Oily materials may be classified according to their properties. Physically, light hydrocarbons or solvents, such as kerosene or gasoline, are less viscous and more volatile than heavy hydrocarbons like tars and residual fuel oils. Chemically, some materials are classed as aliphatic, i.e., straight or branched chain, saturated or unsaturated. Still others are classed as aromatic (unsaturated and with ring structure). They may have chemical functionality. Their structure may contain acid, carbonyl or other functional groups and have elements other than carbon, hydrogen and oxygen, such as nitrogen or sulfur.
Oily materials can be classified as to use, such as fuels, lubricants, coatings, cleaners, solvents, cutting and rolling fluids, hydraulic fluids, carriers, and cooking fats and oils. Many uses are both domestic and industrial. Light hydrocarbons and solvents are found in industrial waste streams, as a result of degreasing or extraction, cleaning, painting, and coating operations. Their vapors represent potential fire and explosion hazards, and their presence makes the removal of heavier oily materials more difficult. The pollution potential of all hydrocarbons is moderately high; however light hydrocarbons are more readily oxidized biologically than heavier fuels, tars, and residues. They are also a potential source of air pollution.
One of the principal industrial sources of oily wastes is the petroleum industry. Oily wastes result from producing, refining, storing, or transporting operations, or in the use of this industry's products. Another major oil source is the metals industry. Most oily wastes result from metalwork-ing or forming operations. Oily materials lubricate and cool instruments or the metals being worked. Emulsified oily materials and finely divided suspended solids make these wastes difficult to handle.
Coke plants generate much oily wastewater, most of which is derived from cooling, quenching coke, or scrubbing gases. Much of the contaminated water is reused or consumed elsewhere in the mill. The wastewater contains phenols, cresol, and related extractable materials. Phenolic-type extractable materials may also be found in water used to cool or wash cupola stack gases at foundries. In processing meat, fish and poultry, oily wastes are produced from cleaning, slaughtering, and processing by-products. A major source of oily wastes is the rendering process. Cooking plant tissues, seeds, grains, and nuts aids in extracting their oils for commercial purposes; cooking and extraction processes result in oily wastewaters.
Most oily wastes in the textile industry result from scouring fibers in an early process step, especially scouring wool. The waste liquor yields valuable lanolin, but the wastewater is also high in extractables and difficult to process.
Oily wastes in the transportation industry result from leaks, spills, or cleaning operations. Tankers, barges, and tank trucks transporting oily materials must be cleaned to prevent possible product contamination. The cleaning solutions contain oily materials and create pollution if discharged without treatment. Latex in wastewaters may be extractable. Latex in the rubber industry is generally removed from waste streams with little difficulty. However, in the paint industry the presence of solvents, resins, and emulsifiers can make removal very difficult.
Some oily materials are introduced into water systems during heating or cooling steps. Oily materials may be derived from leaks in seals, condensers, or heat exchangers from the process side of the equipment. When steam used for direct heating of fatty or oily products, the recovered condensate will likely be contaminated. Run-off from industrial areas following storms may be contaminated with oily materials. The rain washes processing units, walkways, buildings, and surrounding grounds, carrying away oily materials deposited there.
The major sources of oily wastes are from food preparation, garbage disposal, and cleaning. Cleaning includes laundry, car washing, and general cleaning jobs where water is the main solvent and carrier. Grease and oily materials are removed at sewage treatment plants. Road oil and degraded asphalt are washed from roads into storm sewers and streams. Rainwater also contains soot and various hydrocarbons washed from the faces of buildings and other structures in communities.
Coniferous trees and shrubs contribute oily materials to run-off water, particularly in areas wooded with pine trees.
DETECTION, IDENTIFICATION, AND SURVEYS
A survey of potential sources of oily materials is initiated with an inventory of known oily products or by-products used or produced in the area. Processes, machinery, and storage areas are checked for leaks, drips, and potential for spills or accidental contamination. Both cooling and condensate-return water are examined. Stack gases are tested for hydrocarbons and soot. Cleaning and wash-down procedures are observed; run-off water is tested and methods of handling the water noted; and potential problems from startup and shutdown of processes or equipment are probed. Field personnel should be familiar with each process, system, unit, and individual piece of equipment. In certain cases material balances are helpful.
Oil-soluble dyes help to check for leaks in complex systems or to locate oil-water interfaces. Ultraviolet light detects as little as 0.02 ppm of some oils by fluorescence in the dark. Dip sticks and sonic probes are useful to check for multiple layers in tanks and sumps. When an oily material is isolated, its source can often be identified by infrared analysis or gas chromatography. Analysis of trace metal content may also help indicate its source. Many oily materials are identified by their characteristic odor. More and more oily materials will be tagged1 for easier identification.
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