Section Five
WASTE MANAGEMENT
A. LANDFILLS/LEACHATE
53    DESIGN OF LANDFILL LEACHATE RECIRCULATION
SYSTEMS BASED ON FLOW CHARACTERISTICS
A. Basel Al-Yousfi, Doctoral Candidate
Department of Civil Engineering
University of Pittsburgh
Pittsburgh, Pennsylvania 15261
Frederick G. Pohland, Professor and Weidlein Chair
Department of Civil Engineering,
University of Pittsburgh
Pittsburgh, Pennsylvania 15261
N. C. Vasuki, Chief Executive Officer
Delaware Solid Waste Authority
Dover, Delaware 19901
INTRODUCTION
Most sanitary landfills are constructed and operated to facilitate single pass leaching of infiltrated
rainfall through the refuse mass. Due to this gradual leaching process, stabilization in such landfills
may require many years, thereby extending the acid formation and methane fermentation phases of
waste stabilization over long periods of time. Under these circumstances, decomposition of biodegradable fractions of solid waste will be impeded and less complete, often disallowing commercial
recovery of methane gas, and delaying closure and possible future reuse of the landfill. In contrast,
leachate recycle may be used as a management alternative which requires the containment, collection
and recirculation of leachate back through the landfill media. Such an option offers more rapid
development of active anaerobic microbial populations and increases reaction rates (and predictability) as well as compresses the time required for stabilization of the readily available organic constituents.1-3 This accelerated stabilization is enhanced by the routine and uniform exposure of microorganisms to constituents in the leachate, thereby providing the necessary contact time, nutrients and
substrates for efficient conversion and degradation. Hence, leachate recirculation essentially converts
the landfill into an anaerobic bioreactor which accelerates the conversion of organic material to end-
products. Moreover, such a landfill exhibits higher and more efficient attenuation of toxic substances,
and a much lower risk of adverse public health and environmental impacts.4"5 In addition, predictable
and economical methane gas recovery can be achieved,6-7 and the landfill space can be reclaimed for
further use much sooner than under single pass operation.
Although, the operational strategy of leachate recirculation has been proven to be a suitable
management option for municipal landfills, design and operational criteria have not been established
to implement and control this technology. Accordingly, the principle objective of this study was to
develop design configurations and criteria for landfill leachate recirculation systems. This objective
was satisfied by examining and utilizing the fundamentals of leachate flow characteristics within the
solid waste matrix, taking into account site-specific circumstances, including solid waste loadings,
meteorological conditions and associated potential for leachate (and gas) generation. This resulted in
a recirculation frequency which was sufficient to encourage leachate contact and distribution
throughout the waste mass, yet restricted in quantity in order to avoid leachate accumulation and
pooling within the landfill. Therefore, moisture was made available to sustain accelerated degradation
of organic materials in accordance with the sequential phases of landfill stabilization, and to minimize
shortcircuiting, channeling and ponding within the landfill.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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