Heavy Metals Removal from
Wood Preserving Wastewater
E. H. TEER, Environmental Engineer
L. V. RUSSELL, Laboratory Director
Russell & Axon Consulting Engineers, Inc.
Daytona Beach, Florida
INTRODUCTION
There are approximately 400 plants in the United States engaged in treating wooden
poles, posts, ties and lumber for protection against decomposition by insects, bacteria and
fungus. The three general types of wood preservatives are creosote, oil-borne such as
pentachlorophenol, and water-borne such as chrome-copper-arsenic solutions.
This paper is concerned with water-borne solutions only and specifically the three
given in Table I.
TABLE I
WATER-BORNE WOOD PRESERVATIVE SOLUTIONS
CCA       For Chrome, Copper, Arsenic
FCAP     For Fluoride, Chrome, Arsenic and Dinitrophenol
FR For fire retardent, in this case a proprietary solution of four salts which
primarily contribute ammonia to the wastewater.
The chromium is present in the wastewater in the hexavalent form and the first step in
removal of the toxic materials listed is the reduction of the chrome to the trivalent form.
In June 1970, the Osmose Company of Griffin, Georgia, contracted with Russell &
Axon Consulting Engineers, Inc., to provide the engineering design for a prototype wood
preserving wastewater treatment system for their licensed plants. The first one of these was
installed, and placed in operation in November 1971, by Dixie Wood Preserving Company
at their Thomson, Georgia plant. This treatment system is the first of its kind in the wood
preserving industry and has been approved by the Georgia Water Quality Control Board.
This paper describes the waste treatment system and the design criteria used based on
laboratory and field studies.
In treating the wood, the lumber is placed in pressure cylinders measuring 5 feet in
diameter by 64 feet long. The first step is the injection of steam into these cylinders at a
pressure of 50 psig. This step drives some of the volatile matter from the wood so that the
pores are free to accept the preservative solutions. After steaming, the cylinders are
evacuated by means of rotary vacuum pumps and a barometric condenser.
The cylinders are then filled with the solutions and held under pressure for 4 hours so
that the chemicals can penetrate the wood cells.
The solutions are pumped back to the process tanks and the cylinders are opened for
removal of the wood. The last traces of solution drain from the cylinder to recovery sumps
which drain to two 5,000 gallon underground tanks. The wood is then placed on concrete
drying slabs where excess solution is collected to the recovery sumps. These recovered
solutions are used as makeup water supplies for mixing the wood treating chemicals. The
excess volume is the plant effluent. Figure 1 illustrates the waste control plan.
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