Treatment of Hospital and Laboratory Waste by Superheated Water Maceration
Richard W. Gilpin, Ph.D., RBP, CBSP - Richard W. Gilpin PhD Ltd, Baltimore, Maryland
The efficacy of an on-site superheated water and steam maceration system (SSM) was evaluated at Johns Hopkins University for its ability to sterilize and render unrecognizable hospital and laboratory waste at a lower cost than incineration and other available treatment systems. The system cost-effectively inactivated Geobacillus stearothermophilus spores, Mycobacterium phlei, Staphylococcus aureus, Candida albicans, Giardia and type 1 Poliovirus in the waste with no chemical emissions from liquid or air effluents while producing a solid residue rendered unrecognizable as medical waste, suitable for use as a source of fuel or recycling.
Biomedical laboratories, hospitals, non-hospital healthcare sites and manufacturing sites generate medical waste that may contain biohazardous microorganisms or materials perceived by the public as potentially infectious. Organizations have a duty to minimize the impacts of medical waste disposal in the 21st Century. Onsite disposal of medical waste satisfies these goals:
• Disposal cost avoidance
• Liability avoidance
• Reduction of institutional health and safety hazards
• Environmental protection
• Regulatory compliance
• Community relations
Congress recognized onsite disposal of medical waste is a national goal: “The Congress hereby declares it to be the national policy of the United States that pollution should be prevented or reduced at the source whenever feasible; pollution that cannot be prevented should be recycled in an environmentally safe manner whenever feasible; pollution that cannot be prevented or recycled should be treated in an environmentally safe manner whenever feasible; and disposal or other release into the environment should be employed only as a last resort and should be conducted in an environmentally safe manner.” (US Code Title 42 Chapter 133 § 13101) Pollution Prevention Act of 1990. Public Law 101-508, 1990).
A technology is needed to provide a cost effective and environmentally friendly solution for dealing with medical waste, blood products, sharps containers and other biohazardous waste products so that 100% of regulated medical waste is diverted from landfills and repurposed into recycling programs and a source of fuel. Medical waste disposal of potentially infectious material continues to be a costly component of the healthcare and biomedical research community. Efficient segregation of clearly non-infectious components of hospital and laboratory medical waste streams reduces the volume of medical waste but treatment and disposal of potentially infectious waste, including hazards from glass, needles and blades remains. For example, steam sterilized waste can be perceived as potentially infectious if recognizable materials such as needles, syringes, gloves, glass or plastic-ware are not destroyed during the process. Incineration or chemical treatment of hospital and laboratory waste produces hazardous air and water emissions. The U.S. Environmental Protection Agency medical waste incinerator regulations require secondary treatment of stack gas, such as alkaline scrubbers, to reduce airborne emissions.
Current costs to transport and incinerate medical waste ranges from seventeen cents to eighty cents per pound. Some institutions pay as much as $8.50 per box containing thirty pounds (28 cents per pound) of laboratory waste taken to an off site incinerator by private contractors. [Costs are higher in 2017]
The Occupational Safety and Health Administration Bloodborne Pathogens Standard caused employers to designate medical waste coming from biomedical and healthcare facilities to be potentially infectious material. Often there is no way to determine whether this waste has been in contact with human blood, internal body fluids, or unfixed tissue once it leaves the area where it was discarded. Employees handling medical waste are often exposed to sharp objects such as needles. Bloodborne pathogen exposure incidents may also involve objects commonly found in laboratory waste that can puncture skin, such as plastic micropipette tips, glass pasteur pipettes and even one milliliter plastic pipettes. Employee exposures to medical waste can become expensive if the exposure is significant and post exposure prophylaxis is given.
The State of Maryland does not permit landfill disposal of any medical waste, termed special medical waste, which appears to come from a hospital, laboratory or other facility that handles material covered by the Bloodborne Pathogens Standard. Public fears of medical waste have also led to restrictive landfill statutes in many states.
Generators of medical waste retain liability for the waste when it is transported offsite for treatment. Medical waste is tracked from the generator to a treatment facility by a manifest system. A contractor receives a manifest for medical waste when it is picked up at the generator's facility and returns a certificate of destruction after the medical waste has been treated to render it suitable for landfill.
The efficacy of an on-site superheated water and steam macerating system was evaluated for its ability to process infectious and perceived hospital and laboratory waste into municipal waste as a source for fuel or recycling at a lower cost than traditional medical waste handling systems.
The SSM system consisted of a process tank to sterilize and macerate medical or laboratory the waste, a boiler to produce steam, a pump that circulates the waste through a macerator during the treatment cycle, a recirculating line that returns the macerated waste from the lower to upper section of the process tank, a filter separator to remove solids at the end of the cycle and a computer system to monitor all aspects of the process.
Decontamination of medical waste by a gravity steam autoclave involves heating the waste material at 121 C (250 F) for 60 to 120 min to ensure all materials are heated uniformly. Fifteen minutes inactivates one million spores of G. stearothermophilus. The overkill method doubles process time to 30 min with inactivation of one quadrillion G. stearothermophilus spores, an accepted practice in the medical waste field to ensure that viable microorganisms are inactivated. Equivalent times at temperatures above 250 F reduce cycle times below 30 min when macerated medical waste is uniformly heated. For example, 260 F cycles, which operate at higher pressures, reduce the cycle time to 8 min. Using 272 F reduces the cycle time to 2 min, instead of 30 minutes. As temperatures increased beyond 250 F there was a reduction in the run time needed to inactivate G. stearothermophilus spores.
Laboratory and hospital medical waste was placed into the processing tank and the autoclave-type door was closed. The tank was pressurized with steam and then filled with 20 gal of superheated water from the boiler. Additional steam and superheated water were added to the macerated slurry to ensure that all particles were surrounded by superheated water and steam. The material was continuously macerated and circulated at a minimum of 250 F for 30 minutes equivalent time, cooled to 165 F, and solids were concentrated by filtration and collected for disposal as general municipal waste. The sterilized liquid was further cooled to 140 F and discarded into a sanitary sewer.
The medical waste processed in the system was randomly selected from biomedical research laboratories and contained large quantities of plastic and glass. Liquid maceration during the sterilization process resulted in efficient destruction of the glass, equivalent to grinding sand, without excessive wear of the grinding blades.
The average load of waste contained: 20% sharps containers with needles, syringes, scalpel blades and glassware; 30% infectious medical waste including microbiological materials, blood and other body fluids, gloves, pathological waste, drapes and disposable instruments; 10% animal bedding and fluids; 35% tubes, pipettes, latex gloves, petri dishes and other laboratory materials; and 5% cardboard containers.
The sterilization cycle was based upon the overkill method for sterilization (250 F for 30 min.) or equivalent minutes at higher temperatures. For example, 1 min at 273 F was equivalent to 19 min at 250 F . The real time of the sterilization cycle varied according the temperature in the process tank and could take approximately 2 to 6 min of real time to equal 30 min equivalent time at 250 F.
The system cycle time from one load to the next was related to time needed to fill the boiler with enough superheated water for the next load. Therefore, it was possible that the equivalent minute system cycle time could be longer than thirty minutes, but never less than thirty minutes.
Analysis of three effluent discharge samples from different sterilization cycles were composited and tested for volatile and semi-volatile organics. Levels above minimum detectable levels but well below discharge limits were found for three volatile organics and three semi-volatile organics.
The highest readings of three replicate samples of the material discharged to a sanitary sewer at the end of three different cycles demonstrated that chemical and particulate emissions were well below the discharge limits set by the City of Baltimore. The discharge limit for biological oxygen demand (BOD) is 300. The system only produced 210 ppm. Total suspended solids were 170 ppm, indicating that the filtration step efficiently removed particulates from the sterilized effluent water.
Background hydrocarbon levels in the area around the system were 2 ppm hexane. Levels of formaldehyde, xylene, and toluene were not detectable. The hexane level inside the process tank after it was loaded with medical waste was 1 ppm. Air samples taken during the cycle and at the end of the cycle during water discharge into the sanitary sewer produced 3 ppm hexane at the drain and no detectable levels of the other hydrocarbons.
Visual inspection of the residue at the end of the sterilization process was an important consideration because of the restrictive landfill statue in Maryland. Several individuals, including an official from the local municipal waste incinerator, inspected the residue. Inspection and handling of the residue showed no obviously recognizable objects. Even 28 gauge tuberculin needles were disfigured enough so that they could not be found in the waste. Local officials accepted the residue as non-medical waste.
The SSM operated as a closed sterilizing and macerating system with no significant air emissions. The effluent waste drain was vented to the outside, per normal practice for sanitary sewer systems. All bacterial and viral biological indicators of sterilization efficacy were negative. Sterilized water effluent chemical and particulate emissions were below regulated levels and hydrocarbons and air emissions were negligible.
Each cycle processed seventy-five pounds of medical waste and took 30 min. The actual time to sterilize each load ranged from 19 to 24 min. Therefore, one worker could process 1,000 lbs of medical waste per work shift. The overall operating cost for the equipment, including maintenance, utility, and labor costs was thirteen cents per pound, five cents per pound less than incineration, using late 1990's cost estimates.
The widely accepted biological indicator approach to testing sterilization efficacy used with this system appeared to be a good outcome predictor because large particles in the medical waste were macerated into a homogeneous mixture during the sterilization cycle, resulting in a uniform heating of all materials within the process tank with no opportunity for large objects to prevent the high temperature water from coming into contact with the medical waste.
The SSM was found to be a cost-effective method to sterilize medical waste. The small size of the system (about the size of a typical autoclave) permitted its installation at many building locations such as loading docks or mechanical rooms. The sterilized residue was not recognizable and therefore could be discarded directly into a landfill, recycled or used as a fuel with no further treatment. No biological, chemical or occupational safety issues were found that would interfere with its placement in public areas. The SSM system reduced waste volume up to 90% and weight up to 30%.
On-site destruction of medical waste may provide cost savings and greatly reduce cradle to grave liability for biohazardous material since medical waste leaves the facility as municipal trash. This system has also been used to destroy paper and computer-generated electronic data.
The manufacturer/supplier of this equipment is Red Bag Solutions