Effluent Decontamination in Biocontainment Facilities
Effluent Decontamination in Biocontainment Facilities
Employing either heat, chemicals, or some combination of both, effluent decontamination systems (EDS) completely destroy the targeted pathogens that may be contained in the liquid effluent (or within solids carried in the effluent) discharged from a biocontainment laboratory. For owners and designers, the conversation about whether an EDS is needed in an individual facility has expanded to include discussion of the best approach for the science concerned.
“Three-fourths of all the disposal systems built are one-off custom designs, so there is no single template to rely on,” observes Joe Wilson, chief executive of Bio-Response Solutions in Danville, Ind.
While not always formally required, an EDS is likely to be specified for any new biocontainment facility of level 3 or higher. According to Wilson, federal government and Biosafety in Microbiological and Biomedical Laboratories (BMBL) guidelines mandate an EDS only at two levels: BSL-3AG, which handles organisms devastating to animals but not humans; and BSL-4, where extremely dangerous organisms are present.
“However, public scrutiny and local sewer authorities are demanding effluent treatment, regardless of what is recommended by the BMBL manual, the U.S. Department of Health and Human Services, the Centers for Disease Control and Prevention, and the National Institutes of Health,” he points out. “From the standpoint of public perception, a level-3 lab cannot be connected to a municipal sewer system without installing an EDS.”
Increasingly, state and local officials are imposing limitations on the kinds of materials that may be handled in a lab that does not have an EDS. Wilson mentions that even big pharmaceutical labs operating at level 1 or 2 have been denied permits for sewer discharge without an EDS due to concerns about liability and public perception.
“I’m currently involved in a level-1 project,” he relates. “Although there will be no problems with the sewer discharge, because of potential liability we are putting in a $500,000 EDS.”
The primary purpose of an EDS is to make sure that any organism that could appear in the lab waste stream is killed. Otherwise, it could enter the municipal sewage system, inadvertently releasing contamination to the outside environment, says Russell McElroy, senior architect over Forensic and Health Laboratories at the architectural and planning firm McClaren, Wilson & Lawrie in Ashland, Va.
There are four ways to kill potential contaminants: either through high heat (250 degrees F or 121 degrees C); lower heat alone (>180 degrees F or >83 degrees C); a combination of lower heat and chemicals; or chemicals alone. Often, the chemical-only approach is quickly dismissed as an alternative, not because making the physical kill is difficult, but out of concern for safety. Before discussing any of the other options, both Wilson and McElroy emphasize that safety is the leading design imperative.
“The most important feature of an EDS is safety,” Wilson insists. “Along with protecting lab occupants and the public, we have to think about the maintenance staff working on the system 10 to 15 years from now. An EDS is not just for containment; it is clearly an occupational safety device.”
System designers and equipment builders must anticipate problems like what might leak that could be unsafe, who is at risk if an EDS fails, and what the public reaction might be to an adverse event.
“We have taken on the huge responsibility of making sure people will be protected. This is the core value that drives us,” Wilson comments.
An Emerging Field
At the same time, biosafety is an emerging field.
“There are many theories for providing biocontainment that must be proven,” remarks McElroy. “Sometimes systems are over- or under-designed. We are learning better ways to do things. The right solutions are not always for the best price.”
Conventional engineering and plumbing principles often do not apply in this highly specialized area. Many of the elements of standard waste disposal are not appropriate when dealing with a potentially harmful microbe.
For example, select agents, whether the anthrax Bacillus or Hanta virus, are transmitted by air, so it is critical for the system not to aerosolize the material. That’s difficult because one common engineering recommendation for transferring the liquid waste from the collection tank to the processing tank (cooker) is via pneumatic pressure.
“You can’t do that when dealing with microbes,” Wilson stresses, explaining that a leak in the system could discharge the agent into the air. “Even today, effluent systems are designed based on this method. It is absolutely unacceptable, yet it is common practice.
“Right now I have two clients with systems that are only three years old, but must be replaced,” he continues. “They are not functioning correctly because they were not properly designed. An EDS should last 25 to 40 years.”
One problem is the low level of expertise that prevails among the engineering and regulatory segments.
Conventional plumbing engineers often do not understand the intricacies of the diverse materials the system might have to handle. Depending on the lab mission, effluent can contain acids or chlorides that eventually corrode the stainless steel holding tanks, drastically shortening their life and potentially creating a dangerous situation. The presence of solids such as plastic, glass, sand, bandages, or feces must be anticipated and provided for.
“The professionals on the cutting edge of this technology work for the companies that build these systems,” Wilson says. “They have to have this knowledge because they are responsible for the warranty performance and the safety of the customer.”
Heat or Thermo-Chemical?
Ruling out the chemical-only approach to organism destruction leaves EDS designers with the options of heat or heat-plus-chemicals to accomplish the task. For a high-temperature EDS the parameters might be operation at 250 degrees F (121 degrees C) or higher to yield sterile effluent for discharge. The thermo-chemical system would operate at 200 degrees F (93 degrees C) with a chemical (KOH, Virkon, H2O2) to yield disinfection before discharge. In some cases, the lower temperature system can be used without a chemical. For example, in a level-3 lab containing only viruses, it would be acceptable to destroy those viruses at 93 degrees C for one hour without a chemical, as opposed to using the same temperature for less time with a chemical.
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Configured in a series of storage and cook tanks, each scheme has trade-offs, often relating to cost.
The chemical/heat combination has the advantages of lower equipment cost due to the lack of a pressure vessel, and less expensive operation since the liquid does not need to be heated to as high a temperature as with heat alone. The lower sterilization temperature also reduces the rate of tank corrosion, Wilson notes.
However, even though the chemical aids in the kill, McElroy points out that its incorporation into the waste stream, and, subsequently, the municipal treatment facility, makes it less attractive. In his view, the additional energy required to reach the higher heat-only temperature is not of great significance.
“The cost of the chemicals also must be factored in,” he says. “My thoughts focus on the trade-off between introducing chemicals into the municipal system as opposed to the additional energy consumption for heating. Energy recovery could be performed in either case.”
Good tank design can promote energy efficiency, McElroy adds, pointing to the way Bio-Response Solutions manufactures its tanks with double walls—an outer stainless steel vessel wrapped around an insulated inner stainless tank.
“All the interstitial space is completely sealed and insulated,” he observes. “The double-walled tank is desirable in its simplicity, which also promotes easier maintenance and safety.”
How It Works
The two primary components of an EDS are the collection (storage) tank and the cook tank. The vessels can be arranged in a variety of configurations, depending on size, space, and budget. Some systems function with one collector and one cooker, but it is not uncommon to add some redundancy, for example, three cookers, or a storage tank and two cookers.
“A storage-and-cook-tank configuration is less expensive than two cook tanks,” McElroy says. “Price helps determines what method is selected.”
As for size, McElroy has seen cook tanks as small as 120 liters, but 1,200 liters seems to be the norm for the custom-made vessels. One of his current projects is a BSL-3 autopsy suite with a single autopsy station. Its EDS consists of a 1,200-liter storage tank and a 1,200-liter cook tank, with a relatively small autoclave. Another project, a BSL-4 cabinet lab, has a much larger storage tank (about 3,000 liters) and a 1,200-liter cook tank, with space for another 1,200-liter cook tank if capacity needs to increase.
“Design for flexibility,” McElroy advises. “Then you can modify the system without having to take it completely down.”
When an EDS is not incorporated into original plans, its configuration might be based on what fits into whatever space designers have been able to carve out, but this does not always deliver optimal results. For example, being located downstream, and lower than the higher containment lab space, is an important system attribute, allowing it to be gravity fed.
“Keep it simple,” he continues. “Avoid pumps, because they need repair and must be decontaminated to be fixed. In a gravity system the effluent flows down the pipe and ends up either in the holding tank before the cook tank or in the cook tank. My preference is a holding tank with a level indicator, so when it is filled to the cook capacity it automatically drops the liquid into the cook tank. The cycle moves forward, so the tank itself can fill up again with liquid or remain as a back-up.”
The cook tank should be sized according to how much liquid comes down the drain from fixtures within the lab and how often the cook cycle runs.
“If the system cooks slower, the reservoir tank must be sized larger,” McElroy points out. “The BSL-4 cabinet lab has a larger reservoir tank, with a volume of water greater than what is cooked. The reservoir tank prevents the liquid from backing up within the piping system, keeping it from overflowing drains in the lab.”
Removing the Mystery
Owners must evaluate EDS needs from several perspectives: the science performed, effluent content, quantity generated, the number of fixtures to collect from, location, utility connections, HEPA filtration, space requirements, redundancies, and even more.
Noting that the EDS can be the most expensive single piece of equipment specified for a biocontainment facility, anywhere from $400,000 to $1.5 million, both Wilson and McElroy urge owners to familiarize themselves with all the elements of a system in order to make the best choices for their individual projects.
To help fill the knowledge gap, Wilson composed a 190-page PowerPoint tutorial that acquaints owners and other professionals with the technologies and decision points required before beginning the design process. Available at no charge upon request, the tutorial provides a framework for envisioning the EDS: how it should be sized, what kind of chemicals to use, metallurgy considerations, handling solids, and other critical design elements.
“We think it is our responsibility to teach owners everything about a system before it is purchased. After the consultants are gone, they have to live with the system they chose. It should not be mysterious,” Wilson concludes.
By Nicole Zaro Stahl
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