Physical-Chemical and Biological Treatability
Investigations and Process Design
For a Tall Oil Wastewater
CARL E. ADAMS, President
FRED G. ZIEGLER, Project Manager
Associated Water and Air Resources Engineers, Inc.
Nashville, Tenneessee 37215
DESCRIPTION OF INDUSTRY
During the Kraft digestion process for pulping of pine wood chips, the wood is treated
with a solution composed of caustic soda and sodium sulfite. The digestion process which is
carried out under heat and pressure dissolves the lignin which binds the cellulose fibers,
freeing the fibers for further processing. The caustic reacts with the rosins and saponifies the
esters of the fatty acids, thus, producing sodium salts which are dissolved in the spent black
liquor. The black liquor is evaporated in multiple effect evaporators and then incinerated to
produce steam. During an intermediate stage in the evaporation of the black liquor, it is
permitted to settle resulting in separation of sodium soap of rosin and fatty acids which are
skimmed for further processing into crude tall oil (1). These skimmings are then acidulated
with sulfuric acid to produce two phases which are crude tall oil and a solution of sodium
sulfate which is recycled within the paper mill.
The crude tall oil which contains some sodium sulfate may be subjected to heating and
vacuum dehydration to flash off the water and precipitate the remaining salts. The crude tall
oil is then subjected to fractionation which separates the material into its principle products
of unsaturated fatty acids and rosin, also producing distilled tall oil and a saturated acid
fraction. Total tall oil production within the United States is approximately 793,000
ton/year.
The wastewater resulting from tall oil production originates from the stripping steam
condensate of the fractionating towers which carry the most volatile and therefore the most
odors of the unsaponifiable materials contained in the crude tall oil. Often, barometric
condensers are used to condense the steam and settle the oily layer before the water is
recirculated through the cooling tower. The condensate from the condenser circuit may
contain between 0.5-3 percent tall oil. Other waste loads originate from satellite production
process which are often batch operations. Washing may create significant fluctuations
within the wastewater characteristics.
BACKGROUND INFORMATION
The plant which was investigated and discussed herein is located in the southeastern
United States and produces fatty acids, pitch rosin, acid and distillation-refined tall oil. The
production of tall oil is approximately 60,000 ton/yr. The industry originally desired to
enter the local city sewerage system, which consisted of oxidation ponds, and retained
Associated Water and Air Resources Engineers, Inc. (AWARE) of Nashville, Tennessee to
assist in delineating the necessary pretreatment requirements. After conducting preliminary
treatability investigations which evaluated pilot systems of the municipal oxidation ponds
with and without the pretreated industrial wastewater, AWARE concluded that extensive
organic removal would be required prior to discharge to the municipal system. After
reviewing pretreatment costs and the surcharge cost of entering the city system, it was
decided that it would be to the industry's advantage to treat its own waste to the level
necessary for direct discharge to the receiving water. The pretreatment investigations have
been reported elsewhere (2) and will not be repeated in this paper.
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