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International Journal of Hydrogen Energy 31 (2006) 12841291

www.elsevier.com/locate/ijhydene

Biohydrogen generation from palm oil mill effluent usinganaerobic contact filter

Krishnan Vijayaraghavan, Desa Ahmad

Department of Biological and Agricultural Engineering, Faculty of Engineering, UPM, 43400 Serdang, Selangor, Malaysia

Available online 14 February 2006

Abstract

In this study treatment of palm oil mill effluent was carried out with the intention to produce hydrogen during the anaerobic

degradation process. The hydrogen generating microflora was isolated from the cow dung based on pH adjustment (pH 5) coupled

with heat treatment (2 h). The microflora was initially tested for its hydrogen generating capability for varying fermentation

pH of 4, 5, 6 and 7 while degrading palm oil mill effluent. The results showed that the biogas generation and its hydrogen

content decreased in the following order of pH 5, 6, 7 and 4. Further treatment of palm oil mill effluent was carried out at an

optimized fermentation pH value of 5, for varying influent COD concentration of 5,000; 10,000; 20,000; 30,000; 40,000 and

59,300 mg/L at a hydraulic retention time of 3; 5 and 7 d, respectively. The average biogas generation was found to be 0.42 L/g

COD destroyed, with a hydrogen content of 57 2% at 7d HRT. The generated biogas was free from methane. As the hydraulic

retention time increased the biogas generation also increased, with a marginal increase in the hydrogen content. For example at

an initial COD concentration of 59,300 mg/L for a hydraulic retention time of 3; 5 and 7 d, the hydrogen generation were found

to be 52.2; 72.4 and 102.6mL respectively. The average volatile fatty acid content in the reactor was found to be in the range

1215 130mg/L when the influent COD concentrations were in the range 20,00059,300mg/L. In the case of influent CODconcentration ranging between 5,000 and 10,000 mg/L, the average volatile fatty acid was found to be 830 90mg/L.

2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Keywords: Palm oil mill effluent; Biohydrogen; Anaerobic digestion; Cow dung; Anaerobic contact filter

1. Introduction

As the reserves of oil and gas are being depleted, se-

curity of energy supply has raised the demand towards

the establishment of hydrogen economy. Sustainablehydrogen energy seems to be a logical conclusion to

numerous environmental problems like acid rain, green

house gases and overcoming the local and transbound-

ary pollutants[1].

Corresponding author. Tel.: +60 6 03 8946 6416;

fax: +60 6 0389466425.

E-mail address: [email protected](K. Vijayaraghavan).

0360-3199/$30.00 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijhydene.2005.12.002

There are many techniques available to harness hy-

drogen from fossil fuel, water and biomass. Among

these hydrogen generation from biomass seemed to be

favored as it takes care of the degradation of the waste

and yield hydrogen as a byproduct. Moreover fermenta-tion reactions are less energy intensive and independent

of light requirement[2,3].

Anaerobic treatment with the intention to generate

hydrogen from wastewater and solid waste has received

considerable attention during the recent years, as the

generated hydrogen and its combustion product are not

green house gases[4]. Various attempts have been made

to generate hydrogen from wastewater like paper mill

[5],municipal solid waste[6,7],starch effluent[8], food
http://www.elsevier.com/locate/ijhydenemailto:[email protected]://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-mailto:[email protected]://www.elsevier.com/locate/ijhydene

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K. Vijayaraghavan, D. Ahmad / International Journal of Hydrogen Energy 31 (2006) 1284 1291 1285

processing[9],domestic waste[10,11],rice winery[12]

dairy waste [13]. Numerous work had been conduced

successfully towards generating hydrogen from sub-

strate like glucose[1418],sucrose[1923].

The major source of wastewater generation from

palm oil mill are namely sterilizer condensate, hydro-cyclone waste and separator sludge[24].On an average

0.91.5 m3 of palm oil mill effluent (POME) is gener-

ated for each ton of crude palm oil produced[25].The

palm oil mill effluent is rich in organic carbon with a

biochemical oxygen demand (BOD) value higher than

20 g/L and nitrogen content around 0.2 and 0.5 g/L as

ammonia nitrogen and total nitrogen [26]. Atif et al.

[27] studied the effect of hydrogen production from

palm oil mill effluent using microflora isolated form

the sludge of an anaerobic pond treating palm oil mill

effluent. The batch experiments showed a total yield of

4708 mL H2/L of POME with a maximum evolutionrate of 454 mL H2/L POME hr.

Microflora isolated for sewage[14,19,2836],tomato

field soil[3]and potatoes/soya field soil demonstrated

hydrogen generating capability[34]. So far much of the

isolated microfloras for hydrogen generation are derived

either from sewage, soil or pure culture.

A new source of microflora was tested for its hy-

drogen generating capability namely cow dung, which

showed a promising sign towards hydrogen generation

using anaerobic agar as substrate. In this article the iso-

lated microflora was tested for its ability to generate hy-drogen from palm oil mill effluent. The efficiency of the

anaerobic process was evaluated based on the amount

of organic matter destroyed, biogas generated and its

hydrogen content for varying influent COD concentra-

tion, pH and hydraulic retention time (HRT).

2. Methods and material

2.1. Anaerobic digester set-up

The experimental set-up of the up-flow anaerobic

contact filter is shown inFig. 1.The reactor unit con-

sists of acrylic column (100 mm ID1200 mm height).

Rigid circular porous plastic balls of 40 mm diameter

served as a packing material. The openings in porous

ball were 3 mm with a cross fluted at every 1/4th of the

ball diameter. The reactor is of complete mixed type.

2.2. Analytical process

The organic strength of the wastewater was deter-

mined by COD. The biodegradability of the wastewa-

ter was measured in terms of BOD5. The total nitro-

gen was determined by Kjeldhal method, whereas the

volatile fatty acid content by distillation method. The

total and volatile solids were determined at 105 C and

550 50 C[37]. The hydrogen and methane content

in the biogas was determined by Drager method[38].

2.3. Preservation of wastewater

The raw palm oil mill effluent was collected from

the collection pit of Golden Hope Plantation, Banting,

Malaysia whose characteristics are shown in Table 1.

The POME was preserved at a temperature less than

4 C but above freezing in order to prevent the waste-

water from undergoing biodegradation due to microbial

action[37].

2.4. Isolation of seed microflora from cow dung

The isolation experiments were carried out by sub-

jecting the cow dung having a solids content of 10%, to

a pH adjustment at 50.1 for a retention period of 3 h.

Thereafter the cow dung was subjected to heat treatment

at 105 C for 2 h. The microflora resulting from isolation

experiments were initially tested for its hydrogen gener-

ating capability for a period of 4 weeks using anaerobic

agar as a substrate. During this period for every 800 mL

of isolated microflora, 6% anaerobic agar was added

as a substrate at a flow rate of 200mL/d. The com-position of the anaerobic agar is presented inTable 2.

The fermentation pH and gaseous constituent namely

hydrogen and methane were analyzed in order to de-

termine the effectiveness of the isolated microflora.

2.5. Start-up

The start-up operation was carried out in two staged

manner consisting of (a) seedling stage: carried out us-

ing isolated microflora from cow dung based on with

pH adjustment coupled with heat treatment, (b) accli-matizing stage: the microflora were acclimatized with

palm oil mill effluent. The anaerobic fermentation was

commenced by charging 100% of the reactor volume

with isolated microflora form cow dung, which was sup-

plemented with 12 g of anaerobic agar medium. The di-

gester content was allowed to remain for a hydraulic

retention time of one week. During the second week

feeding were carried out using palm oil mill effluent

having a COD of 24,000150 mg/L supplemented with

1% glucose and 0.5% anaerobic agar at a hydraulic

retention time of 7 d. The same feed characteristics

were maintained till the end of 3rd week. On the 4th
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13

5

12

100 mm

1

2

3

4

7

6

9

10

11

8

200 mm

310 mm

180 mm

600 mm

1. Feed tank 8. Gas collection zone

2. Feed pump 9. Gas flow meter

3. Inlet line 10. Outlet line

4. Sampling port 11. Packing zone5. Scum breaking pump 12. Sludge accumulation zone6. Recirculation line 13. Bottom sludge wasting line7. Scum breaking line

Fig. 1. Schematic diagram of upflow anaerobic contact filter.

week the reactor was fed with palm oil mill effluent

(24,000150 mg/L) supplemented with 0.5% of glu-

cose. From the 5th week onwards palm oil mill efflu-

ent alone was fed into the anaerobic reactor at a COD

24,000150 mg/L till the end of 10th week.

2.6. Optimization of digestion pH

The treatment of palm oil mill effluent was carried

out at varying digestion pH namely 4, 5, 6 and 7 for

a hydraulic retention time of 5 d. During the anaerobic

digestion process the reactor was monitored with respect

to pH, volatile fatty acids (VFA), biogas generation,

hydrogen content and COD removal.

2.7. Effect of hydraulic retention time on digestion

efficiency

Based on the optimized pH value, the digester

efficiency was tested for varying influent COD con-

centrations of 5,000; 10,000; 20,000; 30,000; 40,000

and 59,300 mg/L for a hydraulic retention time of 3,

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Table 1

Characteristics of raw palm oil mill effluent (POME)

Parametersa Concentration

pH 3.5 0.1

BOD 24,710

COD 59,300Suspended solids 17,260

Total nitrogen 692

Temperature 84 1

aExcept for pH and temperature all other parameters are in mg/L,

temperature in (C).

Table 2

Characteristics of anaerobic agar medium

Parametersa Concentration

pH 5 0.2

Casein enzymic hydrolysate 20

Dextrose 10

Sodium chloride 5

Sodium thioglycollate 2

Sodium formaldehyde sulphoxylate 1

Methylene blue 0.002

Agar 20

aExcept for pH all other parameters are in g/L.

5 and 7 d, respectively. The digester performance was

evaluated with respect to biogas generation, hydrogen

yield and COD reduction.

3. Results and discussion

3.1. Isolation of microflora

The microflora was isolated from cow dung based on

pH adjustment coupled with heat treatment. The rea-

son for adopting pH adjusted coupled with heat treat-

ment is to kill or suppress the methanogenic and non-

sporulating bacteria. Lay et al. [39] stated that heat

shock treatment resulted in enriching sporulating hydro-gen bacteria like Clostridia. Oh et al. [40] investigation

revealed that the heat treated inoculum at pH 6.2 or 7.5

resulted in higher hydrogen production when compared

to inoculum which has been subjected to pH adjusted

alone at 6.2. The viability of the isolated microflora

from cow dung was tested in an anaerobic jar having a

capacity of 1 L at a fermentation pH of 5 0.1. Dur-

ing the fermentation period the substrate (6% anaerobic

agar) addition was kept in continuous mode at a rate of

200 mL/d. The advantage in adopting continuous mode

is that to over come substrate limitation. Cohen et al.

[17]stated that interruption of feed could lead to sporu-

Table 3

Microflora viability test

Fermentation

period (week)

Cumulative biogas

generation (L/week)

Average hydrogen

content (%)

1 2.9 53

2 5.1 543 8.4 54

4 11.8 56

0

1

2

3

4

5

6

7

8

9

10

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 690

10

20

30

40

50

60

70

Days of operation

Cumulative

biogasgenerated(l/d)

Hydrogencontentinbiogas(%)

Biogas (l/d)

Hydrogen (%)

Fig. 2. Experimental set-up of anaerobic digester.

lation.Table 3shows the cumulative biogas generation

and its hydrogen content during the fermentation period

of the microflora viability test. The biogas generationshowed a gradual rise with the fermentation period but

the hydrogen content showed a marginal rise. For ex-

ample during the end of 2nd and 4th week the cumula-

tive biogas generation was 5.1 and 11.8 L/week, while

its hydrogen content were 54 and 56%, respectively.

In this present study microflora isolated from cow

dung based on pH adjustment coupled with heat treat-

ment resulted in a biogas free from methane. Hence it

can be concluded that the methanogenic and non sporu-

lating bacteria are either killed or suppressed during

isolation. Further experiments were carried out in the

anaerobic contact filter using the isolated microflora.

3.2. Start-up

Fig. 2shows the cumulative biogas generation and its

hydrogen content during the start-up period. During the

initial period of acclimatization the biogas generation

showed a gradual rise till the 5th week, thereafter a

drop in biogas generation was noticed from the early of

6th week to mid of 8th week. The reason for this type

of behavior could be that, till the 4th week the palm

oil mill effluent was supplemented with glucose and

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0

10

20

30

40

50

60

70

80

3 5 7pH

CODrem

oval(%)

10,000

59,300

HRT: 5 d

Influent COD (mg/l)

4 6 8

Fig. 3. COD removal versus fermentation pH.

thereafter its addition was stopped leading to this type ofbiogas generation pattern. Glucose being a simple sugar

is preferred by the microflora, whereas the palm oil mill

effluent is a complex substance that needs sufficient

time for the degradation to occur. On the mid of 8th

week onwards a gradual rise in biogas generation pattern

was observed. This clearly shows that the microbes are

adapted to degrade the palm oil mill effluent. On the 9th

and 10th week of start-up period the biogas generation

were almost consistent. Hence it can be concluded that

the reactor is in stable operating condition. Moreover

the hydrogen content of biogas was 52

3% during the3rd to 5th week, thereafter it ranged between 57 2%

till the end of 10th week.

3.3. Effect of pH on hydrogen generation from palm

oil mill effluent

The effect of pH on the degradation of palm oil mill

effluent for a HRT of 5 d is shown inFig. 3. The anaer-

obic digestion was carried out for varying initial pH of

4, 5, 6, and 7, respectively, for an influent COD concen-

tration of 10,000 and 59,300 mg/L. At pH 4, irrespec-tive of the initial COD concentration the COD removal

percent was found to be lowest when compared to other

operating pH namely 5, 6 and 7. A maximum COD re-

moval occurred when the digester was operated at pH 5.

The digester showed COD removal efficiency in the de-

creasing order of pH 5, 6, 7 and 4, respectively. For an

initial COD concentration of 10,000 mg/L at a digestion

pH of 4, 5, 6 and 7, the COD removal efficiencies were

found to be 36, 67, 62 and 59%, respectively. In the

case of an influent COD concentration of 59,300 mg/L

at pH 4, 5, 6 and 7, the corresponding COD removals

were found to be 15, 29, 25 and 22%, respectively. The

0

10

20

30

40

50

60

70

80

3 5 7pH

10,000

59,300

Influent COD (mg/l)

HRT: 5 d

Cumulativebiogasgenerated(l)

4 6 8

Fig. 4. Cumulative biogas generation versus fermentation pH.

0

10

20

30

40

50

60

3 6pH

10,000

59,300

Hydrogencontent(%)

4 5 7 8

Influent COD(mg/l)

HRT: 5 d

Fig. 5. Hydrogen content versus fermentation pH.

possible reason for low COD removal efficiency at pH

4 could be due to the change in metabolic reaction re-

sulting in shift in intermediate production pathway from

acid production phase to solvent production phase as

stated by Khanal et al.[41]and Byung and Zeikus[42].

Figs. 4and5show the cumulative biogas generation

and its corresponding hydrogen content during varying

digestion pH of 4, 5, 6 and 7, respectively. The cumu-lative biogas generation and its hydrogen content var-

ied depending on the digestion pH for a given organic

strength. As shown in Fig. 4 for an influent COD of

59,300mg/L of palm oil mill effluent at 5 d HRT for

a digestion pH of 4, 5, 6 and 7, the cumulative bio-

gas generation were found to be 42, 73, 69 and 60 L

respectively. Whereas the corresponding hydrogen con-

tents for the above said condition were found to be 31,

56, 53 and 51%, respectively, as shown inFig. 5. At pH

5 the biogas generation and its hydrogen content was

high, while at pH 6 and 7 there was a marginal drop.

Irrespective of digestion pH the biogas was free from

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0

10

20

30

40

50

60

70

80

0 10000 20000 30000 40000 50000 60000 70000

3

5

7

Influent COD (mg/l)

CODrem

oval(%)

HRT (d)

Fig. 6. COD removal versus varying influent COD concentration.

methane content. Earlier research have stated that themaximum hydrogen generation occurred at a pH of 6.2

[40]and 5.56.0[36,41].

3.4. Treatment of palm oil mill effluent based on the

optimized pH value

A pH value of 5 was found to be the optimum towards

hydrogen generation from the palm oil mill effluent.

Based on the optimized pH value the treatment of palm

oil mill effluent was carried out at varying influent COD

concentrations of 5,000; 10,000; 20,000; 30,000; 40,000and 59,300 mg/L for different hydraulic retention time

of 3, 5 and 7 d, respectively. Fig. 6 shows the COD

removal percent versus influent COD concentration for

an HRT of 3, 5 and 7 d. In the case of 3, 5 and 7 d HRT,

for an influent COD concentration above 20,000 mg/L

the COD removal efficiency decreased with the increase

in the influent COD concentration. However, as the HRT

increased the COD removal also increased. For example

at an influent COD concentration of 20,000 mg/L for a

HRT of 3, 5 and 7 d, the COD removal were found to

be 48, 66 and 73%, respectively.Fig. 7 shows the cumulative biogas generation ver-

sus influent COD concentration. The biogas generation

showed an increasing trend with the rise in hydraulic re-

tention time. For example above an influent COD con-

centration of 20,000 mg/L the biogas generation low-

ered with the increase in influent COD concentration.

Whereas as the hydraulic retention time increased the

biogas generation also increased. The possible reason

for low biogas generation at 3 d HRT could be due to

the accumulation of intermediate products. As the HRT

increased to 5 and 7 d a higher percentage of metabolic

reaction could have reached the end point resulting in a

0

20

40

60

80

100

120

0 10000 20000 30000 40000 50000 60000 70000

3

5

7

Influent COD (mg/l)

Cumulativebiog

asgenerated(L) HRT (d)

Fig. 7. Cumulative biogas generation versus influent COD.

0

10

20

30

40

50

60

70

80

90

100

0 10000 20000 30000 40000 50000 60000 70000

3

5

7

Hydrogencontentinbiogas(%)

HRT (d)

Influent COD (mg/l)

Fig. 8. Hydrogen content versus influent COD.

higher gaseous end product.Fig. 8shows the hydrogen

content of the biogas for varying hydraulic retention and

influent COD concentrations. Even though the biogas

generation (Fig. 7) increased with the increase in hy-

draulic retention time the corresponding hydrogen con-

tent (Fig. 8) showed a marginal rise. For example at an

influent COD concentration of 20,000 mg/L for a HRTof 3, 5 and 7 d, the biogas generation were found to be

45.2, 56.3 and 63.9 L, whereas the corresponding hydro-

gen content were 53, 55 and 56%, respectively. In the

case of influent COD concentration of 59,300 mg/L for

a HRT of 3, 5 and 7 d, the biogas generation were found

to be 52.2; 72.4 and 102.6 L, whereas the corresponding

hydrogen content were 56, 57 and 59%, respectively. In

hydrogen content in the biogas did not show any vari-

ation as the influent COD concentration was increased.

Hence it can be concluded that the metabolic reaction

of the hydrogen generating bacterial species occurs in

a steady phase.
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0

200

400

600

800

1000

1200

1400

1600

0 10000 20000 30000 40000 50000 60000 70000

3

5

7

Volatilefattyacids(mg/l)

Influent COD (mg/l)

HRT (d)

Fig. 9. Volatile fatty acid content versus influent COD.

The volatile fatty acid content versus influent COD

concentration for varying hydraulic retention time is

shown in Fig. 9. At an influent COD concentration

ranging between 5,000 and 10,000 mg/L the VFA con-

tent ranged between 830 90mg/L as acetate. In the

case of influent COD concentration ranging between

20,000 and 59,300 mg/L the VFA content ranged be-

tween 1215130 mg/L as acetate. Irrespective of influ-

ent COD concentration the volatile fatty acids showed

an increasing trend as the hydraulic retention time in-

creased. Lay et al. [39]stated that high solid organic

waste such as egg, lean meat, fat meat, chicken skin,

potato and rice yielded a VFA content of 18; 35; 4; 11;23 and 5 g/L as acetate at 6.25 d HRT, when heat shock

digested sludge from pig manure was used as a seeding

material. Horiuchi et al.[43]stated an average volatile

fatty content of 3500 mg/L during the anaerobic acido-

genesis at pH 5. While Chang et al. [23]stated a VFA

value ranging between 11,083 and 13,693 mg COD/L at

an HRT of 4 to 24 h, while treating synthetic substrate

in UASB reactor.

4. Conclusion

The microflora isolated from cow dung based on pH

adjustment coupled with heat treatment proved to be

promising candidate towards hydrogen generation. The

isolation experiments were carried out by subjecting the

cow dung to an initial pH of 5 for 3 h, followed by heat

treatment at 105 C for 2 h. As pH play a vital role to-

wards the metabolic reaction, optimization of pH were

carried out by conducting the experiments at different

fermentation pH namely 4; 5; 6 and 7, respectively. At

pH 5 maximum COD removal, biogas generation and

hydrogen content were observed while treating palm oil

mill effluent. Based on the optimized pH value, treat-

ment of palm oil mill effluent was carried out using vary-

ing influent COD concentrations namely 5000; 10,000;

20,000; 30,000; 40,000 and 59,300 mg/L for a hydraulic

retention time of 3, 5 and 7 d, respectively. For the above

said influent COD concentration at a hydraulic retentiontime of 7 d, the COD removal efficiencies were 64; 70;

73; 52; 44 and 40%, respectively. The average volatile

fatty acid content in the reactor was found to be in the

range of 1215130 mg/L when the influent COD con-

centration was in the range of 20,00059,300 mg/L. In

the case of influent COD concentration ranging between

5,000 and 10,000 mg/L the average volatile fatty acid

was found to be 830 90mg/L, respectively.

Acknowledgements

This research was supported by the Fundamental

Research Grant of Universiti Putra Malaysia, Project

Number: 02-03-03-057J/55180.

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