BIOLOGICAL TREATABILITY OF UNDERGROUND
COAL GASIFICATION WASTEWATER
Timothy P. Caire, Graduate Student
Desmond F. Lawler, Assistant Professor
Department of Civil Engineering
University of Texas, Austin
Austin, Texas 78712
Michael J. Humenick, Jr., Professor
Department of Civil and Architectural Engineering
University of Wyoming
Laramie, Wyoming 82071
INTRODUCTION
Coal gasification is of interest in the United States because it is a promising method of utilizing
one of the country's largest natural energy resources, coal, as a substitute for a more limited resource,
natural gas. Coal gasification processes convert coal into a methane-rich gaseous product. There are
several coal gasification processes, with most currently at the pilot stage. They differ with respect to
operating conditions, coal types accepted, and consequently, with respect to the characteristics of the
wastewater produced.
Many coal gasification processes produce wastewater effluents which contain large amounts of
both organic and inorganic pollutants. Biological treatment of these wastewaters is favored because
they contain high concentrations of phenolic compounds, which are removed efficiently by an
acclimated biomass. Unfortunately, these wastewaters typically contain compounds which can be toxic to microorganisms and thereby impair the biological treatment process.
The wastewater investigated in this study was generated by an undergound gasification process in
Hanna, Wyoming. No other studies of the treatability of wastewaters from underground coal
gasification are known to these investigators. Above-ground gasification effluents previously studied
for biological treatability include Hygas [1], GFETC [2], Synthane [3,4], and MERC [5] process effluents. Also, Singer et al [6] have reported on the treatment of synthetic coal gasification wastewater.
These wastes have been successfully treated by the activated sludge process. Raw product gas quench
condensates from these gasification processes are quite similar with respect to the nature of the contaminants present; accordingly, they can be considered as a family of related industrial wastewaters.
However, because of differences in relative proportion and concentration of various contaminants
among the wastewaters, they may require different pretreatments and exhibit different treatability
characteristics. Investigators have found that treatment of these wastewaters generates a low cell yield
in comparison to that observed with domestic waste. As a result, these effluents must be treated within
a range of high sludge ages (and correspondingly low specific substrate utilization rates).
Underground coal gasification (UCG) generates a heavily contaminated condensate which forms
on cooling the product gas and yields an aqueous phase and an organic phase. The wastewater treated
during this project was a composite sample of the aqueous fraction generated from the Hanna IVB
field test in Hanna, Wyoming. Measurements performed as part of this research indicated that the
wastewater had a very high COD and high concentrations of phenolics and ammonia, as shown in
Table I. The measured inorganic carbon and pH correspond to an alkalinity of 8200 mg/1 as CaC03.
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