food processors that causes the most concern
is the quaternary ammonium chlorides
(QACs). These sanitizers are stable and effec-
tive over a broad pH range. However, there are
four factors that may counteract the microbial
activity of the sanitizers that may reach a treat-
ment plant. They are: inactivation, adsorption,
biodegradation, and acclimation. In most
treatment plants, there are enough cationic
chemicals entering the waste treatment system
to inactivate the QACs. Furthermore, chlorine
and iodine rapidly lose activity in the waste
stream and rarely enter the treatment plant.
The dilution of acid sanitizers or carboxylic
acid sanitizers normally raises the pH above
4.0 reducing their antimicrobial activity. Perox-
yacetic acid sanitizers are like chlorine, very
unstable when mixed with general plant efflu-
ent and are not expected to reach the treatment
plant.
It is practical to disinfect moderate vol-
umes of effluent with ultraviolet irradiation
equipment, an effective method with no
residual effects that harm flora or fauna in
receiving water. Thermal treatment is effec-
tive but is impractical for large volumes of
effluent. Membrane technology in the appli-
cation of water treatment for the beverage
industry will be discussed in Chapter 20.
Deodorization
Treated water may be safe to drink, yet have
an unpleasant taste and odor because of the
activity of some microscopic organisms such
as algae, especially during the summer months.
Thus, deodorization is essential to remove the
taste and odor in treated water. Air stripping
and aeration is a treatment to bring water
into contact with air to expedite the transfer
of a gas between the two phases. Applications
include the removal of hydrogen sulfide that
causes an unpleasant odor, carbon dioxide to
reduce the demand of lime in the subsequent
softening treatment, and trace volatile organic
contaminants. Packed tower, diffused aeration,
spray nozzles, and tray aerators are equipment
involved (Wang et al., 2003).Summary
To determine the optimal waste treat-
ment systems, it is necessary to conduct
a survey to ascertain waste volume and
characteristics and water consumption
records. Waste pollution is measured
through BOD, COD, DO, TOC, SS, TSS,
TDS, and FOG.
Wastewater can be salvaged through recy-
cling and reuse and recovery of solids. The
basic phases of wastewater treatment are
pretreatment by flow equalization, screen-
ing, and skimming; primary treatment by
sedimentation and flotation; secondary
treatment by anaerobic lagoons, aerobic
lagoons, trickling filters, activated sludge,
oxidation ditch processes, land application,
RBCs, and tertiary treatment by physical
separation, tertiary lagoons, and chemical
oxidations. Disinfection of treated waste-
water should follow other treatment phases
to reduce the reaction of organic matter with
the disinfectant.Study questions
- What is biochemical oxygen demand?
- What is chemical oxygen demand?
- What are the advantages and disad-
vantages of pretreatment of waste-
water? - What are three methods of wastewater
pretreatment? - Briefly describe two methods of pri-
mary treatment of wastewater. - Why are anaerobic lagoons used as a
method of secondary treatment of
wastewater?
Waste Product Handling 233