27    REMOVAL OF COLOR FROM SYNFUEL WASTEWATER
M. Tony San, Environmental Engineer
Law Environmental, Inc.
Charlotte, North Carolina 28217
Charles D. Turner, Professor and Chairperson
Department of Civil Engineering
University of Texas at El Paso
El Paso, Texas 79902
John R. Gallagher, Research Microbiologist
Energy and Environmental Research Center
University of North Dakota
Grand Forks, North Dakota 58202
INTRODUCTION
The University of North Dakota Energy and Environmental Research Center (UNDEERC), and
Civil Engineering Department conducted research associated with the treatment of wastewater generated from the Great Plains Gasification Plant (GPGP) near Beulah, North Dakota. Treatment processes commonly used for coal conversion wastewater include solvent extraction, air stripping, biological oxidation and nitrification. An additional concern with the wastewater is the presence of color.
High levels of color are common in coal conversion wastewater, even subsequent to secondary
treatment. Since the discharge of colored water presents an environmental concern due to the loss of
aesthetic value of the receiving water and the negative effects on aquatic life due to decreased light
transmittance and toxic effects,1 the need for an economical, effective method to remove the color
exists.
Much research has been conducted on color removal of pulp mill effluent for the pulp mill industry.
Pulp mill effluent is highly colored due to the presence of lignin. The current color removal methods
for the pulp industry include lime coagulation, resin absorption, physical adsorption, ultrafiltration,
reverse osmosis, solvent extraction and biological treatment.
This paper contains the results of color removal research on GPGP bio-treated stripped gas liquor
(SGL) using bench scale solvent extraction, adsorption (activated carbon, fly ash, lignite and peat),
biological removal (fungi) and pH adjustment methods.
BACKGROUND
San2 has reviewed the methods of color removal of GPGP synfuel wastewater. The color of the
SGL from that gasification plant was found to be about 5250 APHA PtCo units with a transmittance
of light at about 2.5% in a spectrophotometer at 465 nm.
GPGP condensate contains a wide variety of pollutants ranging from COD to ammonia. The plant
has invested considerable resources with the cooperation and funding of the USDOE to reduce the
pollutants in its wastewater discharge.3"6 In spite of years of research, an effective and economical
process to remove color from the wastewater has not been found.
COLOR-CAUSING COMPONENTS
The color-causing components are believed to be colloids (polymers). Filtration with microporous
filters of pore sizes less than 0.45 microns removes some of the color. The dark color is completely
removed when the pH of the wastewater is brought down to 3 and below, and then filtered to remove
the black precipitate. When the pH is brought back up to 7, without removal of the precipitate, the
precipitate redissolves and the color returns. This behavior fits that of a natural plant-derived humic
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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