1.2 - Disposal of Waste

Disposal of Waste into Sinks

Waste substances are divided into:

substances that can be disposed of into sinks; and
substances that cannot be disposed of into sinks.

Can be disposed of into sinks

Substances with a low concentration that are non-hazardous.
Examples: neutral substances, weak acids and weak alkalis.

Cannot be disposed of into sinks

Solid waste.
Substances with a pH value lower than 5 or higher than 9.
Organic solvent compounds.
Chemical substances such as acid, grease, oil, oil paint and hydrogen peroxide.
Toxic substances.
Heavy metals.
Organic waste substances such as microbes and carcasses.
Radioactive waste.
Volatile substances.
Reactive substances.

These substances can pollute the environment and are hazardous to living things.

Management of Biological Waste Substances

Biological waste substances are discarded biological materials that can cause serious harm or biological hazards.
Examples include waste materials, tissue, carcasses, culture medium, plastic containers, glass and gloves.
They must be managed according to the Standard Operating Procedure (SOP) for the disposal of biological waste substances.
Separate each waste at its source into the correct category.

Category A — Sharp equipment

Examples: syringe, needle, scalpel blade.
Place in a special sharps waste bin.
Do not autoclave.
Store the container temporarily in a safe place before disposal.

Category B — Non-sharp solids

Examples: gloves, tissue, culture medium.
Package in a leak-proof autoclave bag.
Autoclave at 121°C, 15 psi for 20 minutes.
Place the decontaminated waste in a biohazard bag and then in a biohazard bin.

Category C — Carcasses and organs

Examples: laboratory animals, experimental animals.
Wrap in absorbent material such as tissue paper.
Package securely in a biohazard plastic bag.
Store temporarily in a freezer before disposal.

Category D — Liquids

Examples: blood, serum.
Decontaminate by autoclaving.
Dispose of directly into the sewage system through a laboratory sink or toilet.

Final handling

Label the packaged waste and place it in a biohazard bin.
Keep the biohazard bin temporarily under safe, controlled and cooled conditions.
Send it for centralised disposal.

Steps to Handle Accidents in the Laboratory

Laboratory accidents may result from carelessness, negligence, unexpected events, or a lack of skill or knowledge while carrying out a science experiment.

Common laboratory accidents

Hand cut by a glass splinter.
Hand splashed by concentrated acid or alkali.
Small fire.
Contact with residue from the reaction of reactive metals.
Broken thermometer.
Gas leak.
Electric shock.

Chemical substance spillage

Inform the teacher or laboratory assistant immediately.
Make the spillage area a restricted zone.
Stop the spillage from spreading by using sand to form a boundary.
Scoop the chemical spillage.
Dispose of it safely.

Mercury spillage from a broken thermometer

Mercury poisoning happens when someone touches mercury or it is absorbed through the skin in a certain quantity.
Mercury can attack the nervous system, digestive tract, reproductive system and kidneys.

Inform the teacher or laboratory assistant immediately.
Make the spillage area a restricted zone.
Sprinkle sulphur powder onto the spillage.
Call the Fire Department.