POLLUTION PREVENTION OPPORTUNITIES AT MEDICAL TREATMENT FACILITIES

Eric Haukdal and 1LT Lisa Strutz
U.S. Army Center for Health Promotion and Preventive Medicine
5158 Blackhawk Road, ATTN: MCHB-DC-EHM, Aberdeen Proving Ground, MD 21010-5422

 

 

This paper identifies common medical treatment facility waste streams, describes how they are generated and disposed of, and describes some of the pollution prevention (P2) technologies and management practices available to help minimize their generation. The paper is organized into two of the major waste categories found at medical treatment facilities: chemical waste and regulated medical waste.

 

CHEMICAL WASTE

 

Used X-ray fixer, ethylene oxide (for use in sterilizing medical instruments), and laboratory chemicals such as formalin, ethanol, and xylene are among the most common chemical waste streams generated at medical treatment facilities. This section describes how each of these waste streams is generated and provides information on the various P2 opportunities available to minimize them.

 

X-ray Fixer and Silver Recovery

During the X-ray development process, fixer solutions acquire large concentrations of silver after coming in contact with the X-ray film. The Resource Conservation and Recovery Act (RCRA) characterizes wastes with silver concentrations above 5 parts per million (ppm) as hazardous. Used fixer solutions typically have concentrations between 1,500 and 4,000 ppm.

Silver recovery systems separate and collect the silver from the used fixer, resulting in both environmental and economic benefits (elimination of a hazardous waste stream, reduced hazardous waste disposal costs, and revenue from precious metal recovery). Three of the most popular types of silver recovery technologies include metallic replacement cells, ion exchange columns, and electrolytic recovery units.

A Metallic Replacement Cell (MRC) consists of a 3-5 gallon bucket which houses a core made of either packed iron fibers (like steel wool) or a tightly wound iron mesh. As the fixer passes over the core, the iron replaces the silver in the fixer. The silver is integrated into the coreís matrix while the iron and de-silvered fixer exit the cell. The longer the contact time, the more silver will be removed. As a result, activities that generate large amounts of fixer use multiple cells in series to increase the contact time. When used and maintained properly, MRCs can reduce fixer concentrations to below the 5 ppm limit.

Advantages to MRC recovery include the simplicity of the equipment, the ability to generate an effluent with less than 5 ppm silver, and their low cost (a single MRC costs about $50). The major disadvantage is the degree of maintenance and attention required to ensure that adequate contact time is provided and that the core does not either oxidize or become overloaded with silver. This often makes MRCs impractical for use in facilities that generate large amounts of used X-ray fixer. Another disadvantage is that MRCs generate a low quality silver which requires refinement before becoming marketable.

Ion exchange technology recovers silver by passing the fixer through a column of synthetic resin. Active chemical groups in the resin allow for an exchange of ions between the resin and the fixer solution, causing the silver to adhere to the resinís surface. Over time, this process depletes the resin which must periodically be sent back to the manufacturer for regeneration (and silver collection).

The major advantage to ion exchange is that it can consistently and reliably reduce silver concentrations to below 5 ppm (as discussed above, MRCs are also capable of achieving this, but only if strictly managed). The largest drawback, however, is that it can only handle solutions with a relatively low initial silver concentration (300 - 500 ppm). As a result, an ion exchange unit would not be suitable as a stand-alone recovery technology for most X-ray processing activities.

The final type of silver recovery technology discussed here, electrolytic recovery, removes silver from used fixer by suspending two electrodes (one cathode, one anode) into the fixer solution and passing an electric current between them. This causes the silver in the fixer to plate onto the cathode.

One of the largest advantages to this technology is that it does not introduce any contaminants into the fixer solution, allowing it to be recycled back into the film development process. To recycle the fixer, however, a continuously recirculating unit (rather than a batch-mode unit) must be used to maintain a consistent fixer composition.

The ability to recirculate the processed fixer is a major advantage since it can reduce the amount of new fixer procurement by about 75% (new fixer would still have to be added to replace that lost to evaporation, drag-out, and carry-over into the rinse water). Another advantage to electrolytic recovery is that the silver which plates onto the cathode is pure enough (90-98%) to be marketable without further refinement.

The major drawback to this technology is that fixer processed through an electrolytic recovery unit may still have a silver concentration in the 50-500 ppm range. Although this is much less than the initial concentration of 1,500 to 4,000 ppm, it is still well above the 5 ppm regulatory limit.

As a result, it is a common practice to use electrolytic recovery as the primary silver recovery system, then use a finishing unit such as a MRC or ion exchange column to complete the recovery process. For larger facilities, combining these technologies is often an excellent way to take advantage of the strengths of each technology while also overcoming their individual deficiencies.

The following table provides a summary of each of the technologies described above.

 

Table 1. Silver Recovery Technology Summary.

 

Technology

Influent

Silver limit

Effluent Silver conc.

Cost

per Unit*

MRC

---

< 5 ppm

$50

Ion exchange

300-500 ppm

< 5 ppm

$2000-3000

Electrolytic

---

300-400 ppm

$3000-5000

* Note that for a complete economic analysis, other costs such as labor, operation, and maintenance must be considered.

 

Digital X-ray Imaging

Digital X-ray imaging or Computed Radiography (CR) provides an alternative to traditional film-based imaging; eliminating the need for chemical processing altogether.

Computed Radiography uses phosphor screens rather than film to capture X-ray images. These screens, which are highly sensitive to ionizing radiation, are able to trap and store the X-raysí energy. To retrieve the image, the plate must then be placed into a reader which scans it with a laser, releasing the stored energy as light. The reader then converts the light into a digital signal which can be saved to a computerís memory, sent to a monitor for viewing, and/or sent to a printing device to produce a hard copy. The phosphor screens, which may be used repeatedly, are available in the same sizes as traditional film grids and can be used with the same equipment and with the same X-ray exposure time as traditional film.

Before purchasing CR equipment, it is important to determine how this technology will fit into the facilityís overall diagnostic imaging system. An emerging trend is for facilities to incorporate all of their imaging modalities (e.g. fluoroscopy, angiography, computed axial tomography, magnetic resonance, etc.) into one electronic network. Under such networks, the images are recorded and stored in a standard electronic format rather than in hard copy. However, hard copies of any image can be generated using printers designed especially for producing medical diagnostic images.

Procuring and installing a CR system (consisting of a CR scanner, several phosphor screens, and a computer system with software able to collect and store the electronic images) will cost anywhere from $250,000 to $1,000,000. The cost will depend mostly on the size of the medical treatment facility and the number of X-ray images it generates.

Distillation of Laboratory Chemicals

Because of their role in tissue processing, formalin, ethyl alcohol, and xylene are among the most common chemicals used in medical treatment facility laboratories. Formalin, an aqueous solution of about 37% formaldehyde (and some buffer salts), is typically diluted to 10% and used as a fixative to preserve tissue samples until they can be prepared for viewing. Once the tissue has been removed from the fixative, the formalin is typically disposed of via the sanitary sewer.

To prepare tissue samples for viewing, the tissue must be sliced, placed onto slides and stained. However, before a tissue sample can be sliced, the water within its cells must first be replaced by paraffin which gives the tissue a rigid structure and prevents the cells from becoming distorted by the cutting blade. This replacement process involves submerging the tissue in a series of graded ethanol solutions, then xylene, then paraffin. Once cut, the tissues slices (containing paraffin) must then be taken through the graded series in reverse to replace the water in the cells, allowing them to be stained. Then, the stained samples are taken back through the series one last time to replace the water with paraffin for long-term preservation. Once a predetermined number of samples have been processed, the used ethanol and xylene, having become contaminated, must then be disposed of as a hazardous waste under RCRA.

As an alternative to disposing of these used chemicals, distillation provides a mechanism to reclaim and reuse them. Distillation separates a liquid from its contaminants by heating the liquid until it vaporizes. The vapors are then collected and condensed while the contaminants are left behind in the boiling chamber as still bottoms. Distillation can be used to recover formalin, ethanol, and xylene. However, the process for recovering formalin differs from that used to recover ethanol and xylene. This difference results from the nature of each of these waste streams.

Formalin is typically contaminated only with tissue particles. As a result, the distillation process only has to separate the formalin from particulate contamination. This can be accomplished with a process known as simple distillation. Simple distillation is used to separate volatile components from non-volatile ones. Therefore, the water and formaldehyde in the formalin mixture will be vaporized, condensed and collected while the non-volatile tissue cells or particles will comprise the still bottoms. The distilled formalin will have the same or very nearly the same concentrations of formaldehyde and water as did the original formalin. One drawback, however, is that any buffer salts in the formalin will remain behind as still bottoms. Therefore, before reuse, it would be necessary to replenish these salts. Kits of pre-measured salts are available from some formalin distillation unit manufacturers which can be added after each batch of formalin is processed. Test kits are also available to help assure that the formalin has been restored to specifications.

The recovery of used ethanol and xylene is more complicated. This is because they are contaminated not only with particulate but also with other volatile substances. If the laboratory segregates its used ethanol and its used xylene, the ethanol will probably be contaminated with tissue cells as well as volatile substances such as water, formalin, and tissue stains. The used xylene could be contaminated with tissue cells, paraffin, and ethanol. If a laboratory does not practice waste segregation, its waste will contain any or all of the above.

Separating a mixture of multiple volatile compounds into its various constituents (or fractions) requires a process known as fractional distillation. Fractional distillation relies on each volatile constituent having different vaporization and condensation temperatures than the other constituents in the mixture.

For waste ethanol (contaminated with water and tissue stains), fractional distillation can recover up to 90% of the ethanol (with 10% left behind in the still bottoms). The distilled ethanol will be up to 95% pure (with water as the remaining 5%). For waste xylene (contaminated with ethanol and water), fractional distillation can recover up to 95% of the xylene (with 5% left behind in the still bottoms). The distilled xylene can be up to 100% pure. For laboratories with combined waste streams (used ethanol and xylene mixed), most fractional distillation units would only be effective in recovering the xylene portion of the waste stream. As a result, it is recommended that histology laboratories maintain proper waste segregation.

The following table provides a summary of the above information.

Note that as an alternative to on-site distillation, contractors may also be available to collect laboratory wastes, distill them off-site, and return the recycled product.

 

 

Table 2. Distillation Unit Summary.

Substance

Dist.

Type

% Recovered

%

Pure

Cost per

Unit

Formalin

Simple

90

100*

$13-15k

Ethanol

Fractional

90

95

$12-16k

Xylene

Fractional

95

100

$12-16k

* After replenishing with buffer salts.

 

Xylene Substitutes

Xylene substitutes are another P2 opportunity available to reduce or eliminate the xylene used in the tissue preparation process (and subsequently disposed of as a hazardous waste). There are currently several commonly used substitutes that have been proven to work as effectively as xylene in most histology applications. One drawback to these substitutes, however, is that they have a much lower flash point than xylene and are classified as a RCRA hazardous waste under the ignitability characteristic once they become used. As a result, xylene substitutes do not actually reduce the amount of hazardous waste generated by a histology laboratory; they merely provide a less hazardous option.

Like xylene, some xylene substitutes may be able to be recovered in a distillation unit. This will depend on whether or not the substitute contains any non-volatile additives that would be lost in the distillation process. Before changing to a xylene substitute, laboratories that are already distilling xylene should contact their stillís manufacturer to determine if it can economically recover the substitute.

 

Ethylene Oxide and Gas Plasma Sterilization

Ethylene Oxide (ETO) is typically used to sterilize surgical instruments. The ETO sterilization process consists of exposing the instruments to heated ETO, which is very effective at destroying bacteria and viruses. The instruments are then aerated (vented to the atmosphere) for at least eight hours to fully remove excess ETO. Since exposure to ETO is a significant health concern, such sterilization systems require constant indoor air monitoring.

Hydrogen peroxide gas plasma sterilization systems are a P2 alternative to the ETO process. This process operates by injecting hydrogen peroxide into a sterilization chamber through a self-contained cartridge. The hydrogen peroxide vaporizes and diffuses throughout the chamber in a deep vacuum. Then, energy is applied, creating a low-temperature plasma which destroys any microorganisms on the equipment. The entire gas plasma sterilization process takes only 75 minutes (as opposed to about 12 hours for ETO sterilization). Like ETO systems, gas plasma waste products are emitted into the atmosphere. However, these emissions contain primarily oxygen and water vapor which are harmless and, therefore, do not require any air monitoring.

The major disadvantage to gas plasma sterilization is that it is currently not effective in sterilizing equipment with long narrow tubing such as endoscopes. As a result, any medical treatment facility employing gas plasma sterilization would have to clean endoscopic tubes by soaking them in an aldehyde-based sterilization solution.

A single gas plasma sterilization unit has a capital cost of about $110,000. Recurring costs include purchasing hydrogen peroxide cartridges about once every 10 sterilization cycles.

 

REGULATED MEDICAL WASTE

 

Inherent to the treatment of patients, medical facilities generate potentially infectious waste or regulated medical waste (RMW). The definition of RMW varies among State and local regulatory bodies, but generally involves items containing blood and blood products, sharps such as syringes, laboratory cultures, animal research wastes, and isolation wastes. This section describes two main P2 areas for RMW: management and treatment.

 

Management

The management of RMW is dependent on the input into the waste stream made by the various clinics and wards throughout a medical facility. Thus, two effective management tools for RMW P2 are segregation and durable medical item procurement.

The most common P2 opportunity for RMW is waste segregation. Segregation involves separating the RMW at the source of generation by distinguishing between which items belong in general solid waste trash receptacles and which items must go in appropriate RMW containers for disposal. Typically, significant amounts of plastic wrapping, rubber gloves, paper, and glassware with an occasional candy wrapper are found in the RMW stream. This practice usually derives from a lack of training or from too convenient access to RMW bags. Not only does poor segregation generate larger RMW volumes and higher disposal costs, but depending on the treatment method, these non-RMW items may adversely affect the functional life of the RMW treatment equipment. For example, the more plastics placed into an RMW incinerator, the more maintenance support it requires and the shorter the incinerator operating life. Simple management tools can be applied to alleviate most segregation problems: training in RMW, posting signage, and limiting access to RMW bags.

Site specific RMW training should be provided to all employees within a medical treatment facility. This training should include the local definition of RMW, proper waste segregation, and the standard operating procedure for its handling. Besides volume reduction, training eliminates confusion and frustration among the generators and handlers of RMW over which wastes belong in the RMW bags. Posting signs near RMW bags throughout the facility stating the items that are defined as RMW serves as a simple reminder that general trash is not an RMW. Periodic spot checks for proper segregation can be used to evaluate the effectiveness of the training and posted signs. A third management tool for effective segregation is limiting access to RMW bags. Limiting access involves removing RMW bags from diagnostic treatment room receptacles and storing them in a nearby cabinet or drawer. This reduces the convenience of placing the general trash in the nearest container instead of the appropriate one while providing for instances when an RMW bag is warranted.

Increased segregation reduces disposal, labor, and maintenance costs by removing non-RMW from the RMW stream. This P2 initiative is easily implemented through management controls.

Durable medical item procurement is another P2 management tool for RMW reduction. Purchasing durable medical items like linens and metal instruments that can be washed, sterilized if needed, and reused, reduces RMW generation. Often, paper treatment table covers and disposable instruments, like scissors and clamps, are purchased for the userís handling convenience. The item is used once and then deposited in a sharps container or RMW bag. Not only does this increase RMW generation, it increases disposal cost. Another issue is the potential maintenance problems often encountered when the facility operates a shredder for secondary treatment of the RMW. The shredding equipment is generally not designed to handle metal objects, causing a shut down of the system and manual removal of the object. These shut downs increase labor and maintenance costs.

While the initial purchase of durable items is greater than for disposable items, the life cycle cost is less than purchasing and discarding disposable items. Therefore, washing, sterilizing, and reusing a durable item as many times as possible is environmentally and economically desirable.

An additional issue in procurement is the impact of the RMW bags themselves. The more RMW, the more RMW bags needed; therefore, a higher procurement cost. Also, if the RMW is treated in an RMW incinerator, low chromium RMW bags should be used so the incinerator ash does not become a hazardous waste due to chromium concentrations.

Effective procurement is a valuable P2 tool to reduce the amounts of RMW generated and the costs associated with RMW management and disposal.

 

Treatment

While reducing the amount of RMW is no longer an option in the treatment stage, treating that RMW in a way that reduces environmental impact fosters good neighbor policies and promotes environmental stewardship. Numerous methods of effective RMW treatment have been developed based on heat, chemical, and radiation technologies. Keeping abreast of these developing technologies that can conserve resources and/or reduce emissions supports the P2 ethic. However, cost always plays a significant role in the decision of which technology to use now and in the future. The following sections discuss the common methods of treatment used within the U.S. Army Medical Command: incineration, autoclaving, and contract disposal.

Incineration is a heat technology that treats RMW using high temperatures in excess of 1400į F to kill the microorganisms. This heat reduces the waste to ashes, or about 10% of the original volume, rendering it unrecognizable and inert. These ashes are usually disposed as a solid waste in a municipal landfill.

A few problems are associated with this form of treatment. One is the possibility of the ash being a hazardous waste due to the concentration of metals, typically chromium and lead found in the waste stream. Additionally, due to pending incinerator air emission regulations, many operational incinerators may require expensive upgrades in the future to maintain regulatory compliance. There are also certain design limitations common to incinerators (e.g., the effects of high heat from burning extremely dry wastes such as paper or quenching effects from liquid wastes) that can reduce the operational life or increase the maintenance costs. All of these problems and their related costs vary with waste load and incinerator type; therefore, extensive investigation must be conducted prior to the selection of an incineration process. Ideally, an energy recovery system should be employed to capture the energy from the burning waste for reuse at the facility.

Autoclaving is the tried and proven method of RMW treatment. Most U.S. Army Medical Facilities that are not using private contractors are using autoclaves to treat the RMW. An autoclave uses high pressure steam to bake the waste raising the temperature to a level sufficient to kill the microorganisms. After the RMW is treated, the waste no longer exhibits an infectious nature; therefore, it can be disposed as a solid waste. There are four variations of the end disposal: direct landfilling, shredding/ grinding, high ratio compacting, and energy recovery.

In direct landfilling, the treated RMW, now a general solid waste, is taken to a municipal landfill. There are no P2 opportunities associated with direct landfilling.

With a shredding/grinding process, the waste is sent from the autoclave into a hammer mill that shreds the waste into confetti. The shredding reduces the volume by 85%, conserving landfill space, and renders it unrecognizable (as required by many State regulatory agencies). Sharps that are treated in an autoclave can be sent through a small sharps grinder and also disposed of as a solid waste. If RMW (minus sharps) is not required by local or State regulation to be rendered unrecognizable, using a general solid waste high ratio compaction process is optimum. This process can reduce, not only the treated RMW volumes, but the volume of all solid waste leaving the facility by 80%, thus making the transportation cheaper and minimizing the volume required in the landfill. Based on environmental impact, cost and maintenance issues, high ratio compaction of all of the installationís solid waste is the ideal P2 opportunity for RMW.

A medical treatment facility may also consider coordinating with a local waste to energy plant in lieu of landfill disposal as the primary method of final disposition. While no cost benefit is derived from this practice, it reduces waste to the environment and provides a viable energy source.

While contract disposal of RMW is not considered a P2 initiative, it is included for comparison purposes. Without the use of the incinerator or other type of treatment technology, RMW disposal costs are generally calculated by weight or roughly $0.30/lb. The amounts of general solid waste and disposables placed in the RMW stream can significantly effect the overall disposal costs. Contracting avoids most of the maintenance and labor costs associated with RMW treatment but, depending on the contractor, may or may not be beneficial to the environment. Potential contractors should be scrutinized prior to awarding of the contract.

 

CONCLUSION

While the medical arena poses some unique waste issues, the P2 initiatives presented in this paper can be used to reduce waste generation and the associated costs.