Upload
cvijica635
View
223
Download
1
Embed Size (px)
Citation preview
7/31/2019 EPSRC Final Report
1/29
Development of sustainable landfill practices
and engineering landfill technology
Final report to the Engineering and Physical Sciences Research Council
(Grant reference GR/L 16149)
W Powrie
A P HudsonR P Beaven
Department of Civil & Environmental Engineering, University of Southampton, Highfield, SouthamptonSO17 1BJ
February, 2000
Note: the format of this report is specified by EPSRC. The main body of the text is limited in length to six
pages of typescript. Further details may be found in the papers listed in Appendix B, copies of which are
available on request from Professor W Powrie.
7/31/2019 EPSRC Final Report
2/29
Research Grant Title: Development of sustainable landfill practices and engineered landfill technology
(GR/L 16149)
Investigators and Institutions: W Powrie, A P Hudson, R P Beaven, C J Banks, D Montagnani and T W Tanton,
Department of Civil and Environmental Engineering, University of Southampton; and J P Robinson, Queen Mary
and Westfield College. Project carried out with additional funding from and in collaboration with Cleanaway Ltd.
Summary: In recent years, the driving principle of landfill management has been to prevent saturation of the waste
to minimize the likelihood of leachate leaking into the surrounding ground. This has resulted in very slow rates of
waste degradation, with projected stabilization times of the order of hundreds of years. Degradation could in
principle be accelerated by circulating fluids through the waste in a controlled manner, and operating the landfill as
an engineered wet bioreactor. This approach is more consistent with the aims of a sustainable waste management
policy than the entombment approach, which leaves landfilled wastes in a potentially polluting state for many
generations.
One of the main uncertainties concerning the practicality of operating a landfill as a controlled bioreactor is the
hydraulic conductivity of the waste, because this governs the ease with which fluids may be introduced into and
extracted from the landfill. The aim of the research described in this report was to develop an understanding of the
factors controlling the hydraulic conductivity of landfilled wastes, in the context of the design and operation of a
landfill as an engineered flushing bioreactor.The research consisted of three components:
large scale experiments on samples of wastes, carried out at Cleanaway Ltds Pitsea landfill site in a purpose-
built compression cell;
laboratory studies to investigate (a) the impact of leachate/liquid recirculation on waste degradation rates, (b)
moisture content suction relationships for certain types of waste, and (c) the feasibility of monitoring
changes in geotechnical and hydraulic properties, settlement and gas generation rates in samples of wastes
during leachate/liquid recirculation under constant applied stress; and
the development of simple models to enable the application of the results of the experimental work to the
sustainable operation of landfills.
A key factual output of the research has been the quantification of relationships between the drainable porosity
and vertical stress, and between hydraulic conductivity and vertical stress, for samples of processed, unprocessed
and aged household waste. On the basis of these data, and using simple analytical models developed to enable
their application to problems in landfill operation, the following conclusions can be made.
At depth, most wastes are likely to be approaching saturation even if they are free to drain under gravity.
Although some differences in hydraulic conductivity between processed, unprocessed and aged household
wastes were apparent, these are generally insignificant in comparison with the orders of magnitude change in
hydraulic conductivity that results from waste compression.
On unloading, very little of the deformation due to loading was recovered, and the hydraulic conductivity
remained substantially unchanged. Thus the hydraulic conductivity of a waste is governed by the maximum
equivalent vertical stress to which the waste has been subjected, so that the stress history or the density of the
waste must be considered when assessing its hydrogeological and geotechnical properties.
During compression, waste develops a layered structure. This results in a degree of anisotropy of hydraulic
conductivity (expressed as the ratio Kh/Kv) that increases with increasing applied stress.
Provided that the dependence of hydraulic conductivity on vertical stress and stress history is taken into
account, calculations suggest that vertical infiltration rates comparable with achieving stabilization of the wastewithin a timescale of one generation can be achieved. Precompaction of the waste to densities greater than 0.9 -
1.1 t/m3, or placement of loose waste unsaturated to a depth in excess of about 40 m prior to saturation, would
both prevent the required infiltration rate from being realised.
Analyses of pumped vertical wells using a stress dependent hydraulic conductivity suggest that there will be
little increase in flowrate for increases in drawdown in excess of about 33% of the initial saturated depth.
Preliminary tests have demonstrated the importance of the interaction between gassing and leachate flow in
terms of the pore volume available for liquid flow, and suggest that changes in gas production rate could affect
the apparent leachate level measured in the field. This is a subject requiring further research.
EPSRC grant and duration For further information please contact
231,226 over 36 months Professor W Powrie, Department of Civil & Environmental
plus project studentship Engineering, University of Southampton SO17 1BJ
(tel. 023 80593214; fax 023 80677519; e-mail [email protected])
7/31/2019 EPSRC Final Report
3/29
1
1. BACKGROUND AND OBJECTIVES
1.1 Background
In recent years, the driving principle of landfill management has been to prevent saturation of the waste to
minimize the likelihood of leachate leaking into the surrounding ground. This has resulted in very slow rates of
waste degradation, with projected stabilization times of the order of hundreds of years (e.g. Knox, 1990).
Degradation could in principle be accelerated by circulating fluids through the waste in a controlled manner, andoperating the landfill as an engineered wet bioreactor. This concept, which is espoused by Waste Management
Paper 26B (DoE, 1995), offers significant economic and environmental benefits and is more consistent with the
aims of a sustainable waste management policy than the entombment approach, which leaves landfilled wastes in
a potentially polluting state for many generations.
One of the main uncertainties concerning the practicality of operating a landfill as a controlled bioreactor is
the hydraulic conductivity of the waste, because this governs the ease with which fluids may be introduced into
and extracted from the landfill. This was the issue addressed by the research described in this report.
1.2 Aims and objectives
The aim of the research was to develop an understanding of the factors controlling the hydraulic conductivity of
landfilled wastes, in the context of the design and operation of a landfill as an engineered flushing bioreactor. As
stated in the original case for support, these included the effects of waste composition, overburden pressure,microbial activity, degradation and two phase flow (gassing). However, a budget reduction of 100,000 from the
329,927 initially requested necessitated a reduction in the scope of the research. In the light of guidance
received from the Waste and Pollution Management Programme Management Committee, the work on the effect
of waste composition was deleted from the programme, and the work on the effects of waste degradation and
gassing (two -phase flow) scaled down considerably. The objectives of the proposed research were revised from
those given in the original case for support. The revised objectives were
to quantify the effects of overburden pressure on the mechanical and hydraulic properties of different types
of waste, and
to carry out a preliminary assessment of the effects of microbial activity on the mechanical and hydraulic
properties of wastes
in the context of the operation of a landfill as an engineered wet bioreactor, as stated in a letter from Professor W
Powrie (UoS) to Dr M Partridge (EPSRC) dated 18 April 1996.
2. PROGRAMME MANAGEMENT
In addition to the EPSRC grant, the project was funded by a donation of 150,000 from Cleanaway Ltd under the
Landfill Tax Credit Scheme. The research may conveniently be divided into three components:
large scale experiments on samples of wastes, carried out at Cleanaway Ltds Pitsea landfill site in a purpose-
built compression cell;
laboratory studies to investigate (a) the impact of leachate/liquid recirculation on waste degradation rates, (b)
moisture content suction relationships for certain types of waste, and (c) the feasibility of monitoring
changes in geotechnical and hydraulic properties, settlement and gas generation rates in samples of wastes
during leachate/liquid recirculation under constant applied stress; and
the development of simple models to enable the application of the results of the experimental work to the
sustainable operation of landfills.
The work using the Pitsea compression cell was carried out by Andrew Hudson, a Research Assistant funded by
the EPSRC grant, under the supervision of Dr R P Beaven (Senior Research Fellow funded from the grant) and
Professor W Powrie (Principal Investigator). The laboratory studies were carried out by (a) Daniele Montagnani,
an EPSRC-funded project research student associated with this grant (supervised by Dr C J Banks); (b) Mansoor
Imam, a research student funded by the Faculty of Engineering and Applied Science and the Department of Civil
and Environmental Engineering at the University of Southampton (supervised by Dr D J Richards); and (c) Lewis
Parker, a research student at QMW (supervised by Professor J K White and Dr J P Robinson). The development
of models for the application of the results to sustainable landfill practice was carried out by Professor W Powrie
and Dr R P Beaven.
The project was overseen by a steering group comprising:
Professor W Powrie, University of Southampton; Dr R P Beaven, University of Southampton;
Dr C J Banks, University of Southampton; Dr J P Robinson, QMW;
Dr L de Rome, ETSU (for EPSRC); and Mr M J Dyer, Cleanaway Ltd.
7/31/2019 EPSRC Final Report
4/29
2
Additional input and advice was provided on an ad hoc basis by Professors T W Tanton and J B Joseph.
Early dissemination of the results has been achieved by means of
papers published in the Sardinia International Landfill Conference, 1999 and the Proceedings of the
Institution of Civil Engineers special issue on Landfill Engineering (October 1999);
an article in Waste Management, (November 1998); presentations at seminars at the Nottingham Trent University (September 1998), University College London
(January 1999), the Institution of Civil Engineers (ICE), London (November 1999), the ICE South Wales
Geotechnical Group, Swansea (November 1999), the University of Southampton (December 1999), and WRc
leachate management workshops; and
Dr Beaven and Professor Powries membership of the Institution of Wastes Management Working Group on
Sustainable Landfill, which published its report in Spring 1999
A full list of papers and reports published to date is given in Appendix B.
3. DESCRIPTION OF THE RESEARCH
3.1 The Pitsea compression cell: modifications, waste testing and new experimental techniques
Most of the experimental research was carried out using the Pitsea compression cell. This is a purpose built
apparatus for determining the hydrogeological and geotechnical properties of 2 m dia. samples of waste atstresses up to 600 kPa (Figure 1). The cell was originally used in research sponsored by the Waste Technical
Division of the Department of the Environment and Cleanaway Ltd. To enhance the testing capabilities and
improve the quality of the data, a number of major modifications were made to the cell and new testing protocols
were developed as part of this research. New techniques for analysing experimental data from the Pitsea
compression cell have also been developed, and applied to the results of both this research and earlier tests
(Section 3.1).
Two new wastes were tested in the Pitsea compression cell. Waste AG2 was a 20 year old (predominantly
household) waste excavated from a landfill (Table 1). Waste DN1 was household waste that had been processed
using the DANO technique (Table 2); it was selected as an example of a processed waste that had previously
been used in field scale research in the Mid-Auchencarroch landfill (Wingfield-Hayes et al, 1997). Initially, it had
been hoped that a t least one other waste type would have been tested in the Pitsea compression cell. However, it
was decided during the course of the research to investigate the properties of the wastes in unloading as well as
loading, which increased considerably the duration of the testing programme for each waste. Data from earlier
tests on crude household waste (DM2 and DM3 -Table 3), pulverised waste (PV1 and PV2 -Table 4) and an aged
waste (AG1 -Table 5) were re-analysed and used together with the new results to develop theories and models
concerning sustainable landfill (Section 3.3).
3.1.1 Building Enclosure
An improved working environment and more controlled test conditions have been created by the construction of
an enclosure to the building (Figure 2). This was financed by a contribution from Cleanaway Ltd through the
landfill tax credit system.
3.1.2 Modifications to allow horizontal hydraulic conductivity to be measured
To measure horizontal hydraulic conductivity in the compression cell, it was necessary to induce horizontal flow
across the samples. This required the addition of eleven inlet ports and eleven diametrically opposite outlet portsto the compression cell wall. Extra piezometer monitoring ports were also added. To monitor the individual flow
rates through each of the inlet ports, eleven small header tanks were constructed and mounted on the header tank
scaffold tower (Figure 3). Inflatable seals were added around the perimeter of the top platen to prevent leakage
through the clearance gap against the cylinder wall.
3.1.3 Modifications to monitor effects of degradation
The construction of landfill gas collection facilities on the Pitsea compression cell and the provision of a sensitive
load cell weighing system has allowed a preliminary assessment to be made of the effect of gas on the
hydrogeological properties of waste, in particular on the drainable porosity and hydraulic conductivity. The
displacement of gas from the waste by liquid flow was measured for a range of flow rates in upward, downward
and horizontal flow.
3.1.4 Measurement of differential waste compression within the cell
Load is applied to the upper surface of waste samples in the compression cell through a hydraulically operated
platen. Sidewall friction between the cylinder walls and the waste causes a reduction with depth in the vertical
7/31/2019 EPSRC Final Report
5/29
3
stress transmitted to the waste. This may result in differential compression of the sample, and hence a variation in
hydrogeological properties with depth. A magnetic ring extensometer has been successfully installed and used to
measure the pattern of waste compression within the cell (Figures 4 & 5).
3.1.5 Load Cells
Accurate measurement of the weight of samples is necessary for density calculations, and for monitoring water
and gas content. The existing equipment was unsatisfactory and had to be replaced.
3.1.6 Data interpretation and analysis of results from Pitsea compression cell
A correction for the effect of sidewall friction has been developed (Powrie and Beaven, 1999), and data are now
reported as functions of the average transmitted vertical stress.
As direct measurement of the horizontal hydraulic conductivity of waste samples is not possible owing to the
geometry of the compression cell, the USGS three dimensional groundwater flow model MODFLOW (in
combination with Groundwater Vistas) was used to model the flow regime (e.g. Figure 6). Measured flow rates
and leachate pressure heads within the waste were matched with computer analyses to obtain the horizontal
hydraulic conductivity of samples at different vertical stresses (Hudson, Beaven and Powrie, 1999).
3.2 Laboratory based tests
3.2.1 Unsaturated suction curve characterisationWaste moisture characteristic curves were determined for samples of Dano processed waste using a filter paper
contact method (ASTM D5298-92).
3.2.2 Effect of flushing rate on waste degradation
The benefits of leachate treatment, either within or external to the landfill, and the effect of leachate recirculation
or flushing rate on optimizing waste degradation were assessed in 1-litre, 21 day batch laboratory experiments on
the organic fraction of municipal solid waste (OFMSW). The initial biological methane potential (BMP) was used
as a benchmark against which to assess the degradation of the waste. The effects of hydraulic retention time
(experimental range 80 to 240 hours) and flushing medium (tap water, aerobically treated leachate and
anaerobically treated leachate) on degradation were assessed by monitoring the change in total and volatile
solids, the organic content (TOC, TON, VFA) of the flushing liquor and the quantity and composition of gas
production. Larger scale experiments, to confirm the findings of the batch experiments, were carried out in 30-litre
static bed upflow lysimeters packed with OFMSW and inert pore rings, which increased the porosity of the waste
material allowing shorter hydraulic retention times (Figure 7).
3.2.3 Effect of degradation on properties of degrading solid waste
A prototype laboratory scale anaerobic refuse digester has b een built to measure the effects of waste degradation
on the physical and hydrogeological properties of refuse whilst subjected to vertical effective stresses typical of
those encountered in a landfill (Figure 8).
The reactor chamber is an acrylic cylinder, 476mm in diameter and 900mm high providing a capacity of 160
litres. The chamber is placed within an Eland Engineering T413/2 loading frame, where it is subjected to a constant
vertical stress while liquid is circulated through the waste. Instrumentation is incorporated to measure the
following:
pore water pressures and leachate recirculation rates reactor chamber temperature
influent/effluent leachate chemistry gas production and composition waste density and settlement hydraulic conductivity
drainable porosity
The successful functioning of the cell and monitoring systems, and the feasibility of assessing the effects of
degradation in this way, have been demonstrated using a 20 year old sample of waste (AG2).
3.3 Development and application of models for flow in landfills
To start applying the results of the research to landfill operations, a number of analytical and numerical flow
models taking into account the variation of hydraulic conductivity with effective stress have been developed:
one dimensional vertical flow or infiltration was modelled using a finite difference method, with density and
hydraulic conductivity dependent on the effective stress (Powrie and Beaven, 1999),
closed form analytical solutions were derived relating the discharge from a well to the drawdown in
unconfined and confined aquifers where the hydraulic conductivity depends on the effective stress (Figure 9:
Powrie and Beaven, 1999), and
7/31/2019 EPSRC Final Report
6/29
4
the USGS three dimensional ground water flow model MODFLOW was modified to incorporate hydraulic
conductivities that vary with effective stress. The model was verified against the simpler analytical and finite
difference solutions above. It was then used to simulate more complex leachate flow problems, including the
performance of a grid of leachate injection and abstraction wells (Figure 10: Beaven and Powrie, 1999).
4. MAJOR RESULTS AND FINDINGS
4.1 Waste density and water contentFigure 11 shows the dry density as a function of effective stress for the different wastes tested. The sample with
the highest dry density was the 20 year old aged waste excavated from a landfill site. This is consistent with the
large proportion of soil type material (represented by the
7/31/2019 EPSRC Final Report
7/29
5
load, or from increases in the pore water pressure. However, no significant changes in drainable porosity or
hydraulic conductivity were detected when the effective stress was reduced. The implication of this is that fluid
flow in landfills will be predominantly controlled by the maximum previous effective stress to which the waste has
been subjected. Any loading process, such as placement of the waste in an unsaturated state or dewatering by
pumping from a vertical well, will probably cause an irreversible reduction in hydraulic conductivity.
4.5 Waste particle density and effective stress theoryThe results of the tests undertaken in the compression cell suggest that the waste particles undergo significant
changes in density as the overburden stress is increased (Table 8). This is in contrast to some of the theories
used in conventional soil mechanics, in which the particles are assumed to be incompressible. On the basis of the
data in Table 8 for raw household refuse at 120 kPa and above, the effective stress for calculations of volume
change would be ' = - A.uw, where A lies in the range 0.19 to 0.57 (Powrie, Beaven and Harkness, 1999). In
general terms, the applicability of the principle of effective stress to landfilled wastes remains a subject requiring
further research.
4.6 Unsaturated waste characteristics
Figure 19 shows the relationship between suction and water content for the Dano processed waste at an average
bulk density of 700 kg/m3. These data will be essential to any future modelling of flow in the unsaturated zone.
4.7 Effect of flushing rate on waste degradation
The batch scale experiments on the degradation of OFMSW showed that solids destruction increased as the
flushing rate increased and HRT reduced (Figure 20). The greatest amount of solid destruction were achieved
with a tap water flush, and the lowest with anaerobically treated leachate. The formation of volatile fatty acid
(VFA) was stimulated by higher flushing rates and is a reflection of the greater solids destruction. Gas production
from the batch reactors depended on the available soluble substrate concentration, and is shown for the various
recirculation systems in Figure 21 (a-d). Gas production in reactors operating at reduced flushing rates (HRTs of
240 and 504 hours) was impeded due to the inhibition of substrate hydrolysis as a result of an accumulation of
VFA and/or a lowered pH. Gas production was also impeded in reactors operating at high flushing rates with
deionised water, due to the washing out of essential ions and poor buffering.
The larger scale experiments generally confirmed the findings of the smaller experiments. A summary of typical
results is given in Table 9, which indicates a substantial increase in degradation on flushing with tap water,
although there was no additional benefit from increasing the flushing rate to give a hydraulic retention time of
less than 4 days. Flushing with untreated leachate significantly reduced the amount of solids destruction.
The work has increased our understanding of how the flushing medium influences degradation, and has
shown quite clearly the beneficial effects of VFA removal in a leachate recirculation system.
5. SIGNIFICANCE OF RESULTS FOR ENGINEERING PRACTICE
5.1 Maximum vertical infiltration rates through landfills
A key constraint on the viability of the flushing bioreactor as a sustainable landfill is the rate at which flushing
can take place. A one dimensional flow model incorporating empirical relations between waste density and
effective stress (e.g. Figure 13) and hydraulic conductivity and effective stress (e.g. Figure 17) was developed to
examine maximum infiltration rates through landfills of various depths with different initial waste densities (Powrie
and Beaven, 1999). These flow rates were related to the minimum required to flush the pollution load from landfills
over a 30 year period, which is consistent with the definition of a sustainable landfill as one that is approachingequilibrium with the surrounding environment within a period of one generation from cessation of landfilling
activities (e.g. IWM, 1999). Greater flushing rates are achieved through saturated than unsaturated waste. Landfill
depths would need to be less than approximately 20 m to achieve the necessary flushing rates through
unsaturated wastes and less than approximately 40 m through saturated waste, if it is assumed that hydraulic
conductivity is governed by the effective stresses applied during placement of the waste in an unsaturated state.
If the waste is placed saturated, there is virtually no limit on landfill depth to achieve the required flushing rate
(Figure 22). Pre-compaction of waste at the tipping face can also affect possible flushing rates (Figure 23): in
general waste should not be compacted to densities greater than between 0.9 and 1.1 t/m3.
5.2 Flow to a pumped leachate well
Flowrate-drawdown curves for pumped wells in confined and unconfined aquifers whose hydraulic conductivity
varies with effective stress are shown in Figure 24. The unconfined aquifer analysis (Figure 24b) is more
representative of field conditions at many landfills. The specific capacity (i.e. the flow rate per unit drawdown)
decreases with increasing drawdown. The flowrate increases with drawdown, but there is little increase in flowrate
7/31/2019 EPSRC Final Report
8/29
6
for increases in drawdown in excess of about 33% of the initial saturated depth. This is an important result that
has significant operational implications for the pumping of leachate from wells on landfills.
5.3 Leachate flushing using a well field
MODFLOW was used to investigate the feasibility of using vertical wells to flush waste horizontally in a 30 metre
deep landfill with a 20 metre confined saturated zone. With a grid spacing of 20 metres, the model (Figure 25)
calculated a steady state pumping and injection rate of 4.3 m3/day based on a fixed hydraulic conductivity profilerelated to the stress distribution in unsaturated waste. This pumping rate is theoretically sufficient to flush and
remove contaminants from all areas of the waste between the wells in approximately 30 years. The flow or flushing
rate at the top of the saturated layer is approximately 20 times the rate at the bottom (Figure 26). If K h is increased
relative to Kv (Figure 18) then the pumping rate is increased and the ratio of the flowrates at the top and bottom is
reduced to 8. Nevertheless, flushing strategies involving vertical wells will probably require the targeting by
discrete well response zones of different horizons in the waste.
6. PRINCIPAL CONCLUSIONS
Relationships between the drainable porosity and vertical stress have been quantified for a number of
wastes. At depth, most wastes are likely to be approaching saturation even if free to drain under gravity.
Relationships between hydraulic conductivity and vertical stress in first compression have also been
determined. Although some differences in hydraulic conductivity between processed, unprocessed and agedhousehold wastes were apparent, these are generally insignificant in comparison with the orders of
magnitude change in hydraulic conductivity that results from waste compression.
On unloading, very little of the deformation caused by loading was recovered, and the hydraulic conductivity
and drainable porosity remained substantially unchanged. This suggests that the hydraulic conductivity of a
waste is governed by the maximum equivalent vertical stress to which the waste has been subjected, so that
the stress history or the density of the waste must be considered when assessing its hydrogeological and
geotechnical properties.
During compression, waste develops a layered structure which results in an anisotropy of hydraulic
conductivity. The degree of anisotropy, expressed as the ratio Kh/Kv, increases with increasing applied
stress.
Provided that the dependence of hydraulic conductivity on vertical stress and stress history is taken into
account, calculations suggest that vertical infiltration rates comparable with achieving stabilization of the
waste within a timescale of one generation can be achieved. Precompaction of the waste to densities greater
than 0.9 - 1.1 t/m3, or placement of loose waste unsaturated to a depth in excess of about 40 m prior to
saturation, would both prevent the required infiltration rate from being achieved.
Analyses of pumped vertical wells using a stress dependent hydraulic conductivity suggest t hat there will be
little increase in flowrate for increases in drawdown in excess of about 33% of the initial saturated depth. If
arrays of vertical wells are used for horizontal flushing, the tendency for preferential flow through the upper
saturated layers will need to be addressed.
Preliminary tests have demonstrated the potential importance of the interaction between gassing and
leachate flow in terms of the pore volume available for liquid flow, and suggest that changes in gas
production rate could affect the apparent leachate level measured in the field. This is a subject requiring
further research.
7. ACKNOWLEDGEMENTSThe research summarized in this report was carried out with the support of the Engineering and Physical Sciences
Research Council (EPSRC), with an additional financial contribution from Cleanaway Ltd.
7/31/2019 EPSRC Final Report
9/29
Figure 1 Pitsea compression cell prior to modifications Figure 2 New enclosure to Pitsea compression cell
7/31/2019 EPSRC Final Report
10/29
8
Figure 3 Configuration of horizontal hydraulic conductivity tests
Supply Tank
Header tanks
Cylinder
Gravel layer
Isolated ports
Seal
Bottom platen
Inlet Ports
Inlet Valves
Gravel layerFlow
outlets (isolated)
Outlets
Piezometer tubesinserted in sampleat various positions
Piezometrichead
New Seals
Top platen
Top platenoutlets
(isolated)
Tomeasuring
cylinder
Waste Sample
Figure 4 Magnet and extensometer method of measuring sample movement
3 way valve mounted on top for either:
* Outflow to reservoir tank
* Outflow to gas collection tank
* Inflow from header tanks
* Isolated
Pointer fixed to framework
Plastic tube - 3m long
Bottom of tube sealed and
resting on bottom platen
Water & gas tight seal
Unclamped to allow
platen movement
Gravel layer - for water
distribution or removal
Dividing Ring - 1400mm dia x 150mm deep
Creates an inner and outer core in the
sample for assessing preferential flow paths
Valve stems
Part of strengthening framework
Extensometer - lowered into
tube. Magnet position indicated
with buzzer and warning light
Magnet & plate
Sample movement causes
magnet to slide on tube
Waste sample
- forced downwards
by applied load
Waste cylinder (ID2000mm)
- fixed position
Inflatable seals(3 off)
Clearance Gap (5mm nominal)
rings for seals
Graduated tape
12 holes through top platen
with flanged extension tubes
Top Platen - Dia 1990mm
Connected to hydraulic rams
for application of load to waste
Fabricated retaining
7/31/2019 EPSRC Final Report
11/29
9
Figure 5 Magnet displacement in waste DN1 between 0 and 87kPa illustrating uniform compression
0
100
200
300
400
500
600
700
800
0 200 400 600 800 1000 1200 1400 1600
Elevation above base of waste (mm)
Downnrddisplacementrelativetopositionat0kPa(mm)
Magnet positions end of 40kPa Magnet positions - end of 87kPa
Uniform compression (40kPa) Uniform compression (87kPa)
Figure 6 Typical MODFLOW simulation to determine KhWest EastCross-Section along Row 29
470
470
490
490
510
510
510
510
530
53
0
530
550
550
570
570
590
590
610
6306
50
670
Top Gravel
layer
Outlet Port
constant head
cells
Pressure head contours (cm AD):
asymmetry reflecting lower
hydraulic conductivity at the top
of the waste
Bottom Gravel
layer
No flow squares
(light grey) denoting
outside wall of
cylinder
Constant head squares
simulating outflow
through the
bottom platen.
Inlet Port
constant head
cells
Constant head squares
simulating outflow
through the
upper platen.
Model calibrated against measured input andoutput flow rates and hea
7/31/2019 EPSRC Final Report
12/29
10
Figure 7 Process diagram for ... dan's work
7/31/2019 EPSRC Final Report
13/29
11
Figure 8 Anaerobic consolidation reactor
7/31/2019 EPSRC Final Report
14/29
12
Figure 9 Ideal (a) confined and (b) unconfined aquifer analyses of flow to a well where K=f(')
h w zh
H , D ( = 2 0 m )
Flow to wel l
b ) U n c o n f i n e d
a ) C o n f i n e d
h w
zh D ( = 1 0 m )
D (=20m)
F low to we l l
Con f in ing laye r
r w r0
In bo th ana lyses ln ( ro /r w) =8 an d t he un it we ig ht of s at ur at ed an d un s at ur at ed
w a s t e = 1 1 k N / m 3
1
2
1
2
(1+)D (=30m)
H ( = 2 0 m )
Figure 10 MODFLOW grid design to simulate operation of injection and abstraction wells
5 1 0 1 5 2 0 2 5 3 0 3 5
35
30
25
20
15
10
5
Elevat ion
P lan
C o n s t a n t h e a d b o u n d a r y c e l l s
( a t e a c h c o r n e r o f t h e g r i d )
r e p r e s e n t h e a d i n 1 / 4 o f e i t h e r
p u m p e d o r i n j e c t i o n w e l l
N o f l o w b o u n d a r y c e l l s1
2
1 1
2 1
West East
Layer
Nu mb e r s
W e l l 2
W e l l 1
W e l l 3
W e l l 4
C o l u m n s
R o w s
20m
10m
20.2m
20.2m
7/31/2019 EPSRC Final Report
15/29
13
Figure 11 Dry density vs effective stress
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 100 200 300 400 500
Average effective stress (kPa)
Drydensity(t/m3)
Household waste DM3 Household waste DM2 Processed waste PV1
Processed waste PV2 Aged waste AG1 Aged waste AG2
Dano waste DN1
Figure 12 Water content at field capacity of crude household waste vs effective stress
40
50
60
70
80
90
100
110
0 100 200 300 400
Av. Stress (kPa)
WCdry(%)
Household waste 3 at Field Capacity Original Water Content
Absorptive
Capacity
(between lines)
7/31/2019 EPSRC Final Report
16/29
14
Figure 13 Average density of Household Waste vs effective stress
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0 100 200 300 400 500 600
Av. vertical stress in waste (kPa)
Density(t/m3)
Dry density of DM2 and DM3 Density at Field CapacitySaturated density Density at original water content
Power (Density at Field Capacity)Power (Density at original water content)
dry = 0.1554.(') 0.248
FC= 0.448.(') 0.1563
sat = 0.6691.(') 0.0899
= 0.236.(') 0.248
B u l k d e n s i t y r a n g e o f
w a s t e s
unsatura ted
Figure 14 Average drainable porosity vs effective stress
0
5
10
15
20
25
0 100 200 300 400 500
Average effective stress (kPa)
Drainab
leporosity(%)
Household waste DM3 Household waste DM2 Processed waste PV1
Processed waste PV2 Aged waste AG1 Aged waste AG2
Dano waste DN1
7/31/2019 EPSRC Final Report
17/29
15
Figure 15 Effect of waste degradation and landfill gas production on the proportion of leachate occupying
drainable porosity voids
Figure 16 Effect of leachate movement on leachate and gas occupation of drainable voids in waste DN1 at 40
kPa: upward flushing
0
1 00
2 00
3 00
4 00
5 00
6 00
7 00
8 00
0 2 4 6 8 10 12
Time(days )
Volumeofgasinwaste(litres)
0
1000
2000
3000
4000
5000
6000
7000
Accumulatedgasvolume(litres)
Volume of gas in waste (based on load ce l l readings and vo lume of leachate d isp laced)
Volume of gas vented to a tmosphere by sample
Leachate occup ied
drainable porosity = 5%
Leachate occup ieddrainable porosity = 0%
Leachate occup ied
drainable porosity =10%
Leachate occup ied
drainable porosity = 15%
Leachate f lushing
event at Q=1.5 l /s
Leachate f lushing
event at Q=1.5 l /s
Leachate f lushing
event at Q=1.5 l /s
0
2
4
6
8
10
12
14
16
0 0 . 0 005 0 . 001 0 . 00 15 0 . 002 0 . 0 025 0 . 00 3 0 . 0 035 0 . 00 4 0 . 004 5
A v e r a g e l i n e a r f l o w v e l o c i ty b a s e d o n l i q u i d f i l l e d v o i d s (m / s )
Leachateoccupieddrainablevoids(%)
Le ac hat e oc cupi ed dr ai nabl e v oi ds D ra ina bl e po ro si ty (10 0% lea ch at e s at ur at io n)
Increas ing t ime
of f lush ing
Increas ing t ime
of f lush ing
Increas ing t ime
of f lush ing
7/31/2019 EPSRC Final Report
18/29
16
Figure 17 Hydraulic conductivity vs stress
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
10.0 100.0 1000.0
Hydraulicconductivity(m/s)
D M 3 P V 1 A G 1 A G 2
D N 1 Ser i es2 Ser i es4
Av. vertical stress (kPa)
K (m/s) = 10(') -3.1
(approx best fit line)
K (m/s) = 80(')-3.63
(approx fit based on
worst case hydraulic
conductivity)
Figure 18 Anisotropy in hydraulic conductivity
1
2
3
4
5
0 100 200 300 400 500 600Applied Stress (kPa)
Kh
/Kv
7/31/2019 EPSRC Final Report
19/29
17
Figure 19 Dano waste moisture characteristic curve
Figure 20 OFMSW total solids destruction in 1 litre anaerobic digestion vessels operating variable
hydraulic retention times and flushing with different liquors, operated over a 21 day time period.
1 0 0 0
1 0 0 0 0
1 0 0 0 0 0
0 1 0 2 0 3 0 4 0 5 0 6 0
Moisture content (w) %
Dry Weight basis
Suction(kPa)
0.00
10.00
20.00
30.00
40.00
50.00
60.00
0 100 200 300 400 500 600
Hydrau l ic Retent ion T ime (hrs)
Solids
destruction(%)
tap water aerob ic trea tment anaerob ic trea tment de- ion ized water
7/31/2019 EPSRC Final Report
20/29
Figure 21 Cumulative biogas production for anaerobic bioreactors with hydraulic retention time of
a) 80 hrs; b) 120 hrs; c) 240 hrs; and 504 hrs. Flush liquors: tap water; de-ionized water; leachate after secondary anaerobic treatment; leachate after
secondary aerobic treatment
a) b)
0
1000
2000
3000
4000
5000
6000
0.00 100.00 200.00 300.00 400.00 500.00 600.00
time (hrs)
biogasproduced(ml
Anaerobic Secondary Treatment Deionized Water Flush Aerobic Secondary Treatment Tap Water Flush
c) d)
0
1000
2000
3000
4000
5000
6000
0.00 100.00 200.00 300.00 400.00 500.00 600.00
time (hrs)
biogas(ml)
Anaerobic Secondary Treatment Deionized Water Flush Aerobic Secondary Treatment Tap Water Flush
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0.00 100.00 200.00 300.00 400.00 500.00 600.00
time (hrs)
biogas(ml)
Anaerobic Secondary Treatment Deionized Water Flush Aerobic Secondary Treatment Tap Water Flush
0
500
1000
1500
2000
2500
3000
3500
0.00 100.00 200.00 300.00 400.00 500.00 600.00
t ime (hrs)
biogas(ml)
Anaerob ic Secondary Treatment De ionized Water Flush Aerob ic Secondary Treatment Tap Water F lush
7/31/2019 EPSRC Final Report
21/29
19
Figure 22 Maximum vertical infiltration rate against landfill depth
0.1
1
10
100
1000
0 10 20 30 40 50 60
Landfill depth (m)
Max.Infiltrationrate(
m/a)
Variable KConstant K based on stress at base of landfillMinimum required flushing rate
7/31/2019 EPSRC Final Report
22/29
20
Figure 23 Infiltration rate for a) K=2.1(')
-2.71(best fit line on Fig. 15 for waste DM3); and
b) K=17(')-3.26
(worst case line on Fig. 15 for waste DM3) against landfill depth for various
precompacted waste densities
0.0001
0.001
0.01
0.1
1
10
0 10 20 30 40 50 60
Landfill depth (m)
Max.infiltrationrate(m/d)
Min. flushing rate No pre-compaction 0.5 Mg/m3 0.75 Mg/m3
0.9 Mg/m3 1.0 Mg/m3 1.1 Mg/m3 1.2 Mg/m3
0.0001
0.001
0.01
0.1
1
10
0 10 20 30 40 50 60
Landfill depth (m)
Max.infiltrationrate(m/d)
Min. flushing rate No pre-compaction 0.5 Mg/m3 0.75 Mg/m3
0.9 Mg/m3 1.0 Mg/m3 1.1 Mg/m3 1.2 Mg/m3
a)
b)
All waste densities at a water content (WCdry) of 51.5% (assumed WC of waste as deposited)
7/31/2019 EPSRC Final Report
23/29
21
Figure 24 Relationship between discharge rate and drawdown for approximate ideal (a) confined and (b)
unconfined aquifer analyses in which the hydraulic conductivity varies with drawdown according
to K=2.1(')-2.71
(best fit line on Fig. 15 for waste DM3).
0.0E+00
5.0E-05
1.0E-04
1.5E-04
2.0E-04
2.5E-04
3.0E-04
3.5E-04
0 2 4 6 8 10
Drawdown (m)
Flowrate(m3/s)
Variable K Constant K ( 4.09x10-6 m/s)
a)
0.0E+00
1.0E-04
2.0E-04
3.0E-04
4.0E-04
5.0E-04
6.0E-04
7.0E-04
0 5 10 15 20
Drawdown (m)
Flowrate(m3/s)
Variable K Constant K (4.09x10-6 m/s)
b)
7/31/2019 EPSRC Final Report
24/29
22
Figure 25 Head distribution for injection wells and abstraction wells on parallel grid, with hydraulic
conductivity based on unsaturated stress distribution.
Figure 26 Variation of well discharge / injection rate with depth
10
12
14
16
18
20
22
24
26
28
30
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Flow rate per linear metre of well (m3/day)
Depth(m)
Pumped / Injection well: Kh=KvPumped / Injection well: Kh=2-5Kv
Average pumped/ injection
rate = 4.3 m3/day per well
Average pumped/ injection rate
= 68.1 m3/day per well
7/31/2019 EPSRC Final Report
25/29
23
Table 1. Size and category analysis of waste AG2
Size mm Weight
%
Pa/Cd PF Dp Tx Mc Mnc Gl Fe nFe Soil
7/31/2019 EPSRC Final Report
26/29
24
Table 5. Size and category analysis of waste AG1
Size mm Weight % Pa/Cd PF Dp Tx Mc Mnc Gl Put Fe nFe
7/31/2019 EPSRC Final Report
27/29
25
Table 8 Variation in particle density, particle compressibility and waste compressibility with applied stress
Average stress at end of stage, kPa 34 65 120 241 463
Average particle density, t/m3 0.88 0.97 1.02 1.17 1.30
Average particle compressibility, MPa-1
- 5.38* 1.62 1.85 0.81
Overall compressibility of waste, MPa-1 7.45 3.75 3.76 2.30 1.07
a) Raw household waste DM3
Average stress at end of stage, kPa 35 68 127 253 486
Average particle density, t/m3 0.59 0.68 0.72 0.78 0.93
Average particle compressibility, MPa-1
- 6.60* 1.65 1.11 1.22*
Overall compressibility of waste, MPa-1 7.29 6.18 4.12 1.45 0.87
b) Pulverized household waste PV1
Average stress at end of stage, kPa 35 67 123 239 458
Average particle density, t/m3
1.64 1.62 1.64 1.69 1.86
Average particle compressibility, MPa-1 - -0.67* 0.36 0.49 0.73*
Overall compressibility of waste, MPa-1
7.38 3.85 2.91 1.57 0.66
c) Aged household waste AG1
* It is not possible for the average compressibility of the particles to be greater than the overall compressibility of
the waste, and unlikely that it is negative. These values must therefore be in error to some extent.
Table 9 Summary of total solids and total volatile solids destroyed in 30 litre SBAFB (Static Bed
Anaerobic Flushing Bioreactor) system.
Substrate: 60 : 40 mixed paper : food waste BMP: 0.546 m3
CH4
/ Kg TS destroyed
Reactor mode of operation % TS destroyed % TVS destroyed
HRT 24 hrs - untreated leachate 6.49 3.92
HRT 24 hrs - clean tap water 43.92 42.58
HRT 48 hrs - clean tap water 41.68 40.55
HRT 96 hrs - clean tap water 45.59 47.43
HRT - hydraulic retention time BMP - biological methane potential
TS - total solids TVS - total volatile solids
7/31/2019 EPSRC Final Report
28/29
26
APPENDIX A
References
ASTM D 5298-92 Standard test method for measurement of soil potential (suction) using filter paper
Committee D-18 on soil and rock. Approved September 15 1992, Published November 1992, Designated as D5298-92
DoE (1994)National Household Waste Analysis Project - Phase 2 Volume 1 Report on composition and weight
data Report No CWM 082/94 produced for the Waste Technical Division of the Department of the Environment
under Research Contract PECD 7/10/288 by Warren Spring Laboratory and Aspinwall & Co.
DoE (1995)Landfill design construction and operational practice Waste Management Paper 26B. HMSO,
London 289pp
Knox, K. (1990) The relationship between leachate and gas Proc. of the International conference on Landfill
Gas: Energy and Environment. ISBN 0-7058-1628-1.
Knox, K. (1996)A review of the Brogborough and Landfill 2000 test cells monitoring data. Final report for the
Environment Agency R&D Technical Report P231. 113pp.
Wingfield-Hayes, C., Fleming, G. and Gronow, J. (1997) Field trials of waste manipulation techniques: the
Mid-Auchencarroch experimental landfill Proc. 6th International Sardinia Landfill Symposium. S. Margherita di
Pula, Cagliari, Italy. Vol I pp 311-322. October 1997
APPENDIX B
Publications arising directly from this research
Beaven, R.P. (1997). Hydraulic and Engineering Properties of Household Waste Proceedings of the IBC
conference on "Designing and Managing Sustainable Landfill". 26-27 February. Scientific Societies Lecture
Theatre. London
Beaven, R.P. (1997). Is accelerated s tabilisation achievable? Paper presented at the IWM 1997 annual
conference - Torbay 10 June.
Beaven, R.P. (2000). The hydrogeological and geotechnical properties of household waste in relation to
sustainable landfilling PhD Dissertation, University of London.
Beaven, R.P. and Powrie, W. (1996). Determination of the Hydrogeological and Geotechnical Properties ofRefuse in relation to Sustainable Landfilling. Paper presented at the Nineteenth International Madison Waste
Conference, September 25-26, 1996, Department of Engineering Professional Development, University of
Wisconsin-Madison. USA.
Beaven, R.P. and Powrie, W. (1999)Analysis of waste flushing and flow to wells using MODFLOW and an
effective stress dependent hydraulic conductivity Proceedings Sardinia 99, Seventh International Waste
Management and Landfill Symposium, S. Margherita di Pula, Cagliari, Italy; 4-8 October 1999. Vol II pp 33-41.
Hudson, A.P., Beaven, R.P. and Powrie, W. (1999)Measurement of the hydraulic conductivity of household
waste in a large scale compression cell Proceedings Sardinia 99, Seventh International Waste Management
and Landfill Symposium, S. Margherita di Pula, Cagliari, Italy; 4-8 October 1999. Vol III pp 461-468.
IWM (1999) The role and operation of the flushing bioreactorReport of the Institute of Wastes Management
Sustainable Landfill Working Group. Pub. IWM Business Services Ltd.
7/31/2019 EPSRC Final Report
29/29
Knox, K. (1996)A review of the Brogborough and Landfill 2000 test cells monitoring data. Final report for the
Environment Agency Technical Report P231
Parker, L.P., White, J.K. and Powrie, W (1999) The measurement of the geotechnical and hydrogeological
properties of degrading solid waste Proceedings Sardinia 99, Seventh International Waste Management and
Landfill Symposium, S. Margherita di Pula, Cagliari, Italy; 4-8 October 1999. Vol III pp 469-478.
Powrie, W. and Beaven, R.P. (1998) Hydraulic conductivity of waste - current research and implications for
leachate management Waste Management November 1998 pp22-23.
Powrie, W. and Beaven, R.P. (1999) The hydraulic properties of household waste and implications for
landfills Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, Vol 137, Oct 1999, pp235-
247.
Powrie, W., Beaven, R.P. and Harkness. (1999).Applicabili ty of soil mechanics principles to household waste
Proceedings Sardinia 99, Seventh International Waste Management and Landfill Symposium, S. Margherita di
Pula, Cagliari, Italy; 4-8 October 1999. Vol III, pp429-436.
Powrie, W., Richards, D. and Beaven, R.P. (1998). Compression of waste and implications for practice. Proc of
the Symposium on Geotechnical Engineering of landfills. pp 3-18. Held at Nottingham Trent University 24
September 1998 by the East Midlands Geotechnical Group of the ICE. Ed. Dixon, N. et al; Pub. Thomas Telford
Ltd. ISBN 0 7277 2708 7.
Walker, A.N., Beaven, R.P. and Powrie, W. (1997). Overcoming problems in the development of a high rate
flushing bioreactor Proc. 6th International Sardinia Landfill Symposium. S. Margherita di Pula, Cagliari, Italy.
Vol I pp 397-408. October 1997.
Walker, A.N., Beaven, R.P. and Powrie, W. (1998). A conceptual design for sustainable landfill Proceedings of
the 18th annual IAH groundwater seminar, Portlaoise, Ireland; April 1998. pp1-13.