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OU resWue from the separation process must be accurately dassrffied and disposed of accondingly ent is allowed to flow slowly through the Chemical Clarifiers container, oil and water separate and the Chemical separation of oil and water oil rises to the surface where it is absorbed produces a very low concentration in the by a moving belt or pad. The materials resulting effluent. Addition of proper from which the pad or belt are composed chemicals to the wastewater causes forma- absorb oil but reject water (Fig. 3). tion of flocculents which carry the oil with Simple and suitable for removal of gross them. Flocculents can be removed by set- x oil contamination, they are not suitable for tling, or by further processing of the efilu- synthetic oils,permanent emulsions,or sol- ent through filters, presses, or centrifuges. uble oils. Pads and belts require regular re- Chemical clarification is applicable to placement and must be disposed of as larger flow rates and requires much periph- semi-hazardous waste. Low concentrations eral equipment. Extremely capable of re- of oil (less than 100 ppm) are not obtain- moving oil waste, these systems are often able with these systems. too complex and costly for consideration Evaporator Systems when small throughput rates are involved. Evaporator units remove the water from Membrane Filters the wastewater, leaving the oil, by boiling Membrane oil/water separators, usually batch type, deliver the effluent under pres- sure to the membrane filter, where a por- "Treat the earth well. It was not tion of the water passes through. The re- maining oil and water are returned to the given to you by your parents. It was holding tank, and again pumped through loaned to you by your children." the system,removing more water with each pass(Fig. 6). Ultimately most of the water Is removed and the remaining oil concen- - Kenyan proverb trate can be disposed of. A storage tank is required to hold in-pro- cess oiUwater effluent during the batch the effluent. Since the boiling point of wa- processing. Some units require a source of ter is below the boiling point of most oils compressed air for operation. (400 For higher),the oil is not vaporized or changed in any way.The water is boiled off Residue Disposal as uncombined water vapor(Fig. 4). All methods of processing oily wastewa- These units can process oily wastewater ter leave an oil residue for disposal. In contaminated with petroleum-based, syn- some cases,where effluent initially contain thetic, and soluble oils, as well as tallows. a large proportion of oil, recovered lubri- Units are available that use steam,electric- cants are reusable in other,less-demanding ity,or gas for heat. Electrical and gas units applications. Normally,however, most res- require sophisticated temperature control idue may be classified as hazardous waste. systems.The cost of energy for operation of Waste oil processors must analyze collected these units varies from$0.05'to 0.15/gal.of material to make this determination. If the effluent processed. Evaporators are not waste oil contains no hazardous substances suitable for use with VOC contaminated (PCBs,VOCs,etc.),reclaimation or dispos- oily wastewater. No EPA permits are re- al is no problem. quired for their operation if only water is Control of small amounts of waste is es- emitted. sential to overall corporate environmental responsibility. Proper waste control on a Centrifuges small scale is often the precursor to larger Centrifugal separation of liquid compo- industrial efforts. nents of oily wastewater is feasible only if the two are Immiscible and of differing spe- cific gravity. These units allow throughput FHecantth>e re information... to be fairly high,since separation allows the components to be drawn off in a continu- hor has expressed his willingness to ous process.These units can easily separate technical questions about the article. solids in solution (Fig. 5). reached at 717-368-8075. Centrifuges require routine maintenance for lubrication and cleaning. Emulsified . . .Dick Johnson, Senior Editor, 708-390- oils and true solutions are not separable by 2622. this process.Electrically operated,there are energy costs associated with this method of For information on how to order copies of wastewater processing. this article circle 13 on post card d8•PLANT ENGINEERING•MARCH 4,1993