Federal Government has placed increased emphasis on these processes and they will
be commonplace, or even mandatory, in the near future. Tertiary wastewater treatment
(also referred to as advanced wastewater treatment) may include, but is not limited to,
any or all of the following processes.
(1) Carbon absorption. Activated carbon particles are contacted with a flow
of wastewater. Dissolved organics are removed from the liquid by adsorption (clinging)
to the surface of the carbon particles. Depending on the method, particulate matter may
also be removed.
(2) Coagulation-sedimentation. A colloidal suspension consists of particles
separated by a dispersing medium. In wastewater, this medium is usually water.
Colloid particles can be removed by coagulation. Coagulation is the process of forming
gelatinous particles by reducing the repulsive forces between colloids as a result of
adding a coagulant. The resulting coagulated groups can be separated from water by
(3) Chemical oxidation. Oxidation by the use of such chemicals as ozone,
hydrogen peroxide, and other chemically unstable substances is used to remove
dissolved organics, phosphates, and nitrogen compounds. By removing unit electrical
charges from these other elements, oxidating agents can alter their physical and
chemical properties so as to cause their removal from the water.
(a) Electrodialysis. Electrodialysis is a means of removing certain
elements from a liquid such as water by electromagnetically forcing the elements
through a semipermeable membrane. This method is based on the fact that all charged
particles in the solution may be attracted, but only particles of a certain kind may
actually physically cross the membrane.
(b) Reverse osmosis. Two solutions of differing strengths are placed
in proximity to one another and separated by a water-permeable membrane. Applying
pressure to the chamber containing the stronger solution causes a flow of water from
the stronger solution to the weaker solution.
(5) Ion exchange. Water containing charged particles can be passed
through a filter containing molecules composed of charge ions. As the water passes
through the filter, charged ions in the water will selectively exchange position with ions
in the filter molecules. Thus, certain ions can be removed from a fluid and replaced by
other more desirable ions.
(6) Chlorination. The combined primary and secondary wastewater
treatment processes remove or stabilize most of the organic matter present and reduce
the bacterial content by 50 percent or more. There is no assurance, however, that the
number of pathogenic organisms has been reduced to a satisfactory level unless some