Treating infectious waste
There are numerous non-incineration technologies sold to treat infectious waste. They can be classified as thermal, chemical, biological or irradiative technologies.
The most common is autoclaving. This uses high pressure steam, usually at 121-134oC, to disinfect waste so that it can be either recycled of disposed of safely.
Autoclaving is a highly flexible technology and one that many hospitals are familiar with as it is used for sterilising surgical instruments and many other sterile products.
Autoclaves are easy to operate, maintain and monitor. The majority of autoclaves operate on electrical power, but they can also use other fuels, predominantly gas.
Models available range from desktop units that process a few litres of waste, to machines for central treatment facilities, which are capable of processing tonnes at a time.
In addition to autoclaves, other waste treatment technologies use steam or dry heat as a disinfection agent. This includes microwaves, electrothermal disinfection, frictional heating and dry heaters. All of these operate below 180oC and do not change the physical or chemical form of the waste. As a result they produce little or no pollution, though care must be taken to ensure that wastes containing volatile chemicals such as solvents and mercury are not treated this way as they will be emitted to the atmosphere.
Chemical disinfectants are used by a number of technology providers. However, the majority of these involve persistent pollutants that will be emitted with the treated waste. An exception to this is ozone treatment, as this rapidly breaks down to oxygen. See the resources section for more information about these and other technologies.
Irradiative techniques that have been tested for infectious waste treatment include electron beams and ultraviolet light (UV-C). However, these are not in commercial use at present. Biological methods are not commercially available either, but biological breakdown in placenta pits and biodigesters can be used for pathological wastes and vermiculture (worm composting) has been tested for soft waste such as used bandages.
Whichever technology is chosen, proper monitoring is essential. Economical and simple tests called self-contained biological indicators, and costing around $2-3 each, can be used to check that the autoclave is operating effectively. UNDP has drafted recommended procedures for regular testing. Other types of test such as colour-changing paper strips can be used in certain circumstances but should not be used as a substitute for biological indicators.
Autoclaves for disinfecting medical waste should also undergo a validation when they are first installed. This will set appropriate operating parameters and should always be carried out, as all waste streams vary, and may also be packed differently. Lower cost autoclaves may be depend on gravity to fill with steam; these benefit from a technique called “pressure pulsing” which helps get steam deep into the waste. See the resources section for more information on this.
Waste treatment technologies
- UNEP Compendium: This is the most comprehensive and up to date document on how all the different waste treatment technologies work and also provides information on suppliers and costs, particularly for large scale models.
- UNEP (2012) Compendium of Technologies for Treatment/Destruction of Healthcare Waste. Publ: UNEP, Division of Technology, Industry and Economics, International Environmental Technology Centre, Osaka, 233 pp.
Alternative Treatment Technologies: HCWH has created a database of non-incineration treatment technologies from all over the world. Users can search by company name, technology, and by the country where the manufacturers operate. It can be found at: http://medwastetech.info/
- HCWH’s Inventory of alternative treatment technologies lists more suppliers of different waste treatment technologies than any other document. To make it easier to find appropriate technologies, they are listed by company name, by technology, and by the countries where companies operate.