Section F
Alternate technologies
Section FAlternate Technologies
Section F
Alternate technologies
Bio-medical waste and technology
Technology is only a fraction of the solution.
Major components of waste management are:
o Segregation of wasteo Waste minimisationo Reducing use of hazardous
substances or processeso Waste Audit
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Treatment technologies
Treatment technology for bio-medical waste should:
Disinfect waste Make waste non-reusable Be environmentally safe Should consider worker safety
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Approved treatment methods
Autoclave Chemical disinfection Hydroclave Microwave Incineration Any other technology after CPCB
approval
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Technologies for bio-medical waste treatment
Thermal processeso Low heato Medium heato High heat
Chemical processes Irradiative processes Biological processes
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Biological indicators
Suspensions of resistant endospores are used as biological indicators for microbial inactivation:
Bacillus stearothermophilus: thermal Bacillus subtilis: chemical Bacillus pumilus: irradiation
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Autoclaves
Saturated steam acts as the disinfecting agent
Pressure, temperature, time combinations
o for gravity flow 121oC, 15psi, 60’/135oC, 31psi,45’/149oC,52psi, 30’
o for pre- vacuum type (121oC, 15psi, 45’/135oC, 31psi, 30`)
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Types of autoclaves
Air is an effective insulator, thus complete disinfection demands removal of air from the chamber. Two methods of removing air are:
Gravity displacement Pre-vacuum
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Components of an autoclave
Major components
A metal chamber that can withstand high pressure
A steam jacket surrounding the chamber
A steam generator A capillary thermometer and 2
pressure gauges to monitor temperatures and pressures respectively
Recording mechanismF8
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Stages in autoclave operation
Pre-heating Loading of waste with an indicator Air evacuation Steam treatment Steam discharge Unloading Mechanical treatment
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Types of waste allowed/ disallowedType of waste allowed category (3,4,6,7): Microbiological and biotechnological
waste Sharps, soiled waste, solid waste
Not to be treated: Volatile and semi-volatile organic
compounds Chemotherapeutic wastes, mercury and
other hazardous chemical waste Radiological waste, Sealed heat
resistant containers Huge and bulky bedding material
Poorly segregated waste can lead to emission of alcohols, phenols, aldehydes, mercury and other toxic contaminants
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Advantages
Proven technology, with disinfection parameters well established
Minimal emissions (with properly segregated waste)
Relatively lower capital costs Automated systems
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Disadvantages
Waste recognisable after treatment No volume reduction (till a shredder
is attached) Odours Emissions (with unsegregated waste) Process gives wet waste, if not
subjected to drying Barriers to direct steam exchange
may compromise efficiency.
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Points to ponder
Segregated waste is a must Air evacuation is necessary Place bags in multi-load trays Proper ventilation to avoid odors Thermocouples and pressure gauges
should be checked frequently
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Hydroclave
Hydroclave is steam treatment with fragmentation and drying of waste
It has a double walled chamber with an agitator inside
Steam is injected into this wall (jacket) and waste is loaded in the inner chamber
The agitator fragments and turns waste
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Hydroclave: treatment mechanism
The moisture in the waste turns to steam and exerts pressure on the inner walls. If this pressure is not sufficient, additional steam may be injected inside.
Cycle runs at 132oC for 15’/ 121oC for 30’
Finally the steam is vented through a condenser while maintaining heat input, causing the waste to dry
Steam is shut off, discharge door is opened and agitator runs in reverse rotation to place the waste on a conveyor belt/ container.
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Hydroclave
Advantages o Shredded, dry wasteo Internal mixing improves transfer
of heat Disadvantages
o Clogging of agitator blades with waste
o Mixed shredded waste makes recycling difficult
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Microwave: action mechanism
Disinfection by moist heat and steam generated by microwave energy
Magnetrons convert high voltage electrical energy into microwave energy
The microwaves create an electromagnetic field
Water and other molecules in waste try to align in the field and in the process they vibrate
Vibration of the molecules produces heat
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Microwave: action mechanism
Microwave kills by two mechanisms:
By heat energy from the steam generated
Changing the biological molecular structure of proteins
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Microwave: operating parameters
Microwaves are high frequency (2450+50mhz) radio waves capable of creating electromagnetic field
Temperatures reached are around 97-100oC. In some new systems, steam under pressure is passed, to achieve temperatures>135oC.
Cycle time is around 25’ Typically, around 2-6 magnetrons are
used with an output of about 1.2KW each
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Stages in microwave operations
Waste loading Steam injection in the hopper Internal shredding Microwave treatment Disinfection cycle Optional secondary shredding Discharge
Category of waste that can be and cannot be treated is similar to the autoclave. Emission parameters are also similar F20
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Advantages and disadvantagesAdvantages In use for more than a decade Minimal emissions if no hazardous waste
fed Automated system No liquid effluent
Disadvantages Relatively high capital cost Toxic emissions if hazardous waste fed Any large metal item can damage
shredders Odour problems Probability of microwave energy
leakage
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Points to ponder
Properly segregated waste is a must. It becomes necessary to ensure:
o absence of large metal blockso absence of hazardous or radiological
waste: Workers to be trained for monitoring
leakage of microwave energy and handle it
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Other thermal technologies
Low heat (dry) technologies (<350oF)o high velocity heated air
Medium heat (350oF-700oF)o reverse polymerization or thermal
depolymerisation High heat technologies (1,000oF-
15,000oF)o pyrolysis
Medium and high heat technologies also produce dioxins and furans and other toxic pollutants, require pollution control devices, and are fairly expensive.
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Chemical methods
(NaOH/ KOH: For treatment of pathological and cytotoxic waste):
Sodium hypochlorite Glutarladehyde Peracetic acid Ozone gas Calcium oxide Sodium hydroxide: alkaline
hydrolysis
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Evolving technologies
Irradiation (ionising radiation): X rays/gamma rays Electron beam
Biological: Enzymes Composting, vermiculture
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Choosing an alternate technology
Throughput capacity Types of waste treated/not suited Microbial inactivation efficiency Environmental emissions and water
residues Regulatory acceptance Space requirements Utility and other installation
requirements
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Choosing an alternate technology Reduction of waste volume and mass Occupational safety and health Noise and odour Automation Reliability Manufacturer background Cost Recurring cost and maintenance After sales service Level of operator training, other
manpower requirementF27
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Centralised facilitiesGuidelines on common facilities
Treatment facilities: 90% non-burn, 10% burn
Limits incineration to Categories 1&2
At least 1 Km from residential areas. Acceptable in industrial area
One operator allowed to cater upto 10,000 beds, situated within 150 km radius
Segregation is the role of generator; operator can report mixing of waste to the prescribed authority
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Chemical Disinfection
Section F
Alternate technologies
Hydroclave
Section F
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Microwave
Section F
Alternate technologies
Autoclave
Section F
Alternate technologies
Incinerator