The primary methods of treatment and disposal of medical waste are:
The treated waste - if sufficiently sterile - can generally be disposed with 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 has dropped.
To ensure that the treatment method provides the proper environment for the destruction of microbes, test indicators for bacterials spores measure the treatment effectiveness. Microbiological spores are among the most difficult of biologicals to destroy, so when the indicator 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 incinerator. Among industry professionals, these units are often referred to as hospital/medical/infectious waste incinerators (HMIWIs).
Engineers often look at expected heat generated by combustion when choosing which incinerator to use: waste with heating value over 3500 kcal/kg is processed in a pyrolysis unit while lower heating value waste is burned in a single-chamber incinerator. Waste is typically heterogeneous, and if the combustible fraction is below 60 percent, it may not be acceptable for incineration. Overly wet waste (over 30 percent water by weight) is probably not good for incineration either as it will require excessive quantities of assist gas/fuel.
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 clinker, was hard to keep under control. 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.
Incineration requires no pretreatment. Because most medical waste can be incinerated, the waste does not always require sorting or separation prior to treatment. Incineration has the benefit of reducing the volume of the waste by 80 percent or more, sterilizing the waste, and reducing the need for pre-processing the waste before treatment. The resulting incinerated waste can be disposed of in traditional methods, such as landfilling. 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. Dioxins and furans can be produced when these plastics burn. Old medical waste incinerators included no pollution control equipment but ones operating in the US today do.
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. The ash can be hazardous waste. Incinerator ash is generally disposed of in landfills after it is stabilized.
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
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.