Treating Milk Wastes By Biological Oxidation
With Plastic Media
JOSEPH G. RICHARD, JR., Southern Regional Sales Manager
ROBERT P. KINGSBURY, Eastern Regional Sales Manager
Environmental Control Division
Ethyl Corporation
Baton Rouge, Louisiana 70801
ORIGIN AND CHARACTERISTICS OF MILK WASTES
The wastewater from milk product processing varies widely in strength and flow rate
on a daily and seasonal basis. Daily flows usually occur overa period of 10 to 12 hours with
highest waste strength resulting during wash-down at the end of the working shift. During a
weekly period the waste strength varies with high production in the early part of the week,
high waste strengths from plant wash-down at the end of the week, and little, if any,
production on the week-end. Seasonal variations occur in milk production with
corresponding changes in wastes. Highest production and strongest wastes usually occur
during June and July, which is simultaneous with low stream flows.
Milk product wastewaters are all similar in that they are organically strong and will
become rapidly acid and odorous by anaerobic fermentation. Whole milk exhibits a 5-day
Biochemical Oxygen Demand (BOD5) of about 100,000 mg/l and is nearly neutral in pH(l,
2). Whole milk is about 3'/2 percent fat. Wide variations in waste characteristics can result
from a variety of products including: fluid milks and creams, butter, dry powdered milk,
cheese, cottage cheese, yogurt, ice cream and desserts, evaporated and condensed milk,
candies and milk chocolate, and egg packaging. Whey results from cheese making and is a
greenish-yellow fluid with a pH in the range of 4 to 7, a BOD5 range of 32,000 to 60,000
mg/l, and a solids content of as much as 3 percent (3).
Recent surveys have indicated that the volume of milk product loss is '/2 percent in large
technologically advanced plants and is as much as 2'/2 percent in small, old plants (4).
However, this volume is reportedly as low as 0.2 percent in the United Kingdom, for
example (1).
The average waste stream is about 1,600 mg/1 BOD and the volume of liquid waste is
roughly 1.5 times the volume of milk handled (4). However, various factors have much
influence on these magnitudes. Milk wastes are as much as 85 percent soluble organics. The
pH of mixed waste streams may be about 4.5 to 6.5 if the main product is yogurt or cottage
cheese. However, the average pH may be as high as 9.0 as a result of caustic cleaning agents
from an integrated creamery. Ammonia in cleaning agents helps, but milk wastes are
deficient in nitrogen nutrient for biological treatment. Phosphorous and other limiting
trace nutrients have been found to be ample.
STATUS OF WASTE TREATMENT
Milk wastes originate from food production, they are autotrophic and they contain no
toxic components. This makes them highly treatable by biological methods with the
following provisions: 1) Wide pH variations must be controlled for optimum biological
treatment; 2) Nutrients, specifically available nitrogen, must be added to satisfy a COD:N
ratio of 100:5; 3) Concentrated whey stream discharges must be treated separately or
diluted; 4) Fat removal may be required to permit optimum biological treatment; and 5)
Treatment of the waste while it is fresh results in optimum performance.
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