Recent Developments in the Design of
Small Milk Waste Disposal Plants
j. p. horton and h. a. trebler
Assistant to the President of Laboratories
and Head of Engineering Research
National Dairy Research Laboratories,  Inc.
Oakdale, L. I., New York
Unlike most other industries that have a serious waste disposal
problem, the dairy industry is faced with the prospect of having to
erect a large number of relatively small treatment plants for country
milk receiving stations or small processing plants which are not on or
near municipal sewerage systems. Because of their rural locations, the
streams to which these plants discharge their wastes frequently are
good fishing streams so that there is considerable pressure to eliminate
pollution.
Many country receiving stations, although presently increasing in
size, are very small by most manufacturing standards, receiving only
30-60,000 pounds of milk per day and employing just two or three
men. The magnitude of the waste disposal problem of each plant is
also small by most waste treatment plant standards. Table I gives
some examples of the waste volume from a few plants of our associated
companies in Pennsylvania. In some locations, it has been necessary to
build treatment plants to take waste volumes as low at 2,000 gallons
per day and B.O.D. loads as low as 5 to 10 pounds per day. This may
seem somewhat absurd to some people, but it may be necessary as part
of a program leading to uniform law enforcement for small and large
alike.
From a technical point of view, many of these small plants do an
excellent job of waste saving and might well be left alone since their
wastes are oftentimes of more benefit than harm to the fish population.
Milk is an excellent food both for human and aquatic life, and so long
as the proper aerobic conditions are maintained in the stream at all
times, milk solids are actually of benefit. An interesting series of
articles by Pien (1) gives a wealth of data on aeration of milk waste
under simulated stream conditions. The results indicate that, wherever
sufficient dilution is available to reduce the B.O.D. to 20-30 p.p.m. in
a fairly shallow stream, natural stream reaeration will always be able
32