In conventional or surface-heating systems, such as those found in autoclaves, a composite part heats from the outside inwards: as heat energy is transferred through the part’s thickness. The process duration is determined by the rate of heat flow into the composite structure. The flow rate depends on the material’s specific heat, thermal conductivity, density and viscosity. As a result, the edges and corners of the part achieve the set point temperature before the centre does. The subject part also heats at an uneven rate, which can stress the finished product. Therefore, the temperature in an autoclave and a conventional oven must be ramped up and down slowly to minimise part stress, a factor that makes overall sterilisation difficult and awkward.
Conversely, microwave technology relies on volumetric heating. Heat energy is transferred electromagnetically and relatively evenly and quickly throughout the part and therefore, not as a thermal heat flux. This enables better process temperature control and less overall energy use and thereby resulting in shorter cure cycles. It also enables the processor to direct heat specifically toward the part to be cured, thus maximising the curing process efficiency. Surprisingly, all this sterilisation is archived more effectively with very high sterilisation quotient. In various studies conducted at the Centre for Innovation and Translational Research (CITAR), CSIR-Indian Institute of Toxicology Research, the disinfection efficacy of a portable batch microwave system was assessed against both gram-negative and gram-positive bacteria and yeast on different types of materials used in hospitals and laboratories such as linen cloth and fabrics, rice husk, corn cob (animal bedding material) and blood culture bottles and from these studies it was concluded that the log reduction efficacy of microwave is much greater than autoclave.
In case of contaminated linen, the efficacy of microwave is up to 8 log reduction, within 10-minute exposure of 2.45 GHz (Gigahertz) at 70 °C. Similarly, a 10-log reduction was achieved after the 30-minute exposure of microwave irradiation at 100 degree C for rice husk and corncob but in case of blood culture bottles the same temperature is sufficient for 10-minutes to inactivate any type of bacteria, fungi, yeast and spores. Inevitably, microwave-based sterilisation is much under 100 Celsius and thereby allowing heat sensitive materials an easy pathway with minimum application of resources.
The following table-1 summaries the comparison outcome between the autoclave and microwave from many different aspects, which any healthcare facility may take into consideration when planning for effective on-site bio-hazardous waste management.
The steam autoclave is the closest market competitor for Microwave (MATS) but the comparison of the technology platform, infrastructure requirement, environmental impact and operational cost would make Microwave of more favourable choice over steam autoclave. As shown in Figure 1, the power consumption, water consumption and cost per kilogram of waste treatment through microwave technology make it an eco-friendly and cost-effective system.
Microwave technologies are available at a global level, which negates all kinds of limitations and challenges usually for disinfection and/or sterilisation of infectious medical waste at the point of generation. Usually, in small and medium size hospitals, it is difficult to follow all the steps and guidelines for medical waste management. However, such hospitals manage the wastes through agencies or vendors to transport at incinerators. Therefore, an on-site solution for medical waste treatment with real-time monitoring is needed, to avoid any kind of security breach during interim storage in the facility and transportation of medical waste from the hospital to treatment site.
The WHO has also recommended “microwaving” as one of the alternative non-burn methods for biomedical waste management. Thus, proper segregation of hazardous and non-hazardous waste and treatment of non-hazardous waste through microwave-based disinfection/sterilisation system will help in the following ways:
1. Drastically reducing the amount of waste going for incineration and thus decreasing the institutions/user carbon footprint as pollution caused by incineration is reduced.
2. Concerning scarce natural resources with almost zero utilisation of water and electric energy.
3. Very high level of microwave sterilisation archived in 1/4th the time reduces infection load and safe disposal.
4. Low cost of installation and maintenance.