Principles of Food Sanitation

can be removed effectively by various physi-
cal/chemical separation methods. One of the
least costly tertiary treatments for removing
refractory organics is activated carbon
adsorption. The affinity of the organic solute
for the carbon depends on the type of car-
bon and the solubility coefficient of the
solute to water.
Ion exchangeprocesses remove minerals,
either cations or anions, by replacing them
with other ions through the medium of
charged resins. Multivalent ions are usually
replaced by monovalents, such as Na+or H+,
and the anions are replaced with OH−or Cl−.
The principle purpose of this technique is to
remove minerals considered harmful to the
water supply or to recover valuable minerals
from industrial processing wastewater.
The ion exchange resin usually consists of
a network of cross-linked organic molecules
known as polymers, which contain reactive
functional groups that are usually strongly
acidic, weakly acidic, or strongly basic. The
resin is charged with ions such as H+or Na+,
which are replaced by multivalent ions from
the wastewater passing through. Periodic
recharging of the resin is necessary. This can
be accomplished using strong acid or base
solution. Ion exchange is especially benefi-
cial for demineralizing water and whey. With
the development of pulse-type ion exchange
units, this method of treatment is becoming
economically feasible.
Electrodialysisis used to remove minerals
from brines and to demineralize whey. This
process functions through the principle of
alternately located cation- and anion-selec-
tive membranes placed in a current path. As
ionic solutions pass through as a function of
electric current, cations are transported
through the cation-selective membrane and
anions through the anion-selective mem-
brane. Portions of the solution within the
electrodialysis unit become concentrated
with ions while the remainder is demineral-

ized. Because of problems related to precipi-

tation of salts, mineral fouling of anion

plates, and membrane clogging by organic

components in the water, electrodialysis as a

tertiary treatment method has limited utility.

Tertiary Lagoons

These maturation lagoons, which are

known as polishing ponds, are used for terti-

ary treatment of secondary effluents from

activated sludge or trickling filter systems.

This type of lagoon is usually from 0.3 to 1.5 m

deep. Natural aeration, mechanical aeration,

or photosynthesis provides the oxygen

source. BOD 5 loading rates normally range

from 17 to 34 kg/ha/day, with a reduction

range for BOD and SS of 80 to 90%. The

waste removal efficiency of this system is

influenced by temperature. This simple

method of treatment requires practically

no equipment or power, and minimal atten-

tion is required for the day-to-day opera-

tion. However, the land requirement of this

process is the highest of the treatment

methods.

Chemical Oxidations

Chemical oxidations through various

chemicals are used for further oxidizing

wastewater components in the tertiary treat-

ment process.Ozoneis a viable chemical oxi-

dation treatment process. Ozone-generation

equipment has made the process economi-

cally feasible. Ozone is a strong oxidant that

breaks down in water to form oxygen and

nascent oxygen, which rapidly reacts with

organic matter. This process also disinfects,

removes taste and odor, and bleaches. Other

chemicals used in chemical oxidations are

chlorine, chlorine dioxide, oxygen, and per-

manganate.

Disinfection

The major purpose of disinfection is to

reduce the total bacterial concentration and

Waste Product Handling 231