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Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

Contents lists available at ScienceDirect

Process Safety and Environmental Protection

journa l h om ep age: www.elsev ier .com/ locate /ps ep

eview

roduction of biodiesel and its wastewaterreatment technologies: A review

urull Muna Daud ∗, Siti Rozaimah Sheikh Abdullah ∗,assimi Abu Hasan, Zahira Yaakob

epartment of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universitiebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia

a b s t r a c t

The development of technologies providing alternatives to petroleum fuel has led to the production of biodiesel

fuel. This paper reviews the methods used to produce biodiesel fuel from various types of sources such as palm oil,

jatropha oil, microalgae, and corn starch. It also includes a brief description of the transesterification process and

the point source of biodiesel wastewater, from which it is mainly generated. Biodiesel wastewater is characterized

by high contents of chemical oxygen demand (COD), biological oxygen demand (BOD5), oil, methanol, soap and

glycerol. The treatments developed so far for biodiesel wastewater are also described. The authors also investigate

the significance, ability and possibility of biological aerated filter (BAF) to treat biodiesel wastewater discharged from

a biodiesel fuel production plant. The whole treatment; coagulation-biological aerated filter (CoBAF); involves the

pre-treatment of biodiesel wastewater using coagulation followed by the treatment using BAF.

© 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Keywords: Biodiesel; Biodiesel production; Transesterification; Biodiesel wastewater; Biodiesel wastewater treatment;

Biodiesel wastewater management

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 488 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 489. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494

ontents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.1. Development of biodiesel production . . . . . . . . . . . . .

1.2. Properties of biodiesel as transportation fuel. . . . .2. Biodiesel production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.1. Source of raw materials/feedstock . . . . . . . . . . . . . . . .

2.2. Biodiesel production process . . . . . . . . . . . . . . . . . . . . . .

2.2.1. Direct use and raw oils blending . . . . . . . . .

2.2.2. Micro emulsions. . . . . . . . . . . . . . . . . . . . . . . . . . .2.2.3. Pyrolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2.2.4. Transesterification . . . . . . . . . . . . . . . . . . . . . . . .

3. Generation of biodiesel wastewater . . . . . . . . . . . . . . . . . . . . . .

3.1. Biodiesel washing process . . . . . . . . . . . . . . . . . . . . . . . . .

3.1.1. Wet washing process . . . . . . . . . . . . . . . . . . . . . . . . . . .

∗ Corresponding authors. Tel.: +60 3 89216407; fax: +60 3 89216148.E-mail addresses: nurullmuna.daud@gmail.com (N.M. Daud), rozaimReceived 23 June 2014; Received in revised form 9 October 2014; AccepAvailable online 27 October 2014

ttp://dx.doi.org/10.1016/j.psep.2014.10.009957-5820/© 2014 The Institution of Chemical Engineers. Published by

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

ah@eng.ukm.my (S.R. Sheikh Abdullah).ted 19 October 2014

Elsevier B.V. All rights reserved.

488 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

3.1.2. Dry washing process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4953.1.3. Membrane extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

3.2. Biodiesel wastewater and its characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4963.3. Level of environmental pollution by biodiesel wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 496

4. Treatment and management of biodiesel wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4964.1. Current treatment technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498

4.1.1. Coagulation treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4984.1.2. Electrocoagulation treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4984.1.3. Biological treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5004.1.4. Adsorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5014.1.5. Microbial fuel cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501

4.2. Integrated system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5014.2.1. Dissolved air flotation–coagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5024.2.2. Photo-Fenton-aerobic sequential batch reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5024.2.3. Acidification–electrocoagulation and anaerobic co-digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5034.2.4. Acidification–electrocoagulation and biomethanization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5034.2.5. Electroflotation and electrooxidation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5034.2.6. Chemical recovery and electrochemical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5034.2.7. Coagulation-biological aerated filter (CoBAF) system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504

5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505

1. Introduction

Vegetable oil based biodiesel was introduced and investigatedin the 1890s, when Rudolph Diesel invented diesel enginesto be used for machines in the agricultural sector (Orchardet al., 2007). In 1920, the availability of low cost petroleumfuel had decreased the demand for biodiesel, leading to themodification of diesel engines to match the properties ofpetroleum diesel fuel. Oil crises in the 1970s renewed inter-est in vegetable oils and gave an advantage to their market(Talebian-Kiakalaieh et al., 2013). However, the usage of tra-ditional vegetable oils in modern diesel engines was notfavourable. The investigation of methods to produce low vis-cosity vegetable oils spread and a variety of methods wereintroduced such as transesterification, pyrolysis, and blend-ing of solvents. The first patent for an industrial process forbiodiesel production was filed in 1977 by a Brazilian scientist,Expedito Parente (Lim and Teong, 2010). In 1979, South Africainitiated research into the production of biodiesel using sun-flower oil (Lin et al., 2011). Starting from 1980, the biodieselrevolution has been quite positive. A small pilot plant was builtin Austria in 1985, and in 1987 a biodiesel production plantbased on microalgae was operated in New Mexico. The com-mercialization of biodiesel using a variety of feedstock such asrapeseed and used cooking oil was boosted in the 1990s and upuntil now. Biodiesel is not only beneficial for transportation, itis also being used in manufacturing, construction machineryand generators for firing boilers purpose as depicted in Fig. 1(Abdullah et al., 2009).

1.1. Development of biodiesel production

The idea of using biodiesel fuel arose when the world started tofind and develop alternative energy resources, influenced bythe depletion of non-renewable energy sources (Berchmansand Hirata, 2008). High dependence on petroleum fuels or

Transportation

Manu fact uri ng

Con str uction

Genera tors

Fig. 1 – Usage of biodiesel.

replace fossil fuels are water, solar, and wind energy andbiofuels (Abbaszaadeh et al., 2012). The increasing demandfor biodiesel is also due to awareness of the environmentalimpact of emissions from conventional fossil fuels combus-tion and the decline in domestic oil production (Mondalaet al., 2009). The production of biodiesel in several Asiancountries is shown in Table 1. The production capacity ofeach country is based on annual reports for the years 2011and 2012. Among Asian countries, production of biodiesel ismainly dominated by Indonesia and Thailand, which pro-duce more than two billion litres every year and are alsoknown as the main producers of biodiesel in SoutheastAsia.

Commercially, biodiesel is produced through a transes-terification process in the presence of alcohol and catalyst.This process involves the conversion of triglycerides (oil) tomethyl ester (biodiesel) and by-product (glycerol) (Chavalparit

fossil fuels has led to uncertainty in price and supply (Rajaet al., 2011). Some alternative sources which are able to

and Ongwandee, 2009; Low et al., 2011) as described by Eq.(1).

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 489

Table 1 – Biodiesel production in several Asian countries.

Country Main feedstock Production capacity(billion litres/year)

Production year

Malaysia Palm oil 0.147 2011Indonesia Palm oil 2.200 2012Thailand Palm oil 2.080 2011Philippines Coconut oil 0.138 2012India Jatropha 0.140–0.300 2011China Waste cooking oil 0.568 2012

O|C|||C +|||C

( rs)

1

Bt(csb5peIf2oimi

toaisdbm

sa(ape2esct

0102030405060708090

100

Yie

ld p

erce

ntag

e (%

)

Source: Biodiesel market reports.

O| ||H2-O-C-R1 CH 3-O-C-R1

O O || (Catalyst) || H-O-C-R2 + 3CH3OH → CH3-O-C-R2

O O || ||H2-O-C-R3 CH 3-O-C-R3

Triglycerides) (Methanol) (Mixture of fatty este

.2. Properties of biodiesel as transportation fuel

iodiesel fuel is used as a substitute for petroleum, whichraditionally has been used to produce transportation fuelChavalparit and Ongwandee, 2009; El Diwani et al., 2009) andonsidered as the best candidate compared to all other energyources (Leung et al., 2010). For use as transportation fuel,iodiesel is blended and named as B5, B10, B20, or B100, where, 10, 20, and 100 represent the percentage of biodiesel in theetroleum diesel (Janaun and Ellis, 2010). Biodiesel is a methylster mixture with long-chain fatty acids (Leung et al., 2010).t is made from a variety of sources of vegetables oil, animalats, and waste cooking oil (Kolesárová et al., 2011; Raja et al.,011). Reportedly, Thailand has claimed that biodiesel is onef the most promising alternative fuels to the diesel fuel used

n that country (Pleanjai et al., 2007). In Malaysia, the imple-entation of the B10 biofuel programme has had a positive

mpact on Malaysia’s biodiesel market (Adnan, 2013).For biodiesel products to be used as transportation fuel,

he fuel grade should fulfil the standard requirements. Twof the international standards are tabulated in Table 2. Therere many studies conducted to produce biodiesel from var-ous kind of feedstock. Each was analyzed according to thetandard to ensure the compatibility of biodiesel to petroleumiesel to be used as transportation fuel. The studies oniodiesel production are summarized in Table 3, while theethyl ester yields for each study are illustrated in Fig. 2.The use of renewable feedstock as biodiesel production

ources has made this fuel to be known as a clean renew-ble fuel that is biodegradable and environmentally friendlyLeung et al., 2010; Kaercher et al., 2013). These characteristicslso provide this liquid fuel with advantage of lowering theroduction of exhaust emissions from diesel engines (Hayyant al., 2010) such as particulate matter (PM) (Kolesárová et al.,011), unburned hydrocarbons (HC) and carbon monoxide (CO)xcept for nitrogen oxides (NOx) (Bouaid et al., 2012). The emis-

ion of nitrogen oxides usually increases due to the oxygenontent in the biodiesel (Sharma et al., 2008). Table 4 showshe emissions percentage from different studies regarding this

CH2-OH|

CH-OH Equation (1)|CH2-OH

(Glycerol) (1)

matter. The percentages were compared to 100% of exhaustemissions from petroleum diesel engines. The variations ineach study usually rely on the feedstock properties as well asoxygen content and viscosity of the methyl esters.

Other advantages from biodiesel usage are the use of agri-cultural surplus and reduce the dependencies on crude oil(Abdullah et al., 2009). As stated by Mondala et al. (2009), theproperties of biodiesel with a flash point above 93.3 ◦C make itsafer and easier to use, handle, and store. Another reason thatmakes biodiesel comparable to petroleum diesel is the high-energy content or also known as heating value. Referring toTable 5, the energy content of biodiesel produced in severalstudies have similar or close value to the energy content ofpetroleum diesel which makes biodiesel comparable and suit-able to be used as transportation fuel. However, Yaakob et al.(2013) addressed that by using biodiesel as transportation fuel,some may face few difficulties such as fuel pumping problems,cold start, poor low temperature flow and high copper stripcorrosion.

Fig. 2 – Methyl ester yields for different study.

490 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

Table 2 – Different standard specification for biodiesel fuel (Abdullah et al., 2009).

Property Units Limits

EN14214 ASTM D6751

Flash point, close cup ◦C 120 min 130 minWater content mg/kg 0.05 max 0.05 maxKinematic viscosity, 40 ◦C mm2/s 3.5–5.0 1.9–6.0Sulphated ash % (m/m) 0.02 max 0.020 maxSulphur content % (m/m) 0.001 max 0.0015 maxCopper corrosion strip (3 h at 50 ◦C) Rating 1a 3a maxCetane index – 51 min 47 minCarbon residue % (m/m) 0.3 max 0.50 maxAcid number mg KOH/g 0.50 max 0.80 maxFree glycerol % (m/m) 0.02 max 0.02 maxTotal glycerol % (m/m) 0.25 max 0.24 maxPhosphorus content mg/kg 10 max 10 max

◦ – 360 max

010203040506070

Soyb

ean

Cano

laAl

gae

Jatr

opha

Palm

oil

Rape

seed

Sunfl

ower

Cast

orCo

rnBa

bass

u oi

lCa

mel

ina

Coffe

eBl

ue w

axw

eed

Hem

pKa

ranj

aLi

nsee

d

% o

il by

wt i

n bi

omas

s

Fig. 4 – Seed oil yield depending on different feedstock.

Distillation temperature (90% recovered) C

The positive impact in environmental aspect may be themain reason why biodiesel starts to gain interest to be usedas transportation fuel. However, the high price of biodieselfuel compared to petroleum fuel has limited the develop-ment of this renewable fuel development (Hayyan et al., 2010).The high production cost due to the high feedstock cost lim-its the commercialization of biodiesel (Hasswa et al., 2013).Another limitation to the development of biodiesel is theusage of edible vegetable oil. It arises the problem of foodsupply competition, which can cause food crises, deforesta-tion, and challenges in oil supply management to ensure theoil supply is well managed for food consumption and con-sumer products (Leung et al., 2010; Talebian-Kiakalaieh et al.,2013). Despite all these limitations, biodiesel industry shouldfind ways to overcome these challenges. In addition, sincethe increasing 53% of world energy demand by the year 2030(Talebian-Kiakalaieh et al., 2013) while the non-renewableenergy; fossil fuel depletes, government should really look for-ward to ensure that biodiesel can fulfil the energy required byour society.

2. Biodiesel production

2.1. Source of raw materials/feedstock

Traditionally, the main source of biodiesel is vegetable oil.The types of vegetable oils available depend on the climateand soil conditions of the country (Siddiquee and Rohani,2011). In Thailand, over 90% of biodiesel production is frompalm oil as raw material (Rattanapan et al., 2011). The mostwidely used biodiesel feedstock in the United States is soy-bean oil (Mondala et al., 2009). Biodiesel feedstock can becategorized into three types: edible oils, non-edible oils, and

reusable sources or wastes, as summarized in Table 6. Someresearchers are interested in biodiesel production using oil

Biodie sel fee dsto

Group II Low free fatty acid

greases an d ani ma(FFA <4%)

Group I Refined oils

(FFA <1.5%)

Fig. 3 – Classification of

from non-edible crops, due to environmental issues. Forinstance, non-edible crops can be grown on waste lands(Leung et al., 2010). Besides, the production of biodiesel usingthese types of feedstock helps governments to find suitableways to treat, recycle, and dispose of wastes (Suehara et al.,2005; Janaun and Ellis, 2010). Yaakob et al. (2013) emphasizedthat waste cooking oil usage can reduce water pollution andalso prevent blockages in water drainage systems.

Free fatty acids (FFAs) and/or triglycerides are an importantcomponent of feedstock to be converted to biodiesel (Janaunand Ellis, 2010). All fatty acids sources are favourable for use inbiodiesel production (Talebian-Kiakalaieh et al., 2013). Kinast(2003) classified biodiesel feedstock based on their FFAs asillustrated in Fig. 3. Types of refined oil feedstock which con-tain FFAs <1.5% are, for example, soybean, canola, and palmoil. Used cooking oil, tallow, and poultry fat are types of feed-stock categorized as group II, having FFA contents below 4%.Waste grease usually falls into group III. However, excess FFAcontent in feedstock might affect biodiesel production. Forinstance, Moser (2009) stated that a content of FFA >3 wt%will lead to soap formation due to the reaction between the

FFA and the catalyst. Consequently, stable emulsion will form,

ck

Group III High free fatty acid

greases and animal fats (FFA ≥20%)

yell ow l fats

biodiesel feedstock.

Process

Safety

an

d En

viro

nm

enta

l Pro

tection

9

4

( 2

0 1

5 )

487–508

491

Table 3 – Biodiesel properties from different feedstocks.

Process Feedstock Yield (%) Purity (%) Viscosity(mm2/s)

Density(kg/m3)

Flash point(◦C)

Cloud point(◦C)

Pour point(◦C)

References

Transesterificationin supercriticalmethanol

Soybean oil 97.8 – – – – – – Wei et al. (2013)

Transesterification Palm oil – – 4.91 878 179 14 5 Atadashi et al. (2012)Transesterification Castor oil 61.0 – 10.75 – 160 −13 – Okullo et al. (2012)Transesterification Jatropha oil 76.0 – 5.25 – 166 −6 – Okullo et al. (2012)Base catalyzed

transesterificationJatropha oil – – 4.82 – 128 8 −2 Raja et al. (2011)

Transesterification Sunflower oil – – 4.72 860 183 4 −5 Ahmad et al. (2010)Base catalyzed

transesterificationJatropha oil 98 5.20 – 162 0 −6 El Diwani et al. (2009)

Base-catalytic andnon-catalyticsupercriticalmethanoltransesterification

Waste cooking oil 87 99.6 5.30 897 196 – −11 Demirbas (2009)

Acid-catalysedtransesterification

Municipal sewage sludge 14.5 – – – – – – Mondala et al. (2009)

Transesterification Waste sunflower cooking oil 99.5 – 9.50 – – – – Hossain and Boyce (2009)

Table 4 – Percentage of exhaust emission from biodiesel engines.

Fuel type Carbon monoxide Hydrocarbon Nitric oxide Sulfur dioxide Particulate matter Polycyclic aromatic hydrocarbons References

B100 52 33 110 – 53 – Lotero et al. (2005)B100 90 90 115 – 67 – Chincholkar et al. (2005)B100 67 23 75 0 33 – Wirawan et al. (2008)B100 50 – 113 0 70 20 Khan et al. (2009)B100 60 50 105 0 35 – Bouaid et al. (2012)B100 87 – 111 – – – Tomic et al. (2013)B100 56 32 – 0 60 25 Talebian-Kiakalaieh et al. (2013)

492 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

Table 5 – Energy content of biodiesel fuel.

Type of fuel Production process Energy content (MJ/kg) References

Petroleum diesel – 45.00 Talebian-Kiakalaieh et al.(2013)

Karanja oil biodiesel Transesterification 39.66 Vivek and Gupta (2004)Tallow – 40.05 Talebian-Kiakalaieh et al.

(2013)WCO biodiesel Base-catalytic and

supercritical methanoltransesterification

42.65 Demirbas (2009)

Algae (Cladophorafracta) biodiesel

– 21.1 Demirbas and Demirbas(2011)

Microalgae (Chorellaprotothecoides)biodiesel

– 25.1 Demirbas and Demirbas(2011)

Jatropha oil biodiesel Transesterification 42.15 Okullo et al. (2012)Castor oil biodiesel Transesterification 30.4 Okullo et al. (2012)Jatropha oil biodiesel Transesterification 39.76 Raja et al. (2011)Rubber seed oil

biodiesel– 36.5 Ramadhas et al. (2005)

Microalgal – 41 Rawat et al. (2013)

preventing the separation of biodiesel from glycerine andconsequently reducing the final yield (Canakci and Gerpen,2001). For FFA >2.5 wt%, a pre-treatment process is usuallyrequired before further processing is carried out (Leung et al.,2010; Talebian-Kiakalaieh et al., 2013). Based on these stud-ies, biodiesel producers using any type of feedstock with FFAcontent above 2.5 wt% need to handle problems of those men-tioned.

In Malaysia, a widely used biodiesel feedstock is palm oil(Siddiquee and Rohani, 2011). Palm oil has dominated thebiodiesel production industry because of its availability andversatile application and because it is easily found (Janaun andEllis, 2010). It is said to be one of the high-oil-yield sources.In research done by Sanford et al. (2009) and Mata et al.(2010), analysis to determine the oil content was conductedfor certain types of feedstock, and the oil content of each feed-stock is illustrated in Fig. 4. Based on their studies, babassuoil is extracted from seeds of the babassu palm tree (Attaleaspeciosa), which have high oil content; however only a fewbiodiesel studies using babassu oil have been reported com-pared to common types of sources, that is, palm oil, jatrophaoil, and so on. Meanwhile the coffee seed has the lowest oil

content. One of the reasons why there is an increment inthe number of researches on finding alternatives for biodiesel

Table 6 – Different feedstocks for biodiesel production.

Ediblefeedstocks

Non-ediblefeedstocks

Others

Soybean Jatropha curcas Waste cooking oilPalm oil Pongamia pinnata AlgalRapeseed Sea mango Municipal

sewage sludgeCanola TallowSunflower PoultryCottonseed Nile tilapiaPeanut CastorCorn Rubber seedOliveCoconut oilButterPumpkinLinseed

feedstock is the high cost of pure vegetables (edible crops)and seed oils, which constitutes about 70–85% of the over-all biodiesel production cost (Mondala et al., 2009; Siddiqueeand Rohani, 2011; Abbaszaadeh et al., 2012). Using reusablesources as biodiesel feedstock, biodiesel production costs canbe reduced by 60–90% since the price of waste edible oils is2.5–3.0 times cheaper than that of vegetable oils (Talebian-Kiakalaieh et al., 2013).

Choosing the right feedstock is very important to ensureit does not increase the production cost (Leung et al., 2010).Even if the production cost can be reduced, the production ofbiodiesel using non-edible oils may sometimes require multi-ple chemical steps due to the high FFA contents (Leung et al.,2010). For instance, Janaun and Ellis (2010) carried out methylester production, with a series of processes: one-step alkaline-based catalyzed transesterification and two-step acid-basedcatalyzed transesterification.

One of the promising non-edible sources for biodiesel feed-stock is Jatropha curcas Linnaeus seed oil. Usage of jatropha oilas the primary feedstock for producing biodiesel is one wayof reducing the production cost (Berchmans and Hirata, 2008).The high dependence on imports of petroleum and abundanceof this non-edible source in India led researchers to investi-gate the ability of jatropha oil to produce biodiesel with similarproperties or closer to those of diesel oil (Raja et al., 2011). Itis also easy to be found and grew, even on gravely, sandy andsaline soils (Bouaid et al., 2012). The source of oil in the J. curcasplant is primarily its seeds, with an oil content of 25–30%.

One of the interesting ideas for achieving low cost biodieselproduction is the usage of low cost feedstock such as wastecooking oil (WCO) (Demirbas, 2009). Usage of WCO is quitebeneficial since it can prevent the WCO from being dischargedinto the drainage system (Yaakob et al., 2013). In Kyoto, theusage of biodiesel from WCO collected from restaurants, cafe-terias, and households to be used as public transport fuelhas been implemented (Takashi, 2009). However, the qualityof the biodiesel produced may vary since the physical andchemical properties of WCO depend on the fresh cookingoil contents (Leung et al., 2010). Siddiquee and Rohani (2011)said that broad WCO properties may affect the consistency of

biodiesel production. Undesired impurities and large amountsof FFAs in the feedstock may also reduce the biodiesel quality

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 493

(oepa

hbmrtfPTpaEbtaB

tTsceub4eHbtbq

imow2aradspdw(Ddbov

2

Butr

Low-cost pro duction ’s feedstock • Munic ipal sludge • Waste coo king oil

High-cost produc tion ’s fee dstock • Su nflower oil • So ybean oil • Rapesee d oil • Cott on oil • Jatropha oil

Moder ate-cos t production’s feedsto ck • Vegeta ble oil

Fig. 5 – Classification of biodiesel production cost based ondifferent feedstock.

Table 7 – Cost of producing biodiesel from differentfeedstock using transesterification process.

Feedstock Biodieselproduction cost(USD per gallon)

References

Municipal sludge oil USD 3.11 per gallon Siddiquee andRohani (2011)

Soybean oil USD 4.00–4.50 pergallon

Siddiquee andRohani (2011)

Animal fats USD 1.59 per gallona Sivasamy et al.(2009)

Rapeseed oil USD 6.51 per gallona Sivasamy et al.(2009)

Palm oil USD 1.26 per gallona Ong et al. (2012)Rapeseed oil USD 10.64 per

gallonaOng et al. (2012)

Castor oil USD 4.04 per gallona Ong et al. (2012)Soybean oil USD 1.70 per gallona Ong et al. (2012)Waste cooking oil USD 1.56 per gallona Ong et al. (2012)

aCalculated production costs after unit conversion.

Demirbas, 2009). It is also lead to the need of pre-treatmentf WCO before further production process take place (Yaakobt al., 2013). Janaun and Ellis (2010) stated that some majorroblems of using this type of feedstock are the infrastructurend logistics needed to collect the waste oil.

The usage of algae as biodiesel feedstock is said to give aigh yield of methyl ester (Janaun and Ellis, 2010). In a reviewy Krishna et al. (2012), the production of biodiesel usingicroalgae with low cost operation and easy handling was

eported. The overall idea of their studies was to investigatehe extraction of biodiesel from the harvested algae collectedrom wastewater treatment ponds called High Rate Algalonds (HRAPs), which were set up near the industrial areas.hey claimed that the system of HRAPs coupled with biodieselroduction was efficient for wastewater management, simplend cost effective in producing biodiesel. However, Janaun andllis (2010) stated that for commercialization of algae-basediodiesel, it may result in a high production cost. For instance,his method requires effective large scale bioreactors and anlgae strain that can produce a high oil yield (Vasudevan andriggs, 2008).

A recent study done by Siddiquee and Rohani (2011) showedhe ability of municipal sewage sludge as biodiesel feedstock.he lipid was extracted from the sewage sludge before beingubjected to the process of biodiesel production and the pro-ess is known as a lipid extraction process. Study of Mondalat al. (2009) showed that, the production of sludge biodieselsing in situ transesterification managed to produce low costiodiesel. The cost was compared to petroleum diesel (USD.80/gallon) and soy biodiesel (USD 4.50/gallon) while the coststimated for their sludge biodiesel only around $4.00/gallon.owever, commercialization of the usage of sewage sludge asiodiesel feedstock has some large challenges, such as the pre-reatment process of raw sludge, the lipid extraction process,iodiesel production methods from solid sludge, biodieseluality, and process economics and safety.

In producing biodiesel, cost of overall production usuallynvolves the cost of feedstock, cost of processing the raw

aterial; purification of raw material and oil pressing, costf transesterification, cost of electricity, transportation andorking capital (Pimentel and Patzek, 2005; Sharma et al.,

008). Siddiquee and Rohani (2011) classified the factors thatffects the production cost into two major factors; the cost ofaw materials and the operating costs. However, Kapilakarnnd Peugtong (2007) stated that almost 80% of biodiesel pro-uction cost was contributed by the cost of feedstock. Theirtudy on palm oil biodiesel production at different reactionrocess conditions showed that for palm oil biodiesel pro-uction, the cost was contributed by three major factors thatere the cost of palm oil (80%), methanol (15%) and energy

5%). Based on several studies done by Mondala et al. (2009),emirbas (2009) and Talebian-Kiakalaieh et al. (2013), the pro-uction cost of biodiesel depending on the feedstock used cane classified as depicted in Fig. 5 while Table 7 shows the costf producing biodiesel from different feedstock based on pre-ious studies.

.2. Biodiesel production process

iodiesel can be produced by four primary techniques: directse and raw oils blending, micro-emulsions, transesterifica-

ion, and pyrolysis (Vyas et al., 2010). However, the commoneaction being used nowadays is transesterification (Janaun

and Ellis, 2010; Siddiquee and Rohani, 2011; Abbaszaadehet al., 2012).

2.2.1. Direct use and raw oils blendingThe direct use method is a method whereby crude vegetableoil is mixed or diluted with diesel fuel in order to improvethe viscosity (Abbaszaadeh et al., 2012). For ratios of 1:10–2:10,use of the diesel was found to be successful. However, Ma andHanna (1999) stated that blends of oils are not practical fordirect and indirect engines. Problems related to this situationare due to the high viscosity, acid composition, FFA content,and gum formation.

2.2.2. Micro emulsionsIt was stated by Abbaszaadeh et al. (2012) that the micro-emulsion process is developed and used to solve the problemregarding high viscosity of vegetable oil. A micro-emulsionis made by blending the vegetable oil with suitable solvents.Solvents that have been used and studied previously aremethanol, ethanol, and 1-butanol. The disadvantages of thisprocess are that it can result in heavy carbon deposits andincomplete combustion.

2.2.3. PyrolysisPyrolysis of oils involves the heating process with or with-out catalyst to convert one organic substance into another(Mohan et al., 2006). It was previously reported that biodieselfuel produced through a pyrolysis process or known as bio-oil is suitable for diesel engines; however, low-value materialsare produced due to the elimination of oxygen during the pro-

cess (Abbaszaadeh et al., 2012). Oxygen elimination is doneto upgrade the fuel produced so that it will be economically

494 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

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attractive and acceptable. Undesirable properties that some-times restrict the application of biodiesel produced throughthis process are low heating value, incomplete volatility, andinstability (French and Czernik, 2010). This process requiresexpensive equipment and has several advantages such aslower processing cost, simplicity, less waste, and no pollution(Singh and Singh, 2010). It was suggested by Ito et al. (2012)that the pyrolysis method is suitable for WCO processing.

2.2.4. TransesterificationTransesterification is said to be the most favourable reactionin producing biodiesel because it can reduce the oil viscos-ity (Abbaszaadeh et al., 2012). The conventional process flowdiagram for transesterification is shown in Fig. 6. The trans-esterification process involves the formation of glycerol andmethyl esters from the reaction of oil feedstock with alco-hol in the presence of catalyst. The process continues withthe separation of biodiesel and glycerol followed by the alco-hol recovery process. Recovered alcohol is recycled back tothe initial process while the methyl ester produced is sentfor purification, also known as the washing step. It will thenundergo a drying process where refined/purified biodiesel isobtained. Factors that might affect the transesterification yieldare the catalyst type, the alcohol/vegetable oil molar ratio, thecontent of water and FFAs, temperature, and reaction duration(Siddiquee and Rohani, 2011; Abbaszaadeh et al., 2012).

There are three types of catalysts: alkalis, acids, andenzymes. Alkali-catalyzed transesterification is widely usedin commercial production because this method produces ahigh conversion of oil in a short time (Srirangsan et al., 2009)and is less corrosive to industrial equipment (Jayed et al.,2009). It is said to have a very fast reaction compared to othercatalysts (Siddiquee and Rohani, 2011; Berrios and Skelton,2008). However, the reaction between FFA and alkali cata-lyst is undesirable because the soap formation can inhibitthe effectiveness of separation of glycerol from methyl esterand lower the biodiesel yield (Atadashi et al., 2012). It alsoleads to the consumption of catalyst. Enzyme catalyst canhelp avoid the formation of soap. Like acid catalysts, this cat-alyst has a longer reaction time and is costly. The catalystchosen is usually depends on the starter material and theconditions of its reaction (Kaercher et al., 2013). Stated byHuang et al. (2010), commonly used alcohols are methanol,ethanol, propanol, butanol, and amyl alcohol. Methanol ismore favourable because has a lower cost (Berrios and Skelton,2008), is easily obtained (Atadashi et al., 2012), and can reactwith triglycerides quickly and dissolve the alkali catalyst easily(Ma and Hanna, 1999). Process conditions of transesterifica-tion reaction with respect to different kind of feedstock aretabulated in Table 8.

3. Generation of biodiesel wastewater

As can be seen from Fig. 6, biodiesel wastewater is mainlygenerated from the washing process. The washing processis important to remove excess contaminants and impuri-ties to ensure that only high quality biodiesel that meetsstringent international standard specifications is produced(Ngamlerdpokin et al., 2011; Atadashi et al., 2012).

3.1. Biodiesel washing process

In the washing process, the undesirable substances beingremoved include soap (Rattanapan et al., 2011), catalyst,

Tab

Fee

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o

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o

Jatr

o

Jatr

o

Jatr

o

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n

Sun

Kar

aW

CO

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O

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 495

rans

faNbTwaw

3IeaadiimiLdlrlbaIa

3TrewBaadmthaaonrpg

polymeric membrane successfully filtered a higher volume

Fig. 6 – Process flow diagram of conventional t

ree glycerol, residual alcohol (Atadashi et al., 2011), water,nd FFAs (Berrios and Skelton, 2008; Leung et al., 2010).on-removed contaminants will reduce the quality ofiodiesel and affect engine performance (Atadashi et al., 2011).he washing process is commonly done via two techniques:et and dry washing (Berrios and Skelton, 2008). Recently,nother alternative washing method has been investigated,hich is membrane extraction (Leung et al., 2010).

.1.1. Wet washing processn the wet washing process, distilled warm water or soft-ned water is used to remove glycerol, alcohol, sodium salts,nd soaps. Water mist is sprayed over the unpurified productnd the mixture of water and impurities will be settled andrained out as effluent. Colourless water obtained on repeat-

ng this process indicates that complete removal of impuritiess achieved (Atadashi et al., 2011). The solubility of glycerol and

ethanol in water make this process favourable and effectiven removing both contaminants (Berrios and Skelton, 2008;eung et al., 2010). However, Low et al. (2011) stated that someisadvantages of this process are long separation time and

oss of yield. The loss of fatty acid methyl ester yields in theinsing water contributes to the generation of highly pollutediquid effluent (Kumjadpai et al., 2011). The large amount ofiodiesel wastewater generated by the washing process cre-tes a significant problem for the industry and environment.n 2011, worldwide generation of biodiesel wastewater waspproximately 28 million m3 (Veljkovic et al., 2012).

.1.2. Dry washing processhe dry washing process involves the use of an ion exchangeesin (Atadashi et al., 2011) or magnesium silicate powder (Lowt al., 2011). These materials are used to replace the usage ofater in order to remove the impurities (Leung et al., 2010;errios and Skelton, 2008). The filtration process is usuallydded in the final stage to enhance the process efficiency. Thedvantages of this treatment are that no wastewater is pro-uced and the total surface area coverage of the wash tank isinimized (Atadashi et al., 2011). Magnesium silicate used in

his process can be reused while synthetic magnesium silicateas added value as it can be used as compost and animal feeddditive (Dugan, 2007). Even though this process offers thedvantage of being waterless, it is reported that the productsbtained from this process never meet the limits of the inter-ational biodiesel standard (Leung et al., 2010). For instance, inesearch done by Berrios and Skelton (2008), their dry washing

rocess was able to produce or provide biodiesel with a freelycerol level less than that specified by the EN14214 Standard

esterification process for biodiesel production.

but failed to meet the standard level for methanol, triglyceri-des, and soap and water contents.

3.1.3. Membrane extractionThe aim of reducing the quantity of water required for thewashing process has led to the development of the membraneextraction method. This method can reduce the environmen-tal impact due to a reduction in the amount of oil in thedischarged water. The usage of membrane extraction is ben-eficial in minimizing the volume of water used (Gomes et al.,2013), effectively avoiding the occurrence of emulsificationduring the washing step and resulting in a decrement of themethyl ester loss during the refining process (Leung et al.,2010), and it is said to be a promising method of biodieselpurification. Membrane studies carried out by Low et al. (2011)involved the usage of two types of membrane: flat microfiltra-tion mixed cellulose acetate (MCA) polymeric membrane andflat ultrafiltration polytetrafluoroethylene (PTFE) polymericmembrane. The experimental set-up of this study is shownin Fig. 7. The crude biodiesel was pumped from the recircu-lation tank to the membrane module, where the methyl esterpermeate that passes through the membrane was collectedin a beaker, and the rejected fluid was sent back to the recir-culation tank. Their study found that the ultrafiltration PTFE

Fig. 7 – Schematic diagram of membrane processexperimental set-up (Low et al., 2011).

496 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

Table 9 – Advantages and disadvantages of each washing process.

Treatment Advantages Disadvantages References

Wet washing Very effective in removingcontaminants. Purifiedbiodiesel obtained directfrom glycerol separationfulfils EN14214 Standardrequirements.

Increased cost andproduction time; largeamount of water used,emulsion formation.

Veljkovic et al. (2012),Berrios and Skelton (2008)and Atadashi et al. (2011)

Dry washing Decreases production time;lower cost; less spacerequired to conduct drywashing process. Waterless.

Exceeds the limit in the ENStandard.

Berrios and Skelton (2008)and Leung et al. (2010)

Membraneextraction

Avoids the formation ofemulsions. Refining lossdecreases. Minimizes thevolume of water used.

Probably high cost. Lowthroughput due to existingcontaminants.

Gomes et al. (2013), Leunget al. (2010), and Atadashiet al. (2011)

Provide cost benefit.

of methyl ester compared to the MCA polymeric membrane.Membrane technology was also used and reported by Gomeset al. (2013). Tubular �-Al2O3/TiO2 membranes with averagepore diameters of 0.2, 0.1, and 0.05 �m and 20 kDa were used.In the investigation using acidified water with a mass con-centration of 10%, glycerol was separated effectively, givingfinal free glycerol content below 0.02% of the maximum value.Table 9 below summarizes the novelty of each treatment.

3.2. Biodiesel wastewater and its characteristics

The large amount of wastewater generated by the com-monly used wet-washing process is drawing the attentionof researchers. It was previously reported that the washingprocess is normally repeated two to five times dependingon the impurity level of methyl ester, with about 20–120 Lof wastewater being generated per 100 L biodiesel produced(Srirangsan et al., 2009). In other literature, it was reportedthat for every 100 L of biodiesel produced, more than 20 Lof wastewater was generated (Suehara et al., 2005). InThailand, production of more than 350,000 L/day biodieselconsequently produced more than 70,000 L of wastewater perday (Ngamlerdpokin et al., 2011; Jaruwat et al., 2010). Sileset al. (2010) stated that wastewater disposal from this highgrowth rate industry may rise the environmental concerns.The characteristics of biodiesel wastewater studied by previ-ous researchers are summarized in Table 10. It is normallyfound with high contents of COD, SS, oil and grease (O&G)with various pH level depending on the type of process beingused.

Biodiesel wastewater is a viscous liquid with an opaquewhite colour (Jaruwat et al., 2010). A high pH, high levelof hexane-extracted oil and low nitrogen and phosphorusconcentrations make this wastewater difficult to degrade nat-urally since these conditions make it unfavourable for thegrowth of microorganisms (Srirangsan et al., 2009; Kolesárováet al., 2011). A study by Suehara et al. (2005) found thatthe main component of biodiesel wastewater is residualremaining oil and this is also supported by Rattanapan et al.(2011). Thus, discharges of biodiesel wastewater into publicdrainage might lead to plugging of the drain due to the highcontent of oil and might also disturb the biological activ-ity in sewage treatment. Investigations by Ngamlerdpokinet al. (2011) and Chavalparit and Ongwandee (2009) found

that biodiesel wastewater contains water, glycerol, soap,methanol, FFAs, catalyst, and a portion of methyl ester. These

contaminants contribute to the high contents of COD and O&G(Srirangsan et al., 2009).

3.3. Level of environmental pollution by biodieselwastewater

In Malaysia, discharge of biodiesel wastewater into drainsmust comply with the Environmental Quality Act and Regu-lations standard for industrial discharge. The parameters ofbiodiesel wastewater are monitored according to the Envi-ronmental Quality (Industrial Effluent) Regulations 2009. Thestandard is governed by Malaysia’s Environmental Law, theEnvironmental Quality Act, 1974. Table 11 shows the industrialeffluent standard limits of the Malaysian government com-pared with other countries. Compared to Thailand, China, andthe Philippines, the standard limits of temperature, pH, andCOD are almost the same. For BOD5, SS, and O&G content,Malaysia’s government requires lower limit values comparedto other countries.

4. Treatment and management of biodieselwastewater

Due to the large amount of biodiesel wastewater gener-ated during the biodiesel production process, the wastewatertreatment should be solved effectively. In Thailand, someproduction plants are more likely to deliver the wastewa-ter to a treatment facility of a water agency due to theirinability to treat this wastewater with high organic mat-ter content (Kumjadpai et al., 2011). They need to payaround USD 128.45–160 for 1 m3 of wastewater as reported byNgamlerdpokin et al. (2011). Other alternative have been triedpreviously was incinerated the wastewater in cement indus-try (Veljkovic et al., 2014). However, no further investigationwas reported. Incineration method is said having a cheapercost rather that the cost they need to pay to water treatmentagency but still expensive when compared to other indus-trial wastewater treatment. Srirangsan et al. (2009) statedthat most previous studies usually focused on the productionof biodiesel without considering the environmental manage-ment and treatment aspect. This has led some researchersto be eager to seek a better treatment in terms of simplic-ity and cost. Certain industries generating oily wastewateremploy dissolved air flotation to separate the oil and grease

before the wastewater is sent to the next process (Chavalparitand Ongwandee, 2009). Some studies have proposed the

Process

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5 )

487–508

497

Table 10 – Characteristics of biodiesel wastewater.

pH COD (mg/L) SS (mg/L) TSS (mg/L) O&G (mg/L) BOD5 (mg/L) References

11.0 – 2670 – 15,100 – Suehara et al. (2005)6.7 18,362 – 8850 – – Berrios and Skelton (2008)8.5–10.5 60,000–545,000 1500–28,790 – 7000–44,300 105,000–300,000 Ruengkong et al. (2008)8.9 30,980 340 – 6020 – Chavalparit and Ongwandee (2009)9.25–10.76 312,000–588,800 – – 18,000–22,000 168,000–300,000 Jaruwat et al. (2010)

10.35 ± 0.03 428,000 ± 12,000 – – – – Siles et al. (2010)8.5–10.5 60,000–150,000 1500–5000 – 7000–15,000 30,000–60,000 Rattanapan et al. (2011)– 312,000–588,800 – – 18,000–22,000 168,000–300,000 Ngamlerdpokin et al. (2011)

10.1–10.2 542,400 – – 21,048 224,630 Kumjadpai et al. (2011)11.11 3681 – – 387 1600 Ramírez et al. (2012)11.21 40,975 – – 459 15,260 Ramírez et al. (2012)

9.25–10.26 29,595–54,362 – 670–690 1040–1710 1492–2286 Pitakpoolsil and Hunsom (2013)4.34–6.56 19,000–37,000 233–405 – – 260–1600 This study (2013)

Table 11 – Standards for industrial effluents in several countries.

Country Malaysia Thailand Taiwan, China Philippines

Parameter Unit A B Underconsideration

of PCC*

Inland waters Coastal waters

OEI* NPI* OEI NPI

Temperature ◦C 40 40 ≤40 ≤40 <35 40 40 40 40pH value – 6.0–9.0 5.5–9.0 5.5–9.0 5.5–9.0 6.0–9.0 6–9 6–9 5–9 5–9BOD5 at 20 ◦C mg/L 20 50 ≤20 ≤60 50 150 120 120 100COD mg/L 80 200 ≤120 ≤400 200 250 200 250 200SS mg/L 50 100 ≤50 ≤150 50 200 150 200 150O&G mg/L 1.0 10.0 ≤5 ≤15 10 – – 15 10Colour ADMI* 100 200 – – – 150 PtCo 150 PtCo 300 PtCo 300 PtCoRegulations Environmental

Quality Act andRegulations 1974

Enhancement andConservation of theNational Quality Act

Water PollutionControl Act

Philippine Regulations on Sanitation andWastewater Systems

References Akta Kualiti AlamSekeliling 1974

Thaveesri (2003) Tang (1993) Magtibay (2006)

*ADMI: American Dye Manufacturers Institute; PCC: Pollution Control Committee; OEI: Old/Existing Industry; NPI: New/Proposed Industry.

498 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

application of pre-treatment before the wastewater flows tothe treatment facility of the wastewater agency and some haveproposed full treatment of biodiesel wastewater.

4.1. Current treatment technologies

The individual treatments that have been reported includecoagulation (Ngamlerdpokin et al., 2011; Kumjadpai et al.,2011), electrocoagulation (Srirangsan et al., 2009; Chavalparitand Ongwandee, 2009), biological processes (Suehara et al.,2005), adsorption (Pitakpoolsil and Hunsom, 2013), and micro-bial fuel cell systems (Sukkasem et al., 2011).

4.1.1. Coagulation treatmentIn coagulation process, coagulant is added to separate thesmall particle content from a solution in a reasonable time.These particles are destabilized and flocculate into larger, set-tleable flocs (Aygun and Yilmaz, 2010). The formation of flocsisresponsible for removing contaminants such as metals andtoxic wastes and reducing COD, BOD5, SS, turbidity, and colour(Saraswathi and Saseetharan, 2012). Two stages of mixing areinvolved in the coagulation process: rapid and slow mixing.The rapid mixing helps the coagulants to disperse uniformlyin aqueous solution, while slow mixing helps the flocs size togrow (Kim et al., 2009). Xie et al. (2011) stated that coagulationprocess offers some advantages such as simple and economi-cal, and proven in reducing COD, BOD5, TSS, colour and organiccompounds levels effectively. According to Butler et al. (2011),the coagulation process can be very expensive depending onthe treated wastewater volume. However, a comparative studyof the coagulation and electrocoagulation process in treatingbiodiesel wastewater showed that coagulation is more eco-nomical but produces treated wastewater of slightly lowerquality (Ngamlerdpokin et al., 2011).

Factors that might affect the efficiency of the coagulationprocess include the type of coagulant used or pre-hydrolyzedmetal salt used (Xie et al., 2011), coagulant dosage, pH (Aygunand Yilmaz, 2010), mixing rate (Zhou et al., 2008), and sett-ling time (Rattanapan et al., 2011; Ngamlerdpokin et al.,2011). Numerous types of coagulants are used, such as alum,polyamine (Xie et al., 2011), polyaluminium chlorides, ferricchloride (Rattanapan et al., 2011), and titanium chloride (Kimet al., 2009). Organic and natural coagulants were also usedbefore, such as Moringa oleifera, Viciafaba, Pisumsativum, andbentonitic clay (Saraswathi and Saseetharan, 2012). In a reviewby Rattanapan et al. (2011) it was stated that ferric chloride,ferrous sulphate, and alum were highly effective coagulantsin reducing COD. However, the performance of each coagu-lant still depends on the overall process, and in choosing thetype of coagulant, the suitability of wastewater and economicreasons should be taken into consideration.

pH control is important in the coagulation mechanismfor generation of flocs or generating flocculation (Rattanapanet al., 2011) and affects the coagulation performance (Aygunand Yilmaz, 2010). It is often efficient in the range of pH 5–7,but the nature of the water might lead to some differencesin finding a suitable pH (Parmar et al., 2011). Sometimes, itis also depends on the type of coagulant; for example; alumis effective at reducing pollutants in wastewater over a rela-tively wide pH range of 6–8 (Ngamlerdpokin et al., 2011), PAClused pH in the range of 7–9 (Xie et al., 2011). Rattanapan et al.(2011) study showed pH of wastewater did affect the dosage of

coagulant used. Investigation they carried out showed at pH6–7, only 1.0 g/L PACl required to remove more than 90% O&G,

however at pH 5, the coagulation process used up to 2.0 g/LPACl to achieve the same removal efficiency.

The effect of retention time on the coagulation process ofbiodiesel wastewater was also studied by Rattanapan et al.(2011). The O&G removal increased from 81.65% at one day-retention time to 95.4% at five day-retention time showingthat the demulsion effectiveness/O&G removal was affectedby the duration of the retention time. Their study also focusedon the pH factor effect (5–7) and coagulants effect with variabledosage (alum and ferric chloride; 0.5–1.5 g/L, PACl: 0.5–2.0 g/L).A study by Ngamlerdpokin et al. (2011) showed that the CODand O&G were independent of the mixing rate, while BOD5

was dependent on the mixing rate, which showed an incre-ment in its removal from 73.5% at 100 rpm to 96.1% at 250 rpm.Zhou et al. (2008) stated that the increment of mixing rateaffects the velocity gradient as well as collision frequency andthis will consequently increase the efficiency of coagulationprocess. Another factor that gaining interest nowadays is theaddition of coagulant aids in the coagulation process. Aygunand Yilmaz (2010) investigated the effect of coagulant aids andthey found that coagulation treatment of detergent wastewa-ter using FeCl3 and clay mineral as coagulant aid managed toincrease the COD removal from 71 to 84%, while the additionof polyelectrolyte aid gave up to 87% COD removal.

Treatment of biodiesel wastewater was done in many ways.For example, in the study done by Ngamlerdpokin et al. (2011),it involved the acidifying process of the wastewater withthree different acids: H2SO4, HNO3, and HCl before coagulationprocess took place. The most effective acid was H2SO4. Theacidified wastewater was subjected to pH adjustment with theaddition of calcium oxide (CaO). CaO was used as a pH adjusterbecause it can work as coagulant coupling. Another factorsbeing manipulated were alum dosage (0–6 g/L) and mixing rate(100–300 rpm). Kumjadpai et al. (2011) carried out an investiga-tion of treatment of wastewater from waste used oil biodieselproduction plant using a two-step process involving chemicalrecovery using three types of acids (H2SO4, HNO3, and HCl)followed by a coagulation process using either Al2(SO4)3 (pH4.5–10) or PAC (pH 2.5–7.0) by the addition of CaO. Optimally,through acidification using H2SO4 at pH 1–2.5, approximately15–30% fatty acid methyl esters (FAMEs) were recovered. Theremoval efficiencies of pollutant’s parameter for each studyare listed in Table 12.

In another study, Xie et al. (2011) identified the performanceof coagulation process in treating raw waste glycerol producedfrom biodiesel production process. The pH of wastewater wasfirst being adjusted from 9 to 3 using HCl and NaOH priorto determine the appropriate pH for soap and oil separation.Through this acidification process, the waste glycerol was pre-treated with appropriate pH before coagulation process tookplaces. In this study, PACl coagulant was used. The coagulant’sdosage and pH were varied from 2 to 6 g/L and 6 to 9 respec-tively. Even coagulation process was proven in treating variouskind of wastewater successfully, some study underlined prob-lems related to this process such as the use of chemicals(Chavalparit and Ongwandee, 2009) and generation of low-density sludge with low-decomposition efficiency (Kumjadpaiet al., 2011). Despite all this problems, reported that many stillchoose to use chemical coagulation since it is one of the waysto enhance the wastewater treatment (Butler et al., 2011).

4.1.2. Electrocoagulation treatment

One of the attractive treatments for biodiesel wastewater isthe electrocoagulation process (Fig. 8). It is also known as

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 499

Tabl

e

12

–

Proc

ess

con

dit

ion

s

of

dif

fere

nt

coag

ula

tion

trea

tmen

ts

for

biod

iese

l was

tew

ater

.

Proc

ess

con

dit

ion

s

Sou

rce

ofw

aste

wat

erW

aste

wat

erch

arac

teri

stic

sR

emov

al

par

amet

ers

(%)

Ref

eren

ces

Typ

e

ofco

agu

lan

tD

osag

e

ofco

agu

lan

tp

H

Mix

ing

rate

Sett

lin

gti

me

CO

D

BO

D5

O&

G

Oth

ers

Alu

m

2

g/L

6

–

–

Was

tew

ater

from

was

hin

g

un

itp

H: 2

.5C

OD

: 271

000–

3417

12

mg/

LB

OD

5: 6

739–

6738

9

mg/

LO

&G

: 210

–421

mg/

L

97.5

97.2

98.2

–

Nga

mle

rdp

okin

et

al.

(201

1)

Alu

m

2

g/L

6

–

–W

aste

wat

er

from

was

hin

g

un

itp

H: 1

0.1–

10.2

CO

D: 2

7120

0–34

1712

mg/

LB

OD

5: 6

739–

6738

9

mg/

LO

&G

: 210

–421

mg/

L

98.8

98.6

99.5

–K

um

jad

pai

et

al.

(201

1)PA

C

1

g/L

4

–

–

98.7

97.9

99.1

–

Alu

m

2

g/L

–

–

1

hW

aste

wat

er

from

biod

iese

l pro

du

ctio

nO

&G

:71

20

mg/

L–

–

99.9

–R

atta

nap

an

et

al.

(201

1)Fe

rric

chlo

rid

e

2

g/L

–

–

1

h

–

–

99.8

–PA

Cl

2

g/L

1

h

–

–

99.7

–PA

Cl

5

g/L

7

35

rpm

15

min

Raw

was

te

glyc

erol

pH

: 9.7

–10.

4C

OD

: 1.7

–1.9

×

106

mg/

LB

OD

5: 0

.9–1

.2

×

106

mg/

LT

SS: 2

1.3–

38.7

×

105

mg/

LG

lyce

rol:

413–

477

g/L

Met

han

ol: 1

12–2

03

g/L

96.2

93.3

–

TSS

: 98.

1G

lyce

rol:

65.4

Met

han

ol:

85.8

Xie

et

al. (

2011

)

Fig. 8 – Schematic diagram of electrocoagulation set-up(Maha Lakshmi and Sivashanmugam, 2013). (1) DC powersupply, (2) anode, (3) cathode, (4) electrocoagulation cell, (5)

effluent, (6) magnetic bead, (7) magnetic stirrer.

an alternative method to chemical coagulation to reduce theusage of chemical coagulants (Butler et al., 2011) This treat-ment has been successfully introduced in treating municipalwastewater, dyeing wastewater (Aoudj et al., 2010), and waste-water containing organic species (phenol) (Chavalparit andOngwandee, 2009). This versatile treatment is said to have sev-eral advantages such as requiring only simple equipment, easeof operation, less treatment time, and use of less or no chem-icals (Tezcan et al., 2009). It also produces a smaller amountof sludge and leads to rapid sedimentation of the flocs gen-erated. Electrocoagulation uses electrochemistry principles,treating the wastewater better by oxidizing the cathode whilethe water is reduced (Butler et al., 2011).

The electrocoagulation process consists of three mainmechanisms: electrode oxidation, gas bubble generation,and flotation or sedimentation of formed flocs (Emamjomehand Sivakumar, 2009). Example of electrochemical reactionsusing alum as anode is described as in Eq. (2) (Chavalparitand Ongwandee, 2009). Listed by Butler et al. (2011) sev-eral considerations that might affect the treatment efficiency;wastewater type, pH, current density, type of metal electrodes,number and size of electrodes as well as metals configuration.However, there is other factor, which was investigated beforesuch as reaction/retention times.

Anodic reactions : Al(s) → Al3+ + 3e−

Cathodic reaction : H2O + 2e− → H2(g) + 2OH−

In the solution : Al3+(aq) + 3H2O− → Al(OH)3 + 3H−

(2)

The efficiency of the electrocoagulation process forbiodiesel wastewater treatment has been investigated by

Chavalparit and Ongwandee (2009). The electrodes used werealuminium and graphite, and the effect of several factors like

500 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

le

13

–

Proc

ess

con

dit

ion

s

of

elec

troc

oagu

lati

on

trea

tmen

ts

for

biod

iese

l was

tew

ater

.

Proc

ess

con

dit

ion

s

Sou

rce

ofw

aste

wat

erW

aste

wat

erch

arac

teri

stic

sR

emov

al

par

amet

ers

(%)

Ref

eren

ces

de

&

Cat

hod

eA

pp

lied

volt

age

pH

Rea

ctio

n

tim

eC

OD

BO

D5

O&

G

Oth

ers

de:

Alu

min

ium

thod

e:

Gra

ph

ite

18.2

V6.

0625

min

Oil

y

was

tew

ater

from

biod

iese

lp

rod

uct

ion

pH

: 8.9

CO

D: 3

0,98

0

mg/

LO

&G

: 602

0

mg/

LT

SS: 3

40

mg/

LG

lyce

rol:

1360

mg/

LM

eth

anol

: 10,

667

mg/

L

55 .4–

98 .4T

SS:

96.6

Ch

aval

par

itan

dO

ngw

and

ee(2

009)

de:

Alu

min

ium

thod

e:

Gra

ph

ite

Cu

rren

t

den

sity

:8.

32

mA

/cm

26.

00

25

min

Was

tew

ater

from

was

hin

g u

nit

pH

: 8.9

CO

D: 3

0,98

0

mg/

LO

&G

: 602

0

mg/

LT

SS: 3

40

mg/

LG

lyce

rol:

1360

mg/

LM

eth

anol

: 10,

667

mg/

L

55 .7–

97 .8SS

:97

.5K

um

jad

pai

et

al.

(201

1)

pla

te

Cu

rren

t

den

sity

:12

.42

mA

/cm

27.

40

4

h

Was

tew

ater

from

biod

iese

l pro

du

ctio

np

H: 2

.5C

OD

: 271

000–

3417

12

mg/

LB

OD

5: 6

739–

6738

9

mg/

LO

&G

: 210

–421

mg/

L

99 .691 .5

–

–

Nga

mle

rdp

okin

et

al.

(201

1)

initial pH, applied voltage, and reaction time were observed.Each factor were varied from 4 to 9, 10 to 30 V and 10 to40 min respectively. Chavalparit and Ongwandee (2009) alsooptimized the process using a Box–Behnken design and foundthat pollutants were efficiently removed at pH 4–7, whilean increment of pH up to 9 resulted in a decrement ofremoval because there was less formation of reactive flocsof aluminium hydroxide. The increment of voltage led to anincrement in final pH greater than 7.5 and resulted in inef-fective removal. Reported that, any additional time more than25 min does not have any significant impact on the removalefficiency. Their study showed under the optimum conditions,electrocoagulation consumed about 5.57 kW h power for thetreatment of 1 m3 biodiesel wastewater.

A study done by Srirangsan et al. (2009) determinedthe ability of the electrocoagulation process to performbiodiesel treatment using different operational conditionsin terms of the types of electrode, current density level,retention time periods, and initial pH levels. Types of elec-trode pairs were Fe–Fe, Fe–C, Al–Al, Al–C and C–C. Range ofcurrent density level, retention times and initial pH were3.5–11 mA/cm2, 10–40 min and 4–9 respectively. The processwas efficient at pH 6 with 25 min retention time and a cur-rent density level of 8.32 mA/cm2 using aluminium and carbon(Al–C) electrodes. The overall removal efficiency was foundto be 55.4, 96.9, and 97.8% for COD, SS, and O&G respec-tively. The electrocoagulation process has also been used byNgamlerdpokin et al. (2011) for treating the same wastewa-ter source, biodiesel wastewater. With a current density of12.42 mA/cm2, COD and BOD5 removals of 99.6 and 91.5%,were achieved respectively. Table 13 shows the process condi-tions for different electrocoagulation treatments for biodieselwastewater.

4.1.3. Biological treatmentVarious researchers have developed biological technologiesfor the treatment of biodiesel wastewater (Siles et al., 2010;Sukkasem et al., 2011; Ramírez et al., 2012; De Gisi et al.,2013). However, the study of this treatment is quite limited.Since the content of solid presents in biodiesel wastewateris quite high, it inhibits the growth of microorganism andreduces the removal efficiencies of biological treatment. Fewstudies reporting on this matter were discussed. Some factorsthat play an important role and influence the effectivenessof biological process are nutrients and oxygen supply, pHvalue, chemical and physical characteristics of the wastewa-ter (Margesin and Schinner, 2001), and hydraulic retentiontime (HRT) (Rajasimman and Karthikeyan, 2007). Sufficientnutrients are usually needed to ensure the sustainability ofbacterial growth and to allow treatment to proceed optimally.For oxygen level in biological treatment, it depends on theprocess type either aerobic or anaerobic. For aerobic process,sufficient oxygen is needed to create the proper environmentfor bacterial inoculation to become dominant. Insufficientoxygen content in aerobic treatment may become a limitingfactor for bacterial growth. However, excess oxygen supplymight lead to high energy consumption and reduce the pro-cess efficiency (Holenda et al., 2008).

pH should be taken into consideration because an unsuit-able pH might lead to washout of the biomass in the reactor(Patel and Madamwar, 2002). A study of HRT effect was inves-tigated by Patel and Madamwar (2002). Their study showed

that petrochemical wastewater are likely to be treated byaerobic process with a shorter HRT compared to anaerobic

Tab

An

o

An

o Ca

An

o Ca

Iron

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 501

dtmhbatrdt

bbtrNfpaiawtbwstiwc4oatpt

swtloK2T11

wYuuMaw22amvtctt

igestion, which requires a longer time and has a slow reac-ion. In another study by Bassin et al. (2011), a longer HRT

ay be beneficial to treatment process since it may result in aigher capacity of biomass and avoid washout of slow-growingacteria. According to Rajasimman and Karthikeyan (2007),t shorter HRTs, there is insufficient time for the biomasso degrade the substrate. This condition may lead to a loweremoval percentage (Mohamad et al., 2008). However, it stillepends on the suitability of the overall process, bacteria, andype of wastewater.

Study of biodiesel wastewater treatment was also doney Suehara et al. (2005). Their aim was to achieve rapidiodegradation of the remaining oil contained in the threeypes of biodiesel wastewaters, that is, artificial wastewater,aw biodiesel wastewater, and diluted biodiesel wastewater.utrients added to make the process conditions favourable

or the growth of bacteria were urea, yeast extract, potassiumhosphate and magnesium sulphate. This was also done tovoid eutrophication. The result showed that the microorgan-sm used, Rhodotorula mucilaginosa HCU-1, was able to degradebout 98% of the oil content in the diluted biodiesel waste-ater. However it gave almost zero degradation efficiency in

he raw biodiesel wastewater, which may be due to the inhi-ition of microorganisms present in the solids of the rawastewater. In another study, Chavan and Mukherji (2008)

howed that they were able to treat diesel-rich wastewa-er using Bacillus cepacia and the treatment was carried outn a rotating biological contactor (RBC). Various N:P rangeere varied in order to observe the performance of RBC at

onstant HRT of 21 h. At N:P ratio of 19:1, 28.5:1, 38:1 and7.4:1, they managed to remove 98.6, 99.4, 99.4 and 99.3%f TPH respectively and they also removed 84.6, 97.8, 97.0nd 95.6% of TCOD respectively. Their investigation concludedhat the use of algal-bacterial biofilm in RBC may suitable foretrochemical industries and petroleum refineries wastewa-er.

Ramírez et al. (2012) conducted a study of an activatedludge biological treatment applied prior to treating biodieselastewater. In this case, 1.5 L of sludge from a biological

reatment plant for textile wastewater was used as the inocu-ums in a reactor with an operating volume of 4.5 L; 2.5 mLf nutrients (38.5 g/L of urea, 33.4 g/L of NaH2PO4, 8.5 g/L ofH2PO4, 21.75 g/L of K2HPO4, and 5 g/L of CaCl2·2H2O) and–4 mg/L of dissolved oxygen were supplied to the tank.he treatment succeeded in reducing COD by 90% after3 days of operation but gave only 21% TOC removal in5 days.

The potential of biological process to be used in biodieselastewater treatment also being reviewed by Khan andamsaengsung (2011). They stated that the biological processsing submerged membrane bioreactor (MBR) could be a pop-lar advanced process for biodiesel wastewater treatment.BR has successfully treated various type of wastewaters such

s refinery wastewater (Rahman and Al-Malack, 2006), oilyastewater (Tri, 2002), petrochemical wastewater (Llop et al.,

009), and oil-contaminated wastewater (Scholz and Fuchs,000). Some main parameters involved in the MBR systemre the configuration of the membrane, membrane material,embrane pore size, and HRT. Based on their study on pre-

ious research showed that MBR was efficiently proven forreating oily wastewater, and the authors concluded that MBRan be used in biodiesel wastewater treatment. Unfortunately,

he cost of the treatment can be higher than that of conven-ional treatment due to the membrane fouling. This includes

the cost of maintenance and cleaning, membrane replace-ment cost, and membrane module cost. Table 14 summarizedthe removal efficiencies of biodiesel wastewater using biolog-ical treatments.

4.1.4. AdsorptionAdsorption process is reported as versatile, easily operated,and effective method of separating a wide range of chemicalcompounds (Zhang et al., 2010). They offer several advan-tages; for example, no additional sludge is produced, no pHadjustment is required, and the pH of the discharged waste-water is unaffected. There are various type of adsorbents,including peat, bentonite clay, activated carbon, agriculturalwaste, and chitosan. The treatment of biodiesel wastewa-ter using adsorption has been conducted by Pitakpoolsil andHunsom (2013). In their investigation, commercial chitosanflakes were used as adsorbent and several operating param-eters were varied, including adsorption time (0.5–5 h), initialwastewater pH (2–8), adsorbent dosage (1.5–5.5 g/L), and mix-ing rate (120–350 rpm). Pre-treatment of biodiesel wastewaterwas carried out first by an acidification process using H2SO4

to reduce the pH to 2.0 before subjecting it to the adsorp-tion process prior to separate the oil-rich phase. By addingNaOH, pH of wastewater was adjusted according to the pre-ferred range. Under optimum conditions (adsorption time of3 h, initial wastewater pH of 4.0, chitosan at 3.5 g/L, and mix-ing rate of 300 rpm), their investigation succeeded in reducingBOD5, COD, and O&G by 76, 90, and 67% respectively. However,these pollutant levels were still not in the acceptable rangefor wastewater to be discharged to the environment. Theyemphasized that further treatment is needed either repeti-tion of adsorption using fresh chitosan or other methods. It isalso might facing difficulties in disposing the usable chitosanflakes.

4.1.5. Microbial fuel cellAnother treatment that has been investigated is the use ofmicrobial fuel cells (MFCs). In a study by Sukkasem et al.(2011), they reinvented and used a kind of biocatalytic MFC,an upflow bio-filter circuit (UBFC). This treatment offers highCOD removal but is costly due to the expensive materials usedsuch as platinum or gold metal catalysts, proton exchangemembranes, mediators, and graphite electrodes. In the study,biodiesel wastewater characterized by 218,000 ± 30,000 mg/LCOD was successfully treated with up to 60% removal. Exist-ing treatments of biodiesel wastewater and their removalefficiency are summarized in Table 15. Each treatment hasadvantages and disadvantages, as listed in Table 16.

4.2. Integrated system

Most of the treatments used on biodiesel wastewater wereable to decrease the contaminants found in it. A specialty ofeach type of treatment lies in its suitability in terms of envi-ronmental and economic factors. Many researchers suggestedan additional treatment for every pre-treatment investigatedin order to achieve the highest efficiency. Several integratedsystems being investigated for biodiesel wastewater treat-ment are dissolved air flotation–coagulation (Rattanapanet al., 2011), the photo-Fenton–aerobic sequential batch reac-tor (Ramírez et al., 2012), acidification–electrocoagulation andbiomethanization (Siles et al., 2011), and electroflotation and

electrooxidation (Romero et al., 2013). Integrated systems andthe proposed integrated coagulation–biological aerated filter

502 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

Tabl

e

14

–

Rem

oval

effi

cien

cies

of

biod

iese

l was

tew

ater

usi

ng

biol

ogic

al

trea

tmen

ts.

Typ

e

of

trea

tmen

t

Typ

e

ofm

icro

orga

nis

mTy

pe

ofw

aste

wat

erW

aste

wat

erch

arac

teri

stic

sR

emov

al

par

amet

ers

Ref

eren

ces

CO

D

BO

D5

O&

G

Oth

ers

Aga

r

pla

teR

hodo

toru

lam

uci

lagi

nosa

Raw

biod

iese

lw

aste

wat

er; a

rtifi

cial

was

tew

ater

Raw

BD

Fw

aste

wat

er:

pH

: 11

Oil

con

cen

trat

ion

:15

.1

g/L

Soli

d

con

ten

t:2.

67

g/L

–

–

–

Oil

:98

.0%

Sueh

ara

et

al. (

2005

)

Rot

atin

g

biol

ogic

alco

nta

ctor

Bac

illu

s

cepa

cia

Die

sel-

rich

was

tew

ater

pH

: 7.5

TC

OD

: 451

2

mg/

LT

PH: 4

961

mg/

L

97 .0%

–

–

TPH

:98

.4%

Ch

avan

and

Mu

kher

ji

(200

8)

Bat

ch

reac

tor

Text

ile

was

tew

ater

trea

tmen

tin

ocu

lum

s

Was

tew

ater

from

pal

m

oil b

iod

iese

lp

rod

uct

ion

pla

nt

pH

11.1

CO

D: 3

681

mg/

LT

OC

: 170

0

mg/

LO

&G

: 387

mg/

L

90 .0%

–

–

TO

C:

21%

Ram

írez

et

al. (

2012

)

(CoBAF) system are further discussed in the following section.The authors are aiming to propose a system that applies greentechnology that requires the use of fewer chemicals and iseconomical and safe for the environment and human beings.

4.2.1. Dissolved air flotation–coagulationA typical treatment of oily wastewater, dissolved air flotation,was studied by Rattanapan et al. (2011). However, the authorssuggested additional methods and pre-treatment of the sys-tems by acidification and a coagulation process. About 1 N ofpure HCl and H2SO4 was used for acidification, and the coagu-lation process was done using a Jar test unit under conditionsof 100 rpm for 1 min followed by 30 rpm for 20 min. A decre-ment in wastewater pH from 7 to 5 made the oil dropletsflocculate with each other and rise to the surface. In the acidi-fication process, the authors found that the COD removal wasefficient at pH 3. Oil recovered in the acidification processwas intended to be used in biodiesel production. Moreover,H2SO4 was found to be a more suitable acid, since the oper-ating cost is cheaper than with HCl. The performance of thecoagulation process was determined for different types ofcoagulants: alum, polyaluminium chloride, and ferric chloride.The authors found that the usage of these three coagulantsprovides almost similar trends of COD and O&G removal,namely more than 30 and 90% removal, respectively. But interms of cost, alum was found to be the more suitable coag-ulant. In the final process of this research, the dissolved airflotation method was used with acidification and coagulation.The pH was maintained at 3 with three days-retention timeand alum as the coagulant. With alum dose ≥150 mg/L and 40%recycle rate, this system was able to give 98–100% SS removal,85–95% O&G removal, and 40–50% COD removal.

4.2.2. Photo-Fenton-aerobic sequential batch reactorRamírez et al. (2012) investigated the efficiency of an inte-grated process which combined the photo-Fenton advancedoxidation technique with an aerobic sequential batch reactor(SBR). Photo-Fenton reaction was said potentially successful inremoving large amount of COD content. It involved the oxida-tion of Fe(II) to Fe(III) to decompose hydrogen peroxide. Theoxidation rate was then increased via the photo-reductionof Fe(III) back to Fe(II) through the exposure to radiation ofUV–vis. The production of hydroxyl radical from this cycle isused for the oxidation of organic compounds.

Fe2+ + H2O2 → Fe3+ + OH• + OH−

Fe3+ + H2O + hv → Fe2+ + OH• + H+

RH + OH• → photo-products + H2O

(3)

This system was applied to the treatment of wastewaterfrom a biodiesel production plant. In this experiment, waste-water with its pH adjusted to 2.3 was treated in a 7 L MightyPure MP-36 commercial UV reactor. Hydrogen peroxide (H2O2)and ferrous ions were added to the wastewater and a sam-ple was taken after 2 h. MnO2 was added to each sample inorder to destroy the H2O2, avoid subsequent reactions, preventinterference with the COD readings, and prevent inhibitionof the bioreactor. The final sample was then sent to a 4.5 Loperating SBR with a dissolved oxygen level between 2 and4 mg/L. Seven days of treatment were applied for the degra-dation of organic matter. Palm oil and castor oil biodiesel

wastewaters were used, and during this experiment morethan 90% of COD and BOD5 and 72% of TOC were removed from

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 503

Table 15 – Summary of other individual process for biodiesel wastewater treatment.

Treatment process COD removal (%) BOD5 removal (%) SS removal (%) O&G removal (%) References

Adsorption 90 76 – 67 Pitakpoolsil and Hunsom (2013)Microbial fuel cell 60 – – – Sukkasem et al. (2011)

Table 16 – Advantages and disadvantages of different individual treatments.

Treatment Advantages Disadvantages/problems References

Coagulation Simple and economical,proven enhancewastewater treatment

Require handling chemical,operation relativelycomplicated, generateslow-density sludge withlow-decompositionefficiency.

Xie et al. (2011), Butler et al.(2011), Chavalparit andOngwandee (2009) andKumjadpai et al. (2011)

Electrocoagulation Less treatment time, nochemical required simpleequipment, ease ofoperation

Higher cost compared tocoagulation, less effectivefor methanol and glycerolremoval

Ngamlerdpokin et al. (2011),Chavalparit andOngwandee (2009) andSrirangsan et al. (2009)

Biological processes Economical, versatilearrangements for smallareas, simple and suitablefor small scale plant

Generates large amounts oflow-density sludge withlow decompositionefficiency, time consuming,need to manage theoptimum condition first

Pitakpoolsil and Hunsom(2013), Ramírez et al. (2012)and Suehara et al. (2007)

Adsorption No additional sludge isproduced, pH of dischargedwastewater is unaffected

Need further treatment,facing difficulties indisposing the adsorbents

Pitakpoolsil and Hunsom(2013)

te6shtphS

4cTwgltoctplcemtuwtwraar

Microbial fuel cell Offers high COD removal

he palm oil biodiesel wastewater. Meanwhile, the removalfficiencies for castor oil biodiesel wastewater were 76.1,9, and 67.7% for COD, BOD5, and TOC respectively. Theytated that through this combined system, wastewater withigh biodegradability rate can be obtained and the treatmentime can be reduced. However, some problems have beenointed such as the cost for UV radiation which is quiteigh and the difficulties to decompose the formed sludge inBR.

.2.3. Acidification–electrocoagulation and anaerobico-digestionhis treatment was carried out by Siles et al. (2010). This studyas initially done to convert biodiesel-by product which is

lycerol into more valuable products. It is said that the pol-ution can be controlled and the energy can be recoveredhrough this treatment. Due to the existence of inhibitorsf anaerobic co-digestion which is long-chain fatty acidsontained in biodiesel wastewater, they decided to add pre-reatment steps; acidification and electrocoagulation processrior to reduce the effect of the inhibitors. It is said that

ong chain fatty acids results in toxicity to the anaerobiconsortium. Through acidification using sulphuric acid andlectrocoagulation with 5 L stirred tank containing eight alu-inium electrodes, the COD content was reduced by 45%. The

reatment was then continued with anaerobic co-digestionsing three 1-L stirred reactor. The reactors were inoculatedith granular biomass obtained from brewery wastewater

reatment anaerobic tank. The organic load of biodiesel waste-ater was varied from 1.0 g to 2.0 and 3.0 g COD in the

ange of 18–45 h retention time. The whole treatment man-ged to remove 80–90% of COD with methane productions an added value to the process (310 mL methane/g COD

emoved).

. The simple and economical operation of the coagulation

Costly Sukkasem et al. (2011)

4.2.4. Acidification–electrocoagulation and biomethanizationIntegrated acidification–electrocoagulation and biometha-nization treatment was applied by Siles et al. (2011).Wastewater derived from biodiesel manufacturing with428,000 mg/L of COD was used and treated by the sys-tem. In this study, another integrated system, acidification–coagulation–flocculation and biomethanization, was also usedprior to comparing the two systems’ efficiencies. Thepre-treatment processes of acidification–electrocoagulationand acidification–coagulation–flocculation gave COD removalrates of 45 and 63% respectively. However, during thewhole treatment, 99% COD removal was recorded usingacidification–electrocoagulation and biomethanization com-pared to only 94% using acidification–coagulation–flocculationand biomethanization.

4.2.5. Electroflotation and electrooxidationThe utilization of electroflotation and electrooxidation intreating biodiesel wastewater treatment was investigated byRomero et al. (2013). A bench scale reactor was used and theoptimum conditions of this combined process were achievedby varying several parameters such as current density, con-ductivity, and reaction time. By using aluminium electrodeswith current density of 8.0 mA cm−2 for a reaction time of60 min, the electroflotation process managed to remove 92,98, 100, 57, and 23% of turbidity, total solids, O&G, COD, andmethanol respectively. The effluent was then subjected toan electrooxidation process using Ti/RuO2 anodes. With anapplied current density of 40.0 mA cm−2 for a reaction timeof 240 min, the methanol and COD were effectively reducedby 68 and 95% respectively.

4.2.6. Chemical recovery and electrochemical

Jaruwat et al. (2010) studied the ability of a combined chemi-cal recovery and electrochemical process. Chemical recovery

504 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

ted p

Fig. 9 – Schematic of proposed integra

by acid protonation was used to recover the biodiesel whilethe second stage treatment was named electrooxidation. Thistreatment managed to recover 6–7% (w/w) biodiesel from theraw biodiesel wastewater through the protonation reactionand decreased the BOD5, COD, and O&G levels by 13–24, 40–74,and 87–98% respectively. More than 95 and 100% of COD wasremoved through electrooxidation.

4.2.7. Coagulation-biological aerated filter (CoBAF)systemThe biological aerated filter (BAF) is one of the biological treat-ment methods which have been proven in treating varioustypes of wastewater such as textiles (Chang et al., 2002; Heet al., 2013), oily wastewater (Zhao et al., 2006; Su et al., 2007),leachate (Wu et al., 2011; Wang et al., 2012), and pulp andpaper mill wastewater (Adachi and Fuchu, 1991). BAF has alsobeen investigated and used as a system for removing ammo-nium (NH4

+–N) and manganese (Mn2+) from drinking water(Abu Hasan et al., 2013). Our study aims to use this systemin the proposed integrated process, which combines coagula-tion treatment and the BAF system (CoBAF), as depicted inFig. 9 process make this treatment favourable to be addedas an initial stage prior to reducing and removing the highsolid content and COD before biological treatment takes place.High solid and COD contents might inhibit the microorgan-isms’ growth (Kumjadpai et al., 2011). It was stated by Sueharaet al. (2007) that the biological process alone is not suitableto treat biodiesel wastewater. Table 17 shows the summaryof integrated system performance for biodiesel wastewatertreatment.

Biological treatment seems suitable for use because of itseconomic value (Jou and Huang, 2003; Gasim et al., 2000)and are proven for its ability to give lower levels of contami-nants (Malakahmad et al., 2011). As shown by previous studies,biological treatment is suitable for treating biodiesel waste-

water because it can reduce the content of methanol andglycerol since they are easily biodegradable (Srirangsan et al.,

Table 17 – Summary of integrated system performance for biod

Treatment process CODremoval (%)

BODremova

Dissolved air flotation–coagulation 40–50 –

Membrane bioreactor–biological activatedcarbon

89.9–99.9 –

Acidification–electrocoagulation andanaerobic co-digestion

80–90 –

Acidification–electrocoagulation andbiomethanization

99 –

Acidification–coagulation–flocculationand biomethanization

94 –

Photo-Fenton-aerobic sequential batchreactor

76.1 69

Electroflotation and electrooxidation 57 –

rocess of CoBAF system in our study.

2009). Biological treatments such as the activated sludge pro-cess have been used widely in treating wastewater from thepetrochemical industry (Shokrollahzadeh et al., 2008; Khainget al., 2010; Sponza and Gök, 2010). Pramanik et al. (2012)stated that BAF usage can provide a secondary treatment inindustrial treatments and is proven to be more reliable thanconventional biological treatment. The normal operation ofthe BAF process with aeration involves the attachment ofa microorganism growth process on media which are sta-tionary (Zhao et al., 2006). Some advantages that make thissystem favourable for use are its flexibility, where solids sep-aration or aerobic biological treatment can be carried out,ease of operation, and relative compactness (Pramanik et al.,2012); it requires a small working space and provides a smallfootprint with a large surface area (Abu Hasan et al., 2009). Sev-eral important criteria in biological aerated systems are themicroorganism growth, flow configuration, aeration system,filter media, media types, size, and BAF design (Abu Hasanet al., 2009).

The BAF system has been studied before by Zhao et al.(2006). The system was used to successfully pre-treat oil fieldwastewater from Renerlian Factory drainage outlet. With theusage of group B350M immobilized microorganisms, the over-all system was able to degrade about 78% of total organiccarbon (TOC) and remove 94% of oil content. It also success-fully removed up to 90% of the PAHs content. The authors alsoemphasized that the BAF system was suitable for use as analternative to the conventional activated sludge system. Suet al. (2007) also investigated the ability of down-flow BAF intreating oil-field produced water. The anaerobic baffled reac-tor (ABR) was combined with the BAF system and the hydraulicloading rates were varied from 0.6 to 1.4 m h−1. The treat-ment effectively removed 76.3–80.3, 31.6–57.9, 86.3–96.3, and76.4–82.7% of oil, COD, BOD, and SS respectively. Chang et al.(2002) used BAF to treat textile wastewater. They found that

the BAF system could remove about 88 and 97% of COD andsuspended solids, respectively.

iesel wastewater treatment.

l (%)SS removal

(%)O&G

removal (%)References

98–100 85–95 Rattanapan et al. (2011)– 97.6–99.9 Tri (2002)

– – Siles et al. (2010)

– – Siles et al. (2011)

– – Siles et al. (2011)

– – Ramírez et al. (2012)

98 100 Romero et al. (2013)

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 505

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A

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The main reason why authors are interested in investi-ating CoBAF integrated system is that we are trying to findimpler and greener processes, which could treat biodieselastewater. So far, none of the discussed treatment pro-

ess could treat biodiesel wastewater alone. For example,issolved air flotation, as currently and widely used treat-ent in biodiesel production plant could not treat biodieselastewater alone. Additional process/processes is/are needed

o ensure that the effluent of biodiesel wastewater meethe effluent standard requirement. Based on previous study,esearchers came out with different type of treatment systemn order to study their performance, capabilities and each hav-ng their own advantages and disadvantages. We aim to useiological process while simultaneously the process requiredo remove the microorganisms inhibitor through coagulations considered. Study of Xie et al. (2011) showed that coagu-ation process was proven in releasing wastewater that wasasily treated by biodegradation. For this reason, the biolog-cal aerated filter combined with the pre-treatment processf coagulation might have a successful potential in treatingiodiesel wastewater. For the time being, we are working onhis integrated system in the lab scale and hoping that it willive a positive outcome on biodiesel wastewater treatment.

. Conclusions

iodiesel is mainly produced from vegetable oils through theransesterification process. Several issues such as economicnd environmental factors have led to the development ofiodiesel production technologies from various types of feed-tock using various types of processes. The development ofiodiesel, due to the scarcity of fossil fuel sources, has ledo the emergence of another issue that needs to be solved.he process results in the production of a high amount ofastewater. Soap, glycerol, methanol, and O&G contents in

he wastewater make it impossible to treat efficiently with aingle treatment. This wastewater, which has a milky colournd bad odour, needs to be treated efficiently. Numerous treat-ents are being studied and proven for treating or pre-treating

iodiesel wastewater and each has its own benefits and disad-antages. The ability and performance of integrated treatmentsing a coagulation–biological aerated filter (CoBAF) systemill be investigated.

cknowledgements

his research was financially supported by the Faculty ofngineering and Built Environment, Universiti Kebangsaanalaysia, through grant number INDUSTRI-2012-029.

eferences

bbaszaadeh, A., Ghobadian, B., Omidkhah, M.R., Najafi, G., 2012.Current biodiesel production technologies: a comparativereview. Energy Convers. Manage. 63, 138–148,http://dx.doi.org/10.1016/j.enconman.2012.02.027.

bdullah, A.Z.Ã., Salamatinia, B., Mootabadi, H., Bhatia, S., 2009.Current status and policies on biodiesel industry in Malaysiaas the world’s leading producer of palm oil. Energy Policy 37(12), 5440–5448, http://dx.doi.org/10.1016/j.enpol.2009.08.012.

bu Hasan, H., Sheikh Abdullah, S.R., Kamarudin, S.K., Tan Kofli,N., 2009. A review on the design criteria of biological aerated

filter for COD, ammonia and manganese. J. Inst. Eng., Malays.70 (4), 25–33.

Abu Hasan, H., Sheikh Abdullah, S.R., Kamarudin, S.K., Tan Kofli,N., Anuar, N., 2013. Simultaneous NH4

+–N and Mn2+ removalfrom drinking water using a biological aerated filter system:effects of different aeration rates. Sep. Purif. Technol. 118,547–556.

Adachi, S., Fuchu, Y., 1991. Reclamation and reuse of wastewaterby biological aerated filter process. Water Sci. Technol. 24 (9),195–204.

Adnan, H., 2013. The Star Online. Malaysia’s B10 BiodieselProgramme and its Benefit, Retrieved from: http://biz.thestar.com.my/news/story.asp?file=/2013/2/12/business/12699472&sec=business

Ahmad, M., Ahmed, S., Fayyaz-Ul-Hassan, A.M., Khan, M.A.,Zafar, M., Sultana, S., 2010. Base catalyzed transesterificationof sunflower oil biodiesel. Afr. J. Biotechnol. 9 (50), 8630–8635.

Akta Kualiti Alam Sekeliling 1974 (Environmental Quality Act1974), 2009. International Law Book Services. Direct ArtCompany, Kuala Lumpur,Malaysia.

Aoudj, S., Khelifa, A., Drouiche, N., Hecini, M., Hamitouche, H.,2010. Electrocoagulation process applied to wastewatercontaining dyes from textile industry. Chem. Eng. Process.:Process Intensif. 49 (11), 1176–1182,http://dx.doi.org/10.1016/j.cep.2010.08.019.

Atadashi, I.M., Aroua, M.K., Abdul Aziz, A.R., Sulaiman, N.M.N.,2011. Refining technologies for the purification of crudebiodiesel. Appl. Energy 88 (12), 4239–4251,http://dx.doi.org/10.1016/j.apenergy.2011.05.029.

Atadashi, I.M., Aroua, M.K., Abdul Aziz, A.R., Sulaiman, N.M.N.,2012. High quality biodiesel obtained through membranetechnology. J. Membr. Sci. 421–422, 154–164,http://dx.doi.org/10.1016/j.memsci.2012.07.006.

Aygun, A., Yilmaz, T., 2010. Improvement ofcoagulation–flocculation process for treatment of detergentwastewaters using coagulant aids. Int. J. Chem. Environ. Eng. 1(2), 97–101.

Bassin, J.P., Dezotti, M., Geraldo, L.S.J., 2011. Nitrification ofindustrial and domestic saline wastewaters in moving bedbiofilm reactor and sequencing batch reactor. J. Hazard. Mater.185 (1), 242–248,http://dx.doi.org/10.1016/j.jhazmat.2010.09.024.

Berchmans, H.J., Hirata, S., 2008. Biodiesel production from crudeJatropha curcas L. seed oil with a high content of free fattyacids. Bioresour. Technol. 99 (6), 1716–1721,http://dx.doi.org/10.1016/j.biortech.2007.03.051.

Berrios, M., Skelton, R.L., 2008. Comparison of purificationmethods for biodiesel. Chem. Eng. J. 144, 459–465,http://dx.doi.org/10.1016/j.cej.2008.07.019.

Biodiesel market reports. Retrieved from:http://www.thecropsite.com/reports/

Bouaid, A., El Boulifi, N., Martinez, M., Aracil, J., 2012.Optimization of a two-step process for biodiesel productionfrom Jatropha curcas crude oil. Int. J. Low Carbon Technol.,331–337, http://dx.doi.org/10.1093/ijlct/ctr047.

Butler, E., Hung, Y.T., Yeh, R.Y.L., Al Ahmad, M.S., 2011.Electrocoagulation in wastewater treatment. Water 3 (4),495–525, http://dx.doi.org/10.3390/w3020495.

Canakci, M., Gerpen, J.V., 2001. Biodiesel production from oils andfats with high free fatty acids. J. Agric. Saf. Health 44 (6),1429–1436.

Chang, W.S., Hong, S., Park, J., 2002. Effect of zeolite media for thetreatment of textile wastewater in a biological aerated filter.Process Biochem. 37, 693–698.

Chavalparit, O., Ongwandee, M., 2009. Optimizingelectrocoagulation process for the treatment of biodieselwastewater using response surface methodology. J. Environ.Sci. 21 (11), 1491–1496,http://dx.doi.org/10.1016/S1001-0742(08)62445-6.

Chavan, A., Mukherji, S., 2008. Treatment of hydrocarbon-richwastewater using oil degrading bacteria and phototrophicmicroorganisms in rotating biological contactor: effect of N:P

ratio. J. Hazard. Mater. 154 (1–3), 63–72,http://dx.doi.org/10.1016/j.jhazmat.2007.09.106.

506 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

Chincholkar, S.P., Srivastava, S., Rehman, A., Dixit, S., Lanjewar,A., 2005. Biodiesel as an alternative fuel for pollution controlin diesel engine. Asian J. Exp. Sci. 19 (2),13–22.

De Gisi, S., Galasso, M., De Feo, G., 2013. Full-scale treatment ofwastewater from a biodiesel fuel production plant withalkali-catalyzed transesterification. Environ. Technol. 34 (7),861–870.

Demirbas, A., 2009. Biodiesel from waste cooking oil viabase-catalytic and supercritical methanol transesterification.Energy Convers. Manage. 50 (4), 923–927,http://dx.doi.org/10.1016/j.enconman.2008.12.023.

Demirbas, A., Demirbas, M.F., 2011. Importance of algae oil as asource of biodiesel. Energy Convers. Manage. 52 (1), 163–170,http://dx.doi.org/10.1016/j.enconman.2010.06.055.

Dugan, J., Biodiesel Magazine, 2007. A Dry Wash Approach toBiodiesel Purification, Retrieved from: http://biodieselmagazine.com/articles/1918/a-dry-wash-approach-to-biodiesel-purification/

El Diwani, G., Attia, N.K., Hawash, S.I., 2009. Development andevaluation of biodiesel fuel and by-products from jatropha oil.Int. J. Environ. Sci. Technol. 6 (2),219–224.

Emamjomeh, M.M., Sivakumar, M., 2009. Review of pollutantsremoved by electrocoagulation andelectrocoagulation/flotation processes. J. Environ. Manage. 90(5), 1663–1679,http://dx.doi.org/10.1016/j.jenvman.2008.12.011.

Enhancement and Conservation of the National Quality Act,1992. Water Quality Standards, Retrieved from:http://www.pcd.go.th/info serv/en reg std water04.html#s1

French, R., Czernik, S., 2010. Catalytic pyrolysis of biomass forbiofuels production. Fuel Process. Technol. 91 (1), 25–32,http://dx.doi.org/10.1016/j.fuproc.2009.08.011.

Gasim, H., Kutty, S.R.M., Isa, M.H., 2000. Biodegradability ofPetroleum Refinery Wastewater in Batch Reactor, PhD thesis,UTP.

Gomes, M.C.S., Arroyo, P.A., Pereira, N.C., 2013. Influence ofacidified water addition on the biodiesel and glycerolseparation through membrane technology. J. Membr. Sci. 431,28–36, http://dx.doi.org/10.1016/j.memsci.2012.12.036.

Hasswa, R., Dubé, M.A., Tremblay, A.Y., 2013. Distribution of soapin a membrane reactor in the production of fame from wastecooking oil. Can. J. Chem. Eng. 91 (3), 459–465,http://dx.doi.org/10.1002/cjce.21686.

Hayyan, A., Alam, Z., Mirghani, M.E.S., Kabbashi, N.A., Irma, N.,Mohd, N., Mohd, Y., 2010. Sludge palm oil as a renewable rawmaterial for biodiesel production by two-step processes.Bioresour. Technol. 101 (20), 7804–7811,http://dx.doi.org/10.1016/j.biortech.2010.05.045.

He, Y., Wang, X., Xu, J., Yan, J., Ge, Q., Gu, X., Jian, L., 2013.Application of integrated ozone biological aerated filters andmembrane filtration in water reuse of textile effluents.Bioresour. Technol. 133, 150–157,http://dx.doi.org/10.1016/j.biortech.2013.01.074.

Holenda, B., Domokos, E., Rédey, A., Fazakas, J., 2008. Dissolvedoxygen control of the activated sludge wastewater treatmentprocess using model predictive control. Comput. Chem. Eng.32, 1270–1278.

Hossain, A.B.M., Boyce, A.N., 2009. Biodiesel production fromwaste sunflower cooking oil as an environmental recyclingprocess and renewable energy. Bulg. J. Agric. Sci. 15 (4),312–317.

Huang, G.H., Chen, F., Wei, D., Zhang, X.W., Chen, G., 2010.Biodiesel production by microalgal biotechnology. Appl.Energy 87 (1), 38–46.

Ito, T., Sakurai, Y., Kakuta, Y., Sugano, M., Hirano, K., 2012.Biodiesel production from waste animal fats using pyrolysismethod. Fuel Process. Technol. 94 (1), 47–52,http://dx.doi.org/10.1016/j.fuproc.2011.10.004.

Janaun, J., Ellis, N., 2010. Perspectives on biodiesel as a

sustainable fuel. Renew. Sustain. Energy Rev. 14 (4), 1312–1320,http://dx.doi.org/10.1016/j.rser.2009.12.011.

Jaruwat, P., Kongjao, S., Hunsom, M., 2010. Management ofbiodiesel wastewater by the combined processes of chemicalrecovery and electrochemical treatment. Energy Convers.Manage. 51 (3), 531–537,http://dx.doi.org/10.1016/j.enconman.2009.10.018.

Jayed, M.H., Masjuki, H.H., Saidur, R., Kalam, M.A., Jahirul, M.I.,2009. Environmental aspects and challenges of oilseedproduced biodiesel in Southeast Asia. Renew. Sustain. EnergyRev. 13, 2452–2462, http://dx.doi.org/10.1016/j.rser.2009.06.023.

Jou, C.G., Huang, G.C., 2003. A pilot study for oil refinerywastewater treatment using a fixed film bioreactor. Adv.Environ. Res. 7, 463–469.

Kaercher, J.A., DeCassia, R., Schneider, D.S., Klamt, R.A.,Leonardo, W., Schmatz, W.L., Szarblewski, S., 2013.Optimization of biodiesel production for self-consumption:considering its environmental impacts. J. Clean. Prod. 46,74–82, http://dx.doi.org/10.1016/j.jclepro.2012.09.016.

Kapilakarn, K., Peugtong, A., 2007. A comparison of costs ofbiodiesel production from transesterification. Int. Energy J. 8,1–6.

Khaing, T.-H., Li, J., Li, Y., Wai, N., Wong, F., 2010. Feasibility studyon petrochemical wastewater treatment and reuse using anovel submerged membrane distillation bioreactor. Sep. Purif.Technol. 74 (1), 138–143,http://dx.doi.org/10.1016/j.seppur.2010.05.016.

Khan, S.A., Hussain, M.Z., Prasad, S., Banerjee, U.C., 2009.Prospects of biodiesel production from microalgae in India.Renew. Sustain. Energy Rev. 13, 2361–2372,http://dx.doi.org/10.1016/j.rser.2009.04.005.

Khan, Y.A., Yamsaengsung, R., 2011. Review of wastewatertreatment methods and MBR technology for application inbiodiesel plants. In: Conference Topic: Environmental andSafety Technology. TIChE International Conference, 10–11November 2011 at Hatyai, Songkhla, Thailand.

Kim, S., Yoon, J., Lee, S., 2009. Utilization of floc characteristics forthe evaluation of seawater coagulation process. Desalin.Water Treat. 10, 95–100.

Kinast, J.A., 2003. National Renewable Energy Laboratory 2003.Subcontractor Report: Production of Biodiesel from MultipleFeedstocks and Properties of Biodiesels and Biodiesel/DieselBlends.

Kolesárová, N., Hutnan, M., Bodík, I., Spalková, V., 2011.Utilization of biodiesel by-products for biogas production. J.Biomed. Biotechnol. 2011, 1–15,http://dx.doi.org/10.1155/2011/126798.

Krishna, A.R., Dev, L., Thankamani, V., 2012. An integratedprocess for industrial effluent treatment and biodieselproduction using microalgae. Res. Biotechnol. 3 (1),47–60.

Kumjadpai, S., Ngamlerdpokin, K., Chatanon, P.,Lertsathitphongs, P., Hunsom, M., 2011. Management of fattyacid methyl ester (fame) wastewater by a combined two stagechemical recovery and coagulation process. Can. J. Chem. Eng.89 (2), 369–376, http://dx.doi.org/10.1002/cjce.20429.

Leung, D.Y.C., Wu, X., Leung, M.K.H., 2010. A review on biodieselproduction using catalyzed transesterification. Appl. Energy87 (4), 1083–1095,http://dx.doi.org/10.1016/j.apenergy.2009.10.006.

Lim, S., Teong, L.K., 2010. Recent trends, opportunities andchallenges of biodiesel in Malaysia: an overview. Renew.Sustain. Energy Rev. 14, 938–954,http://dx.doi.org/10.1016/j.rser.2009.10.027.

Lin, L., Cunshan, Z., Vittayapadung, S., Xiangqian, S., Mingdong,D., 2011. Opportunities and challenges for biodiesel fuel. Appl.Energy 88 (4), 1020–1031.

Llop, A., Pocurull, E., Borrull, F., 2009. Evaluation of the removal ofpollutants from petrochemical wastewater using a membranebioreactor treatment plant. Water Air Soil Pollut. 197,349–359.

Lotero, E., Liu, Y., Lopez, D.E., Suwannakarn, K., Bruce, D.A.,Goodwin, J.G., 2005. Synthesis of biodiesel via acid catalysis.

Ind. Eng. Chem. Res. 44 (14), 5353–5363,http://dx.doi.org/10.1021/ie049157g.

Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 507

L

M

M

M

M

M

M

M

M

M

M

N

O

O

O

P

P

P

P

ow, S.C., Gan, G.K., Cheong, K.T., 2011. Separation of methylester from water in a wet neutralization process. J. Sustain.Energy Environ. 2, 15–19.

a, F., Hanna, M.A., 1999. Biodiesel production: a review.Bioresour. Technol. 70, 1–15.

agtibay, B.B., 2006. Philippines Regulations on Sanitation andWastewater System. Biosphere Environment and HealthSystem Series. B.B. Magtibay’s Publishing House, Philippines.

aha Lakshmi, P., Sivashanmugam, P., 2013. Treatment of oiltanning effluent by electrocoagulation: influence ofultrasound and hybrid electrode on COD removal. Sep. Purif.Technol. 116, 378–384,http://dx.doi.org/10.1016/j.seppur.2013.05.026.

alakahmad, A., Hasani, A., Eisakhani, M., Isa, M.H., 2011.Sequencing batch reactor (SBR) for the removal of Hg2+ andCd2+ from synthetic petrochemical factory wastewater. J.Hazard. Mater. 191 (1–3), 118–125,http://dx.doi.org/10.1016/j.jhazmat.2011.04.045.

argesin, R., Schinner, F., 2001. Biodegradation andbioremediation of hydrocarbons in extreme environments.Appl. Microbiol. Biotechnol. 56 (5–6), 650–663,http://dx.doi.org/10.1007/s002530100701.

ata, T.M., Martins, A.A., Caetano, N.S., 2010. Microalgae forbiodiesel production and other applications: a review. Renew.Sustain. Energy Rev. 14 (1), 217–232,http://dx.doi.org/10.1016/j.rser.2009.07.020.

ohamad, A.B., Abd Rahman, R., Hassan Kadhum, A.A., SheikhAbdullah, S.R., Wan Sudin, Z., Shaari, S., 2008. Removal ofadsorbable organic halides (AOX) from recycled pulp andpaper (P&P) mill effluent using granular activatedcarbon-sequencing batch biofilm reactor (GAC-SBBR). Mod.Appl. Sci. 2 (5), 37–45.

ohan, D., Pittman Jr., C.U., Steele, P.H., 2006. Pyrolysis ofwood/biomass for bi-oil: a critical review. Energy Fuel 20,848–889.

ondala, A., Liang, K., Toghiani, H., Hernandez, R., French, T.,2009. Biodiesel production by in situ transesterification ofmunicipal primary and secondary sludges. Bioresour.Technol. 100 (3), 1203–1210,http://dx.doi.org/10.1016/j.biortech.2008.08.020.

oser, B.R., 2009. Biodiesel production, properties andfeedstocks. In Vitro Cell. Dev. Biol. Plant 45,229–266.

gamlerdpokin, K., Kumjadpai, S., Chatanon, P., Tungmanee, U.,Chuenchuanchom, S., Jaruwat, P., Lertsathitphongs, P.,Hunsom, M., 2011. Remediation of biodiesel wastewater bychemical- and electro-coagulation: a comparative study. J.Environ. Manage. 92 (10), 2454–2460,http://dx.doi.org/10.1016/j.jenvman.2011.05.006.

rchard, B., Denis, J., Cousins, J., 2007. Developments in biofuelprocessing technologies. World Pumps 2007 (487), 24–28.

kullo, A., Temu, A.K., Ogwok, P., Ntalikwa, J.W., 2012.Physico-chemical properties of biodiesel from jatropha andcastor oil. Int. J. Renew. Energy Res. 2 (1), 47–52.

ng, H.C., Mahlia, T.M.I., Masjuki, H.H., Honnery, D., 2012. Lifecycle cost and sensitivity analysis of palm biodieselproduction. Fuel 98, 131–139.

armar, K.A., Prajapati, S., Patel, R., Dabhi, Y., 2011. Effective useof ferrous sulfate and alum as a coagulant in treatment ofdairy industry wastewater. J. Eng. Appl. Sci. 6 (9), 42–45.

atel, H., Madamwar, D., 2002. Effects of temperatures andorganic loading rates on biomethanation of acidicpetrochemical wastewater using an anaerobic upflowfixed-film reactor. Bioresour. Technol. 82 (1), 65–71,http://dx.doi.org/10.1016/S0960-8524(01)00142-0.

itakpoolsil, W., Hunsom, M., 2013. Adsorption of pollutants frombiodiesel wastewater using chitosan flakes. J. Taiwan Inst.Chem. Eng. 44 (6), 963–971,http://dx.doi.org/10.1016/j.jtice.2013.02.009.

imentel, D., Patzek, T.W., 2005. Ethanol production using corn,switchgrass, and wood; biodiesel production using soybean

and sunflower. Nat. Resour. Res. 14 (1), 65–76,http://dx.doi.org/10.1007/s11053-005-4679-8.

Pleanjai, S., Gheewala, S.H., Garivait, S., 2007. Environmentalevaluation of biodiesel production from palm oil in a life cycleperspective. Asian J. Energy Environ. 8 (1), 15–32.

Pramanik, B.K., Suja, F., Shahrom, Z., Ahmed, E., 2012. Biologicalaerated filters (BAFs) for carbon and nitrogen removal: areview. J. Eng. Sci. Technol. 7 (4), 428–446.

Rahman, M., Al-Malack, M., 2006. Performance of a cross-flowmembrane bioreactor (CF-MBR) when treating refinery.Desalination 191, 16–26.

Raja, S.A., Robinson, D.S., Lee, C.L.R., 2011. Biodiesel productionfrom jatropha oil and its characterization. Res. J. Chem. Sci. 1(1), 81–87.

Rajasimman, M., Karthikeyan, C., 2007. Aerobic digestion ofstarch wastewater in a fluidized bed bioreactor with lowdensity biomass support. J. Hazard. Mater. 143, 82–86.

Ramadhas, A., Jayaraj, S., Muraleedharan, C., 2005. Biodieselproduction from high FFA rubber seed oil. Fuel 84 (4), 335–340,http://dx.doi.org/10.1016/j.fuel.2004.09.016.

Ramírez, X.M.V., Mejía, G.M.H., López, K.V.P., Vásquez, G.R.,Sepúlveda, J.M.M., 2012. Wastewater treatment from biodieselproduction via a coupled photo-Fenton – aerobic sequentialbatch reactor (SBR) system. Water Sci. Technol. 66 (4), 824–830,http://dx.doi.org/10.2166/wst.2012.250.

Rattanapan, C., Sawain, A., Suksaroj, T., Suksaroj, C., 2011.Enhanced efficiency of dissolved air flotation for biodieselwastewater treatment by acidification and coagulationprocesses. Desalination 280 (1–3), 370–377,http://dx.doi.org/10.1016/j.desal.2011.07.018.

Rawat, I., Ranjith Kumar, R., Mutanda, T., Bux, F., 2013. Biodieselfrom microalgae: a critical evaluation from laboratory to largescale production. Appl. Energy 103, 444–467,http://dx.doi.org/10.1016/j.apenergy.2012.10.004.

Romero, J.A.P., Cardoso Junior, F.S.S., Figueiredoa, R.T., Silvaa, D.P.,Cavalcantia, E.B., 2013. Treatment of biodiesel wastewater bycombined electroflotation and electrooxidation processes.Sep. Sci. Technol. 48, 2073–2079.

Ruengkong, J., Krimpikun, S., Toonguri, C., Boonsawang, P., 2008.Biogas production from wastewater of biodiesel process. In:7th National Environmental Conference, Bangkok, Thailand.

Sanford, S.D., White, J.M., Shah, P.S., Wee, C., Valverde, M.A.,Meier, G.R., 2009. Feedstock and Biodiesel CharacteristicsReport. Renewable Energy Group, Inc, Retrieved from:www.regfuel.com

Saraswathi, R., Saseetharan, M.K., 2012. Simultaneousoptimization of multiple performance characteristics incoagulation–flocculation process for Indian paper industrywastewater. Water Sci. Technol. 66 (6), 1231–1238,http://dx.doi.org/10.2166/wst.2012.304.

Scholz, W., Fuchs, W., 2000. Treatment of oil contaminatedwastewater in a membrane bioreactor. Water Res. 34,3621–3629.

Sharma, Y.C., Singh, B., Upadhyay, S.N., 2008. Advancements indevelopment and characterization of biodiesel: a review. Fuel87, 2355–2373.

Shokrollahzadeh, S., Azizmohseni, F., Golmohammad, F.,Shokouhi, H., Khademhaghighat, F., 2008. Biodegradationpotential and bacterial diversity of a petrochemicalwastewater treatment plant in Iran. Bioresour. Technol. 99(14), 6127–6133,http://dx.doi.org/10.1016/j.biortech.2007.12.034.

Siddiquee, M.N., Rohani, S., 2011. Lipid extraction and biodieselproduction from municipal sewage sludges: a review. Renew.Sustain. Energy Rev. 15 (2), 1067–1072,http://dx.doi.org/10.1016/j.rser.2010.11.029.

Siles, J.A., Martín, M.A., Chica, A.F., Martín, A., 2010. Anaerobicco-digestion of glycerol and wastewater derived frombiodiesel manufacturing. Bioresour. Technol. 101 (16),6315–6321, http://dx.doi.org/10.1016/j.biortech.2010.03.042.

Siles, J.A., Gutiérrez, M.C., Martín, M.A., Martín, A., 2011.Physical–chemical and biomethanization treatments ofwastewater from biodiesel manufacturing. Bioresour. Technol.

102 (10), 6348–6351,http://dx.doi.org/10.1016/j.biortech.2011.02.106.

508 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508

immobilized microorganisms. Process Biochem. 41,1475–1483.

Singh, S.P., Singh, D., 2010. Biodiesel production through the useof different sources and characterization of oils and theiresters as the substitute of diesel: a review. Renew. Sustain.Energy Rev. 14 (1), 200–216,http://dx.doi.org/10.1016/j.rser.2009.07.017.

Sivasamy, A., Cheah, K.Y., Fornasiero, P., Kemausuor, F., Zinoviev,S., Miertus, S., 2009. Catalytic applications in the productionof biodiesel from vegetable oils. ChemSusChem 2 (4), 278–300,http://dx.doi.org/10.1002/cssc.200800253.

Sponza, D.T., Gök, O., 2010. Effect of rhamnolipid on the aerobicremoval of polyaromatic hydrocarbons (PAHs) and CODcomponents from petrochemical wastewater. Bioresour.Technol. 101 (3), 914–924,http://dx.doi.org/10.1016/j.biortech.2009.09.022.

Srirangsan, A., Ongwandee, M., Chavalparit, O., 2009. Treatmentof biodiesel wastewater by electrocoagulation process.Environ. Asia 2, 15–19.

Su, D., Wang, J., Liu, K., Zhou, D., 2007. Kinetic performance ofoil-field produced water treatment by biological aerated filter.Chin. J. Chem. Eng. 15 (4), 591–594.

Suehara, K., Kawamoto, Y., Fujii, E., Kohda, J., Nakano, Y., Yano, T.,2005. Biological treatment of wastewater discharged frombiodiesel fuel production plant with alkali-catalyzedtransesterification. J. Biosci. Bioeng. 100 (4), 437–442,http://dx.doi.org/10.1263/jbb.100.437.

Suehara, K., Owari, K., Kohda, J., Nakano, Y., Yano, T., 2007. Rapidand simple determination of oil and urea concentrations andsolids content to monitor biodegradation conditions ofwastewater discharged from a biodiesel fuel production plant.J. Near Infrared Spectrosc. 15 (2), 89,http://dx.doi.org/10.1255/jnirs.721.

Sukkasem, C., Laehlah, S., Hniman, A., Sompong, O.,Boonsawang, P., 2011. Upflow bio-filter circuit (UBFC):biocatalyst microbial fuel cell (MFC) configuration andapplication to biodiesel wastewater treatment. Bioresour.Technol. 102 (22), 10363–10370,http://dx.doi.org/10.1016/j.biortech.2011.09.007.

Takashi, O., 2009. Challenge of Climate Protection and BDF fromused Cooking Oil in the City of Kyoto, Japan, Retrieved from:http://www.iclei.org/documents/Japan/O. Takashi.pdf

Talebian-Kiakalaieh, A., Amin, N.A.S., Mazaheri, H., 2013. Areview on novel processes of biodiesel production from wastecooking oil. Appl. Energy 104, 683–710,http://dx.doi.org/10.1016/j.apenergy.2012.11.061.

Tang, D.T.C., 1993. Water Pollution Control Act. (1993). TheEnvironmental Laws and Policies of Taiwan: A ComparativeLaw Perspective. Pacific Rim Law & Policy Association.

Tezcan, U.U., Koparal, A.S., Bakir Ogutveren, U., 2009.Electrocoagulation of vegetable oil refinery wastewater usingaluminum electrodes. J. Environ. Manage. 90 (1), 428–433,http://dx.doi.org/10.1016/j.jenvman.2007.11.007.

Thaveesri, J., 2003. Expert Meeting on Definitions andDimensions of Environmental Goods and Services in Tradeand Development. Geneva, 9–11 July 2003.

Tomic, M.D., Savin, L.Dj., Micic, R.D., Simikic, M.Dj., Furman, T.F.,2013. Effects of fossil diesel and biodiesel blends on theperformances and emissions of agricultural tractor engines.Therm. Sci. 17 (1), 263–278.

Tri, P., (thesis) 2002. Oily Wastewater Treatment by Membrane

Bioreactor Process Coupled with Biological Activated CarbonProcess. AIT, Bangkok, Thailand.

Vasudevan, P.T., Briggs, M., 2008. Biodiesel production-currentstate of the art and challenges. J. Ind. Microbiol. Biotechnol. 35(5), 421–430.

Vivek, Gupta, A., 2004. Biodiesel production from Karanja oil. J.Sci. Ind. Res. 63, 39–47.

Veljkovic, V.B., Stamenkovic, O.S., Tasic, M.B., 2012. WastewaterManagement in Biodiesel Production. Reporting forSustainability., pp. 471–475.

Veljkovic, V.B., Stamenkovic, O.S., Tasic, M.B., 2014. Thewastewater treatment in the biodiesel production withalkali-catalyzed transesterification. Renew. Sustain. EnergyRev. 32, 40–60, http://dx.doi.org/10.1016/j.rser.2014.01.007.

Vyas, A.P., Verma, J.L., Surahmanyam, N., 2010. A review on FAMEproduction processes. Fuel 89, 1–9.

Wan Omar, W.N.N., Amin, N.A.S., 2011. Biodiesel production fromwaste cooking oil over alkaline modified zirconia catalyst.Fuel Process. Technol. 92 (12), 2397–2405,http://dx.doi.org/10.1016/j.fuproc.2011.08.009.

Wang, X., Han, J., Chen, Z., Jian, L., Gu, X., Lin, C., 2012. Combinedprocesses of two-stage Fenton-biological anaerobic filter –biological aerated filter for advanced treatment of landfillleachate. Waste Manage. 32 (12), 2401–2405,http://dx.doi.org/10.1016/j.wasman.2012.06.022.

Wei, C.Y., Huang, T.C., Chen, H.H., 2013. Biodiesel productionusing supercritical methanol with carbon dioxide and aceticacid. J. Chem. 2013, 1–6, http://dx.doi.org/10.1155/2013/789594.

Wirawan, S.S., Tambunan, A.H., Djamin, M., Nabetani, H., 2008.The effect of palm biodiesel fuel on the performance andemission of the automotive diesel engine. Agric. Eng. Int.:CIGR Ejournal, Manuscript EE 07 005.

Wu, Y., Zhou, S., Ye, X., Chen, D., Zheng, K., Qin, F., 2011.Transformation of pollutants in landfill leachate treated by acombined sequence batch reactor, coagulation, Fentonoxidation and biological aerated filter technology. Process Saf.Environ. Prot. 89, 112–120.

Xie, Q., Taweepreda, W., Musikavong, C., Suksaroj, C., 2011.Separation of oily sludge and glycerol from biodieselprocessing waste by coagulation. Songklanakarin J. Sci.Technol. 33 (6), 699–703.

Yaakob, Z., Sukarman, I.S., Narayanan, B., Sheikh Abdullah, S.R.,2012. Utilization of palm empty fruit bunch for the productionof biodiesel from Jatropha curcas oil. Bioresour. Technol. 104,695–700, http://dx.doi.org/10.1016/j.biortech.2011.10.058.

Yaakob, Z., Mohammad, M., Alherbawi, M., Alam, Z., Sopian, K.,2013. Overview of the production of biodiesel from Wastecooking oil. Renew. Sustain. Energy Rev. 18, 184–193,http://dx.doi.org/10.1016/j.rser.2012.10.016.

Zhang, M.H., Zhao, Q.L., Bai, X., Ye, Z.F., 2010. Adsorption oforganic pollutants from coking wastewater by activated coke.Physico. Chem. Eng. Asp. 62, 140–146.

Zhou, Y., Liang, Z., Wang, Y., 2008. Decolorization and CODremoval of secondary yeast wastewater effluents bycoagulation using aluminium sulfate. Desalination 225,301–311.

Zhao, X., Wang, Y., Ye, Z., Borthwick, A.G.L., Ni, J., 2006. Oil fieldwastewater treatment in biological aerated filter by