holistic pome

Biotechnology Advances 27 (2009) 40–52

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Research review paper

A holistic approach to managing palm oil mill effluent (POME): Biotechnologicaladvances in the sustainable reuse of POME

Ta Yeong Wu, Abdul Wahab Mohammad ⁎, Jamaliah Md. Jahim, Nurina AnuarScale-up and Downstream Processing Research Group, Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan,Malaysia

⁎ Corresponding author.E-mail addresses: [email protected] (T.Y. Wu), w

(N. Anuar).

0734-9750/$ – see front matter © 2008 Elsevier Inc. Aldoi:10.1016/j.biotechadv.2008.08.005

a b s t r a c t
a r t i c l e i n f o
Article history:
During the last century, a gr Received 24 December 2007Received in revised form 19 August 2008Accepted 21 August 2008Available online 27 August 2008
Keywords:Cleaner productionPalm oil mill effluent (POME)Waste reusabilityFermentation substrateFertilizerAnimal feeds

eat deal of research and development as well as applications has been devoted towaste. These include waste minimization and treatment, the environmental assessment of waste,minimization of environmental impact, life cycle assessment and others. The major reason for such hugeefforts is that waste generation constitutes one of the major environmental problems where productionindustries are concerned. Until now, an increasing pressure has been put on finding methods of reusingwaste, for instance through cleaner production, thus mirroring rapid changes in environmental policies. Thepalm oil industry is one of the leading industries in Malaysia with a yearly production of more than13 million tons of crude palm oil and plantations covering 11% of the Malaysian land area. However, theproduction of such amounts of crude palm oil result in even larger amounts of palm oil mill effluent (POME),estimated at nearly three times the quantity of crude palm oil. Normally, POME is treated using end-of-pipeprocesses, but it is worth considering the potential value of POME prior to its treatment through introductionof a cleaner production. It is envisaged that POME can be sustainably reused as a fermentation substrate inthe production of various metabolites, fertilizers and animal feeds through biotechnological advances. Thepresent paper thus discusses various technically feasible and economically beneficial means of transformingthe POME into low or preferably high value added products.

© 2008 Elsevier Inc. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411.1. A brief glance at palm oil mill effluent (POME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411.2. Cleaner production as a sustainable strategy for POME management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

2. POME as a reusable product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423. Biotechnological advances in the sustainable reuse of POME. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.1. Sustainable reuse of POME as fermentation media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.1.1. Antibiotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.1.2. Bioinsecticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.1.3. Solvents (acetone–butanol–ethanol: ABE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453.1.4. Polyhydroxyalkanoates (PHA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.1.5. Organic acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463.1.6. Enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.1.7. Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

3.2. Sustainable reuse of POME as fertilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 483.3. Sustainable reuse of POME as live food for animals and aquacultural organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

[email protected], [email protected] (A.W. Mohammad), [email protected] (J.M. Jahim), [email protected]

l rights reserved.

mailto:wahabm@vlsi.�eng.ukm.my

http://dx.doi.org/10.1016/j.biotechadv.2008.08.005

http://www.sciencedirect.com/science/journal/07349750

Fig. 1. The 5 R policy (Olguín et al., 2004).

41T.Y. Wu et al. / Biotechnology Advances 27 (2009) 40–52

1. Introduction

1.1. A brief glance at palm oil mill effluent (POME)

The Malaysian palm oil industry has grown rapidly over the yearsandMalaysia has become the world's largest producer and exporter ofpalm oil and its products. In 2003, more than 3.79 million hectares ofland were under oil palm cultivation, occupying more than one-thirdof the total cultivated area in Malaysia and 11% of the total land area(Yusoff and Hansen, 2007). In total, the palm oil industry contributessignificantly towards the country's foreign exchange earnings and theincreased standard living among Malaysians.

In general, the palm oil milling process can be categorized into a dryand a wet (standard) process. The wet process of palm oil milling is themost common and typical way of extracting palm oil, especially inMalaysia. It is estimated that for each ton of crude palm oil that isproduced, 5–7.5 t of water are required, andmore than 50% of this waterendsupaspalmoilmill effluent (POME) (Ahmadet al., 2003). RawPOMEis a colloidal suspension containing95–96%water, 0.6–0.7% oil and 4–5%total solids. Included in the total solids are 2–4% suspended solids,whichare mainly constituted of debris from palm fruit mesocarp generatedfrom three main sources, i.e. sterilizer condensate, separator sludge andhydrocyclone wastewater (Borja and Banks, 1994; Khalid and WanMustafa, 1992; Ma, 2000). If the untreated effluent is discharged intowatercourses, it is certain to cause considerable environmentalproblems (Davis and Reilly, 1980) due to its high biochemical oxygendemand (25,000 mg/l), chemical oxygen demand (53,630 mg/l), oil andgrease (8370 mg/l), total solids (43,635 mg/l) and suspended solids(19,020mg/l) (Ma,1995). The palm oilmill industry inMalaysia has thusbeen identified as the one discharging the largest pollution load into therivers throughout the country (Hwang et al., 1978).

Ponding system is themost conventional method for treating POME(Ma and Ong, 1985; Khalid andWanMustafa,1992) but other processessuch as aerobic and anaerobic digestions, physicochemical treatmentsandmembrane filtrationmay also provide the palm oil industrieswith apossible insight into the improvement of current POME treatmentprocess. However, the treatment that is based mainly on biologicaltreatments of anaerobic and aerobic systems, is quite inefficient to treatPOME, which unfortunately leads to environmental pollution issues(Ahmad et al., 2005). This is because the high BOD loading and lowpHofPOME, togetherwith the colloidal nature of the suspended solids, render

Table 1The approximate composition (%) of major constituents, amino acids, fatty acids and miner

Major constituents Composition (%) Amino acids Composition (%) Fatty acids

Moisture 6.99 Aspartic acid 9.66 Caprylic acCrude protein 12.75 Glutamic acid 10.88 Capric acidCrude lipid 10.21 Serine 6.86 Lauric acidAsh 14.88 Glycine 9.43 Myristic acCarbohydrate 29.55 Histidine 1.43 PentadecanNitrogen-free extract 26.39 Arginine 4.25 Palmitic acTotal carotene 0.019 Threonine 2.58 HeptadecanTotal 100.789 Alanine 7.70 10-Heptade

Proline 4.57 Stearic acidTyrosine 3.16 Oleic acid (Phenylalanine 3.20 Linoleic aciValine 3.56 Linolenic acMethionine 6.88 ϒ-linolenicCystine 3.37 Arachidic aIsoleucine 4.53 EicosatrienLeucine 4.86 EicosatetraLysine 2.66 EicosapentaTryptophan 1.26 TotalTotal 90.84

treatments by conventional methods difficult (Olie and Tjeng, 1972;Stanton, 1974). A detailed cost calculation for Indonesia has also shownthat the conventional system of POME treatment, such as the pondingsystem, is not only the systemwith the highest environmental pollutionand the lowest utilization of renewable resources, but also the systemgiving rise to the lowest profit (Schuchardt et al., 2005).

1.2. Cleaner production as a sustainable strategy for POME management

Currently, end-of-pipe standards imposed through “command andcontrol regulations” are the basis of environmental legislation (Olguínet al., 2004). However, an international trend promoting pollutionprevention through cleaner production, which is based on the 5 Rpolicy (Fig. 1); namely reduction, replacement, reuse, recovery andrecycling, is emerging. Within this context, it is proposed herewiththat a wastewater management based on the promotion of cleanerproduction and environmentally sound biotechnologies could be

als in raw POME (adapted from Habib et al., 1997)

Composition (%) Minerals Composition (μg/g dry weight)

id (8:0) 2.37 Fe 11.08(10:0) 4.29 Zn 17.58(12:0) 3.22 P 14377.38id (14:0) 12.66 Na 94.57oic acid (15:0) 2.21 Mg 911.95id (16:0) 22.45 Mn 38.81oic acid (17:0) 1.39 K 8951.55canoic acid (17:1) 1.12 Ca 1650.09(18:0) 10.41 Co 2.4018:1n−9) 14.54 Cr 4.02d (18:2n−6) 9.53 Cu 10.76id (18:3n−3) 4.72 Ni 1.31acid (18:3n−6) 0 S 13.32cid (20:0) 3.56 Se 12.32oic acid (20:3n−6) 2.04 Si 10.50enoic acid (20:4n−6) 1.12 Sn 2.30enoic acid (20:5n−3) 0.36 Al 16.60

95.99 B 7.60Mo 6.45As 9.09V 0.12Pb 5.15Cd 0.44

Fig. 3. Absorption curves for the rod-like particles after treatment with phenol/sulphuric acid and for a number of other simple sugars (Ho and Tan, 1983).

42 T.Y. Wu et al. / Biotechnology Advances 27 (2009) 40–52

included as a part of the POME management in Malaysia in order toattain a sustainable development. Such a strategy could takeadvantage of the current international interest in promoting cleanerproduction as the driving force of a new and sustainable industrialdevelopment style. This review paper thus describes various techni-cally feasible means of transforming the POME into different added-value products through cleaner production and environmentallysound biotechnologies for enabling the balance between environ-mental protection and a sustainable reuse of bioresources found in thePOME.

2. POME as a reusable product

The high compositions and concentrations of carbohydrate,protein, nitrogenous compounds, lipids and minerals in POME(Hwang et al., 1978; Phang, 1990; Habib et al., 1997) render it possibleto reuse the effluent for biotechnological means (Table 1). Chemicalanalysis indicates that the rod-like particle fraction (Fig. 2) available inthe POME corresponds to carbohydrate in nature. After treatmentwith phenol/sulfuric acid, the fraction shows a maximum absorptionat approximately 480 nm (Fig. 3), indicating the possible presence ofpentose, a building unit for insoluble carbohydrates (Ho and Tan,1983). The presence of pentose in POME has been reported previously(Hwang et al., 1978) and its most likely sources are the cell walls.Water-soluble carbohydrates, in terms of glucose, reducing sugars andpectin, are also found to be present in the soluble fraction of POME.However, the low concentrations of total soluble carbohydrate(0.390 g/100 ml POME) may restrict the usefulness of the solublefraction of POME as a possible feedstock for substrate conversion viadirect single-cell protein production (Ho et al., 1984). Preliminaryinvestigations on enzymatically hydrolyzed substrates from POMEhave indeed demonstrated the possibility of such substrates support-ing the growth of Candida tropicalis (Wang et al., 1981). On the otherhand, Barker and Worgan (1981) noted that unhydrolyzed POME

Fig. 2. Centrifugal fractionation o

could support good growth of Aspergillus oryzae in the presence of anadded inorganic nitrogen source. Their results also revealed thatcelluloses, polyphenols and nitrogenous compounds were the leastbiodegradable of the substrate constituents. This lends furthersupport to the view that a proper hydrolysis step is essential inobtaining an optimal level of readily biodegradable sugars from theplant cell materials for a meaningful microbial bioconversion.

f POME (Ho and Tan, 1983).

Table 2Various products or metabolites produced in bioprocesses during the reuse of POME or its derivatives as substrates

Product Microorganism Fermentation medium based on POME Fermentation conditions Fermentation timea

(h)Maximum production Reference

Penicillin Penicillium chrysogenumFR2284

50% (v/v) concentrated POME+KH2PO4+(NH4)2SO4

300 rpm, 30 °C, 2% (v/v) inoculum, flaskfermentation

72 ≈602 U/ml Suwandi (1991)

Penicillin Penicillium chrysogenumFR2284

50% (v/v) concentrated POME+KH2PO4+(NH4)2SO4+NH4 lactate

300 rpm, 30 °C, 2% (v/v) inoculum,flask fermentation

72 ≈715 U/ml Suwandi (1991)

Bioinsecticide Bacillus thuringiensis H-14 Raw POME 150 rpm, 30 °C, initial pH=6.9, flaskfermentation

72 7.0×103 spores/ml Suwandi (1991)

Bioinsecticide Bacillus thuringiensis H-14 1% (w/v) concentrated POME in powderform

150 rpm, 30 °C, initial pH=6.9, flaskfermentation

72 2.0×108 spores/ml Suwandi (1991)

ABE Clostridium saccharoperbutylacetonicumN1-4 (ATCC 13564)

Separator sludge 30 °C, 10% (v/v) inoculum, initial pH=5.8, flaskfermentation

Not clearly stated A=0.45 g/l, B=2.47 g/l,E=0.49 g/l

Mun et al. (1995)

ABE Clostridium saccharoperbutylacetonicumN1-4 (ATCC 13564)

Sterilized condensate 30 °C, 10% (v/v) inoculum, initial pH=5.8, flaskfermentation

Not clearly stated A=0.33 g/l, B=2.30 g/l,E=0.43 g/l

Mun et al. (1995)

ABE Clostridium aurantibutyricumATCC 17777

Model medium for raw POME 200 rpm, 37 °C, 10% (v/v) inoculum, pH wasswitched from 6.2 to 5.5 at 9 h, 2 g/l/h glucosefeeding started at 10 h, bioreactor fermentation

≈35 (for A) ≈45 (forB)

A=5.78 g/l, B=6.78 g/l Somrutai et al.(1996)

ABE Clostridium acetobutylicumNCIMB 13357

90% (v/v) particulate fraction of rawPOME

35 °C, 10% (v/v) inoculum, initial pH=5.8, flaskfermentation

48 (for ABE) A=1.97 g/l, B=1.74 g/l,E=0.3 g/l

Kalil et al. (2003),Pang et al. (2004)

ABE Immobilized ClostridiumsaccharoperbutylacetonicumN1-4

Raw POME Not clearly stated 36 (for ABE) ABE=3.8 g/l Kalil et al. (2003)


Particulate fraction of raw POME 35 °C, 10% (v/v) inoculum, initial pH=6, flaskfermentation

≈30 (for A) ≈24 (forE)

A=1.2 g/l, B=0 g/l,E=0.5 g/l

Takriff et al. (2005)


Particulate fraction of raw POME Oscillated at 0.45 Hz, 35 °C, 10% (v/v) inoculum,initial pH=6, oscillatory flow bioreactorfermentation

≈42 (for A) ≈30 (forE)

A=0.7 g/l, B=0 g/l,E=0.6 g/l

Takriff et al. (2005)


Particulate fraction of raw POME Oscillated at 0.78 Hz, 35 °C, 10% (v/v)inoculum, initial pH=5.8, oscillatory flowbioreactor fermentation

48 (for ABE) A=0.05 g/l, B=1.54 g/l,E=0 g/l

Masngut et al.(2006, 2007)


Particulate fraction of raw POME 250 rpm, 35 °C, 10% (v/v) inoculum,initial pH=5.8, stirred tank bioreactorfermentation

60 (for ABE) A=0.13 g/l, B=0.50 g/l,E=0.24 g/l

Masngut et al. (2007)

PHA Rhodobacter sphaeroidesIFO 12203

Synthetic waste based on organicacids profiles obtained during POMEtreatment

30 °C, pH was controlled at 7, photobioreactorfermentation

≈200 ≈4 g/l Hassan et al. (1996)

PHA Rhodobacter sphaeroidesIFO 12203

Anaerobically digested POME 30 °C, pH was controlled at 7, photobioreactorfermentation

Dilution rate=0.024d−1

N2 g/l Hassan et al. (1997b)

PHA Alcaligenes eutrophus H16(ATCC 17699)

Standard medium with feeding ofacetic acid obtained fromanaerobically digested POME

400 rpm with an aeration rate of 0.75 l/min,30 °C, pH was controlled at 7, stirred tankbioreactor fermentation

17 1.8 g/l Hassan et al. (1997c)

PHA Ralstonia eutrophaATCC 17699

Concentrated organic acids from the anaerobically digestedPOME (100 g/l of total acids with acetic:propionic=3:1)

400 rpm with an aeration rate of 0.75 l/min,30 °C, pH was controlled at 7, bioreactorfermentation

≈65 ≈6.25 g/l Hassan et al. (2002)

PHA Mixed cultures High concentration of POME with490 COD/N ratio (g COD/g N) and160 COD/P ratio (g COD/g P)

1,000 rpm with an aeration rate of 1.5 l/min,30 °C, pH was controlled at 7, sequencing batchreactorfermentation

Not clearly stated 24.24 g/l Md Din et al. (2006b)

Organic acids Mixed cultures POME+palm oil sludge 30 °C, pH was controlled at 7, bioreactorfermentation

24 7.8 g/l Hassan et al. (1996)

Organic acids Mixed cultures POME+palm oil sludge in the ratio of 1:1 300 rpm, 30 °C, pH was controlled at 5,stirred tank bioreactor fermentation

84 10–14 g/l Yee et al. (2003)

Citric acid Aspergillus (A103) 1% (w/w) POME+2% (w/w) wheat flour 150 rpm, 27–30 °C, initial pH=3, inoculum sizeof 2% (106 spores/ml), flask fermentation

48 0.28 g/l Jamal et al. (2005)

Citric acid Aspergillus niger (A103) 2% (w/w) POME+4% (w/w)wheat flour+4% (w/w) glucose with noadded ammonium nitrate (optimized medium)

150 rpm, 32 °C, initial pH=5, inoculum size of2% (106 spores/ml),flask fermentation

168 5.2 g/l Alam et al. (2008)

Itaconic acid Aspergillus terreus IMI 282743 Retentate of POME 300 rpm, 35 °C, 5% (v/v) inoculum, flaskfermentation

120 0.079 g/l Wu et al. (2005)

(continued on next page)

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Table 2 (continued)

Product Microorganism Fermentation medium based on POME Fermentation conditions Fermentation timea

(h)Maximum production Reference

Cellulase(CMCase)

Aspergillus niger ATCC 6275 POME with added nutrients+0.6 g/l NH4NO3

200 rpm, room temperature, inoculum size was7.5×105

spores/ml, flask fermentation

72 1.09 U/ml Prasertsan et al.(1997)

Cellulase(CMCase)

Aspergillus niger 50% (v/v) raw POME 300 rpm with an aeration rate of 4 l/min, 30 °C,10% (v/v) inoculum, bioreactor fermentation

51 1.040 U/ml Mashitah et al.(2002)

Cellulase(CMCase)

Trichoderma harzianum 50% (v/v) raw POME 300 rpm with an aeration rate of 4 l/min, 30 °C,10% (v/v) inoculum, bioreactor fermentation


Cellulase(CMCase)

Mixed culture (1:1) of Aspergillusniger and Trichoderma harzianum

50% (v/v) raw POME 300 rpm with an aeration rate of 4 l/min, 30 °C,10% (v/v) inoculum, bioreactor fermentation


Cellulase(CMCase)

Myceliophthora thermophila 50% (v/v) raw POME 300 rpm with an aeration rate of 4 l/min, 45 °C,10% (v/v) inoculum, initial pH 5.5 wasuncontrolled until 6.0, bioreactorfermentation


Cellulase(FPase)

Trichoderma harzianum 2% (w/v) particulate fraction ofPOME+3% (w/v) wheat flour

250 rpm, 30 °C, 3% (v/v) inoculum,initial pH=4, flask fermentation

96 13.44 U/ml Alam et al. (2006a)

Cellulase(FPase)

Penicillium (P1-EFB) 1% (w/w) POME sludge Not clearly stated 144 33 U/ml Chowdhury et al.(2006)

Cellulase Isolate SO1 10% (v/v) supernatant of POME+anothernine different types of supporting nutrients


48 12.11 U/ml Laohaprapanon et al.(2007)

Ligninperoxidase

Phanerochaete chrysosporium 2% particulate fraction of POME+1%wheat flour


96 3.373 U/ml Alam et al. (2006b)

Ligninperoxidase

Penicillium (P1-EFB) 1% (w/w) POME sludge Not clearly stated 144 5.038 U/ml Chowdhury et al.(2006)

Lipase Clostridium aurantibutyricumATCC 17777

Model medium for raw POME 200 rpm, 37 °C, 10% (v/v) inoculum, constantpH at 6.8,bioreactor fermentation

≈20 0.4 U/ml Somrutai et al.(1996)

Xylanase Aspergillus niger ATCC 6275 POME with added nutrients+0.6 g/l NH4NO3

200 rpm, room temperature, inoculum sizewas 7.5 x 105

spores/ml, flask fermentation

96 22.77 U/ml Prasertsan et al.(1997)

Xylanase Aspergillus terreus SUK-1 Raw POME Aeration rate of 2.5 l/min, 30 °C, 10% (v/v)inoculum, bioreactor fermentation

96 0.448 U/ml Cheng (2006)

Xylanase Isolate SO1 10% (v/v) supernatant of POME+another nine different types of supportingnutrients


96 50.98 U/ml Laohaprapanon et al.(2007)

Protease Aspergillus terreus IMI 282743 75% (v/v) retentate of POME 250 rpm, 37 °C, 5% (v/v) inoculum, flaskfermentation

96 129 U/ml Wu et al. (2006a)

Hydrogen Mixed culture from POME sludge 1% glucose+0.2% yeast extract+0.018%magnesium chloride hexahydrate+0.5%(w/v) POME sludge

60 °C, pH was uncontrolled, bioreactorfermentation

Not clearly stated 23.82 mmol H2/(1-medium)

Morimoto et al.(2004)

Hydrogen Mixed culture from POME sludge Raw POME+2.5% (w/v) POME sludge 200 rpm, 60 °C, pH was controlled at 5.5,bioreactor fermentation

38 4,708 ml H2/(l-medium) Atif et al. (2005)

Hydrogen Mixed culture(isolated from cow dung)

Raw POME pH was controlled at 5, anaerobic contactfilter fermentation

168 0.42 l biogas/gCODdestroyed

with 57% hydrogencontent

Vijayaraghavanand Ahmad (2006)

Hydrogen Thermophilic microflora Raw POME 200 rpm, 60 °C, pH was controlled at 5.5,anaerobic sequencing batch reactorfermentation

At steady state(during day 22–28)

4.4 l H2/(1-medium)per day

O-Thong et al. (2007)

Hydrogen Thermophilic microflora Raw POME+Fe2++peptone+Na2HPO4·2H2O

200 rpm, 60 °C, pH was controlled at 5.5,anaerobic sequencing batch reactorfermentation

At steady state(during day 22–28)

6.1 l H2/(1-medium)per day

O-Thong et al. (2007)

Hydrogen Thermoanaerobacterium-richsludge

Raw POME+257 mg Fe2+/l+aC/N ratio of 74+aC/P ratio of 559+0.3 g NaHCO3

(optimized medium)

60 °C, initial pH=5.5, 10 ml seed sludgeinoculum, serum bottle fermentation

48 6.33 H2/(1-medium) O-Thong et al.(2008a)

A = Acetone, B = Butanol, E = Ethanol.PHA = Polyhydroxyalkanoates.

a The fermentation time is the time required to reach a maximum product concentration.

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Nitrogen is originally present inPOME in the formoforganic (protein)nitrogen and as time progresses the organic nitrogen is graduallyconverted to ammoniacal nitrogenwith amolecular weight of 17–35 kg/kmol (Chow,1991). According to Ho and Tan (1988), the nutrient balancein terms of the average ratio of BOD:N:P for raw POME is 100:4:0.3.Muhrizal et al. (2006) reported that POME is characterized by a low C:Nratio (C:NPOME=6.54) as compared to sawdust (C:Nsawdust=185.74),purun (C:Npurun=88.32) and peat (C:Npeat=50.31). The amino acids ofPOME and their approximate compositions (%) are shown in Table 1. Themajor portion of proteins in POME is tightly associatedwith its insolublepart (Hoet al.,1984). Thismayperhaps account for the lowdigestibilityofproteins in POME found by Devendra et al. (1981).

Only N, P, K, Mg and Ca are consistently present in relatively largeamounts in the POME (Ho et al.,1984; Habib et al.,1997;Muhrizal et al.,2006) (Table 1). Muhrizal et al. (2006) also reported that POME has ahigh content of Al as compared to chicken manure and compostedsawdust. It would thus seem that the probable usefulness of POME asfertilizer or animal feed substitute, in terms of providing sufficientmineral requirements, depends mainly on the soluble fraction ofPOME. Toxicmetals, such as Pb, can also be found in POME (Habib et al.,1997) but their concentrations are usually below sublethal levels(N17.5 μg/g) (James et al., 1996). POME is thus not toxic for plants andanimals. Pb is found in POME due to contamination from plastic andmetal pipes, tanks and containers where Pb is widely employed inpaints and glazing materials (James et al., 1996).

The reusability of POME especially as animal feed is arguablebecause another important factor that needs to be taken intoconsideration is its lignin content. Lignin is a recalcitrant, water-insoluble organic chemical (Palm and Rowland, 1997). A high contentof lignin in organic materials is known to slow down their decom-position (Klepper et al., 1990; Tian et al., 1992). High lignin contents(0.412 g/100 ml POME) also present major barriers with regard todigestion of roughage by-product feeds from field and tree crops byboth ruminants and non-ruminants (Ho et al.,1984). Lignin is known tobe highly resistant to chemical degradation thus giving rise to its lowdigestibility. This has been clearly illustrated by the work of Devendraet al. (1981) on the use of POME, in both raw and dehydrated forms, asanimal feed. Therefore, to allow the POME to be reused effectively asanimal feed, Webb et al. (1975) have suggested that effluent productscan be nutritionally improved by reducing the ash and fiber content aswell as increasing the protein content on par with imported feedmeal.

The composition of raw POME with regard to saturated andunsaturated fatty acids other than polyunsaturated fatty acids isshown in Table 1. Here, myristic acid, palmitic acid, stearic acid andoleic acid are present in compositions higher than other saturatedfatty acids. The 20 carbon chained polyunsaturated fatty acids such aseicosatrienoic acid (20:3n−6), eicosatetraenoic acid (20:4n−6) andeicosapentaenoic acid (20:5n−3), which are available in raw POME, areessential for the proper development ofmarine fish, shrimp larvae andfry (Oka et al., 1982). According to Habib et al. (1997), these substanceshave been accumulated and synthesized in higher amounts forchironomid larvae grown in POME than those grown in algal culture.

3. Biotechnological advances in the sustainable reuse of POME

Chemical analyses of POME with respect to its proximate composi-tion have been carried out (Wood, 1977; Hwang et al., 1978; Ho et al.,1984;Habib et al.,1997), and theseanalyses areof vital importance in theunderstanding of the properties of POME in relation to formulatingwaste-utilization programs and efficient wastewater managementprocesses. This is particularly true in view of the increasing emphasisplaced on the zero discharge concept and innovative technology forsustainable development. An important case is the production of biogasand othermetabolites by fermentation processes. Of no less importanceis thepossibilityof recoveringbioresources fromPOME, or its conversioninto useful substitutes for animal feed and fertilizer.

3.1. Sustainable reuse of POME as fermentation media

The possibility of reusing POME as fermentation media is largelydue to the fact that POME contains high concentrations of carbohy-drate, protein, nitrogenous compounds, lipids and minerals (Hwanget al., 1978; Phang, 1990; Habib et al., 1997). Suwandi, (1991) and Wuet al., (2006b) pointed out the possibility of recovering and con-centrating the available bioresources in POME by an ultrafiltrationprocess in order for the concentrated bioresources to be reused moreeffectively as fermentation media. According to Wu et al. (2007),POME and its derivatives have been exploited as fermentation mediato produce various products/metabolites such as antibiotics, bioin-secticides, solvents, polyhydroxyalkanoates, organic acids as well asenzymes to varying degrees of success. The hydrogen production fromPOME during anaerobic treatment has also been intensively studied(Atif et al., 2005; Vijayaraghavan and Ahmad, 2006) since thegenerated hydrogen and its combustion products do not count asgreen house gases (Koroneos et al., 2004). However, it has been re-ported that POME also contains certain powerful water-solubleantioxidants, phenolic acids and flavonoids (Wattanapenpaiboonand Wahlqvist, 2003) that may inhibit the growth development inmicroorganisms (Lin et al., 2005; Uzel et al., 2005).

Table 2 displays the various products or metabolites produced inbioprocesses by reusing POME or its derivatives as substrates.

3.1.1. AntibioticsStudies on ultrafiltered POME concentrates or retentates as growth

media for Penicillium chrysogenum in the production of antibiotics havebeen conducted some time ago (Suwandi and Mohammad, 1984;Suwandi, 1991). It was found that a supplementary nitrogen sourcewasrequired in the ratio C:N=20:1 to produce a maximum mass ofP. chrysogenum (Suwandi andMohammad,1984). However, no attemptswere made to assay the penicillin produced during the process ofincubation. Suwandi (1991) later determined the effect of the POMEconcentration and the addition of chemicals on the production ofpenicillin in cultured broths for periods of 4 days. He found that smalleramounts of penicillin were produced in POME as compared to in DeoandGaucher's (1984) standardmedium. Suwandi (1991) argued that thelow production of penicillin was due to the lower concentration ofcarbohydrates (23 g/l) in POME as compared to in the standardmedium,which contained 35 g/l carbohydrates. The addition of ammoniumlactate to POME stimulated the production of penicillin.

3.1.2. BioinsecticidesNor and Mahadi (1986) as well as Suwandi (1991) embarked on a

research topic related to the use of ultrafiltered POME concentrate orretentate as a medium for Bacillus thuringiensis to produce bioinsecti-cide for mosquito control. Suwandi (1991) observed that a mediumcontaining 1% (w/v) retentate in powder form was as good as thestandard medium of glucose yeast extract salts in terms of sporeproduction by B. thuringiensis. The ability of the retentate to supportand stimulate the growth of B. thuringiensis could be attributed to theproper ratio of carbon and nitrogen as well as to sufficient levels ofions (such as Mg, Ca, Mn, etc.) in the POME.

3.1.3. Solvents (acetone–butanol–ethanol: ABE)Separator sludge and sterilized condensate from POME have been

tested for their suitability to be reused as fermentation media for ABEproduction by Clostridium saccharoperbutylacetonicum N1-4 (ATCC13564) (Mun et al., 1995). Separator sludge was found to be the bettermedium between the two for supporting the production of ABE as nomineral supplements were required. The enzymes produced byC. saccharoperbutylacetonicum N1-4 (ATCC 13564) were sufficient tohydrolyze the mixed carbohydrates and celluloses found in theseparator sludge. Hipolito et al. (2007) later reconfirmed that enzymatichydrolysates of separator sludge could be used as media for inoculum


development since the cultures inoculated with C. saccharoperbutylace-tonicum N1-4 (ATCC 13564) using the sludge hydrolysate produced thesame concentration of butanol as compared to in a potato glucosemedium, whereas the corresponding ethanol productionwas increasedby over 100%. The authors concluded that the enzymatic hydrolysates ofseparator sludge could serve as growth and ABE fermentation media aswell as a source of nitrogen and trace elements.

Somrutai et al. (1996) investigated the possibility of acetone–butanolfermentation by C. aurantibutyricumATCC 17777 in amodelmedium forraw POME. They found that by decreasing the pH from 6.2 to 5.5 at 9 hand starting an hourly glucose feeding (2 g/l) at 10 h, it was possible toobtain30%of the oil hydrolysis aswell as a productionof 5.78g/l acetoneand 6.78 g/l butanol. Kalil et al. (2003) studied the direct use of rawPOME as a fermentation medium for ABE production byC. acetobutylicum NCIMB 13357 and immobilized C. saccharoperbutyla-cetonicum N1-4 in a batch culture system. It was found thatC. acetobutylicum NCIMB 13357 produced the highest total ABE in 90%(v/v) particulate fraction of raw POME after 48 h of fermentation at aninitial pHof 5.8while immobilized cells ofC. saccharoperbutylacetonicumN1-4 could be reused for at least 5 times in 100% (v/v) particulatefraction of raw POME without losing their performance (Kalil et al.,2003). Similar results were also obtained by Pang et al. (2004) with theaddition of hydrogen production up to 28.5 ml.

An oscillatory flow bioreactor was used to enhance the productionof ABE in the raw POME (Takriff et al., 2005; Masngut et al., 2006,2007), and initial results showed that by using a particulate fraction ofraw POME as the fermentation medium, C. acetobutylicum NCIMB13357 could produce 31% higher concentrations of ABE, especiallyacetone, in flask as compared to an oscillatory flow bioreactor (Takriffet al., 2005). On the other hand, Masngut et al. (2006, 2007) found thatC. acetobutylicum NCIMB 13357 could only produce higher amounts ofbutanol in shorter periods of time when particulate fractions of rawPOMEwere used in an oscillatory flow bioreactor as opposed to with areinforced clostridial medium in a stirred tank bioreactor. Pang et al.(2004) also claimed that the concentration of ABE produced byC. acetobutylicum NCIMB 13357 in a particulate fraction of raw POMEwas 20-fold that obtained in the reinforced clostridial medium.

3.1.4. Polyhydroxyalkanoates (PHA)Over 40% of the total polyhydroxyalkanoates (PHA) production

cost is estimated to account for the raw materials of the overallprocess and more than 70% of this cost is attributed to the carbonsource (Lee et al., 1999). POME can be considered as an alternative, no-cost reusable substrate for PHA production. According to Hassan et al.,(1997a), with a content of 50% PHA in the dried cells and 2% dissolvedin the chloroform, the calculated minimum cost for obtaining PHAfrom POME is below 2 US$/kg. By increasing the PHA content in thecell from 50% to 80%, the unit cost of PHA could be slightly reduced;whereas an increase in the amount of PHA dissolved in chloroformfrom 2% to 5% would result in a remarkable reduction of the PHA costto less than 1 US$/kg (Hassan et al., 1997a).

Nevertheless, POME is usually presented in complicated forms thatcannot be directly reused by PHA-producing species such as Ralstoniaeutropha, a representative bacterium for PHA synthesis (Salim et al.,2006). It was proposed that an anaerobic treatment of POME could becoupled with PHA production using photosynthetic bacteria to reducePHA production costs (Hassan et al., 1996,1997b). According to Hassanet al. (1996), it was critical to maintain the pH at 7 in the anaerobictreatment of POME by sludge in the first stage of the process, in orderfor only acetic and propionic acid to be produced and not formic acidand biogas. With increasing concentrations of formic acid (for a pHmaintained below 4), the PHA yield and content in Rhodobactersphaeroides IFO 12203 dropped from 0.50 g/g and 67% to 0.21 g/g and18%, respectively. Hassan et al. (1997b) later found that the presence ofsludge in the anaerobically treated POME inhibited PHA accumulationby R. sphaeroides IFO 12203. This was attributed to the PHA being

produced in a POME without sludge as opposed to a treated POMEwith sludge. A low concentration of ammonium would accelerate thePHA production in a synthetic waste with an organic acid profile,which was observed during POME treatment (Hassan et al., 1996).However, Hassan et al. (1997b) found that addition of ammonium andphosphate to anaerobically treated POME was required to maintainthe cell activity and production of PHA since neither ammonium norphosphate was present in the anaerobically treated POME. In total, theorganic acid concentrations obtained from anaerobically treatedPOME were too low (Hassan et al., 1996) for it to be reused as rawmaterial in the production of PHA on an industrial scale. Theunderlying reason was that this would require a production reactorwith a much larger size than that of a reactor for normal bioplasticproduction.

Therefore, Hassan et al. (1997c) used an anion exchange resin toseparate and concentrate the acetic acid from the anaerobically treatedPOME so that the concentrated acetic acid could be reused as a substratein the fed-batch production of PHA by Alcaligenes eutrophus H16 (ATCC17699). They found that the PHA content was comparable to that of thebatch and fed-batch PHA production by Alcaligenes (around 18% to 76%),but the overall PHA productivity obtained was less than the 0.5–3 gPHAs/l h obtained by other researchers (Suzuki et al., 1986; Ishizaki andTanaka, 1991; Lee et al., 1993; Yamane et al., 1996). This might be due tothe lowcell concentrationwhen concentratedacetic acid separated fromPOME was incorporated into the standard medium.

Hassan et al. (2002) showed that organic acids in the anaerobicallydigested POME could be concentrated by evaporation for use assubstrates in the fed-batch non-sterile PHA fermentation systemusing R. eutropha ATCC 17699. Although the proposed overall zeroemission system appeared to be practical, major drawbacks werefound, including the rather low yield and productivity of PHA by R.eutropha when the concentrated organic acids from POME were usedas compared to synthetic organic acids. This could be due to the highpresence of ammonium (1.5 g/l) or other compounds in theanaerobically digested POME concentrate (Hassan et al., 2002).

According to Md Din et al. (2006a,b), it was possible to use mixedcultures to produce PHA in POME sincemost prokaryotes are capable ofPHA production (Chua et al., 2003). Md Din et al. (2006a) noted that byusing mixed cultures and POME, different types of PHA-constituentscould be obtained. The harvesting of these PHA-constituents was morereliable for use as biodegradable plasticsmaterials as opposed to a singlePHA-constituent. Md Din et al. (2006b) maintained a type of mixedculture in a sequencing batch reactor, and a high concentration of POMEwas proposed for this system in order to generate autotrophic ratherthan heterotrophic bacteria in the production of PHA. However, theaverage PHA production by using POME could only reach 44% of thecells' dry weight, indicating that an optimization of the PHA sludgecontent must be carried out by varying the oxygen rate, feeding regimeor transient conditions.

3.1.5. Organic acidsIt is a well-known fact that a variety of organic acids are produced

as intermediates during the anaerobic treatment of biological wastes(Kotzé et al., 1969; Zeikus, 1980; Archer, 1983). As mentioned earlier,POME could be put to sustainable use for organic acid production,whereby the latter could be utilized as raw material for PHAproduction (Hassan et al., 1996, 1997b,c, 2002). According to Hassanet al. (1996), the conversion to organic acids from the BOD sources inPOME by R. sphaeroides IFO 12203 was more than 70%, and acetic acidand formic acid were the predominant substances at higher and lowerpH, respectively. Yee et al. (2003) showed that by incorporating asludge recycling system with the freezing–thawing method in theanaerobic treatment of POME, the retention time could be lowered to3.5 days without affecting the organic acid production. Moreover, Yeeet al. (2003) found that the effect of freezing and thawing producedconcentrated viable and ruptured cells in recycled sludge with a total


nitrogen source of 4–5 g/l as a result of the ruptured cells releasing thenitrogen sources that were required to support the growth of highercell densities.

Some organic acids, such as citric acid (Jamal et al., 2005; Alamet al., 2008) and itaconic acid (Wu et al., 2005), could be producedunder aerobic conditions using POME as the substrate. Jamal et al.(2005) screened potential microorganisms for citric acid productionand found that Aspergillus (A103) produced the highest concentrationof citric acid after 2 days of fermentation by using POME and wheatflour as medium. Alam et al. (2008) later found that higher productionof citric acid could be obtainedwith longer time of fermentation (up to7 days of fermentation) and addition of co-substrates (glucose andwheat flour) into POME. Wu et al. (2005) employed raw POME and itsderivatives to produce itaconic acid by using Aspergillus terreus IMI282743. However, only little itaconic acid could be obtained. It waspostulated that this low production was mainly due to the wild andunsuitable strain of A. terreus IMI 282743.

3.1.6. EnzymesThe particulates in the POME, comprisedmainly of plant cell debris

and fragments, are entirely organic in nature as indicated by the verylow ash contents (Ho et al., 1984). The availability of such particulatesmay provide a potential substrate for production of cellulase(Prasertsan et al., 1997; Mashitah et al., 2002; Alam et al., 2006a;Chowdhury et al., 2006; Laohaprapanon et al., 2007), xylanase(Prasertsan et al., 1997; Cheng, 2006; Laohaprapanon et al., 2007)and lignin peroxidase (Alam et al., 2006b; Chowdhury et al., 2006) inPOME. The optimization of cellulase (CMCase) and xylanase produc-tions from Aspergillus niger ATCC 6275 was investigated under bothsubmerged and solid state fermentation (Prasertsan et al., 1997).Prasertsan et al. (1997) found that the addition of 0.6 g/l NH4NO3 intothe POME during submerged fermentation increased the maximumproduction of xylanase and CMCase with up to 156% and 43%,respectively.

Prasertsan et al. (1997) also revealed that the enzyme productionwas lower in POME when the fermentation process was conducted ina fermenter, which might be due to the destruction of mycelium byshearing forces, thus causing the cessation of enzyme synthesis andthe induction of enzyme inhibition (Wase et al., 1985). Contrarily,Cheng (2006) reported on 107% higher activity of xylanase obtainedby A. terreus SUK-1 in the fermenter as compared to the shake flaskwhen raw POME was used as the substrate. However, Cheng (2006)also found a 31% lower activity of xylanase with the raw POME asopposed to the Mandels medium (Mandels, 1974).

Mashitah et al. (2002) used axenic and mixed cultures ofmesophilic and thermophilic fungi to produce cellulase in thePOME, in which case they found that the axenic culture of Tricho-derma harzianum was superior to the mixed culture of A. niger and T.harzianum in terms of CMCase and exoglucanase production. This lowproduction of cellulase in the mixed culture was believed to be due tothe competition of nutrient consumptions between the fungi in thePOME. Moreover, the genus Aspergillus is known to release othermetabolites such as endotoxins (Debeaupuis and Lafont, 1978) andproteases (Aunstrup, 1974), which may inhibit the activity of cellulase.Mashitah et al. (2002) also noted that the thermophilic fungi, namelyMyceliophthora thermophila grew well and produced a higher amountof cellulase in POME as compared to themesophilic fungus. Alam et al.(2006a) utilized a combination of POME and wheat flour as thesubstrate in the optimization process for maximizing cellulaseproduction by T. harzianum. They found that the linear effect ofagitation was not highly significant for cellulase production but thisparameter should not be totally overruled because of its interactiveeffect with wheat flour.

Six out of twenty strains of Penicillium were isolated from fourdifferent sources of POME sludge and selected for the production ofcellulase and lignin peroxidase in the POME (Chowdhury et al., 2006).

The results revealed Penicillium (P1-EFB), which was isolated fromempty fruit bunches, displayed the best potential strain for biode-gradation in liquid state bioconversion of POME at pH 7.3. The white-rot fungus Phanerochaete chrysosporium was used for lignin perox-idase production with a combination of POME and wheat flour as thesubstrate (Alam et al., 2006b). It was observed that, although wheatflour could be used as an additional carbon source to enhance theinitial growth of P. chrysosporium, more than 2% wheat flour wasexpected to further decrease the enzyme activity of the ligninperoxidase. Laohaprapanon et al. (2007) found that the isolate SO1,which was isolated from a soil near to the first anaerobic pond of palmoil mill, produced the highest activity of cellulase and xylanase incomparison with other isolate of microorganisms. Isolate SO1 was anaerobic, Gram-positive, rod-shaped and thermo-tolerant microorgan-ism, which was able to reduce the oil content in the sediment of POMEup to 85.32%.

In view of the fact that POME contains considerable amounts of oiland grease, it is possible to reuse POME as a substrate in lipaseproduction and isolate oil-degrading microorganisms from effluenttreatment ponds of POME. Somrutai et al. (1996) found that Clostri-dium aurantibutyricum ATCC 17777 was able to produce lipase in themodel medium for POME in which high rate of oil hydrolysis (46.0%)was observed at pH of 6.8. Razak et al. (1997) were able to isolatethermophilic fungi, namely Rhizopus oryzae and Rhizopus rhizopodi-formis, from POME. They found that the fungi could produceremarkable amounts of extracellular lipases in the defined medium.Furthermore, the isolated R. oryzae from POME could producemembrane-bound lipases that were active in both acidic and alkalineconditions as opposed to extracellular lipases from the same fungi(Razak et al., 1999). Apart from thermophilic fungi, thermophilicbacteria such as Geobacillus sp. strain T1 (Leow et al., 2004; Rahmanet al., 2007) and Bacillus sp. strain 42 (Eltaweel et al., 2005), whichwere isolated from POME, were found to be lipase producers too.

The concentrated bioresources from POME or its retentate (Wuet al., 2006b, 2007) could be reused as effective substrates to produceprotease (Wu et al., 2006a,b). According to Wu et al. (2006a), a wild-type strain of A. terreus IMI 282743 produced a maximum proteaseactivity in the medium containing 75% (v/v) POME retentate as thesole carbon and nitrogen source without addition of extra nutrients oradjustment of the initial pH. However, using pure retentate, i.e.without slightly diluting it, was not recommended since it waspresumed that an increase in the retentate concentration would bringabout a decrease in the free water level in the medium andconsequently reduce the solubility and availability of nutrients tothe culture (Wu et al., 2006a).

3.1.7. HydrogenAccording to Morimoto et al. (2004), it was possible to use natural

anaerobic microflora from POME sludge, instead of pure culture ofisolated strain, to produce significant amounts of hydrogen underanaerobic fermentation in a batch culture. The anaerobic microflora inthe POME sludge was found to produce hydrogen whereas nomethane gas was observed in the evolved gas (Morimoto et al.,2004; Atif et al., 2005). Thus, anaerobic microflora found in the POMEsludge might be useful for the production of hydrogen from POMEbiomass resources without sterilization. Vijayaraghavan and Ahmad(2006) tested a new source of microflora from cow dung for itshydrogen-generating capability in POME. They pointed out that thehighest biogas generation and hydrogen content occurred at pH 5. O-Thong et al. (2007) highlighted that a raw POME supplemented withnutrients (N, P and Fe) gave a 20% increase in hydrogen productionyields as well as 58–61% higher hydrogen contents as compared to rawPOME. The hydrogen production rate could be increased by 60% if rawPOME was adjusted to an optimized iron concentration of 257 mg/l, aC/N ratio of 74 and a C/P ratio of 559 (O-Thong et al., 2008a). Thenutrient supplementation strategy was found to increase the bacterial

Table 4The application of POME (m3/acre/year) as fertilizer for palm oil plantations (Onyiaet al., 2001)

Crops N P K Mg

Young palms 25–70 27.5–32 5.1–10 1.2–10Adults palms 90–128 52.5 10–18.5 15Old palms 162 52 18 20


diversity in the anaerobic sequencing batch reactor and promote thegrowth of hydrogen-producing bacteria, namely Thermoanaerobac-terium thermosaccharolyticum (O-Thong et al., 2007). Later, O-Thonget al. (2008b) were able to isolate T. thermosaccharolyticum PSU-2from a sequencing batch reactor, which was used to digest POME forcontinuous hydrogen production. They found that the isolated strainof PSU-2 produced higher amounts of hydrogen, up to 68%, in organicnitrogen amended medium as compared to inorganic nitrogenamended medium.

3.2. Sustainable reuse of POME as fertilizer

The application of raw or digested POME as fertilizer on land wasinitially thought to be impractical because of the effluent killingvegetation and leading to the blocking of percolation and water-logging, thus resulting in anaerobic conditions. However, Wood et al.(1979) found that although raw POME would readily cause cloggingandwaterlogging of the soil, these problems could be overcome by thecontrolled application of small quantities of POME at a time. Thetesting of ground waters after 6 to 12 months of trial applications ofraw POME as fertilizer showed no substantial percolation of oxygen-demanding or other polluting elementswithout excessive run-off overthe surface during wet weather (Wood et al., 1979). It was thusestablished that the water quality in the applied areas was unaffected(Dolmat et al., 1987). Oviasogie and Aghimien (2003) later recon-firmed that a proper use and safe disposal of POME in the landenvironment would lead to improved soil fertility and contribute toenvironmental sustainability. Their results showed an enrichment ofthe soils with regard to phosphorus, nitrogen, calcium, magnesium,sodium and potassium following the application of the POME. Copper,iron and leadwere predominant in their organic forms, while zinc wasparticularly present in its exchangeable form.

The potential for using POME as a cheap organic fertilizer may offeran alternative to the excessive application of chemical fertilizers,especially phosphorus, for which cost is a severe economic constraint.For example, biologically treated POME has beenwidely used in the oilpalm plantations for irrigation purposes and can be employed as aliquid fertilizer. It is estimated that each 15 million tonnes of POMEwould have a fertilizer value of RM 95.41 million (Table 3). Accordingto Wood et al. (1979), an application of POME at 4.5×106 l per appliedhectare was estimated to represent a fertilizer application of about30 kg ammonium sulfate, 7 kg rock phosphate, 52 kg potash and 18 kgkieserite per palm per year. The nutrient composition of the fertilizersis shown in Table 3.

An incorporation of POMEmay help to increase the organic matterin the soil, which may turn into humus after decomposition andbecome an active soil component. Thus, POME application wouldresult in changes in the chemical properties of the soil. According toFerreira and Araujo (2002), average contents of calcium, magnesium,potassium and phosphorus were found to increase in the soil with anincrease in POME dosage, especially at a depth of 0–20 cm but anapplication of 120 m3/ha of POME to the soil reduced the aluminumcontent to zero at a depth of 20 cm after 12 months. Such a reduction

Table 3Estimated fertilizer values from POME, which is based on 15 million tonnes of POME

Fertilizer Tonnes(×1000)

December 2002 price(RM/ton)

Fertilizer value(RM million)

Ammoniumsulphate

75.5 580 43.79

Rock phosphate 19.5 545 10.63Muriate of potash 68.6 250 17.15Kieserite 59.6 400 23.84Total 95.41

of aluminum in the soil would eventually help prevent toxicity andgrowth hindrance for plants in acid soils (Matsumoto, 2000; Guo et al.,2007). Nevertheless, variations in POME quality among the mills andthe rate of application as well as other details need to be determinedin relation to local situations (Agamuthu et al., 1992). Moreover, theuse of POME as fertilizer must be carried out with caution because ofimbalances in the nutrient composition. A prolonged improperutilization may cause an accumulation of magnesium and therebyinhibit the availability of potassium (Onyia et al., 2001). Table 4 showsthe nutrient requirements for the various growth stages of plants aswell as the suitable amount of POME for reuse as fertilizer in order toavoid soil damage.

According to Chan et al. (1980), the use of POME has been shown toimprove soil productivity and increase the yield of crops as well ascontribute to better root health by improving the soil structure. Anincrease in crop yield on the order of 10 to 24% has been reported (Tamet al., 1982; Lim et al., 1984). Teoh and Chew (1983) have furthershown that mixtures of soil and POME in a ratio of 1:5 resulted inmore vigorous growth of cocoa seedlings and decreased nurseryrotation without the addition of supplementary fertilizers. With thehelp of organic matter consisting of peat and the sludge from POME,Shamshuddin et al. (2004) confirmed that aluminum toxicity towardsthe growth of cocoa seedlings on acid sulfate soil could be reduced to acertain extent. Agamuthu (1994) stated that the application of POMEalone as fertilizer provided the highest yield of Napier grass(Pennisetum purpureum), up to 3276 kg/ha, as a result of POMEcontaining almost all the major and minor elements required for itsgrowth (Agamuthu et al., 1992). Although the application of freshdung also gave rise to high yields of Napier grass, up to 2574 kg/ha,POME was preferred since fresh dung releases an unwanted odor thatmight attract flies (Agamuthu, 1994).

Shamshuddin et al. (1998) indicated that the application of POMEtogether with ground magnesian limestone, which might last for3 years, was a sound agronomic option to alleviate the soil acidity andimprove the fertility in Ultisol for maize production. They alsorevealed that a POME application up to 40 t/ha did not significantlychange the topsoil pH and exchangeable calcium, magnesium andaluminum, in which case the calcium and magnesium from the POMEwere held by the negative charge present on the exchange complex.Salètes et al. (2004) conducted a trial on a composting platform inwindrows comprised of shredded empty fruit bunches that werewatered weekly with POME. They found that the resulting composthad a good agronomic value but that the mineral balance wasconsiderably affected due to the nutrients provided by POME beingpoorly retained by the substrate and partially lost in percolationfollowing the weekly watering operations.

According to Salètes et al. (2004), a better distribution of POMEapplications together with a system for recovering the leaching mightsubstantially reduce the nutrient losses while maintaining a suitablehumidity for microbial degradation. In a similar case to that of Salèteset al. (2004), Aisueni and Omoti (2002) also used shredded empty fruitbunches together with POME in the composting process but with theaddition of poultry droppings as nutrient supplements. They notedthat the use of POME in the composting process was particularlybeneficial in significantly reducing the amount of poultry droppings,which were required to produce the same amount of final compost.

Table 6The chemical composition of “Prolima” as compared to palm oil sludge (Agamuthu,1995)

Composition “Prolima” Palm oil sludge

Moisture, % 5.1 6.9Crude protein (N×6.25), % 43.3 12.4Crude fiber, % 7.6 15.2Ether extract, % 12.0 24.1Ash, % 4.1 11.2Nitrogen-free extract, % 27.9 46.7Calcium, % 0.19 0.28Phosphorus, % 0.52 0.18Magnesium, % 0.17 0.25Iron, mg/l 365 1757Copper, mg/l 42 36Manganese, mg/l 56 62Zinc, mg/l 145 1075Gross energy, MJ/kg 18.5 19.6

Table 5Chemical attributes of humic substances derived from POME (adapted from Siva et al,2000)

Chemical attribute Humic acid

Clarified POME Decomposed POME

Percent yield 3.47 1.82Percent loss on ignition 97.5 99.5Elemental make-up (%)C 57.87 48.94H 8.26 5.76N 2.91 8.05O 30.96 37.25O:H 3.75 6.47C:N 19.89 6.08C:H 7.01 8.50Functional groups (meq/g)Quinonoid (C=O) 2.52 2.85Carboxylic (COOH) 2.22 2.08Phenolic (OH) 3.34 3.27Total acidity (carboxylic+phenolic) 5.56 5.35Optical density (E4:E6 ratio) 4.22 6.09


The slow release of the total N and P after the first 12 weeks couldalso become a limiting factor if these nutrients were to be madeavailable for plant growth (Palaniappan et al., 1983). Therefore, AzizahChulan (1991) suggested that if POME were to be reused as fertilizer,the soil should be inoculated with vesicular–arbuscular mycorrhizal(VAM) fungus Scutellospora calospora because the combinationbetween POME and VAM will form mycorrhizae that may enhancethe breakdown of certain soluble phosphates and insoluble organicphosphate such as phytate by roots (Gianinazzi-Pearson, 1985). Onyiaet al. (2001) stated that the application of organic nitrogen from rawPOME has been associated with lower yields due to ammonia beingliberated during the mineralization of organic matter. Onyia et al.(2001) therefore suggested that nitrification of POME was necessarysince a nitrified POME would be more easily absorbed by most plantsthan a raw POME with a high organics content, especially in thetropics where nitrate leaching does not present a major problem.

Numerous studies have identified ammonia volatilization as themajor cause of low N efficiencies in urea (Mikkelsen et al., 1978; Filleryet al., 1984), in which case up to 80% of the applied urea-N may be lostwithin 2–3 weeks of application (Hargrove and Kissel, 1979; Torelloet al., 1983). Siva et al. (2000) reported that POME is rich in organicmatter and varying amounts of humic substances across theirrespective organic matrices (Table 5). Seeing as humic substanceshave been reported to interact with ammonia compounds (Banerjeeand Basak, 1978; Thorn and Mikita, 1992) and urea (Patti et al., 1992),Siva et al. (1999, 2000) investigated the effects of POME-derivedhumic substances on ammonia volatilization from urea. Initial studiesby Aminuddin (1994) showed that POME could introduce a preferredenvironment within the urea–soil reaction zone (microsite) andsuccessfully reduce ammonia volatilization to 8% of the applied N. Sivaet al. (1999) displayed that this reduction in ammonia volatilizationwas accompanied by a corresponding increase in ammonium recoveryand a decrease in pH, particularly at the microsite. The performance ofhumic fractions from POME also indicated an interplay of severalmechanisms that could possibly include urease inhibition, ureaabsorption and ammonia fixation (Siva et al., 2000). These resultshave implications to the reduction of N loss by ammonia volatilizationfrom urea applied to the soil during crop production.

According to Muhrizal et al (2006), the incorporation of organicmaterial into iron-poor acid sulfate soil might enhance the beneficialeffects of reducible Fe(III) oxides or S in the soil and eventually promotean increase in pH under flooded conditions. However, not all organicmaterials are able to alleviate acid sulfate soil infertility with equalefficacy (Muhrizal et al., 2003). Although POME contains considerableamounts of organic materials, Muhrizal et al. (2006) revealed that

POME did not significantly affect the pH and redox potential in theiron-poor acid sulfate soil during submergence. They also claimed thatPOME contains high concentrations of lignin that presumably decom-poses slowly under anaerobic condition. Thus, these materials couldnot become active electron donors in the reduction process.

3.3. Sustainable reuse of POME as live food for animals and aquaculturalorganisms

The reuse of POME as a dietary substitute for pigs, poultry and smallruminants as well as aquacultural organisms is gaining importance.Apart from oil palm fronds, palm press fiber and palm kernel cake,Devendra (2004) pointed out that POME was especially important forfeeding ruminants. Using POME as animal feeds, however, could onlybe considered as a co-management of the effluent because, accordingto Agamuthu (1995), a 40-ton-per-hour mill would require around44,000 pigs or 43,000 cattle for the entire effluent to be utilized.

Hutagalung et al. (1977) investigated the use of POME as animalfeed for growing–finishing pigs, in which case two types of “meals”known as censor tk8 (35% palm oil sludge, 32.5% cassava root meal,32.5% palm kernel cake) and tkg (32% palm oil sludge, 34% cassava rootmeal, 17% palm kernel cake, 17% grass meal) were used. They foundthat it was economical to replace 50% maize (the regular dietconstituent) with a POME-based animal feed, thus saving up to RM0.02 per pig per day. In Colombia, POME has been fed with goodresults directly to pig (10–12 l/head/day) together with palm oil andother ingredients (Devendra, 2004).

POME could also be used as supplementary food inpoultry farming.According to Ho (1976), animal feed production from palm oil wastescan replace at least half of the amount of imported maize for poultrydiets and up to 100% for pig diets. Yeong et al. (1980) investigated thenutritive values of a POME product known as “Prolima” (Table 6) as theprotein source in broiler chicken diets. It was observed that the aminoacid content of palm kernel cake and palm oil sludge were somewhatclose to cereal by-products and that of “Prolima”was between soybeanmeal and peanut meal, in which case the overall percentage of aminoacid availability for palm kernel cake, palm oil sludge and “Prolima”were 74.4%, 24.8% and 71.0%, respectively. Therefore, the concentra-tions of “Prolima” up to 30% could be included in broiler diets as areplacement for soybean meal without causing any adverse effect onthe growth performance of the chickens (Yeong et al., 1980). Later,Yeong and Azizah (1987) reported the optimum levels of using 10–15%of dried POME in chicken feed for the growth and egg production.Pasha (2007) also reported that the optimum levels of POME in the dietfor broilers and layers are 15% and 10%, respectively.

The Malaysian Agricultural Research Development (MARDI) provedthatwastes from thepalmoil industry (such as oil palm sludge and palmpress fiber) alone or in combination, dried to moisture contents of 7%,


could be used as supplementary food for sheep (Devendra andMuthurajah, 1976). Vadiveloo (1988) fed Katjang and Katjang×GermanFawn crossbred goats with Napier grass and Leucaena leucocephala,which were supplemented with dried POME. He found that supple-menting with POME at all levels did not significantly depress forageintake but rather increased the total intake. Vadiveloo (1989b) furtherconfirmed that L. leucocephala, which was supplemented with dehy-drated POME, allowed mature regrowths of the crop (increased withregard to both drymatter and neutral detergent fiber digestibility) to befed to goats. Agamuthu et al. (1996) also found that goats and sheepdigested POME-treated Napier grass significantly faster than Napiergrass alone. Feeding studies with goats have also shown that rice straw,which was properly supplemented with dehydrated POME, couldpromote satisfactory performance levels (Phang and Vadiveloo, 1991).According to Vadiveloo (1989a), NaOH treatment of rice straw togetherwith dehydrated POME and Leucaena promoted an even higher strawintake among the goats. The increased intake and dry matterdigestibility with the NaOH treatment might be due to an enhancededibility and digestible energy of the roughage (Kellaway and Leibholz,1983). It was concluded by Vadiveloo (1989a) that diets comprising 25%NaOH-treated straw, 50% dehydrated POME and 25% Leucaenapermitted dietary nutrients to be reused efficiently and maximizedthe inclusion of agro by-products. According to Devendra (2004), 10% ofPOME in diets for sheep gave the best result in terms of digestibilitybecause crude fiber digestibility dropped significantly from 80.6% in a10% POME diet to 27.0% in a 60% POME diet. Ether extract digestibilitydecreased progressively with increasing dietary POME.

It should be stressed that the utilization of POME as animal feedscould be enhanced further by addition of molasses and palm pressfiber or other oil palm by-products. According to Devendra (2004), themaximum suitable level of inclusion of molasses appeared to be onepart molasses for every 1.2 parts of palm press fiber+POME. It wasfound that combining palm kernel cake and oil palm fronds withPOME could create a low-cost and excellent feeding system. Accordingto Pasha (2007), 50% palm kernel cake, 30% oil palm fronds and 20%POME can produce a reasonably good diet for moderate growth rateand acceptable meat quality in beef cattle.

Two agricultural waste products, namely YM20 (a mixture of peaand corn) and POME, were evaluated in a closed recirculation systemfor their suitability to replace a costly diet of live algae in the culture ofthe Sudanese fairy shrimp, Streptocephalus proboscideus (Jawahar Aliand Brendonck, 1995). They found that the results in terms of growth(increase in length), cyst production and mortality were moresuccessful when S. proboscideus were supplied with high densities ofYM20 as compared to POME and algae. Habib et al. (1997) pointed outthat POME could also be reused as a food source by aquatic organismssuch as chironomid larvae knownas “bloodworms”. They reported thatthe production of chironomid larvae was significantly higher in POME(580 g/20 l POME) than in algal cultures (35 g/20 l algal culture). Thesechironomid larvae, in turn, present valuable live food for fish orcultured invertebrates (Shaw andMark,1980; Yusoff et al., 1996). Babuet al. (2001) studied the use of POME for the culturing of four species offish, i.e. silver carp, catla, rohu andmrigal. Thefishwere harvested after9 months and the maximum individual growths of silver carp, rohuandmrigal were 700, 550 and 600 g, respectively whereas the averagegrowth of catla was 35.3 g. Vairappan and Yen (in press) showed thatIsochrysis sp., which was grown in a modified medium of aerobicallydigested POME, was suitable to be reused as a supplement to furtherenrich and improve the rotifer cultures. These rotifer cultures, in turn,play their role as food organisms for fish larvae (Lubzens et al., 2001).

4. Conclusions

On thewhole, it is an undeniable fact that POMEhas its ownpotentialfor sustainable reuse through biotechnological advances. Moreover, it isunderstood that a cleaner production is, in the long run, a better option

for managing POME as opposed to end-of-pipe processes. However,although the emphasis ona cleaner production for POMEmanagement iswell-intentioned, it may sometimes raise false expectations. The limitsimposed by the economic and social frameworks present obviouslimitations to sustainable practices that couldbe applied in the industries(Fricker, 2003), especially inmost developing countries such asMalaysia.Consequently, there is usually no economic incentive to develop waste-free processes. A cleaner production is therefore limited unless it issubsidized, externalities are factored in, products are successfullydesigned for commercial reuse and, most importantly, the governmenttakes the initiative in legislating fora sustainable industrialdevelopment.Since the economic framework depends on growth, production andconsumption, the initiatives to promote a cleaner production for POMEmanagement can only come from the palm oil industries themselvessince their subtle actions could accelerate the research and developmentfor an enhanced POME management. In short, we need to becomeresponsible citizens rather than mere consumers.

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