b. Anaerobic. In this aquatic environment, "free" or dissolved oxygen is not
present in the wastewater to supply bacteria the oxygen to breathe. The bacteria must
break down chemical compounds that contain oxygen to survive. The decomposition
and decay of organic material or digestion of the sludge by bacteria is the anaerobic
process. Highly putrescible solids in the sludge are reduced in volume and character to
relatively inert matter. Ammonia, hydrogen sulfide, and methane are liberated in the
process. Carbon dioxide is also liberated, but in lesser amounts. Anaerobic
decomposition is invariably foul smelling and is referred to as "septic." It is a slow
process which may require weeks or months for complete stabilization.
2-8. BIOCHEMICAL AND CHEMICAL PROCESSES/OXIDATION
a. Chemical Oxidation. Besides biological oxidation processes taking place,
there is a chemical oxidation process that is initiated at various stages in the treatment
of wastewater. The biological aerobic and anaerobic terms were explained previously.
Chemical oxidation is now explained.
(1) Oxidation process. Oxidation is the addition of oxygen to something or
when one chemical is stripped of unit electrical charge (electrons) by another chemical
due to the difference in their abilities to attract and hold this charge in tertiary
wastewater treatment. In the treatment of wastewater, organic matter is oxidized to
more stable substances. In this particular case, prior to disposing of the
sediment/sludge, an "oxidizing agent" (chlorine) is added to strip or to remove the
ammonia, reduce the concentration of residual organics, and reduce the bacterial and
viral content of wastewaters.
(2) Chlorination. Chlorination is a form of oxidation which has been found
to be operationally dependable in the removal of ammonia nitrogen. Once the
undesirable water-carried material has been oxidized, it has a physical and chemical
state which allows it to be removed from the water more readily. Oxidation of the
organic material in wastewater with chlorine has been found to be enhanced by
exposure to sunlight. The sunlight enhances the completion of the desired chemical
reaction. When these occur, the material is disinfected. The amount of chlorine needed
to oxidize the material is called chlorine demand. The amount of chlorine needed or left
to keep the material disinfected is called chlorine residual (see table 2-1).
(3) Ozonization. Another type of chemical oxidation process is ozonization.
Ozone is a form of oxygen found naturally in the earth's atmosphere. It can be
produced industrially and sprayed into water to serve as a deodorant, dechlorant, and
disinfectant. Ozone is toxic to organisms, which accounts for its disinfectant ability.
Currently, however, this type of treatment is very expensive. (Chlorine is used more
often to disinfect waste, but it, too, is expensive.)