Experiment 5

Water Purification

Process of eliminating impurities from contaminated water that can be detrimental to human health.

Common contaminants of water:

suspended solid particles

colloids

dissolved inorganic salts

dissolved organic compounds microorganisms

pyrogens

dissolved gases

Purification Methods

Different water treatment technologies are generally classified into chemical methods, physical methods, and biological treatments.

Five steps to basic water purification:

1. Aeration 2. Coagulation 3. Sedimentation 4. Filtration 5. Disinfection

Aeration

Introduction of air into the water in order to remove constituents (e.g. dissolved gases and dissolved metals) that can interfere with the next steps.

Aeration

“Scrubbing off” dissolved gases from solution to the surrounding air.

Aeration

Oxidizing metals in water by O2 in air → oxidized metals in water to be removed by filtration or flotation.

Coagulation

Chemicals (i.e. alum) are added to allow dirt and other suspended solid particles to “stick together” forming flocs.

Coagulation

Flocs “trap” most of the color, dissolved organic matter and pathogens from water.

Coagulation

Heavy flocs settle at the bottom while smaller and lighter ones float to the surface.

Sedimentation

Gravity pulls the heavy flocs to the bottom of the container.

Sedimentation

This forms 2 layers – clarified water at the top and the “undisturbed” flocs at the bottom.

Filtration

Separates the suspended solid particles from water by causing the mixture to pass through a filter medium.

Filtrate

water that passed through the column.

Filter Cake

solids that retained on the filter.

Disinfection

Final step – to remove bacteria and other microorganisms

Disinfection

Examples of disinfection methods – boiling, chlorination, UV treatment

Dissolved Oxygen (DO)

Supersaturated water (air saturation > 115- 120%) can cause “bubble disease” in fish and invertebrates causing higher death rates

Dissolved Oxygen (DO)

Most aquatic organisms use oxygen for growth and survival, i.e. at low DO level, fish mortality rates will rise and their reproduction will be greatly affected

Dissolved Oxygen (DO)

Amount of free O2 molecules present in water