International Conference on Environmental Technologies: Today and Tomorrow, L.D College of Engineering, Ahmedabad, Gujarat State, India, 18th and 19th May, 2012.

1. GEONETS AND GEOTEXTILES AS
LEACHATE CONTAINMENT MATERIALS
IN LANDFILLS: SYSTEM DYNAMICS
MODELING APPROACH
By
Samson O. OJOAWO, Ph.D
Jamiu A. DAUDA
& Olatunde A. Salami
Department of Civil Engineering,
Ladoke Akintola University of Technology Ogbomoso,
Nigeria

2. OVERVIEW
PREAMBLE
INTRODUCTION
METHODOLOGY
RESULTS AND DISCUSSION
FINDINGS
CONCLUSIONS
RECOMMENDATION
CONTRIBUTION TO KNOWLEDGE
REFERENCES

3. Figure 1. Map of Africa showing Nigeria
PREAMBLE

4. Figure 2. Map of Nigeria showing the 36 States

5. Figure 3. Map of Nigeria showing Oyo State & Oriire LGA

6. Figure 4. Map of Oyo State showing the 33 Local Govt Areas (LGA)

7. Figure 5. Map of Oriire, the Study Area

8. INTRODUCTION
Solid Waste Management (SWM)
PRACTICE IN NIGERIA
(a) Determining factors
i. Location: urban, semi-urban & rural centres
ii. Income of residents: high, medium & low
iii. Education level: literates, semi-literates &
illitrates

9. (b) The practice
(i) Generation: per capita = between 0.4 and
0.5kg/day (Ojoawo, 2011)
(ii) Collection and Storage from source:
bucket, calabash, bin, etc
(iii)Transportation: compactor trucks

10. Figure 6 Typical waste collection bins in rural centres

11. Figure 7. Typical waste collection bin in Urban centres

12. (iv) Disposal of wastes in the study area:
- Indiscriminate dumping: rural areas, about 35%
of general practice
-Open burning: rural areas, about 25%
-Composting: rural areas, about 17%
-Incineration: urban centres, about 7%
-Landfilling: urban centres, about 2 in a state,
about 15%

13. Figure 8. Typical compactor truck in Urban centres (LAWMA, 2012)

14. Figure 9. Some waste collectors at work

15. Figure 10. Indiscriminate refuse dumping in a rural area

16. Figure 11. Typical aged dumpsite

17. Figure 12. Refuse dump near uncompleted buildings

18. Leachates
*Leachates result from excess water passing
through dumped wastes (Ojoawo, 2009;
Brachman, et.al 2004)
*Leachate control (Pfeffer, 1992)
: cover provision
: liner application
* Liners protect underground water

19. * Liners usually in double layers, Rowe et. al,
2004:
(a) Upper = leachate collection
(b) Lower = secondary check, back-up
* Types of liner: geo-membranes
geonets
geotextiles etc
* Paper focuses on geonets and geotextiles

20. Figure 13. Schematic diagram of a liner system in landfills

21. * Geonet and geotextile materials are usually being employed as
geocomposite materials in leachate containments during the operation
of landfills
* This geotextile is bonded to the geonet either on one side or both
(Gundle Lining Technology, 1996)
* The purpose of the geotextile is to prevent any soil from clogging the
geonet.
* System dynamics model = one of the latest and comprehensive and is
therefore extensively applied in WM (Ojoawo, 2009)
*System dynamics modeling technique thus employed in this paper

22. CENTRAL AIM
To model the applications of Geonets
and Geotextiles as landfill liners using
case study of Oriire Local Government
Area (LGA) of Oyo State Nigeria, in
Africa

23. The Case Study
• Oriire LGA, Oyo State
Nigeria, in Africa & has an average
population of 150,628 (National Population
Commission, 2011)
• It lies on Long 40 18’East, Lat 80 10’ North
• It’s situated in the transitional zone
between rain forest and savannah region
(Edward and Joel, 1998)

24. METHODOLOGY
(a) Materials studied:
Geonet
Geotextile
Geo-composite

25. Figure 14 . Sample of the Geonet

26. Figure 15 . Sample of the Geotextile

27. Figure 16 . Sample of the Geocomposite

28. (b) Properties considered:
Water Absorption
Hydraulic conductivity
Porosity
Thickness

29. (c) Governing Equations:
(i) For leachate generation (Safari and Baronian, 2002)
N cells
LQnT (nΔt) = W4(t) – Wg(t) + Σ LQn( i, (n – i + 1) Δt
i = 1 -------(1)

30. where
LQnT = Accumulative amount of leachate
generated from the system
nΔt = No of waste cells at the given time
W4 = Overall mass of water entering or
leaving the dumpsite
Wg = Total water loss due to degradation
LQn = Overall leachate quantity generated
from a single cell
n & i = Counters
t = Breakthrough time of the liner
d = Thickness of the liner
α’ = Effective porosity
K = Coefficient of permeability and
h = Hydraulic head

31. (ii) Breakthrough time, t (Kadlec and
Knight, 1996)
t = d2α’ / K( d + h) ------(2)
where
d = thickness of the liner (m)
α’ = effective porosity
K = coefficient of permeability (m/s)

32. (iii ) Leackage rate through the liners
qi, also by Kadlec & knight, 1996:
qi = K [ 1 + y cos ϕ ]
d
----- (3)
where
K = coefficient of permeability (m/s)
d = liner thickness (m)
ϕ = the liner slope (measured in angles)
y = the leachate depth over liner (m)

33. (d) Computer programming and Simulation:
*V B language was employed in coding the equations
*Key elements of the Model were defined and quantified as
variables
*Relationships were formulated mathematically
*System dynamics structures applied in developing
the source codes
*Stock flow diagram of the system designed using
STELLA 9.1.4 software and simulation package

34. Population
Births
?
BirthRate
Death Rate
Deaths
?
Initial Field Capactiy
Runoff Coefficient
Total Precipitation
Chemical Reaction
Total Waste Generated
?
Initial Dry Weight of SW
Primary Leachate
Gas Generation Rate Increasing
?
Decay Process
Water Consumption DueTo Waste Decomposition
?
Mass of Water Consumed per CubicMeter of Ga Produced Decreasing
?
Effective Precipitation
Overall mass of WaterEntering or Leaving Dumpsite
?
Actual Evapotranspiration
?
Correction Factor
Overall leachate
Quantity for Single Cell
?
Field Capacity
?
Accumulative Amount of Lechate
?
Moisture Content of Waste
?
Estimated Population
Effective Porosity
Coefficient of Permeability
Hydraulic Head
Breakthrough Time
Saturated Vertical
Hydraulic Conductivity
Liner Slope in angle
Rate of Leakage
Thickness of Liner
?
Figure 17. The Stella flow diagram of the system

35. (e) Validation of the model:
Through assessment of practical
problems of leachate pollution
containment with Geonets,
Geotextiles and Geocomposite of
Oriire LGA

36. TABLE I: VALIDATION DATA FOR THE SAMPLES
Material Water
absorption
(%)
Hydraulic
Conductivity
(x 10-9) m/s
Porosity Thick-
ness
(m)
Geonet, GN 2.65 1.74 2.58 0.075
Geotextile,
GT
2.34 1.50 2.29 0.060
Geocomposi
te, GC
2.59 2.31 2.52 0.010

37. RESULTS AND DISCUSSION
On Simulation for 100 years the yearly
behavioural patterns are as shown below:

38. 9:15 AM Tue, Apr 24, 2012
Fig 18. Breakthrough time graph for Geonet (GN) in Oriire LGA
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10037250
10037250
10037250
1: Selected Breakthrough Time
1 1
1
1

39. 9:43 AM Tue, Apr 24, 2012
Fig 19. Breakthrough time graph for Geotextile (GT) in Oriire LGA
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10039523
10039523
10039523
1: Selected Breakthrough Time
1
1
1
1

40. 9:54 AM Tue, Apr 24, 2012
Fig 20. Breakthrough time graph for Geocomposite (GC) in Oriire LGA
Page 1
0.00 25.00 50.00 75.00 100.00
Time (yrs)
1:
1:
1:
10033746
10033746
10033746
1: Selected Breakthrough Time
1
1
1
1

41. TABLE II
BREAKTHROUGH TIMES OF THE STUDIED LINERS
Material Breakthrough
time (s)
Breakthrough
time (day)
Geonet (GN) 10,037,250 117
Geotextile (GT) 10,039,523 118
Geocomposite
(GC) 10,033,746 116

42. FINDINGS
*Geotextile has the highest
simulated retention capability
for the leachate volume

43. **The Geocomposite on the
other hand recorded the lowest
breakthrough period

44. CONCLUSIONS

45. *effectiveness of the studied liner
materials in leachate containment
is of the order
Geocomposite< Geonet < Geotextile

46. **The longest breakthrough period
discovered for the application of
the studied liners in Oriire LGA of
Nigeria was 118 days

47. RECOMMENDATION

48. ***For landfill leachate
containment in the study
area, Geotextile liners are
recommended

49. CONTRIBUTION TO
KNOWLEDGE
* The model is universal and thus a
handy tool for dumpsite/landfill
leachate control world-wide

50. THANK YOU ALL
FOR THE ATTENTION

51. REFERENCES
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Ph.D Thesis, Faculty of Technonoly, University of Ibadan, Ibadan, Nigeria, pp 51-52, 2009.
[2] Gundle Lining Systems. GSE Lining Technology. [Brochure]. Gundle Lining Technology Inc., pp 27-
36, 1996.
[3] J. Dauda and B. Salami “ An investigation into the physical properties of landfill liners”. Unpublished
B. Tech Project Report, Department of Civil Engineering, Ladoke Akintola University of
Technology, Ogbomoso, Nigeria, pp 18-21, 56-59, 2012
[4] J.T Pfeffer “Solid waste management in Engineering”. Prentice Hall, pp 235 -249, 1992.
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[9] B. Edward and L.M Joel “World Atlas”. 16th ed., USA, pp 21-35, 1978.
[10] E. Safari and C. Baronian “ Modelling temporal variations in leachate quantity generated at
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[11] T. Kadlec and M. Knight “Leachate management in landfills”. Environmental Hydrology, Chapter
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[12] R.J Petrov and R.K Rowe “ Geosynthetic clay liner: chemical capability by hydraulic conductivity
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