Treatment Technologies for Hospital Waste:
There are five broad categories of medical waste treatment technologies:
(i) Mechanical.
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(ii) Thermal.
(iii) Chemical.
(iv) Irradiation.
(v) Biological.
(i) Mechanical Process:
Mechanical processes are used to change the physical form or characteristics of the waste either to facilitate waste handling or to process the waste in conjunction with other treatment steps.
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The two primary mechanical processes are compaction and shredding. Compaction involves compressing the waste into containers to reduce its volume. Shredding, which also includes granulation, grinding, pulping etc., is used to break the waste into smaller pieces.
Compaction and shredding are not considered acceptable medical waste treatment systems by themselves. Compaction and shredding of untreated medical waste may result in aerosoling or spilling of micro-organisms. Typically, compaction and shredding are adopted after the waste has been decontaminated in order to reduce the volume and to make it un-recognisable.
(ii) Thermal Process:
Thermal processes use heat to decontaminate or destroy medical waste. Most micro-organisms are rapidly destroyed at temperatures ranging from 49 to 91°C, and most living organisms are killed at 100°C.
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There are two categories of thermal processes viz. low-heat systems and high-heat systems. Low- heat systems use steam, hot water, or electromagnetic radiation to heat and decontaminate the waste.
They typically operate at temperatures of less than 150°C. High-heat systems employ combustion, pyrolysis and high-temperature plasma to decontaminate and destroy the waste. These systems operate at temperatures ranging from as low as 600°C to more than 5500°C.
The thermal treatment processes include the following:
a. Autoclaving:
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Autoclave (steam sterilisation) is a low-heat thermal process and is designed to bring steam into direct contact with the waste in a controlled manner and for sufficient duration to disinfect the waste.
The three basic types of steam autoclave systems are gravity, pre-vacuum, and retort systems. Gravity-type autoclaves, in which pressure alone is used to evacuate air from the treatment chamber, operate with steam temperatures of about 121°C.
These systems require a cycle time of approximately 60-90 minutes in order to achieve full steam penetration into the most densely packed waste loads. Pre- vacuum-type autoclave systems evacuate air from the treatment chamber using vacuum pumps.
This enables them to reduce cycle times to about 30-60 minutes, as the time to heat the air within the chamber is eliminated. Pre-vacuum systems operate at about 132°C. Retort-type autoclaves comprise large volume treatment chambers designed for much higher steam temperatures and pressures, and, therefore, their cycle times can be substantially less than those of the other systems.
An innovation of autoclave is hydroclave. Here, indirect heating is done by providing steam into the outer jacket of a double-walled container, while the waste inside the wall is turned on by a mechanism.
This causes the waste to be fragmented and continuously tumbled against the hot vessel walls. The moisture content of the waste turns into steam, and the vessel start to pressurise.
In the absence of enough moisture in the waste to pressurise the vessel, a small amount of steam is added until the desired pressure is reached. The treatment time is 15 minutes at 132°C, or 30 minutes at 121°C to achieve sterilisation. In the process, the resultant waste is fragmented and dehydrated with reduction in volume and weight.
b. Microwave Treatment:
Unlike other thermal treatment systems, which heat 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 95°C under a series of microwave units.
Microwave radiation is designated as that portion of the electromagnetic radiation spectrum lying between the frequencies 300 and 300,000 MHz and the microbial inactivation occurs as a result of the thermal effect of the radiation and not from any intrinsic non-thermal property.
c. Incineration:
Incineration systems use high-temperature combustion under controlled conditions to convert wastes containing infectious and pathological material to inert mineral residues and gases.
The three types of incinerators used for hospital waste treatment are multiple-hearth, rotary kiln, and controlled-air. All these three types can have primary and secondary combustion chambers to ensure maximum combustion of the waste.
Multiple-hearth incinerators consist of two or more combustion chambers. The primary chamber is for solid-phase combustion, whereas the secondary chamber is for gas-phase combustion. These incinerators are often referred to as excess-air incinerators because they operate with excess air levels in both the primary and secondary combustion chambers.
The rotary kiln is a cylindrical refractory-lined shell that is mounted at a slight incline from the horizontal plane to facilitate mixing the waste materials with circulating air. Rotary-kiln systems usually have a secondary combustion chamber after the kiln to ensure complete combustion of the waste.
The kiln acts as the primary chamber to volatilise and oxidise combustibles in the waste. Both the secondary combustion chamber and kiln are usually equipped with an auxiliary fuel-firing system to bring the units upto the desired operating temperature.
Controlled-air incinerators burn waste into two or more chambers under conditions of both low and excess stoichiometric oxygen requirements. In the primary chamber, waste is dried, heated and burnt at 40-80% of the stoichiometric oxygen requirement. Combustible gas produced by this process is mixed with excess air and burnt in the secondary chamber at usually between 100-150% of the stoichiometric requirement.
A supplementary fuel burner is used to maintain elevated gas temperatures and provide for complete combustion. One advantage of using low levels of air in the primary chamber is that there is very little entrainment of particulate matter in the fuel gas.
Plasma System:
These systems utilise a plasma torch or burner for heating the waste to super-high temperatures. A plasma is basically a material in which the temperature is high that some of its electrons are separated from its atoms. Some plasma fired systems are designed to operate with furnace temperature of as high as 10,000°C.
These systems are, in many respects, very similar to incineration systems except that conventional combustion does not take place. The plasma-fired chambers operate in an oxygen- deficient mode, and off-gases need to be combusted separately. The residue produced is a glass-like substance, rather than particulate ash typical of incinerators.
(iii) Chemical Process:
Chemical treatment involves the use of chemicals for disinfection. Disinfectants are mostly chlorine compounds, phenolic compounds, iodine, alcohols, hexachlorophene, formaldehydes, iodine-alcohol combinations, formaldehyde-alcohol combination etc.
Most of the chemical disinfectants are used as aqueous solutions. Water is needed to bring the chemicals and microorganisms together as necessary to achieve inactivation.
Most of these systems start with a shredding step in order to provide sufficient contact between the waste and disinfectants. The shredding step, in turn, disfigures the waste such that recognisability is not a problem.
(iv) Irradiation Process:
Irradiation exposes wastes to ultraviolet or ionizing radiation in an enclosed chamber. Processes utilising Cobalt-60, and electron beam accelerator unit or electron beam gun, for irradiating and sterilising the medical waste have been developed. These systems require post-shredding to render the waste un-recognisable.
(v) 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 inerts will remain in the residues.
Comparison of Treatment Technologies:
All the treatment technologies explained above have their own advantages and disadvantages. Table 35.2, overleaf, gives the relative advantages and disadvantages of the treatment technologies.
Emissions from Medical Waste Incineration:
Emissions from medical waste incinerators are generated from either waste constituents, components of combustion air, or by-products of the combustion process itself.
Pollutants, that provide cause for concern, include:
1. Particulate matter,
2. Toxic metals,
3. Toxic organics,
4. Carbon monoxide, and
5. Acid gases (hydrogen chloride, sulphur dioxide, and nitrous oxide).
1. Particulate matter – Particulate Matter is generated when non-combustible material is suspended, when incomplete combustion of combustible materials occurs and the vapourous materials condense.
2. Toxic metals – Toxic Metals appear in emissions as particulates. The concentration of metal emissions depends on the quantity of metals in the waste material. The metals of concern which are expected to be emitted are arsenic, cadmium, lead, mercury, etc.
3. Toxic organics – Toxic Organics can be formed because of incomplete combustion. For instance, Chlorine, which is derived from the incineration of PVC plastics, can combine with organics to form toxic chlorinated organics, such as dioxins and furans which are best avoided.
4. Carbon monoxide – Carbon Monoxide is a product of in-complete combustion and is a good measure of incinerator efficiency. Carbon monoxide production is limited when oxygen concentrations, mixing, and temperatures are adequate.
5. Acid gases – Acid Gases (hydrogen chloride, sulphur dioxide, nitrous oxides) are formed when nitrogen, sulphur, and chlorine are released during combustion. Atmospheric nitrogen also combines with oxygen to produce nitrogen oxides.
Draft Bio-Medical (Handling and Management) Rules:
The Ministry of Environment and Forests has issued draft rules for management of bio-medical wastes.
The following are some of the salient features of these rules:
(i) The rules will apply to hospitals, nursing homes, veterinary institutions, animal houses or slaughter houses generating bio-medical wastes.
(ii) State Government can notify authorities for the purpose of granting authorisation for collection, reception, storage, treatment and disposal of bio-medical wastes, from –
(a) Directorate of Health Services.
(b) Directorate of Animal Husbandry or Veterinary Services.
(c) State Pollution Control Boards/Committees.
(d) Municipal Authorities.
(iii) Every hospital, nursing home, veterinary institution, animal house or slaughter house generating bio-medical wastes need to install an appropriate facility in the premises or shall set up a common facility within a period of nine months from the date of commencement of these Rules.
(iv) Any person generating/handling bio-medical wastes or operating bio-medical waste treatment facility needs to take authorisation from appropriate authority.
(v) A generator or an operator of a bio-medical waste facility needs to take all measures necessary to prevent damages or adverse effects to the environment. He is also required to submit detailed information about the types and quantities of bio-medical wastes collected or handled by him. This must be done every year.
(vi) An authorised person handling any bio-medical waste needs to segregate various categories of wastes (Table 35.3) as per classification specified in Table 35.1. The containers to be used shall be of such colour and type as specified in Table 35.1.
(vii) The bio-medical wastes shall not to be stored beyond 48 hours without permission of the appropriate authority.
(viii) Wastes of different categories shall be segregated, stored, treated and disposed as per procedure prescribed in Tables 35.1 and 35.3.
(ix) The authorised person needs to maintain records about the category of waste generated, quantity, storage, transportation and treatment details, which are subject to verification by the appropriate authority.
Standards and Guidelines for Incineration, Autoclaving and Microwaving of Medical Waste:
Incineration:
The infectious wastes which cannot be effectively treated and safely disposed through other methods should be subjected to incineration.
Incinerators for this purpose could be of the following two types:
(i) Incinerators for individual hospitals/nursing homes/medical colleges/veterinary centres.
(ii) Common incinerators to handle the wastes from a number of hospitals/nursing homes/ pathological laboratories/medical colleges and veterinary centres.
Incinerators should be installed at appropriate locations to avoid nuisance to patients and the neighbourhood. An incinerator shall consist of two chambers a primary chamber and a secondary chamber.
Emission Standards for incinerator should meet:
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(i) Waste heat recovery boiler is recommended to be installed to recover the sensible heat from exhaust gases.
(ii) Suitable air pollution control devices shall be installed to meet the above- mentioned emission standards.
(iii) All hospitals shall install suitable shredders/crushers for the preliminary treatment- of waste sharps, discarded glasswares and disposables.
(iv) For setting up of incinerator, necessary clearance/consent shall be obtained from the concerned State Pollution Control Board/Committee. Special care must be taken while transporting the wastes from the hospital(s) to the incinerator in closed containers. The protocol for transportation shall be finalised by the local authority in consultation with the State Pollution Control Board/Committee.
The vehicle(s) carrying wastes should be labelled accordingly and hospital(s), nursing home(s) etc., which are unable to set up incinerators within their premises because of lesser quantum of incinerable waste generation or for other reasons, may collectively install common incinerators or avail the incinerator facility of other hospitals through mutual agreement among themselves.
Autoclaving:
In this process, the wastes are heated at specified temperature for a period of time in a chamber into which pressurised steam is introduced. The steam penetration ensures destruction of bacteria and pathogenic micro-organisms. The technologies used during autoclaving are induced vacuum, where the steam entering the chamber displaces the air.
For decontamination of waste by autoclaving, loosely-packed material should be exposed at least for 1 hour at a temperature not below 121°C and 15 psig pressure. Autoclaves shall be regularly monitored for adequate sterilisation performance as part of the regular quality control practice.
Microwaving:
(i) Microwave treatment shall not be used for cytotoxic, hazardous or radioactive wastes, contaminated animal carcasses, body parts, and large metal items.
(ii) The microwave system shall comply with the efficacy test/routine tests, and a performance guarantee may be provided by the supplier before operation of the unit.
(iii) The microwave should completely and consistently kill the approved biological indicator at the maximum design capacity of each microwave unit. Biological indicators for microwave shall be Bacillus subtilis spores using vials or spore strips, with at least 1 × 104 spores per millilitre.
Liquid Waste:
The effluents generated from the hospital shall conform to the following limits:
Note:
The above limits are applicable to hospitals which are either connected with sewers without terminal sewage treatment plant or are not connected to public sewers at all. For discharge into public sewers having terminal treatment facility, the general standards, as notified under the Environment (Protection) Act, 1986, shall be applicable.
Guidelines for Autoclaving:
(i) Types of Wastes to be Autoclaved:
The categories of wastes which can be autoclaved are:
(a) Waste sharps.
(b) Infectious wastes.
(c) Isolated wastes.
(d) Discarded glasswares.
(e) Soiled wastes.
(f) Disposables (PVC/plastics, cardboard and thermocol).
Recognisable human body parts, recognisable animal carcasses and body parts, pathological wastes, antineoplastic wastes, bulk liquids and chemotherapeutical wastes may not be autoclaved.
(ii) Procedure:
The autoclave to be used shall be specially engineered and dedicated for the treatment of the medical wastes. Medical wastes shall be autoclaved in the container which is received at the facility, unless reusable containers are utilised.
Medical waste shall not be considered properly treated unless all time/temperature/pressure indicators indicate that the required time/temperature/pressure is reached during the autoclave process.
If for any reason a time/temperature/pressure indicator does not indicate that the required temperature or residence time is reached, the entire load of medical waste must be autoclaved again until the proper temperature, pressure and residence time is achieved.
(iii) Operating Parameters:
An autoclave used to treat medical waste shall be operated in accordance with the following minimum requirements:
I. When operating a gravity flow autoclave, medical waste shall be subjected to:
(a) A temperature of not less than 121°C and a pressure of 15 pounds per square inch gauge (psig) for an autoclave residence time of not less than 60 minutes.
(b) A temperature of not less than 135°C and a pressure of 31 psig for an autoclave residence time of not less than 45 minutes.
(c) A temperature of not less than 149°C accompanied by a pressure of 52 psig for an autoclave residence time of not less than 30 minutes.
II. When operating a vacuum autoclave, medical wastes shall be subjected to a minimum of one pre-vacuum pulse to purge the autoclave of all air, and the following:
(a) A temperature of not less than 121°C and a pressure of 15 psig for an autoclave residence time of not less than 45 minutes; or
(b) A temperature of not less than 135°C and a pressure of 31 psig for an autoclave residence time of not less than 30 minutes.
(iv) Recording of Operational Parameters:
Each autoclave shall have graphic or computer recording devices which will automatically and continuously monitor and record dates, time or day, load identification number and operating parameters throughout the entire length of the autoclave cycle.
(v) Validation Test:
(a) Spore Testing:
The autoclave shall completely and consistently kill the approved biological indicator at the maximum design capacity of each autoclave unit. Biological indicators for autoclave shall be Bacillus stearothermophilus spores using vials or spore strips, with at least 1 × 104 spores per millilitre.
Under no circumstances will an autoclave have minimum operating parameters less than a residence time of 30 minutes, regardless of temperature and pressure, a temperature less than 121°C or a pressure less than 15 psig.
(b) Colour Change:
A chemical indicator strip/tape, that changes colour when a certain temperature is reached, can be used to verify if a specific temperature has been achieved. It may be necessary to use more than one strip over the waste package at different location to ensure that inner content of the package has been adequately autoclaved.
(vi) Sterilisation of Steam Condensate:
There shall be provision of a secondary steriliser for sterilisation of steam condensate.