Autoclaving
Autoclaving is a sterilisation method that uses high-pressure steam. The autoclaving process works by the concept that the boiling point of water (or steam) increases when it is under pressure[1].
History
The name Autoclave comes from the Greek "auto" ultimately meaning self and the Latin term "clavis" meaning key, thus a self locking device[1]. The first autoclave was essentially a pressure cooker and was originally invented as a method for preparing food by French physician Denis Papin around 1681. He called his invention a "steam digester" and described benefits of using the device to process food for easier digestion[1].
The autoclave was re-invented for medical and scientific use by Charles Chamberland in 1879. Chamberland was a microbiologist who worked with Louis Pasteur[1].
Application to Waste Sector in UK
Whilst Autoclaves are used for the disinfection of medical equipment to allow them to be reused, the application of Autoclaving in the UK for waste as a Mechanical Heat Treatment (MHT) has focused on three main waste streams to date:
- Healthcare Waste is the most wide spread application of the use of Autoclaving as a treatment process, with more recent applications to specific waste streams such as single use nappies.
- Municipal Solid Waste [2] applications have been developed in the past, which focused on the production of a Waste Derived Fuel.
- Graphite Resources (Derwenthaugh EcoParc - Newcastle)
- Orchid Environmental (Merseyside)
- Sterecycle (Rotherham) - closed and company went into liquidation following an explosion at the plant in 2011 with a resulting fatality[3]
- Aero Thermal (Plymouth) - not progressed
- Food Waste Autoclaving as part of a pre-treatment process prior to Anaerobic Digestion is still being promoted[4] as increasing biogas yields by Aero Thermal
Operation of an Autoclave with Healthcare Waste
Items to be autoclaved are subjected to gradual temperature increases under high pressure until 121 °C is reached and then steamed for around 15–20 minutes[1]. The autoclave allows steam to flow around items in the chamber. The length of time and temperature necessary for sterilization depend on the items to be sterilized and whether they are wrapped or left directly exposed to the steam,[1]. Items should be separated to allow the steam to penetrate the load evenly. The steam can reach in small crevices and can kill all bacteria, viruses and bacterial spores[1].
Autoclaves can be used to eliminate microorganisms and for hydrothermal synthesis[1]. Autoclaving is a very dependable method for the sterilization and decontamination of laboratory glassware, medical instruments and certain types of Healthcare Waste, reagents, and other media. Autoclaves can inactivate fungi, bacteria, spores, viruses and other microorganisms on surgical instruments such as scalpels, scissors and other metal items[1].
Some autoclaves are designed to shred Healthcare Waste during the treatment cycle; other systems rely on the use of a pre-treatment process to macerate the waste before the waste is heated[5].