There are many options, because medical wastes vary in its characteristics and degree of risk and because treatment methods vary in their capabilities, cost, availability to generators, and impacts on the environment (Table 33.4).
1. Infectious Wastes and Sharps:
ADVERTISEMENTS:
Major portion of the sharps are the needles, which can be cut by needle cutter and contained in a bleaching powder solution or autoclaved or/and shredded or be destroyed by a needle destroyer (NACO, n.d.). Sharps should undergo incineration whenever possible, and can be incinerated together with other infectious waste.
Unless there is an adequate wastewater treatment plant, blood should be disinfected before discharge to a sewer; it may also be incinerated. Sewer disposal of blood and body fluids should be done in a sink used only for that purpose. For discharge into public sewers with terminal facilities, the general standards as notified under the Environment Protection Act, 1986 shall be applicable.
i. Landfill Disposal:
Small quantities of pharmaceutical waste produced on a daily basis may be landfilled provided that they are dispersed in large quantities of general waste. Cytotoxic and narcotic drugs, however, should never be land filled, even in small quantities.
ADVERTISEMENTS:
ii. Discharge to a Sewer:
Moderate quantities of relatively mild liquid or semi-liquid pharmaceuticals, such as solutions containing vitamins, cough syrups, intravenous solutions, eye drops, etc., (but not antibiotics or cytotoxic drugs), may be diluted in a large flow of water and discharged into municipal sewers. It is not acceptable, however, to discharge even small quantities of pharmaceutical waste into slow-moving or stagnant water bodies.
iii. Incineration:
Small quantities of pharmaceutical waste may be incinerated together with infectious or general waste, provided that they do not form more than 1% of the total waste (in order to limit potentially toxic emissions to the air).
ADVERTISEMENTS:
Ideally, large amounts of pharmaceuticals should be treated in incinerators designed for industrial waste (including rotary kilns), which can operate at high temperatures (>1200°C). Cement kilns are also particularly suited to the treatment of pharmaceuticals; in many countries, cement producers accept pharmaceutical waste as an alternative fuel, thus reducing fuel costs. As a ‘rule of thumb’, however, it is suggested that no more than 5% of the fuel fed into the furnace at any time is pharmaceutical material.
iv. Encapsulation:
Solid, liquid, and semi-liquid waste can be encapsulated in metal drums. Intravenous fluids and glass ampoules are special cases. Intravenous fluids (salts, amino acids, lipids, glucose, etc.), which are relatively harmless, can be disposed of to a landfill or discharged into a sewer.
Ampoules can be crushed on a hard impermeable surface (e.g., concrete) or in a metal drum or bucket using a stout block of wood or a hammer; workers should wear protective clothing, eye protection, gloves, etc. The glass should then be swept up, placed in a container suitable for sharp objects, sealed and disposed of in a landfill. Ampoules should not be incinerated as they may explode, damaging the incinerator or injuring workers.
ADVERTISEMENTS:
i. Return to Original Supplier:
Safely packaged but outdated drugs and drugs that are no longer needed should be returned to the supplier. This is currently the preferred option for countries that lack the facilities for incineration. Drugs that have been unpacked should be repackaged in a manner as similar as possible to the original packaging and marked ‘outdated’ or ‘not for use’.
ii. Incineration at High Temperatures:
Full destruction of all cytotoxic substances may require temperatures up to 1200°C. Incineration at lower temperatures may result in the release of hazardous cytotoxic vapours into the atmosphere.
Modern double-chamber pyrolytic incinerators are suitable, provided that a temperature of 1200°C with a minimum gas residence time of 2 seconds or 1000°C with a minimum gas residence time of 5 seconds can be achieved in the second chamber. The incinerator should be fitted with gas-cleaning equipment. Incineration is also possible in rotary kilns designed for thermal decomposition of chemical wastes, in foundries, or in cement kilns, which usually have furnaces operating well in excess of 850°C.
Incineration in most municipal incinerators, in single-chamber incinerators, or by open-air burning is inappropriate for the disposal of cytotoxic waste.
iii. Chemical Degradation:
Chemical degradation methods, which convert cytotoxic compounds into non-toxic/non-genotoxic compounds, can be used not only for drug residues but also for cleaning of contaminated urinals, spillages, and protective clothing. The methods are appropriate for developing countries. Most of these methods are relatively simple and safe; they include oxidation by potassium permanganate (KMnO4) or sulphuric acid (H2SO4), denitrosation by hydrobromic acid (HBr), or reduction by nickel and aluminium. The methods are not appropriate for the treatment of contaminated body fluids.
It should be noted that neither incineration nor chemical degradation currently provides a completely satisfactory solution for the treatment of waste, spillages, or biological fluids contaminated by antineoplastic agents. Until such a solution is available, hospitals should use the utmost care in the use and handling of cytotoxic drugs.
Where neither high-temperature incineration nor chemical degradation methods are available and where exportation of cytotoxic wastes for adequate treatment to a country with the necessary facilities and expertise is not possible, encapsulation or inertization may be considered as a last resort.
4. Chemical Waste:
As for pharmaceutical waste, improving the management of chemical waste starts with the waste minimization efforts.
Disposal of General Chemical Waste:
Non-recyclable, general chemical waste, such as sugars, amino acids, and certain salts, may be disposed of with municipal waste or discharged into sewers. The discharge into sewers of aqueous chemical wastes that arise in health-care establishments, together with their associated suspended colloidal and dissolved solids, has traditionally been accepted by sewerage authorities in many countries unless such disposal is prohibited in their jurisdiction.
Petroleum spirit, calcium carbide, and halogenated organic solvents should not be discharged into sewers.
5. Wastes with High Heavy-Metal Content:
Wastes containing mercury or cadmium should never be burned or incinerated because of the risk of atmospheric pollution with toxic vapours, and should never be disposed of in municipal landfills as they may pollute the groundwater.
In countries with ‘cottage’ industries specializing in the recovery of heavy metals, mercury and/or cadmium-containing wastes can be sent to these facilities for recovery of the valuable materials. Exporting the waste to countries with the expertise and facilities for its adequate treatment should also be considered.
Establishments that apply minimal programmes may also consider encapsulation, followed by disposal in an impermeable landfill (if available). Where the production of waste with high heavy-metal content is minimal (e.g., in similar quantities to that present in municipal waste) and there are no facilities for recovery of heavy metals within the country, this waste may join the municipal waste stream.
i. Undamaged Containers:
The following containers should be returned to the supplier:
a. Nitrous oxide cartridges or cylinders attached directly to the anaesthesia equipment;
b. Ethylene oxide cartridges or cylinders, which are usually attached to specially designed sterilizers; and
c. Pressurized cylinders for other gases, such as oxygen, nitrogen, carbon dioxide, compressed air, cyclopropane, hydrogen, petroleum gases (for heating and cooking), and acetylene (for welding).
Pressurized containers that have been damaged and are unsuitable for refilling may be crushed after being emptied completely; they can then be disposed of in any landfill. This option may also be selected when the return of empty containers to the gas suppliers is uneconomical. ‘Cottage’ industries specializing in recovery of metals may also accept damaged pressurized containers.
In extreme cases, where containers have corroded valves and still have residual pressure, the only safe solution is to assemble them at a safe location (e.g., a military training area) and arrange for qualified specialists to destroy them by controlled explosion.
Aerosol Cans:
Small aerosol cans should be collected and disposed of with general waste in black waste bags, but only if this waste is not destined for burning or incineration. They should never be placed in yellow bags, which will go for incineration. Large quantities of disposable aerosol cans may be returned to the supplier or sent to waste recycling plants where possible.
Radioactive health-care waste should be treated and conditioned in accordance with the national radioactive waste management strategy and, in particular, to meet any waste acceptance criteria laid down by the regulatory authority.
(i) There are three practical methods by which cultures may be sterilized—incineration, autoclaving and chemical disinfection—but only the first two can guarantee sterility.
(ii) Autoclaving must be used for culture of Mycobacterium tuberculosis and sporing organisms such as Clostridium tetany and Bacillus anthracis. Note the importance of allowing adequate steam penetration in autoclaving; lids of metal and plastic buckets must be removed and placed in the autoclave and permeable autoclavable bags must be opened at the loading stage.
In exceptional emergency situations, such as outbreaks of communicable diseases, burning of infectious health-care waste in open trenches may also be envisaged if it is not possible to use any of the treatment options described above.
Health care workers (HCWs) are normally at very low risk of acquiring HIV infection during management of the infected patient. However, the absence of a vaccine or effective curative treatment makes the HCWs apprehensive and they experience significant fear, anxiety, and emotional distress following a needle stick injury, sometimes resulting in occupational and behaviour changes. Most exposures do not result in infection.
The risk of infection varies with (a) amount of blood, body fluid and other potentially infectious material involved in exposure (b) number of viruses in patient blood at the time of exposure, and (c) whether post exposure prophylaxis (PEP) was taken within recommended time. Exposure may be due to percutaneous injury (needle stick exposure or cut with a sharp instrument) or contact of mucous membrane or non-intact skin (abraded and afflicted with dermatitis).
Risk of transmission of blood-borne viruses to HCW by percutaneous exposure is 0.05- 0.4%, 9-30% and 3-10% for Human Immunodeficiency Virus (HIV), Hepatitis B Virus (HBV) and Hepatitis C Virus (HCV), respectively. Following exposure, wash needle-stick exposures and cuts with soap and water.
Flush with water splashes to the nose, mouth or skin. Irrigate eyes with clean water. Do not put pricked finger into mouth. Squeeze the wound to encourage bleeding. Administration of PEP to HCW depends upon the exposure code (EC) of the HCW and HIV status code (HIV SC) of exposure source.
PEP drugs are supplied by National AIDS Control Organisation to all cases in government hospitals through the State AIDS (Acquired Immunodeficiency Syndrome) Control Societies. HCWs should have prophylactic vaccination against HBV.
8. Treatment and Disposal Technologies for Health Care Waste:
Advantages and drawbacks of the various treatment and disposal technologies are summarized in Table 33.5. Most hospitals in the country do not have adequate systems for safe disposal of hospital wastes. The most common method of burning in diesel incinerators has several problems, including the gases that pollute the atmosphere.
In view of this, following a public interest petition, the Supreme Court ruled that safe disposal systems have to be made mandatory for hospitals with over 50 beds. The government has also issued a gazette notification, giving the dates of compliance at various parts of the country. Though gazette notification specifies microwave incinerators as a better alternative, these systems are expensive and complex to maintain. Further they just disinfect the wastes and the disposal problem still remains.
i. Needle Cutters or Destroyers:
Needle cutters or destroyers are of two types—mechanical or electrically operated. This equipment can be fixed on the bench and are light and portable. They can be used at blood collection centres, nursing stations, clinics and at all locations where needles are used. The purpose of using these instruments is to avoid the reuse of disposable syringes.
The cost of the mechanically-operated instrument is between Rs.2,000 and Rs.3,000 and the electrically-operated instrument ranges from Rs.4,500 to Rs.15,000. Care should be taken while handling the instrument, as needle stick injuries are possible. Hence, the personnel operating the instrument should wear gloves.
These are not popular. However, they can be used to safely destroy the syringe after the needle has been removed. This is mainly to prevent the reuse of syringes, especially those used to draw blood samples. This instrument is usually used in immunization camps and health camps where large numbers of disposable syringes are used and waste shredders are not available. The syringe crushers consist of two plates—one fixed and the other movable.
The movable plate is operated by a lever. The syringes are kept between the two plates and crushed. More than one syringe, depending on the size of the plates, can be crushed at a time. The cost of this instrument is approximately Rs.2000.
Incineration:
Incineration is a high-temperature dry oxidation process that reduces organic and combustible waste to inorganic, incombustible matter and results in the reduction of waste volume and weight by 95%.
As per Ministry of Environment and Forests Notification, New Delhi, the 24th April, 1995:
i. Every hospital, nursing home and clinic by whatever name called, having more than 30 beds or catering to more than one thousand patients per month shall install an incinerator in its premises.
ii. Hospitals, nursing homes and clinics having less than 30 beds or catering to less than one thousand patients per month, shall set up a common incinerator.
iii. Every veterinary institution, animal house or slaughter house generating more than 200 kilograms of biomass waste per day, shall install an incinerator in its premises.
Incinerators shall be installed at appropriate location, to avoid nuisance to patients and neighbourhood. An incinerator should consist of 2 chambers—primary and secondary. The temperature of the primary chamber should be 750-850°C while the temperature in the secondary chamber should be 100-1100°C.
Combustion efficiency (C.E.) of the incinerator should be at least 99%.
It is computed as follows:
Toxic metals in incineration ash shall be limited within the regulatory quantities as defined under the Hazardous Waste (Management and Handling Rules), 1989. Only low sulphur fuel like L.D.0dLS.H.S.1 diesel shall be used as fuel in the incinerator. The minimum stack (chimney) height of incinerator should be 30 metres above the ground.
The waste types not to be incinerated include:
i. Pressurized gas containers.
ii. Large amounts of reactive chemical waste.
iii. Silver salts and photographic or radiographic wastes.
iv. Halogenated plastics such as polyvinyl chloride (PVC).
v. Waste with high mercury or cadmium content, such as broken thermometers, used batteries, and lead-lined wooden panels.
vi. Sealed ampoules or ampoules containing heavy metals.
To avoid dioxin production, no chlorinated plastic bags (and preferably no other chlorinated compounds) should be introduced into the incinerator. Red bags must not be incinerated as red colour contains cadmium, which causes toxic emissions.
Three basic kinds of incineration technology are of interest for treating health-care waste:
i. Double-chamber pyrolytic incinerators, which may be especially designed to burn infectious health-care waste;
ii. Single-chamber furnaces with static grate, which should be used only if pyrolytic incinerators are not affordable; and
iii. Rotary kilns operating at high temperature, capable of causing decomposition of genotoxic substances and heat-resistant chemicals.
Mobile incinerators for health care waste have been found satisfactory in terms of function, performance, and air pollution in Brazil. These units permit on-site treatment in hospitals and clinics, thus avoiding the need to transport infectious waste through city streets.
Pyrolytic Incinerators:
The most reliable and commonly used treatment process for health care waste is pyrolytic incineration, also called controlled air incineration or double-chamber incineration.
The pyrolytic incinerator comprises a pyrolytic chamber and a post-combustion chamber and functions as follows:
i. In the pyrolytic chamber, the waste is thermally decomposed through an oxygen-deficient, medium-temperature combustion process (800-900°C), producing solid ashes and gases. The pyrolytic chamber includes a fuel burner, used to start the process. The waste is loaded in suitable waste bags or containers.
ii. The gases produced in this way are burned at high temperature (900-1200°C) by a fuel burner in the post-combustion chamber, using an excess of air to minimize smoke and odours.
Fuel consumption of pyrolytic incinerators is between 0.03 and 0.08 kg of fuel-oil per kg of waste, or between 0.04 and 0.1 m3 of gas fuel per kg of waste.
Investment and Operating Costs:
Capital costs for pyrolytic incinerators, suitable for treating health care waste, vary widely. The operating and maintenance costs for a small-scale hospital pyrolytic incinerator may reach about Rs.19,000 per tonne of waste incinerated.
Most large, modern incinerators include energy-recovery facilities. In cold climates, steam and/or hot water from incinerators can be used to feed urban district-heating systems, and in warmer climates the steam from incineration is used to generate electricity. The heat recovered from small hospital incinerators is used for preheating of waste to be burnt.
Rotary Kilns:
The rotary kiln is a cylindrical refractory-lined shell that is mounted at a slight incline (3-5% slope) from the horizontal plane to facilitate mixing the waste materials with circulating air. The kiln rotates 2 to 5 times per minute and is charged with waste at the top. Ashes are evacuated at the bottom end of the kiln. Rotary kiln system usually has a secondary combustion chamber after the kiln to ensure complete combustion of the waste.
The kiln acts as the primary chamber to volatilize and oxidize combustible in the waste. Both the secondary combustion chamber and kiln are usually equipped with auxiliary fuel-firing system to bring the units up to the desired operating temperatures. Rotary kilns may operate continuously and are adaptable to a wide range of loading devices.
Incineration in Municipal Incinerators:
It is economically attractive to dispose of infectious health-care waste in municipal incinerators if these are located reasonably close to hospitals. As the heating value of health-care waste is significantly higher than that of domestic refuse, the introduction of relatively small quantities of health care waste will not affect the operation of a municipal incinerator.
Incineration Options that Meet Minimum Requirements:
Single-Chamber Incinerator:
If a pyrolytic incinerator cannot be afforded, healthcare waste may be incinerated in a static-grate, single-chamber incinerator. It is adequate for the following waste categories – infectious waste (including sharps) and pathological waste, and general health care waste (similar to domestic refuse).
The incineration temperature is 300-400°C and the capacity is 100- 200 kg day–1. Exhaust gas cleaning is usually not practicable; this type of incinerator should, therefore, not be installed where air pollution is already a problem. The different types of single-chamber incinerators range from the simple to the sophisticated.
Drum Incinerator and Brick Incinerator:
A ‘drum’ or ‘field’ incinerator is the simplest form of single-chamber incinerator. It should be used only as a last resort as it is difficult to burn the waste completely without generating potentially harmful smoke. The option is appropriate only in emergency situations during acute outbreaks of communicable diseases and should be used only for infectious waste.
The drum incinerator should be designed to allow the intake of sufficient air and the addition of adequate quantities of fuel—essential to keep the temperature as high as possible. A 210-litre (55 US gallons) steel drum should be used, with both ends removed; this will allow the burning of one bag of waste at a time.
A fine screen placed on the top of the drum will prevent some of the ash or light material from blowing out. Another screen or fine grate should be placed under the drum, and a chimney may also be fitted. This type of incinerator can also be fabricated from sheet metal or clay.
A ‘brick incinerator’, for use in similar circumstances, may be built by constructing a closed area with brick or concrete walls. The efficiency of this type of incinerator may reach 80-90% and result in destruction of 99% of micro-organisms and a dramatic reduction in the volume and weight of waste. However, many chemical and pharmaceutical residues will persist if temperatures do not exceed 200°C. In addition, the process will cause massive emission of black smoke, fly ash, and potentially toxic gases.
Environmental Control Technology for Incinerators:
Flue (exhaust) gases from incinerators contain fly ash (particulates), composed of heavy metals, dioxins, furans, thermally resistant organic compounds, etc., and gases such as oxides of nitrogen, sulphur, and carbon, and hydrogen halides. If flue gases are to be treated, this must be done in at least two different stages—’de-dusting’, to remove most of the fly ash, followed by washing with alkaline substances to remove hydrogen halides and sulphur oxides.
Select technology projects for Fly ash disposal and utilisation programme is being implemented by Technology Information, Forecasting and Assessment Council (TIFAC) in close collaboration with the Ministry of Environment and Forests, Ministry of Power and Industry/user agencies. The main objective of the programme is to take up technology demonstration projects towards large scale adoption of these technologies for utilisation and safe disposal of fly ash.
Depending upon the contents of the waste, the emissions from incinerator could be toxic and hence incinerator requires extensive air pollution control equipment. Several types of air pollution control equipment are available to reduce particulate and other gaseous emissions. Some of the commonly used air pollution control devices include venturi scrubbers, packed towers, bag filters, multi-cyclones, etc.
Chemical Disinfection:
Chemical disinfection is most suitable for treating liquid waste such as blood, urine, stools, or hospital sewage.
However, solid—and even highly hazardous—health care wastes, including microbiological cultures, sharps, etc., may also be disinfected chemically, with the following limitations:
i. Shredding and/or milling of waste are usually necessary before disinfection; the shredder is often the weak point in the treatment chain, being subject to frequent mechanical failure or breakdown.
ii. Powerful disinfectants are required, which are themselves also hazardous and should be used only by well trained and adequately protected personnel.
iii. Disinfection efficiency depends on operational conditions.
iv. Only the surface of intact solid waste will be disinfected.
Microbial resistance to disinfectants has been investigated and it is possible to list the major groups of micro-organisms from most to least resistant as follows – bacterial spores—mycobacteria— hydrophilic viruses—lipophilic viruses—vegetative fungi and fungal spores—vegetative bacteria.
A disinfectant known to be effective against a particular group of micro-organisms will also be effective against all the groups that are less resistant. Most parasites, such as Giardia and Cryptosporidium spp., are significantly resistant to disinfection and are usually rated between the mycobacteria and the viruses.
At present, chemical disinfection of health care waste is limited in industrialized countries. However, it is an attractive option for developing countries, particularly for treating highly infectious physiological fluids, such as patients’ stools in case of cholera outbreaks.
Types of Chemical Disinfectants:
Most of the disinfectants (formaldehyde, gluteraldehyde, ethylene oxide, chlorine dioxide) are stable for at least 5 years and—with the exception of sodium hypochlorite—remain effective for 6-12 months after opening of the container. The use of ethylene oxide is no longer recommended for waste treatment because of the significant hazards related to its handling.
Small amounts of disinfectants can be discharged into sewers without pre-treatment, provided that there is an adequate sewage-treatment process; large amounts of disinfectants should never be discharged into sewers. No disinfectants should be discharged into natural water bodies.
i. Commercial Treatment Systems Based on Chemical Disinfection:
Several self-contained waste-treatment systems, based on chemical disinfection, have been developed specifically for health care waste and are available commercially; some have been officially approved for use in several countries. Certain systems are fully automatic and equipped with air filtration systems; they are thus easy to operate and have a lesser impact on the environment.
Most of these commercial systems shred the waste, and some combine a thermal process; they may be based on wet or dry chemical disinfection. They are not usually adequate for cytotoxic or chemical waste, but some may treat pathological waste. Waste volume is reduced by about 80%.
Shredding of solid health care waste before disinfection is essential for the following reasons:
i. To increase the extent of contact between waste and disinfectant by increasing the surface area and eliminating any enclosed spaces;
ii. To render any body parts unrecognizable to avoid any adverse visual impact on disposal; and
iii. To reduce the volume of waste.
Only waste that is disinfected should be used in a shredder. The waste is fed into a hopper leading to a set of revolving blades/shafts which cut the waste into small pieces. A shredder occupies around 1.5 m2 and consumes about 15 kW of power. It weighs around one tonne.
The cost of the equipment varies from Rs.50,000 to Rs.2,00,000 depending on the capacity of waste shredded per operation and the number of shafts or blades (the ones usually available in the market are with 2 or 4 shafts). These are available in the Indian market and can be made to order.
a. Autoclave:
Autoclaving is a time-tested process of sterilization of medical waste using high temperature and high-pressure steam. Effective sterilization results in the destruction of bacteria, viruses, spores, fungi and other pathogenic micro-organisms.
Conventional autoclaves are essentially cylindrical vessels with a provision for loading and unloading waste. Steam at high temperature and pressure is introduced into the vessel jacket. The steam transmits heat rapidly to the waste which in turn produces steam of its own. The process effectively destroys pathogens and renders the waste dry.
Typical operating conditions for an autoclave are a temperature of at least 121°C at a pressure of 105 kPa for a period of at least 60 minutes. The widely used autoclaving methods include – the induced vacuum method, where the steam is introduced into a vacuum, and the gravity displacement method, where in the steam entering the chamber displaces the air.
The penetration of steam into the waste is crucial to the effectiveness of the treatment and therefore attention must be paid to packing the waste in a manner promoting penetration. Any liquid waste formed may need to be treated before disposal.
The autoclave process is an appropriate technology for the treatment of microbiology laboratory waste, human blood and body fluid waste, waste sharps and non-anatomical waste. The treated residue is acceptable for disposal in a municipal landfill, if shredded or macerated to render it unrecognizable and in the case of sharps, incapable of causing injury.
The Bio-Medical Waste (Management and Handling) Rules, 2000 recommend autoclaving for disposables, microbiological waste and sharps. Waste is reduced by an estimated 30% of its volume, enhanced, if accompanied by mechanical shredding and can either be land filled directly or compacted further. Anatomical and pathological wastes, low-level radioactive waste, organic solvents, laboratory chemicals and chemotherapy waste should not be treated in an autoclave.
In a process combining shredding, direct heated steam, and high pressure to achieve complete sterilization of infectious materials, the contaminated waste is loaded into the top of the machine in which a heavy-duty shredder is mounted. Once the machine is sealed, the waste, including the containers and other large resistant material, is shredded and falls by gravity into the lower chamber.
A minimal temperature of 121°C and a pressure usually of 2-5 bar (200-500 kPa) should be maintained during the total contact time of 1-4 hours. Sterilized fragments are discharged from the bottom of the machine. The final treated waste is harmless and safe to dispose of as ordinary municipal waste.
b. Hydroclave or Modified Autoclave:
An improvement over the autoclave is hydroclave. The hydroclave is an innovative combination of waste sterilization (similar to autoclaving), and waste fragmentation and dehydration. A hydroclave is a double-walled cylindrical vessel, horizontally mounted, with one or more top-loading doors, and a smaller unloading door at the bottom, the vessel is fitted with a motor-driven shaft, to which are attached powerful fragmenting/mixing arms that slowly rotate inside the vessel. When steam is introduced in the vessel jacket, it transmits heat rapidly to the fragmented waste, which in turn, produces steam of its own.
The resultant dynamic interaction within the hydroclave will:
i. Sterilize the waste by high temperature and pressure steam, similar to an autoclave but with faster and more even heat penetration.
ii. Hydrolyze the organic components of the waste.
iii. Remove the water content (dehydrate) the waste.
iv. Reduce the waste substantially in volume (80%).
v. Reduces the mass of waste significantly (50%).
Hydroclaves achieve a 6 log bacterial spore reduction. Thus, they offer both pathogen destruction and waste reduction. Waste treated in a hydroclave qualifies for disposal in a landfill like any other municipal solid waste. The waste is rendered unrecognizable.
c. Screw-Feed Technology:
Screw-feed technology is the basis of a non-burn, dry thermal disinfection process in which waste is shredded and heated in a rotating auger. Continuously operated units, also called continuous feed augers, are commercially available and already in use in several hospitals.
The principal steps of the process are the following:
i. The waste is shredded to particles about 25 mm in diameter.
ii. The waste enters the auger, which is heated to a temperature of 110-140°C by oil circulating through its central shaft.
iii. The waste rotates through the auger for about 20 minutes, after which the residues are compacted.
The waste is reduced by 80% in volume and by 20-35% in weight. This process is suitable for treating infectious waste and sharps, but it should not be used to process pathological, cytotoxic, or radioactive waste. Exhaust air should be filtered, and condensed water generated during the process should be treated before discharge.
d. Microwave:
Microwave disinfection technology is relatively advanced and the latest in the field of medical waste management. The microwave process is widely used in several countries and is becoming increasingly popular. Unlike other thermal treatment system, which heats wastes externally, microwave heating occurs inside the waste material. This process involves pre-shredding the waste, injecting it with steam and heating it for 25 minutes at 94°C under a series of microwave units.
The water contained within the wastes is rapidly heated by the microwaves and the infectious components are destroyed by heat conduction. Microwave disinfection is appropriate for the treatment of microbiology laboratory waste, human blood, body fluid waste and waste sharps.
Microwave technology is generally considered effective for viruses also but the specific effectiveness on viruses related to animal waste should be confirmed. The technology is not appropriate for the treatment of human and animal anatomical waste.
The treated residue is acceptable for disposal in municipal landfills especially if shredded or macerated to render it unrecognizable and incapable of causing injury. Microwave systems are available in two size ranges, 100-200 kg h–1 and 250 to 400 kg h–1. Smaller units are also available. However, relatively high costs coupled with potential operation and maintenance problems mean that it is not yet recommended for use in developing countries. Indian manufacturers are not known.
However, Indian vendors are available. The landed cost for the units ranges from Rs.12 lakh to Rs.1.5 crore. The system requires minimal operator training Operational costs are very low. Eighty per cent reduction in volume is achieved. The equipment is compact and limited space is required to set up the equipment.
e. Superheated Steam Sterilization:
This technology comprises a heated shredder and sterilization unit. In the shredder, organic liquids are vaporized and solids reduced to gas by ‘super-heated’ steam at temperatures between 500°C and 700°C. The sterilization unit also employs steam at high temperatures and increased atmospheric pressure further reducing the overall weight of waste. The temperatures used up to 1500°C—exceed ordinary steam sterilization.
The process employs a continuous batch-system and has been shown to reduce medical waste by 50% to 80% of its original volume. It is claimed that this technology can handle all waste including chlorinated plastic products and low-level radioactive waste.
However, the superheating of PVC plastic waste can result in the formation of hydrochloric acid (HCl). HCl can, in turn, react with the many additives present in PVC, creating even greater volumes of toxic fumes. Its projected costs are high. The capital and operating costs of this technology are prohibitively high.
f. Gas Sterilization:
Gas sterilization is the treatment of infectious waste by exposing it to an especially high concentration of a sterilizing gas under the required conditions for the designated treatment period. Ethylene oxide and formaldehyde are sterilizing agents usually used in gas sterilization.
There is now substantial evidence that both ethylene oxide and formaldehyde are probable human carcinogens. The hazards that accompany the use of these chemicals impose strict constraints on gas sterilization operations and greatly limit the usefulness of this technology for treatment of infectious wastes.
g. Wet Oxidation Technology:
In this technology, the shredded waste is dropped into a spinning basket in an oxidation chamber containing a water-based solution having 10% sulphuric acid, an iron ion catalyst and a co-catalyst. Sulphuric acid maintains a very acidic pH while mechanical agitation ensures that the entire waste mass is saturated with the solution. Tests have also shown air pollution to be lower for this type of hazardous waste treatment than for other methods. The technology is not commercially used for cost and other considerations.
h. Electron Beam Gun Technology:
Hospital waste is exposed to an ionized electron beam inducing chemical and biological changes in the waste material. Decontamination occurs when nucleic acids in living cells are irradiated. The volume of waste is reduced by about 20% and the disinfected remains are shredded and land filled. The high capital and operating cost are limiting factors for commercial utilization of this technology.
i. Plasma System:
Indian scientists have developed a new environment-friendly biomedical waste disposal system, which will soon be installed in six major hospitals in the country (including Gujarat Cancer Research Institute, Ahmedabad; New Civil Hospital, Ahmedabad. Sri Sayaji Rao General Hospital Baroda, AIIMS, Delhi, St. Martha’s Hospital, Bangalore and New Bombay Hospital, Mumbai).
The system has been developed by the Facilitation Centre for Industrial Plasma Technologies (FCIPT) of the Institute of Plasma Research, Gandhinagar, Gujarat, with support from the Department of Science and Technology. The unit is operating at the Gujarat Cancer Research Institute at Ahmedabad and the technology has been transferred to a private entrepreneur M/s Bhagwati Pyrotech Pvt. Ltd., Ahemdabad, Gujarat. The technology uses plasma pyrolysis and eliminates the problem of toxic fumes encountered in conventional incinerators.
Plasma is the state of matter obtained by breaking down atoms into ions and electrons by the process of ionization. Plasmas can quite easily reach temperatures of 10,000 °C. It is fast heating –5,000 °C can be achieved in milliseconds. The high ultraviolet radiation flux destroys pathogens and waste to be treated, could be dry or wet. The technology can handle all types of hospital wastes, besides eliminating the need for waste segregation. The new system, which has a capacity of 25 kg h–1, can handle waste produced by a 300- bed hospital.
It utilizes a plasma torch for heating the waste to super-high temperatures to completely decompose waste in an oxygen-starved environment into very simple molecules. Plasma pyrolysis gasifies all organic material, while non-combustible materials—such as glass and metals—are reduced to an inert material with toxicity several orders of magnitudes lower than current landfill regulations.
It is possible to recover energy in the form of carbon monoxide and hydrogen.
j. Biological Process:
A system is being developed using biological enzymes for treating medical waste. It is claimed that biological reactions will not only decontaminate the waste but also cause the destruction of all the organic constituents so that only plastics, glass, and other inert will remain in the residues.
Municipal Disposal Sites:
If a municipality or medical authority genuinely lacks the means to treat wastes before disposal, the use of a landfill has to be regarded as an acceptable disposal route.
There are two distinct types of waste disposal to land—open dumps and sanitary landfills.
i. Open dumps – Health-care waste should not be deposited on or around open dumps.
ii. Sanitary landfills are designed to have at least four advantages over open dumps –geological isolation of wastes from the environment, appropriate engineering preparations before the site is ready to accept wastes, staff present on site to control operations, and organized deposit and daily coverage of waste.
Health-care waste is deposited in one of the two following ways:
i. In a shallow hollow excavated in mature municipal waste in the layer below the base of the working face, and immediately covered by a 2 m layer of fresh municipal waste. Scavenging in this part of the site must be prevented. The same method is often used for hazardous solid industrial wastes; it is specifically intended to prevent animals and scavengers from re-excavating the deposited healthcare waste.
ii. In a deeper (1-2 m) pit excavated in mature municipal waste (i.e., waste covered at least 3 months previously). The pit is then backfilled with the mature municipal waste that was removed. Scavenging in this part of the site must be prevented.
Alternatively, a special small burial pit could be prepared to receive health care waste only. The pit should be 2 m deep and filled to a depth of 1-1.5 m. After each waste load, the waste should be covered with a soil layer 10-15 cm deep. If coverage with soil is not possible, lime may be deposited over the waste. In case of outbreak of an especially virulent infection (such as Ebola virus), both lime and soil cover may be added. A typical example of pit design for health care waste is shown in Fig. 33.8.
Leachate Migration:
Leachates are wastewater generated principally from landfills and solid waste disposal sites. This is due to production of leachate by degradation processes operating within the waste, in addition to the rainwater percolating down through the waste. Leachates emanating from municipal wastes are a major source of surface and groundwater pollution worldwide.
Globally, leachates have been implicated in low yield of farm produce, developmental anomalies, low birth weights, leukaemia incidence, and other cancers in communities around the site. They have also been implicated in hazards to the environment, loss of biodiversity, and contamination of water sources.
Encapsulation:
One option for pre-treatment is encapsulation, which involves filling containers with waste, adding an immobilizing material, and sealing the containers. The primary objective of these encapsulation methods is to physically immobilize the wastes to prevent contact with leaching agents such as water.
The process uses either cubic boxes made of high density polyethylene or metallic drums, which are three-quarters filled with sharps and chemical or pharmaceutical residues. The containers or boxes are then filled up with a medium such as plastic foam, bituminous sand, cement mortar, or clay material. After the medium has dried, the containers are sealed and disposed of in landfill sites.
This process is relatively cheap, safe, and particularly appropriate for establishments that practise minimal programmes for the disposal of sharps and chemical or pharmaceutical residues. Encapsulation alone is not recommended for non-sharp infectious waste, but may be used in combination with burning of such waste. The main advantage of the process is that it is very effective in reducing the risk of scavengers gaining access to the hazardous health-care waste.
Inertization:
The process of ‘inertization’ involves mixing waste with cement and other substances before disposal in order to minimize the risk of toxic substances contained in the waste migrating into surface water or groundwater. It is especially suitable, for pharmaceuticals and for incineration ashes with a high metal content (in this case the process is also called ‘stabilization’). For the inertization of pharmaceutical waste, the packaging should be removed, the pharmaceuticals ground, and a mixture of water, lime, and cement added.
A homogeneous mass is formed and cubes (e.g., 1 m3) or pellets are produced on site and then can be transported to a suitable storage site. Alternatively, the homogeneous mixture can be transported in liquid state to a landfill and poured into municipal waste.
The following are typical proportions for the mixture – 65% pharmaceutical waste, 15% lime, 15% cement and 5% water.