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Hydraulic conductivity of zeolite-sand mixtures permeated with landfill leachate
Conductivité hydaulique de mélanges zéolithe-sable infiltrés par des écoulements de décharge de
déchets
Fronczyk J., Garbulewski K.
Department of Geotechnical Engineering, Warsaw University of Life Science, Warsaw, Poland
ABSTRACT: The study presented in this paper has been undertaken to evaluate the influence of leachate from landfill collected
the municipal solid wastes at Warsaw district onto the hydraulic conductivity of zeolite-sand mixtures (with 50% and 20% content
of zeolite). The long-term hydraulic conductivity tests with distilled water and landfill leachate collected from the landfill drainge
were carried out using Trautwein equipment. Results of study indicated that hydraulic conductivity of reactive material tested have
changed almost by two orders of magnitude (from 9.23E-5 to 1.24E-6 m/s). The decrease of hydraulic conductivity can
be caused by reduction of the effective porosity due to pore clogging. The analysis of the calcium carbonate content using Scheibler
method showed no significant increase of carbonates in the samples, while research in scanning electron microscope showed
increased calcium content and crystals of calcium carbonate in the samples. Moreover, the presence of microbial activity
had been observed. The conclusions drawn based on tests results should be considered in designing of PRB.
RÉSUMÉ : L'étude présentée dans cet article a été entreprise afin d'évaluer l'influence des écoulements des sites d'enfouissement des
déchets du district de Varsovie sur la conductivité hydraulique de mélanges de zéolithe et de sable (avec 50% et 20% de teneur en
zéolithe). La conductivité hydraulique à long terme a été mesurée avec de l'eau distillée et un liquide provenant du drainage d’une
décharge, à l’aide d’un appareil de Trautwein. Les résultats de l'étude ont montré que la conductivité hydraulique du matériel réactif
testé a changé de deux ordres de grandeur (de 9,23E-5 à 1,24E-6 m/s). La diminution de la conductivité hydraulique peut être due à la
réduction de la porosité effective due à l'obstruction des pores. L'analyse de la teneur en carbonate de calcium en utilisant la méthode
de Scheibler n’a montré aucune augmentation significative de carbonates dans les échantillons, alors que l’analyse par microscopie
électronique à balayage a montré une augmentation de la teneur en calcium et des cristaux de carbonate de calcium dans les
échantillons. En outre, la présence d’une activité microbienne a été observée. Les conclusions basées sur le résultat de ces essais
doivent être prises en compte dans la conception des barrières réactives de protection.
KEYWORDS: permeable reactive barrier, landfill leachate, reactive materials, hydraulic conductivity.
1 INTRODUCTION
Throughout the world the pollution of groundwater
by hazardous substances (e.g. landfill leachate) is one of the
most crucial environmental problems. To protect the natural
groundwater environment many technologies were developed
in the last decade. One of the most effective and simultaneously
low-cost technology is a method based on permeable reactive
barriers - PRBs - that improves natural attenuation processes
(Fig. 1). PRBs can be an effective remedy in many
environmental
settings
with
varying
hydrogeologic
and geochemical conditions.
According to ITRC publication (2011), ideal case for PRB
application is ground containing cohesive silts and sands with
hydraulic conductivity values lower than 3.5E-6 m/s.
However, ITRC proposes to extend this criteria and also check
the ground with hydraulic conductivity and groundwater
velocity in range of 3.5E-6 to 3.5E-5 m/s as the most suitable
conditions for application of PRBs.
The proper functioning of PRBs depends on the hydraulic
properties of reactive materials that fullfield reaction zone
of the barriers. The hydraulic criterion in the evaluation
of reactive materials such as zeolites and zeolite-sand mixtures
is expressed as the ratio of hydraulic conductivity of the reactive
material (k
s
) to the hydraulic conductivity of the aquifer (k
g
),
which, according to common recommendation, should be higher
than one. This parameter governs the rate of occurring processes
(sorption, biological and chemical reduction etc.) and in some
circumstances can lead to changing groundwater flow direction
ever to wrap the PRBs by contaminated groundwater.
In this regard, it is necessary to identify changes of hydraulic
conductivity as a result of contact with liquid pollutants.
The hydraulic conductivity of reactive materials and their
changes during exploitation should be taken into account for
design of PRB, particularly their thickness (b), which can be
estimated from the equation (Czurda and Haus 2002):
R
ik t b
PRB
(1)
where:
t
PRB
- "working time” (s), time required for contaminant
reduction to acceptable level,
k - hydraulic conductivity (m/s),
i - hydraulic gradient,
R - retardation factor, that depend on sorption processes
intensity.
The changes of permeability of zeolite-sand mixtures,
proposed as low-cost reactive materials, caused by landfill
leachate are presented in this paper. The leachate samples were
taken from municipal solid waste site in Warsaw (Radiowo
site).
