High-Solids, Biological Aeration of
Unneutralized, Unsettled
Tannery Wastes
DWIGHT B. EMERSON Research Assistant
NELSON L. NEMEROW, Professor
Department of Civil Engineering
Syracuse University
Syracuse,   New York
INTRODUCTION
In 195 2, there were 443 reported tanneries in the United States (1). About 60
per cent of these tanneries were located in the northeast. In 1965, the number has
been reported to have dwindled to about 200 relatively large plants (1).
In 1952, Harnley indicated that about 20 bil gal of waste were generated
yearly by the tanning industry in the United States. In 1963, an estimated 16 bil gal
were discharged by the industry (1). There appears to have been a trend toward
centralization during this period in Chicago, Milwaukee, and the northeast.
In 1967, the tanneries of the United States represented a five billion dollar
industry and employed approximately 40,000 workers. The estimated per capita
expenditure for leather goods that year was about 29 dollars. Hide and skin exports
are reported to have increased to 82 million dollars during the period between 1963-
64 (1). A current trend has been to export cattle hides to countries which can produce leather at a lower cost. Leather substitutes and imported leather goods have cut
into the United States' leather tanner's market. The ability of the United States
tanners to meet this competition will depend primarily on economic factors, one of
which is the cost of waste water treatment.
An estimated 34 million cattle are butchered annually in the United States.
About 25 million of these skins are tanned in the United States, with the remainder
being exported to foreign markets (1). About 85 per cent of all leather used in the
United States is made into shoes, 80 per cent of which is chrome tanned upper
leather (1).
THE TANNING PROCESS
The chrome tanning of cattle hides may be broken down into several process
steps, which are indicated in Figure 1. Each step performs an important function in
the tanning process and produces a liquid waste.
Curing of the hide is usually the first process step performed after the hide is
removed from the animal. Bacteria are often abundant on the skin and upon the
death of the animal, proteolytic bacteria attack the skin and destroy its potential
value as leather. A common method of reducing bacterial action is by dehydrating the
skin by treating with salt.
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