50    A COMPARISON OF COUPLED UPFLOW AND COUPLED
DOWNFLOW
FLUID BED REACTORS TREATING SYNFUEL
WASTEWATER
Charles D. Turner, Professor
Michael J. Koehmstedt, Graduate Research Assistant
Department of Civil Engineering
John R. Gallagher, Research Microbiologist
Energy and Mineral Research Center
University of North Dakota
Grand Forks, North Dakota 58202
INTRODUCTION
This chapter presents a comparison of downflow and upflow coupled biological fluid bed reactor
research that has been conducted at the University of North Dakota (UND) using Great Plains
Gasification Plant (GPGP) wastewater. A coupled downflow bench scale unit,1 a coupled upflow
bench scale unit2 and a coupled downflow process development unit3 have been operated over a three
year span. These units have demonstrated that both upflow and downflow coupled biological processes can be highly effective in removing biodegradable organics and nitrogen.
Synfuel conversion processes produce wastewater from product gas cleanup and auxiliary operations. These wastewaters typically contain high concentrations of ammonia and organics. In addition,
they generally contain priority pollutants such as phenol and cyanide. The most commonly chosen
process for such wastewater, activated sludge, is not well suited to the treatment of synfuel wastewaters if nitrogen must be removed. Activated sludge is a suspended growth process that requires
clarifiers and high mean cell residence times to maintain a nitrifying population. Oxygen is required
for both organic and ammonia oxidation and an additional carbon source must be supplied for the
anoxic removal of nitrate.
Coupled biological fluidized bed reactors are well suited to treatment of synfuels wastewaters
containing high concentrations of ammonia and organics. The process converts ammonia to nitrite
and nitrate in an oxic reactor. The nitrate and nitrite are subsequently converted to nitrogen gas in an
anoxic reactor. The organics present in the feed wastewater are used as a carbon and energy source in
the anoxic reactor.
BACKGROUND
North Dakota is home of the United States largest coal to methane conversion facility. The plant
converts 14,000 tons of lignite into 124 million standard cubic feet of gas per day. This plant, the
Great Plains Gasification Plant (GPGP), is located north of Beulah, North Dakota. This region is
underlain with large quantities of strippable lignite coal. The wastewater used in this research was
produced at GPGP using Indian Head Lignite.4 This coal has an energy content of 7200 btu per
pound, a moisture content of 35% and a low sulfur content of approximately 1%.5
The Energy and Mineral Research Center (EMRC) has conducted research on the treatability of
synfuel wastewaters produced using GPGP, KILnGAS, BGC/Lurgi and the UND-EMRC gasifiers.
Table I shows several representative parameters such as ammonia and chemical oxygen demand
(COD) for these wastewaters. These values represent wastewater that has been pretreated using
solvent extraction and ammonia stripping. Solvent extracted and ammonia stripped wastewater is
termed stripped gas liquor (SGL).
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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