WASTEWATER TREATMENT FOR THE
SMALL WOOD PRESERVER
E. H. Teer, Engineer
Harry Hendon and Associates, Inc.
Atlanta, Georgia 30324
L. V. Russell, President
Russell Laboratories, Inc.
Holly Hill, Florida 32017
INTRODUCTION
Wood preserving is a large industry in the U.S. and is spread throughout the country
in small plants located in practically all the states.   It is concerned with the impregnation
of poles, posts and railroad ties with creosote and oil solutions of pentachlorophenol,
and the treating of finished lumber with water solutions of inorganic chemcials such as
chromium, copper and arsenic.   Additional chemicals may be used, but these are the
major ones.
There are many alternates of chemical use. Posts may be treated with chrome-copper-
arsenic (CCA) and finished lumber may be treated with pentachlorophenol. The finished
product requirement is closely tied to the construction industry.
Treating of the wood generally takes place in large pressurized cylinders.   Cylinders of
5 ft in diameter by 60 to 100 ft long are common.   Quite often the wood is green and
not kiln-dried and contains all the cellular materials found in the trees.   To successfully
impregnate the wood, these materials must be removed and replaced by the treating
chemical.
The wood is charged batch-wise to the cylinder. The cylinder is closed, and then the
wood is steamed at high pressure. A vacuum is then pulled on the cylinder to withdraw
the materials steamed from the wood. The cylinder is then fully charged with the treating chemical, creosote, penta or CCA waterborne solution and cooked to drive the chemical into the cells of the wood. Upon completion, the chemical is pumped back to a
holding tank. The entire sequence may take 4 to 8 hr depending on the treatment type
and the cylinder size.
When the cylinder is opened to remove the wood, the residual steam condensate, wood
extracts, and treating chemical or oil drains from the cylinder to sumps where it must be
collected for waste treatment.  When the wood is pulled out it is allowed to sit on a
cooling and drying pad where drips, especially during rainy weather, will contribute further
to the waste problem.
In addition, the creosote and penta oil used for treating become contaminated with
condensate and emulsions form.   It is necessary to provide some clean-up of the oil before reuse, and this produces wastewater containing the emulsions which have not been
broken.
A wood preserving plant may have a single cylinder and treat only lumber with water-
borne salt solutions such as CCA.   A plant may treat only with creosote or pentachlorophenol.   Some plants treat with all three.   The plant considered here has one creosote
cylinder, three penta cylinders, and a CCA cylinder.
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