to Cut Waste to
Reduce Surcharges for Your Dairy
you know that your dairy plant may be producing a waste load
of 800,000 pounds of BOD5 per year - equivalent to the load
from a city of 13,000 people?
Wastewater from most dairy plants is discharged to publicly
owned treatment works (POTWs), where the majority of the pollutants
are removed before the water is discharged to the environment.
Treating the water costs money, and most treatment works charge
according to the volume of sewage treated. In addition, they
commonly charge extra (apply a surcharge) if the waste load
exceeds certain specified levels because it costs more to treat
water that contains more pollutants.
Waste load can be determined by a number of different measurements,
including BOD5, the biochemical oxygen demand; COD, the chemical
oxygen demand, TSS, the total suspended solids concentration,
TKN, the total Kjeldahl nitrogen content, and FOG, the concentration
of fats, oils, and grease.
Wastewater from dairy plants is most often tested for BOD5,
a measure of the amount of oxygen needed to degrade the organic
matter carried by the water. The BOD5 concentration is measured
in milligrams per liter (mg/l). When the level exceeds 250 to
300 mg/l, many treatment plants apply a surcharge.
Some dairy plants discharge as much as 12 pounds of BOD5 per
1,000 pounds of milk received. More than 90 percent of a plant's
total waste load comes from milk components that are lost and
flow into floor drains during processing. Lactose, proteins,
and butterfat are the major components. The wastewater may also
contain cleaning agents, lubricants, and solids removed from
equipment and floors.
Loads Can Affect Profits
In the past, most dairy plant managers did not concern themselves
with reducing their plant's waste load because treatment costs
were minimal and restrictions few. Over the past 25 years, however,
some cities have increased their surcharges ninefold. BOD5 surcharges
now exceed 30 cents per pound in some cities. Pretreatment ordinances
in some localities may limit the level of wastes that can be
discharged into the sewers. In that case the waste load must
be reduced before the wastewater leaves the dairy plant.
Sewer costs, once a minor operating expense, have become something
that every cost-conscious manager must consider. At today's
rates, a plant's waste load can have a real effect on profitability.
Realizing this, some plant managers have been able to cut waste
discharges to as little as 1 pound of BOD5 per thousand pounds
of milk received.
The total amount of BOD5 in a plant's wastewater can be calculated
by multiplying the BOD5 concentration in milligrams per liter
by the amount of effluent in millions of gallons
of BOD5 = 8.34 x BOD5 concentration x effluent volume
example, if a plant discharges 3.7 million gallons of wastewater
per month with a BOD5 concentration of 2,300 mg/l, the total
amount of BOD5 discharged during the month is calculated
of BOD5 = 8.34 x 2,300 x 3.7 = 70,973 pounds
The monthly surcharge is normally based on the amount that
the BOD5 concentration exceeds a specified limit. To find
the monthly surcharge cost, multiply the excess amount of
BOD5 by the surcharge rate:
cost = Excess amount of BOD5 x surcharge rate
If the plant with a BOD5 concentration of 2,300 mg/l is
subject to a surcharge on BOD5 in excess of 250 mg/l, the
concentration subject to surcharge is 2,050 mg/l:
BOD5 subject to surcharge
= 8.34 x (2,300 - 250) x 3.7
= 8.34 x (2,050) x 3.7
= 63,259 lb
If the surcharge rate is 20 cents per pound of excess BOD5,
the monthly cost is:
= 63,259 lb x 20 cents/lb
In addition to the charge for excess BOD5, surcharges may
also be made for excessively high levels of COD, TSS, FOG,
Money by Cutting Waste Load: An Example
How much money could a dairy plant save by reducing its
BOD5 load to only 1 pound per thousand pounds of milk? To
find out, consider two dairy plants that each process 645,000
pounds of milk per day. Both pay a BOD5 surcharge of 20
cents per pound. Processor A discharges 1 pound of BOD5
per thousand pounds of milk processed (1 pound for every
116 gallons), while Processor B discharges 5 pounds in processing
the same amount of milk.
The table shows the daily and annual surcharge costs for
the two plants. The operators of Plant A save 80 cents per
thousand pounds of milk processed. That means they can bank
an extra $516 per day, or almost $130,000 annually if the
plant operates 250 days each year. In effect, Processor
B is pouring that amount of money down the drain.
Sewer Surcharge Comparison for Two Dairy Plants Processing
645,000 Pounds (75,000 gallons) of Milk per Day
load (lb of BOD5 per thousand lb of milk)
per thousand pounds of milk processed
per thousand gallons of milk processed
It is also important to remember that the excess waste load
reflects milk lost during processing, and the cost of this
lost product must be added to the surcharge to find the
To estimate the potential savings for your plant, determine
the sewer surcharges in your community and the current waste
load produced by your plant per thousand pounds of milk
processed. Then calculate the amount you think the waste
load could be decreased by improved operating practices.
Enter the values in the work sheet to compute your savings.
Surcharge Savings for Your Plant
current and target waste load in pounds of BOD5 per
thousand pounds of milk processed
daily production in thousands of pounds of milk
current and target waste loads by daily production
to find daily waste load in pounds
your BOD5 surcharge cost per pound
the daily waste load by the surcharge cost to find
your daily surcharge cost
the number of days your plant operates each year
the daily surcharge cost by the number of days your
plant operates annually to find the annual surcharge
the annual surcharge cost for the target waste load
from the annual cost for the current waste load to
find your annual savings
Can Reduce Waste Load and Save Money in Your Plant
You can take positive steps to reduce the waste load produced
by your plant. Some suggestions are given in the box. To
keep tabs on your progress, use the work sheet to calculate
your plantís waste load. Youíll not only help protect the
environment, youíll also show the people in your community
that your firm is a responsible corporate citizen. AND you
will send more money to the bank instead of down the drain.
waste reduction a management priority.
waste load reduction goals for your plant.
waste load reduction goals for all important processes
and areas of the plant where waste can be monitored
maintenance to prevent product leaks from valves, piping,
water use; remember that water used in processing becomes
wastewater that must be treated.
drain product from tanks and vats before cleaning.
solids from floors and equipment by sweeping. Shovel
the wastes into containers before actual cleanup begins.
Do not use hoses as brooms.
the attitude that waste load reduction is one of the
best managerial decisions you can make.
employees toward preventing pollution, and train them
how to do their jobs in a way that will reduce the discharge
of wastes from your plant.