Heba Numan Harara
Dr. Thaer AbuShbak
The effects of leachate recirculation with
supplemental water addition on methane
production and waste decomposition in a
simulated tropical landfill
• A landfill, also
known as a dump,
is a site for the
disposal of waste
materials by burial
and is the oldest
form of waste
have been the most
common methods of
disposal and remain
so in many places
around the world.
6. LANDFILL LEACHATE
During landfill site
operation, a liquid known as
leachate is produced.
It is a mixture of organic
degradation products, liquid
waste and rain water.
It has high organic carbon
content, high concentrations
of nitrogen and is usually
9. Leachate effects
the pipes become weakened by chemical attack (acids,
solvents, oxidizing agents, or corrosion) and may then be
crushed by the tons of garbage piled on them.
Leachate contains a host of toxic and carcinogenic
chemicals, which may cause harm to both humans and
leachate-contaminated groundwater can adversely affect
industrial and agricultural activities that depend on well
The use of contaminated water for irrigation can decrease
soil productivity, contaminate crops, and move possibly
toxic pollutants up the food chain as animals and humans
10. Gasses found in landfills:
The typical constituents of gases produced by a municipal solid waste
• Component Percent (dry volume basis)
Carbon Dioxide 40-60%
Methane : It is often flammable and sometimes even explosive.
• Carbon Dioxide: Non harmful to the environment
• Nitrogen: Non harmful to the environment
• Ammonia: Ammonia in air is an irritant and causes burning of
the eyes, nose, throat and lungs.
11. Leachate collection and treatment:
Leachate collection systems are installed
above the liner and consist of a perforated
piping system which collects and carries the
leachate to a storage tank.
Periodically, leachate removed from the
storage tank and treated or disposed of.
Most common leachate management
methods are: discharge to wastewater
treatment plant, on-site treatment and
recirculation back into the landfill.
13. Leachate recirculation
the practice of retraining leachate to
landfill from which it has been
This technology could be more cost-
effective than other treatment
14. Benefits of leachate recirculation
-reduction in leachate treatment and
- Accelerated decomposition and
settlement of waste.
- Acceleration in gas production.
- Accelerating stabilization of organic
- Potential reduction in cost and
environmental impact after closure.
15. After weighing these advantages and
disadvantages, federal regulators in
the US decided to allow leachate
recirculation only at landfills that have
a composite liner and a leachate
collection system that meets specified
16. An example of the electrical generation equipment in one of the
System Plants. These engines burn only landfill gas as a fuel and
operate 24 hours a day. Each engine produces 750 kw of
17. Bioreactor Defined
“……a sanitary landfill operated for the
purpose of transforming and
stabilizing organic waste
constituents by purposeful control to
enhance microbiological processes.
18. Why Operate a Landfill as a
to increase potential for waste to energy
to store and/or treat leachate,
to recover air space,
to ensure sustainability.
19. Objective of study:
to determine the effects of leachate
recirculation and supplemental water addition
on municipal solid waste decomposition and
methane production in three anaerobic
The effects of leachate recirculation with supplemental water
addition on methane production and waste decomposition in a
simulated tropical landfill
20. Used Techniques for improving methane production
• Bioreactor technology is becoming more widely
accepted in landfill design and operation
• This technique enhances waste decomposition
rates and methane production.
• An increase in moisture content in a landfill
enhances the anaerobic degradation processes by
facilitating the redistribution of substrates and
nutrients and the spreading of microorganisms
between the micro environments in the landfill,
leading to an increase in the methane production
The most common problem associated with
landfill operations is the generation of
leachate and gases.
The results from this investigations
might not be applicable to landfills in Thailand
due to the differences in waste type and
In tropical landfills, where high temperature
and high evaporation lead to insufficient
moisture content in the cell.
22. However, during the dry season, leachate
recirculation may be insufficient to
maintain the moisture content, and
supplemental water addition into the cell is
then necessary to stabilize moisture levels
as well as stimulate biological activity.
leachate recirculation not only helps to
increase the moisture content but also to
circulate organic matter back into the cell.
23. Reactor preparation
The study was conducted by constructing
three simulated landfill reactors from
Material and methods
24. These reactors had
a diameter and
height of 0.30 and
collection pipe with
a diameter of 1.8
cm was installed at
the center of the
bottom of the
collected in a
25. • A leachate
sampling port was
installed in the
• A tap-water
addition port was
installed at the top
of the reactor.
• A distribution pipe
was installed at
the top of the
reactor to add liquid
to the waste mass.
• A 1.8cm diameter
PVC pipe was used
to construct a gas-
26. The concept of using a gas meter to
calculate gas production is based on the
liquid displacement by gas in the fixed
volume chamber which causes a chamber
All connections (ports and the lid) were
checked for leakages by using a soap
solution before waste loading.
27. Soil preparation
The soil, which was taken from Bangkhuntien
Campus,was sampled and sent to the Department of
Soil Science, Faculty of Agriculture, Kasetsart
University for texture analysis.
The result showed that the soil, consisting of
45%sand, 16% silt and 39% clay, had a sand-clay
(SC) texture and had acceptable
characteristics for use as soil
covering in sanitary landfills
28. MSW preparation
The MSW was collected from Nongkham transfer
station, Bangkok, Thailand.
Bulky wastes and recyclable materials (glass,
metal and non-metal materials) were removed.
Large plastic and paper materials were torn into
1–2 cm size pieces.
The sample was then mixed with abackhoe to
maximize the homogeneity of wastes.
Approximately 1000 kg of MSW
moisture content of the MSW was 70.28% on a
wet basis and the C/N ratio was 21.79.
30. Solid wastes loading
Before the reactors were filled with waste, an
8 cm thick layer of 2.5 cm diameter gravel
was placed at the bottom of each reactor.
A circular nylon screen with 1-mm diameter
holes was placed over the gravel layer to
prevent clogging of the reactor drainage
During loading, the MSW was manually
compacted and then covered with a 3 cm
thickness of soil every 30 cm for the bottom
and medium layers and a 6 cm thickness of
final cover soil.
31. In this investigation, the waste was
compacted to a density of 600 kg/m3.
The soil was compacted to 1300 kg/m3.
to ensure anaerobic conditions in the
reactors, a rubber gasket was placed
between an acrylic flange and the top lid.
After the reactor was closed, the top lid was
screwed down and sealed with the silicone
rubber to make the reactor gas tight.
33. Experimental design and operation
One reactor was operated as a control
.without leachate recirculation (RC)
while the other two served as
experimental reactors, one with leachate
and the other with leachate recirculation
and supplemental water addition (R2).
35. the buffer capacity (proportion of
TVA and alkalinity) for all reactors
was controlled to not exceed more
than 0.8 by adding sodium
bicarbonatec(NaHCO3) to the water
before introduction into the reactors
on day 200,
except R2 which had a high pH and
36. The total amounts of NaHCO3 added
to RC and R1 were 877 and 858 g,
it was difficult to recirculate at the
same rate for both reactors because
of the variation of leachate quantity
circulating from the reactors.
37. Laboratory analysis
Gas volume in the reactor was measured by
a gas meter.
the gas composition was analyzed by gas
chromatography and a Thermal Conductivity
The leachate volume collected at the bottom
of each reactor was quantified and sampled.
Leachate was analyzed for pH, alkalinity,
TVA and COD by standard methods
38. RC :control reactor Without LEACTAH
RC provide 9.02
l/kg dry weight
at a rate of
0.10 l/kg dry
phase on day
39. R1 : WITH LEACTAH RECRIULATION
dry weight at
of 0.14 l/kg
phase on day
40. The effects of leachate recirculation
• waste decomposition was in the acid phase
approximately 210 days after loading as
indicated by the high concentration of TVA (8.13
gAA/l from RC and 7.91 gAA/l from R1) in the
• low leachate alkalinity (5.12 gCaCO3/l from RC
and 5.31 gCaCO3/l from R1) and a subsequent.
• drop in leachate pH to approximately 5.7.
• The natural buffering capacity of the waste was
insufficient to overcome the effects of the TVA
41. • The acidic environment resulted in the
inhibition of methanogenesis as indicated by
the continued high COD concentration(21.59
g/l from RC and 22.61 g/l from R1)
• no methane was produced before recirculation
• The addition of a buffer compound (NaHCO3)
on day 200 provided the environment required
for methanogens to utilize substrates and
methane composition and production
42. • The remaining COD concentrations of RC and R1
on day 330 were 1.26 and 5.99 g/l, respectively,
• while the remaining TVA concentrations were 0.73
and 3.11 gAA/l, respectively.
• The steady remaining values of COD and TVA
concentrations in the leachate indicated that the
reactors entered into the stabilization phase.
• the control reactor (RC) reached the stabilization
phase more quickly than the leachate recirculation
reactor (R1) (day 270 for RC and day 290 for R1).
43. • This was unexpected and was attributed to the
exhaustion of the substrates for methanogens due to
• However, leachate recirculation with buffer addition
(R1) provided a greater methane production rate (0.10
l/kg dry weight/d from RC and 0.14 l/kg dry weight/d
• and greater cumulative methane production than the
control reactor (RC) (9.02 l/kg dry weight and 17.04
l/kg dry weight from RC and R1, respectively).
• Therefore, it can beconcluded that leachate
recirculation with buffer addition accelerates
waste stabilization and enhances methane
44. R2 :with leachate recirculation an
supplemental water additions
dry weight of
MSW at an
of 0.58 l/kg
phase on day
45. • supplemental water addition in the early acid
phase helped to dilute inhibitory substances and
negated the need for buffer addition to vercome
the acid phase.
• In addition, R2 entered the methanogenesis
phase on day 75, which was 135 days earlier
than RC and R1.
• The results show similar methane production
rates from both reactors from day 75 to 140.
• The average methane production rate of R1 was
0.10 l/kg dry weight/d while that of R2 was 0.11
l/kg dry weight/d.
The effects of leachate recirculation with supplemental
46. • However, it was observed that R1 was in
an acid phase while R2 was in a
methanogenesis phase, as indicated by
the increasing methane content and
leachate pH and decreasing leachate
concentrations of e.g. COD and TVA.
• This meant that supplemental water
addition in the early acid phase helped
accelerate waste decomposition but did
not result in higher methane yield rates
47. • methane production was found to gradually
• In RC, the substrates and essential
nutrients for methanogens were removed
by leachate drainage whereas in the R2
reactor the substrates for methanogens
were captured, reapplied and utilized by the
• This also increased contact opportunity
between the nutrients and microbes.
48. • Recirculation into R2 was started on day 203,
which was after the waste had nearly reached the
stabilization phase (day 180), whereas leachate
recirculation into R1 was started on day 203, which
was before the waste had reached the stabilization
• This result shows that when the leachate
recirculation is started after the waste has reached
the stabilization phase, a much higher methane
production can be produced than when the
recirculation is started before the waste has
reached the stabilization phase.
49. The effects of leachate recirculation with increasing organic
The results during the stabilization phase for all reactors
revealed that higher OLR led to a higher CH4 production
rate, CH4 composition and COD removal.
50. This reveals that a reactor that has entered into the
stabilization phase not only enhances methane production
through leachate recirculation, but can also help to increase
the OLR in the circulated leachate.
-The leachate recirculation reactor provided a
greater degree of stabilization than the
single pass leachate recirculation reactor.
-the effect of leachate recirculation along with
buffer addition could enhance methane
production and reduce the stabilization
-Supplemental water addition increase dilution
of inhibitory substances and reduce leachate
strength resulting in favorable conditions for
-Supplemental water addition in acid phase
can be used as an effective operational
strategy to accelerate the methanogenesis
-Starting to recirculate leachate after the
waste had reached the stabilization phase
produced much more methane than when
starting recirculation before the waste had
reached the stabilization phase.