Production of Biogas

7/25/2019 Production of Biogas

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Production of biogas and performance evaluation of existing treatmentprocesses in palm oil mill efuent (POME)

Yunus Ahmed a,c, Zahira Yaakob a,b,n, Parul Akhtar a, Kamaruzzaman Sopian b

a Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia,

Bangi, 43600, Selangor, Malaysiab Solar Energy Research Institute (SERI), Universiti Kebangsaan Malaysia (UKM), Bangi, 43600 Selangor, Malaysiac Department of Chemistry, Chittagong University of Engineering and Technology (CUET), Chittagong-4349, Bangladesh

a r t i c l e i n f o

Article history:

Received 17 January 2014

Received in revised form

18 September 2014

Accepted 22 October 2014Available online 18 November 2014

Keywords:

Renewable biogas

POME

Anaerobic

Aerobic

Physiochemical treatment

Upow anaerobic sludge-xed

lm (UASFF) reactor

Membrane separation treatment

a b s t r a c t

Palm oil is an important edible oil in the global fats and oil market and its industry is also one of the

prominent global agricultural industries. The production of crude palm oil reached 62.34 million tonnes

in 2014. However, enormous volumes of production has subsequently discharged large volumes of a

palm oil mill efuent (POME). POME is a remarkably contaminating efuent due to its high amount of

COD, BOD and colour concentrations, which can affect the environment, especially water resources.

However, it was recognized as a prospective source of renewable biogas such as biomethane and

biohydrogen. Nowadays, with the global emphasis on sustainability, if we simultaneously operate

wastewater treatment and produced renewable bio energy in the palm oil industry, then this industry

can be environmentally sound, with cleaner production and greater sustainability. The aim of this

review is to discuss various existing treatment processes (mainly anaerobic and aerobic digestion,

physicochemical treatment and membrane separation) and factors that inuence the treatment methods

and conversion of POME to renewable biogas such as biomethane and biohydrogen on a

commercial scale.

& 2014 Elsevier Ltd. All rights reserved.

Contents

1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1261

2. Characteristics of palm oil mill efuent (POME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1261

3. Regulatory standards for palm oil mill efuent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263

4. Process description of palm oil mill process and sources of water pollution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1263

4.1. Reception, transfer and storing of fresh fruit bunches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

4.2. Sterilization of fresh fruit bunches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/rser

Renewable and Sustainable Energy Reviews

http://dx.doi.org/10.1016/j.rser.2014.10.073

1364-0321/&2014 Elsevier Ltd. All rights reserved.

Abbreviations: AD, anaerobic digestion; AF, anaerobic lter; AFBR, anaerobic uidized bed reactor; ABR, anaerobic bafed reactors; ASBR, anaerobic sequencing batch

reactor; Alk, total alkalinity; AOPs, advanced oxidation processes; AT-POME, anaerobically treated palm oil mill efuent; BOD, biochemical oxygen demand; BPAC, banana

peel activated carbon; BT-POME, biologically treated palm oil mill efuent; BSA, bovine serum abumine; BFR, Bio-fouling reducers; CA, cellulose acetate; CPO, crude palm oil;

CSTR, continuous stirred tank reactor; CRT, cell retention time; COD, chemical oxygen demand; CGAs, colloidal gas aphrons; CH 4, methane; CO2, carbon dioxide; DoE,

Department of Environment; DAF, dissolved air otation; DMF, N,N-dimethylformamide; EQA, Environmental Quality Act; EGSB, expanded granular sludge blanket; EC,

electrocoagulation; FFB, fresh fruit bunches; FBR, uidized bed reactor; FFA, free fatty acid; GAC, granular activated carbon; GHG, greenhouse gas; H2, hydrogen; H2O2,

hydrogen peroxide; HRT, hydraulic retention time; MLVSS, mixed liquor volatile suspended solids (MLVSS); MIRHA, microwave incinerated rice husk ash; MAS, membrane

anaerobic system; MF, micro-ltration; NF, nanoltration; nZVI, nano zero-valent iron; OLR, organic loading rate; O&G, oil and grease; POME, palm oil mill efuent; PAC,

powdered activated carbon; PAMS, propenoic acid modied sawdust; POMSE, palm oil mill secondary efuent; PES, polyethersulfone; PEG, polyethylene glycol; RBC, rotating

biological contactor; RO, reverse osmosis; SCAR, suspended closed anaerobic reactor; SBR, sequencing batch reactor; SVI, sludge volume indices; SRT, solid retention time; SS,

suspended solids; SG, specic gravity; TVS, total volatile solid (mg/l); TKN, total Kjeldahl nitrogen; TS, total solids; TSS, total suspended solids; UFF, upow xedlm; UASB,

up-ow anaerobic sludge blanket reactors; UASFF, upow anaerobic sludge-xed lm reactor; UF, ultra-ltration; US-EPA, US Environmental Protection Agency; VFAs,

volatile fatty acids; VSS, volatile suspended solids; VUV, vacuum ultravioletn Corresponding author at: Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi, 43600,

Malaysia. Tel.: 60 389216420; fax: 60 389216148.

E-mail address:[email protected](Z. Yaakob).

Renewable and Sustainable Energy Reviews 42 (2015) 1260 1278
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4.3. Stripping, digestion and extraction of crude palm oil (CPO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

4.4. Clarication and purication of the crude palm oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

4.5. Depericarping and nutber separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

4.6. Separation of kernels and drying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

5. The treatment or digestion processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

5.1. Anaerobic digestion or treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

5.1.1. Anaerobic ponds or lagoon system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264

5.1.2. Anaerobicltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267

5.1.3. Fluidized bed reactor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267

5.1.4. Up-ow anaerobic sludge blanket (UASB) reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12675.1.5. Expanded granular sludge bed (EGSB) reactor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268

5.1.6. Anaerobic bafed reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268

5.1.7. Anaerobic sequencing batch reactor (ASBR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269

5.1.8. Continuous stirred tank reactor (CSTR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269

5.1.9. Up-ow anaerobic sludge xed-lm (UASFF) reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1269

5.2. Aerobic digestion or treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1270

5.3. Physicochemical treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1271

5.3.1. Coagulation andocculation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1271

5.3.2. Electrocoagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272

5.3.3. Sedimentation and centrifugation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272

5.3.4. Flotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272

5.3.5. Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1272

5.3.6. Other physio-chemical methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1273

5.4. Membrane separation processes (MSPs). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1274

6. Future development and conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1275

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1275

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1275

1. Introduction

The last decade, consumption of palm oil in the world has

massively improved and is controlled by Indonesia and Malaysia. It

is calculated that the global production of palm oil is 62.34 million

tonnes in 2014, but 6.14 million or 9.85 percent from last year and

85 percent productions coming from two largest palm oil-

producing countries such as Indonesia (30.5 million tonnes) and

Malaysia (19.9 million tonnes)[1]. The global production of palm oilhas been more than doubled every 10 years, and by 2020, it is

expected to increase to 78 million tonnes[2]. The world population

is predictable to grow from 7 billion in 2011 to 9 billion by 2043. So,

production of food must meet this rate increased rate of population.

By 2043, world demand of fats and oils will reach 360 million

tonnes[3]. From this statistics, we can expect that the production of

palm oil will continue to rise in quantity with the world demand of

fats and oils. It is measured that, one tonne of fresh fruit bunch

releases almost 0.50.75 t of POME[4]. Therefore, huge volume of

crude palm oil and POME will be produced within 2043.

Dumping of this wastes is now a nancial problem in societies and

industries, and therefore, researcher have been trying to generate a

demandable end-product from these wastes, which would reduce the

efuent treatment as well as production cost. It is calculated thataround 28 m3 of biogas is generated from 1 m3 of POME in the

treatment plant[5]. Solid wastes (fruit ber and kernel shell), which

are use to generate steam and power in mills. The availability of

energy sources and other valuable products from the mills helps

minimize the operation and efuent treatment cost, while presenting

an alternative to the use of fossil fuels in palm mills. Chin and

coworkers calculated that, net income in Malaysian Ringgit (RM) is

3.8 million per year that can be obtained by the generation of

electricity using biogas from POME treatment[6].

Palm oil mill efuent could become a hopeful source of

renewable energy because of its plentiful organic matters. Little

research has been attained with a view to discovering an environ-

mental friendly solution for POME and their highlighting engaged

in the existing treatment processes in the palm oil industries.

Nonetheless, several treatment methods executed in bench scales

and reprocessing POME as an ecologically sustainable bio resource.

These up-to-date processes may, nevertheless, excavate a different

eld in POME treatment and may offer the industry with a

conceivable awareness into superior development in the existing

treatment processes.

The purpose of this article is to represent a full-scale review,

which reconsiders and updates recent treatment processes for

palm oil mill efuent and adds the latest contemporary techniqueswith the view to reach an understanding of standing end-of-

pipe processes for POME treatment and a number of prospective

approaches to reduce the environmental difculties caused by

POME enclosed with renewable biogas generation, such as biohy-

drogen and biomethane.

2. Characteristics of palm oil mill efuent (POME)

Palm oil industry generated huge volume of palm oil mill

efuent (POME) by the oil extraction process. Enormous amounts

of water are required to extract the crude palm oil (CPO). It is

calculated that around 1.5 m3 of water are typically used in each

tonne of fresh fruit bunches (FFB) processing and almost half ofthe water discharge as POME[7]. This POME is a combination of

wastes, which are produced and discharged from the three

principal sources such as clarication wastewater (60%), sterilizer

condensate (36%) and hydrocyclone wastewater (4%) [8]. Subse-

quently, around 0.9, 1.5 and 0.1 m3 of POME will be discharged

from these sources respectively for the handing out of one tonne

of CPO [9]. The characteristics of the dispersed efuent from

different sources are displayed inTable 1.

The raw POME is a thick brownish, viscous and voluminous

colloidal matters, containing 9596% of water, 45% total solids

including 24% suspended solids as well as 0.60.7% of oil and grease

which discharged at a temperature of 8090 1C. It is also acidic[10].

POME containing a vigorous amount of amino acids, inorganic

nutrients (Na, K, Ca, Mg, Mn, Fe, Zn, Cu, Co and Cd), short bres,

Y. Ahmed et al. / Renewable and Sustainable Energy Reviews 42 (2015) 12601278 1261


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nitrogenous compounds, free organic acids and carbohydrates[11]. It

contains small pH value, suspended solids (SS), nitrogen content asammoniacal nitrogen and total nitrogen[12]. It also contains organic

matters such as lignin (4700 ppm), phenolics (5800 ppm), pectin

(3400 ppm) and carotene (8 ppm) [13]. Even though it is non-toxicwith unfriendly odour, but containing biological oxygen demand and

Nomenclature

AD Anaerobic digestion

AF Anaerobic lter

AFBR Anaerobic uidized bed reactor

ABR Anaerobic bafed reactor

ASBR Anaerobic sequencing batch reactor

Alk Total alkalinityAOPs Advanced Oxidation Processes

AT-POMEAnaerobically treated palm oil mill efuent

BOD Biochemical oxygen demand

BPAC Banana peel activated carbon

BT-POMEBiologically treated palm oil mill efuent

BSA Bovin serum abumine

BFR Bio-fouling reducer

CA Cellulose acetate

CPO Crude palm oil

CSTR Continuous stirred tank reactor

CRT Cell retention time

COD Chemical oxygen demand

CGAs Colloidal gas aphrons

CH4 MethaneCO2 Carbon dioxide

DoE Department of Environment

DAF Dissolved air otation

DMF N, N-dimethylformamide

EQA Environmental Quality Act

EGSB Expanded granular sludge blanket

EC Electrocoagulation

FFB Fresh fruit bunches

FBR Fluidized bed reactor

FFA Free fatty acid

GAC Granular activated carbon

GHG Greenhouse gas

H2 Hydrogen

H2O2 Hydrogen peroxide

HRT Hydraulic retention time

MLVSS Mixed liquor volatile suspended solids (MLVSS)

MIRHA Microwave incinerated rice husk ash

MAS Membrane anaerobic system

MF Micro ltration

NF Nanoltration

nZVI Nano zero-valent iron

OLR Organic loading rate

O&G Oil and grease

POME Palm oil mill efuent

PAC Powdered activated carbon

PAMS Propenoic acid modied sawdust

POMSE Palm oil mill secondary efuent

PES Polyethersulfone

PEG Polyethylene glycol

RBC Rotating biological contactor

RO Reverse osmosis

SCAR Suspended closed anaerobic reactor

SBR Sequencing batch reactorSVI Sludge volume indices

SRT Solid retention time

SS Suspended solids

SG Specic gravity

TVS total volatile solid

TKN Total Kjeldahl Nitrogen

TS Total solids

TSS Total suspended solids

UFF Upow xed lm

UASB Up-ow anaerobic sludge blanket reactors

UASFF Upow anaerobic sludge-xed lm reactor

UF ultra-ltration

US-EPA US Environmental Protection Agency

VFAs Volatile fatty acids

VSS Volatile suspended solids

VUV Vacuum ultraviolet

Subscripts

min Minute

ha Hectare

t Tonne

m3 Cubic meter

kPa Kilopascal

MPa Megapascal

mg/L Milligram per litre

m3(CH4)/ kg CODrem Cubic meter methane per kilogram COD

removedm3(H2)/ kg CODrem Cubic meter hydrogen per kilogram COD

removed

kg COD/m3d Kilogram COD per cubic meter per day

kg COD/m3h Kilogram COD per cubic meter per hour

w/v Weight to volume ratio

h Hour

d Day

V Volt

A/m2 Ampere per square meter

RM Malaysian Ringgit

Table 1

Characteristics of individual wastewater streams in Palm oil mill

Parameter Sterilizer condensate Clarication wastewater Hydrocyclone wastewater

Chemical oxygen demand (COD) (mg/L) 47,000 64,000 15,000

Biochemical oxygen demand (BOD3, 30oC) (mg/L) 23,000 29,000 5000

Dissolved solid (DS) (mg/L) 34,000 22,000 100

Suspended solid (SS) (mg/L) 5000 23,000 7000

Total nitrogen (TN) (mg/L) 500 1200 100

Ammoniacal nitrogen (mg/L) 20 40

Oil and grease (mg/L) 4000 7000 300

pH 5.0 4.5



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chemical oxygen demand values are high and have an adverse effect

on the environment.Table 2shows the characteristics of raw POME

[1416].

3. Regulatory standards for palm oil mill efuent

Type or age of fruit, different efuent treatment processing system

as well as varied batches, days and factories signicantly change thecharacteristics of POME[17], factory discharge standard, climate and

condition of the processes and cropping season, activities of the palm

oil mill also effect on the quality and quantity of POME[14].

Malaysia rst introduces the efuent discharge system, speci-cally for palm oil and rubber mills. The country's Department of

Environment announced discharge standards for BOD on palm oil

efuent in 1977. Before the introduction of the regulation, crude

oil palm was the single worst pollution source in the country. Daily

discharge alone increased by more than 300% from 1965 to 1977.

The purpose of the regulation was to reduce pollution created by

the sector without hampering its growth. In order to control the

industrial pollution in the country, regulatory control over dis-

charges from palm oil mills is instituted through the Environ-

mental Quality (Prescribed Premises) (Crude Palm Oil) Regulations

1977, promulgated under the allowing powers of Section 51 of the

Environmental Quality Act (EQA), 1974, which are the central

regulations and contain the efuent discharge standards. The

discharge standards of POME into water sources in Malaysia [18]

are presented inTable 3.

4. Process description of palm oil mill process and sources of

water pollution

The most usual palm oil extracting process in Malaysia from

fresh fruit bunches (FFB) is the wet process[8].Enormous volumes

of water and steam are necessary for removing dirt and sterilizing

in different steps of the wet process. Thus, the giving raises to the

huge volume of the palm oil mill efuent simply known as POME.

Fig. 1shows a chart for the usual extraction process of palm oil,

Table 3

Discharge standards of POME into water resources in Malaysia[18].

Parameters

Limits of discharge according to times

1/7/7830/6/79 1/7/7930/6/80 1/7/8030/6/81 1/7/8130/6/82 1/7/8231/12/83 1/1/1984 and thereafter

Chemical oxygen demand (COD) (mg/L) 10,000 4000 2000 1000

Biochemical oxygen demand (BOD3, 30oC) (mg/L) 5000 2000 1000 500 250 100

Total solids (mg/L) 4000 2500 2000 1500

Suspended solids(mg/L) 1200 800 600 400 400 400

Total nitrogen (mg/L) 200 100 75 50 300a 200a

Ammoniacal nitrogen (mg/L) 25 15 15 10 150a 150a

Oil and grease (mg/L) 150 100 75 50 50 50

pH 59 59 59 59 59 59

Temperature (oC) 45 45 45 45 45 45

a

Value ofltered sample.

Table 2

General characteristics of POME[1416].

Parameter Concentration range Element Concentration range (mg/L)

Chemical oxygen demand (COD) (mg/L) 15,000100,000 Potassium 12811928

Biochemical oxygen demand (BOD3, 30oC) (mg/L) 10,25043,750 Calcium 276405

Total solid (SS) (mg/L) 11,50079,000 Magnesium 254344

Total suspended solid (TSS) (mg/L) 500054,000 Phosphorus 94131

Total volatile solid (TVS) (mg/L) 900072,000 Manganese 2.14.4

Total nitrogen (TN) (mg/L) 1801400 Iron 75164

Ammoniacal nitrogen (mg/L) 480 Zinc 1.21.8

Oil and grease (mg/L) 13018,000 Copper 0.81.6

Temperature (1C) 8090 Chromium 0.050.43

pH 3.45.2 Cobalt 0.040.06

Colour (ADMI) 4500 Cadmium 0.010.02

Fresh fruit bunches (FFB)

Sterilization of FFB

(140C, 2.9 atm, 75-90 mins)

Stripping

Digestion tank

Steam, 80-90C

Pressing

Crude palm oil (CPO)

Clarification tank

(90C)

Sludge Oil

Separator Centrifuge

Vacuum dryer

Dry oil

Oil

Press cake

Fiber for boiler fuel

Depericarper

Nuts

Nutcracker

Hydrocyclon 0.1 T POME

Empty fruit bunches

Sterilizer condensate 0.9 T POME

KernelsShells for boiler fuel

1.5 T POME

Storage

Fig. 1. Flow diagram in a typical palm oil extraction process.



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and the explanations of different stages are in the subsequent

section.

4.1. Reception, transfer and storing of fresh fruit bunches

Fresh fruit bunches (FFB) are reaped in the farmsteads and

transported as soon as possible to the mills for instant processing.

Various transportation systems are used to carry the fruit bunches

to the mills. The fresh fruit bunches (FFB) are generally droppedonto a ramp and then to sterilizer cages. Attention must be taken

in handling and transportation of fresh fruit bunches so that fruit

bunches are not damaged. The damaged palm fruits will give rise

to poor-quality palm oil because growing of free fatty acid (FFA)

content.

4.2. Sterilization of fresh fruit bunches

After loading into the sterilizer cages, the fresh fruit bunch is

exposed to the steam-heat in horizontal sterilizers for 75 90 min

at around 140 1C and a pressure of 293.84 kPa. This stage prevents

free fatty acids formation of by the action of enzymes, to permit

the stripping of the fruits from spikelets, to make the fruit

mesocarp for consequent processing by coagulating the mucilagi-

nous material which facilitates the breaking of the oil cells and

minimizes the breakage of the kernel during pressing and nut

cracking. The sterilizer discharged POME from this section, and

about 0.9 t of sterilizer condensate produced in this step to process

every tonne of oil.

4.3. Stripping, digestion and extraction of crude palm oil (CPO)

Now the sterilized fruits are fed into a stripper where the fruits

are detached from the spikelets or bunch stalks. As the drum-

stripper rotates, the bunches are lifted up and then dropped

constantly along the stripper. The fruits are knocked off the bunch

by this action. The separated fruits are passed into a digester

followed by a screen and a bucket conveyor. Fruits are softened or

mashed under steam heated conditions (8090 1C) by a steamjacket in the digester or by direct live steam injection. The mashed

fruits under heating and high pressure break the oil-bearing cells

of the mesocarp and then channelled to a mechanical twin-screw

machine to press out the CPO and the addition of hot water to

increase the oil ow.

4.4. Clarication and purication of the crude palm oil

The digested crude palm oil (CPO) contains 3545% of palm oil,

4555% of water and the rest of the brous materials. It is pumped

into a clarication tank to separate the oil from CPO and tem-

perature is retained at 90 1C to enrich the oil separation. After

parting the oil, it is constantly skimmed-off from the top of the

tank. The bottom phase of the clarication tank still contains someoil and it is well again by passing through the sludge separator.

The recovered oil is returned to the clarication tank. Subse-

quently, it is passed through a high speed centrifuge and a vacuum

dryer. Finally, it sent to the storage tanks. The other stream

consisting of water and brous debris are drained off as a sludge

waste. About 1.5 t of sludge waste are generated during the

processing of each tonne of CPO.

4.5. Depericarping and nutber separation

After pressing by screw press, press cake formed, which

involves of moisture, oily ber and nuts. After that, all the

materials are carried to a depericarper for the separation ofbre

and nut. After parting, the ber is sent to a boiler house as fuel.

4.6. Separation of kernels and drying

In this step, nuts are again processed in hydrocyclone, where

the palm kernel is separated from shells based on the difference of

specic gravity (SG). The remaining wastewater is discharged, i.e.

hydrocyclone wastewater and about 0.1 t of hydrocyclone efuent

formed per tonne of palm oil production.

5. The treatment or digestion processes

5.1. Anaerobic digestion or treatment

Through the years, the use of anaerobic digestion (AD) has

grown rapidly due to the increasing signicant deployment of

renewable energy concerning mitigation of greenhouse gas (GHG)

emissions and the need for sustainable industrial wastewater

treatment. Anaerobic digestion is the effective efuent treatment

method, containing a huge amount of organic substances such as

POME [19]. It is demarcated as the methanogenic anaerobic

degradation of organic and inorganic matters in the absence of

oxygen. It includes diverse species of anaerobic microbes, which

are responsible for the degradation of organic matter and requires

time to adapt to the new environment before they start toconsume on organic matters to grow. The efciency of this system

mainly depends on the structure of microbial community and

environmental factors, for example, pH and temperature [20].

It is a multi-stage (hydrolysis, acidogenesis, acetogenesis and

methanogenesis) degradation of organic matters and transformed

into CH4 and CO2 by the action of a group of microorganisms

[2123]. Wong also revealed that, the fresh POME was rst

changed into volatile fatty acids (VFAs) by acid-forming bacteria

then transformed into CH4 and CO2 in the anaerobic digestion

process [24]. This process produced biogas such as biomethane

and biohydrogen through the fast degradation of organic com-

pounds [25] from POME. Moreover, it established a unique and

useful stabilization system, which is biologically active and

diminishes the sludge. Various types of an anaerobic digestionsystem exist in the world. The most recommended digestion

processes for POME include anaerobic lters and anaerobic ui-

dized bed reactors, up-ow anaerobic sludge blanket reactors

(UASB), expanded granular sludge blanket (EGSB), anaerobic

bafed reactors (ABR), anaerobic sequencing batch reactor (ASBR),

continuous stirred tank reactor (CSTR) and upow anaerobic

sludge-xed lm reactor (UASFF). The performances of various

anaerobic treatment processes are summarized in Table 4. The

mentioned anaerobic treatment processes for POME are explained

in the subsequent section.

5.1.1. Anaerobic ponds or lagoon system

Anaerobic pond is most useable POME treatment system in the

palm oil mills and around 85% of the mills implemented thismethod owing to only its low capital and operational cost [26].

Nowadays, Harsono and his coworkers observed that about 50% of

the mill used anaerobic ponds for the treatment of POME, while

the remaining 50% mill used various anaerobic digester [5]. It

consists of a number of ponds of different functions such as

cooling pond, a mixing pond(de-oiling), acidication ponds, anae-

robic ponds, facultative and algae (aerobic) pond, which are made

up of earthen structures with no lining at the bottom [12,27].

However, it needs an enormous land area to produce efuent that

complies with Federal Subsidiary Legislation, 1974 efuent dis-

charge standards.

A typical size of an anaerobic pond in a palm oil mill which has

a processing capacity of 54 t per hour is 60.029.65.8 m3

(lengthwidthdepth) [28], which is approximately equivalent



6/19

Table 4

The summarization of various anaerobic treatment processes.

Anaerobic

treatment

systems

Advantages Disadvantages COD

removal

efciency

(%)

CH4/H2composition

(%)

Yield of

CH4/

H2m3(CH4/

H2)/kg

CODrem.

HRT

(days

or

hrs)

OLR

(kg

COD

/m3 d)

Reference

Anaerobic

pondingsystem

Cheap, simple design, stable and

reliable system.

Large areas of land are re quired. 97.8 54.4 40 1.4 [28]

Control and monitoring is difcult dueto their sizes and structures.The energy needed is minimal and has

low operatin g c osts. Accu mu lation of slu dge is hi gh.

Sludge production is very little.

Nutrient requirement is very low.

The removal of P, N and solids are

usually unacceptable.

Recovered sludge used as fertilizer.

Digested POME could be used for algae

culture.

Biogas and emission of CH4are low.

Able to tolerate a high range of OLR

thus can easily handle POME discharge

during a high crop season.

Methane, H2S and CO2directly release

to the environment.Long startup and HRT (450 days).

Always required post treatment to

remove remaining organic matter.

Anaerobic

ltration

Construction, operation and

maintenance costs are lower.

Deterioration of the bed structure

through a gradual accumulation of

non-biodegradable solids.

94 63 0.79 15 4.5 [10]

High biomass concentration retained

in the packing.

93 61 0.78 10 6.6

High media maintenance and support

cost.High removal efciency of COD, BOD

and suspended solids. Requires a constant source of water.

91 62 0.69 6 11.4

Long start up time.Smaller reactor volume needed.

Removal of pathogens and nutrients are

low.

73 5772(H2) 0.239(H2) 7 20.0 [34]

Able to handle high volume of loads.

Efuent require post treatment and/or

appropriate discharge.

Sensitive to shock loading with HRT is

low.

6094 0.822 (H2) 510 5.8

10.9

[35]

Incompatible for high suspended solid

wastewater.

No electrical energy required. 90 6 h 10 [39]

Producing high quality efuent.

Clogging occurs at high OLRs.

Long service life. 91.6 50 0.482 13.5 1.1 [40]

80.9 0.42 2 7.5

Anaerobic

uidized

bed

reactor

Rates of organic loading are high at

short HRT.

High energy requirements 78 6 h 40 [39]

Carrier media is costly.

Small areas are required. Highly turbulent conditions

microorganism like bacteria are

willingly adhered to the reactor bed.

Good potential for maintaining a

high biomass concentration at long

SRT.

93 6 h 10

Channelling, plugging and gas hold

up problem is minimum.

Large surface area for mass transfer

and biomass attachment.

Oxygen distribution system, biolm

thickness and consumption power are

high.

85 12 h 4.0 [45]

Uniform liquid ow distribution.Used to treat high strength

wastewater at both ambient and

elevated temperatures.

65 4 h 13.8

Inappropriate for high-suspended solid

waste-water.

Low sludge production and ability to

tolerate shock loads.

Unable to capture produced biogas.

95 12 h 4.7 [49]

80 4 h 10.8

Upow

anaerobic

sludge

blanket

(UASB)

COD removal efciency and methane

emission rate is high.

Highly dependent on the ability of sludge

settle.

8090 121

149

4560 [19]

High biomass concentration reserved

in the reactor.

Separation between treated efuent and

biomass is poor.

96.798.4 54.262 4 1.3

10.6

[57]

Superior is settling characteristics of

granular sludge at higher OLRs.

Foaming and sludge oatation at high

organic loading rates (OLRs).

96.3 0.012 20 2.5 [40]

At higher organic loading treatment,

biomass retained is unable.

80.5 0.058 3.33 15Produced with high quality efuent.

High degree of waste stabilization 82.4 48 0.91 120 12.5 [62]

Nutrient requirement is minimal.

Possibility of biomass washout is more

prominent at lower HRTs.

Long start-up time lacking of granulated

seed sludge. 65 0.38 (H2) 16 h 30 [66]

62 52 (H2) 0.35 (H2) 12 h 120 [67]

It exhibits superior performance dueto the good maintenance of

methanogenic sludge with long

sludge retention time.

Granulation inhibited at high volume of

volatile fatty acid.

9799 7080 16.2 711 1.54.8 [68]

95.5 66 0.361 5 2.9 [75]

Used to treat high-strength

wastewater under mesophilic or

thermophilic conditions.

It is inactive at a higher organic loading

rate (OLR) in the presence of high

amount of suspended solids.

92.5 61 0.448 5 5.865 58 0.438 5 10.496.5 55 0.265 10 2

94 72 0.484 5 1.3

Expanded

granular

sludge bed

reactor

(EGSB)

Improve substratebiomass contact in

the system.

Elimination of particulate organic matter

is tough because of high upow velocity.

91 70 2 17.5 [73]

Efuent recirculation is possible. The granular bed is unable to retain the

suspended matters, thereby leave with

the efuent.

8590 - 20 [74]

Higher organic loading rate

achieved.

Better performance and stability. Used to treat the low-strength

wastewater, especially low to mid

temperature.

97 51 0.372 10 2 [75]

Removal efciency COD was

proportional to upow velocity.

95 61 0.417 5 2.9

Separation of dispersed sludge from

mature granules is possible.

Active biomass needed for granular

anaerobic sludge.

91.6 60 0.436 5 5.8

53 59 0.339 5 10.4



7/19

to half the size of a soccer eld. Size of the pond depends on the

capacity of the palm oil mill as well as the area available for ponds.

Anaerobic ponds have the longest retention time in ponding

system, which is around 20200 days[29]. The depth of the pond

shows an important effect on the determination of nature of a

biological process. The optimum ranges of depth for anaerobic

ponds are 57 m with HRT of 3045 days, while the depths and

HRT are 1

1.5 m and 15

20 days respectively for facultative ponds

[26,27]. A lower depth of around 0.51.0 m is necessary for aerobic

ponds with HRT of 24 days [27]. Yacob et al. showed that above

97.8% COD reduction was achieved at HRT of 40 days and OLR of

1.4 kilogram COD per cubic meter per day (kg COD/m3 d). How-

ever, methane gas emission recorded in the anaerobic pond was

only 54.4%[28].In addition to that, the methane composition from

anaerobic ponds was observed to be more consistent in the

gaseous mixture. Mill activities and seasonal cropping of oil palm

Table 4 (continued )

Anaerobic

treatment

systems


removal

efciency

(%)

CH4/H2composition

(%)

Yield of

CH4/

H2m3(CH4/

H2)/kg

CODrem.

HRT

(days

or

hrs)

OLR

(kg

COD

/m3 d)

Reference

Higher methane yield and easy

degradation occurred in case of

deoiled POME.To obtain greater upow velocity

required higher ratio of reactor

height/surface area.

94a 70 0.409 5 1.3

92.3

a

73 0.555 5 2.6

Anaerobic

bafed

reactor

(ABR)

Simple and economical construction. Satisfactory recycling is wanted for

reactor stability.

77.3 69.1 0.33 3 5.33 [81]

Higher cell retention time and

effective treatment could be

obtained.

95.3 71.2 0.32 10 1.6

Stability to shock loading are capable

to achieve at high volumetric rates.

Nutrient supplementation is needed. 84.6 67.4 0.18 2.5 10.9 [82]

High degree of waste stabilization.

98 4 34 [83]

Anaerobic

sequen-

cing batch

reactor

(ASBR)

Comparatively low cost and energy

demand.

Nutrient supplementation is needed for

relatively resistant organic wastes to

improve the treatment of wastewater.

437 50 (H2) 0.34 3 6.6 [64]

Produced minimum pollution. 5772.5 60 (H2) 0.27 2 60 [65]

Favourable and efcient technology

for hydrogen production.

Flexibility and simple operation

without requiring any separateClariers.

Reactor geometry effect on process

performance.35.56 8.2 5861 (H2) 1.62.3 Mol

H2mol

1

hex

4 7090 [85]Low performance efciency at higher

OLR.

High biomass retaining reactor. 58 60(H2) 6.5(H2) 2 85 [86]

Rate of digestion and stability are good

Different reactor shapes or geometry

imposes distinct selective pressure on

the microbial components of the

biomassNo short circuit due to xed-bed

continuous systems.

37 58(H2) 4.2(H2) 2 85

37.7 2.05(H2) 4 11.3 [96]

Continuous

stirred

tank

reactor

(CSTR)

Relatively cheap and simple to

construct.

Less efcient for the production of gas at

high treatment volume and short

hydraulic retention time (HRT).

80 62.5 18 3.33 [88]

Provides more contact between

wastewater and biomass through

mixing.

82.9 70.1 7 1.41 [90]

90.4 69.5 6 1.89

Easy to control temperature in each

stage.

77 63 0.17 8 1.7 [91]

Time-consuming operation with

continuous feeding because of a

degradation of microorganisms.

Relatively easy to clean and

maintenances.

70 67 0.16 4 1.6

69.89

71.10

0.460.51 7 9.72

12.25

[92]

Increased gas production compared to

conventional method.

Less biomass retention

Reactant added to mixture which is rich

in product in this reactor will affect the

quality and yield.

68.20

70.32

0.44 5 15.2

17.01Lower operating cost due to low

amount of electrical energyrequired.

30(H2) 1.05(H2) 2 5060 [93]

It operates in a steady state.

It is well controllable and large heat

transfer areas can be installed

66.09 48.05 0.532 12 6.9 [94]

44.8 2.16(H2) 4 11.3 [96]

Upow

anaerobic

sludge

xed lm

(UASFF)

At higher organic loading treatment

able to retain biomass in the reactor.

Separation between treated efuent and

biomass are poor.

89.597.5 6284 0.280.29 1.53 1. 75

23.15

[98]

Shorter start-up times for the sludge

granulation and higher biomass

retention.

92.62 70.83 0.31 1.5 9.3 [101]Stability and efciency of the reactor

depend on internal packing, efuent

recycling ratio, rate of feed ow and

up-ow velocity.

96.1 80.5 0.33 2.9 14.93

Achieved higher organic loading

compare UASB and anaerobic

ltration.

Pretreatment of efuent is required for

incomprehensible suspended solids and

reduce the treatment efciency.

92.3 3.5 16.2 [99]

Reduce the clogging. 95.1 0.32 2.2 12.9 [102]

COD removal efciency and

methane emission rate is higher at a

lower HRT.

92.62 0.31 1.5 9.3

Stable operating conditionsAble to tolerate shock loadings.

80.698.6 55.3 0.290.35 16 0.88

34.7

[100]

Most of the value indicated for methane composition and yield and the rest of signed for hydrogen value.

Hydraulic retention time (HRT) expressed as day but in few cases as hours.a Deoiled palm oil mill efuent (POME)



8/19

inuenced methane emission in anaerobic ponds [28]. However,

creation of scum on the surface and body be subject to build-up at

the bottom of the pond is main difculties with this system, which

lowered the efciency. So, regular desludging either using sub-

mersible pumps or excavators to continue the preferred efciency.

Ismail and co-workers analysed various parameters such as

COD, BOD, Fe, Zn and Mn and turbidity using the conventional

ponding system in mills consists of a series of seven ponds. The

POME at Pond 2 (Mixing) has the highest concentration of alltested ponds because it is the rst receiver of POME. The activity of

desludging at Pond 4 (Anaerobic 2) and Pond 5 (Facultative), BOD

concentration in Pond 7 (Algae 1) was appeared slightly higher.

The POME at Pond 2, 4, 5 and 7 has been treated through the

adsorption process by sunlight. The adsorption process shows a

considerable reduction of the above parameter and indicates the

performance of zeolite as adsorbent is promising. The highest

removal concentration of turbidity, COD and BOD observed at

Pond 2 and removal capacity were 80.5%, 54.5% and 78.0%

respectively [30]. Chin and his co-workers also assessed the

treatment efciency of an anaerobic pond, which consists of eight

ponds in series and treating 600 m3 POME per day. The inuent

concentration ranges of COD were 45,00065,000 mg/l, BOD518,00048.000 mg/l and oil and grease larger than 2000 mg/l.

After treatment, the efuent containing the concentration of COD,

BOD5, ammonia-N, nitrate nitrogen, TKN and phosphate were

1725, 610, 115, 5, 200, and 60 mg/l respectively [31].

5.1.2. Anaerobicltration

The idea of anaerobic lter (AF) was primarily expressed by

Coulter et al. [32], but the rst demonstration of this treatment

system came from Young and McCarty, who fruitfully operated an

upow anaerobic lter to treat the rum distillery wastewater[33].

This lter has been used in bench scale to treat the POME

[10,34,35]. Borja and Banks used an upow anaerobic lter to

treat the POME, achieved up to 90% COD removal efciency at

organic loads ranging from 1.2 to 11.4 kg COD/m3 d and reduced

HRT from 15 to 6 days and the production of methane varied from20 to 165 dm3 per day, was about 60%. However, maximum 94% of

COD remove was reached at OLR of 4.5 kg COD/m3 d and HRT of 15

days [10]. Filter clogging is a major problem in the nonstop

operation of anaerobic lters [3638]. So far, clogging has been

reported at an OLR of 20 kg COD/m3 d for POME [39]. They also

showed that after adaptation, above 90% COD removals were

reached at 6 h HRT and OLR of 10 kg COD/m3 d[39]. Chaisri and

coworkers investigated the effect of organic loading rate (OLR) for

the productions of methane and volatile fatty acid in UASB and

UFAF reactors. They obtained the optimum OLR for UASB and UFAF

reactors were 15.5 and 7.5 kg COD/m3 d respectively in the

laboratory scale. They produced maximum 2.54 l/day of methane

at OLR of 7.5 kg COD/m3 d and removed 91.6% of COD at OLR of

1.1 kg COD/m3 d and HRT of 13.5 days by using UFAF[40].Upow anaerobic lters (UAF) can be operated at either

mesophilic or thermophilic temperature ranges. Thermophilic

anaerobic lters offer an alternative treatment system for high

and medium strength wastewaters, especially for those waste-

waters which released at high temperatures like POME [35].

Thermophilic POME sample gave higher yields than the mesophi-

lic POME sample [41]. Concentration of volatile suspended solid

(VSS) increased steadily from week 5 in the lter, and it varied

from 1.8 to 6.1 kg m3 during the start-up stage (10 weeks). The

start-up stage achieved a chronological rise of temperature of

0.51 1C per day in which seeds of bacteria were steadily adapted

to the thermophilic conditions. The Upow anaerobic lter (UAF)

indicated a satisfactory performance in organic removal efciency

(up to 97% and 94% for BOD and COD, respectively). The

production rate and yield of biogas were 1.16103 m3 d1 and

0.822 m3/kg COD respectively [35]. The production of methane

from POME is the most commonly used method, but fed batch

production of hydrogen from POME has been considered by using

anaerobic microora[42]. The hydrogen generating microora has

been isolated from various sources. Vijayaraghavan and Ahmad

isolated a microora from cow dung at pH of 5 and treatment with

heat (2 h) and produced biohydrogen from POME by the used

anaerobic contact lter. The produced biogas was free frombiomethane. With the increase of HRT, increased the production

of biohydrogen content and maximum biohydrogen was 102.6 mL

and average hydrogen content of 5772% at 7 d HRT and yield of

biogas was 0.42 m3/kg COD[34].

5.1.3. Fluidized bed reactor

The attached growth anaerobic uidized bed reactor (AFBR) is

the treatment methods for low strength wastewater, and it offers a

good mass transfer between substrate and medium. The high

upow liquid velocities give a bed growth of almost 100% and

short HRT[43]. Switzenbaum and Jewell rst assessed the treat-

ment efciency of dilute synthetic wastewater above a range of

1030 1C and achieved COD removal efciencies ranges from about

40% at 10 1C to about 50% at 30 1C with HRT of 0.33 h [44]. Thereare much evidence, which supports the ndings of POME

[29,39,45]. Fluidized bed reactor provided a greater treatment

efciency at higher loadings; even at 40 kg COD/m3 d, with 6-h

residence times and degraded about 78% COD whereas an anae-

robic lter could be worked below 20 kg COD/m3 d shorn

of clogging. After adaptation, removals of COD were reached

higher than 90% in both reactors at 6 h HRT and OLR of 10 kg

COD/m3 d[39].

The efciency of the uidized bed reactor (inverse and up-ow)

depends on the nature of support material [46]. The inverse ow

uidized reactor showed outstanding stability when overload is

applied [47]. Small porous uidized media retain high biomass

concentrations in the reactor and thus decreased HRT. Smaller HRT

(6 h) and greater CH4production showed a benet ofuidized bedover an anaerobic lter (AF) to treat the POME [29]. Granular

activated carbon (GAC) removed about 60% COD in the uidized

bed system [48] while saponite removed 94.4% of COD [39].

Mamun and Idris operated a pilot plant at ambient temperatures

with diluted POME as a substrate. It took 17 days for the start-up of

the reactor with pre-seeded sand media. The reactor was capable

to remove a large portion of organics at relatively shorter retention

time. Maximum and minimum COD removal efciency of 85% and

65% were attained at a loading rate of 4.0 and 13.8 kg COD/m3 d.

The elimination rates of BOD and TSS varied in the range of 64

91% and 6889% respectively [45]. The anaerobic uidized bed

reactor exhibited lower sludge volume indices (SVI). Low SVI

values indicated that, this reactor generated less sludge with fast

settling properties. Whereas Ahmed and Idris used a biofuel ofSaccharomyces cerevisiaefor xing with sand as supporting mate-

rial on a uidized bed reactor (FBR) for the treatment of POME.

After 5 days adaptation, 92% BOD, 95% COD, 85% TKN, 94% SS, 95%

VSS and 90% turbidity removal were achieved in a batch experi-

ment with OLR of 4.7010.82 kg COD/m3 d and HRT of 12 h[49].

5.1.4. Up-ow anaerobic sludge blanket (UASB) reactor

The upow anaerobic sludge blanket (UASB) reactor is the

prominent expansions in anaerobic digestion system for waste-

water treatment and more than 1000 such type of reactors are

used in worldwide (especially in tropical countries) [50,51].

Lettinga developed UASB reactor [52], and this process has been

effectively used to treat the wide range of industrial efuent[53].

This reactor shows a good performance for high-suspended solid



9/19

wastewater and generates higher volume of methane[54]. Popu-

lation of microorganism (acetogenic bacteria and Methanosaeta

sp.) considerably speeds up the growth of granule [55]. Formation

of granular sludge is the core distinctive feature as against of other

anaerobic processes. The removal efciency of COD depends on

the availability of granular sludge. Moreover, natural turbulence

oats the sludge, affords resourceful efuents and biomass con-

tact. As granulation/blanketing generate in the reactor, which

could be regulated the solids and hydraulic retention timesindividually and efciently, thus reduce the treatment times from

days to hours[56].

The treatment of POME has been effective with UASB reactor.

Borja and Banks used a 16L bench scale UASB reactor and controlled

OLR of 5.142.5 kg COD/m3 at 4 days HRT and achieved 98.4% COD

removal efciency with the maximum OLR of 10.63 kg COD/m3 d

[57]. Chaisri and coworkers investigated the effect of organic

loading rate (OLR) for the productions of bio-gas, methane and

volatile fatty acid in UASB and UFAF reactors. They obtained the

optimum OLR for UASB and UFAF reactors were 15.5 kg COD/m3 d

and 7.5 kg COD/m3 d respectively in the laboratory-scale. They

obtained 96.3% COD removal efciency at OLR of 2.5 kg COD/m3 d

and HRT 20 days and the maximum production of biogas, methane

and methane yield were 25.5, 0.695 and 7.01 l/day, respectively at

OLR of 15 kg COD/m3 d and HRT of 3.33 days. They also achieved

maximum 5.50 g/l of VFA accumulation at OLR of 17.5 kg COD/m3 d

and HRT of 2.86 days in UASB reactor [40]. However, at higher OLR

of 17.5 kg COD/m3 d with 23 h HRT, the method was unstable due to

higher volatile fatty acids (VFA) content and H2 accumulation,

which reduced the COD removal efciency to 62.5% as well as

inherent the methane fermentation because the growth rate of

acidogenic bacteria was faster (10-fold) than the methanogenic

bacteria[40]. Miyamoto developed two-stages fermentation system

consisting of acidogenic and methanogenic due to operate at higher

OLR[58]. Torkian and coworkers applied this system for treatment

of slaughterhouse wastewater and observed methanogenic reactor

acclimate rapidly with the feed from the acidogenic reactor and

allow higher organic loadings (highest 30 kg-COD/m3 d) and

removed about 90% COD and convert to efcient biogas. Thesuspended and colloidal components such as protein, fat and

cellulose stuck the reactor performance and weakening the micro-

bial activities and wash out active biomass [59].

Granulation process altered its activity with the change of

environmental and operational systems[60]and granules disinte-

grate their strength and stability due to the lack of substrate

concentration, which can be prevented to operate the reactor under

low OLR. It was possible to achieve maximum 2.42 m3/m3 of biogas

and 0.992 m3/m3 of methane production rates were at an OLR of

6.0 kg-COD/m3 d[61]. Ahmad et al.[62] used calcium oxide (CaO) to

accelerate the granulation system in UASB reactor and removed

94.9% of COD with the fed of 15.565.5 kg COD/m3 at OLR of 4.5

12.5 kg-COD/m3 d. An average 82.4% of COD removal was achieved

with the fed of 10 kg/m3 CaO at an OLR of 12.5 kg-COD/m3 d in themesophilic state. The average yield of methane was 0.91 Cubic

meter methane per kilogram COD removed (m3 CH4/kg-CODrem)

and the removed 88.6% of COD was reformed to biomethane.

The production of fermentative hydrogen depends on the

effects of HRT and OLR. Few researchers used POME with micro-

ora, or mixed cultures of POME sludge for the production of

hydrogen [6367]. Singh and his coworkers used polyethylene

glycol (PEG) gel to immobilize Clostridium sp. LS2 bacteria for the

production of hydrogen by using UASB reactor. 10% weight to

volume ratio (w/v) of PEG-immobilized cell packing used for the

production of hydrogen and obtained maximum 0.365 m3 H2/

m3-h of hydrogen at OLR of 30 kg COD/m3-h and 16 h HRT. The

average 68% of hydrogen contained in biogas and removed 65% of

COD. Whereas 12% of w/v of PEG-immobilized cell packing also

used in another test and highest production rate of hydrogen was

0.336 l H2/l h at 12 h HRT and an OLR of 5.0 kg COD/m3 h. The

removal of COD and average hydrogen content in biogas were 62%

and 52% respectively [67]. Ahmed and his coworkers used con-

centrated butyrate for the treatment POME and production of

methane at 37 1C and pH of 6.57.5 and achieved 9799% of COD

removal efciency at OLR of 1.54.8 kg COD/m3 d by varying HRT

(117.2 days). Highest 20.17 m3/m3-day of biogas and 16.2 m3/m3-

day of methane were obtained at OLR of 4.8 kg COD/m3

d and HRTof 7.2 days. The methane content in the biogas was higher about

7080% in the presence of butyrate [68].

5.1.5. Expanded granular sludge bed (EGSB) reactor

Expanded granular sludge blanket (EGSB) reactor is a modied

hydrodynamics UASB reactor. Lettinga and co-workers used this

reactor for low strength and complex wastewaters[69,70]. Now it

is the second most extensively used anaerobic reactors [71]. The

upow liquid velocity (410 m/h) of this reactor, causes the sludge

bed to expand or by the efuent recirculation (or both) and offers

superior hydraulic mixing and diminishes the dead zones inside

the reactor [72]. Zhang and coworkers used this reactor to treat

the POME under mesophilic conditions. Only 46% COD of raw

POME converted into biogas in which the methane content wasabout 70% (V/V). They showed that it had a good COD removal

efciency and removed 91% of COD at HRT of 48 h and OLR of

17.5 kg COD/m3 d. A 30 days discontinuous experiment quantied

that highest 56% of organic substances were transformed into

methane [73]. Frankin compared the performance efciency of

UASB and EGSB. It showed that both reactors are able to remove

COD approximately 8590%, but UASB showed better performance

at lower OLR of 10 kg COD/m3 d, while EGSB showed in average of

OLR of 20 kg COD/m3 d[74].

Fang and his coworkers used EGSB reactors to investigate the

anaerobic digestion of raw and deoiled POME both in batch and

continuous experiment and achieved higher yields of methane

from deoiled POME because it contained small amounts of bio

bres which were more recalcitrant compared the raw POME. Thedeoiled POME produced more than 90% of the methane within 14

days and the methane yield was 0.555 m3-CH4/kgVS-added at

lower OLR of 2.6 kgVS/m3-day. While the raw POME, removed 90%

of COD at HRT of 5 days with OLR of 5.8 kgVS/m3-day and yields of

methane were 0.438 m3-CH4/kgVS-added[75].

5.1.6. Anaerobic bafed reactor

McCarty and coworkers developed the anaerobic bafed reactor

(ABR) by removing rotating discs from the rotating biological

contactor (RBC), where most of the suspended biomass exist [76].

The anaerobic bafed reactor (ABR) is a series of UASBs, where

granulation do not require for its operation [77]. A series of vertical

bafes forces the wastewater to ow under, and over them as it

passes from inlet to outlet. Bacteria gradually rise and settle withinthe reactor due to ow characteristics and produced gas in each

compartment, but move horizontally down the reactor at a com-

paratively slow rate giving rise to cell retention time (CRT) of 100

days at HRT of 20 h[78]. Therefore, the wastewater comes in a close

contact with a huge amount of active biomass with short HRTs

(620 h), while the efuent remains relatively free of microbes[79].

A number of researchers used this reactor in laboratory and

pilot scales for the treatment of industrial wastewater [80],

including POME[81,82]. Setiadi and coworkers used ABR system

to treat the POME and maintaining pH upper than 6.8 in the

absence of alkalinity. The maximum 25 times recycled allowed to

remove the COD, BOD as well as oil and grease up to 84.6%, 86.04%

and 72.7% separately and maximum production of methane was

13.34103

m3

/day at OLR of 10.9 kg COD/m3

d and HRT of



10/19

2.5 days[82]. Faisal and Unno have been improved the Bachmann

proposed ABR designs and produced bio-methane keeping the low

concentration of volatile fatty acid (0.608 kg/m3) at longer 10 days

HRT and showed high removal efciency of COD and grease/oil up

to 95.3% and 91.3%, respectively. Production and yield of methane

gas were in the range of 8.7110327.4103 m3CH4/day and

0.320.42 m3-CH4/kg-COD respectively and the methane content

in the biogas was higher about 67.371.2% at HRT of 310 days

[81]. Arizwan showed that the ABR system has a high potential oftreating POME in short HRT due to the presence of bafes in the

system. The ABR system was initially operated with diluted factor

of I:25 of the samples in order to decrease the high value of COD

with four days HRT and the dilution factor was continuous

decreasing by the factor of 19, 15, 8, 5, 2 and lastly without any

dilution. The highest COD removal efciency was found at dilution

factor of 8 where 34 kg/m3 of COD inuent with 98% of COD

removed and methane gas production of 0.941 m3/day[83].

5.1.7. Anaerobic sequencing batch reactor (ASBR)

Anaerobic sequencing batch reactor (ASBR) is an improved form

of activated sludge process and operated under non-steady state

conditions. In recent years, ASBR has been used as an effective

wastewater treatment system due to its better process control andhigher removal efciency of BOD and SS [84]. It works in a batch

style with lling, aeration, settling and decantation taking place in

the same tank. Badiei et al. used mixed microora for the produc-

tion hydrogen by using ASBR reactor and achieved the highest rate

of hydrogen 6.7 m3 H2/m3 d and removed higher than 37% of COD

at 3 days HRT, an OLR of 6.6 kg COD/m3 d, a pH of 6.8 and a

temperature of 37 1C[64]. Prasertsan and coworkers produced the

highest rate of hydrogen 9.1 m3 H2/ m3 d together with removed

5772.5% of COD at HRT of 48 hours, OLR of 60 kg COD/m3 d, pH of

5.5 and a temperature of 60 1C. The hydrogen content, total

carbohydrate consumption and removal of suspended solids (SS)

were 5573.5%, 9273% and 7872%, respectively[65].

Up to now, most of the researcher produced hydrogen from

organic wastes and wastewater using mixed microora andimproved yield of hydrogen production. Microora such as T.

thermosaccharolyticum was the dominant hydrogen producing

microorganisms in the fermentation process. For example, O-

Thong and coworkers used thermophilic microora (T. thermosac-

charolyticum) as a seed into an ASBR for the production of hydrogen

from POME with nutrient supplement. Nutrient supplement

increased the bacterial diversity, strength of the system and also

increased the removal efciency COD from 35.579.8% to

68.272.8%, residual oil (from 7573% to 8071.5%) and suspended

solids (from 9173.8% to 93.671.1%). It also increased the produc-

tion rate of hydrogen from 4.470.38 to 6.170.03 m3 H2/m3

POME d [85]. Presence of macronutrients and iron improved the

production of bio-hydrogen and reduction of pollution from POME.

They also investigated the production of hydrogen and CODremoval efciencies in batch cultures by Thermoanaerobacterium

rich sludge under thermophilic (60 1C) conditions and adjusting the

optimum nutrient ratio (C/P ratio from 650 to 559, C/N ratio from

95 to 74 and concentration of iron from 2 to 257 103 kg m3).

The productions of hydrogen and COD removal efciency were 6.5

(m3H2/ m3 POME) and 58% respectively[86].

However, a few researchers used ASBR for the post-treatment

of anaerobically digested POME and obtained a promising result

with maximum COD and TSS removal efciency of 82% and 62%

respectively at MLSS of 25004000 mg/L and HRT of 72 h [87].

5.1.8. Continuous stirred tank reactor (CSTR)

Continuous stirred tank reactor (CSTR) is a well-stirred tank

containing the immobilized biomass. The substrate is constantly

pumped into the reactor, and the product stream is removed at the

same time. This reactor is categorized by mixing the contents

either continuously or periodically. In POME treatment, Keck Seng

(Malaysia) Berhad in Masai has been successfully used CSTR, and

the COD removal efciency was about 83% and the production of

biogas was minimum 62.5% of methane [88]. Another study on

POME treatment using CSTR has been investigated by Ugoji [89]

and specied that BOD and COD removal efciencies were 96.5%

and 93.6% respectively at HRT of 10 days but retention timeincreased up to 30 days, it removal efciencies improved only 2%.

Poh and coworkers have been cultivated a thermophilic mixed

culture, specically for the treatment POME at thermophilic

conditions using a batch CSTR and successfully reduced minimum

90% of COD and 64% of methane produced at HRT of six days along

with 14 kg/m3 of MLSS[90]. Irvan and his coworkers studied the

emission of methane from CSTR digestion of POME at the thermo-

philic temperature (55 1C) on a laboratory scale. A real liquid

wastewater from palm oil mill was used as a raw material. The

results obtained maximum COD, VS decomposition rate were 77%,

63.5% respectively and generation of methane of 64% at HRT of 8

days but maximum generation of methane of 67% was obtained at

HRT of 4 days[91]. Whereas Choorit and Wisarnwan investigated

the performance CSTR under various organic loading rates (OLRs)

using POME and operated at 37 1C and 55 1C respectively. They

achieved 71.10% of COD removal efciency and production biogas

was 3.73 m3 of gas/m3 d in which 71.04% of biomethane at OLR of

12.25 kg COD/m3 d, HRT of 7 days and 37 1C. Whereas 70.32% of

COD removal efciency and production rate of bio-gas of 4.66 m3

of gas/m3 d in which 69.53% of biomethane obtained at OLR of

17.01 kg COD/m3 d, HRT of 5 days and 55 1C[92].

Hydraulic retention time (HRT) shows a signicant role to

increase the production of biohydrogen. Yusoff and his coworkers

investigated the effect of HRT and VFAs during biohydrogen

fermentation from POME in a 50 L CSTR bioreactor. They used three

different HRTs (5, 3 and 2 days) and evaluated their performance on

production of biohydrogen. They achieved maximum hydrogen

production rate and biohydrogen yield were 44 N ml/h/l-POME

and 1054 N ml/l-POME respectively at HRT of 48 h, OLR of 50

60 kg COD/m3 d, a pH of 5.5 and a temperature of 2226 1C[93].

Wong and coworkers attempted to upgrade the performance of

CSTR by incorporating microorganisms within the existing reactor

at mesophilic temperatures of 35 1C and investigated the perfor-

mance of suspended growth anaerobic degradation process in

terms of pH, COD reduction, and biogas production. The result

showed that the continuous stirrer suspended closed anaerobic

reactor (SCAR) can achieve COD reduction of 66.09%, methane

composition of 48.05% and rate of production methane of

532.06106 m3 CH4/d of at HRT of 12 days, and pH values lower

than 7[94]. Biohydrogen production is usually conducted via CSTR

because it is easy to work and provide a good substrate biomass

contact by vigorous mixing[95]. Seengenyoung et al.[96]recently

compared the performance of ASBR and CSTR reactor for thehydrogen production from POME byT. thermosaccharolyticumPSU-

2. They found CSTR was more stable in terms of hydrogen

production and soluble biomass concentration than ASBR under

the same OLR (11.3 kg COD/m3 d) and HRT (4 days). They also

obtained average biohydrogen production rates of 2.05 and

2.16 m3 H2/ m3 d and removal efciency of COD were 37.7% and

44.8% from ASBR and CSTR, respectively.

5.1.9. Up-ow anaerobic sludge xed-lm (UASFF) reactor

The upow anaerobic sludge-xed lm (UASFF) reactor is an

anaerobic hybrid reactor, which is a combination of two anaerobic

systems into a single bioreactor [97]The upow xed lm (UFF)

located on the UASB portion, which hinders the sludge washout



11/19

and holding high biomass. A number of researchers have effec-

tively used the UASFF reactor for the treatment of POME [98102].

This hybrid reactor combines the benets of both reactors while

excluding their respective drawbacks. As such, UASFF is superior in

terms of biomass retention, operation at high OLRs and reactor

stability at shock loadings while removing the problems of clog-

ging and biomass washout in anaerobic lter and UASB.

The internal packing effectively contributed to the performance

of the UASFF reactor by capturing the solids that oated from

sludge bed. These results allowed a high volume of efuent

recycling for the treatment of higher organic loadings in POME

[98]. The major weakness of UASB reactors is the long startup time

(24 months). Najafpour el al. [98] used the UASFF reactor to

reduce the start-up time to 26 days and developed the granular

sludge within 20 days at mesophilic temperature (38 1C). They

removed 89% and 97% of COD and methane yields were 0.346 and

0.344 m3/kg CODremoved at OLR of 23.15 and 8.74 kg COD/m3 d andHRT of 1.5 and 3 days respectively. Borja and coworkers used same

hybrid reactor for the treatment of POME under mesophilic

conditions wherein PVC rings immersed upper one-third and

sludge blanket engaged by the remaining two-thirds. They

removed maximum 92.3% of COD and yield of methane was

0.335 m3/kg CODrem at OLR of 16.2 kg COD/m3 d and HRT of

3.5 days[99]. Zinatizadeh and coworkers used this reactor to treat

POME at mesophilic temperature (38 1C) and removed maximum

90% of COD at a very short HRT of 1.5 days and higher OLR of

23.15 kg COD/m3 d. They removed 98.6% of COD at HRT of 6 days

with an inuent COD concentration of 34.73 kg/m3 [100]. They

concluded that, it became unstable under a stressful condition

imposed by overloading of suspended solids at short HRT (24 h)

and OLR of 34.73 kg COD/m3 d. Therefore, complete digestion ofraw POME required a high HRT without pre-treatment [100].They

used chemical coagulation and occulation process for the treat-

ment of pre-treated POME in a UASFF reactor and removed COD to

2.45103 m3/d at HRT of 1.5 d and recycle ratio of 23.4:1 [101].

They also used same reactor to treat the physically and chemically

pre-treated palm oil mill efuent (POME) and achieved higher

(9094%) COD removal efciency at OLR of 16.5 kg COD/m3 d

against to the chemically pre-treated POME (8288%)[102].

5.2. Aerobic digestion or treatment

Aerobic treatment process is a process that occurs in the

presence of oxygen and stabilizes the particulate organic sub-

stances arising from primary clarication (mainly biodegradable

organic matter) and biological treatment (mostly biomass) of

wastewaters. Biodegradable organic matter is hydrolyzed and

converted into CO2, water and active biomass through the action

of heterotrophic bacteria[103].Karim and Kamil investigated the

treatment efciency of POME by the use of Trichoderma viride

fungus and reduced more than 95% of COD of POME [104].

Najafpour and coworkers used S. cerevisiae as an initial biomass

in a rotating biological contactor (RBC) to treat the POME, which

contains high COD of about 16 kg/m3. They showed a removal

efciency of BOD5, COD, SS, TN up to 91%, 88%, 89% and 80%

respectively with the lowest 1.1103 m3/h of POME volumetric

ow rate and 55 h HRT of in a batch experiment[105]. Norulaini

and coworkers estimated the efciency of a trickling lter as a

model of aerobic attached-growth system for the treatment super-

natants of POME. The trickling lter removed more than 90% of

BOD and COD at hydraulic loading of below 1 m3/m2 d. The higher

removal efciencies of BOD and COD were due to two reasons.Firstly, the sedimentation of settleable solids of POME and the

chemical coagulation reduced the organic load applied to the lter.

Secondly, these restricted the hydrolysis of non-diffusible organics

into soluble substrates[106].

Ho and Tan used pressurized activated sludge process to treat

the secondary anaerobically digested POME. The reductions of

BOD, COD, SS, oil and grease as well as TS were up to 98.4%, 97.7%,

99.2%, 93.3% and 87.5%, respectively [107]. Vijayaraghavan and

coworkers investigated the treatment efciency of anaerobically

digested and diluted raw POME by the use of aerobic oxidation

and they removed COD, BOD, residual oil and grease as well as

total kjeldahl nitrogen (TKN) up to 98%, 93%, 0.024 kg/m3 and

0.058 kg/m3 respectively for anaerobically digested POME whereas

the values were 89%, 82%, 0.112 kg/m3 and 0.003 kg/m3 respec-tively for diluted raw POME at HRT of 2.5 days [108].

Nowadays, sequencing batch reactor (SBR) has been used as a

developed form of activated sludge process and cost-effective

treatment system due to its high removal activity of BOD and SS.

Chan and coworkers investigated the aerobic treatment of anae-

robically digested POME by using SBR reactor. They achieved

maximum 9596% of COD, 9798% of BOD and 9899% of TSS

removal efciencies at OLR of 1.84.2 kg COD/m3 d, SLR of

2.54.6 kgTSS/m3 d and MLVSS concentration ranges of 22

25 kg/m3 [109]. They examined the practicability of aerobic

biological treatment under thermophilic conditions for anaerobi-

cally treated POME and removed up to 72% of total COD and 76% of

BOD with an OLR of 2.870.3 kg COD/m3 d [110]. They showed

aerobic treatment produced better efuent quality at mesophilic

Table 5

The summarization of aerobic treatment process.


removal

efciency

(%)

HRT

(days

or hrs)

OLR (kg

COD

/m3 d)

Reference

High biochemical oxygen demand removal

efciency and good efuent quality.

Minimum odour, when properly loaded andmaintained.

At small scale, the treatment efciency is high.

Low land area is required.

The nal discharge may contain huge amount of

oxygen, which diminishes the instant demand of

oxygen in water body.

It eliminates many pathogens from wastes. Reduces

ammonia discharged to water resources

Some organics cannot be efciently disintegrated aerobically because of

biologically non-reactive components, mainly composed of insoluble

materials.Production rate of biomass is high due to active aerobic growth powered

by a sufcient oxygen supply by aeration, potentially leading to

reduction in storage capacity of lagoons and/or ponds.

High operating costs due to aeration, nutrients (N, P) and sludge

disposal.

Requires routine maintenance.

88 55 h 38210 [105]

490 1 5.0 [106]

97.7 0.417 0.40.65 [107]98 2.5 3.91 [108]

89 2.5 3.93

9596 1.84.2 [110]

72 2.8

86 2 h 2.5 [111]

95 2 7.6 [125]

Hydraulic retention time (HRT) expressed as day, but in few cases as hours.



12/19

conditions as against thermophilic conditions. They improved

aerobic treatment efciency under thermophilic conditions by

optimizing the concentrations of MLSS, DO, OLR and settling time

and achieved 86% of COD, 87% of BOD and 89% of TSS removal

efciency at the concentration of MLSS of 27 kg/m3, OLR of 2.5 kg

COD/m3 d and settling time of 2 h [111]. The performance of an

aerobic treatment process is summarized in Table 5.

5.3. Physicochemical treatment

Several POME treatment processes exist in the mill, which

failed to full the discharge standard even though they have used

various anaerobic and aerobic treatment systems. Consequently, a

substitute POME treatment process is required to meet the

standard discharge limits prescribed by the Department of Envir-

onment (DOE). Apart from biological treatment, several alternative

physicochemical processes could be used to treat the POME.

Physicochemical treatment of wastewater predominantly focuses

on the separation of colloidal particles. This is obtained using

various chemicals named coagulants and occulants, which

change the physical state of the colloids, allowing them to remain

in an indeterminately stable form and therefore, form into

particles or ocs. The recommended physicochemical treatmentprocesses for POME are explained in the subsequent sections.

5.3.1. Coagulation andocculation

The coagulationocculation process shows an important char-

acteristic as a pretreatment process, where raw POME reduces its

suspended solids (SS) to a satisfactory level. Although the wordscoagulation and occulation are frequently used interchange-

ably, they mention two different systems. In coagulation process,

colloidal and very ne solid suspensions are destabilized so that

they can begin to agglomerate whereas occulation refers to the

process by which destabilized particles actually conglomerate into

larger aggregates so that they can be separated from the waste-

water. Before applying the physicochemical processes, the raw

POME would have to be destabilized to occulate the particulatematter. Ferric chloride, aluminium chloride, aluminium sulphate

(alum), polyaluminum chloride (PAC), ferrous sulphate and

hydrated lime are the most commonly used coagulants due to its

recognized performance, efciency, economy and ease of use in

the wastewater treatment[112]. Karim and his coworkers inves-

tigated the reduction of pollution strength of POME by applying

nine polymers and ve inorganic salts, and showed that the

cationic polymer Magnaoc LT22 (0.080.1 kg/m3) reduced the

turbidity, TSS, COD and TS up to 96%, 9394%, 63% and 53%

respectively. Nevertheless, combined FeCl3 (0.20.3 kg/m3) and

Magnaoc LT22 (0.070.1 kg/m3) reduced higher pollution as

against Magnaoc alone, which reduced COD, TS and TSS by 47

53%, 4349% and 9294%, respectively [113]. Ng and coworkers

tested different coagulants to evaluate their destabilize ability ofPOME suspensions and to occulate the particulate matter. They

found that synthetic polymers are more operative than lime or

alum [17]. Khadidi and his coworkers have prepared a new

occulant from waste Activated Bleaching Earth (wABE) for treat-

ment of POME. The highest removals of COD, turbidity and TSS

achieved were 81.15%, 82.54% and 89.91% respectively in presence

of POME with 2%(v/v) H2SO4-occulant [114].

In POME treatment, Ahmed and his coworkers completely

replaced the inorganic coagulants with organic polymers. They

showed that the anionic polymers have only bridging attraction

but cationic polymer has both the charge neutralization and

bridging attraction. They achieved removal efciency of suspended

solids of 99.66%, 55.79% of COD, 99.74% of oil and grease and

80.78% of water recovery efciency at the optimum occulation

states and proved that, direct occulation method considerably

decreased 3.6 times treatment cost against to the traditional

coagulationocculation method[115].

Arifn and coworkers produced a cationic polyacrylamides to

evaluate the performance as a occulant in POME and found that

the polymer charge density from 48.2 to 485C/g considerably

shakes the occulants activity. Adsorption capacity of polymer

increased with the increase of charge density. Cationic polyacry-

lamide had high charge density (485C/g) and was the most activepolymer and permitted to remove turbidity, suspended solids and

COD of 98%, 98.7% and 54% respectively with lower dosages of

0.032 kg/m3 at pH of 3 [116]. They also observed that the size of

occule increased with the increasing of dosages, charge density

and weight of polymer, and bigger occule improved the treat-

ment efciency[117]. High molecular weight cationic polyacryla-

mide (1500 kg mol1) is the most effective polymer and achieved

high removal efciency with a dosage as low as 60 mg L1 at pH

3 of POME. However, over 5 million g mol 1 produced very poor

occule and do not freely dissolve but form gel lumps [118].

Chitosan is a natural organic polyelectrolyte obtained from dea-

cetylation of chitin. Ahmad et al.[119]investigated the possibility

and efciency of chitosan against PAC and alum for the treatment

of POME and showed that chitosan was reasonably more procient

and cost-effective coagulant in contrast to alum and PAC. Chitosan

removed higher than 95% of SS and residual oil at the dosage of

0.5 kg/m3, 15 min of contact time at 100 rpm, 20 min of sedimen-

tation time and pH of 4.0. Whereas alum and PAC achieved the

same removal efciency at the 30 min of mixing time of 100 rpm,

dosages of 8.0 and 6.0 kg/m3, 50 and 60 min of sedimentation

time, respectively and pH of 4.5. Hassan and Puteh discovered the

efciency of chitosan and alum for the treatment of POME.

Chitosan presented superior efciency with much lower dosage

(0.4 kg/m3) consumption than conventional alum (8 kg/m3) and

reduced 99.90% of turbidity, 99.15% of TSS and 60.73% of COD at pH

of 6, whereas alum reduced 99.45%, 98.60% and 49.24% of

turbidity, TSS and COD respectively at pH of 7. The effectiveness

of combined chitosan and alum exhibited very little increment

against the use of chitosan alone [120]. Saifuddin and Dinaradiscovered Chitosan-magnetite particles and showed it can per-

form better than natural chitosan. They achieved 98.8% of turbid-

ity, 97.6% of TSS and 62.5% of COD removal efciency at the

optimum dosage of 0.25 kg/m3and pH of 6. While chitosan

removed 97.7% of turbidity, 91.7% of TSS and 42.70% of COD at

higher dosage of 0.37 kg/m3 [121]. Malakahmad and Chuan inves-

tigated the post-treatment of anaerobically treated POME using

metal salt (alum) as a coagulant and removed 59% of COD at the

optimum conditions (dosage: 2.124 kg/m3, contact time: 20 min,

and pH 6.4). This decreases the COD level less than the POME

discharge standard enforced by DOE[122].

Nowadays, many researchers use an environmental friendly

coagulant for the treatment of POME where the technology moves

from biological treatment to chemical treatment to improve theefuent quality. Bhatia and coworkers developed a natural coagu-

lant (Moringa oleiferaseeds) for POME[123,124]. M. oleifera seeds

reduced a signicant amount of TSS, COD and 87% of the sludge

was recovered at pH of 5, settling time of 114 min by combining

3.469 kg/m3 of M. oleifera seeds [123]. They also found the

performance of coagulationocculation of M. oleifera seeds

extract and occulant (NALCO 7751), removed 99.3% of suspended

solids and 52.5% of COD and recovered more than 87.25% of sludge

and 50.3% of water. The coagulationocculation process showed a

better performance in the removal of SS and COD at the tempera-

ture of 30 1C with comparing of 40, 55 and 70 1C. It might be due

to the strength of macrooccule, which became weaker and easily

broke with raising the temperature [124]. Oswal used tropical

marine hydrocarbon-degrading yeast, Yarrowia lipolytica (NCIM



13/19

3589) for the treatment of POME and reduced 95% of chemical

oxygen demand (COD) at HRT of 2 days. They also showed a

treatment of POME with Yarrowiawas consecutively treated with

ferric chloride as occulant and reduced 99% of COD from the

original[125].

5.3.2. Electrocoagulation

Electrocoagulation (EC) is becoming an effective technology for

wastewater treatment and recovered valuable chemicals fromvarious industries. EC not only provides a fast rate of pollutant

removal and simplicity of operation but no chemi

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Production of Biogas

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