NON-COMBUSTION TECHNOLOGIES FOR MEDICAL PLASTIC WASTE

Under normal circumstances medical facilities generate significant quantities of medical waste, including infectious medical waste that must be carefully managed to ensure its disposal does not lead to unnecessary human exposure and spread of disease. A significant fraction of this waste is plastic and can include personal protective equipment (PPE), such as face masks and shields, hoods, gloves, aprons, and over-boots. It can also be found in the form of medical equipment, such as syringes, blood bags, tubing, bags, and so on. In unusual circumstances such as pandemics, the rate of accumulation of used medical waste plastic can accelerate rapidly, and management options will require capacity to treat such waste that may require transportable disinfection units.

In the past medical waste incinerators were often used to dispose of infectious plastic medical waste. However, the high proportion of PVC used in medical PPE and other equipment leads to elevated dioxin emissions and contaminated ash from many incinerators, particularly in low-income countries, where waste incinerators are of rudimentary construction with little or no air pollution controls. The chlorine content of PVC has a significant influence on dioxin generation in combustion chambers.

Fortunately, there are commercially available and well-established noncombustion technologies to treat this form of waste. Most are different forms and sizes of autoclave disinfection units using steam treatment to disinfect medical waste. These range from quite small units for community clinics to large-scale industrial units for hospitals and medical waste treatment contractors. Some operate in fixed form and others are mobile. The autoclaves are relatively easy to operate compared to waste incinerators, and do not require the prohibitively expensive air pollution control (APC) equipment of medical waste incinerators. At a minimum, medical waste incinerators must be fitted with APC including electrostatic precipitators for particulates, activated carbon injection for dioxin and UPOPs minimization, and lime injection to reduce acid gas emissions. Some may also be equipped with baghouses which are expensive to install and maintain. Incinerators also generate significant greenhouse gases when compared to steam and microwave based non-combustion technologies.

Both the United Nations Environment Programme (UNEP) and the World Health Organization (WHO) support the use on non-combustion technologies ahead of incineration due to the UPOPs released from incineration technology (UNEP 2003, UNEP 2012). Combustion technologies other than incineration, such as cement kilns, are sometimes proposed for burning medical waste. However, cement kilns are not suitable for burning medical waste according to the Stockholm BAT BEP Guidance Part II Source category (b): Cement kilns firing hazardous waste.

Figure 39. L-R: Bondtech autoclave, on-site autoclaev with lift table at a hospital, waste dumper

Figure 40a. Sanitech medical waste disinfection system as truck mounted and stationary units.

Figure 40b. Disinfected, shredded waste output from a Sanitech unit

There are a large range of steam and microwave units available to suit most clinical applications and bulk treatment. A detailed assessment including throughput rates and residues are available in the 2012 UNEP Compendium of Technologies for Treatment /Destruction of Healthcare Waste.

Autoclave units use steam instead of combustion for disinfection and do not require APC as they have no hazardous emissions. They do not produce a hazardous ash residue after treatment, rather they produce a disinfected version of the waste they treat. Most autoclave units are fixed, but there are some designs that are highly mobile such as Sanitech units. In Sanitech units, the waste is shredded and subject to steam disinfection via microwave heating. The Sanitech company suggests that the resulting waste stream is capable of being recycled as lower grade plastic products. This would depend to some degree on the feed input and separation of other materials, such as sharps and bandages, that would contaminate a potential recycling stream. The priority of autoclave technologies is disinfection and not recycling, so most outputs of the process are landfilled.

Sanitech units are operated with a top feed shredder that exposes the waste material to a high temperature, microwave heated steam environment via a worm screw to ensure residence time is sufficient to destroy any pathogens in the waste. A periodic test is conducted using Bacillus atrophaeus spores to validate microbial inactivation by inserting a capsule in waste batches, which is retrieved at the end of the process and analyzed to ensure full destruction of pathogens has taken place. It has a relatively high throughput at 810 kg/hr and operates in stationary configurations, which can be accommodated on hospital grounds, and in transportable mode (they are built within shipping container specifications). They also have purpose-converted trucks that house Sanitech units for rapid despatch to multiple facilities for batch treatment.

In pandemic situations, multiple units can be rapidly installed to treat higher than usual waste volumes or can be driven or shipped to more remote locations where outbreaks have occurred helping to minimize the transport of infectious waste and potential exposures. The Sanitec company claims that the residues from process can be recycled in lower grade plastic products but are commonly sent to municipal landfill.