Early process control can reduce the quantity of treatable waste. Segregation as a part of early control can simplify treatment processes. The presence of emulsifiers, wetting agents, soaps, deflocculants, and dispersants, as well as finely divided suspended solids, makes separation of oily materials and the treatment of wastes more difficult. Advantages can be realized from high temperatures and low pH levels, and the presence of substances that make necessary pH adjustments impractical may be avoided.
Control at the source may reduce raw material and product losses. Oily materials recovered downstream in a treatment plant are usually more contaminated and require more costly refining for reuse. The ability of one process over another to produce less oily or more easily handled wastes must be considered in initial planning, along with plant site selection, availability of suitable raw materials, labor, product markets, utilities, transportation, and wa
1. A tag substance is any material not normally found in oils, which will stay with the oily phase and be detectable in low concentrations. Such substances can be dyes, radioactive materials or, if there are no other sources of lead in the process, lead.
ter supply. Questions concerning waste treatment methods and facilities must be thoroughly examined. Plant layout must be the best compromise between efficient production, storage of materials, and segregation, collection, and treatment of wastes.
In selecting plant equipment, pollution potential should be considered in addition to cost, performance, and service life. Raw materials, processing aids, and cleaners should be selected to simplify oily waste treatment problems. Cleaners containing oils or solvents that might end up in waste streams should be avoided. Materials that form difficult-to-break emulsions should be avoided. Impurities in raw materials can add to oily waste problems, yielding bottoms, tailings, or unusable by-products from production. Poor quality raw materials may lead to off-spec finished products, which must be wasted, blended off, or sold at lower profit. If an oily waste or used solvent cannot be reused, it may be taken by a jobber for re-refining or by a scavenger. Finally, it may be burned, perhaps recovering its heating value. In general, wastes containing high concentrations of oily materials should not be discharged to lagoons or through deep well disposal.
Often oily materials recovered early in a process can be reused following a simple cleanup step such as filtration. At other times it may be necessary to reconstitute the oily product by reblending certain components depleted in use or during re-refining. This service is also offered by some suppliers or jobbers.
One of the most important factors in preventing or reducing oily wastes is housekeeping and maintenance. Good practices are largely a matter of adequate planning, training, and followup. Employees need to know the accepted practices in handling each oily waste. Regular inspections of operations must be made. Procedures should be reviewed on a regular basis for possible revision. A good preventative maintenance program will do much to prevent accidental losses. Safe procedures for special emergencies should be developed, particularly for handling sudden releases of large quantities of oily materials. Proper plant design and layout helps, but specialized equipment may be required and employees must know how to use it.
Improved recovery and re-refining methods for oily materials should increase their reuse, and attention should be given to developing useful by-products from oily wastes. The food industry already uses some waste fats and oils in animal feeds, and the pulping industry recovers useful tall oil which was once wasted with black liquor.
Improved methods of cleaning tanks and vessels are greatly needed. More efficient use of dry cleaning techniques should be employed. Cleaning solutions should be kept segregated and renovated or fortified for reuse wherever possible. The dry-cleaning industry has learned this in the reuse of its cleaning fluids. Disposable tank liners or inserts should find use in some instances; ultrasonic cleaning techniques might help reduce the volume of cleaning wastes.
Finally, there is a continuing need for simple, rapid methods of detection and identification of oily materials. Some progress is being made with continuous ultraviolet and infrared detectors and by the addition of tag materi-
Methods of Control
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