GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
Evaluation of Landfill Gas Recovery System: Case Study for a Ghana Landfill
Sattler, Melanie, L.1; Jangikhatoonabad, Neda1; Afotey, Benjamin2 ; Hossain, M. Sahadat 1
1University
of Texas at Arlington, sattler@uta.edu, 817-272-5410
Nkrumah University of Science and Technology
2Kwame
In 2013-2014, the Global Methane Initiative (GMI)1 sponsored a study to evaluate the feasibility
of a landfill gas to energy project for Tema Kpone Engineered Landfill. Capture of landfill gas
(LFG) can not only provide a clean energy resource, but also encourage proper waste disposal
and landfill management, as well as reduce emissions of the potent greenhouse gas methane.
Facilitating faster waste decomposition for energy production can also free up landfill space for
depositing additional waste, extending the life of the current landfill and saving costs.
The Kpone Engineered Landfill Site is located at Kpone, a suburb of Tema. Owned by the Tema
Municipal Assembly and managed by Zoomlion Company, the landfill opened in January 2013.
For 2013 and most of 2014, it accepted 95% of waste generated in the greater Accra
metropolitan area (1250 tons/day), and is thus expected to be filled in 2015. The engineered
landfill consists of 4 cells with liners with a gas venting system.
The study included several steps:
1.
2.
3.
4.
5.
Determination of waste composition and moisture content,
Estimation of landfill gas generation potential,
Estimation of electricity generation potential,
Identification of preliminary landfill gas recovery and use system,
Estimation of project costs and benefits.
Each of these steps is now discussed in turn.
1.0 Determination of Waste Composition and Moisture Content
Kwame Nkrumah University of Science and Technology personnel collected 10 working face
samples (7 at the municipal working fact, and one each at the commercial, industrial, and market
faces), and 15 landfilled waste samples (5 at each of 3 locations), of at least 30 pounds each.
Waste composition was then determined by sorting and weighing. Figure 1 shows the process of
collecting and sorting samples.
Figure 2 shows Tema waste composition, based on analysis of the 25 samples. As shown in
Figure 1, 27% of Tema’s waste is food waste, which quickly degrades to form biogas. A portion
of paper (10%) and textiles (9%) will also degrade to form, given the right conditions. Plastic
(26%) can be mined as a resource for industrial production. Most of the remaining waste (22%)
is soil and fines, which could be used for landfill daily cover or pavement subbase materials.
1
GMI promotes cost-effective, near-term methane recovery through partnerships between developed and developing
countries, with participation from the private sector, development banks, and nongovernmental organizations.
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
Figure 2. Tema Kpone Engineered Landfill Waste Composition
Moisture content was determined by weighing samples before and after drying in an oven at
105°C for 24 hours. Moisture data for Tema is summarized in Table 1. Although food waste is
only 27% overall, the landfill’s moisture content is fairly high, averaging 43.8% over all
samples, ranging from a low of 27% at the industrial working face to a high of 55% at landfill
location 1.
For a typical landfill, the range of moisture content is 15%-40%. For moisture content of about
20% or below, the moisture in the waste is not sufficient to support the biological activity of the
methanogenic bacteria. The moisture content of the Tema landfill is high enough to support
methane gas production.
Table 1. Moisture Content Summary
Type
Sample
Landfill
Working
Face
of Location
1
2
3
Municipal
Industrial
Commercial
Market
Number
Samples
5
5
5
7
1
1
1
of Moisture Content
Min.
Max.
45.0
62.9
27.3
44.8
34.6
61.8
22.7
58.3
27.2
27.2
44.5
44.5
40.7
40.7
Avg.
55.0
36.2
43.4
44.4
27.2
44.5
40.7
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
2.0 Estimation of Landfill Gas Generation Potential
Using the waste composition data, methane recovery was modeled using US EPA’s LandGEM,
for both conventional operation and bioreactor perpetual operation (Fig. 3). In bioreactor (or
enhanced leachate recirculation, ELR) landfill operation, water is added &/or leachate
recirculated to provide optimum moisture for waste decomposition. ELR advantages include:
 Decomposition and biological stabilization in years for bioreactor landfills vs. decades
for conventionally operated landfills,
 More favorable economics for landfill gas (LFG) collection and beneficial reuse, due to
faster gas generation,
 A 15 to 30% gain in landfill space due to an increase in density of waste mass,
 Reduced leachate disposal costs,
 Reduced post-closure care.
For the bioreactor scenario, a user-defined waste degradation rate-constant of 0.17 yr -1
(equivalent to the Intergovernmental Panel on Climate Change value) was used, since the default
LandGEM bioreactor rate-constant is thought to overestimate gas production). Bioreactor
perpetual operation assumed the entire landfill volume would be available for new waste
placement every 8 years. This allowed additional waste placement for Tema in years 2023, 2031,
and 2039. Organic decomposition would reduce waste volume by 33% due to compaction
(EREF, 2003), and operators would dig out remaining material, consisting of plastics, other nondegradables, and soil/fertilizer from organics degradation. New waste placement produces a new
peak in gas generation every 8 years. As expected, cumulative gas volume generated from 20162060 for the perpetual bioreactor scenario (9.6 billion SCF, according to LandGEM estimate)
exceeded that from the conventional scenario (2 billion SCF).
Figure 3. Methane Recovery for Tema Landfill for Conventional & Bioreactor Perpetual
Operation Scenarios
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
3.0 Estimation of Electricity Generation Potential
Using the methane recovery modeled values, electricity generation potential was estimated using
EPA’s LFG-cost Web Model (Version 2.2). Figure 4 shows electricity generation vs. time for
conventional and bioreactor operation. Engines generate more electricity compared to
microturbines. Regular turbines, direct use, and leachate evaporation were also examined, but did
not have payback periods within 15 years. Bioreactor operation substantially increases electricity
generation potential, as expected. The second peak in electricity generation for bioreactor
operation, which occurs in 2024, is due to addition of new waste made possible by degradation
of waste previously placed.
Figure 4. Tema Kpone Engineered Landfill Average Annual Power Production with
Conventional and Bioreactor Operation
Annual electricity consumption in Ghana is about 2400 kWh per household. Table 2 shows
number of households to which electricity would be provided based on the minimum and
average electricity generation value between 2016 to 2030. For the perpetual bioreactor scenario,
microturbines could provide electricity to an average of around 5000 households, and engines to
an average of around 6900 households.
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
Table 2. Number of households to be provided with electricity under different operation
scenarios
Parameter
Average Electricity Generation Between 2016-2030
(million KWh /yr)
# Households to which electricity would be provided
based on average values
Minimum Electricity Generation Between 2016-2030
(million KWh /yr)
# Households to which electricity would be provided
based on minimum values
Conventional
Operation
Microturbine
Engine
Bioreactor
Operation
Microturbine Engine
3.9
5.4
11.9
16.6
1622
2258
4961
6916
2.9
4.0
4.6
6.4
1208
1667
1912
2667
4.0 Identification of preliminary landfill gas recovery and use system
Figure 5 shows a layout for a landfill gas collection system for the Tema landfill (dimensions are
in meters). The system includes 4 6” diameter headers, each carrying gas flow from 11 wells (44
wells total, shown as circles). The system with conventional operation was designed for the peak
annual recovered methane flow modeled using LandGEM with inventory defaults – 5 m3/min
(177 cfm). The LFG was assumed to be 50% methane, so the methane recovery rate was doubled
to give the LFG maximum flow rate (10 m3/min, or 353 cfm). Head losses for conventional
operation were calculated as 28.3 inches water column, including losses incurred due to pulling
gas through the waste, within the radius of influence; wall friction losses; valve and fitting
losses; and 2 inches negative water column maintained for the system. For the Tema landfill
bioreactor operation scenario, the peak LFG flow rate doubles to 20 m3/min (706 cfm), resulting
in a head loss of 70 inches water, assuming the same header diameters.
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
360.0
22.5
45.0
a
b
45.0
45.0
a
b
45.0
45.0
a
b
45.0
45.0
a
b
22.5
25.0
25.0
c
c
c
c
25.0
d
d
d
d
25.0
e
e
e
f
f
f
e
f
25.0
25.0
g
g
g
h
h
h
g
300.0
h
25.0
25.0
i
i
i
i
25.0
j
j
j
j
25.0
k
k
k
k
25.0
l
l
l
l
25.0
m4
m3
m2
m1
Figure 5. Tema Kpone Engineered Landfill Proposed Gas Collection System
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
5.0 Estimation of project costs and benefits
EPA’s LFGcost-Web Model (Version 2.2) was used to conduct an initial economic feasibility
analysis for installation of LFG collection and use systems for Tema. Table 3 compares net
present value, payback period, capital cost, annual O&M cost, as well as average annual power
production and methane utilized, for combined heat and power (CHP) microturbines and engines
for Tema for conventional and bioreactor operation. Values presented in Table 3 assume a 2016
start date for gas collection, 20% interest rate, 20% down payment, 25 wells, and 15 year timeframe, except for the bioreactor operation engine scenario, which uses a 100% down payment
because a 20% down payment gave a payback time greater than 15 years.
Although engines generate more electricity, microturbines have shorter payback periods (3 years
to recoup the initial $4 million capital cost for the gas collection system and turbines, via
electricity sales, vs. 12 years for engines). Whether an engine or microturbine is preferable
depends on whether maximizing electricity generation or minimizing payback period is more
important. Installation of a microturbine at the Tema landfill with bioreactor operation would
provide estimated average annual power of 9.2 million kWh, with a payback time of 2 years.
Initial capital cost would be $4.3 million, with average O&M costs of around $200,000.
Although an engine would produce 12.9 million kWh with landfill bioreactor operation, its
payback time would be 11 years, capital cost $7.1 million, and annual O&M cost around
$970,000. Given the costs of the engine, we recommend the microturbine as the preferred option.
Tema landfill with conventional operation does not produce a payback time within 15 years, so
bioreactor operation is recommended.
GLOBAL WASTE MANAGEMENT SYMPOSIUM 2016
Table 3. Net Present Value and Payback Year Comparisons for Tema Operation Scenarios and
Electricity Generation Options
Landfill
Operation
Conventional
Bioreactor
Project Type
CHP
Microturbine
Engine
CHP
Microturbine
Engine
Annual
power
production
(million
kWh)
Min.
Avg.
Number of
households
powered
Min.
Avg.
2.9
3.9
1208
4.0
5.4
4.6
11.9
6.4
16.6
Average methane
utilized
(MMTCO2E/yr)
Net present
value
at
year
of
construction
Net
present
value
payback
year
Capital
Cost
(million
US$)
Annual
O&M
Cost
1622
0.026
$433,626
5
$2.1
$190,400
1667
2258
0.026
$303,346
10
$2.9
$286,800
1912
4961
0.087
$3,858,028
2
$4.2
$118,700
2667
6916
0.087
$120,553
15
$8.9
$824,600
6.0 Conclusions and Recommendations
Based on the feasibility study presented here, we recommend the following:



Operation of the Tema landfill as a bioreactor, to increase gas production and improve
economic benefits.
Installation of a landfill gas collection and recovery system. Specifically, install 7 300
kW microturbines to provide estimated average annual power of 11.9 million kWh (1912
households minimum, and 4961 average). Initial capital cost would be $4.2 million, with
average O&M costs of $118,700, and a payback time of 2 years.
Mining the landfill periodically for waste plastics, which can be used as feedstock for
industrial production.
Benefits of these changes would include:




Cost-effective electricity production for almost 5000 households in the Accra region;
Perpetual recovery of landfill space, which would eliminate the need for costly
construction of future landfills;
A new industrial production facility, which would create jobs for local residents.
Income from electricity sales, after an initial 2-year period to recoup capital costs.