51    COMPARISON OF ADSORPTIVE AND NON-ADSORPTIVE
BIOFILM CARRIERS IN BIOLOGICAL FLUIDIZED BED
REACTORS FOR THE TREATMENT OF
GROUNDWATER CONTAMINATED WITH BENZENE,
TOLUENE AND XYLENE
Xianda Zhao, Research Assistant
Department of Civil and Environmental Engineering
Michigan State University
East Lansing, Michigan 48824
Jing Shi, Environmental Engineer
Robert F. Hickey, Director
Waste Treatment Technologies
Michigan Biotechnology Institute
Lansing, Michigan 48909
Thomas C. Voice, Associate Professor
Department of Civil and Environmental Engineering
Michigan State University
East Lansing, Michigan 48824
INTRODUCTION
The contamination of groundwater by volatile organic compounds (VOCs) is being reported with
increasing frequency. More than 40% of US. population uses groundwater as a drinking water supply,
often without any treatment other than disinfection. Groundwater contamination is thus a serious
public health concern. Among the most common types of groundwater contamination are those
resulting from petroleum products. This frequently produces elevated levels of benzene, toluene, and
xylenes (BTX) because these compounds are the most soluble and are poorly retarded by the soil
matrix.
The conventional approaches to remediation of BTX contaminated groundwater involve either
liquid-phase adsorption by granular activated carbon (GAC) or air stripping. In these processes, the
VOCs are simply transferred from one phase to another.1,2 Further treatment or disposal of the
receiving phase is often required. Biological treatment of contaminated groundwater would appear to
be a desirable alternative to such techniques. This approach has the potential to destroy the pollutant
and is often less expensive than physical-chemical treatment. Biological processes are frequently
perceived as being less stable than physical-chemical approaches, however, and thus are not always
considered for groundwater treatment.
The beneficial aspects of integrated biodegradation/adsorption systems were reported in the early
work on the use of GAC for secondary and tertiary treatment of municipal wastewater.3 In systems
designed as adsorbers, it has been shown that biodegradation increases the period between GAC
regeneration cycles.4"11 In biofilm systems, the use of GAC as a biomass carrier has been shown to
provide for removal of compounds resistant to biodegradation.12'13 In a treatment process for
groundwater contaminated with relatively low levels of volatile organic compounds, a biological
activated carbon fluidized-bed reactor (BAC-FBR) system has been demonstrated to provide both the
efficiency of biological removal and the positive effluent protection capability of activated carbon
adsorption.14"16
Previous work in this laboratory compared the performance of adsorptive and non-adsorptive
biofilm carriers in biological fluidized-bed reactors (BAC-FBR) for the treatment of groundwater
contaminated with benzene, toluene and p-xylene.16 The results demonstrated that the BAC system
functioned primarily as a biological reactor under steady-state conditions, but that the GAC carrier
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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