33    BIODEGRADATION OF PENTACHLOROPHENOL IN SOIL
ENVIRONMENTS
Chung J. Kim, Graduate Student
Walter J. Maier, Professor
Civil-Environmental Engineering Department
University of Minnesota
Minneapolis, MN 55455
INTRODUCTION
Pentachlorophenol has many beneficial uses as a wood preservative and insecticide. Unfortunately,
improper disposal has resulted in contamination of soils and groundwater at numerous locations.
Because it is potentially toxic, cleanup has been mandated by regulatory agencies. The costs of
cleaning contaminated soils and aquifers by physical-chemical methods are very high and there is
interest in finding alternative methods. Engineered systems for biological treatment of soils and
groundwater appear to be a promising alternative. It has been estimated that the cost of cleanup using
biological treatment would be less than 10% of physical-chemical cleanup costs [1].
Biological treatment of pentachlorophenol containing wastewaters has been reported by several
investigators [2-8]. Complete biodegradation using pure cultures and mixed cultures has been demonstrated. Stanlake and Finn [9] isolated and characterized an Arthrobacter sp. capable of utilizing
PCP. The specific growth rate of their culture increased with increasing PCP concentration to a
maximum of 0.1 hr at 130 mg/L but decreased significantly at higher concentration, 0.05 hr"1 at 300
mg/L. Crawford et al. [10] isolated a Flavobacterium capable of biodegrading PCP as a sole carbon
source or in mixtures with conventional substrates. They report that glutamate grown inoculum
capability for PCP biodegradation can be induced by short exposure to PCP. Moos et al. [6] showed
that PCP removal in continuous flow activated sludge pilot plants was enhanced by concurrent
feeding of conventional organic substrates. Fluctuation in effluent quality was ascribed to substrate
inhibition effects. However, Guo et al. [8] reported that activated sludge treatment of PCP containing
wastewaters was unreliable. Klecka and Maier [11] isolated mixed cultures growing on PCP as the
only source of carbon and energy from industrial wastewater by continuous flow enrichment in
chemostats. Kinetic parameters determined in batch experiments showed low cell mass yields and
growth rate coefficients, 0.136 g/g and 0.074 hr"1, respectively. The cultures had a high affinity for
PCP, as evidenced a low Monod coefficient, Ks = 0.06 mg/L. Significant substrate inhibition effects
were noted at PCP concentrations above 1 mg/L. Substrate inhibition effects are not uncommon with
industrial chemicals and phenolic compounds specifically [12,13].
On the basis of the information presented in the literature, it was concluded that biological treatment for removal of PCP from groundwater and soils should be feasible. However, further testing is
needed to define rates and limitations of microbial degradation processes in soils and groundwater.
More specifically there is need for engineering oriented studies to describe kinetic parameters that
prevail in the presence of soil surface and to establish the effects of transport and availability of
nutrients and oxygen. This chapter describes the initial phase of such studies. The research focused on
low organic content sandstone material as a model system of subsoil materials.
MATERIALS AND METHODS
PCP Acclimated Enrichment Culture
A mixed culture capable of utilizing PCP as sole carbon and energy source was isolated from
activated sludge obtained from the Minneapolis, St. Paul Sewage Treatment Plant. Sludge solids were
inoculated into minimal salts medium containing 100 mg/L PCP and incubated in shake flasks. PCP
concentration was monitored by UV absorbance at 380 nm. There was an initial lag period of 6-7
days, but essentially all PCP had disappeared in 10 days. The shake flask culture was expanded in
chemostats fed with 100 mg/L PCP minimal salts medium at a dilution ratio of 0.25 days'. PCP was
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