THE ACCUMULATION OF MUTAGENIC POLYCYCLIC AROMATIC
HYDROCARBONS IN BIOLOGICAL SLUDGE
Charles J. Moretti, Acting Manager
Waste Management Division
University of North Dakota Energy Research Center
Grand Forks, North Dakota 58202
Ronald D. Neufeld, Professor
Department of Civil Engineering
University of Pittsburgh
Pittsburgh, Pennsylvania 15261
INTRODUCTION
Mutagenic polycyclic aromatic hydrocarbons (PAH) are produced during fixed-bed coal gasification as a result of coal devolatilization. When the raw syngas from the gasification process is
quenched, a highly-polluted quench condensate wastewater is generated. Previous research [1,2] has
shown that trace amounts of mutagenic PAH are present in the condensate wastewater. Other studies
[3] have shown that treatment of this wastewater with an activated-sludge operation reduces the PAH
content. Activated sludge treatment of coal gasification wastewater, however, creates a separate waste
disposal problem since it produces a biological sludge which accumulates the lipophilic PAH.
The disposal of biological sludge produced from fixed-bed coal gasification wastewater treatment
must be carefully controlled to protect the public health. To aid in this control effort, a research
project was performed both to study the accumulation of mutagenic PAH in biological sludge and
to evaluate the relationship between sludge PAH content and sludge mutagenicity. A general equation
was developed as a result of this work to predict the mutagenic potential of the sludge from wastewater PAH concentrations in the activated-sludge system. The equation can be used as a rapid means
of estimating the degree of hazard associated with the biological sludge directly from wastewater
PAH analyses.
WASTEWATER COMPOSITION
The diversity of chemical species present in fixed-bed coal gasification quench condensate is directly attributable to the complex organic nature of the coal itself. Table I is a compilation of selected
trace organics that were detected in condensate wastewater from two different fixed-bed coal gasification processes [1,4]. The two processes were the Grand Forks slagging gasifier and the experimental gasifier located at Research Triangle. The chemicals listed in Table I were selected from
hundreds of different trace organics found in the wastewater and were included in the table because
of their significant adverse health effects. Most of these compounds are known or suspected carcinogens, mutagens (as defined by the Salmonella reverse mutation bioassay) and priority pollutants,
as well as being highly bioaccumulative.
The coal gasification wastewater used for this research was obtained from an experimental slagging fixed-bed gasifier located at the University of North Dakota Energy Research Center
(UNDERC). The wastewater was steam stripped and solvent extracted to remove phenol and ammonia respectively before being treated by an activated sludge system. The principal constituents in
this wastewater which serve as substrates for microbial growth are phenol and methanol and to a
lesser extent ammonia and thiocyanate.
937