SOME PROBLEMS AND ALTERNATIVES IN APPLYING
BIOLOGICAL TREATMENT MODELS TO A
COAL CONVERSION WASTEWATER
Brian R. Marshall, Environmental Engineer
CH2M HILL
Reston, Virginia 22091
James C. Lamb III, Professor
David A. Reckhow, Research Assistant
Department of Environmental Sciences and Engineering
University of North Carolina
Chapel Hill, North Carolina 27514
Wastewaters from the conversion of coal to liquid or gaseous fuels contain very high
concentrations of organic compounds, ammonia, carbonate alkalinity, sulfur and chloride.
Most of the organic carbon (60-80%) consists of phenolics, while other important organics
include nitrogen-containing aromatics, oxygen- and sulfur-containing heterocyclics, poly-
nuclear aromatic hydrocarbons, and aliphatic acids [ 1 ]. The mixture of compounds in a
specific wastewater depends on the conversion technology employed and the composition
of the coal [2]. Detaded summaries of chemical compositions of coal conversion wastewater are presented elsewhere [ 1,3,4,5].
At present, there are no full-scale coal conversion facdities in the United States, so
wastewater treatment technology is still developing. However, biological treatment is gen-
erady included in the proposed treatment schemes [ 1 ] because it is often an economical
method for removing organics from complex wastewater mixtures [31. Also, biological
oxidation has been used successfully for treating other wastewaters with high phenolic
concentrations, such as coking wastes, which are simdar in composition to coal conversion
wastewaters. Activated sludge is often the preferred method of biological treatment because
it provides a high removal efficiency and can be controlled most easdy [6].
Many models have been used to describe biological treatment processes. Most differences
between these models reflect varying assumptions concerning hydraulic configuration,
process dependence on time, influent characteristics, environmental conditions and the
mathematical description of microbial growth kinetics. However, included in most commonly used models is a relationship between microbial utilization rate of organic substrate
and the growth rate of organisms, referred to as cell yield [7-9]. The net rate of growth is
obtained by subtracting the decrease in cell mass due to endogenous decay and is depicted
by the rate equation:
dX       dS
 = Y— - bX (1)
dt dt
where dX/dt = net rate of microorganisms growth (mass/volume-time)
dS/dt = rate of substrate utilization (mass/volume-time)
Y  = growth yield coefficient (mass of cells formed/mass of substrate consumed)
b   = endogenous decay coefficient (time   )
X  = microbial mass concentration (mass/volume).
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