Biomedical Waste Treatment and Disposal Principles

High Temperature Processes

The following principal systems are used:

Incineration

BIOMEDICAL HEALTHCARE WASTE incinerators generally have a primary combustion chamber operating at 800-1 000°C and a secondary chamber operating at 850-1 100°C with gas retention times of two seconds. The incinerator plant includes gas-cleaning equipment to reduce emissions to air and comply with the EU Waste Incineration Directive.

Pyrolysis

PYROLYSIS INVOLVES the high temperature (545-1 000°C) combustion of waste in the absence of oxygen. This treats the waste, destroys pathogens and reduces the volume of clinical waste.

Plasma Technology

IN A plasma system, an electric current is passed through an inert gas (eg argon) to ionise it and this causes an electric arc to create temperatures as high as 6 000°C.

The clinical waste within the system is brought to temperatures of 1 300-1 700°C, destroying pathogenic microbes and converting the waste into a glassy rock or slag, ferrous metal and inert gases.

Gasification

THE WASTE materials are thermally decomposed in an oxygen-starved atmosphere during gasification.

No additional fuel is required except for that required to initiate combustion. The decomposition results in the generation of volatile gases and, depending on the waste content, various vaporised tar-oil substances. The waste gas is passed through a series of scrubbers, filters and cyclonic separators to provide a clean "producer gas".

Non-Burn/Low-Temperature Treatments

Thermal Disinfection Systems:

The Autoclave: saturated steam is introduced into a vessel above atmospheric pressure. Some autoclaves shred the waste during treatment whilst others require the waste to be macerated before treatment.

The Steam Auger: waste is shredded prior to introduction into a steam auger at atmospheric pressure.

Dry Heat: pathogens are destroyed by electrically generated hot oil.

Microwaves: electromagnetic waves with a frequency between radio waves and infrared waves, thermally destroy pathogens. It is important for the waste to be wet, either as a result of moisture naturally occurring in the waste stream or by the addition of moisture in the form of steam. The combination of the two - microwaves and moisture - creates the thermal process.

"Dry" microwave systems are also available, which use direct microwave energy in a nitrogen atmosphere to treat the waste and produce higher treatment temperatures.

Macrowaves: low-frequency radio waves inactivate microbes by heating the waste from the inside of the materials to the outer surface.