Introduction to Water Technology

The most common techonologies used today for water purification

Filtration
The process of removing suspended particles from water by passing it through one or more permeable membranes or media of limited porosity (e.g., sand, diatomaceous earth). Requires periodic cleaning and maintenance.
What can remain: salts, bacteria, viruses, pesticides, and gases


Micro- and Ultra-Filtration
Similar to filtration, except the average pore size of the filtration media is less than one micron or 0.1 micron, respectively. Typical media are synthetic oxides and ceramics. Requires periodic cleaning and maintenance as the media binds easily.
What can remain: salts, bacteria, viruses, pesticides, and gases


Activated Carbon Absorption
Absorption is the weak attachment and sequestration of molecules by a solid surface as a result of Van der Waal, polar, or dipole interaction. Activated carbon is used because of its very high surface area and because the carbon particles also perform ordinary filtration. Requires periodic regeneration and cleaning.
What can remain: salts, bacteria, viruses, pesticides, and gases


Reverse Osmosis (R/O)
Removes dissolved salts from water by differential permeation of charged ions. In R/O, water passes through a semi-permeable membrane that separates ionized salts from pure water. Requires periodic cleaning and maintenance.
What can remain: bacteria, viruses, pesticides, gases and bad taste/odors


Distillation
The process of heating a liquid to its boiling point, removing the vapors through a cooling and condensing apparatus, and finally collecting the condensed liquid in a separate container. Typically a single bath process requires cleaning after each batch. Carbon filters are commonly needed for odor/smell removal.
What can remain: volatile liquids, gases, bad taste/odors, dead viruses (pyrogenic)


Ozonation and U.V. light
Ozone is a strong oxidant and germicide. It kills microorganisms and precipitates certain salts. UV radiation also kills microorganisms. Neither can remove dirt, most dissolved salts, or most organic contaminants.
What can remain: volatile liquids, gases, some bad taste/odors, and dead viruses (pyrogenic)


Electrophoresis or Electrodialysis
Uses the motion of charged ions in response to an electrostatic field. In electrophoresis, water passes through a semi-permeable membrane driven by an electric field that separates ionized salts from pure water. Requires periodic cleaning and maintenance.
What can remain: bacteria, viruses, pesticides, gases and bad taste/odors