Section Nine
COAL, COKE, AND POWER PLANT WASTES
64    DEVELOPMENT OF A MIXED AEROBIC CULTURE
FOR DEGRADING COAL-TAR
Jeffrey D. Enzminger, Graduate Student
John V. Lepore, Graduate Student
Carolyn Gleason, Graduate Student
Catherine Dreyer, Graduate Student
Robert C. Ahlert, Professor
Department of Chemical and Biochemical Engineering
Rutgers, The State University of New Jersey
Piscataway, New Jersey 08854
INTRODUCTION
Coal-tar has been generated as a byproduct of coking and coal-gas works since the beginning of the
19th century. Where it is improperly landfilled, coal-tar may pose a threat to groundwater resources.
At St. Louis Park, Minnesota, a suburb of Minneapolis, residues from a tar distillation and wood
preserving plant, operated between 1918 and 1972, contaminated the principal local aquifer, forcing
the closure of a number of wells up to two miles from the source. A hydrocarbon phase with an
associated total organic carbon content of 6000 ppm was discovered moving downwards through the
aquifer [I].
Coal tar is a heterogeneous substance containing up to 10,000 species of which 462 have been
characterized [2]. Selected coal tar constituents are shown in Table I. The largest distillate fraction is
the pitch, which is the residue after distillation up to 647 K. Tar pitch contains polynuclear aromatic
hydrocarbons (PAHs) of from four to 30 aromatic rings which may be substituted and homo- or
heterocyclic. Higher molecular weight compounds may not be fully condensed. Table II lists some of
the four to six ring compounds contained in the pitch fraction, several of which are carcinogenic.
The toxicity of coal-tar has been well documented with respect to skin contact and fume inhalation
|3]. There is sufficient evidence that topical application causes skin cancer and that inhalation of tar
fumes causes lung cancer. Coal tar exposure has also been connected to bladder cancer and several
PAHs found in coal tar are known carcinogens. Little is known concerning the health effects of
chronic exposure to dilute aqueous solutions of tar constituents.
Of the remediation options at coal-tar-contaminated sites, on-site treatment is the most desirable
since the expense and hazards of transportation off-site are avoided. One on-site treatment option
under consideration is biological decomposition. However, the low aqueous solubility and high average molecular weight of the tar compounds present a major obstacle to biodegradation. In this paper,
preliminary results on the biological degradation of a gasification-tar are presented, focusing on the
ability of a surfactant to improve the biological removal of PAHs.
MATERIALS AND METHODS
Maintenance Culture Development
The mixed culture used in this work was derived from sewage sludge and was developed in two I-
liter fill-and-draw reactors with 750 mL working volumes. Half of the reactor volume was replaced
with fresh medium daily; at the same time 1 g of gas-tar was added to the reactors. Reactors were
stirred with magnetic stirring bars and aerated using coarse fritted gas dispersion tubes.
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