Oily water clarification

In oil-containing aqueous effluents the oil is present as finely dispersed droplets in a relatively clean water phase, for example oilfield produced water, refinery process water, ballast water from cargo tankers [32]. Factors preventing coalescence include the droplet s negative electrostatic charge, stabilisation by surface active components and steric stability caused by fine solids. 

Further benefits can be obtained by the use of high molecular weight cationic acrylamide copolymers that build up aggregate size and offer shear resistance to breakdown. 

These custom oil/water separators are designed per American Petroleum Institute standards (API) for above and below ground installations. Prefabricated assemblies are available up to 14-ft wide by 140 ft long [33,34]. 

Polyelectrolytes may be used to assist solid-liquid separation at the primary and secondary stages. A high molecular weight, medium copolymer ratio cationic polyacrylamide can be used on its own as a flocculant to improve removal of suspended solids and thus increase the efficiency of the settlement basins. More advanced chemical treatment can be carried out at the primary stage to assist removal of colloidal and some dissolved organics 

Inlet works Primary settlement Biological treatment Secondary settlement 

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Precipitation occurs simultaneously with the use of inorganic coagulants (iron and aluminum salts) during clarification of surface water and physicochemical treatment of oily water. 

In surface water clarification, the added FeClj, 6H2O can be 25 to 50 mg l h Doses two to three times greater are involved in flocculating oily emulsions. From 1 to 6° of alkalinity can be "consumed" in this case and die pH must be kept neutral. 

The technique then developed greatly for use in clarification of turbid or waste water thanks to the manufacture of one-piece plastic plate packages. Interest in applying lamellar separation to oily water was immediately revived. 

At the secondary settler outlet, the water undergoes further clarification. Twenty per cent of the flow goes into the flocculator-setcler (AP and polymer) and 80% goes into the oily water flotation cell. The main reagent consumed is H2SO4 (98%) 5500 t-y-i. 

Palm oil is the pulp oil extracted promptly after harvesting from the fleshy mesocarp of the oil palm fruit using continuous screw presses. The liquid coming from the press is a mixture of oil, water and non-oily solids (NOS). After separation from sludge in a setthng tank, clarification, purification and vacuum drying, crude pahn oil (CPO) is yielded from the press liquid. 

Abcor (now a division of Koch Industries) installed the first industrial ultrafiltration plant to recover electrocoat paint from automobile paint shop rinse water in 1969. Shortly afterwards, systems were installed in the food industry for protein separation from milk whey and for apple juice clarification. The separation of oil emulsions from effluent wastewaters has also become a significant application. The current ultrafiltration market is approximately US 200 million/ year, but because the market is very fragmented no individual end-use segment is more than US 10-30 million/year. In the chemical and refining industries, the principal application of ultrafiltration is the treatment of oily wastewater. 

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