Citric Acid from
Citrus Processing Wastes
STERLING K. LONG, Assistant Industrial Bacteriologist
University of Florida
Citrus Experiment Station
Lake Alfred, Florida
INTRODUCTION
The development of a fermentation process for converting the carbohydrates
of citrus wastes to citric acid is a new, although not necessarily novel, approach
to disposal of liquid wastes in the citrus industry.
Approximately 100 million lbs of citric acid are produced annually in the
U. S., primarily by fermentation. This fermentation has been a commercial
process for many years and provides about 90 per cent of the world supply of citric
acid. No commercially feasible method exists for producing this compound by
chemical synthesis.
Citric acid is produced from various sugars by the mold Aspergillus niger,
usually employing such cheap raw materials as beet and cane blackstrap molasses.
Although citrus molasses is comparable in most respects to these types of molasses
and is considerably cheaper, only one reported attempt (1), which was unsuccessful, has been made to utilize it in this manner. According to published analyses
(2), citrus molasses contains all of the constituents required for fermentation by
Aspergillus niger. A comparison of citrus and blackstrap molasses is given in
Table I. Adding to the attractiveness of this picture is the fact that a ready market for citric acid already exists in Florida where various industries utilize approximately five million Ids of this compound annually.
An expanding citrus industry, and the phenomenal and continuous growth in
population of the State of Florida are factors which could, predictably, lead to
friction over the mounting problem of disposal of citrus canning plant wastes. In
the early days of the industry, most of the canning plants were located outside of
small Florida towns and were sufficiently remote from residential areas that they
caused few problems. Now, however, extensive residential construction to accommodate the heavy influx of immigrants to Florida has resulted in engulfment
of most of these plants by residential areas.
Canning plants which dump their wastes onto surrounding vacant land or release them directly to streams and lakes, now find themselves under ever increasing pressure from the public, and State and Federal agencies to dispose of their
wastes in a less offensive manner.
PRESENT METHODS OF WASTE DISPOSAL
There is no uniform method in the citrus industry for disposal of cannery waste
water. Probably the most common method is spray irrigation, in which the wastes,
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