Treatment of Milk Truck Washing Wastes
By Anerobic Digestion
DONALD B. AULENBACH, Associate Professor
RUSSELL V. HALLOCK, Graduate Student
Bio-Environmental Engineering Division
Rensselaer Polytechnic Institute
Troy, New York
INTRODUCTION
Generally the first thought that comes to the mind of a regulatory agency at the
mention of the world milk wastes is an activated sludge treatment system, usually a package
plant. There are many milk handling plants for which a package activated sludge unit will
provide adequate treatment. Milk truck washing wastes from a milk transfer station,
however, present a somewhat different type of waste which is also amendable to treatment
by other techniques.
The route taken by milk from the farm to the consumer has changed considerably over
the years. A few older persons can still remember when each farmer brought his milk to the
city market in the familiar five gallon metal cans. With the raising of the standards for the
bacterial quality of milk, pasteurization became a necessity. Larger farms installed their
own pasteurizing equipment and smaller farms delivered their milk to the larger farms.
With time, pasteurization and processing plants were built which served larger farm areas.
Many such plants grew up in the areas of northeastern New York and Vermont. In the
beginning, the milk was still carried in the metal cans from the farm to the plant. With
improvements in roads, trucks, and insulating materials, the bulk handling of milk
supplanted the metal milk can. Today the milk is stored on the farm in a refrigerated
holding tank and a truck usually of about 2,500 gallon capacity pumps the milk from the
storage tank into the truck tank. This milk is then carried over the road to the processing
plant. In more recent years, the smaller milk plants have proven uneconomical and larger
scale plants have taken over. This requires the transportation of the milk over greater
distances. The small 2500 gallon tank trucks are not economical for long hauls; therefore,
the milk is transferred to either railroad cars or more recently to 4,500 — 5,000 gallon over-
the-road tank trucks. What was formerly the pasteurizing plant has become a milk transfer
station where the milk is transferred from the smaller trucks which can negotiate the farm
roads to the larger trucks which haul the milk the great distances to the pasteurizing or
processing plants.
Such is the case with the Hood Milk Transfer Station at Eagle Bridge, New York. The
main milk processing plant for the Hood Corp, is in Boston. Up until about 1970, the milk
was transferred to railroad cars for transport to Boston. Since that time however, over-the-
road trucks have been used, primarily due to the better insulating capabilities of the newer
trucks. Since the waste from the washing to the trucks reaches the Hoosick River,
provisions must be made to treat the waste prior to discharge into the stream.
The waste produced is somewhat different from strickly milk waste. The smaller farm
trucks make usually one to two collections in a day. On the last trip for the day, the outside
of the truck is sprayed with a high pressure jet of water and scrubbed with a brush to remove
the road grit. The compartment housing the pump and the transfer hose is then thoroughly
washed with soapy water and sprayed with the same jet. The small amount of milk in the end
of the transfer hose (approximately 2 lbs.) is discharged to waste. This hose is then
connected to the plant pumping system and the milk emptied from the tank truck into 1) the
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