BIOLOGICAL TREATMENT OF COAL GASIFICATION WASTEWATER
William A. Sack, Professor
Department of Civil Engineering
West Virginia University
Morgan town, West Virginia 26506
William R. Bokey, Engineer
U.S. Environmental Protection Agency
Atlanta, Georgia 30308
INTRODUCTION
Coal-associated wastes (air, water, and solid) have presented a challenge to the profession for many years.    They occur in great variety including acid mine drainage,
power plant residuals, and coal conversion wastes.   The treatment and recycle of coal
conversion wastewaters, both from liquefaction and gasification, will undoubtedly command increasing attention in the next decade.
The Morgantown Energy Research Center (MERC) operates a stirred fixed-bed gasifier
to produce low-Btu gas.   The gasifier is 42 inches in diameter and typically processes
about 17 ton per day of coal.   The purpose of this work is to evaluate the amenability
to biological treatment of the gasifier wastewater.    Figure 1  presents a simplified process
diagram showing some of the main components of the cleanup system.   Coals of any
rank may be gasified without pretreatment in the process.   Coal enters via a lock
hopper and is contacted with air and superheated stream necessary for gasification.
After gasification, a cyclone separator is used to remove large solids from the gas
stream.    The gas is then saturated at system pressure (typically using recycled water
from the decanter) and tars and some water are separated from the stream.    After a
planned pressure drop, the supersaturated gas releases additional tar and water in the
disengagement chamber.    Additional scrubbing is accomplished in the tray separator
prior to decantation.    All wastewaters are sent to the decanter where separation of
condensed low boiling tars is allowed to occur.   Wastewater used for this work was
condensate collected from the decanter.
Biological treatment, not withstanding its drawbacks and limitations, is often the
most cost-effective way to treat organic wastewaters. In the coking industry, which
produces an effluent similar in many respects to coal conversion wastewaters, biological
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Figure 1.   Simplified process diagram of gasification at MERC.
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