Production of biodiesel and its wastewater treatment technologies: A review

Accepted Manuscript Title: Production of biodiesel and its wastewater treatment technologies: A review Author: Nurull Muna Daud Siti Rozaimah Sheikh Abdullah Hassimi Abu Hasan Zahira Yaakob PII: DOI: Reference:

S0957-5820(14)00171-2 http://dx.doi.org/doi:10.1016/j.psep.2014.10.009 PSEP 493

To appear in:

Process Safety and Environment Protection

Received date: Revised date: Accepted date:

23-6-2014 9-10-2014 19-10-2014

Please cite this article as: Daud, N.M., Abdullah, S.R.S., Hasan, H.A., Yaakob, Z.,Production of biodiesel and its wastewater treatment technologies: A review, Process Safety and Environment Protection (2014), http://dx.doi.org/10.1016/j.psep.2014.10.009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Highlights  Biodiesel is one of the promising alternative energy resources.  Biodiesel production generates highly polluted wastewater.  Biodiesel wastewater treatments developed so far have their own novelty and weaknesses.  Coagulation-BAF processes seem feasible for biodiesel wastewater treatment.

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Title: Production of biodiesel and its wastewater treatment technologies: A review Authors: Nurull Muna Daud, Siti Rozaimah Sheikh Abdullah, Hassimi Abu Hasan, ZahiraYaakob Institute/University: Department of Chemical and Process Engineering, Faculty of Engineering and Built

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Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia Email addresses: [email protected], [email protected]. Phone: +603-89216407; Fax:

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+603-89216148

Acknowledgements: This work was supported by the Faculty of Engineering and Built Environment,

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Universiti Kebangsaan Malaysia under grant number INDUSTRI-2012-029.

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Production of biodiesel and its wastewater treatment technologies: A review Nurull Muna Daud, Siti Rozaimah Sheikh Abdullah, Hassimi Abu Hasan, Zahira Yaakob

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Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia Corresponding author: Email addresses: [email protected], [email protected] Phone: +603-89216407; Fax: +603-89216148

Abstract

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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 pretreatment of biodiesel wastewater using coagulation followed by the treatment using BAF.

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Introduction

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Keywords: Biodiesel, transesterification, biodiesel wastewater, biodiesel wastewater treatment.

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Vegetable oil based biodiesel was introduced and investigated in the 1890s, when Rudolph Diesel invented diesel engines to be used for machines in the agricultural sector (Orchad et al., 2007). In 1920, the availability of low cost petroleum fuel had decreased the demand for biodiesel, leading to the modification of diesel engines to match the properties of petroleum diesel fuel. Oil crises in the 1970s renewed interest in vegetable oils and gave an advantage to their market (Talebian-Kiakalaieh et al., 2013). However, the usage of traditional vegetable oils in modern diesel engines was not favourable. The investigation of methods to produce low viscosity vegetable oils spread and a variety of methods were introduced such as transesterification, pyrolysis, and blending of solvents. The first patent for an industrial process for biodiesel production was filed in 1977 by a Brazilian scientist, Expedito Parente (Lim & Teong, 2010). In 1979, South Africa initiated research into the production of biodiesel using sunflower oil (Lin et al., 2011). Starting from 1980, the biodiesel revolution has been quite positive. A small pilot plant was built in Austria in 1985, and in 1987 a biodiesel production plant based on microalgae was operated in New Mexico. The commercialization of biodiesel using a variety of feedstock such as rapeseed and used cooking oil was boosted in the 1990s and up until now. Biodiesel is not only beneficial for transportation, it is also being used in manufacturing, construction machinery and generators for firing boilers purpose as depicted in Figure 1 (Abdullah et al., 2009).

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Development of biodiesel production

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Figure 1. Usage of biodiesel

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The idea of using biodiesel fuel arose when the world started to find and develop alternative energy resources, influenced by the depletion of non-renewable energy sources (Berchmans & Hirata, 2008). High dependence on petroleum fuels or fossil fuels has led to uncertainty in price and supply (Raja et al., 2011). Some alternative sources which are able to replace fossil fuels are water, solar, and wind energy and biofuels (Abbaszaadeh et al., 2012). The increasing demand for biodiesel is also due to awareness of the environmental impact of emissions from conventional fossil fuels combustion and the decline in domestic oil production (Mondala et al., 2009). The production of biodiesel in several Asian countries is shown in Table 1. The production capacity of each country is based on annual reports for the years 2011 and 2012. Among Asian countries, production of biodiesel is mainly dominated by Indonesia and Thailand, which produce more than two billion litres every year and are also known as the main producers of biodiesel in Southeast Asia.

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Table 1. Biodiesel production in several Asian countries (Source: www.thecropsite.com) Production capacity Country Main feedstock Production year (billion litres/year) Malaysia Palm oil 0.147 2011 Indonesia Palm oil 2.200 2012 Thailand Palm oil 2.080 2011 Philippines Coconut oil 0.138 2012 India Jatropha 0.140–0.300 2011 China Waste cooking oil 0.568 2012

Commercially, biodiesel is produced through a transesterification process in the presence of alcohol and catalyst. This process involves the conversion of triglycerides (oil) to methyl ester (biodiesel) and by-product (glycerol) (Kolesárová et al., 2007; Chavalparit & Ongwandee, 2009; Low et al., 2011) as described by Equation (1).

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3CH3OH

O || CH3-O-C-R2

+

O || CH3-O-C-R3 (Methanol)

(Mixture of fatty esters)

CH2-OH | CH-OH | CH2-OH

Equation (1)

(Glycerol)

Properties of biodiesel as transportation fuel

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+

(Catalyst) →

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(Triglycerides)

O || CH3-O-C-R1

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O || CH2-O-C-R1 | | O | || CH-O-C-R2 | | O | || CH2-O-C-R3

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Biodiesel fuel is used as a substitute for petroleum, which traditionally has been used to produce transportation fuel (Chavalparit & Ongwandee, 2009; El Diwani et al., 2009) and considered as the best candidate compared to all other energy sources (Leung et al., 2010). For use as transportation fuel, biodiesel is blended and named as B5, B10, B20, or B100, where 5, 10, 20, and 100 represent the percentage of biodiesel in the petroleum diesel (Janaun & Ellis, 2010). Biodiesel is a methyl ester mixture with long-chain fatty acids (Leung et al., 2010). It is made from a variety of sources of vegetables oil, animal fats, and waste cooking oil (Kolesárová et al., 2011; Raja et al., 2011). Reportedly, Thailand has claimed that biodiesel is one of the most promising alternative fuels to the diesel fuel used in that country (Pleanjai et al., 2007). In Malaysia, the implementation of the B10 biofuel programme has had a positive impact on Malaysia’s biodiesel market (Adnan, 2013).

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For biodiesel products to be used as transportation fuel, the fuel grade should fulfil the standard requirements. Two of the international standards are tabulated in Table 2. There are many studies conducted to produce biodiesel from various kind of feedstock. Each was analysed according to the standard to ensure the compability of biodiesel to petroleum diesel to be used as transportation fuel. The studies on biodiesel production are summarized in Table 3, while the methyl ester yields for each study are illustrated in Figure 2. The use of renewable feedstock as biodiesel production sources has made this fuel to be known as a clean renewable fuel that is biodegradable and environmentally friendly (Leung et al., 2010; Kaercher et al., 2013). These characteristics also provide this liquid fuel with advantage of lowering the production of exhaust emissions from diesel engines (Hayyan et al., 2010) such as particulate matter (PM) (Kolesárová et al., 2011), unburned hydrocarbons (HC) and carbon monoxide (CO) except for nitrogen oxides (NOx) (Bouaid et al., 2012). The emission of nitrogen oxides usually increases due to the oxygen content in the biodiesel (Sharma et al., 2008). Table 4 shows the emissions percentage from different studies regarding this matter. The percentages were compared to 100% of exhaust emissions from petroleum diesel engines. The variations in each study usually rely on the feedstock properties as well as oxygen content and viscosity of the methyl esters.

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Table 2. Different standard specification for biodiesel fuel (Abdullah et al. 2009) Limits 120 min 0.05 max 3.5–5.0 0.02 max 0.001 max 1a 51 min 0.3 max 0.50 max 0.02 max 0.25 max 10 max –

130 min 0.05 max 1.9–6.0 0.020 max 0.0015 max 3a max 47 min 0.50 max 0.80 max 0.02 max 0.24 max 10 max 360 max

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°C mg/kg mm2/s % (m/m) % (m/m) Rating – % (m/m) mg KOH/g % (m/m) % (m/m) mg/kg °C

ASTM D6751

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Flash point, close cup Water content Kinematic viscosity, 40 °C Sulphated ash Sulphur content Copper corrosion strip (3h at 50°C) Cetane index Carbon residue Acid number Free glycerol Total glycerol Phosphorus content Distillation temperature (90% recovered)

EN14214

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Property

Pour point (˚C) –

Palm oil

–

–

4.91

878

179

14

5

Transesterification

Castor oil

61.0

–

10.75

–

160

–13

–

Transesterification

Jatropha oil Jatropha oil Sunflower oil Jatropha oil Waste cooking oil

76.0

–

5.25

–

166

–6

–

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Transesterification in supercritical methanol Transesterification

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Table 3. Biodiesel properties from different feedstocks Feedstock Yield Purity Viscosity Density Flash Cloud (kg/m3) point point (%) (%) (mm2/s) (˚C) (˚C) Soybean 97.8 – – – – – oil

Process

Base catalysed transesterification Transesterification

Base catalysed transesterification Base-catalytic and non-catalytic supercritical methanol transesterification Acidcatalysedtransester ification Transesterification

Municipal sewage sludge Waste sunflower cooking oil

–

–

4.82

–

128

8

–2

–

–

4.72

860

183

4

–5

5.20

–

162

0

–6

98

References

Wei et al. (2013) Atadashi et al. (2012) Okullo et al. (2012) Okullo et al. (2012) Raja et al. (2011) Ahmad et al. (2010) El Diwani et al. (2009) Demirbas (2009)

87

99.6

5.30

897

196

–

–11

14.5

–

–

–

–

–

–

Mondala et al. (2009)

99.5

–

9.50

–

–

–

–

Hossain and Boyce (2009)

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52 90 67 50 60 87 56

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B100 B100 B100 B100 B100 B100 B100

Table 4. Percentage of exhaust emission from biodiesel engines References Hydrocarbon Nitric Sulfur Particulate Polycyclic oxide dioxide matter aromatic hydrocarbons 33 110 53 Lotero et al. (2005) 90 115 67 Chincholkar et al. (2005) 23 75 0 33 Wirawan et al. (2008) 113 0 70 20 Khan et al. (2009) 50 105 0 35 Bouaid et al. (2012) Tomić et al. (2013) 111 32 0 60 25 Talebian-Kiakalaieh et al. (2013)

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Carbon monoxide

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Fuel type

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Figure 2. Methyl ester yields for different study

Other advantages from biodiesel usage are the use of agricultural surplus and reduce the dependencies on crude oil (Abdullah et al., 2009). As stated by Mondala et al. (2009), the properties of biodiesel with a flash point above 93.3°C make it safer and easier to use, handle, and store. Another reason that makes biodiesel comparable to petroleum diesel is the high-energy content or also known as heating value. Referring to Table 5, the energy content of biodiesel produced in several studies have similar or close value to the energy content of petroleum diesel which makes biodiesel comparable and suitable 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 strip corrosion

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Table 5. Energy content of biodiesel fuel

Transesterification Base-catalytic and supercritical methanol transesterification -

References Talebian-Kiakalaieh et al. (2013) Vivek and Gupta (2004) Talebian-Kiakalaieh et al. (2013) Demirbas (2009)

21.1

Demirbas and Demirbas (2011)

-

25.1

Demirbas and Demirbas (2011)

Transesterification Transesterification Transesterification -

42.15 30.4 39.76 36.5 41

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Petroleum diesel Karanja oil biodiesel Tallow WCO biodiesel

Okullo et al. (2012) Okullo et al. (2012) Raja et al.(2011) Ramadhas et al. (2005) Rawat et al. (2013)

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Algae (Cladophora fracta) biodiesel Microalgae (Chorella protothecoides) biodiesel Jatropha oil biodiesel Castor oil biodiesel Jatropha oil biodiesel Rubber seed oil biodiesel Microalgal

Energy content (MJ/kg) 45.00 39.66 40.05 42.65

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Production process

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Type of fuel

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The positive impact in environmental aspect may be the main reason why biodiesel starts to gain interest to be used as transportation fuel. However, the high price of biodiesel fuel compared to petroleum fuel has limited the development of this renewable fuel development (Hayyan et al., 2010). The high production cost due to the high feedstock cost limits the commercialization of biodiesel (Hasswa et al., 2013). Another limitation to the development of biodiesel is the usage of edible vegetable oil. It arises the problem of food supply competition, which can cause food crises, deforestation, and challenges in oil supply management to ensure the oil supply is well managed for food consumption and consumer products (Leung et al., 2010; Talebian-Kiakalaieh et al., 2013). Despite all these limitations, biodiesel industry should find ways to overcome these challenges. In addition, since the increasing 53% of world energy demand by the year 2030 (Talebian-Kiakalaieh et al., 2013) while the non-renewable energy; fossil fuel depletes, government should really look forward to ensure that biodiesel can fulfil the energy required by our society. 3.

Biodiesel production

3.1

Source of raw materials/feedstock

Traditionally, the main source of biodiesel is vegetable oil. The types of vegetable oils available depend on the climate and soil conditions of the country (Siddiquee & Rohani, 2011). In Thailand, over 90% of biodiesel production is from palm oil as raw material (Rattanapan et al., 2011). The most widely used biodiesel feedstock in the United States is soybean oil (Mondala et al., 2009). Biodiesel feedstock can be categorized into three types: edible oils, non-edible oils, and reusable sources or wastes, as summarized in Table 6. Some researchers are interested in biodiesel production using oil from non-edible crops, due to environmental issues. For instance, non-edible crops can be grown on waste lands (Leung et al. 2010). Besides, the production of biodiesel using these types of feedstock helps governments to find suitable ways to treat, recycle, and dispose of wastes (Suehara et al., 2005; Janaun & Ellis, 2010). Yaakob et al. (2013) emphasized that waste cooking oil usage can reduce water pollution and also prevent blockages in water drainage systems.

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Table 6. Different feedstocks for biodiesel production Edible feedstocks Non-edible feedstocks Others Soybean Jatropha curcas Waste cooking oil Palm oil Pongamia pinnata Algal Rapeseed Sea mango Municipal sewage sludge Canola Tallow Sunflower Poultry Cottonseed Nile tilapia Peanut Castor Corn Rubber seed Olive Coconut oil Butter Pumpkin Linseed

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Free fatty acids (FFAs) and/or triglycerides are an important component of feedstock to be converted to biodiesel (Janaun & Ellis, 2010). All fatty acids sources are favourable for use in biodiesel production (Talebian-Kiakalaieh et al. 2013). Kinast (2003) classified biodiesel feedstock based on their FFAs as illustrated in Figure 3. Types of refined oil feedstock which contain FFAs<1.5% are, for example, soybean, canola, and palm oil. Used cooking oil, tallow, and poultry fat are types of feedstock categorized as group II, having FFA contents below 4%. Waste grease usually falls into group III. However, excess FFA content in feedstock might affect biodiesel production. For instance, Moser (2009) stated that a content of FFA>3wt% will lead to soap formation due to the reaction between the FFA and the catalyst. Consequently, stable emulsion will form, preventing the separation of biodiesel from glycerine and consequently reducing the final yield (Canakci & Gerpen, 2001). For FFA>2.5wt%, a pretreatment process is usually required before further processing is carried out (Leung et al., 2010; Talebian-Kiakalaieh et al., 2013). Based on these studies, biodiesel producers using any type of feedstock with FFA content above 2.5wt% need to handle problems of those mentioned.

Group I Refined oils (FFA <1.5%)

Biodiesel feedstock

Group II Low free fatty acid yellow greases and animal fats (FFA <4%)

Group III High free fatty acid greases and animal fats (FFA ≥20%)

Figure 3. Classification of biodiesel feedstock

In Malaysia, a widely used biodiesel feedstock is palm oil (Siddiquee & Rohani, 2011). Palm oil has dominated the biodiesel production industry because of its availability and versatile application and because it is easily found (Janaun & Ellis, 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

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conducted for certain types of feedstock, and the oil content of each feedstock is illustrated in Figure 4. Based on their studies, babassu oil is extracted from seeds of the babassu palm tree (Attalea speciosa), which have high oil content; however only a few biodiesel studies using babassu oil have been reported compared to common types of sources, that is, palm oil, jatropha oil, and so on. Meanwhile the coffee seed has the lowest oil content. One of the reasons why there is an increment in the number of researches on finding alternatives for biodiesel feedstock is the high cost of pure vegetables (edible crops) and seed oils, which constitutes about 70 to 85% of the overall biodiesel production cost (Mondala et al., 2009; Siddiquee & Rohani, 2011; Abbaszaadeh et al., 2012). Using reusable sources as biodiesel feedstock, biodiesel production costs can be reduced by 60 to 90% since the price of waste edible oils is 2.5 to 3.0 times cheaper than that of vegetable oils (Talebian-Kiakalaieh et al., 2013).

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Choosing the right feedstock is very important to ensure it does not increase the production cost (Leung et al., 2010). Even if the production cost can be reduced, the production of biodiesel using nonedible oils may sometimes require multiple chemical steps due to the high FFA contents (Leung et al., 2010). For instance, Janaun and Ellis (2010) carried out methyl ester production, with a series of processes: one-step alkaline-based catalysed transesterification and two-step acid-based catalysed transesterification.

Figure 4. Seed oil yield depending on different feedstock

One of the promising non-edible sources for biodiesel feedstock is Jatropha curcas Linnaeus seed oil. Usage of jatropha oil as the primary feedstock for producing biodiesel is one way of reducing the production cost (Berchmans & Hirata, 2008). The high dependence on imports of petroleum and abundance of this non-edible source in India led researchers to investigate the ability of jatropha oil to produce biodiesel with similar properties or closer to those of diesel oil (Raja et al., 2011). It is also easy to be found and grew, even on gravely, sandy and saline soils (Bouaid et al., 2012). The source of oil in the Jatropha curcas plant is primarily its seeds, with an oil content of 25–30%. One of the interesting ideas for achieving low cost biodiesel production is the usage of low cost feedstock such as waste cooking oil (WCO) (Demirbas, 2009). Usage of WCO is quite beneficial since it can prevent the WCO from being discharged into the drainage system (Yaakob et al., 2013). In Kyoto, the usage of biodiesel from WCO collected from restaurants, cafeterias, and households to be used as public

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transport fuel has been implemented (Takashi, 2009). However, the quality of the biodiesel produced may vary since the physical and chemical properties of WCO depend on the fresh cooking oil 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 amounts of FFAs in the feedstock may also reduce the biodiesel quality (Demirbas, 2009). It is also lead to the need of pre-treatment of WCO before further production process take place (Yaakob et al., 2013). Janaun and Ellis (2010) stated that some major problems of using this type of feedstock are the infrastructure and logistics needed to collect the waste oil.

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The usage of algae as biodiesel feedstock is said to give a high yield of methyl ester (Janaun & Ellis, 2010). In a review by Krishna et al. (2012), the production of biodiesel using microalgae with low cost operation and easy handling was reported. The overall idea of their studies was to investigate the extraction of biodiesel from the harvested algae collected from wastewater treatment ponds called High Rate Algal Ponds (HRAPs), which were set up near the industrial areas. They claimed that the system of HRAPs coupled with biodiesel production was efficient for wastewater management, simple and cost effective in producing biodiesel. However, Janaun and Ellis (2010) stated that for commercialization of algae-based biodiesel, it may result in a high production cost. For instance, this method requires effective large scale bioreactors and an algae strain that can produce a high oil yield (Vasudevan & Briggs, 2008).

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A recent study done by Siddiquee and Rohani (2011) showed the ability of municipal sewage sludge as biodiesel feedstock. The lipid was extracted from the sewage sludge before being subjected to the process of biodiesel production and the process is known as a lipid extraction process. Study of Mondala et al. (2009) showed that, the production of sludge biodiesel using in situ transesterification managed to produce low cost biodiesel. The cost was compared to petroleum diesel (USD 4.80/gallon) and soy biodiesel (USD 4.50/gallon) while the cost estimated for their sludge biodiesel only around $4.00/gallon. However, commercialization of the usage of sewage sludge as biodiesel feedstock has some large challenges, such as the pre-treatment process of raw sludge, the lipid extraction process, biodiesel production methods from solid sludge, biodiesel quality, and process economics and safety. In producing biodiesel, cost of overall production usually involves the cost of feedstock, cost of processing the raw material; purification of raw material and oil pressing, cost of transesterification, cost of electricity, transportation and working capital (Pimentel & Patzek, 2005; Sharma et al. 2008). Siddiquee and Rohani (2011) classified the factors that affects the production cost into two major factors; the cost of raw materials and the operating costs. However, Kapilakarn and Peugtong (2007) stated that almost 80% of biodiesel production cost was contributed by the cost of feedstock. Their study on palm oil biodiesel production at different reaction process conditions showed that for palm oil biodiesel production, the cost was contributed by three major factors that were the cost of palm oil (80%), methanol (15%) and energy (5%). Based on several studies done by Mondala et al. (2009), Demirbas (2009) and Talebian-Kiakalaieh et al. (2013), the production cost of biodiesel depending on the feedstock used can be classified as depicted in Figure 5 while Table 7 shows the cost of producing biodiesel from different feedstock based on previous studies.

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Moderate-cost production’s feedstock  Vegetable oil

High-cost production’s feedstock  unflower oil  oybean oil 

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Low-cost production’s feedstock  unicipal sludge  Figure 5. Classification of biodiesel production cost based on different feedstock

Biodiesel production process

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Table 7. Cost of producing biodiesel from different feedstock using transesterification process Feedstock Biodiesel production cost (USD per gallon) References Municipal sludge oil USD 3.11 per gallon Siddiquee and Rohani (2011) Soybean oil USD 4.00-4.50 per gallon Siddiquee and Rohani (2011) Animal fats USD 1.59 per gallon* Sivasamy et al. (2009) Rapeseed oil USD 6.51 per gallon* Sivasamy et al. (2009) Palm oil USD 1.26 per gallon* Ong et al. (2012) Rapeseed oil USD 10.64 per gallon* Ong et al. (2012) Castor oil USD 4.04 per gallon* Ong et al. (2012) Soybean oil USD 1.70 per gallon* Ong et al. (2012) Waste cooking oil USD 1.56 per gallon* Ong et al. (2012) * Calculated production costs after unit conversion

3.2.1

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Biodiesel can be produced by four primary techniques: direct use and raw oils blending, micro-emulsions, transesterification, and pyrolysis (Vyas et al., 2010). However, the common reaction being used nowadays is transesterification (Janaun & Ellis, 2010; Siddiquee & Rohani, 2011; Abbaszaadeh et al., 2012). Direct use and raw oils blending

The direct use method is a method whereby crude vegetable oil is mixed or diluted with diesel fuel in order to improve the viscosity (Abbaszaadeh et al., 2012). For ratios of 1:10 to 2:10, use of the diesel was found to be successful. However, Ma and Hanna (1999) stated that blends of oils are not practical for direct and indirect engines. Problems related to this situation are due to the high viscosity, acid composition, FFA content, and gum formation. 3.2.2

Micro emulsions

It was stated by Abbaszaadeh et al.(2012) that the micro-emulsion process is developed and used to solve the problem regarding high viscosity of vegetable oil. A micro-emulsion is made by blending the vegetable oil with suitable solvents. Solvents that have been used and studied previously are methanol,

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ethanol, and 1-butanol. The disadvantages of this process are that it can result in heavy carbon deposits and incomplete combustion. 3.2.3

Pyrolysis

3.2.4

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Pyrolysis of oils involves the heating process with or without catalyst to convert one organic substance into another (Mohan et al., 2006). It was previously reported that biodiesel fuel produced through a pyrolysis process or known as bio-oil is suitable for diesel engines; however, low-value materials are produced due to the elimination of oxygen during the process (Abbaszaadeh et al., 2012). Oxygen elimination is done to upgrade the fuel produced so that it will be economically attractive and acceptable. Undesirable properties that sometimes restrict the application of biodiesel produced through this process are low heating value, incomplete volatility, and instability (French & Czernik, 2010). This process requires expensive equipment and has several advantages such as lower processing cost, simplicity, less waste, and no pollution (Singh & Singh, 2010). It was suggested by Ito et al. (2012) that the pyrolysis method is suitable for WCO processing. Transesterification

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Transesterification is said to be the most favourable reaction in producing biodiesel because it can reduce the oil viscosity (Abbaszaadeh et al., 2012). The conventional process flow diagram for transesterification is shown in Figure 6. The transesterification process involves the formation of glycerol and methyl esters from the reaction of oil feedstock with alcohol in the presence of catalyst. The process continues with the separation of biodiesel and glycerol followed by the alcohol recovery process. Recovered alcohol is recycled back to the initial process while the methyl ester produced is sent for purification, also known as the washing step. It will then undergo a drying process where refined/purified biodiesel is obtained. Factors that might affect the transesterification yield are the catalyst type, the alcohol/vegetable oil molar ratio, the content of water and FFAs, temperature, and reaction duration (Siddiquee & Rohani, 2011; Abbaszaadeh et al., 2012). There are three types of catalysts: alkalis, acids, and enzymes. Alkali-catalysed transesterification is widely used in commercial production because this method produces a high 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 other catalysts (Siddiquee & Rohani, 2011; Berrios & Skelton, 2008). However, the reaction between FFA and alkali catalyst is undesirable because the soap formation can inhibit the effectiveness of separation of glycerol from methyl ester and lower the biodiesel yield (Atadashi et al., 2012). It also leads to the consumption of catalyst. Enzyme catalyst can help avoid the formation of soap. Like acid catalysts, this catalyst has a longer reaction time and is costly. The catalyst chosen is usually depends on the starter material and the conditions of its reaction (Kaercher et al., 2013). Stated by Huang et al. (2010), commonly used alcohols are methanol, ethanol, propanol, butanol, and amyl alcohol. Methanol is more favourable because has a lower cost (Berrios & Skelton, 2008), is easily obtained (Atadashi et al., 2012), and can react with triglycerides quickly and dissolve the alkali catalyst easily (Ma & Hanna, 1999). Process conditions of transesterification reaction with respect to different kind of feedstock are tabulated in Table 8.

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Refined biodiesel Drying

Fat/oil

Transesterification

Washing Water + acid

Glycerol Acid

us

Alcohol

Wastewater for treatment

cr

Alcohol recovery

Biodiesel/glycerol Separator

ip t

Biodiesel

Figure 6. Process flow diagram of conventional transesterification process for biodiesel production

Generation of biodiesel wastewater

an

4.

Biodiesel washing process

d

4.1

M

As can be seen from Figure 6, biodiesel wastewater is mainly generated from the washing process. The washing process is important to remove excess contaminants and impurities to ensure that only high quality biodiesel that meets stringent international standard specifications is produced (Ngamlerdpokin et al., 2011; Atadashi et al., 2012).

4.1.1

Ac ce p

te

In the washing process, the undesirable substances being removed include soap (Rattanapan et al., 2011), catalyst, free glycerol, residual alcohol (Atadashi et al., 2011), water, and FFAs (Berrios & Skelton, 2008; Leung et al., 2010). Non-removed contaminants will reduce the quality of biodiesel and affect engine performance (Atadashi et al., 2011). The washing process is commonly done via two techniques: wet and dry washing (Berrios & Skelton, 2008). Recently, another alternative washing method has been investigated, which is membrane extraction (Leung et al., 2010). Wet washing process

In the wet washing process, distilled warm water or softened water is used to remove glycerol, alcohol, sodium salts, and soaps. Water mist is sprayed over the unpurified product and the mixture of water and impurities will be settled and drained out as effluent. Colourless water obtained on repeating this process indicates that complete removal of impurities is achieved (Atadashi et al., 2011). The solubility of glycerol and methanol in water make this process favourable and effective in removing both contaminants (Berrios & Skelton, 2008; Leung et al., 2010). However, Low et al. (2011) stated that some disadvantages of this process are long separation time and loss of yield. The loss of fatty acid methyl ester yields in the rinsing water contributes to the generation of highly polluted liquid effluent (Kumjadpai et al., 2011). The large amount of biodiesel wastewater generated by the washing process creates a significant problem for the industry and environment. In 2011, worldwide generation of biodiesel wastewater was approximately 28 million m3 (Veljković et al., 2013).

14 Page 14 of 41

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Process

Catalyst

Jatropha oil

Heterogeneous catalysed transesterification Heterogeneous catalysed transesterification Two-step transesterification Two-step catalysed transesterification Base catalysed transesterification Transesterification

EFB

Table 8. Process conditions of transesterification reaction Catalyst: oil Methanol: oil Reaction time Reaction weight ratio ratio (min) temperature (ºC) 20:1 15:1 90 65

KOH/EFB

15:1

H2SO4 NaOH H2SO4 KCH3O

-

Jatropha oil Jatropha oil

H2SO4

us

98.5

Yaakob et al. (2012)

65

99.5

Yaakob et al. (2012)

24:1

120

65

90.0

6:1

60

45

98.0

Berchmans and Hirata (2008) Bouaid et al. (2012)

-

6:1

60

60

-

-

6:1

-

65

98.0

20:1

NaOH KOH NaOH

-

6:1

180

40

99.0

Sunflower oil

Two-step transesterification Transesterification

-

6:1

-

60

80.0

Karanja oil

Transesterification

KOH

-

8-10:1

68-70

30-40

88.0

WCO

Transesterification

-

29:1

169

115

79.7

WCO

Supercritical methanol transesterification

Alkaline modified zirconia No catalyst

-

41:1

30

286

99.6

Ac

Sunflower oil

NaOH

M an

Jatropha oil

References

45

ed

Jatropha oil

Yield (%)

15:1

ce pt

Jatropha oil

cr

Feedstock

Raja et al. (2011) El Diwani et al. (2001) Hossain & Boyce (2009) Ahmad et al. (2010) Vivek and Gupta (2004) Wan Omar and Saidina Amin (2011) Demirbas (2009)

15 Page 15 of 41

4.1.2

Dry washing process

Membrane extraction

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4.1.3

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The dry washing process involves the use of an ion exchange resin (Atadashi et al., 2011) or magnesium silicate powder (Low et al., 2011). These materials are used to replace the usage of water in order to remove the impurities (Leung et al., 2010; Berrios & Skelton, 2008). The filtration process is usually added in the final stage to enhance the process efficiency. The advantages of this treatment are that no wastewater is produced and the total surface area coverage of the wash tank is minimized (Atadashi et al., 2011). Magnesium silicate used in this process can be reused while synthetic magnesium silicate has added value as it can be used as compost and animal feed additive (Dugan, 2007). Even though this process offers the advantage of being waterless, it is reported that the products obtained from this process never meet the limits of the international biodiesel standard (Leung et al., 2010). For instance, in research done by Berrios and Skelton (2008), their dry washing process was able to produce or provide biodiesel with a free glycerol level less than that specified by the EN14214 Standard but failed to meet the standard level for methanol, triglycerides, and soap and water contents.

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The aim of reducing the quantity of water required for the washing process has led to the development of the membrane extraction method. This method can reduce the environmental impact due to a reduction in the amount of oil in the discharged water. The usage of membrane extraction is beneficial in minimizing the volume of water used (Gomes et al., 2013), effectively avoiding the occurrence of emulsification during the washing step and resulting in a decrement of the methyl ester loss during the refining process (Leung et al., 2010), and it is said to be a promising method of biodiesel purification. Membrane studies carried out by Low et al. (2011) involved the usage of two types of membrane: flat microfiltration mixed cellulose acetate (MCA) polymeric membrane and flat ultrafiltration polytetrafluoroethylene (PTFE) polymeric membrane. The experimental set-up of this study is shown in Figure 7. The crude biodiesel was pumped from the recirculation tank to the membrane module, where the methyl ester permeate that passes through the membrane was collected in a beaker, and the rejected fluid was sent back to the recirculation tank. Their study found that the ultrafiltration PTFE polymeric membrane successfully filtered a higher volume of methyl ester compared to the MCA polymeric membrane. Membrane technology was also used and reported by Gomes et al. (2013). Tubular α-Al2O3/TiO2 membranes with average pore diameters of 0.2, 0.1, and 0.05 μm and 20 kDa were used. In the investigation using acidified water with a mass concentration of 10%, glycerol was separated effectively, giving final free glycerol content below 0.02% of the maximum value. Table 9 below summarizes the novelty of each treatment.

16 Page 16 of 41

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Table 9. Advantages and disadvantages of each washing process Advantages Disadvantages References

M

Treatment

an

Figure 7. Schematic diagram of membrane process experimental set-up (Low et al. 2011)

Very effective in removing contaminants. Purified biodiesel obtained direct from glycerol separation fulfils EN14214 Standard requirements.

Increased cost and production time; large amount of water used, emulsion formation

Veljković et al. (2013); Berrios and Skelton (2008); Atadashi et al. (2011)

Dry washing

Decreases production time; lower cost; less space required to conduct dry washing process. Waterless.

Exceeds the limit in the EN Standard

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

Avoids the formation of emulsions. Refining loss

Probably high cost. Low throughput due to existing contaminants.

Gomes et al. (2013); Leung et al. (2010); Atadashi et al. (2011)

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Wet washing

Membrane extraction

decreases. Minimizes the volume of water used. Provide cost benefit

4.2

Biodiesel wastewater and its characteristics

The large amount of wastewater generated by the commonly used wet-washing process is drawing the attention of researchers. It was previously reported that the washing process is normally repeated two to five times depending on the impurity level of methyl ester, with about 20–120 L of wastewater being generated per 100 L biodiesel produced (Srirangsan et al., 2009). In other literature, it was reported that for every 100 L of biodiesel produced, more than 20 L of wastewater was generated (Suehara et al., 2005). In Thailand, production of more than 350000 L/day biodiesel consequently produced more than 70000 L of wastewater per day (Ngamlerdpokin et al., 2011; Jaruwat et al., 2010). Siles et al. (2010)

17 Page 17 of 41

stated that wastewater disposal from this high growth rate industry may rise the environmental concerns. The characteristics of biodiesel wastewater studied by previous researchers are summarized in Table 10. It is normally found with high contents of COD, SS, oil and grease (O&G) with various pH level depending on the type of process being used.

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Biodiesel wastewater is a viscous liquid with an opaque white colour (Jaruwat et al., 2010). A high pH, high level of hexane-extracted oil and low nitrogen and phosphorus concentrations make this wastewater difficult to degrade naturally since these conditions make it unfavourable for the growth of microorganisms (Srirangsan et al., 2009; Kolesárová et al., 2011). A study by Suehara et al. (2005) found that the main component of biodiesel wastewater is residual remaining oil and this is also supported by Rattanapan et al. (2011). Thus, discharges of biodiesel wastewater into public drainage might lead to plugging of the drain due to the high content of oil and might also disturb the biological activity in sewage treatment. Investigations by Ngamlerdpokin et 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).

8.9

30980

Table 10. Characteristics of biodiesel wastewater SS TSS O&G BOD5 (mg/L) (mg/L) (mg/L) (mg/L) 2670 – 15100 – – 8850 – – 1500– – 7000–44300 105000– 28790 300000 340 – 6020 –

9.25–10.76

312–588800

–

10.35±0.03 8.5–10.5

428000±12000 60000–150000

– 1500–5000

– –

–

–

–

10.1–10.2

312000– 588800 542400

–

–

11.11 11.21 9.25–10.26

3681 40975 29595–54362

– – –

4.34–6.56

19000–37000

233–405

– – 670– 690 –

4.3

Ac ce p

te

d

M

11.0 6.7 8.5–10.5

COD (mg/L) – 18362 60000–545000

pH

–

18000– 22000 – 7000–15000

168000– 300000 – 30000–60000

18000– 22000 21048

168000– 300000 224630

387 459 1040–1710

1600 15260 1492–2286

–

260–1600

References Suehara et al. (2005) Berrios et al. (2008) Ruengkong et al. (2008) Chavalparit and Ongwandee (2009) Jaruwat et al. (2010) Siles et al. (2010) Rattanapan et al. (2011) Ngamlerdpokin et al. (2011) Kumjadpai et al. (2011) Ramírez et al. (2012) Ramírez et al. (2012) Pitakpoolsil and Hunsom (2013) This study (2013)

Level of environmental pollution by biodiesel wastewater

In Malaysia, discharge of biodiesel wastewater into drains must comply with the Environmental Quality Act and Regulations standard for industrial discharge. The parameters of biodiesel wastewater are monitored according to the Environmental Quality (Industrial Effluent) Regulations 2009. The standard is

18 Page 18 of 41

governed by Malaysia's Environmental Law, the Environmental Quality Act, 1974. Table 11 shows the industrial effluent standard limits of the Malaysian government compared with other countries. Compared to Thailand, China, and the Philippines, the standard limits of temperature, pH, and COD are almost the same. For BOD5, SS, and O&G content, Malaysia’s government requires lower limit values compared to other countries.

A

B

Temperature pH value BOD5 at 20°C COD SS O&G Colour

°C – mg/L

40 6.0–9.0 20

40 5.5–9.0 50

mg/L mg/L mg/L ADMI

80 50 1.0 100

200 100 10.0 200

Environmental Quality Act and Regulations 1974

≤40 5.5–9.0 ≤20

Under consideration of PCC ≤40 5.5–9.0 ≤60

<35 6.0–9.0 50

≤120 ≤50 ≤5 –

≤400 ≤150 ≤15 –

Enhancement and Conservation of the National Quality Act

Akta Kualiti Alam Thaveesri (2003) Sekeliling 1974 *ADMI: American Dye Manufacturers Institute *PCC: Pollution Control Committee *OEI: Old/Existing Industry *NPI: New/Proposed Industry

Coastal waters

OEI

NPI

OEI

NPI

40 6–9 150

40 6–9 120

40 5–9 120

40 5–9 100

200 50 10 –

250 200 – 150 PtCo

200 150 – 150 PtCo

250 200 15 300 PtCo

200 150 10 300 PtCo

Water Pollution Control Act

Philippine Regulations on Sanitation and Wastewater Systems

Tang (1993)

Magtibay (2006)

5.

Ac ce p

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d

References

Inland waters

cr

Unit

Philippines

us

Parameter

Regulations

Taiwan, China

Thailand

an

Malaysia

M

Country

ip t

Table 11. Standards for industrial effluents in several countries

Treatment and management of biodiesel wastewater

Due to the large amount of biodiesel wastewater generated during the biodiesel production process, the wastewater treatment should be solved effectively. In Thailand, some production plants are more likely to deliver the wastewater to a treatment facility of a water agency due to their inability to treat this wastewater with high organic matter content (Kumjadpai et al., 2011). They need to pay around USD 128.45 to 160 for 1 m3 of wastewater as reported by Ngamlerdpokin et al. 2011. Other alternative have been tried previously was incinerated the wastewater in cement industry (Veljković et al. 2014). However, no further investigation was reported. Incineration method is said having a cheaper cost rather that the cost they need to pay to water treatment agency but still expensive when compared to other industrial wastewater treatment. Srirangsan et al. (2009) stated that most previous studies usually focused on the production of biodiesel without considering the environmental management and treatment aspect. This has led some researchers to be eager to seek a better treatment in terms of simplicity and cost. Certain industries generating oily wastewater employ dissolved air flotation to separate the oil and grease before the wastewater is sent to the next process (Chavalparit & Ongwandee, 2009). Some studies have proposed the application of pre-treatment before the wastewater flows to the treatment facility of the wastewater agency and some have proposed full treatment of biodiesel wastewater.

19 Page 19 of 41

5.1

Current treatment technologies

5.1.1

ip t

The individual treatments that have been reported include coagulation (Ngamlerdpokin et al., 2011; Kumjadpai et al., 2011), electrocoagulation (Srirangsan et al., 2009; Chavalparit & Ongwandee, 2009), biological processes (Suehara et al., 2005), adsorption (Pitakpoolsil & Hunsom, 2013), and microbial fuel cell systems (Sukkasem et al., 2011). Coagulation treatment

M

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cr

In coagulation process, coagulant is added to separate the small particle content from a solution in a reasonable time. These particles are destabilized and flocculate into larger, settleable flocs (Aygun & Yilmaz, 2010). The formation of flocsis responsible for removing contaminants such as metals and toxic wastes and reducing COD, BOD5, SS, turbidity, and colour (Saraswathi & Saseetharan, 2012). Two stages of mixing are involved in the coagulation process: rapid and slow mixing. The rapid mixing helps the coagulants to disperse uniformly in aqueous solution, while slow mixing helps the flocs size to grow (Kim et al. 2009). Xie et al. (2011) stated that coagulation process offers some advantages such as simple and economical, and proven in reducing COD, BOD5, TSS, colour and organic compounds levels effectively. According to Butler et al. (2011), the coagulation process can be very expensive depending on the treated wastewater volume. However, a comparative study of the coagulation and electrocoagulation process in treating biodiesel wastewater showed that coagulation is more economical but produces treated wastewater of slightly lower quality (Ngamlerdpokin et al., 2011).

Ac ce p

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Factors that might affect the efficiency of the coagulation process include the type of coagulant used or pre-hydrolyzed metal salt used (Xie et al. 2011), coagulant dosage, pH (Aygun & Yilmaz, 2010), mixing rate (Zhou et al. 2008), and settling 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, ferric chloride (Rattanapan et al., 2011), and titanium chloride (Kim et al., 2009). Organic and natural coagulants were also used before, such as Moringa oleifera, Viciafaba, Pisumsativum, and bentonitic clay (Saraswathi & Saseetharan, 2012). In a review by Rattanapan et al. (2011) it was stated that ferric chloride, ferrous sulphate, and alum were highly effective coagulants in reducing COD. However, the performance of each coagulant still depends on the overall process, and in choosing the type of coagulant, the suitability of wastewater and economic reasons should be taken into consideration. pH control is important in the coagulation mechanism for generation of flocs or generating flocculation (Rattanapan et al., 2011) and affects the coagulation performance (Aygun & Yilmaz, 2010). It is often efficient in the range of pH 5 to 7, but the nature of the water might lead to some differences in finding a suitable pH (Parmar et al., 2011). Sometimes, it is also depends on the type of coagulant; for example; alum is effective at reducing pollutants in wastewater over a relatively wide pH range of 6–8 (Ngamlerdpokin et al., 2011), PACl used pH in the range of 7 to 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 pH 6-7, 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/L PACl to achieve the same removal efficiency.

20 Page 20 of 41

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The effect of retention time on the coagulation process of biodiesel 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 showing that the demulsion effectiveness/O&G removal was affected by the duration of the retention time. Their study also focused on the pH factor effect (5-7) and coagulants effect with variable dosage (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 COD and O&G were independent of the mixing rate, while BOD5 was dependent on the mixing rate, which showed an increment 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 rate affects the velocity gradient as well as collision frequency and this will consequently increase the efficiency of coagulation process. Another factor that gaining interest nowadays is the addition of coagulant aids in the coagulation process. Aygun and Yilmaz (2010) investigated the effect of coagulant aids and they found that coagulation treatment of detergent wastewater using FeCl3 and clay mineral as coagulant aid managed to increase the COD removal from 71 to 84%, while the addition of polyelectrolyte aid gave up to 87% COD removal.

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Treatment of biodiesel wastewater was done in many ways. For example, in the study done by Ngamlerdpokin et al. (2008), it involved the acidifying process of the wastewater with three different acids: H2SO4, HNO3, and HCl before coagulation process took place. The most effective acid was H2SO4. The acidified wastewater was subjected to pH adjustment with the addition of calcium oxide (CaO). CaO was used as a pH adjuster because it can work as coagulant coupling. Another factors being manipulated were alum dosage (0-6 g/L) and mixing rate (100-300 rpm). Kumjadpai et al. (2011) carried out an investigation of treatment of wastewater from waste used oil biodiesel production plant using a two-step process involving chemical recovery using three types of acids (H2SO4, HNO3, and HCl) followed by a coagulation process using either Al2(SO4)3 (pH 4.5–10) or PAC (pH 2.5–7.0) by the addition of CaO. Optimally, through acidification using H2SO4 at pH 1–2.5, approximately 15–30% fatty acid methyl esters (FAMEs) were recovered. The removal efficiencies of pollutant’s parameter for each study are listed in Table 12. In another study, Xie et al. (2011) identified the performance of coagulation process in treating raw waste glycerol produced from biodiesel production process. The pH of wastewater was first being adjusted from 9 to 3 using HCl and NaOH prior to 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 took places. In this study, PACl coagulant was used. The coagulant’s dosage and pH were varied from 2 to 6 g/L and 6 to 9 respectively. Even coagulation process was proven in treating various kind of wastewater successfully, some study underlined problems related to this process such as the use of chemicals (Chavalparit & Ongwandee 2009) and generation of low-density sludge with low-decomposition efficiency (Kumjadpai et al. 2011). Despite all this problems, reported that many still choose to use chemical coagulation since it is one of the ways to enhance the wastewater treatment (Butler et al. 2011).

21 Page 21 of 41

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Alum Ferric chloride PACl PACl

2 g/L 2 g/L

-

2 g/L 5 g/L

7

cr

6 4

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2 g/L 1 g/L

M an

Alum PAC

Others

References

-

Ngamlerdpokin et al. (2011)

-

Kumjadpai et al. (2011)

-

Rattanapan et al. (2011)

TSS: 98.1 Glycerol: 65.4 Methanol: 85.8

Xie et al. (2011)

Ac

6

ed

pH

Table 12. Process conditions of different coagulation treatments for biodiesel wastewater Removal parameters (%) Source of Wastewater Mixing Settling wastewater characteristics COD BOD5 O&G rate time Wastewater from pH: 2.5 97.5 97.2 98.2 washing unit COD: 271000-341712 mg/L BOD5: 6739-67389 mg/L O&G: 210-421 mg/L Wastewater from pH: 10.1-10.2 98.8 98.6 99.5 washing unit COD: 271200-341712 98.7 97.9 99.1 mg/L BOD5: 6739-67389 mg/L O&G: 210-421 mg/L 1 hr O&G: 7120 mg/L 99.9 Wastewater from 1 hr 99.8 biodiesel production 1 hr 99.7 96.2 93.3 35 rpm 15 min Raw waste pH: 9.7-10.4 glycerol COD: 1.7-1.9 x 106 mg/L BOD5: 0.9-1.2 x 106 mg/L TSS: 21.3-38.7 x 105 mg/L Glycerol: 413-477 g/L Methanol: 112-203 g/L

ce pt

Process conditions Type of Dosage of coagulant coagulant Alum 2 g/L

22 Page 22 of 41

5.1.2

Electrocoagulation treatment

cr

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One of the attractive treatments for biodiesel wastewater is the electrocoagulation process (Figure 8). It is also known as an alternative method to chemical coagulation to reduce the usage of chemical coagulants (Butler et al., 2011) This treatment has been successfully introduced in treating municipal wastewater, dyeing wastewater (Aoudj et al., 2010), and wastewater containing organic species (phenol) (Chavalparit & Ongwandee, 2009). This versatile treatment is said to have several advantages such as requiring only simple equipment, ease of operation, less treatment time, and use of less or no chemicals (Tezcan et al., 2009). It also produces a smaller amount of sludge and leads to rapid sedimentation of the flocs generated. Electrocoagulation uses electrochemistry principles, treating the wastewater better by oxidizing the cathode while the water is reduced (Butler et al., 2011).

M

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The electrocoagulation process consists of three main mechanisms: electrode oxidation, gas bubble generation, and flotation or sedimentation of formed flocs (Emamjomeh & Sivakumar, 2009). Example of electrochemical reactions using alum as anode is described as in equation (2) (Chavalparit & Ongwandee 2009). Listed by Butler et al. (2011) several 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 before such as reaction/retention times.

Equation (2)

Ac ce p

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Anodic reactions: Al(s) → Al3+ + 3e¯ Cathodic reaction: H2O +2e¯→ H2(g) + 2OH¯ In the solution: Al3+(aq) + 3H2O¯ → Al(OH)3 + 3H¯

Figure 8. Schematic diagram of electrocoagulation set-up (Maha Lakshmi & Sivashanmugam, 2013) (1. DC power supply, 2. Anode, 3. Cathode, 4. Electrocoagulation cell, 5. Effluent, 6. Magnetic bead, 7. Magnetic stirrer)

The efficiency of the electrocoagulation process for biodiesel wastewater treatment has been investigated by Chavalparit and Ongwandee (2009). The electrodes used were aluminium and graphite, and the effect of several factors like initial pH, applied voltage, and reaction time were observed. Each factor were varied from 4 to 9, 10 to 30 V and 10 to 40 minutes respectively. Chavalparit and Ongwandee

23 Page 23 of 41

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(2009) also optimized the process using a Box-Behnken design and found that pollutants were efficiently removed at pH 4–7, while an increment of pH up to 9 resulted in a decrement of removal because there was less formation of reactive flocs of aluminium hydroxide. The increment of voltage led to an increment in final pH greater than 7.5 and resulted in ineffective removal. Reported that, any additional time more than 25 minutes does not have any significant impact on the removal efficiency. Their study showed under the optimum conditions, electrocoagulation consumed about 5.57 kWh power for the treatment of 1 m3 biodiesel wastewater.

5.1.3

M

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A study done by Srirangsan et al. (2009) determined the ability of the electrocoagulation process to perform biodiesel treatment using different operational conditions in terms of the types of electrode, current density level, retention time periods, and initial pH levels. Types of electrode pairs were Fe-Fe, Fe-C, Al-Al, Al-C and C-C. Range of current density level, retention times and initial pH were 3.5 to 11 mA/cm2, 10 to 40 minutes and 4 to 9 respectively. The process was efficient at pH 6 with 25 minutes’ retention time and a current density level of 8.32 mA/cm2 using aluminium and carbon (Al-C) electrodes. The overall removal efficiency was found to be 55.4, 96.9, and 97.8% for COD, SS, and O&G respectively. The electrocoagulation process has also been used by Ngamlerdpokin et al. (2011) for treating the same wastewater source, biodiesel wastewater. With a current density of 12.42 mA/cm2, COD and BOD5 removals of 99.6 and 91.5%, were achieved respectively. Table 13 shows the process conditions for different electrocoagulation treatments for biodiesel wastewater. Biological treatment

Ac ce p

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Various researchers have developed biological technologies for the treatment of biodiesel wastewater (Siles et al., 2010; Sukkasem et al., 2011; Ramirez 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 wastewater is quite high, it inhibits the growth of microorganism and reduces the removal efficiencies of biological treatment. Few studies reporting on this matter were discussed. Some factors that play an important role and influence the effectiveness of biological process are nutrients and oxygen supply, pH value, chemical and physical characteristics of the wastewater (Margesin & Schinner, 2001), and hydraulic retention time (HRT) (Rajasimman & Karthikeyan, 2007). Sufficient nutrients are usually needed to ensure the sustainability of bacterial growth and to allow treatment to proceed optimally. For oxygen level in biological treatment, it depends on the process type either aerobic or anaerobic. For aerobic process, sufficient oxygen is needed to create the proper environment for bacterial inoculation to become dominant. Insufficient oxygen content in aerobic treatment may become a limiting factor for bacterial growth. However, excess oxygen supply might lead to high energy consumption and reduce the process efficiency (Holenda et al., 2008). pH should be taken into consideration because an unsuitable pH might lead to washout of the biomass in the reactor (Patel & Madamwar, 2002). A study of HRT effect was investigated by Patel and Madamwar (2002). Their study showed that petrochemical wastewater are likely to be treated by aerobic process with a shorter HRT compared to anaerobic digestion, which requires a longer time and has a slow reaction. In another study by Bassin et al. (2011), a longer HRT may be beneficial to treatment process since it may result in a higher capacity of biomass and avoid washout of slow-growing bacteria. According to Rajasimman and Karthikeyan (2007), at shorter HRTs, there is insufficient time for the

24 Page 24 of 41

biomass to degrade the substrate. This condition may lead to a lower removal percentage (Mohamad et al. 2008). However, it still depends on the suitability of the overall process, bacteria, and type of wastewater.

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Study of biodiesel wastewater treatment was also done by Suehara et al. (2005). Their aim was to achieve rapid biodegradation of the remaining oil contained in the three types of biodiesel wastewaters, that is, artificial wastewater, raw biodiesel wastewater, and diluted biodiesel wastewater. Nutrients added to make the process conditions favourable for the growth of bacteria were urea, yeast extract, potassium phosphate and magnesium sulphate. This was also done to avoid eutrophication. The result showed that the microorganism used, Rhodotorula mucilaginosa HCU-1,was able to degrade about 98% of the oil content in the diluted biodiesel wastewater. However it gave almost zero degradation efficiency in the raw biodiesel wastewater, which may be due to the inhibition of microorganisms present in the solids of the raw wastewater. In another study, Chavan and Mukherji (2008) showed that they were able to treat dieselrich wastewater using Bacillus cepacia and the treatment was carried out in a rotating biological contactor (RBC). Various N:P range were varied in order to observe the performance of RBC at constant HRT of 21 hours. At N:P ratio of 19:1, 28.5:1, 38:1 and 47.4:1, they managed to remove 98.6, 99.4, 99.4 and 99.3% of TPH respectively and they also removed 84.6, 97.8, 97.0 and 95.6% of TCOD respectively. Their investigation concluded that the use of algal-bacterial biofilm in RBC may suitable for petrochemical industries and petroleum refineries wastewater.

te

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Ramírez et al. (2012) conducted a study of an activated sludge biological treatment applied prior to treating biodiesel wastewater. In this case, 1.5 L of sludge from a biological treatment plant for textile wastewater was used as the inoculums in a reactor with an operating volume of 4.5 L; 2.5 mL of nutrients (38.5 g/L of urea, 33.4 g/L of NaH2PO4, 8.5 g/L of KH2PO4, 21.75 g/L of K2HPO4, and 5 g/L of CaCl2.2H2O) and 2 to 4 mg/L of dissolved oxygen were supplied to the tank. The treatment succeeded in reducing COD by 90% after 13 days of operation but gave only 21% TOC removal in 15 days.

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The potential of biological process to be used in biodiesel wastewater treatment also being reviewed by Khan and Yamsaengsung (2011). They stated that the biological process using submerged membrane bioreactor (MBR) could be a popular advanced process for biodiesel wastewater treatment. MBR has successfully treated various type of wastewaters such as refinery wastewater (Rahman & AlMalack, 2006), oily wastewater (Tri, 2002), petrochemical wastewater (Llop et al., 2009), and oilcontaminated wastewater (Scholz & Fuchs, 2000). Some main parameters involved in the MBR system are the configuration of the membrane, membrane material, membrane pore size, and HRT. Based on their study on previous research showed that MBR was efficiently proven for treating oily wastewater, and the authors concluded that MBR can be used in biodiesel wastewater treatment. Unfortunately, the cost of the treatment can be higher than that of conventional treatment due to the membrane fouling. This includes the cost of maintenance and cleaning, membrane replacement cost, and membrane module cost. Table 14 summarized the removal efficiencies of biodiesel wastewater using biological treatments.

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6.00

Iron plate

Current density: 12.42 mA/cm2

7.40

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Current density: 8.32 mA/cm2

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References

Others

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pH

Anode: Aluminium Cathode: Graphite

Type of treatment

Table 13. Process conditions of electrocoagulation treatments for biodiesel wastewater Removal parameters (%) Source of Wastewater Reaction wastewater characteristics COD BOD5 O&G time 25 min Oily wastewater pH: 8.9 55.4 98.4 from biodiesel COD: 30980 mg/L production O&G: 6020 mg/L TSS: 340 mg/L Glycerol: 1360 mg/L Methanol: 10667 mg/L 25 min Wastewater from pH: 8.9 55.7 97.8 washing unit COD: 30980 mg/L O&G: 6020 mg/L TSS: 340 mg/L Glycerol: 1360 mg/L Methanol: 10667 mg/L 4 hours Wastewater from pH: 2.5 99.6 91.5 biodiesel COD: 271000-341712 production mg/L BOD5: 6739-67389 mg/L O&G: 210-421 mg/L

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Process conditions Anode & Applied Cathode voltage Anode: 18.2 V Aluminium Cathode: Graphite

TSS: 96.6

Chavalparit and Ongwandee (2009)

SS: 97.5

Kumjadpai et al. (2011)

-

Ngamlerdpokin et al. (2011)

Table 14. Removal efficiencies of biodiesel wastewater using biological treatments Type of wastewater Wastewater characteristics Type of microorganism Removal parameters

Rhodotorula mucilaginosa

Rotating biological contactor

Bacillus cepacia

Diesel-rich wastewater

Batch reactor

Textile wastewater treatment inoculums

Wastewater from palm oil biodiesel production plant

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Agar plate

Raw biodiesel wastewater; artificial wastewater

Raw BDF wastewater: pH: 11 Oil concentration: 15.1 g/L Solid content: 2.67 g/L pH: 7.5 TCOD: 4512 mg/L TPH: 4961 mg/L pH 11,1 COD: 3681 mg/L TOC: 1700 mg/L O&G: 387 mg/L

References

COD -

BOD5 -

O&G -

Others Oil: 98.0%

97.0%

-

-

TPH: 98.4%

90.0%

-

-

TOC: 21%

Suehara et al. (2005) Chavan and Mukherji (2008) Ramirez et al. (2012)

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5.1.4

Adsorption

5.1.5

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Adsorption process is reported as versatile, easily operated, and effective method of separating a wide range of chemical compounds (Zhang et al. 2010). They offer several advantages; for example, no additional sludge is produced, no pH adjustment is required, and the pH of the discharged wastewater is unaffected. There are various type of adsorbents, including peat, bentonite clay, activated carbon, agricultural waste, and chitosan. The treatment of biodiesel wastewater using adsorption has been conducted by Pitakpoolsil and Hunsom (2013). In their investigation, commercial chitosan flakes were used as adsorbent and several operating parameters were varied, including adsorption time (0.5 to 5 hours), initial wastewater pH (2 to 8), adsorbent dosage (1.5 to 5.5 g/L), and mixing rate (120-350 rpm). Pre-treatment of biodiesel wastewater was carried out first by an acidification process using H2SO4 to reduce the pH to 2.0 before subjecting it to the adsorption process prior to separate the oil-rich phase. By adding NaOH, pH of wastewater was adjusted according to the preferred range. Under optimum conditions (adsorption time of 3 hours, initial wastewater pH of 4.0, chitosan at 3.5 g/L, and mixing rate of 300 rpm), their investigation succeeded in reducing BOD5, COD, and O&G by 76, 90, and 67% respectively. However, these pollutant levels were still not in the acceptable range for wastewater to be discharged to the environment. They emphasized that further treatment is needed either repetition of adsoption using fresh chitosan or other methods. It is also might facing difficulties in disposing the usable chitosan flakes. Microbial fuel cell

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Another treatment that has been investigated is the use of microbial 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 high COD removal but is costly due to the expensive materials used such as platinum or gold metal catalysts, proton exchange membranes, mediators, and graphite electrodes. In the study, biodiesel wastewater characterized by 218 000 ± 30 000 mg/L COD was successfully treated with up to 60% removal. Existing treatments of biodiesel wastewater and their removal efficiency are summarized in Table 15. Each treatment has advantages and disadvantages, as listed in Table 16. Table 15. Summary of other individual process for biodiesel wastewater treatment SS O&G References Treatment process COD BOD5 removal removal removal removal (%) (%) (%) (%) Adsorption 90 76 – 67 Pitakpoolsil and Hunsom (2013) Microbial fuel cell 60 – – – Sukkasem et al. (2011)

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Table 16. Advantages and disadvantages of different individual treatments Advantages Disadvantages/Problems References Simple and economical, Require handling chemical, Xie et al. (2011); Butler proven enhance wastewater operation relatively et al. (2011); Chavalparit treatment complicated, generates lowand Ongwandee (2009); density sludge with lowKumjadpai et al. (2011) decomposition efficiency. Less treatment time, no chemical required simple equipment, ease of operation

Higher cost compared to coagulation, less effective for methanol and glycerol removal

Biological processes

Economical, versatile arrangements for small areas, simple and suitable for small scale plant

Generates large amounts of low-density sludge with low decomposition efficiency, time consuming, need to manage the optimum condition first

Adsorption

No additional sludge is produced, pH of discharged wastewater is unaffected Offers high COD removal

Need further treatment, facing difficulties in disposing the adsorbents Costly

5.2

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

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Pitakpoolsil and Hunsom (2013) Sukkasem et al. (2011)

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Microbial fuel cell

Ngamlerdpokin et al. (2011); Chavalparit and Ongwandee (2009); Srirangsan et al. (2009)

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Electrocoagulation

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Treatment Coagulation

Integrated system

5.2.1

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Most of the treatments used on biodiesel wastewater were able to decrease the contaminants found in it. A specialty of each type of treatment lies in its suitability in terms of environmental and economic factors. Many researchers suggested an additional treatment for every pre-treatment investigated in order to achieve the highest efficiency. Several integrated systems being investigated for biodiesel wastewater treatment are dissolved air flotation–coagulation (Rattanapan et al., 2011), the photo-Fenton–aerobic sequential batch reactor (Ramírez et al., 2012), acidification–electrocoagulation and biomethanization (Siles et al., 2011), and electroflotation and electrooxidation (Romero et al., 2013). Integrated systems and the proposed integrated coagulation–biological aerated filter (CoBAF) system are further discussed in the following section. The authors are aiming to propose a system that applies green technology that requires the use of fewer chemicals and is economical and safe for the environment and human beings. Dissolved air flotation-coagulation

A typical treatment of oily wastewater, dissolved air flotation, was studied by Rattanapan et al. (2011). However, the authors suggested additional methods and pre-treatment of the systems by acidification and a coagulation process. About 1 N of pure HCl and H2SO4 was used for acidification, and the coagulation process was done using a Jar test unit under conditions of 100 rpm for 1 minute followed by 30 rpm for 20 minutes. A decrement in wastewater pH from 7 to 5 made the oil droplets flocculate with each other and rise to the surface. In the acidification process, the authors found that the COD removal was efficient at pH 3. Oil recovered in the acidification process was intended to be used in biodiesel production. Moreover, H2SO4 was found to be a more suitable acid, since the operating cost is cheaper than with HCl. The performance of the coagulation process was determined for different types of coagulants: alum, polyaluminium chloride, and ferric chloride. The authors found that the usage of these three coagulants

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5.2.2

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provides almost similar trends of COD and O&G removal, namely more than 30 and 90% removal, respectively. But in terms of cost, alum was found to be the more suitable coagulant. In the final process of this research, the dissolved air flotation method was used with acidification and coagulation. The pH was maintained at 3 with three days-retention time and 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. Photo-Fenton-aerobic sequential batch reactor

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Ramírez et al. (2012) investigated the efficiency of an integrated process which combined the photoFenton advanced oxidation technique with an aerobic sequential batch reactor (SBR). Photo-Fenton reaction was said potentially successful in removing large amount of COD content. It involved the oxidation of Fe (II) to Fe (III) to decompose hydrogen peroxide. The oxidation rate was then increased via the photo-reduction of Fe (III) back to Fe (II) through the exposure to radiation of UV-VIS. The production of hydroxyl radical from this cycle is used for the oxidation of organic compounds.

Equation (3)

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Fe2+ + H2O2→ Fe3+ +OH• + OH¯ Fe3++ H2O + hv → Fe2+ +OH•+ H+ RH + OH•→ photo-products + H2O

5.2.3

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This system was applied to the treatment of wastewater from a biodiesel production plant. In this experiment, wastewater with its pH adjusted to 2.3 was treated in a 7 L Mighty Pure MP-36 commercial UV reactor. Hydrogen peroxide (H2O2) and ferrous ions were added to the wastewater and a sample was taken after 2 hours. MnO2 was added to each sample in order to destroy the H2O2, avoid subsequent reactions, prevent interference with the COD readings, and prevent inhibition of the bioreactor. The final sample was then sent to a 4.5 L operating SBR with a dissolved oxygen level between 2 and 4 mg/L. Seven days of treatment were applied for the degradation of organic matter. Palm oil and castor oil biodiesel wastewaters were used, and during this experiment more than 90% of COD and BOD5 and 72% of TOC were removed from the palm oil biodiesel wastewater. Meanwhile, the removal efficiencies for castor oil biodiesel wastewater were 76.1, 69, and 67.7% for COD, BOD5, and TOC respectively. They stated that through this combined system, wastewater with high biodegradability rate can be obtained and the treatment time can be reduced. However, some problems have been pointed such as the cost for UV radiation which is quite high and the difficulties to decompose the formed sludge in SBR. Acicidification-electrocoagulation and anaerobic co-digestion

This treatment was carried out by Siles et al. (2010). This study was initially done to convert biodiesel-by product which is glycerol into more valuable products. It is said that the pollution can be controlled and the energy can be recovered through this treatment. Due to the existence of inhibitors of anaerobic codigestion which is long-chain fatty acids contained in biodiesel wastewater, they decided to add pretreatment steps; acidification and electrocoagulation process prior to reduce the effect of the inhibitors. It is said that long chain fatty acids results in toxicity to the anaerobic consortium. Through acidification using sulphuric acid and electrocoagulation with 5 L stirred tank containing eight aluminium electrodes, the COD content was reduced by 45%. The treatment was then continued with anaerobic co-digestion

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5.2.4

Acidification-electrocoagulation and biomethanization

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using three 1-L stirred reactor. The reactors were inoculated with granular biomass obtained from brewery wastewater treatment anaerobic tank. The organic load of biodiesel wastewater was varied from 1.0 g to 2.0 and 3.0 g COD in the range of 18-45 h retention time. The whole treatment managed to remove 80-90% of COD with methane production as an added value to the process (310 mL methane/g COD removed).

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Integrated acidification–electrocoagulation and biomethanization treatment was applied by Siles et al. (2011). Wastewater derived from biodiesel manufacturing with 428 000 mg/L of COD was used and treated by the system. In this study, another integrated system, acidification–coagulation–flocculation and biomethanization, was also used prior to comparing the two systems’ efficiencies. The pre-treatment processes of acidification–electrocoagulation and acidification–coagulation–flocculation gave COD removal rates of 45 and 63% respectively. However, during the whole treatment, 99% COD removal was recorded using acidification–electrocoagulation and biomethanization compared to only 94% using acidification–coagulation–flocculation and biomethanization. Electroflotation and electrooxidation

5.2.6

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The utilization of electroflotation and electrooxidation in treating biodiesel wastewater treatment was investigated by Romero et al. (2013). A bench scale reactor was used and the optimum conditions of this combined process were achieved by varying several parameters such as current density, conductivity, and reaction time. By using aluminium electrodes with current density of 8.0 mA cm-2 for a reaction time of 60 minutes, the electroflotation process managed to remove 92, 98, 100, 57, and 23% of turbidity, total solids, O&G, COD, and methanol respectively. The effluent was then subjected to an electrooxidation process using Ti/RuO2 anodes. With an applied current density of 40.0 mA cm-2 for a reaction time of 240 minutes, the methanol and COD were effectively reduced by 68 and 95% respectively. Chemical recovery and electrochemical

Jaruwat et al. (2010) studied the ability of a combined chemical recovery and electrochemical process. Chemical recovery by acid protonation was used to recover the biodiesel while the second stage treatment was named electrooxidation. This treatment managed to recover 6–7% (w/w) biodiesel from the raw biodiesel wastewater through the protonation reaction and decreased the BOD5, COD, and O&G levels by 13–24, 40–74, and 87–98% respectively. More than 95 and 100% of COD was removed through electrooxidation. 5.2.7

Coagulation-biological aerated filter (CoBAF) system

The biological aerated filter (BAF) is one of the biological treatment methods which have been proven in treating various types of wastewater such as textiles (Chang et al., 2002; He et al., 2013), oily wastewater (Zhao et al., 2006; Su et al., 2007), leachate (Wu et al., 2011; Wang et al,. 2012), and pulp and paper mill wastewater (Adachi & Fuchu, 1991). BAF has also been investigated and used as a system for removing ammonium (NH4+-N) and manganese (Mn2+) from drinking water (Abu Hasan et al., 2013). Our study

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aims to use this system in the proposed integrated process, which combines coagulation treatment and the BAF system (CoBAF), as depicted in Figure 9. The simple and economical operation of the coagulation process make this treatment favourable to be added as an initial stage prior to reducing and removing the high solid content and COD before biological treatment takes place. High solid and COD contents might inhibit the microorganisms’ growth (Kumjadpai et al., 2011). It was stated by Suehara et al. (2007) that the biological process alone is not suitable to treat biodiesel wastewater.

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Table 17. Summary of integrated system performance for biodiesel wastewater treatment Treatment process COD BOD SS O&G References removal (%) removal (%) removal (%) removal (%) Dissolved air flotation– 40–50 – 98–100 85–95 Rattanapan et al. coagulation (2011) Membrane bioreactor–biological 89.9–99.9 – – 97.6–99.9 Tri (2002) activated carbon Acidification-electrocoagulation 80-90 Siles et al. (2010) – – – and anaerobic co-digestion Acidification–electrocoagulation 99 – – – Siles et al. (2011) and biomethanization Acidification–coagulation– 94 – – – Siles et al. (2011) flocculation and biomethanization Photo-Fenton-aerobic sequential 76.1 69 – – Ramírez et al. batch reactor (2012) Electroflotation and 57 – 98 100 Romero (2013) electrooxidation

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Biological treatment seems suitable for use because of its economic value (Jou & Huang, 2003; Gasim et al., 2000) and are proven for its ability to give lower levels of contaminants (Malakahmad et al., 2011). As shown by previous studies, biological treatment is suitable for treating biodiesel wastewater because it can reduce the content of methanol and glycerol since they are easily biodegradable (Srirangsan et al., 2009). Biological treatments such as the activated sludge process have been used widely in treating wastewater from the petrochemical industry (Shokrollahzadeh et al., 2008; Khaing et al., 2010; Sponza & Gök, 2010). Pramanik et al. (2012) stated that BAF usage can provide a secondary treatment in industrial treatments and is proven to be more reliable than conventional biological treatment. The normal operation of the BAF process with aeration involves the attachment of a microorganism growth process on media which are stationary (Zhou et al., 2006). Some advantages that make this system favourable for use are its flexibility, where solids separation 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 small footprint with a large surface area (Abu Hasan et al., 2009). Several important criteria in biological aerated systems are the microorganism growth, flow configuration, aeration system, filter media, media types, size, and BAF design (Abu Hasan et al., 2009).

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Figure 9. Schematic of proposed integrated process of CoBAF system in our study

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The BAF system has been studied before by Zhao et al. (2006). The system was used to successfully pre-treat oil field wastewater from Renerlian Factory drainage outlet. With the usage of group B350M immobilized microorganisms, the overall system was able to degrade about 78% of total organic carbon (TOC) and remove 94% of oil content. It also successfully removed up to 90% of the PAHs content. The authors also emphasized that the BAF system was suitable for use as an alternative to the conventional activated sludge system. Su et al. (2007) also investigated the ability of down-flow BAF in treating oil-field produced water. The anaerobic baffled reactor (ABR) was combined with the BAF system and the hydraulic loading rates were varied from 0.6 to 1.4 m.h-1. The treatment effectively removed 76.3–80.3, 31.6–57.9, 86.3–96.3, and 76.4–82.7% 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 and suspended solids, respectively.

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The main reason why authors are interested in investigating CoBAF integrated system is that we are trying to find simpler and greener processes, which could treat biodiesel wastewater. So far, none of the discussed treatment process could treat biodiesel wastewater alone. For example, dissolved air flotation, as currently and widely used treatment in biodiesel production plant could not treat biodiesel wastewater alone. Additional process/processes is/are needed to ensure that the effluent of biodiesel wastewater meet the effluent standard requirement. Based on previous study, researchers came out with different type of treatment system in order to study their performance, capabilities and each having their own advantages and disadvantages. We aim to use biological process while simultaneously the process required to remove the microorganisms inhibitor through coagulation is considered. Study of Xie et al. (2011) showed that coagulation process was proven in releasing wastewater that was easily treated by biodegradation. For this reason, the biological aerated filter combined with the pre-treatment process of coagulation might have a successful potential in treating biodiesel wastewater. For the time being, we are working on this integrated system in the lab scale and hoping that it will give a positive outcome on biodiesel wastewater treatment. 6.

Conclusions

Biodiesel is mainly produced from vegetable oils through the transesterification process. Several issues such as economic and environmental factors have led to the development of biodiesel production technologies from various types of feedstock using various types of processes. The development of biodiesel, due to the scarcity of fossil fuel sources, has led to the emergence of another issue that needs to be solved. The process results in the production of a high amount of wastewater. Soap, glycerol, methanol, and O&G contents in the wastewater make it impossible to treat efficiently with a single

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treatment. This wastewater, which has a milky colour and bad odour, needs to be treated efficiently. Numerous treatments are being studied and proven for treating or pre-treating biodiesel wastewater and each has its own benefits and disadvantages. The ability and performance of integrated treatment using a coagulation–biological aerated filter (CoBAF) system will be investigated. Acknowledgements

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This research was financially supported by the Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, through grant number INDUSTRI-2012-029. References

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Abbaszaadeh, A., Ghobadian, B., Omidkhah, M.R. & Najafi, G. (2012). Current biodiesel production technologies: A comparative review. Energy Convers. Manag.,63, 138–148. doi:10.1016/j.enconman.2012.02.027

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

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Abu 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. Journal-The Institution of Engineers, Malaysia,70(4), 25–33.

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Adnan, H. The Star Online. (2013). Malaysia’s B10 biodiesel programme 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 transesterification of sunflower oil biodiesel. Afr. J. Biotechnol., 9(50), 8630–8635. Akta Kualiti Alam Sekeliling 1974 (Environmental Quality Act 1974). (2009). International Law Book Services. Direct Art Company, Kuala Lumpur, Malaysia. Aoudj, S., Khelifa, A., Drouiche, N., Hecini, M. & Hamitouche, H. (2010). Electrocoagulation process applied to wastewater containing dyes from textile industry. Chem. Eng. and Process.: Process Intensif., 49(11), 1176– 1182. doi: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 crude biodiesel. Appl. Energy, 88(12), 4239–4251. doi: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 membrane technology. J. Memb. Sci., 421-422, 154–164. doi:10.1016/j.memsci.2012.07.006

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

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