effect of leachate recirculation and aeration on volatile fatty acid concentrations in aerobic and...

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published online 18 September 2011Waste Manag ResMehmet Sinan Bilgili, Ahmet Demir and Gamze Varank

anaerobic landfill leachateEffect of leachate recirculation and aeration on volatile fatty acid concentrations in aerobic and

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Research Article

Effect of leachate recirculationand aeration on volatile fatty acidconcentrations in aerobic and anaerobiclandfill leachate

M. Sinan Bilgili, Ahmet Demir and Gamze Varank

AbstractThe main aim of this study was to investigate the effect of leachate recirculation and aeration on volatile fatty acid (VFA)

concentrations in aerobic and anaerobic landfill leachate samples. In this study, two aerobic (A1, A2) and two anaerobic

(AN1, AN2) reactors with (A1, AN1) and without (A2, AN2) leachate recirculation were used in order to determine the

change of volatile fatty acids components in landfill leachate. VFA degradation rate was almost 100% in each reactor but the

degradation rate show notable differences. In aerobic landfill reactors, total VFA concentrations decreased below 1000mg

L�1 after 120 days of operation and only caproic and acetic acids were determined at this time. The stabilization of the VFA

concentrations takes about 350 and 450 days for AN1 and AN2 reactors, respectively. VFA concentrations were higher than

that of aerobic reactors because of the acidogenic phase occurred in anaerobic environment. According to the results of VFA

components, the stabilization of the waste was achieved after 120 days of operation in aerobic landfills. At this time, anaer-

obic reactors were in the acidogenic phase which results with the high concentrations of VFA. The results also indicated that

leachate recirculation does not affect the degradation rate in aerobic landfills as much as it does in anaerobic landfills

KeywordsSolid waste, aerobic landfill, leachate, volatile fatty acid, gas chromatography

Date received: 14 January 2011; accepted: 20 June 2011

Introduction

The aim of this study was to investigate the effect of leachate

recirculation and aeration on volatile fatty acid (VFA)

concentrations in aerobic and anaerobic landfill leachate

samples. Bioreactor landfills or leachate recirculation is a

growing approach to improve the slow degradation of

waste in landfills. The main aim of these modern landfills is

to reduce landfill emissions in terms of landfill gas and leach-

ate such that environmental problems are not left to future

generations (Cossu and Rossetti, 2003). The design objectives

of these landfills are to minimize leachate migration into the

subsurface environment and maximize landfill gas generation

rates under controlled conditions. Experimental and field

scale studies have been conducted to develop and improve

landfill techniques and designs, the goal being to control the

negative effects of landfill sites on the environment (Warith,

2002). The bioreactor landfill provides control and process

optimization, primarily through the addition of leachate.

The advantages of leachate recirculation include distribution

of nutrient and enzymes, pH buffering, dilution of inhibitory

compounds, recycling and distribution of methanogens,

liquid storage and evaporation opportunities (Reinhart,

1996). The effectiveness of leachate recirculation has been

well documented in lysimeter, test cell and full-scale studies

(Bilgili et al., 2007 a; Chan et al., 2002; Demir et al., 2004;

Huo et al., 2008; Mehta et al., 2002; Pohland and Kim, 2000;

Price et al., 2003; Reinhart et al., 2002; Wang et al., 2006).

Recently, increased interest has been focused on introduc-

ing air into the waste mass for aerobic degradation of solid

wastes. Aerobic bioreactors have been promoted as a

Department of Environmental Engineering, Yildiz TechnicalUniversity, Esenler, Istanbul, Turkey.

Corresponding author:M. Sinan Bilgili, Department of Environmental Engineering, YildizTechnical University, 34220, Esenler, Istanbul, TurkeyEmail: [email protected]

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method for accelerating waste stabilization. Studies of aerobic

biodegradation processes have demonstrated that the organic

parts of the refuse can be degraded in a relatively short

time compared with anaerobic degradation (Hudgins and

Harper, 1999). The concept of aerobic degradationby injecting

air into a landfill presents significant alternatives in waste

management both for existing andnew systems.Air is typically

injected into the landfill with the same devices used for

extracting gas or injecting leachate, vertical and horizontal

wells (Reinhart et al., 2002). There has been increasing interest

in aerobic landfilling during recent years, andmany pilot-scale

and field-scale studies have been recently undertaken (Bilgili

et al., 2007 a; Borglin et al., 2004; Cossu et al., 2003; Smith

et al., 2000; Themelis and Kim, 2002). However, there are

some disadvantages of aerobic landfills such as energy con-

sumption for forced aeration, complex operation andmanage-

ment, and fire and exploitation risks according to high

temperatures measured as a result of aerobic degradation.

Landfill leachate is a high-strength wastewater character-

ized by extremes of pH, chemical oxygen demand (COD),

biochemical oxygen demand (BOD), and heavy metals. The

volatile fatty acids (VFA) contribute most of these charac-

teristics and adversely affect the microbial activity. To under-

stand the stability status of organic wastes in landfills and to

find the best conditions for the treatment of leachate, it is

necessary to determine the VFA content.

Volatile fatty acids (VFA) and volatile organic acids (VOA)

affect micro-organisms and the degradation processes in two

primary ways. First, they have a low ionization constant

(i.e. low pKa) and can readily dissociate, releasing Hþ ions

that cause the pH of the system to decrease and therefore

become destabilized. Second, when the acids are non-

dissociated (as is typical at low pH levels), the acids are able

to penetrate microbial cell membranes, establishing a pH gra-

dient by actively transporting protons out of the cell and reduc-

ing the internal cell pH (Aguilar et al. 1995; Zoetemeyer et al.,

1982). The decrease in intracellular pH in turn leads to an

increased energy demand by the cell to restore pH levels

leaving less energy for growth (Gonzalez et al., 2005;

Yamaguchi et al., 1989). These processes lead to reduction in

the rate of solid waste degradation. VOA concentrations that

are in excess of 6000mg L�1 can inhibit microbial processes

(Pohland et al., 1993). However, most research regarding solid

waste degradation has not focused on VOAs, but rather has

investigated the effect of VFAs on the methanogenic popula-

tion within the landfill (US EPA, 2006).

The aim of the existing research was to investigate the

effect of leachate recirculation and aeration on the behavior

of volatile fatty acid (VFA) concentrations of leachate sam-

ples and using the method concluded by Yan and Jen (1992)

for pretreatment of leachate samples for chromatographic

analysis. In this study, leachate samples from aerobic

(A1 and A2) and anaerobic (AN1 and AN2) landfill reactors

with (A1 and AN1) and without (A2 and AN2) leachate

recirculation were determined and compared. VFA concen-

trations were determined by its acetic, propionic, isobutyric,

butyric, isovaleric, valeric, isocaproic, caproic, and heptanoic

acid constituents.

Material and methods

Aerobic and anaerobic reactors

The laboratory-scale landfill reactors were constructed from

0.5 cm polypropylene with an inner diameter of 50 cm and a

height of 200 cm (Figure 1). A second layer with the diameter

of 60 cm was constructed around the reactors and the

blank between these two layers was filled with heat isolation

material to prevent temperature redistribution between the

reactors and the surrounding environment. The MSW leach-

ate did not significantly degrade or alter the physical or

mechanical properties of the polypropylene material (TRI/

Environmental, 2008). Landfill reactors were located in the

Environmental Engineering Department Laboratory of our

university at ambient temperature.

The lower part of the reactors consists of 15 cm gravel

drainage with a perforated pipe which has 2.5 cm diameter

inserted to collect and discharge the generated leachate.

Leachate collection was realized by opening the dis-

charge valve on a daily basis at the beginning of the exper-

iment, and at 1- or 2-week intervals for the following period.

Leachate samples were collected while discharging leachate

from the landfill reactors and kept at 4�C in a refrigerator in

plastic bottles. After sampling of leachate, the excess amount

was collected separately in order to use for leachate

recirculation.

The solid waste added to the landfill reactors obtained

from Odayeri Sanitary Landfill (Istanbul, Turkey). The aver-

age composition of solid wastes removed at Odayeri landfill

is 44% organic, 8% paper, 6% glass, 6% metals, 5% plastic,

5% textile, 9% nylon, 8% baby napkins and 9% ash and

others (Demir et al., 2004). A1, A2, AN1, and AN2 reactors

were filled with approximately 175 kg of fresh solid waste,

with the waste representing the bulk composition of MSW

determined by waste composition analysis. Moisture content,

volatile solids content, and ash content of the raw solid waste

landfilled in the reactors were measured as 65, 75, and 25%,

respectively.

Aeration and leachate recirculation

The aeration was achieved by a compressor that was con-

nected to the aeration pipes at the bottom of aerobic reac-

tors. Air was introduced at the bottom of the waste and

passed through the waste in an upward direction by the

help of the perforated aeration pipes with 60 and 120 cm

length in each aerobic reactor (Bilgili et al., 2006).

2 Waste Management & Research 0(0)



Leachate was recirculated using a peristaltic pump located

at the top of the recirculated reactors. The recirculated leach-

ate quantity was low at the beginning of the study. After

reaching to methanogenic phase, the recirculated leachate

quantity is increased in AN1 reactor. Temperature and leach-

ate generation rates are used to determine the leachate

recirculation rate in A1 reactor. Leachate recirculation and

aeration rates are given in Table 1 (Bilgili et al., 2007b).

In total, 5400 m3 air was added to each aerobic landfill

reactor (during 250 days) and the aeration rates were equal to

0.084 and 0.086L min�1kg�1 waste, respectively, for A1 and

A2 reactors. Additionally, 29.4L of leachate (29.4 L/250

Landfill gasmeasurement

Temperatureprobes

Gravel

50,00cm

Solidwaste

Leac

hate

rec

ircul

atio

n

Aer

atio

n pi

pe

Compressor

Leachate sampling and discharge

Peristalticpump

200,

00cm

170,

00cm

Figure 1. Schematic view of landfill reactors.

Bilgili et al. 3



days/0.334 m3 waste¼ 0.35L day�1 m�3 waste) was recircu-

lated within the A1 landfill reactor, while this quantity was

35L (35L/500 days/0.334 m3¼ 0.21L day�1 m�3 waste) in

AN1 reactor (Bilgili, et al., 2007a).

VFA determination

In the standard method for the examination of water and

wastewater (APHA, 2005), volatile acids are removed from

aqueous solution by distillation or separated by flash chro-

matography, and titrated with standard alkaline solution to a

phenolphthalein end-point. The acids are determined as a

whole with the risk of interference from inorganic acids

(Yan and Jen, 1992). The application of gas chromatography

(GC) to volatile organic acids determination has been studied

extensively in the literature. However, landfill leachate is very

complicated. Suspended matter and inorganic salts can

damage the packing material and retain in the column.

Hence, the pretreatment of leachate samples for chromato-

graphic analysis appeared to merit further investigation.

VFA components in landfill leachate were determined by

using gas chromatography (GC). In this study, the method

determined by Yan and Jen (1992) was applied to leachate

samples for pretreatment prior to chromatographic analysis

to achieve optimum conditions for distillation procedure.

Sample pretreatment: Yanand Jen (1992) determined

the optimum conditions for the distillation procedure used for

sample pretreatment prior to chromatographic analysis.

Sulfuric acid was added to acidify the leachate and convert

the acid salts into free acids during distillation. A 100mL

volume of sample solution was placed in a 250mL distillation

flask. The solution was cooled in an ice bath, then 5mL of

sulfuric acid (1þ 1) were gradually added and mixed thor-

oughly. When no more gas was evolved, which is clearly visi-

ble, the flask was removed from the ice bath and warmed to

room temperature. The temperature of the heating mantel in

the distillation apparatus was controlled to produce distillate

at the rate of 5mL min�1. The first 10mL of the distillate was

discarded and 50mL of distillate was collected for chromato-

graphic analysis (Yan and Jen, 1992).

Apparatus: An Agillent 6890N model gas chromato-

graph equipped with a flame ionization detector (FID) and

0.00 2.00 4.00 6.00 8.00

Min

10.00 12.00 14.00

A W

1

1.

2.3.

4.

5.

6.

7.

8.

9.

10.

2

34 5

67 8 9

10

A

W

Air

Water (solvent)

Acetic acid

Formic acid*Propionic acid

Isobutyric acid

Butyric acid

Isolvaleric acid

Valeric acid

Isocaproic acid

Caproic acid

Heptanoic acid

* Supplemented to enhancedetector response

Figure 2. Volatile acid standard mixture chromatogram.

Table 1. Operational conditions used in the reactors tosimulate different landfill concepts

Column Operatingcondition

Refuse(kg)

Air flowa

(L min�1 kgwaste�1)

Water flowb

(L day�1 m�3

waste)

A1 Aerobic withleachaterecirculation

179 0.084 0.35

A2 Aerobic dry 174 0.086 –

AN1 Anaerobic withleachaterecirculation

173 – 0.21

AN2 Traditionallandfill

175 – –

– No air/water flow.aCalculated according to the total air flow used during the study.bCalculated according to the total water flow used during the study




a Restek-5 Wax column of 60m� 0.25mm ID� 0.50 mm

was used. The injection port and column were operated at

temperatures of 220 and 230�C, respectively. The detector

temperature was maintained at 280�C, the carrier gas was

helium at a flow rate of 30mL min�1. One microlitre of

pretreated sample was injected into the gas chromatograph

for analysis. Volatile fatty acids were identified by comparing

their retention time with those of volatile acid standard

mixture (Volatile Free Acid Mix, Supelco, 46975-U).

The chromatogram of the standard mixture is given in

Figure 2.

Results and discussion

Four landfill reactors were used in order to investigate the

effect of leachate recirculation and aeration on the degrada-

tion of solid wastes in landfills. The results of leachate quality

and quantity are given in the authors’ previous papers (Bilgili

et al., 2006, 2007a, b).

The variations of pH, COD, and total volatile acids con-

centrations for both aerobic and anaerobic reactors are given

in Figure 3. Initial leachate analysis indicated high concentra-

tions for VFA (40 000 and 60 000mg L�1 for aerobic and

anaerobic reactors, respectively) and COD (50 000 and 80

000mg L�1 for aerobic and anaerobic reactors, respectively)

parameters. As a result of the high degradation rate in aerobic

landfill reactors, the concentrations of VFA and COD

decreased rapidly. Maximum COD and VFA concentrations

were determined to be 47 900 and 33 930mg L�1, for A1

reactor, and 45 450 and 38 270mg L�1 for A2 reactor, respec-

tively. After 120 days of operation, COD concentrations were

determined at stable values around 5000 and 10 000mgL�1 for

A1 and A2 reactors, respectively. At the initial stage of land-

filling, VFA concentrations were around 30 000 and 40 000mg

L�1 for A1 and A2 reactors, respectively. During the opera-

tional period, VFA concentrations showed similar behaviour

of CODand decreased below 1000mgL�1 for bothA1 andA2

reactors. pH was not affected because of the continuous alka-

linity production by longer-chain VFA oxidation

(Erdirencelebi and Ozturk, 2006). The pH of leachate samples

taken from aerobic reactors reached neutral values after about

50 days of operation and became stable after 100 days of oper-

ation at pH 8.

Observed maximum concentrations for COD were 80 000

and 100 000mg L�1 for AN1 and AN2 reactors, respectively,

and 60 000mg L�1 for VFA concentrations for both reactors.

The same decreasing trend that was observed in the aerobic

reactors was determined with a slower trend in anaerobic

landfill reactors. COD concentrations decreased below

5000mg L�1 after 350 and 450 days of operation for AN1

and AN2 reactors, respectively. Additionally, the concentra-

tions of VFA decreased below 1000mg L�1 after these oper-

ation times for AN1 and AN2 reactors, respectively. The

effect of leachate recirculation was more detectable in these

reactors. The minimum values of COD and VFA observed

were lower than that of aerobic reactors. The measured COD

and VFA concentrations at the end of the operational period

(250 days for aerobic and 600 days for anaerobic) for A1, A2,

0

10000

20000

30000

40000

50000

60000

0 100 200 300

Time (day)

Con

cent

ratio

n (m

g L–1

)

5

6

7

8

9

10

pH

COD_A1 VFA_A1 pH_A1

0

10000

20000

30000

40000

50000

60000

0 100 200 300

Time (day)

Con

cent

ratio

n (m

g L–1

)

5

6

7

8

9

10pH

COD_A2 VFA_A2 pH_A2

0

20000

40000

60000

80000

100000

120000

0 200 400 600 800

Time (day)

Con

cent

ratio

n (m

g L–1

)1

4

5

6

7

8

pH

COD_AN1 VFA_AN1 pH_AN1

0

20000

40000

60000

80000

100000

120000

0 200 400 600 800

Time (day)

Con

cent

ratio

n (m

g L–1

)

4

5

6

7

8

pH

COD_AN2 VFA_AN2 pH_AN2

Figure 3. pH, Total VFA and COD concentrations in aerobic and anaerobic reactors.

Bilgili et al. 5



AN1, and AN2 reactors were 5120:446, 8260:528, 1200:148

and 1800:386mg L�1, respectively, but the time required for

degradation was a considerable point for landfill owners.

Thus, the aerobic landfill system has advantages such as

rapid organic matter degradation, less leachate production,

and more settlement (Read et al., 2001; Ritzkowski et al.,

2006). Total VFA degradation rate was almost 100% at

the end of the operational period in all reactors.

As a result of the acidogenic phase in anaerobic reactors,

VFA concentrations were determined at higher values than

that of aerobic reactors (40 000 to 60 000mg L�1). The deg-

radation of organic matter in conventional landfills is a

sequential process initiated by hydrolysis of complex organic

matter into simple carbohydrates, amino acids, and fatty

acids. The simple carbohydrates and acids provide energy

for growth of fermenting bacteria, producing volatile acids

and hydrogen. The volatile acids are then partially oxidized

to produce additional hydrogen and acetic acid, which are

the main substrates used by methanogens to produce meth-

ane (Cardoso et al., 2006; Tchobanoglous et al., 1993). The

volatile acid concentration therefore can be used as a key

indicator of microbial activity. Total VFA concentrations

decreased below 1000mg L�1 after 350 and 450 days in

AN1 and AN2 reactors, respectively, indicating the positive

effect of leachate recirculation on the anaerobic degradation

of solid waste.

In the second part of the study acetic, propionic, isobu-

tyric, butyric, isovaleric, valeric, isocaproic, caproic, and

heptanoic acid components of leachate samples were deter-

mined. The results are given in Figures 4–7 for A1, A2, AN1

and AN2 reactors, respectively.

Rees (1980) reported that the leachate generated from

fresh waste contained mainly acetic acid. Due to the favour-

able environment for the acid formers other acids start to

appear. These acids primarily consist of propionic, butyric,

valeric, and hexanoic acids, the products of digestion of

carbohydrates. Butyric acid is a major acid formed by the

hydrolysis of lipids. Concentrations of iso-butyric and iso-

valeric acids are primarily formed during the digestion of

proteins. Chugh et al. (1999) explained that low quantities

of these acids in leachate indicate that the protein content of

the waste is also low.

Caproic and acetic acids are the largest components of

leachate VFA for both A1 and A2 reactors. As can be seen

from Figure 4, the initial concentrations of caproic and acetic

acids were about 13 000 and 8000mg L�1, respectively, in A1

reactor. At the same period butyric, isocaproic, and propionic

acid concentrations were around 4000mgL�1. Heptanoic, iso-

butyric, and valeric acids were below 1000mgL�1 at this stage.

As a result of the rapid degradation of organic matter in

aerobic landfill system VFA concentrations decreased rapidly

to 350 for A1 reactor, and after 120 days only acetic and

Time (day)

Time (day)

0 50 100 150 200 250 300

Con

cent

ratio

n (m

g L–1

)

0

2000

4000

6000

8000

10000

12000

14000AceticButyricCaproicIsocaproicPropionic

0 50 100 150 200 250 300

Con

cent

ratio

n (m

g L–1

)

0

500

1000

1500

2000

2500HeptanoicIsobutyricValeric

Figure 5. VFA components in A2 reactor.

Time (day)

Time (day)

0 50 100 150 200 250 300

Con

cent

ratio

n (m

g L–1

)

0

2000

4000

6000

8000

10000

12000


0 50 100 150 200 250 300

Con

cent

ratio

n (m

g L–1

)

0

500

1000

1500

2000


Figure 4. VFA components in A1 reactor.




caproic acids were determined in leachate samples. Acetic acid

concentrations were below 50mg L�1 while caproic acid con-

centrations were around 200mg L�1 at the end of the degra-

dation, as it is produced from the breakdown of the propionic

acid.

In A2 reactor (Figure 5), acetic and caproic acid concen-

trations were almost at the same levels and determined to be

around 10 000mg L�1 at the beginning period. All other acids

determined were at the same range observed in A1 reactor.

VFA concentrations decreased rapidly in A2 reactor and

reached to 730mg L�1 after 120 days of operation. Acetic

and caproic acid concentrations were determined around

200mg L�1 during the rest of the study. Additionally, isoca-

proic and propionic acids were determined in trace amounts

(below 20mg L�1 for all measurents) from day 120 to the end

of the study. According to these results, it was observed that

leachate recirculation does not affect the degradation rate sig-

nificantly in aerobic landfill system. However, leachate recir-

culation can be used for the control of temperature and

moisture in aerobic landfills.

Figure 6 shows the VFA components determined

from leachate samples of AN1 reactor. Caproic acid concen-

tration was about 30 000mg L�1 in AN1 reactor and it was the

largest component of VFA in leachate samples. Propionic,

isocaproic, and acetic acids were about 10 000, 8500,

and 5500mg L�1, respectively, at the beginning period.

Isobutyric and heptanoic acids were determined as 1388 and

258mgL�1.Onday 120,when the total VFAconcentrations in

aerobic landfill reactors decreased to below 1000mg L�1, the

concentrations in AN1 reactor were 13 300, 4600, 4000, 2750

and 1250mgL�1 for caproic, acetic, propionic, isocaproic, and

butyric acid, respectively. After 350 days of operation, the

concentrations decreased to below 1000mg L�1 that were

observed in aerobic landfill reactors.

Figure 7 shows the VFA components of leachate samples

taken fromAN2 reactor. At the beginning of the operation the

concentrations of caproic, acetic, propionic, isocaproic, and

butyric acid were 31 500, 4750, 10 600, 10 500, and 4600mg

L�1, respectively. This shows that the degradation is still in the

acidogenic phase in this reactor. After 350 days when the

concentrations decreased to below 1000mg L�1 in AN1

reactor, the concentrations of caproic, acetic, propionic, and

isobutyric acids were 4200, 1250, 1800 and 1350mg L�1,

respectively, in AN2 reactor. Butyric acid concentration was

below 300mg L�1 at this stage. The concentrations decreased

below 1000mgL�1 after 450 days of operation inAN2 reactor.

The only difference between AN1 and AN2 reactors was

that the time required to reach the low concentrations (below

1000mg L�1) observed in AN1 reactor. The results clearly

show that the degradation of the organic matter realizes

rapidly with leachate recirculation in anaerobic landfills.

These data shows similar results to those obtained by

0 100 200 300 400 500 600 7000

5000

10000

15000

20000

25000

30000


0 100 200 300 400 500 600 7000

200

400

600

800

1000

1200


Time (day)

Con

cent

ratio

n (m

g L–1

)

Time (day)

Con

cent

ratio

n (m

g L–1

)

Figure 7. VFA components in AN2 reactor.

0 100 200 300 400 500 600 7000

5000

10000

15000

20000

25000

30000


0 100 200 300 400 500 600 7000

200

400

600

800

1000

1200

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1600


Time (day)

Con

cent

ratio

n (m

g L–1

)

Time (day)

Con

cent

ratio

n (m

g L–1

)

Figure 6. VFA components in AN1 reactor.

Bilgili et al. 7



Iglesias et al. (2000), Reinhart and Al Yousfi (1996) and

Sponza and Agdag (2004).

The percentage distribution of VFA components in

aerobic and anaerobic landfill reactors is given in Figure 8.

The main components of VFA in A1 and A2 reactors are

acetic and caproic acids. Acetic acid and caproic acid consti-

tuted 20 and 40% of the total VFA, respectively, at the

beginning of the study in the A1 reactor. After 150 days of

operation, the rest of the concentration of the rest of the

VFA components were below detection limits and only

acetic and caproic acids are determined in leachate samples

with the approximate percentages of 60 and 40%, respec-

tively. Similarly, the A2 reactor had the same trend as the

A1 reactor for the VFA proportions.

During the operational period of the anaerobic landfill

reactors, the VFA distribution showed similar behaviour

for the AN1 and AN2 reactors. Of these, VFA caproic acid

was the most abundant which consisted of almost 50% of the

total VFA in all stages of the study for both AN1 and AN2

reactors. Iglesias et al. (1998) in their column study, concluded

that butyric acid was the most abundant, while Nakakubo

et al. (2008) determined acetic and propionic acids as the

most abundant in their study. The main observation from

Figure 8 is that, although the concentrations of the individual

acids decreased during anaerobic degradation of solid waste,

their percentages do not change significantly during the study.

Conclusion

The aim of this study was to investigate the effect of leachate

recirculation and aeration in landfills on the change in VFA

components in leachate samples by using the pretreatment

method demonstrated by Yan and Jen (1992) for chromato-

graphic analysis. VFA concentrations were determined

by acetic, propionic, isobutyric, butyric, isovaleric, valeric,

isocaproic, caproic, and heptanoic acid constituents.

Total VFA concentrations decreased from 33 930 and 38

270 to 500 and 800mg L�1 in A1 and A2 reactors, respec-

tively, after 120 days of operation. The same but slow trend

was observed in anaerobic reactors and VFA concentrations

decreased to 820mg L�1 after 350 days and 786mg L�1 after

450 days for AN1 and AN2 reactors, respectively. As a result

of the acidogenic phase in anaerobic reactors, VFA concen-

trations determined in higher values than that was observed

in aerobic reactors (60 000 to 40 000mg L�1). In the second

part of the study the components of VFA were determined.

Caproic and acetic acids were the major components

and were determined around 12 000 and 10 000mg L�1 for

VF

A c

ompo

nent

(%

)

100

80

60

40

20

00 50 100 150

Time (day)200 250 300

VF

A c

ompo

nent

(%

)

100

80

60

40

20

00 50 100 150

Time (day)200 250 300

VF

A c

ompo

nent

(%

)

100

80

60

40

20

00 100 200 300

Time (day)

400 500 700600

VF

A c

ompo

nent

(%

)

100

80

60

40

20

00 100 200 300

Time (day)

400 500 700600

AceticButyricCaproicIsocaproicPropionicHeptonicIsobutyricValeric




A1 A2

AN2AN1

Figure 8. The change of VFA components in aerobic and anaerobic reactors.




A1 and A2 reactors, respectively. After 120 days, only these

two acids can be determined in aerobic reactors. Acetic acid

concentrations were higher than caproic acid concentrations

at the end of the study, as it is produced from the breakdown

of the propionic acid. According to the VFA measurements,

it can be concluded that leachate recirculation does not affect

the degradation rate in the aerobic landfill system.

In the anaerobic reactors, caproic acid concentrations

were about 30 000mg L�1 at the beginning of the operation.

Propionic, isocaproic and acetic acid concentrations were

between 5000 and 10 000mg L�1 at this period. After 120

days, when the concentrations in the aerobic landfill reactors

decreased to below 1000mg L�1, the concentrations in AN1

reactor were 13 300, 4600, 4000, 2750, and 1250mg L�1 for

caproic, acetic, propionic, isocaproic, and butyric acid,

respectively. There was no considerable change in the AN2

reactor at this time in the VFA concentration measurements.

This situation shows that the degradation was still in the

acidogenic phase in the AN2 reactor. The concentrations

decreased to below 1000mg L�1 after 350 and 450 days for

AN1 and AN2 reactors, respectively, indicating the rapid

degradation of solid waste in aerobic landfills.

This study focused on the determination of the VFA

components in aerobic and anaerobic landfill leachate sam-

ples. The results indicated that the degradation of VFAs

occur rapidly in aerobic landfills.

Funding

This research received no specific grant from any funding agencyin the public, commercial, or not-for-profit sectors.

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