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Recycling xylene saves money and the environment.

Buying and disposing of xylene used to cost the authors' laboratory many thousands of dollars a year. A small but potent "still" has turned the situation around.

To comply with Federal and state regulations, our lab at Tucson Medical Center had been spending a great deal of time, effort, and money purchasing virgin xylene and disposing of its waste after use. That changed last fall when we established a highly economical xylene recycling system that is a model of waste minimization as well.

The histology lab at our 562-bed community hospital used about 50 gallons of technical-grade xylene a month at $5.23 per gallon. Another substantial expense involved proper disposal of discharge from slide stainers and tissue processors as spelled out in today's cradle-to-grave hazardous waste management regulations.

* $5,000 headache. In 1987, the authors headed a team that solved a problem of wastewater pollution by xylene used in an automatic slide stainer at our facility.[1] Even after we had created a filtration system for the stainer, xylene remained an expensive problem.

The contractor who removed waste from our xylene tissue processor charged $175 per 55-gallon drum. We were spending over $5,000 each year to buy and dispose of xylene. That sum didn't include indirect labor and administrative costs, such as hauling 55-gallon waste barrels around the hospital and filling out reams of forms to satisfy the EPA.

Federal and state regulations from the late 1970s and early 1980s on the management of hazardous waste emphasized safe storage, correct labeling, controlled transportation, proper disposal, and accurate documentation. The regs embodied but did not mandate minimizing waste. Facilities that produce hazardous waste were urged to reduce the volume produced, to diminish its hazardous properties, or both. How could we respond to this valuable precept?

* Distilling solutions. By recycling the xylene used at our lab, we would lower the costs of purchase and disposal. The closer we could come to achieving a closedloop system, the more money we would save. After some discussion, we decided to take another look at distillation systems.

Distillation is commonly used in labs to recycle organic chemicals. A volatile liquid is brought to its boiling point. The resulting vapor is withdrawn, leaving contaminants behind. Finally, purified liquid is reconcentrated through condensation.

Our previous investigation of distillation systems had been discouraging. Most commercial units were too large and too expensive for our needs. They would have been hard to modify for our small physical space and for the relatively low volume we used.

In recent years, however, smaller units had appeared that were capable of reclaiming a single solvent from organic mixtures effectively. We read current manufacturers' literature to find benchtop units that were affordable, easy to use, and fairly maintenance free.

Several manufacturers whose units we liked best referred us to sites where their equipment was installed. Most of these places were industrial settings--auto body and machine shops, for example. Telephone conversations with these enthusiastic nonlaboratory consumers prompted us to take the next step toward on-site distillation.

To conduct a surrogate trial of one of the more promising systems, we sent a sample of xylene waste from one of our tissue processors to a manufacturer for reclamation. The results indicated that our lab could recover waste xylene effectively and inexpensively. In fact, the system we chose will have paid for itself in about two years.

* Backing. Armed with financial data (Figure I), we obtained letters of support from our facility's department of environmental health and safely. Laboratory management convinced our hospital administration to permit us to pursue the project.

* Components. The system we chose has three major parts: a solvent boiling chamber, a watercooled condenser, and a vacuum assist unit (Figure II).

[paragraph] Solvent boiling chamber. Before startup, contaminated xylene is poured into a stainless steel chamber that acts as the system's "crockpot." Electric elements in the chamber transfer heat evenly through the liquid via conduction.

The chamber is lined with a disposable temperature-resistant nylon bag that facilitates cleanup and collects sediment. After the xylene has boiled out, the bag is removed. The paraffin that constitutes the bulk of the residue solidifies and is disposed of as nonhazardous waste. Tests performed on the residue showed trace amounts of xylene in levels considered acceptable by Federal standards.

[paragraph] Water-cooled condenser. Located at the top of the boiling chamber, the condenser cools solvent vapors, condensing them into a pure liquid that flows into a reservoir and ultimately into a recovery vessel.

[paragraph] Vacuum assist unit. The third component reduces atmospheric pressure inside the boiling vessel. This process lowers the solvent's boiling temperature and reduces the time needed to recycle it.

* Safety. Because flammable solvents such as xylene must be handled with absolute safety, the manufacturer recommends surrounding the device with an explosion-proof area to a radius of at least 10 feet. Forbidden in the safety zone are Bunsen burners, electrical switches, electrical appliances, and non-explosion-proof electrical outlets.

We created a small explosion-proof area by placing the still inside a special ventilation hood. The hood is equipped with Underwriters Laboratories-approved vapor-tight, explosion-proof electrical equipment; an automatic sprinkler system; and multiple safety interlocks to shut down the entire system if it malfunctions. Dual thermostats turn off the vessel if it overheats.

Making our project a reality required the help of the vendor and outside contractors as well as the lab purchasing, environmental health and safety, and facility planning and design departments. The participation of the histology staff was essential. It took several months to make the physical modifications needed for installation.

* Allaying fears. Histology personnel expressed understandable concern about processing hazardous chemicals in their lab section. The hospital architect and representatives from the safety department allayed their concerns at an in-service program that included a question-and-answer session. Key areas discussed are listed in Figure III.

Startup of the unit was directly supervised by hospital safety personnel and a representative from the manufacturer. These extra efforts went far toward relieving the staff's concerns.

* Running the still. The first distillation proceeded without a hitch. A keen sense of anticipation pervaded the histology staff when they used the first batch of "home-brewed" xylene. As we had planned and hoped, the reprocessed xylene worked as well as the original product.

We found that five gallons of waste xylene could be processed in five to six hours. Two runs per week are usually sufficient to keep the staff in supply.

Recovery of xylene by volume has consistently been 95% to 98%. Gas chromatography in our laboratory revealed technical-grade xylene with no peaks for other substances.

It takes about 30 minutes to prepare the still. First, the sealing surfaces of the boiling chamber are cleaned of residual paraffin. Next, a new nylon liner is inserted. Finally, the gasket that seals the lid of the boiling vessel is replaced.

* Kinks in the system. Although our system worked well from the start, a few bugs remained to be straightened out.

[paragraph] Noise. The lab staff was annoyed and distracted by noise from the vacuum assist unit. Running the instrument only during the third lab shift, when staffing is lowest, relieved the problem. We felt comfortable doing this because the multiple safety systems built into the still, including the fire protection system, make direct staff observation during operation unnecessary.

[paragraph] Rust. Another unexpected problem was the appearance of rust and water in the distillate. The cause was found to be two-fold: water contamination from the processing machinery and the steel containers and the distillate's low pH--5 to 6.

We now treat all waste xylene with about 100 g of anhydrous sodium sulfate before processing. The sodium sulfate crystals, which act as a desiccant for the waste, help neutralize the pH. Recently we eliminated rust as a concern by replacing the steel containers with nonmetallic safety cans.

[paragraph] Pressure. After about six weeks of operation, vacuum began to drop. We discovered that a small washer used to seal a connection between the boiling vessel and the vacuum assist unit had become chemically degraded and thus lost its shape. The manufacturer corrected this problem by replacing the washer with a seal made of Viton, a material more resistant to chemicals.

It is imperative to maintain a good vacuum so that the contents of the vessel will boil consistently and distillation will proceed efficiently. Vacuum is even more critical if the user intends to reprocess chemicals with boiling temperatures higher than 300 [degrees] F.

Without vacuum assist, the boiling temperature of the xylene we use is just under 300 [degrees] F. When xylene is heated in the boiling vessel under vacuum conditions of - 26 inches of mercury, however, the boiling temperature drops to 175 [degrees] F. With no vacuum in place, it would take 8 to 12 hours rather than 4 to 6 to process five gallons of xylene.

* Advantages. What began as a search for a waste management minimization technique has drastically lowered our laboratory costs for xylene. Before distillation, we ordered about 50 gallons of xylene a month through the Voluntary Hospitals Association at the bulk rate of $5.23 a gallon. In the first six months of the still's operation, we purchased a total of 44 gallons at the same rate. Expenses will drop dramatically: to nearly zero in the third quarter of 1992.

Our histology staff enjoys using the device. We are delighted to protect our environment while saving many dollars. The apparatus may be too simple and ugly for a moonshiner to admire, but we love her still. [1]Grushka, M.J., and Spark, R.P. How our histology lab became a |clean' industry. MLO 20(6): 67-71, June 1988. Mark J. Grushka, M.S., and Ronald P. Spark, M.D. Grushka is director of environmental health and safety at the Tucson Medical Center. Dr. Spark is a pathologist in the laboratory at the medical center and clinical instructor of pathology at the University of Arizona College of Medicine, Tucson.
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Author:Grushka, Mark J.; Spark, Ronald P.
Publication:Medical Laboratory Observer
Date:Jul 1, 1991
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