CASE HISTORY: CONTROL OF ODORS AT A TANNERY
WASTEWATER TREATMENT PLANT
Pamela B. Katz, Project Engineer
TRC - THE RESEARCH CORPORATION
of New England
Wethersfield, Connecticut 06109
INTRODUCTION
In 1977 odorous emissions from a New England tannery brought about complaints from
the surrounding residential neighborhood causing the local municipal government into seeking an investigation of the situation. TRC—The Research Corporation of New England —was
engaged by the city to determine the impact of the tannery and its onsite wastewater treatment plant on community odor levels and to determine what controls might be applied to
these odor sources. During the subsequent odor measurement task, TRC determined, using
dynamic dilution olfactometry and fugitive emission measurement methods, that almost 75%
of the odor emissions from the site were generated by the tannery's wastewater treatment
plant. The paper addresses the cause of odors in the treatment plant and how these odors
were subsequently controlled and reduced over the period 1977-1979.
THE SOURCES OF THE TANNERY WASTE STREAM
A short summary of the sources of tannery wastewater is presented below. The reader is
referred to Liquid Waste of Industry by Nemerow [ 1 ] for a more detailed description of tannery processes.
The tannery has both a beamhouse and a tanyard, each producing very different wastes.
In the beamhouse, hides which arrive packed and cured in salt are initially washed and
soaked to remove dirt, salts, manure and blood, and to restore moisture. Utilizing lime and
sodium sulphydrate, the hair is removed from the hide and the hides are rinsed and relimed.
The bating process then removes residual dehairing chemicals and makes the skin smoother
and more porous.
These beamhouse processes produce a wastewater high in biochemical oxygen demand
(BOD), chemical oxygen demand (COD), suspended solids, salt, total solids, sulfides, alkalinity, ammonia, and nitrogen. The pH of the wastewater is 11.5-12.5.
While the beamhouse produces a very alkaline waste with hair and organic matter, the tannery process produces a very acidic waste. The pickling process tranforms the hides to an acid
environment and prevents the precipitation of chromium salts on the skin fibers. Chrome
tanning of the pickled hide then converts the skin into a stable material and gives the skins a
blue-like color. The hides are then rinsed, split, retanned, washed and colored. A fat liquoring process lubricates the fibers for flexibility. Other dry processes subsequently dry, buff
and finish the leathers. The total discharge from these processes produces an acidic wastewater high in chromium, oil and grease, COD, suspended solids, total solids and salt.
DESCRIPTION OF THE TANNERY WASTEWATER TREATMENT PLANT
The New England tannery, under discussion, ended direct discharge to the stream in 1976
with construction of its own onsite wastewater treatment plant. The treatment plant, which
was brought online in late 1976, was not fully operational until Spring 1977. The average
flow of the plant was 180,000 gpd until Spring 1979.
A schematic diagram of the treatment plant as it existed in 1977 is presented in Figure 1.
The alkaline stream from the beamhouse processes and the acid stream from the tanning process entered the plant through separate wet wells to a hydrasieve where hair and fleshings were
removed by screening. The beamhouse wastes with high sulfide content were kept separated
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