The proper management of hospital/healthcare/biomedical waste has become topic of enormous concern having global implications and attention. Healthcare facilities such as hospitals, physician clinics, dental facilities, laboratories, medical research facilities, veterinary clinics, etc., produce 10 to 15 per cent infectious waste of total general waste according to World Health Organization (WHO). The waste generated in such facilities is termed as biomedical waste. The mushrooming of the healthcare industry within the milieu of the developing countries coinciding with the drift towards greater environmental consciousness, and greater accountability of both the occupier and the common bio medical waste treatment facility operator, bring the concept of reducing, recycling and reusing to the fore.
A study by Marinkovic et al. (2007) indicated that the hazardous medical waste including infectious waste, sharps, pathological waste, chemical waste, pharmacological waste and cytostatics corresponded to 14 per cent of the waste generated from healthcare services in Croatia. Similarly, the amount of infectious waste was determined as 15 to 20 per cent of healthcare waste, and in the U.S. this rate was around 15 per cent according to Lee and Hufman (1996). In a case study it was found that the major producers of hazardous waste are state hospitals with a generation rate of 57.9 per cent.
As of now the untreated infectious waste is directly sent to common bio medical waste treatment facility for incineration or final disposal. Thereby, the chance of infection during transportation, interim storage and handling is greater.
Therefore, due importance must be given to disinfection or sterilisation of infectious laboratory and bio-hazardous wastes at the point of generation, to find a better solution or appropriate technology for the proper management. However, various technologies are available in the market at a global level, in which the most commonly used technology for biomedical waste management are incineration, chemical disinfection, steam sterilisation, land disposal and inertisation. Recently, microwave technological leaps have opened new horizons for medical waste treatment and are promising an opportunity that has less burden on the environment, shorter time of treatment and are more cost effective. The aim of this study is to explore the efficacy and benefits of microwave technology in comparison to the existing available methods of bio-hazardous wastes treatment.Comparison of microwave to other waste treatment technologies
Among all the technologies, steam autoclave is a broadly used technology as an alternative to conventional incinerators. However, steam-based sterilisation has several limitations such as slow heating, penetration depth, pre-and post-treatment process, size and load limitations. Concerning operating costs, the compendium noted for autoclaves between US$0.14 and US$0.33 per kg, and for batch microwaves about US$0.13 per kg, respectively (UNEP, 2012). Other limitations of steam sterilisations like some plastic ware melts in the high heat, and sharp instruments often become dull. Moreover, many chemicals breakdown during the sterilisation process and oily substances cannot be treated because they do not mix with water. Previously it was reported that the anatomical and pathological wastes, low-level radioactive waste, organic solvents, laboratory chemicals, and chemotherapy waste should not be treated in an autoclave.
From the above mentioned four methods (i.e. thermal, chemical, irradiative and biological), the irradiation is very effective as well as rapid. The irradiation-based technologies involve ultraviolet, gamma, electron beam as well as the microwave. However, radiation sterilisation techniques do have a number of drawbacks. Capital costs are high and specialised facilities are often needed. Gamma radiation requires a nuclear reactor; E-beam/X-ray radiation is generated using electron beam accelerators. Common plastics such as polyvinyl chloride (PVC), acetyl and polytetrafluoroethylene (PTFE) are sensitive to gamma radiation, thereby limiting the use of Gamma. The high energies involved in e-beam radiation can also lead to main chain scission (breaking of the long chain backbone) and chemical cross linking of packaging polymers.
But in case of microwave irradiation such types of limitations are overruled. This technology is based on the low heat thermal process where disinfection occurs through action of dielectric heating. In this process, the changing electric field forces the molecular dipoles (such as water) to be aligned according to field, which creates rapid heat due to molecular friction. However, back and forth movement of ionic molecules in the oscillating electric field is another reason for instant heat generation and subsequent annihilation of virus, fungus, yeast, bacteria and spores. In a study, the efficacy of a batch microwave was evaluated by Dhole and his team at Sanjay Gandhi Postgraduate Institute of Medical Sciences against the NPEB/Polio-1 virus of NIBSC strain and for quantitative analysis and the viral load was determined via 50 per cent tissue culture infective dose (TCID-50), and it was found that the value of TCID-50 is zero, which means no contaminants were found after 360 seconds of microwave exposure at 100 degree C and there is no cytopathic effect (CPE), as was observed (Qualitative Analysis).
Comparison of microwave to autoclave
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.
Exciting outcomes from various studies using microwave (MATS)
In further studies at CITAR, a microwave unit was shown to provide multiple logarithm reductions in both vegetative bacterial cell counts, and bacterial spore counts in laboratory-inoculated samples. From this study a 10-log disinfection efficacy of representative bacteria and fungi (in liquid cultures) was achieved via microwave (2.45 GHz) treatment at 70 degree C with a hold time of 20 min. A 6-log disinfection efficacy of representative heat resistant Bacillus subtilis spores was also achieved at 100 degree C with a hold time of 30 minutes.
On the other hand, the effective disintegration of gram-negative cell walls in municipal secondary sludge by microwave was confirmed by scanning electron microscopy and it was suggested that this technology could be an effective pre-treatment method for sludge that is dominated by gram-negative microorganisms. It was already said that due to exposure to the microwave, E. Coli and B. subtilis was entirely due to thermal energy.
For healthcare waste, scientists at the National Institute of Standards have devised a way to sterilise medical instruments and waste for hospitals in a device similar to a conventional microwave oven and termed this the “sterilisation wave of the future”. In 2007, an experiment was designed to simulate a poultry mass mortality event and generated a 7-log reduction in the microbial load of Salmonella enterica and a 5-log reduction in Bacillus atrophaeus spores. Therefore, the literature review and ongoing researches show clear evidence base that the use of microwave for the management of biomedical waste is a promising concept.
Ongoing research and applications of microwave technologies (MATS) have shown and proven that microwave devices are an effective tool for the inertia of biohazard waste to control the spreading of highly pathogenic microbes present in waste during the interim storage in healthcare facilities and transportation when the infectious waste is treated at the point of generation. When compared to other technologies especially autoclave, microwave MATS is likely to have similar sterilisation efficacy if not better in protecting the integrity of heat sensitive materials, has shorter processing time, and takes advantage of microwave-assisted processes requiring control of water content. In addition, it saves energy, cost and thus leads to a low carbon footprint.
In our opinion, for those healthcare facilities seeking operational excellence and sustainable resources in line with the untied nation (UN) goals and WHO initiatives in reducing infections worldwide, global warming and energy/water consumption, microwave technologies provide promising clean solutions and are becoming the leading cutting-edge solution for the biomedical waste management industry thanks to its supportive applications. References available on request.