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Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
Contents lists available at ScienceDirect
Process Safety and Environmental Protection
journa l h om ep age: www.elsev ier .com/ locate /ps ep
eview
roduction of biodiesel and its wastewaterreatment technologies: A review
urull Muna Daud ∗, Siti Rozaimah Sheikh Abdullah ∗,assimi Abu Hasan, Zahira Yaakob
epartment of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universitiebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
a b s t r a c t
The development of technologies providing alternatives to petroleum fuel has led to the production of biodiesel
fuel. This paper reviews the methods used to produce biodiesel fuel from various types of sources such as palm oil,
jatropha oil, microalgae, and corn starch. It also includes a brief description of the transesterification process and
the point source of biodiesel wastewater, from which it is mainly generated. Biodiesel wastewater is characterized
by high contents of chemical oxygen demand (COD), biological oxygen demand (BOD5), oil, methanol, soap and
glycerol. The treatments developed so far for biodiesel wastewater are also described. The authors also investigate
the significance, ability and possibility of biological aerated filter (BAF) to treat biodiesel wastewater discharged from
a biodiesel fuel production plant. The whole treatment; coagulation-biological aerated filter (CoBAF); involves the
pre-treatment of biodiesel wastewater using coagulation followed by the treatment using BAF.
Vegetable oil based biodiesel was introduced and investigatedin the 1890s, when Rudolph Diesel invented diesel enginesto be used for machines in the agricultural sector (Orchardet al., 2007). In 1920, the availability of low cost petroleumfuel had decreased the demand for biodiesel, leading to themodification of diesel engines to match the properties ofpetroleum diesel fuel. Oil crises in the 1970s renewed inter-est in vegetable oils and gave an advantage to their market(Talebian-Kiakalaieh et al., 2013). However, the usage of tra-ditional vegetable oils in modern diesel engines was notfavourable. The investigation of methods to produce low vis-cosity vegetable oils spread and a variety of methods wereintroduced such as transesterification, pyrolysis, and blend-ing of solvents. The first patent for an industrial process forbiodiesel production was filed in 1977 by a Brazilian scientist,Expedito Parente (Lim and Teong, 2010). In 1979, South Africainitiated research into the production of biodiesel using sun-flower oil (Lin et al., 2011). Starting from 1980, the biodieselrevolution has been quite positive. A small pilot plant was builtin Austria in 1985, and in 1987 a biodiesel production plantbased on microalgae was operated in New Mexico. The com-mercialization of biodiesel using a variety of feedstock such asrapeseed and used cooking oil was boosted in the 1990s and upuntil now. Biodiesel is not only beneficial for transportation, itis also being used in manufacturing, construction machineryand generators for firing boilers purpose as depicted in Fig. 1(Abdullah et al., 2009).
1.1. Development of biodiesel production
The idea of using biodiesel fuel arose when the world started tofind and develop alternative energy resources, influenced bythe depletion of non-renewable energy sources (Berchmansand Hirata, 2008). High dependence on petroleum fuels or
Transportation
Manu fact uri ng
Con str uction
Genera tors
Fig. 1 – Usage of biodiesel.
replace fossil fuels are water, solar, and wind energy andbiofuels (Abbaszaadeh et al., 2012). The increasing demandfor biodiesel is also due to awareness of the environmentalimpact of emissions from conventional fossil fuels combus-tion and the decline in domestic oil production (Mondalaet al., 2009). The production of biodiesel in several Asiancountries is shown in Table 1. The production capacity ofeach country is based on annual reports for the years 2011and 2012. Among Asian countries, production of biodiesel ismainly dominated by Indonesia and Thailand, which pro-duce more than two billion litres every year and are alsoknown as the main producers of biodiesel in SoutheastAsia.
Commercially, biodiesel is produced through a transes-terification process in the presence of alcohol and catalyst.This process involves the conversion of triglycerides (oil) tomethyl ester (biodiesel) and by-product (glycerol) (Chavalparit
fossil fuels has led to uncertainty in price and supply (Rajaet al., 2011). Some alternative sources which are able to
and Ongwandee, 2009; Low et al., 2011) as described by Eq.(1).
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 489
Table 1 – Biodiesel production in several Asian countries.
Country Main feedstock Production capacity(billion litres/year)
O O || (Catalyst) || H-O-C-R2 + 3CH3OH → CH3-O-C-R2
O O || ||H2-O-C-R3 CH 3-O-C-R3
Triglycerides) (Methanol) (Mixture of fatty este
.2. Properties of biodiesel as transportation fuel
iodiesel fuel is used as a substitute for petroleum, whichraditionally has been used to produce transportation fuelChavalparit and Ongwandee, 2009; El Diwani et al., 2009) andonsidered as the best candidate compared to all other energyources (Leung et al., 2010). For use as transportation fuel,iodiesel is blended and named as B5, B10, B20, or B100, where, 10, 20, and 100 represent the percentage of biodiesel in theetroleum diesel (Janaun and Ellis, 2010). Biodiesel is a methylster mixture with long-chain fatty acids (Leung et al., 2010).t is made from a variety of sources of vegetables oil, animalats, and waste cooking oil (Kolesárová et al., 2011; Raja et al.,011). Reportedly, Thailand has claimed that biodiesel is onef the most promising alternative fuels to the diesel fuel used
n that country (Pleanjai et al., 2007). In Malaysia, the imple-entation of the B10 biofuel programme has had a positive
mpact on Malaysia’s biodiesel market (Adnan, 2013).For biodiesel products to be used as transportation fuel,
he fuel grade should fulfil the standard requirements. Twof the international standards are tabulated in Table 2. Therere many studies conducted to produce biodiesel from var-ous kind of feedstock. Each was analyzed according to thetandard to ensure the compatibility of biodiesel to petroleumiesel to be used as transportation fuel. The studies oniodiesel production are summarized in Table 3, while theethyl ester yields for each study are illustrated in Fig. 2.The use of renewable feedstock as biodiesel production
ources has made this fuel to be known as a clean renew-ble fuel that is biodegradable and environmentally friendlyLeung et al., 2010; Kaercher et al., 2013). These characteristicslso provide this liquid fuel with advantage of lowering theroduction of exhaust emissions from diesel engines (Hayyant al., 2010) such as particulate matter (PM) (Kolesárová et al.,011), unburned hydrocarbons (HC) and carbon monoxide (CO)xcept for nitrogen oxides (NOx) (Bouaid et al., 2012). The emis-
ion of nitrogen oxides usually increases due to the oxygenontent in the biodiesel (Sharma et al., 2008). Table 4 showshe emissions percentage from different studies regarding this
CH2-OH|
CH-OH Equation (1)|CH2-OH
(Glycerol) (1)
matter. The percentages were compared to 100% of exhaustemissions from petroleum diesel engines. The variations ineach study usually rely on the feedstock properties as well asoxygen content and viscosity of the methyl esters.
Other advantages from biodiesel usage are the use of agri-cultural surplus and reduce the dependencies on crude oil(Abdullah et al., 2009). As stated by Mondala et al. (2009), theproperties of biodiesel with a flash point above 93.3 ◦C make itsafer and easier to use, handle, and store. Another reason thatmakes biodiesel comparable to petroleum diesel is the high-energy content or also known as heating value. Referring toTable 5, the energy content of biodiesel produced in severalstudies have similar or close value to the energy content ofpetroleum diesel which makes biodiesel comparable and suit-able to be used as transportation fuel. However, Yaakob et al.(2013) addressed that by using biodiesel as transportation fuel,some may face few difficulties such as fuel pumping problems,cold start, poor low temperature flow and high copper stripcorrosion.
Fig. 2 – Methyl ester yields for different study.
490 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
Table 2 – Different standard specification for biodiesel fuel (Abdullah et al., 2009).
Property Units Limits
EN14214 ASTM D6751
Flash point, close cup ◦C 120 min 130 minWater content mg/kg 0.05 max 0.05 maxKinematic viscosity, 40 ◦C mm2/s 3.5–5.0 1.9–6.0Sulphated ash % (m/m) 0.02 max 0.020 maxSulphur content % (m/m) 0.001 max 0.0015 maxCopper corrosion strip (3 h at 50 ◦C) Rating 1a 3a maxCetane index – 51 min 47 minCarbon residue % (m/m) 0.3 max 0.50 maxAcid number mg KOH/g 0.50 max 0.80 maxFree glycerol % (m/m) 0.02 max 0.02 maxTotal glycerol % (m/m) 0.25 max 0.24 maxPhosphorus content mg/kg 10 max 10 max
◦ – 360 max
010203040506070
Soyb
ean
Cano
laAl
gae
Jatr
opha
Palm
oil
Rape
seed
Sunfl
ower
Cast
orCo
rnBa
bass
u oi
lCa
mel
ina
Coffe
eBl
ue w
axw
eed
Hem
pKa
ranj
aLi
nsee
d
% o
il by
wt i
n bi
omas
s
Fig. 4 – Seed oil yield depending on different feedstock.
Distillation temperature (90% recovered) C
The positive impact in environmental aspect may be themain reason why biodiesel starts to gain interest to be usedas transportation fuel. However, the high price of biodieselfuel compared to petroleum fuel has limited the develop-ment of this renewable fuel development (Hayyan et al., 2010).The high production cost due to the high feedstock cost lim-its the commercialization of biodiesel (Hasswa et al., 2013).Another limitation to the development of biodiesel is theusage of edible vegetable oil. It arises the problem of foodsupply competition, which can cause food crises, deforesta-tion, and challenges in oil supply management to ensure theoil supply is well managed for food consumption and con-sumer products (Leung et al., 2010; Talebian-Kiakalaieh et al.,2013). Despite all these limitations, biodiesel industry shouldfind ways to overcome these challenges. In addition, sincethe increasing 53% of world energy demand by the year 2030(Talebian-Kiakalaieh et al., 2013) while the non-renewableenergy; fossil fuel depletes, government should really look for-ward to ensure that biodiesel can fulfil the energy required byour society.
2. Biodiesel production
2.1. Source of raw materials/feedstock
Traditionally, the main source of biodiesel is vegetable oil.The types of vegetable oils available depend on the climateand soil conditions of the country (Siddiquee and Rohani,2011). In Thailand, over 90% of biodiesel production is frompalm oil as raw material (Rattanapan et al., 2011). The mostwidely used biodiesel feedstock in the United States is soy-bean oil (Mondala et al., 2009). Biodiesel feedstock can becategorized into three types: edible oils, non-edible oils, and
reusable sources or wastes, as summarized in Table 6. Someresearchers are interested in biodiesel production using oil
Biodie sel fee dsto
Group II Low free fatty acid
greases an d ani ma(FFA <4%)
Group I Refined oils
(FFA <1.5%)
Fig. 3 – Classification of
from non-edible crops, due to environmental issues. Forinstance, non-edible crops can be grown on waste lands(Leung et al., 2010). Besides, the production of biodiesel usingthese types of feedstock helps governments to find suitableways to treat, recycle, and dispose of wastes (Suehara et al.,2005; Janaun and Ellis, 2010). Yaakob et al. (2013) emphasizedthat waste cooking oil usage can reduce water pollution andalso prevent blockages in water drainage systems.
Free fatty acids (FFAs) and/or triglycerides are an importantcomponent of feedstock to be converted to biodiesel (Janaunand Ellis, 2010). All fatty acids sources are favourable for use inbiodiesel production (Talebian-Kiakalaieh et al., 2013). Kinast(2003) classified biodiesel feedstock based on their FFAs asillustrated in Fig. 3. Types of refined oil feedstock which con-tain FFAs <1.5% are, for example, soybean, canola, and palmoil. Used cooking oil, tallow, and poultry fat are types of feed-stock categorized as group II, having FFA contents below 4%.Waste grease usually falls into group III. However, excess FFAcontent in feedstock might affect biodiesel production. Forinstance, Moser (2009) stated that a content of FFA >3 wt%will lead to soap formation due to the reaction between the
FFA and the catalyst. Consequently, stable emulsion will form,
ck
Group III High free fatty acid
greases and animal fats (FFA ≥20%)
yell ow l fats
biodiesel feedstock.
Process
Safety
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tection
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487–508
491
Table 3 – Biodiesel properties from different feedstocks.
Process Feedstock Yield (%) Purity (%) Viscosity(mm2/s)
492 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
Table 5 – Energy content of biodiesel fuel.
Type of fuel Production process Energy content (MJ/kg) References
Petroleum diesel – 45.00 Talebian-Kiakalaieh et al.(2013)
Karanja oil biodiesel Transesterification 39.66 Vivek and Gupta (2004)Tallow – 40.05 Talebian-Kiakalaieh et al.
(2013)WCO biodiesel Base-catalytic and
supercritical methanoltransesterification
42.65 Demirbas (2009)
Algae (Cladophorafracta) biodiesel
– 21.1 Demirbas and Demirbas(2011)
Microalgae (Chorellaprotothecoides)biodiesel
– 25.1 Demirbas and Demirbas(2011)
Jatropha oil biodiesel Transesterification 42.15 Okullo et al. (2012)Castor oil biodiesel Transesterification 30.4 Okullo et al. (2012)Jatropha oil biodiesel Transesterification 39.76 Raja et al. (2011)Rubber seed oil
biodiesel– 36.5 Ramadhas et al. (2005)
Microalgal – 41 Rawat et al. (2013)
preventing the separation of biodiesel from glycerine andconsequently reducing the final yield (Canakci and Gerpen,2001). For FFA >2.5 wt%, a pre-treatment process is usuallyrequired before further processing is carried out (Leung et al.,2010; Talebian-Kiakalaieh et al., 2013). Based on these stud-ies, biodiesel producers using any type of feedstock with FFAcontent above 2.5 wt% need to handle problems of those men-tioned.
In Malaysia, a widely used biodiesel feedstock is palm oil(Siddiquee and Rohani, 2011). Palm oil has dominated thebiodiesel production industry because of its availability andversatile application and because it is easily found (Janaun andEllis, 2010). It is said to be one of the high-oil-yield sources.In research done by Sanford et al. (2009) and Mata et al.(2010), analysis to determine the oil content was conductedfor certain types of feedstock, and the oil content of each feed-stock is illustrated in Fig. 4. Based on their studies, babassuoil is extracted from seeds of the babassu palm tree (Attaleaspeciosa), which have high oil content; however only a fewbiodiesel studies using babassu oil have been reported com-pared to common types of sources, that is, palm oil, jatrophaoil, and so on. Meanwhile the coffee seed has the lowest oil
content. One of the reasons why there is an increment inthe number of researches on finding alternatives for biodiesel
Table 6 – Different feedstocks for biodiesel production.
sewage sludgeCanola TallowSunflower PoultryCottonseed Nile tilapiaPeanut CastorCorn Rubber seedOliveCoconut oilButterPumpkinLinseed
feedstock is the high cost of pure vegetables (edible crops)and seed oils, which constitutes about 70–85% of the over-all biodiesel production cost (Mondala et al., 2009; Siddiqueeand Rohani, 2011; Abbaszaadeh et al., 2012). Using reusablesources as biodiesel feedstock, biodiesel production costs canbe reduced by 60–90% since the price of waste edible oils is2.5–3.0 times cheaper than that of vegetable oils (Talebian-Kiakalaieh et al., 2013).
Choosing the right feedstock is very important to ensureit does not increase the production cost (Leung et al., 2010).Even if the production cost can be reduced, the production ofbiodiesel using non-edible oils may sometimes require multi-ple chemical steps due to the high FFA contents (Leung et al.,2010). For instance, Janaun and Ellis (2010) carried out methylester production, with a series of processes: one-step alkaline-based catalyzed transesterification and two-step acid-basedcatalyzed transesterification.
One of the promising non-edible sources for biodiesel feed-stock is Jatropha curcas Linnaeus seed oil. Usage of jatropha oilas the primary feedstock for producing biodiesel is one wayof reducing the production cost (Berchmans and Hirata, 2008).The high dependence on imports of petroleum and abundanceof this non-edible source in India led researchers to investi-gate the ability of jatropha oil to produce biodiesel with similarproperties or closer to those of diesel oil (Raja et al., 2011). Itis also easy to be found and grew, even on gravely, sandy andsaline soils (Bouaid et al., 2012). The source of oil in the J. curcasplant is primarily its seeds, with an oil content of 25–30%.
One of the interesting ideas for achieving low cost biodieselproduction is the usage of low cost feedstock such as wastecooking oil (WCO) (Demirbas, 2009). Usage of WCO is quitebeneficial since it can prevent the WCO from being dischargedinto the drainage system (Yaakob et al., 2013). In Kyoto, theusage of biodiesel from WCO collected from restaurants, cafe-terias, and households to be used as public transport fuelhas been implemented (Takashi, 2009). However, the qualityof the biodiesel produced may vary since the physical andchemical properties of WCO depend on the fresh cookingoil contents (Leung et al., 2010). Siddiquee and Rohani (2011)said that broad WCO properties may affect the consistency of
biodiesel production. Undesired impurities and large amountsof FFAs in the feedstock may also reduce the biodiesel quality
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 493
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Low-cost pro duction ’s feedstock • Munic ipal sludge • Waste coo king oil
High-cost produc tion ’s fee dstock • Su nflower oil • So ybean oil • Rapesee d oil • Cott on oil • Jatropha oil
Moder ate-cos t production’s feedsto ck • Vegeta ble oil
Fig. 5 – Classification of biodiesel production cost based ondifferent feedstock.
Table 7 – Cost of producing biodiesel from differentfeedstock using transesterification process.
Feedstock Biodieselproduction cost(USD per gallon)
References
Municipal sludge oil USD 3.11 per gallon Siddiquee andRohani (2011)
Soybean oil USD 4.00–4.50 pergallon
Siddiquee andRohani (2011)
Animal fats USD 1.59 per gallona Sivasamy et al.(2009)
Rapeseed oil USD 6.51 per gallona Sivasamy et al.(2009)
Palm oil USD 1.26 per gallona Ong et al. (2012)Rapeseed oil USD 10.64 per
gallonaOng et al. (2012)
Castor oil USD 4.04 per gallona Ong et al. (2012)Soybean oil USD 1.70 per gallona Ong et al. (2012)Waste cooking oil USD 1.56 per gallona Ong et al. (2012)
aCalculated production costs after unit conversion.
Demirbas, 2009). It is also lead to the need of pre-treatmentf WCO before further production process take place (Yaakobt al., 2013). Janaun and Ellis (2010) stated that some majorroblems of using this type of feedstock are the infrastructurend logistics needed to collect the waste oil.
The usage of algae as biodiesel feedstock is said to give aigh yield of methyl ester (Janaun and Ellis, 2010). In a reviewy Krishna et al. (2012), the production of biodiesel usingicroalgae with low cost operation and easy handling was
eported. The overall idea of their studies was to investigatehe extraction of biodiesel from the harvested algae collectedrom wastewater treatment ponds called High Rate Algalonds (HRAPs), which were set up near the industrial areas.hey claimed that the system of HRAPs coupled with biodieselroduction was efficient for wastewater management, simplend cost effective in producing biodiesel. However, Janaun andllis (2010) stated that for commercialization of algae-basediodiesel, it may result in a high production cost. For instance,his method requires effective large scale bioreactors and anlgae strain that can produce a high oil yield (Vasudevan andriggs, 2008).
A recent study done by Siddiquee and Rohani (2011) showedhe ability of municipal sewage sludge as biodiesel feedstock.he lipid was extracted from the sewage sludge before beingubjected to the process of biodiesel production and the pro-ess is known as a lipid extraction process. Study of Mondalat al. (2009) showed that, the production of sludge biodieselsing in situ transesterification managed to produce low costiodiesel. The cost was compared to petroleum diesel (USD.80/gallon) and soy biodiesel (USD 4.50/gallon) while the coststimated for their sludge biodiesel only around $4.00/gallon.owever, commercialization of the usage of sewage sludge asiodiesel feedstock has some large challenges, such as the pre-reatment process of raw sludge, the lipid extraction process,iodiesel production methods from solid sludge, biodieseluality, and process economics and safety.
In producing biodiesel, cost of overall production usuallynvolves the cost of feedstock, cost of processing the raw
aterial; purification of raw material and oil pressing, costf transesterification, cost of electricity, transportation andorking capital (Pimentel and Patzek, 2005; Sharma et al.,
008). Siddiquee and Rohani (2011) classified the factors thatffects the production cost into two major factors; the cost ofaw materials and the operating costs. However, Kapilakarnnd Peugtong (2007) stated that almost 80% of biodiesel pro-uction cost was contributed by the cost of feedstock. Theirtudy on palm oil biodiesel production at different reactionrocess conditions showed that for palm oil biodiesel pro-uction, the cost was contributed by three major factors thatere the cost of palm oil (80%), methanol (15%) and energy
5%). Based on several studies done by Mondala et al. (2009),emirbas (2009) and Talebian-Kiakalaieh et al. (2013), the pro-uction cost of biodiesel depending on the feedstock used cane classified as depicted in Fig. 5 while Table 7 shows the costf producing biodiesel from different feedstock based on pre-ious studies.
.2. Biodiesel production process
iodiesel can be produced by four primary techniques: directse and raw oils blending, micro-emulsions, transesterifica-
ion, and pyrolysis (Vyas et al., 2010). However, the commoneaction being used nowadays is transesterification (Janaun
and Ellis, 2010; Siddiquee and Rohani, 2011; Abbaszaadehet al., 2012).
2.2.1. Direct use and raw oils blendingThe direct use method is a method whereby crude vegetableoil is mixed or diluted with diesel fuel in order to improvethe viscosity (Abbaszaadeh et al., 2012). For ratios of 1:10–2:10,use of the diesel was found to be successful. However, Ma andHanna (1999) stated that blends of oils are not practical fordirect and indirect engines. Problems related to this situationare due to the high viscosity, acid composition, FFA content,and gum formation.
2.2.2. Micro emulsionsIt was stated by Abbaszaadeh et al. (2012) that the micro-emulsion process is developed and used to solve the problemregarding high viscosity of vegetable oil. A micro-emulsionis made by blending the vegetable oil with suitable solvents.Solvents that have been used and studied previously aremethanol, ethanol, and 1-butanol. The disadvantages of thisprocess are that it can result in heavy carbon deposits andincomplete combustion.
2.2.3. PyrolysisPyrolysis of oils involves the heating process with or with-out catalyst to convert one organic substance into another(Mohan et al., 2006). It was previously reported that biodieselfuel produced through a pyrolysis process or known as bio-oil is suitable for diesel engines; however, low-value materialsare produced due to the elimination of oxygen during the pro-
cess (Abbaszaadeh et al., 2012). Oxygen elimination is doneto upgrade the fuel produced so that it will be economically
494 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
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attractive and acceptable. Undesirable properties that some-times restrict the application of biodiesel produced throughthis process are low heating value, incomplete volatility, andinstability (French and Czernik, 2010). This process requiresexpensive equipment and has several advantages such aslower processing cost, simplicity, less waste, and no pollution(Singh and Singh, 2010). It was suggested by Ito et al. (2012)that the pyrolysis method is suitable for WCO processing.
2.2.4. TransesterificationTransesterification is said to be the most favourable reactionin producing biodiesel because it can reduce the oil viscos-ity (Abbaszaadeh et al., 2012). The conventional process flowdiagram for transesterification is shown in Fig. 6. The trans-esterification process involves the formation of glycerol andmethyl esters from the reaction of oil feedstock with alco-hol in the presence of catalyst. The process continues withthe separation of biodiesel and glycerol followed by the alco-hol recovery process. Recovered alcohol is recycled back tothe initial process while the methyl ester produced is sentfor purification, also known as the washing step. It will thenundergo a drying process where refined/purified biodiesel isobtained. Factors that might affect the transesterification yieldare the catalyst type, the alcohol/vegetable oil molar ratio, thecontent of water and FFAs, temperature, and reaction duration(Siddiquee and Rohani, 2011; Abbaszaadeh et al., 2012).
There are three types of catalysts: alkalis, acids, andenzymes. Alkali-catalyzed transesterification is widely usedin commercial production because this method produces ahigh conversion of oil in a short time (Srirangsan et al., 2009)and is less corrosive to industrial equipment (Jayed et al.,2009). It is said to have a very fast reaction compared to othercatalysts (Siddiquee and Rohani, 2011; Berrios and Skelton,2008). However, the reaction between FFA and alkali cata-lyst is undesirable because the soap formation can inhibitthe effectiveness of separation of glycerol from methyl esterand lower the biodiesel yield (Atadashi et al., 2012). It alsoleads to the consumption of catalyst. Enzyme catalyst canhelp avoid the formation of soap. Like acid catalysts, this cat-alyst has a longer reaction time and is costly. The catalystchosen is usually depends on the starter material and theconditions of its reaction (Kaercher et al., 2013). Stated byHuang et al. (2010), commonly used alcohols are methanol,ethanol, propanol, butanol, and amyl alcohol. Methanol ismore favourable because has a lower cost (Berrios and Skelton,2008), is easily obtained (Atadashi et al., 2012), and can reactwith triglycerides quickly and dissolve the alkali catalyst easily(Ma and Hanna, 1999). Process conditions of transesterifica-tion reaction with respect to different kind of feedstock aretabulated in Table 8.
3. Generation of biodiesel wastewater
As can be seen from Fig. 6, biodiesel wastewater is mainlygenerated from the washing process. The washing processis important to remove excess contaminants and impuri-ties to ensure that only high quality biodiesel that meetsstringent international standard specifications is produced(Ngamlerdpokin et al., 2011; Atadashi et al., 2012).
3.1. Biodiesel washing process
In the washing process, the undesirable substances beingremoved include soap (Rattanapan et al., 2011), catalyst,
Tab
Fee
Jatr
o
Jatr
o
Jatr
o
Jatr
o
Jatr
o
Jatr
oSu
n
Sun
Kar
aW
CO
WC
O
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 495
rans
faNbTwaw
3IeaadiimiLdlrlbaIa
3TrewBaadmthaaonrpg
polymeric membrane successfully filtered a higher volume
Fig. 6 – Process flow diagram of conventional t
ree glycerol, residual alcohol (Atadashi et al., 2011), water,nd FFAs (Berrios and Skelton, 2008; Leung et al., 2010).on-removed contaminants will reduce the quality ofiodiesel and affect engine performance (Atadashi et al., 2011).he washing process is commonly done via two techniques:et and dry washing (Berrios and Skelton, 2008). Recently,nother alternative washing method has been investigated,hich is membrane extraction (Leung et al., 2010).
.1.1. Wet washing processn the wet washing process, distilled warm water or soft-ned water is used to remove glycerol, alcohol, sodium salts,nd soaps. Water mist is sprayed over the unpurified productnd the mixture of water and impurities will be settled andrained out as effluent. Colourless water obtained on repeat-
ng this process indicates that complete removal of impuritiess achieved (Atadashi et al., 2011). The solubility of glycerol and
ethanol in water make this process favourable and effectiven removing both contaminants (Berrios and Skelton, 2008;eung et al., 2010). However, Low et al. (2011) stated that someisadvantages of this process are long separation time and
oss of yield. The loss of fatty acid methyl ester yields in theinsing water contributes to the generation of highly pollutediquid effluent (Kumjadpai et al., 2011). The large amount ofiodiesel wastewater generated by the washing process cre-tes a significant problem for the industry and environment.n 2011, worldwide generation of biodiesel wastewater waspproximately 28 million m3 (Veljkovic et al., 2012).
.1.2. Dry washing processhe dry washing process involves the use of an ion exchangeesin (Atadashi et al., 2011) or magnesium silicate powder (Lowt al., 2011). These materials are used to replace the usage ofater in order to remove the impurities (Leung et al., 2010;errios and Skelton, 2008). The filtration process is usuallydded in the final stage to enhance the process efficiency. Thedvantages of this treatment are that no wastewater is pro-uced and the total surface area coverage of the wash tank isinimized (Atadashi et al., 2011). Magnesium silicate used in
his process can be reused while synthetic magnesium silicateas added value as it can be used as compost and animal feeddditive (Dugan, 2007). Even though this process offers thedvantage of being waterless, it is reported that the productsbtained from this process never meet the limits of the inter-ational biodiesel standard (Leung et al., 2010). For instance, inesearch done by Berrios and Skelton (2008), their dry washing
rocess was able to produce or provide biodiesel with a freelycerol level less than that specified by the EN14214 Standard
esterification process for biodiesel production.
but failed to meet the standard level for methanol, triglyceri-des, and soap and water contents.
3.1.3. Membrane extractionThe aim of reducing the quantity of water required for thewashing process has led to the development of the membraneextraction method. This method can reduce the environmen-tal impact due to a reduction in the amount of oil in thedischarged water. The usage of membrane extraction is ben-eficial in minimizing the volume of water used (Gomes et al.,2013), effectively avoiding the occurrence of emulsificationduring the washing step and resulting in a decrement of themethyl ester loss during the refining process (Leung et al.,2010), and it is said to be a promising method of biodieselpurification. Membrane studies carried out by Low et al. (2011)involved the usage of two types of membrane: flat microfiltra-tion mixed cellulose acetate (MCA) polymeric membrane andflat ultrafiltration polytetrafluoroethylene (PTFE) polymericmembrane. The experimental set-up of this study is shownin Fig. 7. The crude biodiesel was pumped from the recircu-lation tank to the membrane module, where the methyl esterpermeate that passes through the membrane was collectedin a beaker, and the rejected fluid was sent back to the recir-culation tank. Their study found that the ultrafiltration PTFE
Fig. 7 – Schematic diagram of membrane processexperimental set-up (Low et al., 2011).
496 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
Table 9 – Advantages and disadvantages of each washing process.
Treatment Advantages Disadvantages References
Wet washing Very effective in removingcontaminants. Purifiedbiodiesel obtained directfrom glycerol separationfulfils EN14214 Standardrequirements.
Increased cost andproduction time; largeamount of water used,emulsion formation.
Veljkovic et al. (2012),Berrios and Skelton (2008)and Atadashi et al. (2011)
Dry washing Decreases production time;lower cost; less spacerequired to conduct drywashing process. Waterless.
Exceeds the limit in the ENStandard.
Berrios and Skelton (2008)and Leung et al. (2010)
Membraneextraction
Avoids the formation ofemulsions. Refining lossdecreases. Minimizes thevolume of water used.
Probably high cost. Lowthroughput due to existingcontaminants.
Gomes et al. (2013), Leunget al. (2010), and Atadashiet al. (2011)
Provide cost benefit.
of methyl ester compared to the MCA polymeric membrane.Membrane technology was also used and reported by Gomeset al. (2013). Tubular �-Al2O3/TiO2 membranes with averagepore diameters of 0.2, 0.1, and 0.05 �m and 20 kDa were used.In the investigation using acidified water with a mass con-centration of 10%, glycerol was separated effectively, givingfinal free glycerol content below 0.02% of the maximum value.Table 9 below summarizes the novelty of each treatment.
3.2. Biodiesel wastewater and its characteristics
The large amount of wastewater generated by the com-monly used wet-washing process is drawing the attentionof researchers. It was previously reported that the washingprocess is normally repeated two to five times dependingon the impurity level of methyl ester, with about 20–120 Lof wastewater being generated per 100 L biodiesel produced(Srirangsan et al., 2009). In other literature, it was reportedthat for every 100 L of biodiesel produced, more than 20 Lof wastewater was generated (Suehara et al., 2005). InThailand, production of more than 350,000 L/day biodieselconsequently produced more than 70,000 L of wastewater perday (Ngamlerdpokin et al., 2011; Jaruwat et al., 2010). Sileset al. (2010) stated that wastewater disposal from this highgrowth rate industry may rise the environmental concerns.The characteristics of biodiesel wastewater studied by previ-ous researchers are summarized in Table 10. It is normallyfound with high contents of COD, SS, oil and grease (O&G)with various pH level depending on the type of process beingused.
Biodiesel wastewater is a viscous liquid with an opaquewhite colour (Jaruwat et al., 2010). A high pH, high levelof hexane-extracted oil and low nitrogen and phosphorusconcentrations make this wastewater difficult to degrade nat-urally since these conditions make it unfavourable for thegrowth of microorganisms (Srirangsan et al., 2009; Kolesárováet al., 2011). A study by Suehara et al. (2005) found thatthe main component of biodiesel wastewater is residualremaining oil and this is also supported by Rattanapan et al.(2011). Thus, discharges of biodiesel wastewater into publicdrainage might lead to plugging of the drain due to the highcontent of oil and might also disturb the biological activ-ity in sewage treatment. Investigations by Ngamlerdpokinet al. (2011) and Chavalparit and Ongwandee (2009) found
that biodiesel wastewater contains water, glycerol, soap,methanol, FFAs, catalyst, and a portion of methyl ester. These
contaminants contribute to the high contents of COD and O&G(Srirangsan et al., 2009).
3.3. Level of environmental pollution by biodieselwastewater
In Malaysia, discharge of biodiesel wastewater into drainsmust comply with the Environmental Quality Act and Regu-lations standard for industrial discharge. The parameters ofbiodiesel wastewater are monitored according to the Envi-ronmental Quality (Industrial Effluent) Regulations 2009. Thestandard is governed by Malaysia’s Environmental Law, theEnvironmental Quality Act, 1974. Table 11 shows the industrialeffluent standard limits of the Malaysian government com-pared with other countries. Compared to Thailand, China, andthe Philippines, the standard limits of temperature, pH, andCOD are almost the same. For BOD5, SS, and O&G content,Malaysia’s government requires lower limit values comparedto other countries.
4. Treatment and management of biodieselwastewater
Due to the large amount of biodiesel wastewater gener-ated during the biodiesel production process, the wastewatertreatment should be solved effectively. In Thailand, someproduction plants are more likely to deliver the wastewa-ter to a treatment facility of a water agency due to theirinability to treat this wastewater with high organic mat-ter content (Kumjadpai et al., 2011). They need to payaround USD 128.45–160 for 1 m3 of wastewater as reported byNgamlerdpokin et al. (2011). Other alternative have been triedpreviously was incinerated the wastewater in cement indus-try (Veljkovic et al., 2014). However, no further investigationwas reported. Incineration method is said having a cheapercost rather that the cost they need to pay to water treatmentagency but still expensive when compared to other indus-trial wastewater treatment. Srirangsan et al. (2009) statedthat most previous studies usually focused on the productionof biodiesel without considering the environmental manage-ment and treatment aspect. This has led some researchersto be eager to seek a better treatment in terms of simplic-ity and cost. Certain industries generating oily wastewateremploy dissolved air flotation to separate the oil and grease
before the wastewater is sent to the next process (Chavalparitand Ongwandee, 2009). Some studies have proposed the
Process
Safety
an
d En
viro
nm
enta
l Pro
tection
9
4
( 2
0 1
5 )
487–508
497
Table 10 – Characteristics of biodiesel wastewater.
Enhancement andConservation of theNational Quality Act
Water PollutionControl Act
Philippine Regulations on Sanitation andWastewater Systems
References Akta Kualiti AlamSekeliling 1974
Thaveesri (2003) Tang (1993) Magtibay (2006)
*ADMI: American Dye Manufacturers Institute; PCC: Pollution Control Committee; OEI: Old/Existing Industry; NPI: New/Proposed Industry.
498 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
application of pre-treatment before the wastewater flows tothe treatment facility of the wastewater agency and some haveproposed full treatment of biodiesel wastewater.
4.1. Current treatment technologies
The individual treatments that have been reported includecoagulation (Ngamlerdpokin et al., 2011; Kumjadpai et al.,2011), electrocoagulation (Srirangsan et al., 2009; Chavalparitand Ongwandee, 2009), biological processes (Suehara et al.,2005), adsorption (Pitakpoolsil and Hunsom, 2013), and micro-bial fuel cell systems (Sukkasem et al., 2011).
4.1.1. Coagulation treatmentIn coagulation process, coagulant is added to separate thesmall particle content from a solution in a reasonable time.These particles are destabilized and flocculate into larger, set-tleable flocs (Aygun and Yilmaz, 2010). The formation of flocsisresponsible for removing contaminants such as metals andtoxic wastes and reducing COD, BOD5, SS, turbidity, and colour(Saraswathi and Saseetharan, 2012). Two stages of mixing areinvolved in the coagulation process: rapid and slow mixing.The rapid mixing helps the coagulants to disperse uniformlyin aqueous solution, while slow mixing helps the flocs size togrow (Kim et al., 2009). Xie et al. (2011) stated that coagulationprocess offers some advantages such as simple and economi-cal, and proven in reducing COD, BOD5, TSS, colour and organiccompounds levels effectively. According to Butler et al. (2011),the coagulation process can be very expensive depending onthe treated wastewater volume. However, a comparative studyof the coagulation and electrocoagulation process in treatingbiodiesel wastewater showed that coagulation is more eco-nomical but produces treated wastewater of slightly lowerquality (Ngamlerdpokin et al., 2011).
Factors that might affect the efficiency of the coagulationprocess include the type of coagulant used or pre-hydrolyzedmetal salt used (Xie et al., 2011), coagulant dosage, pH (Aygunand Yilmaz, 2010), mixing rate (Zhou et al., 2008), and sett-ling time (Rattanapan et al., 2011; Ngamlerdpokin et al.,2011). Numerous types of coagulants are used, such as alum,polyamine (Xie et al., 2011), polyaluminium chlorides, ferricchloride (Rattanapan et al., 2011), and titanium chloride (Kimet al., 2009). Organic and natural coagulants were also usedbefore, such as Moringa oleifera, Viciafaba, Pisumsativum, andbentonitic clay (Saraswathi and Saseetharan, 2012). In a reviewby Rattanapan et al. (2011) it was stated that ferric chloride,ferrous sulphate, and alum were highly effective coagulantsin reducing COD. However, the performance of each coagu-lant still depends on the overall process, and in choosing thetype of coagulant, the suitability of wastewater and economicreasons should be taken into consideration.
pH control is important in the coagulation mechanismfor generation of flocs or generating flocculation (Rattanapanet al., 2011) and affects the coagulation performance (Aygunand Yilmaz, 2010). It is often efficient in the range of pH 5–7,but the nature of the water might lead to some differencesin finding a suitable pH (Parmar et al., 2011). Sometimes, itis also depends on the type of coagulant; for example; alumis effective at reducing pollutants in wastewater over a rela-tively wide pH range of 6–8 (Ngamlerdpokin et al., 2011), PAClused pH in the range of 7–9 (Xie et al., 2011). Rattanapan et al.(2011) study showed pH of wastewater did affect the dosage of
coagulant used. Investigation they carried out showed at pH6–7, only 1.0 g/L PACl required to remove more than 90% O&G,
however at pH 5, the coagulation process used up to 2.0 g/LPACl to achieve the same removal efficiency.
The effect of retention time on the coagulation process ofbiodiesel wastewater was also studied by Rattanapan et al.(2011). The O&G removal increased from 81.65% at one day-retention time to 95.4% at five day-retention time showingthat the demulsion effectiveness/O&G removal was affectedby the duration of the retention time. Their study also focusedon the pH factor effect (5–7) and coagulants effect with variabledosage (alum and ferric chloride; 0.5–1.5 g/L, PACl: 0.5–2.0 g/L).A study by Ngamlerdpokin et al. (2011) showed that the CODand O&G were independent of the mixing rate, while BOD5
was dependent on the mixing rate, which showed an incre-ment in its removal from 73.5% at 100 rpm to 96.1% at 250 rpm.Zhou et al. (2008) stated that the increment of mixing rateaffects the velocity gradient as well as collision frequency andthis will consequently increase the efficiency of coagulationprocess. Another factor that gaining interest nowadays is theaddition of coagulant aids in the coagulation process. Aygunand Yilmaz (2010) investigated the effect of coagulant aids andthey found that coagulation treatment of detergent wastewa-ter using FeCl3 and clay mineral as coagulant aid managed toincrease the COD removal from 71 to 84%, while the additionof polyelectrolyte aid gave up to 87% COD removal.
Treatment of biodiesel wastewater was done in many ways.For example, in the study done by Ngamlerdpokin et al. (2011),it involved the acidifying process of the wastewater withthree different acids: H2SO4, HNO3, and HCl before coagulationprocess took place. The most effective acid was H2SO4. Theacidified wastewater was subjected to pH adjustment with theaddition of calcium oxide (CaO). CaO was used as a pH adjusterbecause it can work as coagulant coupling. Another factorsbeing manipulated were alum dosage (0–6 g/L) and mixing rate(100–300 rpm). Kumjadpai et al. (2011) carried out an investiga-tion of treatment of wastewater from waste used oil biodieselproduction plant using a two-step process involving chemicalrecovery using three types of acids (H2SO4, HNO3, and HCl)followed by a coagulation process using either Al2(SO4)3 (pH4.5–10) or PAC (pH 2.5–7.0) by the addition of CaO. Optimally,through acidification using H2SO4 at pH 1–2.5, approximately15–30% fatty acid methyl esters (FAMEs) were recovered. Theremoval efficiencies of pollutant’s parameter for each studyare listed in Table 12.
In another study, Xie et al. (2011) identified the performanceof coagulation process in treating raw waste glycerol producedfrom biodiesel production process. The pH of wastewater wasfirst being adjusted from 9 to 3 using HCl and NaOH priorto determine the appropriate pH for soap and oil separation.Through this acidification process, the waste glycerol was pre-treated with appropriate pH before coagulation process tookplaces. In this study, PACl coagulant was used. The coagulant’sdosage and pH were varied from 2 to 6 g/L and 6 to 9 respec-tively. Even coagulation process was proven in treating variouskind of wastewater successfully, some study underlined prob-lems related to this process such as the use of chemicals(Chavalparit and Ongwandee, 2009) and generation of low-density sludge with low-decomposition efficiency (Kumjadpaiet al., 2011). Despite all this problems, reported that many stillchoose to use chemical coagulation since it is one of the waysto enhance the wastewater treatment (Butler et al., 2011).
4.1.2. Electrocoagulation treatment
One of the attractive treatments for biodiesel wastewater isthe electrocoagulation process (Fig. 8). It is also known as
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 499
Tabl
e
12
–
Proc
ess
con
dit
ion
s
of
dif
fere
nt
coag
ula
tion
trea
tmen
ts
for
biod
iese
l was
tew
ater
.
Proc
ess
con
dit
ion
s
Sou
rce
ofw
aste
wat
erW
aste
wat
erch
arac
teri
stic
sR
emov
al
par
amet
ers
(%)
Ref
eren
ces
Typ
e
ofco
agu
lan
tD
osag
e
ofco
agu
lan
tp
H
Mix
ing
rate
Sett
lin
gti
me
CO
D
BO
D5
O&
G
Oth
ers
Alu
m
2
g/L
6
–
–
Was
tew
ater
from
was
hin
g
un
itp
H: 2
.5C
OD
: 271
000–
3417
12
mg/
LB
OD
5: 6
739–
6738
9
mg/
LO
&G
: 210
–421
mg/
L
97.5
97.2
98.2
–
Nga
mle
rdp
okin
et
al.
(201
1)
Alu
m
2
g/L
6
–
–W
aste
wat
er
from
was
hin
g
un
itp
H: 1
0.1–
10.2
CO
D: 2
7120
0–34
1712
mg/
LB
OD
5: 6
739–
6738
9
mg/
LO
&G
: 210
–421
mg/
L
98.8
98.6
99.5
–K
um
jad
pai
et
al.
(201
1)PA
C
1
g/L
4
–
–
98.7
97.9
99.1
–
Alu
m
2
g/L
–
–
1
hW
aste
wat
er
from
biod
iese
l pro
du
ctio
nO
&G
:71
20
mg/
L–
–
99.9
–R
atta
nap
an
et
al.
(201
1)Fe
rric
chlo
rid
e
2
g/L
–
–
1
h
–
–
99.8
–PA
Cl
2
g/L
1
h
–
–
99.7
–PA
Cl
5
g/L
7
35
rpm
15
min
Raw
was
te
glyc
erol
pH
: 9.7
–10.
4C
OD
: 1.7
–1.9
×
106
mg/
LB
OD
5: 0
.9–1
.2
×
106
mg/
LT
SS: 2
1.3–
38.7
×
105
mg/
LG
lyce
rol:
413–
477
g/L
Met
han
ol: 1
12–2
03
g/L
96.2
93.3
–
TSS
: 98.
1G
lyce
rol:
65.4
Met
han
ol:
85.8
Xie
et
al. (
2011
)
Fig. 8 – Schematic diagram of electrocoagulation set-up(Maha Lakshmi and Sivashanmugam, 2013). (1) DC powersupply, (2) anode, (3) cathode, (4) electrocoagulation cell, (5)
effluent, (6) magnetic bead, (7) magnetic stirrer.
an alternative method to chemical coagulation to reduce theusage of chemical coagulants (Butler et al., 2011) This treat-ment has been successfully introduced in treating municipalwastewater, dyeing wastewater (Aoudj et al., 2010), and waste-water containing organic species (phenol) (Chavalparit andOngwandee, 2009). This versatile treatment is said to have sev-eral advantages such as requiring only simple equipment, easeof operation, less treatment time, and use of less or no chem-icals (Tezcan et al., 2009). It also produces a smaller amountof sludge and leads to rapid sedimentation of the flocs gen-erated. Electrocoagulation uses electrochemistry principles,treating the wastewater better by oxidizing the cathode whilethe water is reduced (Butler et al., 2011).
The electrocoagulation process consists of three mainmechanisms: electrode oxidation, gas bubble generation,and flotation or sedimentation of formed flocs (Emamjomehand Sivakumar, 2009). Example of electrochemical reactionsusing alum as anode is described as in Eq. (2) (Chavalparitand Ongwandee, 2009). Listed by Butler et al. (2011) sev-eral considerations that might affect the treatment efficiency;wastewater type, pH, current density, type of metal electrodes,number and size of electrodes as well as metals configuration.However, there is other factor, which was investigated beforesuch as reaction/retention times.
Anodic reactions : Al(s) → Al3+ + 3e−
Cathodic reaction : H2O + 2e− → H2(g) + 2OH−
In the solution : Al3+(aq) + 3H2O− → Al(OH)3 + 3H−
(2)
The efficiency of the electrocoagulation process forbiodiesel wastewater treatment has been investigated by
Chavalparit and Ongwandee (2009). The electrodes used werealuminium and graphite, and the effect of several factors like
500 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
le
13
–
Proc
ess
con
dit
ion
s
of
elec
troc
oagu
lati
on
trea
tmen
ts
for
biod
iese
l was
tew
ater
.
Proc
ess
con
dit
ion
s
Sou
rce
ofw
aste
wat
erW
aste
wat
erch
arac
teri
stic
sR
emov
al
par
amet
ers
(%)
Ref
eren
ces
de
&
Cat
hod
eA
pp
lied
volt
age
pH
Rea
ctio
n
tim
eC
OD
BO
D5
O&
G
Oth
ers
de:
Alu
min
ium
thod
e:
Gra
ph
ite
18.2
V6.
0625
min
Oil
y
was
tew
ater
from
biod
iese
lp
rod
uct
ion
pH
: 8.9
CO
D: 3
0,98
0
mg/
LO
&G
: 602
0
mg/
LT
SS: 3
40
mg/
LG
lyce
rol:
1360
mg/
LM
eth
anol
: 10,
667
mg/
L
55 .4–
98 .4T
SS:
96.6
Ch
aval
par
itan
dO
ngw
and
ee(2
009)
de:
Alu
min
ium
thod
e:
Gra
ph
ite
Cu
rren
t
den
sity
:8.
32
mA
/cm
26.
00
25
min
Was
tew
ater
from
was
hin
g u
nit
pH
: 8.9
CO
D: 3
0,98
0
mg/
LO
&G
: 602
0
mg/
LT
SS: 3
40
mg/
LG
lyce
rol:
1360
mg/
LM
eth
anol
: 10,
667
mg/
L
55 .7–
97 .8SS
:97
.5K
um
jad
pai
et
al.
(201
1)
pla
te
Cu
rren
t
den
sity
:12
.42
mA
/cm
27.
40
4
h
Was
tew
ater
from
biod
iese
l pro
du
ctio
np
H: 2
.5C
OD
: 271
000–
3417
12
mg/
LB
OD
5: 6
739–
6738
9
mg/
LO
&G
: 210
–421
mg/
L
99 .691 .5
–
–
Nga
mle
rdp
okin
et
al.
(201
1)
initial pH, applied voltage, and reaction time were observed.Each factor were varied from 4 to 9, 10 to 30 V and 10 to40 min respectively. Chavalparit and Ongwandee (2009) alsooptimized the process using a Box–Behnken design and foundthat pollutants were efficiently removed at pH 4–7, whilean increment of pH up to 9 resulted in a decrement ofremoval because there was less formation of reactive flocsof aluminium hydroxide. The increment of voltage led to anincrement in final pH greater than 7.5 and resulted in inef-fective removal. Reported that, any additional time more than25 min does not have any significant impact on the removalefficiency. Their study showed under the optimum conditions,electrocoagulation consumed about 5.57 kW h power for thetreatment of 1 m3 biodiesel wastewater.
A study done by Srirangsan et al. (2009) determinedthe ability of the electrocoagulation process to performbiodiesel treatment using different operational conditionsin terms of the types of electrode, current density level,retention time periods, and initial pH levels. Types of elec-trode pairs were Fe–Fe, Fe–C, Al–Al, Al–C and C–C. Range ofcurrent density level, retention times and initial pH were3.5–11 mA/cm2, 10–40 min and 4–9 respectively. The processwas efficient at pH 6 with 25 min retention time and a cur-rent density level of 8.32 mA/cm2 using aluminium and carbon(Al–C) electrodes. The overall removal efficiency was foundto be 55.4, 96.9, and 97.8% for COD, SS, and O&G respec-tively. The electrocoagulation process has also been used byNgamlerdpokin et al. (2011) for treating the same wastewa-ter source, biodiesel wastewater. With a current density of12.42 mA/cm2, COD and BOD5 removals of 99.6 and 91.5%,were achieved respectively. Table 13 shows the process condi-tions for different electrocoagulation treatments for biodieselwastewater.
4.1.3. Biological treatmentVarious researchers have developed biological technologiesfor the treatment of biodiesel wastewater (Siles et al., 2010;Sukkasem et al., 2011; Ramírez et al., 2012; De Gisi et al.,2013). However, the study of this treatment is quite limited.Since the content of solid presents in biodiesel wastewateris quite high, it inhibits the growth of microorganism andreduces the removal efficiencies of biological treatment. Fewstudies reporting on this matter were discussed. Some factorsthat play an important role and influence the effectivenessof biological process are nutrients and oxygen supply, pHvalue, chemical and physical characteristics of the wastewa-ter (Margesin and Schinner, 2001), and hydraulic retentiontime (HRT) (Rajasimman and Karthikeyan, 2007). Sufficientnutrients are usually needed to ensure the sustainability ofbacterial growth and to allow treatment to proceed optimally.For oxygen level in biological treatment, it depends on theprocess type either aerobic or anaerobic. For aerobic process,sufficient oxygen is needed to create the proper environmentfor bacterial inoculation to become dominant. Insufficientoxygen content in aerobic treatment may become a limitingfactor for bacterial growth. However, excess oxygen supplymight lead to high energy consumption and reduce the pro-cess efficiency (Holenda et al., 2008).
pH should be taken into consideration because an unsuit-able pH might lead to washout of the biomass in the reactor(Patel and Madamwar, 2002). A study of HRT effect was inves-tigated by Patel and Madamwar (2002). Their study showed
that petrochemical wastewater are likely to be treated byaerobic process with a shorter HRT compared to anaerobic
Tab
An
o
An
o Ca
An
o Ca
Iron
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 501
dtmhbatrdt
bbtrNfpaiawtbwstiwc4oatpt
swtloK2T11
wYuuMaw22amvtctt
igestion, which requires a longer time and has a slow reac-ion. In another study by Bassin et al. (2011), a longer HRT
ay be beneficial to treatment process since it may result in aigher capacity of biomass and avoid washout of slow-growingacteria. According to Rajasimman and Karthikeyan (2007),t shorter HRTs, there is insufficient time for the biomasso degrade the substrate. This condition may lead to a loweremoval percentage (Mohamad et al., 2008). However, it stillepends on the suitability of the overall process, bacteria, andype of wastewater.
Study of biodiesel wastewater treatment was also doney Suehara et al. (2005). Their aim was to achieve rapidiodegradation of the remaining oil contained in the threeypes of biodiesel wastewaters, that is, artificial wastewater,aw biodiesel wastewater, and diluted biodiesel wastewater.utrients added to make the process conditions favourable
or the growth of bacteria were urea, yeast extract, potassiumhosphate and magnesium sulphate. This was also done tovoid eutrophication. The result showed that the microorgan-sm used, Rhodotorula mucilaginosa HCU-1, was able to degradebout 98% of the oil content in the diluted biodiesel waste-ater. However it gave almost zero degradation efficiency in
he raw biodiesel wastewater, which may be due to the inhi-ition of microorganisms present in the solids of the rawastewater. In another study, Chavan and Mukherji (2008)
howed that they were able to treat diesel-rich wastewa-er using Bacillus cepacia and the treatment was carried outn a rotating biological contactor (RBC). Various N:P rangeere varied in order to observe the performance of RBC at
onstant HRT of 21 h. At N:P ratio of 19:1, 28.5:1, 38:1 and7.4:1, they managed to remove 98.6, 99.4, 99.4 and 99.3%f TPH respectively and they also removed 84.6, 97.8, 97.0nd 95.6% of TCOD respectively. Their investigation concludedhat the use of algal-bacterial biofilm in RBC may suitable foretrochemical industries and petroleum refineries wastewa-er.
Ramírez et al. (2012) conducted a study of an activatedludge biological treatment applied prior to treating biodieselastewater. In this case, 1.5 L of sludge from a biological
reatment plant for textile wastewater was used as the inocu-ums in a reactor with an operating volume of 4.5 L; 2.5 mLf nutrients (38.5 g/L of urea, 33.4 g/L of NaH2PO4, 8.5 g/L ofH2PO4, 21.75 g/L of K2HPO4, and 5 g/L of CaCl2·2H2O) and–4 mg/L of dissolved oxygen were supplied to the tank.he treatment succeeded in reducing COD by 90% after3 days of operation but gave only 21% TOC removal in5 days.
The potential of biological process to be used in biodieselastewater treatment also being reviewed by Khan andamsaengsung (2011). They stated that the biological processsing submerged membrane bioreactor (MBR) could be a pop-lar advanced process for biodiesel wastewater treatment.BR has successfully treated various type of wastewaters such
s refinery wastewater (Rahman and Al-Malack, 2006), oilyastewater (Tri, 2002), petrochemical wastewater (Llop et al.,
009), and oil-contaminated wastewater (Scholz and Fuchs,000). Some main parameters involved in the MBR systemre the configuration of the membrane, membrane material,embrane pore size, and HRT. Based on their study on pre-
ious research showed that MBR was efficiently proven forreating oily wastewater, and the authors concluded that MBRan be used in biodiesel wastewater treatment. Unfortunately,
he cost of the treatment can be higher than that of conven-ional treatment due to the membrane fouling. This includes
the cost of maintenance and cleaning, membrane replace-ment cost, and membrane module cost. Table 14 summarizedthe removal efficiencies of biodiesel wastewater using biolog-ical treatments.
4.1.4. AdsorptionAdsorption process is reported as versatile, easily operated,and effective method of separating a wide range of chemicalcompounds (Zhang et al., 2010). They offer several advan-tages; for example, no additional sludge is produced, no pHadjustment is required, and the pH of the discharged waste-water is unaffected. There are various type of adsorbents,including peat, bentonite clay, activated carbon, agriculturalwaste, and chitosan. The treatment of biodiesel wastewa-ter using adsorption has been conducted by Pitakpoolsil andHunsom (2013). In their investigation, commercial chitosanflakes were used as adsorbent and several operating param-eters were varied, including adsorption time (0.5–5 h), initialwastewater pH (2–8), adsorbent dosage (1.5–5.5 g/L), and mix-ing rate (120–350 rpm). Pre-treatment of biodiesel wastewaterwas carried out first by an acidification process using H2SO4
to reduce the pH to 2.0 before subjecting it to the adsorp-tion process prior to separate the oil-rich phase. By addingNaOH, pH of wastewater was adjusted according to the pre-ferred range. Under optimum conditions (adsorption time of3 h, initial wastewater pH of 4.0, chitosan at 3.5 g/L, and mix-ing rate of 300 rpm), their investigation succeeded in reducingBOD5, COD, and O&G by 76, 90, and 67% respectively. However,these pollutant levels were still not in the acceptable rangefor wastewater to be discharged to the environment. Theyemphasized that further treatment is needed either repeti-tion of adsorption using fresh chitosan or other methods. It isalso might facing difficulties in disposing the usable chitosanflakes.
4.1.5. Microbial fuel cellAnother treatment that has been investigated is the use ofmicrobial fuel cells (MFCs). In a study by Sukkasem et al.(2011), they reinvented and used a kind of biocatalytic MFC,an upflow bio-filter circuit (UBFC). This treatment offers highCOD removal but is costly due to the expensive materials usedsuch as platinum or gold metal catalysts, proton exchangemembranes, mediators, and graphite electrodes. In the study,biodiesel wastewater characterized by 218,000 ± 30,000 mg/LCOD was successfully treated with up to 60% removal. Exist-ing treatments of biodiesel wastewater and their removalefficiency are summarized in Table 15. Each treatment hasadvantages and disadvantages, as listed in Table 16.
4.2. Integrated system
Most of the treatments used on biodiesel wastewater wereable to decrease the contaminants found in it. A specialty ofeach type of treatment lies in its suitability in terms of envi-ronmental and economic factors. Many researchers suggestedan additional treatment for every pre-treatment investigatedin order to achieve the highest efficiency. Several integratedsystems being investigated for biodiesel wastewater treat-ment are dissolved air flotation–coagulation (Rattanapanet al., 2011), the photo-Fenton–aerobic sequential batch reac-tor (Ramírez et al., 2012), acidification–electrocoagulation andbiomethanization (Siles et al., 2011), and electroflotation and
electrooxidation (Romero et al., 2013). Integrated systems andthe proposed integrated coagulation–biological aerated filter
502 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
Tabl
e
14
–
Rem
oval
effi
cien
cies
of
biod
iese
l was
tew
ater
usi
ng
biol
ogic
al
trea
tmen
ts.
Typ
e
of
trea
tmen
t
Typ
e
ofm
icro
orga
nis
mTy
pe
ofw
aste
wat
erW
aste
wat
erch
arac
teri
stic
sR
emov
al
par
amet
ers
Ref
eren
ces
CO
D
BO
D5
O&
G
Oth
ers
Aga
r
pla
teR
hodo
toru
lam
uci
lagi
nosa
Raw
biod
iese
lw
aste
wat
er; a
rtifi
cial
was
tew
ater
Raw
BD
Fw
aste
wat
er:
pH
: 11
Oil
con
cen
trat
ion
:15
.1
g/L
Soli
d
con
ten
t:2.
67
g/L
–
–
–
Oil
:98
.0%
Sueh
ara
et
al. (
2005
)
Rot
atin
g
biol
ogic
alco
nta
ctor
Bac
illu
s
cepa
cia
Die
sel-
rich
was
tew
ater
pH
: 7.5
TC
OD
: 451
2
mg/
LT
PH: 4
961
mg/
L
97 .0%
–
–
TPH
:98
.4%
Ch
avan
and
Mu
kher
ji
(200
8)
Bat
ch
reac
tor
Text
ile
was
tew
ater
trea
tmen
tin
ocu
lum
s
Was
tew
ater
from
pal
m
oil b
iod
iese
lp
rod
uct
ion
pla
nt
pH
11.1
CO
D: 3
681
mg/
LT
OC
: 170
0
mg/
LO
&G
: 387
mg/
L
90 .0%
–
–
TO
C:
21%
Ram
írez
et
al. (
2012
)
(CoBAF) system are further discussed in the following section.The authors are aiming to propose a system that applies greentechnology that requires the use of fewer chemicals and iseconomical and safe for the environment and human beings.
4.2.1. Dissolved air flotation–coagulationA typical treatment of oily wastewater, dissolved air flotation,was studied by Rattanapan et al. (2011). However, the authorssuggested additional methods and pre-treatment of the sys-tems by acidification and a coagulation process. About 1 N ofpure HCl and H2SO4 was used for acidification, and the coagu-lation process was done using a Jar test unit under conditionsof 100 rpm for 1 min followed by 30 rpm for 20 min. A decre-ment in wastewater pH from 7 to 5 made the oil dropletsflocculate with each other and rise to the surface. In the acidi-fication process, the authors found that the COD removal wasefficient at pH 3. Oil recovered in the acidification processwas intended to be used in biodiesel production. Moreover,H2SO4 was found to be a more suitable acid, since the oper-ating cost is cheaper than with HCl. The performance of thecoagulation process was determined for different types ofcoagulants: alum, polyaluminium chloride, and ferric chloride.The authors found that the usage of these three coagulantsprovides almost similar trends of COD and O&G removal,namely more than 30 and 90% removal, respectively. But interms of cost, alum was found to be the more suitable coag-ulant. In the final process of this research, the dissolved airflotation method was used with acidification and coagulation.The pH was maintained at 3 with three days-retention timeand alum as the coagulant. With alum dose ≥150 mg/L and 40%recycle rate, this system was able to give 98–100% SS removal,85–95% O&G removal, and 40–50% COD removal.
4.2.2. Photo-Fenton-aerobic sequential batch reactorRamírez et al. (2012) investigated the efficiency of an inte-grated process which combined the photo-Fenton advancedoxidation technique with an aerobic sequential batch reactor(SBR). Photo-Fenton reaction was said potentially successful inremoving large amount of COD content. It involved the oxida-tion of Fe(II) to Fe(III) to decompose hydrogen peroxide. Theoxidation rate was then increased via the photo-reductionof Fe(III) back to Fe(II) through the exposure to radiation ofUV–vis. The production of hydroxyl radical from this cycle isused for the oxidation of organic compounds.
Fe2+ + H2O2 → Fe3+ + OH• + OH−
Fe3+ + H2O + hv → Fe2+ + OH• + H+
RH + OH• → photo-products + H2O
(3)
This system was applied to the treatment of wastewaterfrom a biodiesel production plant. In this experiment, waste-water with its pH adjusted to 2.3 was treated in a 7 L MightyPure MP-36 commercial UV reactor. Hydrogen peroxide (H2O2)and ferrous ions were added to the wastewater and a sam-ple was taken after 2 h. MnO2 was added to each sample inorder to destroy the H2O2, avoid subsequent reactions, preventinterference with the COD readings, and prevent inhibitionof the bioreactor. The final sample was then sent to a 4.5 Loperating SBR with a dissolved oxygen level between 2 and4 mg/L. Seven days of treatment were applied for the degra-dation of organic matter. Palm oil and castor oil biodiesel
wastewaters were used, and during this experiment morethan 90% of COD and BOD5 and 72% of TOC were removed from
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 503
Table 15 – Summary of other individual process for biodiesel wastewater treatment.
Treatment process COD removal (%) BOD5 removal (%) SS removal (%) O&G removal (%) References
Adsorption 90 76 – 67 Pitakpoolsil and Hunsom (2013)Microbial fuel cell 60 – – – Sukkasem et al. (2011)
Table 16 – Advantages and disadvantages of different individual treatments.
Xie et al. (2011), Butler et al.(2011), Chavalparit andOngwandee (2009) andKumjadpai et al. (2011)
Electrocoagulation Less treatment time, nochemical required simpleequipment, ease ofoperation
Higher cost compared tocoagulation, less effectivefor methanol and glycerolremoval
Ngamlerdpokin et al. (2011),Chavalparit andOngwandee (2009) andSrirangsan et al. (2009)
Biological processes Economical, versatilearrangements for smallareas, simple and suitablefor small scale plant
Generates large amounts oflow-density sludge withlow decompositionefficiency, time consuming,need to manage theoptimum condition first
Pitakpoolsil and Hunsom(2013), Ramírez et al. (2012)and Suehara et al. (2007)
Adsorption No additional sludge isproduced, pH of dischargedwastewater is unaffected
Need further treatment,facing difficulties indisposing the adsorbents
Pitakpoolsil and Hunsom(2013)
te6shtphS
4cTwgltoctplcemtuwtwraar
Microbial fuel cell Offers high COD removal
he palm oil biodiesel wastewater. Meanwhile, the removalfficiencies for castor oil biodiesel wastewater were 76.1,9, and 67.7% for COD, BOD5, and TOC respectively. Theytated that through this combined system, wastewater withigh biodegradability rate can be obtained and the treatmentime can be reduced. However, some problems have beenointed such as the cost for UV radiation which is quiteigh and the difficulties to decompose the formed sludge inBR.
.2.3. Acidification–electrocoagulation and anaerobico-digestionhis treatment was carried out by Siles et al. (2010). This studyas initially done to convert biodiesel-by product which is
lycerol into more valuable products. It is said that the pol-ution can be controlled and the energy can be recoveredhrough this treatment. Due to the existence of inhibitorsf anaerobic co-digestion which is long-chain fatty acidsontained in biodiesel wastewater, they decided to add pre-reatment steps; acidification and electrocoagulation processrior to reduce the effect of the inhibitors. It is said that
ong chain fatty acids results in toxicity to the anaerobiconsortium. Through acidification using sulphuric acid andlectrocoagulation with 5 L stirred tank containing eight alu-inium electrodes, the COD content was reduced by 45%. The
reatment was then continued with anaerobic co-digestionsing three 1-L stirred reactor. The reactors were inoculatedith granular biomass obtained from brewery wastewater
reatment anaerobic tank. The organic load of biodiesel waste-ater was varied from 1.0 g to 2.0 and 3.0 g COD in the
ange of 18–45 h retention time. The whole treatment man-ged to remove 80–90% of COD with methane productions an added value to the process (310 mL methane/g COD
emoved).
. The simple and economical operation of the coagulation
Costly Sukkasem et al. (2011)
4.2.4. Acidification–electrocoagulation and biomethanizationIntegrated acidification–electrocoagulation and biometha-nization treatment was applied by Siles et al. (2011).Wastewater derived from biodiesel manufacturing with428,000 mg/L of COD was used and treated by the sys-tem. In this study, another integrated system, acidification–coagulation–flocculation and biomethanization, was also usedprior to comparing the two systems’ efficiencies. Thepre-treatment processes of acidification–electrocoagulationand acidification–coagulation–flocculation gave COD removalrates of 45 and 63% respectively. However, during thewhole treatment, 99% COD removal was recorded usingacidification–electrocoagulation and biomethanization com-pared to only 94% using acidification–coagulation–flocculationand biomethanization.
4.2.5. Electroflotation and electrooxidationThe utilization of electroflotation and electrooxidation intreating biodiesel wastewater treatment was investigated byRomero et al. (2013). A bench scale reactor was used and theoptimum conditions of this combined process were achievedby varying several parameters such as current density, con-ductivity, and reaction time. By using aluminium electrodeswith current density of 8.0 mA cm−2 for a reaction time of60 min, the electroflotation process managed to remove 92,98, 100, 57, and 23% of turbidity, total solids, O&G, COD, andmethanol respectively. The effluent was then subjected toan electrooxidation process using Ti/RuO2 anodes. With anapplied current density of 40.0 mA cm−2 for a reaction timeof 240 min, the methanol and COD were effectively reducedby 68 and 95% respectively.
4.2.6. Chemical recovery and electrochemical
Jaruwat et al. (2010) studied the ability of a combined chemi-cal recovery and electrochemical process. Chemical recovery
504 Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508
ted p
Fig. 9 – Schematic of proposed integra
by acid protonation was used to recover the biodiesel whilethe second stage treatment was named electrooxidation. Thistreatment managed to recover 6–7% (w/w) biodiesel from theraw biodiesel wastewater through the protonation reactionand decreased the BOD5, COD, and O&G levels by 13–24, 40–74,and 87–98% respectively. More than 95 and 100% of COD wasremoved through electrooxidation.
4.2.7. Coagulation-biological aerated filter (CoBAF)systemThe biological aerated filter (BAF) is one of the biological treat-ment methods which have been proven in treating varioustypes of wastewater such as textiles (Chang et al., 2002; Heet al., 2013), oily wastewater (Zhao et al., 2006; Su et al., 2007),leachate (Wu et al., 2011; Wang et al., 2012), and pulp andpaper mill wastewater (Adachi and Fuchu, 1991). BAF has alsobeen investigated and used as a system for removing ammo-nium (NH4
+–N) and manganese (Mn2+) from drinking water(Abu Hasan et al., 2013). Our study aims to use this systemin the proposed integrated process, which combines coagula-tion treatment and the BAF system (CoBAF), as depicted inFig. 9 process make this treatment favourable to be addedas an initial stage prior to reducing and removing the highsolid content and COD before biological treatment takes place.High solid and COD contents might inhibit the microorgan-isms’ growth (Kumjadpai et al., 2011). It was stated by Sueharaet al. (2007) that the biological process alone is not suitableto treat biodiesel wastewater. Table 17 shows the summaryof integrated system performance for biodiesel wastewatertreatment.
Biological treatment seems suitable for use because of itseconomic value (Jou and Huang, 2003; Gasim et al., 2000)and are proven for its ability to give lower levels of contami-nants (Malakahmad et al., 2011). As shown by previous studies,biological treatment is suitable for treating biodiesel waste-
water because it can reduce the content of methanol andglycerol since they are easily biodegradable (Srirangsan et al.,
Table 17 – Summary of integrated system performance for biod
2009). Biological treatments such as the activated sludge pro-cess have been used widely in treating wastewater from thepetrochemical industry (Shokrollahzadeh et al., 2008; Khainget al., 2010; Sponza and Gök, 2010). Pramanik et al. (2012)stated that BAF usage can provide a secondary treatment inindustrial treatments and is proven to be more reliable thanconventional biological treatment. The normal operation ofthe BAF process with aeration involves the attachment ofa microorganism growth process on media which are sta-tionary (Zhao et al., 2006). Some advantages that make thissystem favourable for use are its flexibility, where solids sep-aration or aerobic biological treatment can be carried out,ease of operation, and relative compactness (Pramanik et al.,2012); it requires a small working space and provides a smallfootprint with a large surface area (Abu Hasan et al., 2009). Sev-eral important criteria in biological aerated systems are themicroorganism growth, flow configuration, aeration system,filter media, media types, size, and BAF design (Abu Hasanet al., 2009).
The BAF system has been studied before by Zhao et al.(2006). The system was used to successfully pre-treat oil fieldwastewater from Renerlian Factory drainage outlet. With theusage of group B350M immobilized microorganisms, the over-all system was able to degrade about 78% of total organiccarbon (TOC) and remove 94% of oil content. It also success-fully removed up to 90% of the PAHs content. The authors alsoemphasized that the BAF system was suitable for use as analternative to the conventional activated sludge system. Suet al. (2007) also investigated the ability of down-flow BAF intreating oil-field produced water. The anaerobic baffled reac-tor (ABR) was combined with the BAF system and the hydraulicloading rates were varied from 0.6 to 1.4 m h−1. The treat-ment effectively removed 76.3–80.3, 31.6–57.9, 86.3–96.3, and76.4–82.7% of oil, COD, BOD, and SS respectively. Chang et al.(2002) used BAF to treat textile wastewater. They found that
the BAF system could remove about 88 and 97% of COD andsuspended solids, respectively.
iesel wastewater treatment.
l (%)SS removal
(%)O&G
removal (%)References
98–100 85–95 Rattanapan et al. (2011)– 97.6–99.9 Tri (2002)
– – Siles et al. (2010)
– – Siles et al. (2011)
– – Siles et al. (2011)
– – Ramírez et al. (2012)
98 100 Romero et al. (2013)
Process Safety and Environmental Protection 9 4 ( 2 0 1 5 ) 487–508 505
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The main reason why authors are interested in investi-ating CoBAF integrated system is that we are trying to findimpler and greener processes, which could treat biodieselastewater. So far, none of the discussed treatment pro-
ess could treat biodiesel wastewater alone. For example,issolved air flotation, as currently and widely used treat-ent in biodiesel production plant could not treat biodieselastewater alone. Additional process/processes is/are needed
o ensure that the effluent of biodiesel wastewater meethe effluent standard requirement. Based on previous study,esearchers came out with different type of treatment systemn order to study their performance, capabilities and each hav-ng their own advantages and disadvantages. We aim to useiological process while simultaneously the process requiredo remove the microorganisms inhibitor through coagulations considered. Study of Xie et al. (2011) showed that coagu-ation process was proven in releasing wastewater that wasasily treated by biodegradation. For this reason, the biolog-cal aerated filter combined with the pre-treatment processf coagulation might have a successful potential in treatingiodiesel wastewater. For the time being, we are working onhis integrated system in the lab scale and hoping that it willive a positive outcome on biodiesel wastewater treatment.
. Conclusions
iodiesel is mainly produced from vegetable oils through theransesterification process. Several issues such as economicnd environmental factors have led to the development ofiodiesel production technologies from various types of feed-tock using various types of processes. The development ofiodiesel, due to the scarcity of fossil fuel sources, has ledo the emergence of another issue that needs to be solved.he process results in the production of a high amount ofastewater. Soap, glycerol, methanol, and O&G contents in
he wastewater make it impossible to treat efficiently with aingle treatment. This wastewater, which has a milky colournd bad odour, needs to be treated efficiently. Numerous treat-ents are being studied and proven for treating or pre-treating
iodiesel wastewater and each has its own benefits and disad-antages. The ability and performance of integrated treatmentsing a coagulation–biological aerated filter (CoBAF) systemill be investigated.
cknowledgements
his research was financially supported by the Faculty ofngineering and Built Environment, Universiti Kebangsaanalaysia, through grant number INDUSTRI-2012-029.
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