and improves treatment efficiency. The sludge from CaCl2 treatment can be removed either by sedimentation or by dissolved air flotation [39,53-56]. For monitoring and control of chemical coagulation, flocculation, sedimentation and flotation processes, many analytical procedures and testing procedures have been developed [57-64].
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