dimanche 15 décembre 2013

The Future of Waste Disposal Systems

A lire sur: http://www.alnmag.com/articles/2013/11/future-waste-disposal-systems

Mon, 11/04/2013 - 4:23pm
Philippe Roe
As the materials within a cage become more varied, it is important that cage dump stations evolve as well.
Material handling of laboratory animal soiled cage content is not as straightforward as it might appear at first glance and matters are getting more complicated with the focus on better habitat and enrichment products for the animals’ well-being.
Material handling of feed and bedding products in the laboratory animal facility represents a considerable operating cost factor in terms of being labor intensive,1risk of injury,2,3 and space utilization. Automating the transport of these materials by conveying systems addresses most of these issues, but presents designers and engineers, as well as managers and operators, with numerous challenges.
What Goes In 
The physical characteristics of spent caging materials are anything but uniform and this promises to get more complicated with the increased focus on animal habitat and enrichment that enable naturalistic behaviors, a real challenge for any conveying approach or regime. Bedding materials themselves range in forms from cob and wood chip to pellets, paper chip, and paper pulp, each having their own material characteristics for their intended application and the property changes of those materials in spent or soiled conditions, as well as in extreme unintended conditions. The spent caging materials are seldom uniform in size, texture, or moisture content. They are often agglomerated (as with autoclaved caging materials or built up fecal matter) and the moisture content may exceed the absorption capacities of the bedding material (typically from diuretic animals or watering systems).
Feed in whole pellets can easily exceed 50% of the waste stream. In the biomedical industry the ability to convey feed pellets is a principle design criteria used in configuring a waste removal system. The carbohydrate content in feed, especially starches as powders or fines, is of concern for all conveying systems. Though starch has a low solubility in water, when the semi-crystalline starch granule absorbs water, it releases amylose, as well as amylopectin, to form a very sticky paste. Materials quickly build onto the adhesive paste and will adhere to the conveying lines’ surfaces. Through retrogradation, the polysaccharide polymers reform semi-crystalline structures, becoming hard and ridged. This build up can to lead to catastrophic failures in all conveying systems.
The composition of the wet agglomerated mass in the cages’ corners and on the bottoms is primarily gnawed food that has retained moisture and a lesser amount of fecal matter. In mouse cages, fecal matter accounts for 100–200 grams of the soiled content of most cages. Dry bedding accounts for 180–300 grams per cage. Combined, these account for less than 40% of the composition of spent caging materials. Gnawed feed tends to range from 50–120 grams (dry) but absorbs moisture at two to three times its weight in the cage. When build up is tested with an iodine test solution, it appears that it is the wetted starch component of the feed that adheres to the various surfaces.
Diverse approaches to environmental enrichment and refined customization are used to meet the needs of the individual strains or protocols. Environmental enrichment materials may be present in whole or partially degraded condition or they may be intended to be recovered for reuse.
Nest building materials, such as cotton fibers or paper strips, are aerodynamically polar opposites of feed pellets and spent bedding, having very low drag coefficients. In dilute phase conveying regimes these materials will flow close to the velocity of the vacuum air and will segregate from both feed and spent bedding to form floating wads that do not easily precipitate in the vacuum receiver (dumpster) or in the cyclone separators. Disposable unspent compressed cotton wads, cardboard tubes and boxes, paper cups, paper huts, and the like comprise another group of objects that share similar properties with each other, but are substantially different from the bulk of the main waste stream and may require special consideration.
Many enrichment objects, such as plastic huts, tubes, gnawing wood or nylon sticks, exercise wheels, and so on, are intended for reuse and require separation prior to entering the waste stream. This often involves additional steps and labor at the dump station or the cage change station.
To further complicate matters, there are often extraneous materials present, such as gloves, tags, clips, and sharps that require special attention or removal prior to entering any waste stream.
Consider All Criteria
Aside from being able to handle diverse bedding and enrichment materials, other important design criteria for conveying systems in the laboratory animal facility must be considered. These include occupational health and safety issues, such as allergens and ergonomics, utility and space demands, flexibility, capital cost, operating utility, labor and maintenance costs, and throughput.
Most conveying application requirements for animal research facilities are limited in distances ranging from 15 to 200 meters and a low volume throughput requirement of 0.4 to 1 cubic meter per hour. (0.5 metric tons per hour) per conveyor washer. All the conveying systems reviewed here exceed this throughput capacity by at least twice.
Test Soiled Bedding Formulas 
Because each facility’s combined spent caging material profile is very individualized based upon the combinations of bedding types, enrichment, and so on, any pretest or acceptance test formula for soiled bedding should reflect the worst case scenario and should be adjusted to reflect the facilities profile. A standardized soiled bedding test formula consists of 1.25 cu ft. of the bedding material used by the facility, 1.25 cu ft. rodent diet, and 50% by weight water, resulting in a density of approximately 52lbs. per cubic foot.4 The entire mixture is presented at once. Enrichment, in spent and un-spent forms, and other frequently encountered objects in the soiled cages should then be added.
Conveying Approaches 
Early on, the value of process automation for the disposal of spent caging materials to reduce personnel, labor, and to control operating costs was recognized. Many approaches to conveying both clean and spent materials have since been used in laboratory animal facilities.
Hydro-macerators, first designed for use on ships to grind and discharge food waste at sea, are still found in many LAFs. Most applications discharge spent caging materials into the sewer, though some systems have extraction of water with solids being deposited into dumpsters. At the dump station, the spent caging material passes through into a centrifugal grinder with water. As the particles become fine enough, running water is used to flush and carry the material to the waste water line. All systems require sufficient flow and amounts of water, upwards of 240 gallons per hour, to overcome the material’s drag and carry it in suspension. Increasing incentives (and costs) for water conservation,6 escalating cost, and growing regional prohibitions of sanitary sewer use, fixed utility location within a facility, as well as the OHS issue of aerosol generation at the dump station, have diminished the desirability for this approach to spent caging material handling.
Chain Drag 
Chain drag or tube conveyors are a recent mechanical approach to spent caging material handling. A chain (or cable) and disc assembly, known as a flight, form a loop that is continuously pulled through a 4–6” (100–200 mm) tube with a motorized sprocket assembly. Spent caging materials are introduced to the tube through a hopper/dump station and conveyed to a discharge section into a dumpster. These systems are robust in terms of their ability to convey most if not all spent caging materials, but are still subject to failures with the accumulation of retro-gradated starch and other objects accidently introduced into the waste stream. The stated limited conveying distance of 250 feet and the fixed ridged mechanical requirements, such as tubing, dump station placement, and drives, restrict many applications. Separate dust collection systems are recommended to be fitted to the dump stations for dust, allergen, and aerosol capture. A chain-wash system is required to remove tenacious materials and prevent retro-contamination, such as fly infestation.
Vacuum Conveying 
Vacuum conveying is considered the most versatile and hygienic5 method of material handling. Generally, there are two categories, or regimes, of vacuum conveying. If the conveyed material is suspended in the vacuum air throughout the pipeline, the mechanism meets the definition of dilute or lean phase conveying.7 If the material is conveyed at low velocity in a non-suspension mode, on the other hand, the system falls under the umbrella of dense phase conveying, also known as poly dense phase or discontinuous dense phase. Both vacuum conveying regimes use some form of vacuum receivers in which the spent bedding material is separated from the vacuum conveying air. The vacuum air then passes through several filtration steps before reaching the vacuum generator (blower). The steps may include a settling tank, a cyclone separator, and/or a bag or filter house.
In dilute phase vacuum, conveying particles are fully suspended in high vacuum air velocities greater than 65 feet per second (20 m/sec), conveying less than 1% volume of material to the conveying vacuum air. This regime has low pressure drop to distance of conveying (5 mbar/m), but requires a continuous flow of high velocity vacuum air sufficient to maintain the material in suspension. Below this velocity is known as the saltation velocity, in which the materials fall out of suspension onto the bottom of the conveying line. Elbow radii of 10x the diameter of the typical 3”, 4”, and 6” conveying lines are recommended to reduce pressure drops and corresponding vacuum air velocity changes within the system. Saltation and adhesion by moist starches to the walls of the conveying lines make this conveying regime susceptible to build up. Many facilities use abrasive materials, such as walnut shells, in routine cleaning to remove this build up. Sealed pressure rated dedicated dumpsters or silos with rotary air lock valves are commonly used with dilute phase vacuum conveying. With few exceptions, in most applications the limitation for conveying is 350 feet and will use one or two 35 to 75 horse power blowers.
In poly dense phase, discontinuous dense phase vacuum conveying, particles are not fully suspended in the vacuum air.8 The particles tend to form permeable slugs or pluses while being conveyed within the 1.5 to 3” (40–75 mm) conveying line. In the poly dense phase regime, accept a wider range of material properties including liquids (empirical observations). Poly dense phase regimes are less susceptible to changes in vacuum air velocities having low velocities of 3.5 to 17 feet per second (1-5 m/s). This regime is more pressure dependent than the dilute phase regime, operating in a typical pressure range of 7.5 to 14 kilopascals, but can carry greater than 30% material to volume of vacuum air. Thus a 2” (50mm) diameter tube will convey the same volume of material with a ten horse power blower, exceeding distances of 750 feet (225 meters) in the poly dense phase regime. Elbows can have much smaller radii of five times or less the tube diameter, without deleterious effect on conveying performance.
Two configurations of vacuum receivers are typical for this regime of conveying. Both configurations discharge the materials into any non-pressurized container, dumpster, or packaging system. And both configurations are unaffected by wads of enrichment and both are better at resisting retrograded starches, but not immune.
The first configuration is a valved receiver, having a louvered valve on the bottom of the receiver and a filtration system contained at the top of the receiver. This is a well understood and efficient means of moving materials with vacuum air and is used extensively for conveying dry materials. Its limitations are that the volume of material conveyed at any given time is less than the volume of the receiver. The gasket on the louvered valve is also subject to fouling with sticky or wet material compromising the seal needed to maintain a vacuum.
The second configuration is a separating valve that combines the features of a continuous feed of a rotary air lock valve and the high efficiency of a valved receiver, with the added advantage of being able to handle very wet bedding, even liquids with which to clean and flush the system. The separating valve consists of four chambers that continually rotate in an assembly. Each chamber contains a coarse filtration screen, which is used to separate the bedding material being collected in the chamber and the vacuum air. The chambers in the separating valve alternate between the vacuum-intake portion of the separating valve and the ambient pressure-discharge portion of the separating valve on the opposite of the intake side. As the chambers rotate to the discharge portion of the assembly, the material leaves the chambers, descending into the receptacle. The separating valve uses a labyrinth seal verses and gasket. The labyrinth seal’s gap must be set so that materials cannot be caught between the rotary chamber and the valve body.
OHS Issues
Allergens and Aerosols 

Down draft is largely ineffective in containing and capturing allergens from rodent dander and urine. Dump stations should be fitted with a Class 1 BSC, HEPA filtered updraft cabinet for BSL-1 applications, having an effective average face air velocity of 100 fpm (0.5 m/s), ranging from 80 to 120 fpm.
NIOSH N100 ratings for equipment meet the Federal Standard 209E certified class 100 tabletop cleanroom. This does not alleviate the need for PPE including gowning, gloves, face, and respiratory protection.9,10,11
The reccurring and chronic nature of most health problems are what causes them to become costly. People who work in animal research facilities are at high risk for injuries that are defined as musculoskeletal disorders (MSDs).12,13 One reportable MSD incidence is likely to occur within two years for every group of 15. When soiled cage manipulation and spent bedding materials is emptied from the cage, several musculoskeletal issues arise from the manipulation, primarily: cage gripping, turning/twisting, impact/shock, and lifting. Automation, in various forms from gantry systems to robotics, are offered to address these issues. Though costs are decreasing, too often the automated solutions are too expensive to acquire and operate, require excess facility support space, or limit the types and sizes used by a facility and reduce throughputs below the needs of most facilities.
Where It’s Going 
Laboratory animal science is in the early stages of a very profound and influential refinement in enrichment and habitat.
There are considerable variations in response and interaction to habitat and enrichment materials by different strains and under different protocols.14 There are as many interoperations to those enrichment efforts and their validity.
The standardization of the animal’s habitat and environmental enrichment will not so much affect the enrichment items themselves, but the physiological and behavioral responses by the groups of animals studied. Physiological responses, both acute—such as in glucocorticoid levels, receptors, and metabolites15,16—and as trans-generational epigenetic expressions represent new insights and a means of understanding or at least account for many confounding results.
What does this mean to conveying of spent caging materials and material handling in the animal facility in general? The materials, bedding, and enrichment will continue to become more numerous, varied, and complex. Regardless of conveying preferences, the dump stations that interface with them will continue to evolve to become more automated, provide more component separation and processing, and become more versatile in the materials they handle. The systems must accommodate the caging and its material contents, and not limit the types of materials that a facility can use. In doing so, these systems will prove themselves cost effective, productive, and safe.
  1. Roe, P, Cage Processing and Waste Management: A Cost Analysis and Decision Making Exercise, 2002 Lab Animal, volume 31, No. 1, January 2002
  2. Occupational Health & Safety in the Care of Research Animals, National Academy Press, 1997.
  3. Robert K. Bush and Gregg M. Stave, Laboratory Animal Allergies: An Update, ILAR Journal V44(1) 2003
  4. Factory Acceptance Test Protocol, VBRS 9400, SMC-Roe, Division of Audubon Machine Corp., 814 Wurlitzer Drive, North Tonawanda, NY
  5. Brian Wilson, Choosing A Vacuum Conveying System For A Pharmaceutical Manufacturing Operation, Pharmaceutical Processing, March 2004
  6. Water Efficiency Guide, Laboratories for the 21st Century: Best Practices, August 2012,
  7. Martian Rhodes, Pneumatic Transport of Powders, Educational Resources for Particle Technology, Particle Technology Forum, a division of the American Institute of Chemical Engineers, accepted October 25, 2005
  8. Basta, Nick, Process engineering: Pneumatic conveying moves ahead, Chemical Processing, April 2005
  9. Harrison, D.J., Controlling Exposure to Laboratory Animal Allergens, ILAR Journal, Volume 42, No.1, 2001
  10. Barbeito, M.S. and Taylor, L.A. 1968. Containment of Microbial Aerosols in a Microbiological Safety Cabinet. Appl. Microbial. 16: 1255-29.
  11. McLeod, Vince, Nothing to Sneeze About: Laboratory Animal Allergens, ALN Mag., October 2010
  12. Analysis of OSHA’s Data Underlying the Proposed Ergonomics Standard And Possible Alternatives Discussed by the SBREFA Panel 3/2/99 –4/30/99. September 22,1999. SBA by Policy Planning & Evaluation, Inc.
  13. Musculosketal Disorders (MSD’s) and Workplace Factors. NIOSH, Department of Health and Human Services, Publication No. 97-141, July 1997
  14. Szczepan Baran, VMD, Marcel Perret-Gentil, DVM, Karen Froberg-Fejko, VMD and Elizabeth Johnson, VMD, A Review of Enrichment and Enrichment Resources Provided to Laboratory Rodents: Standardization of Rodent Enrichment Protocols, ALN Mag March 2013
  15. Wein, Harrison, Stress Hormone Causes Epigenetic Changes, NIH Research Matters, September 27, 2010
  16. Popoli,Maurizio, Yan,Z, McEwen, B and Sanacora,G, The stressed synapse: the impact of stress and glucocorticoids on glutamate transmission, Nature, JANUARY 2012, VOLUME 13
  17. Müjdat Zeybel, T. Hardy, Y Wong, J C Mathers, C R Fox, A Gackowska, F Oakley, A D Burt, C L Wilson, Q M Anstee, M J Barter, S Masson, A M Elsharkawy, D A Mann & J Mann, Multigenerational epigenetic adaptation of the hepatic wound-healing response, Nature Medicine,Volume:18,Pages: 1369–1377 Year published: (2012)
  18. Michael Skinner, M Manikkam, M Haque, B Zhang and M Savenkova, Epigenetic transgenerational inheritance of somatic transcriptomes and epigenetic control regions, Genome Biology 2012, 13:R91
  19. Fabiola C.R., Zucchi 1, Youli Yao and Gerlinde A.Metz, The secret language of destiny: stress imprinting and transgenerational origins of disease Front. Genet., 04 June 2012
Additional Reading
Philippe Roe is currently the Product Director at SMC-Roe division of Audubon Machine Corp., North Tonawanda, NY. He continues as an affiliate of the award winning Giannotti Associates, Turbo Engineers, and serves as a board member of 800-Charity Cars, (www.800CharityCars.org). He began his career in the department of genetics at Albert Einstein College of Medicine, 1973.

1 commentaire:

  1. As waste management operations all over the world attempt to become cleaner and greener in the face of new legislation, some companies are looking to move away from the older systems of collecting and transporting waste by road – and are taking the whole thing underground.