80    MUNICIPAL SOLID WASTE LANDFILL LEACHATE
TREATMENT WITH A PILOT-SCALE, HYBRID
UPFLOW ANAEROBIC SLUDGE BED FILTER
REACTOR, EMPHASIZING INORGANIC SOLIDS
DEVELOPMENT
Peter J. Keenan, Graduate Student
Jon Iza, Assistant Provessor
Department of Chemical and Environmental Engineering
ETSIIelT, University of the Basque Country
Bilbao 48013, Spain
Michael S. Switzenbaum, Associate Professor
Department of Civil Engineering
University of Massachusetts at Amherst
Amherst, Massachusetts 01003
INTRODUCTION
The bulk of municipal solid waste generated in the United States is ultimately disposed of in
sanitary landfills.1 Rainwater which percolates through the refuse contracts a wide variety of organic
and inorganic contaminants.2 The migration of leachate into groundwater and nearby surface waters
is one of the major environmental hazards associated with this method of waste disposal.3 Current
practice is to prevent moisture from infiltrating into the landfill, however leachate production can
never be completely eliminated.4 Leachate collection systems are included in the design of most new
landfills, to minimize hydraulic head development above the liner, and prevent leachate from seeping
into surrounding soils.5 Since leachate is often highly contaminated, some sort of treatment or
pretreatment is usually necessary prior to discharge of the wastewater.
BACKGROUND
Leachate characteristics are directly related to the biological phenomena occurring inside the landfill, as well as the characteristics of the solid waste.' As such, leachates produced from young landfills
are generally characterized by the presence of substantial amounts of volatile fatty acids (VFA), the
products of naturally occurring anaerobic fermentations. These readily degradable acids account for
the bulk of the chemical oxygen demand (COD) of young leachates, making them amenable to
anaerobic treatment.7
Boyle and Ham first demonstrated that greater than 90% of the total COD (tCOD) could be
removed from leachate in a bench-scale anaerobic digester.8 Henry et al. achieved greater than 85%
removal of soluble COD (sCOD) in both laboratory and pilot-scale anaerobic filters (AF).9,10 COD
removals between 65 and 90% at organic loading rates (OLR) up to 18 kg/m3/d have been reported
using anaerobic filters.4,7,11
Mennerich and Albers achieved 60% removal of tCOD in a laboratory-scale upflow anaerobic
sludge bed reactor (UASB) operating at 35°C and an OLR of 10.7 kg/m3.d." In a similar study,
greater than 90% sCOD was removed in a UASB at loadings up to 9.4 kg/m3/d.12 Kennedy et al.
proposed the use of a hybrid upflow anaerobic sludge bed / anaerobic filter reactor (UASBF) for the
treatment of leachate.2 This type of reactor consists of an anaerobic filter above an unpacked zone
containing accumulated granular sludge. They reported 95% removal of sCOD at 35°C and loadings
up to 33 kg/m3/d. Chang measured greater than 92% sCOD removal at OLR up to 13 kg/m3/d in a
hybrid UASBF operating at 35°C.13
Besides the presence of large amounts of organics, soluble metals can also be present in high
concentrations. Free heavy metal ions are known to cause toxicity to anaerobic bacteria.14 Sulfur
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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