SELECTION OF HEALTH CARE RISK WASTE TREATMENT TECHNOLOGIES FOR GAUTENG
Dave Baldwin
Director, Environmental & Chemical Consultants, PO Box 2856, Cresta, 2118
Co-Author:
Torben Kristiansen, Chief Technical Advisor, Gauteng Department of Agriculture, Conservation, Environment and Land Affairs, Rambøll, Hannemann & Hojland
ABOUT THE SPEAKER
Dave Baldwin graduated with a BSc Honours and PhD in chemistry from the University of Manchester Institute of Science and Technology in 1967. After three years of postdoctoral research in inorganic chemistry at the University of Washington, Seattle and University College London, he joined the Chemistry Department, University of the Witwatersrand in 1970 as a lecturer in Inorganic Chemistry and was involved in teaching and research, largely in inorganic chemistry for the next 16 years. This period included one-year sabbatical leaves at the California Institute of Technology, Pasadena in 1977and the Albert Einstein College of Medicine, New York in 1984. In 1982, Dave developed a strong interest in general and hazardous waste management and became a consultant to industry initially on all aspects of hazardous waste treatment and disposal. In 1986, he joined the CSIR as a programme manager, where he developed his interest in providing consulting services to industry in analytical chemistry, the development of chemical processes and solid and liquid waste management. He left the CSIR in 1990 to start Environmental and Chemical Consultants cc and has since provided consulting services in this area and been a director of Waste-tech (Pty) Ltd and Fraser Alexander Holdings. He was involved in the introduction of commercial “medical waste” treatment services into South Africa and developed a system for chemical waste management for small producers. He was a member of the working group that developed the Minimum Requirements for the Handling, Classification and Disposal of Hazardous Waste, which was published in 1994 and was the South African Hazardous Waste Consultant during the development of the National Waste Management Strategy in 1997 and 1999. Clients include waste management companies, the chemical and allied industries, mining industry and national, provincial and local government.
ABSTRACT
During the development of a Sustainable Health Care Waste Management Programme for Gauteng, a comparison was made of the environmental, health and safety impact and the advantages and disadvantages of the various treatment technologies for health care risk waste, i.e. burn technologies such as incineration, and non-burn technologies, such as microwaving and autoclaving. The cost-estimates are based the price level of 2002 and on South African manufactured incinerators, whereas the key technology component of non-burn treatment plants was assumed to be imported typically from the US or Europe. Furthermore, the costs are based on the environmental minimum requirements set out in the Health Care Waste Management Policy (November 2001) by the Gauteng Legislature and the current draft Health Care Waste Management Regulations that are expected to be promulgated in Gauteng in 2003. These requirements result in the need to install flue gas cleaning systems for all incinerators for the removal of acid gases, dioxins and heavy metals as well as the removal of dust, whereas the non-burn treatment plants will need to carry out detailed verification of the level of disinfection achieved. The study also included a cost comparison of the various technologies, which showed that microwaving was generally more expensive up to a capacity of 2000kg/hr. At low throughput capacities, i.e. <200kg/hr, incineration was more expensive than autoclaving but the costs became more comparable once the throughput increased above 500kg/hr. The costs of monitoring the emissions from incinerators and the sterilisation efficacy of non-burn technologies were also evaluated and will be presented.
SELECTION OF HEALTH CARE RISK WASTE TREATMENT TECHNOLOGIES FOR GAUTENG
INTRODUCTION
South Africa has mainly used incineration as the technology of choice for the treatment of health care risk waste. However, an investigation into the status quo of health care risk waste management in Gauteng completed in 2000 (GDACEL, 2000) confirmed the general impression held by many practitioners that the management of this hazardous waste was in a parlous state. Most incinerators, particularly those in the public and private hospitals, were not operated to the required standards and, therefore, represent a significant environmental and health risk. During the subsequent development of a Sustainable Health Care Waste Management Programme for Gauteng, a comparison was made of the environmental, health and safety impact and the advantages and disadvantages of the various treatment technologies for health care risk waste, i.e. burn technologies such as incineration, and non-burn technologies, such as microwaving and autoclaving. Since, health care risk waste consists of four major waste types, i.e. infectious waste including sharps, chemical waste including pharmaceutical waste, pathological waste and radioactive waste, a waste management programme must cater for all four types of waste. A treatment technology, which is normally developed for sterilisation of the infectious component of the waste, must either be able to treat all waste streams or the different types must be separated at source. The main treatment options for health care risk waste include:
- Combustion Technologies, i.e. thermal treatment/combustion technologies:
Incineration which includes: excess air, controlled air, rotary kiln and fluidised bed
Plasma Arc and
Pyrolysis
- Sterilisation/Disinfection Technologies,
Steam sterilisation, e.g. Autoclaving
Chemical sterilisation, e.g. with chlorine, glutaraldehyde
Gas sterilisation, e.g. with ethylene oxide, formaldehyde
Dry heat sterilisation, e.g. oil heated screw feed technology
Electro-thermal deactivation (ETD),
Microwave sterilisation,
Irradiation sterilisation
Cobalt-60 gamma rays
Ultra violet
Electron beam sterilisation
The technologies indicated in italics are experimental or have limited commercial application internationally: UV treatment is largely effective only as surface treatment. Recent developments have resulted in the introduction of commercial non-burn facilities using Electrothermal Deactivation in Gauteng and the Western Cape, and Autoclaving in KwaZulu-Natal and a number companies are proposing the introduction of microwave facilities and a chemical sterilisation technology. Also, modern incinerators with scrubbers are being introduced or existing facilities are being modified to meet the expected more stringent gas emission standards. All of the above treatment technologies result in a residue, i.e. ash in the case of burn technologies or a sterilised/disinfected waste that has to be disposed to landfill. Note that in terms of the South African Minimum Requirements for the Handling, Classification and Disposal of Hazardous Waste, health care risk waste cannot be landfilled unless it is incinerated or otherwise sterilised.
There are significant differences between burn and non-burn technologies and the most important of these are the types of health care risk waste that can be treated and the residues that are generated, as well as the type of emissions and where they occur; these are illustrated in figure 1. In the diagram it is assumed that the combustion treatment facility meets all the National and Provincial Standards and, therefore, can accept three of the major types of health care risk waste, i.e. infectious waste including sharps, chemical waste including pharmaceuticals and pathological waste, and that a gas cleaning system is used. Pathological (Anatomical) waste, which includes recognisable human parts, and chemical waste should not be handled by non-burn technologies and alternative technologies must be used for their treatment and disposal. Radioactive waste is not included in Figure 1, although selected low radioactive waste that comes from health care facilities could be treated, subject to permits. However, no radioactive waste can be treated by non-burn technologies and all must be disposed to special permitted waste landfills/depositories.
Figure 1: Generic Differences Between Non-burn and Burn Technologies for the Treatment of Health Care Risk Waste
Incineration/Combustion Technology
The main elements of modern incineration technology are illustrated schematically in Figure 2. Historically single chambered incinerators have been used for the treatment of health care risk waste and there are many still in use in Gauteng and the rest of the country. Further, developments included the introduction of multi-chambered incinerators, both excess air and starved air/controlled air types specifically designed and permitted for the treatment of the infectious waste stream. These incinerators are potentially capable of handling small quantities of chemical hazardous waste. An automatic feeding system is used for feeding the waste into the incinerator. The waste is combusted/pyrolysed in the primary combustion chamber with a stoichiometric deficit of air at temperatures ranging from 650oC to 1100oC. A support burner, usually fired by fuel oil or gas, is used both during start up and intermittently during operation to achieve and maintain the required temperature. The result is a bottom ash or slag and a gas stream containing combustible volatile organic compounds, particulates and potential pollutants. In the secondary combustion chamber, an excess of air is added and a secondary support burner fired by fuel oil or gas is used, if required, to maintain the temperature above 1100 oC to give complete burning of the combustible gases and solids from the primary chamber. A minimum retention time of 2 seconds is usually required. Energy can be recovered via a water/steam boiler but in South Africa this has been found to be uneconomic largely due to the small size of the incinerator and the relatively low cost of energy. The flue gas is cleaned using either wet, dry or semi-dry flue gas cleaning including a dust filter. Normally wet flue gas cleaning is not economic for health care risk waste incinerators because of their small size; hence, most plants make use of semi-dry or dry flue gas cleaning. Using flue gas cleaning systems, the strict emission limits for acid gases, particulates, heavy metals and dioxins set by many countries can be achieved. Common filters used are bag house filters or the more temperature tolerant ceramic filters. Typical neutralising agents for acid gases used are lime or bicarbonate products, possibly with activated carbon added for dioxin or heavy metal removal.
Figure 2: Flow Diagram of a Modern Incineration Plant.
The typical inputs and outputs of materials and energy for the modern incineration process are also indicated in figure 2. The ash and any other solids and liquid wastes, e.g. from gas cleaning, must be classified, as required by the Department of Water Affairs and Forestry’s Minimum Requirements for the Handling, Classification and Disposal of Hazardous Waste, and disposed to an appropriate hazardous or general waste landfill.
Advantages and Disadvantages of Incineration
The main advantages and disadvantages of incineration as a technology for the treatment of health care risk waste are listed in table 1.
Table 1: Advantages and Disadvantages of Incineration
Advantages of incineration / Disadvantages of incinerationSafe elimination of all infectious organisms in the waste at temperatures above ~700oC
Flexible, as it can accept pathological waste and depending on the technology chemical waste.
Residues are not recognisable
Reduction of the waste by up to 95% by volume or 83 to 95% by mass: typically 5-17% ash is obtained.
Very well proven technology
No pre-shredding required
No special requirements for packaging of waste
Full disinfection is assumed to have occurred provided the high temperatures are maintained and the ash quantity is adequate. No monitoring of sterilisation efficiency is required. / Normally higher investment costs required for incinerator and flue gas cleaning compared to non-burn technologies
Point source immediate emissions to the air (as opposed to attenuated emission of CH4 and CO2 from landfill body over a period of decades)
High cost of monitoring gas emissions and demonstrating compliance to emission standards.
Solid and liquid by-products must be handled as potentially hazardous waste (may not apply to bottom ash if waste is well sorted and FGC residues handled separately)
Incineration is perceived negatively by many sections of the community.
PVC and heavy metals in the waste provide a significant pollutant load on the gas cleaning system (and for heavy metals on the quality of bottom ash also).
Existing health care risk waste incinerators in South Africa cannot accept significant amounts of chemical waste because of refractory damage (but above you argue that modern plants can to some extent.)
Separation at source is a key requirement for the correct management of health care risk waste, but incineration with flue gas cleaning is more forgiving than many other technologies, as it can accept pathological waste and, depending on the amount, the type of incinerator and its construction, chemical waste. For many of the pyrolytic dual chamber incinerators currently in use in South Africa, the amounts of chemical, including pharmaceutical waste that can be accepted is low. Thus, like normal household waste, which contains small amounts of hazardous chemical waste, the infectious waste stream must be expected to include small amounts of pharmaceuticals, chemicals used in wards, such as disinfectants, solvents, etc., even when a programme for separation at source has been instituted. An incinerator can readily accept this waste stream. However, most of the current incinerators available in South Africa should not deliberately accept chemical including pharmaceutical waste due to damage to the incinerator and significantly increased requirements for gas cleaning.
Environmental, Health and Safety Impact of Incineration
Incineration has proven to be a very effective way of sterilising health care risk and no special tests to determine the efficacy of the sterilisation process is normally required. However, in the past, most of the health care risk waste incinerators in South Africa have been poorly operated and almost all have not been fitted with emission control equipment. Tests on the emissions have shown that the incinerators are unable to meet the current DEAT Emission Guidelines for a Schedule 39 Process for some heavy metals and for HCl. Gauteng Province has decided to insist that, in future, incinerators meet the DEAT Emission Guidelines as a minimum requirement and this means that gas-cleaning equipment will be needed. With modern wet or dry gas cleaning techniques, incinerators have been able to meet the strict standards imposed in the USA and the European Union.
Apart from gas emissions, incinerators produce an ash, which normally classifies as hazardous, although it can be delisted to general sites, if chemically stabilised with lime or treated by cementation; the volumes of ash generated are small. Source separation can result in reduced amounts of heavy metals being present in incinerator ash and potentially facilitate delisting of the ash, although two of the major problem metals, lead and zinc, are introduced with PVC because of the use of lead and zinc soaps during the production process. Gas cleaning can be accomplished by both wet and dry scrubbing. Dry scrubbing is generally preferred, as it is more economic for the typical HCRW incineration plant capacity, and, the resulting solid, which may be classified as hazardous, can be disposed to hazardous waste landfill, whereas the liquid wastes generated by wet scrubbing is charged a premium when disposed to landfill.
Incineration is still a very common technology for health care risk waste treatment internationally, as it can meet the required strict environmental requirements, provided they are well operated and have good emission control equipment. However, in world regions with no or limited mass incineration of domestic or commercial waste steam sterilisation, microwave treatment and other non-burn technologies are fast becoming the most effective HCRW treatment technology with increasing costs of flue gas cleaning.
Microbial Inactivation using Non-burn Technologies
Increasing emission requirements resulting in increasing cost of flue gas cleaning for incineration plants as well as an unfavourable perception of incineration has lead to the development of a range of sterilisation/disinfection technologies for the treatment of health care risk waste (see the introduction). Autoclaving, microwaving and ETD sterilise result in heating of the waste to moderate temperatures, 90oC to 160 oC, which results in its sterilisation, provided all the waste is subjected to the required temperatures for sufficient time. The sterilisation standards are discussed in the following paper (L Godfrey et al., 2003). Chemical treatment on the other hand uses a chemical sterilising agent to achieve equivalent treatment standards. In this paper, microwave technology will be briefly discussed as a typical non-burn technology. In the microwaving process, infectious waste is normally wetted or exposed to high-temperature steam, shredded and the moisture in the waste heated by a series of microwave generators for a specified period. The temperatures reach ~95oC and the microorganisms are killed in the process, resulting in a residue that is confetti-like and slightly moist. Microwaving has been used to treat such items as sharps, microbiological materials, blood, and biological fluids. It is not suitable for the treatment of pathological chemically hazardous, or radioactive wastes and large quantities of metals can reduce the effectiveness of the microwaves’ penetration of the waste. Air emissions from the shredder and treatment plant are usually treated to remove moisture and volatile organic carbon compounds. The volume of the final waste product is reduced significantly by shredding and compaction of the final product, but almost no mass reduction occurs.