body of water. If this condition continues,
the ecological balance of the receiving body
of water will be harmed.
We currently have available coagulants
and polymers derived of cellulose, starch,
and sugar destined to the removal of oils and
greases by flotation generating a material
that can be processed in digesters. This
approach is possible mainly due to the
absence of metallic ions (iron and alu-
minum). The challenge, in the use of these
products, is to find the ideal balance between
the costs and benefits.
Frequently it is more economical to invest
in waste prevention techniques and utiliza-
tion of waste products than in waste treat-
ment facilities. Yet many food plants
generate waste effluents that pollute. Insuffi-
cient treatment capacity of many municipal
waste treatment plants necessitates special
waste facilities for a large percentage of food
plants. Wastewater treatment is still a devel-
oping technology, and one that is going to
need the cooperation of the EPA, suppliers,
and processors.
Pretreatment
The pretreatment of food processing
wastewater is frequently required prior to
discharge into a municipal waste treatment
system. A sewer use ordinance defines speci-
fied municipal discharge limitations that
determine the degree of pretreatment
required. The EPA has previously concluded
that many wastewaters from processing
plants are compatible and biodegradable.
Municipal sewage plants normally place
certain restrictions on wastewater discharge
from food processing plants. Although toxic
substances are not frequently associated with
food process waste streams, certain wastes
that are present cannot be treated and can
cause obstruction and require additional
maintenance. Troublesome wastes include
oils and fats, plant and animal tissues, and
waste materials. Therefore, some form of iso-
lation and pretreatment of the waste stream
is essential prior to discharge in a municipal
waste treatment facility.
If increased waste load reduces the ability
of the municipal waste treatment system to
treat the additional waste adequately, the
food processor usually has to accept more
responsibility related to pretreatment or sup-
port of a municipal waste treatment plant
modification or expansion program. The
processor should calculate the cost of the
added sewage treatment load and deter-
mine that the projected cost should be han-
dled by pretreatment or by paying a
surcharge to a municipal expansion program
keyed to specific wastewater parameters.
Surcharge calculations start with a flow
base rate and utilize multipliers for concen-
trations of such ingredients as BOD 5 , sus-
pended solids, and grease. An example
would be to charge the flow base rate to all
sewer users as 50% of the water bill, includ-
ing flow from private supplies. Treatment
costs chargeable to BOD and suspended
solids frequently include surcharges for con-
centrated wastes when above an established
minimum based on normal load criteria.
Small plants frequently determine that it is
advantageous to provide only enough pre-
treatment of wastewater to ensure compli-
ance with municipal regulations. Yet, larger
processors, in contrast, have discovered that
providing pretreatment beyond the level
required by the ordinance can be advanta-
geous. Some plants provide enough pretreat-
ment to reduce the surcharge for discharging
untreated wastewater. Many large volume
processors treat all of their wastewater to
avoid high surcharges or because the munic-
ipal plant lacks the capacity to handle the
additional effluent.
The following advantages of pretreatment
of wastewater beyond the level required by
the local ordinance should be considered: