Treatment of Medical Waste
The primary methods of treatment and disposal of medical waste are:
The treated waste - if sufficiently sterile - can generally be disposed with general waste in a sanitary landfill, or in some cases discharged into the sewer system. In the past, treatment of medical waste was primarily performed on-site at hospitals in dedicated medical waste facilities. Over time, the expense and regulation of these facilities have prompted organizations to hire contractors to collect, treat, and dispose of medical waste, and the percentage of medical organizations that perform their own treatment and disposal is expected to drop.
To ensure that each treatment method provides the proper environment for the destruction of biologicals, test indicators for microbiological spores measure the treatment effectiveness. Microbiological spores are the most difficult of biologicals to destroy, so when the test package cannot be cultured after treatment, the waste is considered properly treated. In treatment methods where shredding or maceration is employed, the test package is inserted into the system after the shredding process to avoid physical destruction of the test package. The test package is then retrieved from the waste after treatment.
Incineration is the controlled burning of the medical waste in a dedicated medical waste incinerator. Among industry professionals, these units are often referred to as hospital/medical/infectious waste incinerators (HMIWIs).
Incineration is an old technology and was widely used in the past for all sorts of waste. Individual buildings had their own waste incinerators in many cases. Incinerators got a bad reputation because of the air pollution they created and because the bottom ash, or sinter, was hard to keep under control. Lay members of the public unfortunately still have negative associations with incinerators. Today’s incineration units are typically much cleaner.
There are parts of the world where open pit burning still take place. And accidental fire - e.g. a house on fire - produce flames and smoke and debris. This makes “burning” and “combustion” bad words, but when approached from a cold hard engineering standpoint, incineration is often the best technology for treating medical waste. It can eliminate pathogens - even hard-to-kill bacterial spores - and can reduce the volume and mass of waste that goes to landfills considerably. Incineration can break down and render harmless hazardous organic chemicals. With proper technology, little acid gas is released to the atmosphere.
There are fewer medical waste incinerators operating in the United States today than there were decades ago when practically every hospital had an incinerator. However, incineration technology is still an important part of the medical waste management landscape.
Because most medical waste can be incinerated, the waste is not sorted or separated prior to treatment. Incineration has the benefit of reducing the volume of the waste, sterilizing the waste, and eliminating the need for pre-processing the waste before treatment. The resulting incinerated waste can be disposed of in traditional methods, such as brought to a landfill. The downside of incineration is potential pollution from emissions generated during incineration. The EPA has stringent requirements on emissions from medical incinerators. The incineration process can be applied to almost all medical waste types, including pathological waste, and the process reduces the volume of the waste by up to 90%.
Modern incinerators can provide a secondary benefit by creating heat to power boilers in the facility.
The largest concern associated with incineration is air pollution from emissions. The EPA says that at least 20% of medical waste is plastic. The biggest concern is that the incinerator may create toxic compounds. Dioxins and furans can be produced when these plastics burn. Older medical waste incinerators included no pollution control equipment. As new federal and state emission regulations are instituted that have more stringent requirements, medical incinerators are often not being replaced at the end of their service life. Over time, the amount of waste being incinerated will be reduced as other technologies replace on-site incinerators.
Another concern is incinerator ash. As incinerators are designed or retrofitted with pollution prevention equipment, more of the potentially toxic chemicals that previously ended up in emissions now remain in the ash. Incinerator ash is generally disposed of in landfills.
Downsides of incinerators
The public often has an aversion to incinerators and may raise objections if they hear one is being put in their area. The popular perception of incineration is informed by pictures of open pit burning done decades ago in the US and still today in some countries. Open pit burning is indeed not effective enough and results in smoke and other undesirable materials being released to the atmosphere. Most people don’t understand how incineration units can be made clean-burning and engineered to reduce the risk of dangerous releases. Most people also don’t understand how many incinerators are in their area already.
However, incineration can be a dirty process if not controlled adequately or if the process has not been designed correctly. Incineration can produce
- Fine particles (in the smoke) - The particles can include heavy metals. If removed from the smoke before release, these particles are called fly ash and constitute another disposal problem.
- Acid gases - these are formed during burning. Chlorine compounds, when burned, yield hydrochloric acid. Sulfur compounds yield sulfur dioxide or sulfur trioxide. Nitrogen oxides are produced in any high temperature treatment.
- Ozone - indirectly. Nitrogen oxides from the exhaust can subsequently react with hydrocarbons in the air to produce ozone.
- Bottom ash or sinter - the ashes after the incineration process is complete. Mostly inorganic material. This is disposed of in a landfill - either sanitary one or a hazardous waste one.
- Heat - While good incinerators are insulated to save energy and protect workers, heat generation must be accounted for in facility and process design.
Ship-mounted incinerators will burn your waste for a fee. The advantages of burning waste at sea is that it is away from population centers and, if far enough from land, is free from national laws and regulations. That means the incinerators can be less efficient and pollute more. Ash from the incinerators is often dropped into the ocean.
There may be international treaties about these operations - such regulations are beyond our scope. The waste manager may have ethical problems with these solutions as they seem an “easy-out” and way to skirt the rules and to be irresponsible.
Mobile incinerators tend to be small and have the same downsides as ship-bourne incinerator. Getting a mobile incinerator to pass EPA regulations can be a challenge. They are usually less efficient and often more prone to creating furans and dioxins in the exhaust. In the past, these were often employed for Principles of Medical Waste Management">treatment of pharmaceutical waste.
Small-scale incinerators were once common in the United States and are still used in much of the world. They are generally less efficient and more prone to releasing pollution than large, well-engineered incineration systems. While small incinerators are almost always superior to dumping medical waste with no treatment, they should be considered only if there is no better solution available.
Even small incinerators can be optimized with good engineering design and operating procedures. The size and the throughput should be balanced to ensure a high residence time in the furnace. A good rule of thumb is to aim for 1200 degrees C with a vapor-phase residence time of 2 seconds.
Guidelines for incinerator operation
- Chlorine-containing materials should be removed from the feed, if feasible. This includes polyvinyl chloride (PVC) plastic. Chlorine burns to hydrochloric acid, and although a pollution control system on the tailpipe should be able to reduce emission to acceptable levels,
- Incinerators should be located in areas away from high population areas and where food is grown.
- In addition to the engineering design and construction, thoughtful development of operating procedures. These should include limits on the type of material that can be put into the incinerator and the flowrate of input.
- Temperature should be monitored at several places in the incinerator and the system should shut down if the temperature falls too low. start-up and cool-down procedures should be spelled out.
- An ash disposal plan and procedure should be implemented. Regular maintenance should be carried out on operating incineration systems.
- Single-chamber incineration systems are considered sub-par. Best available technology is a two-chamber system with a fired afterburner to ensure complete combustion of off-gases.