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Membrane Technologies for Oil–Water Separation 641
from gas production operations generally contains higher levels of Benzene, Toluene, Ethylbenzene,
and Xylene (BTEX) than those generated from oil production (4). Chapelle et al. (5)
has reported that relatively water soluble light aromatics of BTEX comprise only 2–3% of
most crude oils as a whole. Stephenson (6) reported mean concentrations of benzene ranging
from 5.8 to 12.2 mg/L and 1.3 to 8.7 mg/L for gas and oil production, respectively.
Other major source of oily wastewater is food processing industry. Oily and fatty materials
are produced mainly from slaughtering, cleaning, and by-product processing (1). The oily
vegetable extraction is also the source of oily waste. Ahmad et al. have reported oil and grease
concentrations from palm oil processing, which produced as high as 4,000 mg/L of oil
resulting in high biochemical oxygen demand (BOD) and chemical oxygen demand (COD)
contents.
In general, oily wastewater found in the industry comes from many sources including floor
wash, machine coolants, alkaline/acid cleaners, and spills from manufacturing process as
shown in Table 15.3. Nature of oily wastewater is varied due to their production source. Oil
from spill is mainly free and emulsified oils, while oil from alkaline and acid cleaning process
is normally highly emulsified due to presence of surfactants. Mixtures of various types of oil
could be found in wastewater generated from floor wash. These oily wastewaters can be
present in both free and emulsified forms stabilized by dirt, debris, and solvents. Oils from
petroleum refining or oil from drilling activity are frequently found in both free and emulsified
oils making it more difficult in later oily–water separation process.
Table 15.3
Sources of oily wastes from industries
Source Industries Nature
Alkaline and acid Metal fabrication, iron and steel, metal Normally highly emulsified due to
cleaners
finishing, industrial laundries surfactants; difficult to treat
Floor washes All industries Mixture of various types of oils from
spills of hydraulic and cutting fluids,
oil mists from spraying/coating, etc.;
Can be present in both free and
emulsified forms stabilized by dirt
and debris, and solvents
Machine coolants Metals manufacturing, machining Normally emulsified and difficult to
Vegetable and
animal fats
splitting, refining,
rendering
Edible oil, detergent manufacture, fish
processing, textile (wool scouring),
leather (hide processing), tank car
washing
treat
Both free and emulsified oils;
difficulty of treatment varies
Petroleum oils Petroleum refining, petroleum drilling Both free and emulsified oils;
difficulty of treatment varies
Adapted from Cheryan and Rajagopolan (7).