Cutting fluid recycling systems based on the centrifugal removal of contaminants are available in sizes that will treat 60 to 300 gallons of cutting fluid per hour. These systems include pumps and hoses to permit fluid recycling directly from a sump or tank. The system removes solids, tramp oil, odors, and controls biological activity. Metallic fines and other solids can be removed down to one micron. The units can be mounted on a cart with brakes to facilitate relocation of the recycler to various sites. The units can be purchased with the following options: a self-cleaning centrifuge, a proportional mixer system, a heat exchanger/economizer, processing tankage, a clean coolant distribution system, and water deionizer.

Another type of modular recycling system collects, treats, and recycles metal working fluids through the process of pasteurization and coalescence. The module provides a central fluid collection point for bacterial control, tramp oil removal, and adjustment of fluid concentration. The fluid is heated to 160 degrees F, which kills most of the bacteria. The elevated fluid temperature improves removal of tramp oil by coalescence. These units typically have basket filters; however, some units are available with additional filtration capacity. This style of recycling system is available in models that can treat 12.5 to 125 gallons of cutting fluid per hour and such a system is currently in operation at the Naval Shipyard in Portsmouth, New Hampshire. The pasteurization process also is being used at both NADEP Jacksonville, FL and SUBASE Kings Bay, GA, with a settling tank and an oil skimmer substituting for the basket filter (for primary solids removal) and the coalescer, respectively. An alternative to the purchase, operation, and maintenance of recycling equipment by the shop is the use of mobile recycling services. Mobile services generally include a truck-mounted fluid-recycling unit that performs the recycling on the generator’s property. Some of these services have the capability of processing fluid at a maximum rate of 300 gallons per hour. The recycling process consists of filtering, pasteurizing, and centrifuging the spent fluid. There is typically a minimum charge per visit plus a rate per gallon of fluid treated. This technology was recently evaluated by the U.S. Environmental Protection Agency (EPA) and found to result in annual cost savings for small- to medium-sized plants.

It is important to mention that used cutting fluid is currently being recycled without the use of cutting fluid recyclers. Defense Supply Center Richmond (DSCR) has a closed-loop re-refined contract in place with Safety-Kleen, whereby Safety-Kleen picks up used oil products and furnishes the requisitioner re-refined engine oil(s). The cost of the used oil pick-up is included in the unit price of the re-refined engine oils, which is competitive with the price of virgin and/or re-refined engine oils without the used oil pick up. The used oil products that Safety-Kleen will pick up under the closed-loop program are any of the following:

• Engine oil
• Synthetic fluids
• Transmission fluids
• Hydraulic fluids
• Petroleum based industrial oils*
• Petroleum based cutting oils*
• Diesel fuel

* Industrial and cutting oils MUST NOT be highly chlorinated.

In short, DSCR customers could be generating used cutting fluids and sending them to Safety-Kleen as part of the closed-loop re-refined program. The used cutting fluids and other oils collected by Safety-Kleen are re-refined, and the re-refined base stocks are blended into oil products (including cutting fluids) that are marketed to consumers, distributors and industrial customers.

Spent metal cutting fluids may be considered hazardous wastes due to the products formulation or by absorbing contaminants through metal working operations. Under 40 CFR Part 279, Used Oil Management Standards, used oil is defined as oil refined from crude (or any synthetic oil), used as a lubricating, hydraulic, or heat transfer fluid that has become contaminated through use. Coolants may be managed under these regulatory provisions and recycled as opposed to discarded.

The compliance benefits listed here are only meant to be used as general guidelineS and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.

The following cost analysis is based using a mobile recycling service. The following example is for a facility that generates a fairly large quantity of spent cutting fluid. Most facilities will generate less than this amount. For smaller shops, off-site recycling services may be more cost effective.

Assumptions:

• Spent cutting fluid generation rate: 2 gal/hr, 4,212 gal/yr (about 35,150 lb/yr)
• Percent of tramp oil from recycling (requiring disposal): 5%
• Fresh make-up fluid required after recycling: 421 gal/yr.
• Recycling cost: $1.35/gal plus labor, transportation, and filters.
• Recycling requires 9 site visits per year.
• Recycling technician labor: 8 hrs/visit.
• Transportation costs: $200/visit.
• Filter costs: $100/visit.
• Off-site recycling is performed at no cost to the facility.
• Cost of fresh cutting fluid: $3/gal.
• Labor cost: $30/hr.

Table 1. Annual Operating Cost Comparison of Diversion and Off-site Disposal for Cutting Fluid Recycler

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