31 Wc?
FERMENTATION PROCESS FOR DILUTE FOOD AND DAIRY WASTES
Vijay Singh, Senior Process Engineer
Chian C. Hsu, Fermentation Microbiologist
David C. Chen, R&D Bio-Engineer
Chu H. Tzeng, Director of Fermentation Technology
Abcor, Inc.
Wilmington, Massachusetts 01887
Many food and dairy operations produce large quantities of high strength waste effluents
that constitute a major disposal problem. Many of these streams are dilute (4-5% total
solids) yet have a biochemical oxygen demand (BOD) in the range of 20,000-50,000 mg/l.
The high BOD levels are chiefly due to sugars and starchy material in the wastewater. Disposal of these waste effluents is becoming increasingly difficult. In cases where municipal
sewers are available, extra charges are levied to treat the high strength wastes. Land spreading
and illegal dumping are being curtailed as exisitng environmental regulations are tightened.
The high strength of the wastes makes conventional aerobic treatment very difficult and
expensive. Anaerobic treatment of the waste to generate methane is possible, but in many
cases has a poor return on investment. Recovery of the sugars, starches, proteins and minerals in the waste effluents by crystallization, evaporation and spray drying are practiced in
many food and dairy plants. Escalating energy costs, especially that of natural gas, have
made many of these operations economically unattractive.
In our opinion, these food and dairy wastewaters should be viewed as a rich, inexpensive
potential source of raw material from which valuable products can be made. Many of the
waste effluents are well defined, sanitary, contain fermentable carbohydrates and nutrients,
and are available year round at fairly constant rates.
One of the products that can be made from waste carbohydrates is ethanol by fermentation. The process described in this paper was developed at Abcor for the fermentation of
whey or milk permeate to ethyl alcohol, though it is, in general, applicable to a variety of
dilute sugar and starch containing streams. In the ultrafiltration of whey or milk for recovery
of proteins considerable quantities of permeate are produced. The permeate has in the past
presented a serious disposal problem due to its high BOD and low market value. BOD levels
are typically in the range of 30,000 to 40,000 mg/l, and are due, in the most part, to the
lactose in the permeate. The Abcor process converts this lactose to ethyl alcohol thereby
producing a profitable product and alleviating a major disposal problem.
ABCOR ETHANOL PROCESS
The basic schematic of the Abcor process for the conversion of permeate to alcohol is
shown in Figure 1. The dilute permeate from ultrafiltration operation is concentrated by
reverse osmosis 3.5 times and then fed to the fermentation unit. During fermentation, the
lactose in the permeate is converted to ethanol; some of the lactose is also converted to carbon dioxide and yeast cells. The alcohol from the fermentation is about 9% by volume. This
dilute alcohol broth is fed to a distillation unit where the alcohol is concentrated. Final
product concentration depends on the application; for power alcohol, 99.5+% purity is required, while many industrial grade applications may require only 95% ethanol. Yeasts are
produced during the fermentation and though these may be recovered for sale as feed, it is
profitable only for very large plants. In our plan* •, the yeast cells are sent on to the still
and recovered in the still bottoms. The still bottoms contain valuable minerals, carbohydrates and nutrients, and when concentrated have a market as an animal feed supplement.
321