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Section F Alternate technologies Section F Alternate Technologies

Section F Alternate technologies Section F Alternate Technologies

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Page 1: Section F Alternate technologies Section F Alternate Technologies

Section F

Alternate technologies

Section FAlternate Technologies

Page 2: Section F Alternate technologies Section F Alternate 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

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Hydroclave

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Microwave

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Autoclave

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Incinerator