Palm oil industry in South East Asia and the effluent treatment technology—A review

Environmental Technology & Innovation 9 (2018) 169–185

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Palm oil industry in South East Asia and the effluent treatment technology—A review✩ Muhammad Johan Iskandar a , Azizah Baharum a,b , Farah Hannan Anuar a,b , Rizafizah Othaman a,b, * a b

School of Chemical Science and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Malaysia Polymer Research Center, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Malaysia

graphical abstract

highlights • • • •

Palm Oil Industry is one of the biggest industry in South East Asia. Larger demand for palm oil will generate more by-product or waste. The conventional method POME treatment is inefficient and causing a pollution. Alternative treatment technology is found to be the best solution to solve this problem.

article

info

Article history: Received 24 May 2017

a b s t r a c t The progress of Palm Oil Mill Effluent (POME) treatment in meeting with the regulation and standard stipulated by the Environmental Authority always been a major issue in Palm

✩ This manuscript aims to discuss the palm oil industry in South East Asia, recent treatment and alternative treatment for the waste from this industry. Corresponding author. E-mail address: [email protected] (R. Othaman).

*

https://doi.org/10.1016/j.eti.2017.11.003 2352-1864/© 2017 Elsevier B.V. All rights reserved.

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Received in revised form 25 October 2017 Accepted 7 November 2017 Available online 5 December 2017 Keywords: Palm oil POME Membrane Aerobic digestion Anaerobic digestion Physicochemical

oil industries. To occupy the palm oil world market demand, palm oil industry needs to produce more than the market demand to supply necessity. Currently, South East Asia country such as Malaysia, Indonesia and Thailand rank the top country with the largest production of palm oil in the world. However, the increasing demand for the palm oil has resulted in even massive waste especially palm oil mill effluent (POME). Direct discharge of POME will adversely affect the environment. In 2011, 53 million tonnes metric of palm oil produced and 89% of this production comes from Malaysia and Indonesia. Thailand, however, used the palm oil solely for domestic usage. Since POME has been declared among the major source of pollution, a great deal of research and development including application devoted to enhance the current treatment method for POME to consistently meet the proposed stringent regulatory requirement by environmental authority. Conventional treatment such as ponding system is the most commonplace method to treat POME through the application of ponding system which is include aerobic and anaerobic treatment. Recently, the alternative methods such as coagulation, flocculation, adsorption, advanced oxidation process (AOP) and membrane technology to treat POME has shown a promising result compared to the conventional method. © 2017 Elsevier B.V. All rights reserved.

Contents 1. 2.

3. 4. 5. 6.

Introduction............................................................................................................................................................................................. Oil processing and waste ........................................................................................................................................................................ 2.1. Oil processing ............................................................................................................................................................................. 2.1.1. FFB reception and transfer ......................................................................................................................................... 2.1.2. FFB sterilization .......................................................................................................................................................... 2.1.3. Threshing, digesting and screw-pressing.................................................................................................................. 2.1.4. Depericarping.............................................................................................................................................................. 2.1.5. Clarification of crude palm oil (CPO) ......................................................................................................................... 2.1.6. Kernel separation and drying..................................................................................................................................... 2.2. Waste .......................................................................................................................................................................................... Characteristic of Palm Oil Mill Effluent ................................................................................................................................................. Conventional Palm Oil Mill Effluent (POME) treatment technologies ................................................................................................ Alternative Palm Oil Mill Effluent (POME) treatment technologies .................................................................................................... Conclusion ............................................................................................................................................................................................... References ...............................................................................................................................................................................................

170 172 172 172 173 173 173 173 173 174 174 175 176 180 181

1. Introduction At present, the palm oil mill industry is being dominated by the Southeast Asia region. Possessing to its suitability to regional climatic conditions and high yield rates, palm oil is the main biodiesel feedstock in Southeast Asia (Mukherjee and Sovacool, 2014). Since the 14th century it was introduced in this region, palm oil has become an important agricultural commodity, especially Malaysia and Indonesia which has dominating this industry since the mid-1960s (Mukherjee and Sovacool, 2014). Palm oil has been recognized as the most utilized vegetable oil globally with the total production up to 40% compared to the other vegetable oil (Hansen et al., 2015; Oosterveer, 2015). Fig. 1 shows the world palm oil production in 2017 (Index Mundi, 2017). Currently, Malaysia and Indonesia are the world’s biggest palm oil producers where the production of both countries is 85% of the world palm oil production. Taking after the rundown is Thailand where it contributes 4% of the world palm oil production (Foreign Agricultural Service, 2005). In 2011 palm oil plantations produced over 53 million metric tonnes of palm oil on 16 million hectares that have been contributed by Indonesia and Malaysia (86%), where palm oil is a key economic driver and is a crucial component of GDP (SSI review, 2014). Malaysia has issued almost 39% and 44% of global palm oil production and global export for palm oil. Over the past half century, palm oil has made an astounding and consistent development in the worldwide market and it is estimated in the time of 2016–2020, the yearly production of Malaysia palm oil will achieve 15.4 tonnes (Teoh, 2000). In 2017, there are 453 operating mills in Malaysia where 245 mills are located in Peninsular whereas 208 is located in Sabah and Sarawak (MPOB, 2017). Currently, Malaysia has produced 21,000 metric tonnes of palm oil (Index Mundi, 2017). As for the Thailand, the palm oil industry has started to monopoly the vegetable oil production and it has been proved by the increasing planting and harvesting area for palm oil that is 9.7% (Dallinger, 2011). Thailand is among the countries which has started to revolutionize the usage of palm oil as the main vegetable oil since the last decade (Silalertruksa et al., 2016) due to the cheaper prices compared to the other oil with the advantages that can be used as a food or nonfood product (Ludin et al., 2014; MPOB, 2013). Surprisingly, starting that date, palm oil plantation in Thailand has enlarged and the plantation area has tripled from the previous (FAOSTAT, 2016; OAE, 2016). Furthermore, palm oil in Thailand has demonstrated a promising future where it covers 70% of the vegetable palm oil market domestically (Chavalparit et al.,

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Fig. 1. World palm oil production in 2017 (Index Mundi, 2017).

2006). The production of vegetable oil annually is approximately 150 million metrics which is one-third of the production of the palm oil (FAO, 2013). Apart from that, the Thailand palm oil industry in 2010 has been operated by 14 bio-diesel plants, 12 palm oil refineries and more than 60 palm oil crushing mill and it is forecasted that these numbers will keep increasing annually (Dallinger, 2011). More than half states in Thailand are currently been planted with palm oil which is 60 from 76 states (OAE, 2014a,b). Pure palm oil is not permitted to be traded in Thailand by the government hence 100% of the oil production is being utilized exclusively for domestic consumption (Preecharjarn and Prasertsri, 2012). The palm oil consumption in Thailand is divided into three parts, which is for edible oil, cosmetic and biodiesel. The local demand for edible oil and cosmetic was plateau while demand for biodiesel has increased 6% as compared to year 2012 (DIT, 2014). The palm oil plantation in Thailand has become a very serious industry since the Ministry of Energy has launched a policy that is an Alternative Energy Development Plan 2015–2036, AEDP to enhance the production of biodiesel (DEDE, 2012) which has been supported by Ministry of Agricultures and Cooperatives (MOAC) for the palm oil plantation addition (OAE, 2014a,b). Driven by the demand from importing nations such as India, China and member states of EU, palm oil has become the most extensively traded vegetables oil globally in the mid-2000s (Sheil et al., 2009). This development and expansion have persuaded the legislature to provide over 20 million hectares of land for the new palm oil estate, which is 330% augmentation over the present land area under agriculture (Milder et al., 2008). Palm oil industry in Indonesia has ballooned from 6.7 Mha to 9 Mha from 1990 to 2013 and majority of the plantation are in Sumatra and Kalimantan (Deptan, 2014). In parallel, between the year of 1990 to 2005, it is reported that palm oil planting area has increased by 3,017,00 ha (FAO, 2007). According to USDA, the export of CPO has increased from 5 to 25.5 Mt while the consumption of CPO has increased from 3 to 9.5 Mt from the year 2000 to 2017 (USDA, 2017). With the production exceeded 19,324 million crude palm oil (CPO), the industry in Indonesia is predicted to emit 15.61 × 106 of greenhouse gas (Tong, 2011). On the other hand, Indonesian Palm Oil Research Institute (PPPK) has aimed for 26% oil extraction rate (OER) (PPKS, 2014) to support the production of palm oil locally. The high demand of palm oil in Indonesia might be due to population expansion, consumption level, and renewable energy interest (Afriyanti et al., 2016). It is clearly shown that there is an increasing trend of the production of the world palm oil by Malaysia, Indonesia, and Thailand (Fig. 2). The crude palm oil (CPO) produced from this industry will generate cooking oil (Corley, 2009) and biodiesel (IEA, 2011). However, the leading trend and development of palm oil industry in these countries have led to a catastrophic environmental issue. This scenario has been condemned by the society as the result of deforestation as well as disturbing the nature of current exhibit flora and fauna (SSI review, 2014). Tan et al. (2009) reported that 25% of palm oil site in Indonesia is being planted on peat soil, which leads to the emission of carbon through an oxidation process. This statement has been supported by a report stating that 17% and 63% of new plantation in Malaysia and Indonesia has been caused by the deforestation of tropical forest starting from 1990–2010 (Gunarso et al., 2013; Koh et al., 2011) and 30% of this plantation occurred on peat soil which leads to huge CO2 emission (Carlson et al., 2012; Miettinen et al., 2012; Omar et al., 2010). There are some factor to be included upon planning on a biofuel production such as energy balance, greenhouse gas emission, land use efficiency and water use (Nonhebel, 2005; Dale, 2007; Prueksakorn and Gheewala, 2008; Gerbens-Leenes et al., 2009). The Roundtable for Sustainable Palm Oil (RSPO) was established in 2004 to promote sustainable production of palm oil worldwide. The RSPO objective is to encourage the growth and use of the sustainable palm oil products through trustworthy global standard and engagement of stakeholders. Since the presence of palm oil industries has caused an environmental issue, the principle and criteria of RSPO were used as a reference. Apart from RSPO, the Malaysian Palm Oil Board (MPOB), Malaysia Palm Oil Council (MPOC) and Ministry of Plantation Industries and Commodities (MPIC) are present to oversee all the matters regarding palm oil industry. A ‘Small Renewable Energy Power Program’ has been launch in 2000 by the Malaysian Government to restore and reuse all the wastes from palm oil industry and utilized them for electricity generation.

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Fig. 2. Malaysia, Indonesia and Thailand Palm Oil Production by Year (Index Mundi, 2017).

Apart from that, the Malaysian Sustainable Palm Oil (MSPO) has been implemented in Malaysia in 2014 with the same objective and function as others (Adnan, 2013). In Thailand, Good Agricultural Practice standard (Thai Gap) was developed in 2010 to monitor issues related to Thai palm oil including the usage of pesticide, water, and fertilizer application. This initiative was introduced to reduce the environmental impact caused by the palm oil industry. In 2011, the implementation of Indonesian Sustainable Palm Oil (ISPO) has been set as a standard rivaling the RSPO (Mukherjee and Sovacool, 2014). It is designed to be a mandatory certification for all palm oil producers in Indonesia. Whereas, The Ministry of Plantation Industries and Commodities (MPIC) had announced in 2006, the RM20 million Malaysia Palm Oil Conservation Fund (MPOCF) had been initiated with aims to help preserve affected wildlife and to sustain biodiversity conservation program (Abdullah and Sulaiman, 2013). Despite contributing lot to the agricultural and economic scenario, palm oil mill also significantly contributes to environmental degradation (Abdullah and Sulaiman, 2013). As a result, the palm waste, which is the byproduct of the manufacturing process will also escalate. Several studies have revealed that palm oil industries contribute to massive environmental pollution which includes global warming, biodiversity loss, eutrophication, acidification and photochemical ozone formation (Saswattecha et al., 2015a). The expanding interests for palm oil in the world market, as well as other biofuels, has prompted more noteworthy worry over effects on the environment, biodiversity and worldwide climate (Fargione et al., 2008; James, 2008; Koh and Ghazoul, 2008; Butler and Laurance, 2009). Fiber combustion in the boilers from the mills itself leads to release of acidifying compound and smog precursor to the open atmosphere (Saswattecha et al., 2015b). Before the palm oil is being retrieved, there are stages of operation that fresh fruit bunch (FFB) need to undergo. The uniqueness of the palm tree is it can produce palm oil and palm kernel oil. However, 67% of POME is produced through these processes. The idea of this article is to represent a general review, which reconsiders and updates about the palm oil scenario in Malaysia, Indonesia, and Thailand, recent treatment processes for palm oil mill effluent (POME) and the latest alternative techniques. This article also will discuss the advantages and disadvantages of the technique used to treat POME along with some result of the conventional method and alternative method. 2. Oil processing and waste 2.1. Oil processing The process of retrieving palm oil on a general basis is the same for Malaysia, Indonesia, and Thailand. However, maybe some of the factory or industry using the biogas from palm oil process will be having an advanced closed reactor for the methane build-up collection. Different type of palm oil seeds will yield a different quality of palm oil. Fig. 3 shows a chart for palm oil extraction and waste generation. 2.1.1. FFB reception and transfer Fresh fruit bunch (FFB) that are retrieved from the farm is being transported to the mills for processing. In this process, the FFB will be weight and grade accordingly to their quality. This is important to ensure that further deterioration can be prevented at the early stage. Then, the FFB will be transferred to the sterilizer.

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Fig. 3. Flow chart for typical palm oil extraction process.

2.1.2. FFB sterilization Once the FFB is received, it will be exposed to high-temperature pressurized steam. The function of the sterilization process is to inhibit the biological factors which accountable for quality deterioration and loosen the fruit in the bunch for maximum fruit recovering during stripping and threshing process (Stork, 1960; Olie and Tjeng, 1982; PORIM, 1987; Whiting, 1990; Hamzah, 2008). In addition, the sterilizing process will help to ensure a smooth process of mechanical threshing to free the palm fruit from the bunches (Liew et al., 2014). Sterilization process stage is crucial in maintaining and ensuring the success of subsequent stage since it is among the earliest stage in palm oil process (Junaidah et al., 2015). 2.1.3. Threshing, digesting and screw-pressing Scraper conveyor will transport sterilized FFB to thresher platform. A drum-like machine will rotate and start to strip all the fruits from the bunch and separate them. Then the desired fruit are transfer into the digester. Digestion is the process of extracting the palm oil by the mechanism of breaking down the fruit under steam heated condition. In this process, the high pressure will rupture the oil-bearing cell of the fruits and will be channeled to the twin-screw machine to press out the CPO (Ahmed et al., 2015). 2.1.4. Depericarping After the pressing process, press cake is formed. This cake consists of moisture, nuts, and oily fiber. Depericarping process will then separate the fiber and the nut for the subsequent process. 2.1.5. Clarification of crude palm oil (CPO) Crude palm oil contains 35%–45% of palm oil, 45%–55% of water and fibrous material after the digestion process (Ahmed et al., 2015). The CPO will enter clarification tank where it contained rotary strainer and sludge centrifuge to separate the oil from the CPO solution and will be transferred back to the clarifier. From this process, palm oil mill effluent (POME) is produced. The recovered oil will be sent to vacuum dryer and storage tank. 2.1.6. Kernel separation and drying In this process, the nut from depericarping process will undergo separation via winnowing and hydrocyclone process. This process will involve separation of palm kernel from their shell. The remaining wastewater will be released and the kernel will be dried in silos.

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2.2. Waste Malaysia has different palm varieties, growth condition, and plantation management compared to Thailand and this will result in a difference in solid waste. Milling process in Thailand consumed more water throughout the process thus they will be having a higher amount of wastewater discharge (Kittikul et al., 1994). Unanimous with the huge production of palm oil, the waste generated will also indirectly increase. Prasertsan and Prasertsan (1996) reported that a solitary palm oil production can yield over 70% of waste. There are many byproducts from the palm oil processing such as oil palm trunks (OPT), oil palm fronds (OPF), palm oil mill effluent (POME), fresh fruit bunch (FFB) empty fruit bunches (EFB), palm press fiber (PPF), shell palm oil mill sludge (POMS), palm kernel cake (PKC) and palm shell (Aziz and Abdul, 2007; Singh et al., 2010; Abdullah and Sulaiman, 2013). In FFB, Pleanjai et al. (2004) reported that the fiber, shell, decanter cake and EFB account for 30%, 6%, 3%, and 28.3% respectively. For EFB itself, it was reported that it has 42% Carbon, 0.8% Nitrogen, 0.006% Potassium, 2.4% Sodium and 0.2% Magnesium (Krause, 1994). The advantages of this industries are that it can produce palm oil which is processed from the mesocarp and palm kernel oil (white palm oil) which is processed from the endosperm. After oil has been extracted from the kernel, it will leave behind palm kernel cake (PKC). Onwueme and Sinha (1991) reported that the palm kernel cake (PKC) is rich in carbohydrate and protein that is 48% and 19% respectively. Palm oil mill effluent (POME) has the capability to cause the most dangerous effect to the environment if not legitimately treated (Rupani et al., 2010; Ahmad et al., 2005a). Around 30 million tonnes of palm oil mill effluent (POME) is and roughly about 26.7 million tonnes of solid biomass is generated in 2004 solely (Yacob et al., 2006a,b). Although there is current ponding system to treat the POME through a series of anaerobic or aerobic pond, unfortunately, these wastes especially POME does not meet the requirement proposed by the Department of Environment thus putting the conventional method of effluent treatment as an inefficient method. This phenomenon is surely disrupting the water ecosystem thus endangering them. The essential of waste management are to reduce and recycle the waste, recover the energy and finally dispose of the waste (Abdullah and Sulaiman, 2013). The interesting facts about Palm Oil Industry are that palm oil mill is self-sufficient in energy by using PPF, EFB, and shell as fuel to produce steam in waste-fuel boilers for processing and power generation with steam turbines (Abdullah and Sulaiman, 2013). Thailand has specific wastewater of 0.87 m3 /ton FFB from palm oil process while Malaysia has the specific wastewater of 0.6 m3 /ton FFB (Hwang et al., 1978). 3. Characteristic of Palm Oil Mill Effluent Sterilizer condensate, decanter or separator sludge and hydrocyclone waste are among the three major source of wastewater from palm oil with the value of 17%, 75% and 8%, respectively (Prasertsan and Prasertsan, 1996). POME is a wastewater comprise of 95%–96% water, 0.6%–0.7% oil and 4%–5% total solids including 2%–4% suspended solids (Khalid and Wan Mustafa, 1992). POME contain cellulosic material, fat, oil and grease (Rupani et al., 2010) The attributes of the resulting POME is completely reliant on the operations and quality control of a processing plant. POME is usually had a brown and pale yellow in color (Bello et al., 2013). Other than having a foul smell, POME also contains organic or natural materials such as lignin, carotene, phenolic and pectin which is 4700 ppm, 8 ppm, 5800 ppm and 3400 ppm, respectively (Ho et al., 1984; Sundram et al., 2003). On the other hand, POME is a colloidal suspension, produce from the mixture of sterilizer condensate, separator sludge, and hydrocyclone waster in a ratio 9:15:1, respectively (Wu et al., 2010). POME can cause contamination due to the existence of easily degradable organic matter thereby referring to the content of high COD and BOD that have a value of 50,000 ppm and 25,000 ppm respectively. Chin et al. (1996) also reported that POME contains 6000 mg/L of oil and grease, 59,530 mg/L of suspended solids and 750 mg/L of nitrogen. Therefore, POME can cause water pollution (Thani et al., 1999). The general idea on how POME can cause water pollution is that the POME discharge contained microorganism that will compete mainly on the uptake of oxygen with the aquatic life. This incident will eventually cause the aquatic life to have less oxygen than previous thus slowly hindered the growth of the aquatic life and in a long term will preventing their existence. The characteristic of POME is given at Table 1. High COD and BOD content might cause the oxygen content in the water to be reduced and this would eventually lead to the death of aquatic life. Usually, the characteristic of POME varies considerably depending on processed batches, days and factories that are also related to the different processing technique and the age or type of fruit (Ng et al., 1987). Different POME characterization might be due to the uncertain discharge limit of the factory, temperature and condition of the palm oil processing (Ahmad et al., 2005c, 2006b). Even though POME is an acidic mixture (Borja and Banks, 1994), however it does contain a compelling amount of amino acids, short fibers, nitrogenous compound, free organic acid, carbohydrates and inorganic nutrients such as sodium, potassium, magnesium, calcium, manganese, ferum, zinc, cobalt, copper and cadmium (Santosa, 2008). The content of amino acid either essential or non-essential, fatty acid and mineral approximate composition (%) are shown in Table 2. Lead (Pb) that are considered as lethal metal can likewise be found in POME (Habib et al., 1997) because of pollution from plastic and metal funnels, tanks and compartments where Pb is generally utilized in paints and coating materials. Nevertheless, their concentrations are usually below the sublethal levels (>17.5 µg/g) (James et al., 1996). POME is thus not toxic for flora and fauna. According to Chow (1991), nitrogen is initially present in POME in the form of organic nitrogen. As time progress, the organic nitrogen is slowly transformed to ammoniacal nitrogen with molecular of 17– 35 kg/kmol.

M.J. Iskandar et al. / Environmental Technology & Innovation 9 (2018) 169–185 Table 1 Characteristic of raw POME. Source: MPOB. Parameter pH Oil and grease Biochemical Oxygen Demand (BOD) Chemical Oxygen Demand (COD) Total solid Suspended solid Total volatile solid Ammoniacal nitrogen (NH3 -N) Total nitrogen All values are in mg/L except pH

POME (average)

Range

4.2 4000 25,000 51,000 40,000 18,000 34,000 35 750

3.4–5.2 – 10,250–43,750 15,000–100,000 11,500–79,000 5000–54,000 9000–72,000 4–80 180–1400

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Table 2 The approximate composition of amino acid, fatty acid and mineral in raw POME. Source: Habib et al. (1997), Ho et al. (1984) and Muhrizal et al. (2006). Amino acids

Composition (%)

Fatty acid

Composition (%)

Mineral

Composition (µg/g dry weight)

Aspartic acid Glutamic acid Serine Glycine Histidine Arginine Threonine Alanine Proline Tyrosine Phenylalanine Valine Methionine Cystine Isoleucine Leucine Lysine Tryptophan

9.66 10.88 6.86 9.43 1.43 4.25 2.58 7.7 4.57 3.16 3.2 3.56 6.88 3.37 4.53 4.86 2.66 1.26

Caprylic acid Capric acid Lauric acid Myristic acid Pentadocanoic acid Palmitic acid Heptadecanoic acid 10-Heptadecanoic acid Stearic acid Oleic acid Linoleic acid Linolenic acid T-linolenic acid Arachidic acid Ecosatrienoic acid Eicosatetraenoic acid Eicosapetaenoic acid

2.37 4.29 3.22 12.66 2.21 22.45 1.39 1.12 10.41 14.54 9.53 4.72 0.00 3.56 2.04 1.12 0.36

Fe Zn P Na Mg Mn K Ca Co Cr Cu Ni S Se Si Sn Al B Mo As V Pb Cd

11.08 17.58 143 777.38 94.57 911.95 38.81 8951.55 1650.09 2.40 5.02 10.76 1.31 13.32 12.32 10.50 2.30 16.60 7.60 6.45 9.09 0.12 5.15 0.44

It is possible to use the Palm Oil Mill Effluent (POME) for biological means because of the existence of huge compositions and concentrations of carbohydrate, protein, nitrogenous compounds, lipids and minerals in POME (Hwang et al., 1978; Phang, 1990; Habib et al., 1997). A report by Ho and Tan (1983) stated that there is a possibility for the presence of pentose in POME. Furthermore, Hwang et al. (1978) have also been reporting the same findings. A pentose is found inside plant by mean of respiration. Water-soluble carbohydrates, in terms of glucose, reducing sugars and pectin, are also found to be present in the soluble fraction of POME (Wu et al., 2009). 4. Conventional Palm Oil Mill Effluent (POME) treatment technologies By utilizing a microbial process, the high concentration of protein, nitrogenous compounds, lipid, carbohydrate and minerals inside POME can be converted into valuable material (Habib et al., 1997; Agamuthu and Tan, 1985). Perez et al. (2001), reported that due to the organic properties of POME, the anaerobic process is the most suitable method of treating POME. Thus, from the earlier stage of palm oil mill industry, ponding system is being used as the conventional method to treat POME (Khalid and Wan Mustafa, 1992; Ma and Ong, 1985). However, there are some parts of POME that need to be given full attention to ensure that this industry will remain sustainable and environmentally friendly. The most common method to treat POME is by using it as a fertilizer and water supply for the palm tree. Despite the facts that POME is non-lethal, treatment of POME is the most crucial part to ensure that there is a balance between the environment protection, economic expansion and sustainable development due to its potential to cause pollution (Rupani et al., 2010). Apart from that, POME treatment is considered a burden rather than part of the production process and not a source of benefit (Ma, 1999). Direct discharge of POME into the water body will cause water contamination and resulted in aquatic endangerment (Hwang et al., 1978). Thus, researchers are experimenting with a new alternative method to treat palm oil mill effluent. Many steps of this POME treatment were done through conventional methods such as

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Table 3 Environment quality restriction on POME discharge by respective countries. Source: DOE, Pollution Control Department (2016), Pelatihan Lingkungan (2016). Palm oil mill effluent discharge standard

a

Parameter

Malaysia

Indonesia

Thailand

pH BOD (mg/L) COD (mg/L) Total solids (mg/L) Suspended solid (mg/L) Oil and grease (mg/L) Ammoniacal Nitrogen (mg/L) Total Nitrogen (mg/L) Temperature (◦ C)

5.0–9.0 100 (20 in Sabah and Sarawak) 50a – 400 50 10 10 45

6.0–9.0 100 350 0 250 25 – 50 –

5.5–9.0 20 120 3000 50 5 – 100 40

Requirement set by Malaysia Sewage and Industrial Effluent Discharge Standard.

an aerobic system, anaerobic system, open decomposing tank, advanced ventilation system, closed anaerobic decomposition tank and composting of organic fertilizer. However, these ponds acquire an extensive open area subsequently producing a foul stench and predicament in maintaining the liquor dissemination and biogas collection which results in harmful effect to the environment (Onyia et al., 2001; Ng et al., 1987; Chin et al., 1996). Every industry that operates the palm oil will have an open tank or pond basically for the anaerobic process to occur and this is applied for Malaysia, Indonesia, Thailand and other countries. Despite the disadvantages of the pond system, a series of shallow pond also have been practiced to minimizes the effect of POME to the environment. Nevertheless, this method also required much larger space and has longer hydraulic retention time (Chan and Chooi, 1984). Since POME is generally made up of organic substances that are biodegradable, therefore the process that is suitable to treat POME is based on anaerobic, aerobic, and facultative process (Sethupathi, 2004). A high value of degradable organic matter inside raw POME might be due to the presence of unrecovered palm oil inside it (Ahmad et al., 2003). Biological treatment has massive advantages towards other method such as less energy demand, minimum sludge accumulation, no liberation of foul odor and production of methane due to the efficient breakdown of organic substances by anaerobic bacteria (Rincón et al., 2006). These methane gas can be used further for the generation of electricity. These conventional methods require a large space to be done (Quah et al., 1982). Unfortunately, the anaerobic and facultative pond rely entirely on bacteria to break down pollution. To guarantee there is a helpful domain for the microorganism to grow well, additional care must be taken since these microorganisms are exceptionally delicate to the encompassing temperature and pH (Ahmad et al., 2003). However, the problem faced by the open system is the liberation of methane gas freely to the atmosphere and this will slowly cause the ozone layer to be thinner and eventually cause a greenhouse effect. Although these processes only require a small capital and operational energy, the drawback is that these processes have a longer retention time which is in the range of 20–60 days and a large area is needed for the process to be operational (Loh et al., 2013; Wu et al., 2010; Choi et al., 2013; Yejian et al., 2008). The changes from open anaerobic system to the closed anaerobic system has drawn many changes towards the regulatory standard. Furthermore, the process will not only reduce water pollution additionally biogas freed and gathered from the closed system can be utilized as fuel for electricity generation (Chotwattanasak and Puetpaiboon, 2011) and palm oil mills could obtain carbon credits as revenue by the full utilization of methane gas as a sustainable and environmentally friendly power vitality from the anaerobic processing of POME (Poh and Chong, 2009). In anaerobiosis process, different sorts of reactor setup like closed-tank anaerobic digester, open digester tank, or covered lagoon have been broadly used to treat POME (Wang et al., 2015). A hybrid system has been used to ensure lesser processing time and higher efficiency, which combines the conventional method with the alternative method such as up-flow anaerobic sludge blanket (UASB) (Khemkhao et al., 2011), anaerobic filter (Bello and Abdul Raman, 2017), anaerobic fluidized bed rector (AFBR) (Borja and Banks, 1995), sequencing batch reactor (SBR) (Chan et al., 2011), expanded granular sludge blanket (EGSB) (Yejian et al., 2008), up-flow anaerobic sludge fixed-film reactor (UASFF) (Najafpour et al., 2006) and rotating biological contactors (RBC) (Najafpour et al., 2005) have been studied. The hybrid methods managed to reduce the hydraulic retention time on a laboratory scale. The discharge POME from the factory must meet the standard requirement provided by the Environmental Department accordingly to the countries itself. The transition of treatment method is mainly due to the changing restriction from the DOE thus making the conventional method outdated and cannot fulfill the new requirement such as the BOD discharge limit has been reviewed from 100 mg/L down to 20 mg/L for Malaysia (Tabassum et al., 2015). Table 3 shows the latest palm oil mill discharge standard for Malaysia, Indonesia and Thailand. 5. Alternative Palm Oil Mill Effluent (POME) treatment technologies In the palm oil industry, 5-7 tonnes of POME is generated with the production of 1 tonne of palm oil. Almost half of the water utilized in the production of palm oil will be POME (Ahmad et al., 2003). The POME treatment is urgently needed,

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especially with the use of alternative method. This is because, biological treatment such as aerobic treatment, anaerobic and facultative pond effluent requires a long retention time and requires a large area (Metcalf, 2003) in addition to requiring a lot of energy for ventilation (Doble and Kumar, 2005). Biological treatment requires microorganism which is certainly very sensitive to changes in weather and temperature. The optimum environment is also required to carry out this treatment process. In addition, these microorganisms will also release biogas which smells like methane and hydrogen sulfide. Thus, biological treatment techniques can derive a negative impact on the environment other than not effective in terms of time and cost performance. Since the conventional method nowadays become out of the league, a new method to treat POME is emerged. The possibility of POME treatment can always be improved by using physicochemical treatment and membrane filtration (Wu et al., 2009). Over the year, alternative methods to treat the POME such as adsorption (Said et al., 2016), coagulation/flocculation (Bhatia et al., 2007a), advanced oxidation processes (AOPs) (Parthasarathy et al., 2016a; Saeed et al., 2016a, b) and membrane filtration (Ahmad et al., 2005a; Mohammad et al., 2009) has been examined by researcher to carter the drawbacks from the ponding or lagoon system for the POME treatment. Despite it is still running on a laboratory-scale, it has shown a good potential compared to the conventional method. In addition, to support the statement that an alternative method for POME treatment is in demand, 90% of publications about POME for the past 2 years are all about the POME alternative treatment technology (Bello and Abdul Raman, 2017). (a) Coagulation/flocculation treatment Other than biological treatment, the physicochemical treatment is also being used to treat POME. The physicochemical treatment uses a chemical such as coagulants and flocculants that mainly focuses on the separation of colloidal particles. Diverse physicochemical treatment processes have been used to treat the POME, but this process will require a very high amount of chemicals and there is no process could be used alone on a commercial scale. These chemicals will amend the physical state of colloid, which allows them to remain in an indeterminately stable form thus forming a particles or flocs (Wu et al., 2010). Ferric chloride, aluminum chloride, aluminum sulfate (alum), polyaluminium chloride (PAC), ferrous sulfate and hydrated lime are the most utilized coagulant nowadays in light of its perceive execution, proficiency, economy, and usability based on the wastewater treatment (Edzwald, 1993). Alum and PAC, compared to the other chemical are being used globally because it is cheap and can be retrieved easily (Keeley et al., 2014). The usage of coagulant and flocculant eventually will separate the suspended solid portion from the POME thus making the POME easier to be filtered with less tendency of using a high-pressure process and flux. Since the usage of large amount of chemicals to treat POME is costly, a natural-based coagulant/flocculant such as chitosan and Moringa oleifera or can be known as horseradish tree have been studied for the POME treatment application. In terms of cost and treatment performance, chitosan has shown a promising potential that it has better performance compared to alum and PAC (Ahmad et al., 2006b). Moreover, the chemicals are not biodegradable and will give negative effects. As one of the solutions, biodegradable and natural chemicals is being used to replace the common one (Ang et al., 2016; Nourani et al., 2016; Bhatia et al., 2007b; Shak and Wu, 2014). However, the usage of coagulation or either flocculation is always being used as a pre-treatment. It is because, in a wastewater treatment, the usage of coagulation/flocculation method is capable to reduce the TSS of the wastewater thus making it easier to be process in the next stage. A combination of micro-bubble flotation and coagulation method has been experimented by Poh et al. (2014) for the treatment of anaerobically treated POME. The reduction in TSS, oil and grease, COD and BOD was 57.3%, 74.5%, 53.7% and 77.0% respectively. By using PAC as the coagulant, the bubbling time was set for 12.5 min with a flowrate of 19.8 L/min. Microbubble flotation was modified from dissolved air flotation (DAF) with the pore size of 100 µm and 10 µm respectively. With a smaller bubble size, a larger surface area and longer residence time can be provided thus increasing the efficiency to oil and suspended solid in wastewater (Parmar and Majumder, 2013). Previously, it is being reported that the combination of DAF method with coagulation addition has the ability remove more than 90% of suspended solid (SS) and oil from wastewater (De Nardi et al., 2008; Liu et al., 2010; Li et al., 2007). The usage of only single coagulation process to treat the POME has been done by Shak and Wu (2015). They combined the usage of alum and extracted natural seed gum to treat the raw POME which the results are slightly similar when using only alum that is 81.58% for suspended solid reduction while 48.22% for COD reduction. Previously by using a natural coagulant, Moringa oleifera for POME pretreatment process, a reduction of COD and SS up to 52% and 95% respectively has been recorded by Bhatia et al. (2007c). On the other hand, the same range of reduction has been retrieved when applying mixture of Moringa oleifera with chemical flocculants NALCO 7751 in which the reduction was 52.5% for COD and 99.3% for TSS. (b) Adsorption treatment Other than coagulation/flocculation method, an adsorption method is one of the alternative methods which is being utilized by researchers to treat the POME. Adsorption treatment also is being considered as a physicochemical treatment. Apart from being unique, these process has been used widely for a wastewater treatment because it is an environmentalfriendly process (Ahmed et al., 2015). Chitosan, barley waste, citrus peel, coconut shell carbon, activated carbon (AC), zeolite, bentonite/organo-clay and fly ash are among the common adsorbents used to remove oil and grease including heavy metals from wastewater (Shavandi et al., 2012a,c). Apart from that, there are other alternatives for adsorbents such as wood sawdust (Sciban et al., 2007), palm kernel fiber (Ofomaja, 2010), garlic peel (Hameed and Ahmad, 2009). The usage of adsorption

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technique alone has been applied for the POME treatment. Particularly, adsorption is being used for the removal of residual oil (Ahmad et al., 2005b), suspended solids (Ahmad et al., 2005c) and heavy metals (Shavandi et al., 2012b) from POME. A study using chitosan as adsorbent in treating POME has been conducted by Ahmad et al. (2005a). He reported that the usage chitosan has removed 97%–99% of residual oil in POME. However, the TSS of the sample was removed prior to oil removal treatment. While in 2014, Mohammed et al. has conducted an experiment by comparing the usage of only adsorption process with combination of magnetic field and adsorption process to treat the treated POME. Activated carbon was chosen as the adsorbent. The results were reduction in color, TSS and COD up to 57.11%, 61.11% and 67.87% respectively for a single adsorption process while 79.303%, 98.455% and 98.99% respectively for a combination of magnetic field and adsorption process. Adsorption process will cause either physical (physisorption) or chemical interactions (chemisorption) between the adsorbent and the adsorbate (Bello and Abdul Raman, 2017). These interaction will bind the unwanted substances to the absorbent and later out from the system. Fu and Wang (2011) stated that, adsorption is a reversible process, in which will offer the possibility of regeneration of adsorbent through desorption process. Shavandi et al. (2012a, c) has investigated the usage of natural zeolite as an absorbent to remove Fe(III), Mn(II) and Zn(II) from POME. They reported that the removal of Zn(II) and Mn(II) was more than 50% each while for Fe was about 60% from POME. The natural zeolite used was clinoptilolite with composition of clinoptilolite (84%), cristobalite (8%), plagioclase (4%), lillit (4%) with a trace amount of quartz. In 2015, Alkhatib et al. has studied the usage of palm kernel shell (PKS) as an adsorbent to remove the color pigment from treated POME. Under an optimum condition, the removal was up to 89.95% and increasing as the contact time and adsorbent dosage increased while decreasing with increasing pH. A study using montmorillonite as an adsorbent to treat palm oil mill effluent (POME) has been conducted by Said et al. (2016). By mixing 5 g/L of adsorbent with POME under 300 rpm for 90 min, the removal of COD, TSS and color reached more than 95% for all the listed parameter. In the work of Adeleke et al. (2017), cow bone powder (CBP) composite was used to treat the COD and ammoniacal nitrogen inside POME; their findings showed that the highest removal of COD and ammoniacal nitrogen was 89.6% and 75.61% respectively. AbdulRahman et al. (2016) has reported that the CBP can be used as an alternative source of activated carbon because of its efficiency. (c) Advance Oxidation Process (AOP) treatment Advanced Oxidation Process (AOP) is the process for generation of strong and responsive hydroxyl radical (OH·) that can degrade organic pollutants under 2.8 eV (Chou et al., 1999). AOP can be classified either as photochemical or nonphotochemical process which rely solely on the process such as the photochemical group that are resulted from direct photolysis by UV light, UV/H2 O2 , UV/TiO2 , photo-Fenton and photo-Fenton-like process while non-photochemical group resulted from ozonation and Fenton process (Carra et al., 2016). Fenton’s reagent in which is a solution of hydrogen peroxide with ferrous iron as catalyst has been considered as a potential tool in the wastewater treatment (Saeed et al., 2015). In 2015, Saeed et al. has conducted an experiment on the usage of central composite design (CCD) which is the Response Surface Methodology (RSM) module to optimize the operating parameters of Fenton process to treat the treated POME before it being release into water body. The highest result recorded was the reduction in color and COD up to 97.36% and 91.11% respectively with pH 3.5 and 30 min of reaction time. While in 2016, Saeed et al. has once again conducted the same experiment but this time he is using high concentrated POME, which is being retrieved after the biological pre-treatment in an open pond. COD was reduced up to 85% at an optimum condition with pH 3.5 and 90 min of reaction time. Based on the obtained result, although this experiment is still on a laboratory scale, it has shown great potential in which can be further utilized and extended for industrial-scale. A study by combining adsorption method with the advanced oxidation method has been done by Parthasarathy et al. (2016b). He combined the usage of activated carbon (AC) adsorption with ultrasonic cavitation (US cavitation) to treat POME. It was recorded that the simultaneous process of both AC adsorption and US cavitation hybrid system has achieved 73.08% COD and 98.33% TSS removals. On the other hand, by dividing both process and put them in order with US cavitation followed by AC adsorption has reduce the COD and TSS of the sample up to 100% and 83.33% respectively. Ng and Cheng (2016) has conducted an experiment on the usage of UV responsive ZnO photocatalyst to treat the POME. It is recorded that the reduction of COD was up to 50% with 1.0 g/L ZnO loading and after 240 min of UV irradiation. Recently, tungsten trioxide (WO3 ) starts to gain attention due to its ability to absorb either visible or UV lights with a band gap energy in the range of 2.5–3.0 eV (Shukla et al., 2016). Thus, it has attracted the attention of Cheng et al. (2017) to study the usage of photocatalytic method using WO3 to treat POME but focusing on COD, pH and color intensity. The recorded result was removal of 51.15% of COD and 96.21% of decolorization while maintaining the pH at 7. On the other hand, Bashir et al. (2017) has conducted a study on the usage electro persulphate oxidation system for the POME treatment. This system was performed using the combination effects of electro-oxidation, electrocoagulation and electro-floatation. The result was reduction in COD, color and TSS up to 77.70%, 97.96% and 99.72% respectively. Even though the POME used was biological treated POME, the result has shown a promising future for the system. (d) Membrane treatment Membrane filtration is one of the most leading methods that is being used to treat POME. The process of separation by membrane filtration technique is one of the effective treatment of POME. This is because the use of membrane filtration process has several advantages which include using less energy, environmentally friendly, easy to operate and does not require much space. Process membrane will become an important tool for improving the water quality (Nusbaum and

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Fig. 4. Technique used by Ahmad et al. (2003) to treat POME.

Fig. 5. Technique used by Ahmad et al. (2006a) to reclaimed water from POME.

Fig. 6. Technique used by Shah and Singh (2003) to treat POME.

Reidinger, 1980). In addition, membrane filtration can be applied across wide range of industries; the quality of treated water is more consistent regardless of influent variation; it can be used in a process to allow the recycling of selected waste streams within a plant; highly skilled operators would not be required since the plant can be fully automated (Cheryan and Rajagopalan, 1998). Recently, membrane separation and filtration has made a remarkable emergence in the industry and concerned an extraordinary attention due to its ability to eliminate an enormous volume of chemical and microorganism from wastewater (Judd, 2011). The advantages of utilizing membranes in water treatment including producing reliable and high-quality water other than simply require a basic arrangement for membrane filtration (Ahmad et al., 2005a). However, filtration through membrane technology also does not always perfect. This is because the membrane permeation flux will decline because of impurities. Impurities will cause clogging or fouling in the membrane pores. In addition, this phenomenon will cause a short life expectancy of the membrane and the costs for membrane cleaning process is also quite high (Metcalf, 2003). The membrane will be damaged due to the frequency of cleaning the fouling hardly (Maartens et al., 2002). As a result, modification of the membrane surface to a more hydrophilic nature can be applied (Ahmad et al., 2005a). In addition, ultrafiltration process is widely used in the refining industry due to its effectiveness. Due to the ultrafiltration process is able to filter out suspended solids and bacteria conveniently, ultrafiltration membranes are used to filter POME. The combination of biological treatment with ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes in treating municipal wastewater was studied by Rautenbach et al. (1996) where 97% water recovery was achieved. In 2003, Ahmad et al. have conducted a study on the use of membranes to treat POME. But in his study, the use of membrane has been coupled with other techniques as a pre-treatment process such as coagulation, sedimentation, and adsorption as the first stage. For the second stage, ultrafiltration and reverse osmosis membranes used in the treatment of POME (Fig. 4). The result obtained is a reduction in turbidity, BOD and COD were 100%, 98.8% and 99.4% of treated and water pH is 7. Ahmad et al. (2006a) reported that the combination coagulation/flocculation treatment with membrane separation to treat POME has successfully reclaimed 78% of drinking water from POME (Fig. 5). By using an Polyvinylidene Fluoride (PVDF) membrane as a medium, reduction of COD, total dissolved solid, organic nitrogen and ammonia nitrogen is up to 99% for POME treatment. Shah and Singh (2003) has conducted a treatment of POME by using centrifugation technique as the pre-treatment process and using hollow fiber polyethersulphone (PES) membrane as the second treatment (Fig. 6) The result obtained for COD, color and suspended solid and turbidity is reduction by 89.9%, 92.9%, 99.4% and 97.9% respectively. The values are comparable to research done by Ahmad et al. (2003) together with Fakhru’l-Razi and Noor (1997).

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Fig. 7. Technique used by Yejian et al. (2008) to treat POME.

In a study using polysulphone ultrafiltration membrane, reduction on the reading of TSS, turbidity, TDS, and COD were 97.7%, 88.5%, 6.5% and 57.0% (Wu et al., 2007). Pre-treatment methods are often used to help optimize the operation of the membrane. However, the main aim of this experiment is to retrieve protein and carbohydrate contain inside POME. This study also focuses on the effect of pressure on membrane fouling. The method of combining conventional method with alternative method always show a better result compared to the isolation of both treatments itself. These are due to the efficiency of both processes to treat POME hence a better result obtained. Yejian et al. (2008) have conducted a study on the integration of biological method and membrane technology in treating POME. The biological treatment used is using anaerobic EGSB bioreactor and aerobic inner-circulation biofilm-reactor. However, the difference in this experiment is it comprises of a series of ultrafiltration membrane and RO membrane (Fig. 7). The average COD removal efficiency in the first stage that is biological stage is 93%. It is also reported that after the treatment using a membrane, the suspended solid and color of the POME were undetectable. A research by Ahmad et al. (2009) has been conducted using a membrane bioreactor to treat POME. This hybrid process consists of an anaerobic, anoxic and aerobic reactor in series. The membrane used in this research was chlorinated polyethylene. The same method of experiment has been done by using a mechanism which is membrane bioreactor conducted by Xing et al. (2000) and Chang et al. (2001) that shows a promising result for POME treatment. The removal of COD, TSS, nitrogen, phosphate that is 94%, 98%, 83% and 64% respectively has been reported. Azmi et al. (2012) has conducted a study on the treatment of POME using a sandwich membrane. This treatment involving ‘green’ pre-treatment prior to filtration using a membrane. The example of green treatment used is sand-filtration and chitosan-based coagulation– flocculation. It is reported that the reduction in suspended solid, BOD and COD was 79%, 95%, and 95% respectively. Shamsuddin et al. (2013) has conducted a study on the usage of a membrane solely to treat POME. The membrane used is Epoxidized Natural Rubber/Polyvinyl Chloride (ENR/PVC) with cellulose and cellulose grafting polymethyl methacrylate (Cell-g-PMMA) as a filler. The combination of ENR and PVC have the potential to produce good and does not require supports membrane. The thermoplastic blends of ENR/PVC have been widely studied due to both of this polymer are compatible with and the original properties of polymer can be enhanced (Margaritis and Kalfagou, 1987; Varughese et al., 1988; Ramesh and De, 1991; Ibrahim and Dahlan, 1998; Ratnam and Zaman, 1999; Ibrahim, 2000) Cellulose has a low mass, high strengthening effect and good thermal stability in a variety of materials that can be used in cars and buildings (Thakur et al., 2014). Based on the studies it is reported that ENR/PVC with 20% cellulose composition as a filler and ENR/PVC with 10% cellulose grafting polymethyl methacrylate as a filler showed the highest decolorization. This shows that the usage of membrane solely can remove some of the organic material contained in POME. In 2014, Azmi & Yunos has conducted an experiment by using an ultrafiltration membrane to treat POME. However, the treatment process is being coupled with adsorption treatment as pre-treatment. The membrane used in the experiment is flat sheet regenerated cellulose (RC) membrane. Adsorption treatment was initially applied before ultrafiltration of POME to reduce the sludge and particles in POME. This step is being done to avoid fouling on the membrane surface. The result reported for the pre-treatment process is a reduction in total solid, dissolve solid, suspended solid, BOD5 , COD and turbidity up to 67.30%, 47.11%, 71.26%, 63.23%, 42.38% and 63.63% respectively. After being treated with ultrafiltration membrane, a better quality of POME was obtained. Ultrafiltration membrane has been widely tested to use for the purpose of desalination and water reclamation from either municipal waste or industrial waste. The comparison of the conventional method and alternative method as general are expressed in Table 4. 6. Conclusion Palm oil industry is an emerging industry that causes massive pollution of waste if not treated well. This industry has caused an undisputable source of pollution. These negative impacts should be counter with wise actions and regulations. Since the early stage of palm oil industries, there is laws and requirement that the industry needs to obey to ensure that no significant effect will occur impromptu. However, as the palm oil industries getting expands due to the demand from the world market, the scenario of discharging the waste into the water stream, river and drain increased. Although there is a method such as aerobic and anaerobic treatment being used to treat these liquid waste, yet, it is still cannot meet the standard required by the authority. These methods contain deficiency such as requiring a large area to operate and high time retention. On the other hand, this method also releases CH4 and CO2 gas and this phenomenon will cause a greenhouse effect. The development of new methods as alternative ways to treat POME is always be sought. Physicochemical is one of the alternative methods used to treat POME. Even though this method has shown a great potential, the usage of coagulant,

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Table 4 Comparison of conventional and alternative method for POME treatment. Advantages

Disadvantages

Reference

Aerobic

High BOD expulsion efficiency and great Aeration process require high Najafpour et al. (2005), Oswal et al. (2002), effluent quality, able to diminish pathogens energy, improper for land utilization, Leslie et al. (1999) and Doble and Kumar from waste, hydraulic retention time is requires periodic check-up (2005). short, practical to control toxic waste

Anaerobic

Cheap, simple design, stable and reliable system, low operating cost, recovered sludge utilized as fertilizer, low energy requirement

Required extensive land use, high sludge accumulation, hydraulic retention time is high, slow start-up

Yacob et al. (2006a, b), Metcalf (2003) and Borja et al. (1996).

Coagulation– flocculation

Quickest path to reduce organic load from POME, varieties of coagulant and flocculant readily available, simple and economical

Sensitive to pH changes for formation of floc and performance of coagulant, sophisticated operation, usage of chemical

Nik Norulaini et al. (2001), Boisvert et al. (1997), Ndabigengesere and Narasiah (1998), Xie et al. (2011), Rattanapan et al. (2011) and Aygun and Yilmaz (2010).

Adsorption

Environmental friendly, low production expenditure, easy process, high efficiency

Need a post treatment, used adsorbents are hard to be disposed

Ahmed et al. (2015), Hadi et al. (2015) and Pitakpoolsil and Hunsom (2013).

Advanced Oxidation Process (AOP)

AOP non-selectively react with most organics, ability to degrade highly defiant compound, easy to be applied.

High operating cost, use a lot of chemical, excessive sludge generation

Adeleke et al. (2017), Bello and Abdul Raman (2017), Glaze et al. (1987) and Saeed et al. (2015)

Membrane

Excellent efficiency of pollution removal, low labor cost, required small area

High maintenance cost, high pressure is required, fouling, short life expectancy

Abdurahman et al. (2011), Fakhru’l-Razi and Noor (1999), Ahmad et al. (2006a) and Metcalf (2003).

flocculant and adsorbent on a commercial scale will be huge and expensive thus making the treatment impractical and uneconomic. For a single process, physicochemical method cannot solely treat the POME, thus by utilizing this method as pre-treatment and coupling the method with other methods will help to increase the efficiency of the treatment. Advance Oxidation Process is one of the alternative methods that emerge in demand of the POME treatment. With varieties of process to be chosen either photochemical or non-photochemical, this process has shown a potential result in treating wastewater and POME. A combination of this method with other methods will enhance the outcome results of the treatment. On the other hand, membrane technology has concern a great attention to treat municipal waste and for desalination purpose. Palm oil industry is no exception to the membrane in the treatment of POME. At the early stage, a combination of conventional method with membrane filtration is being used to treat POME. Surprisingly, the result of the treated waste is encouraging. A great deal of research has been devoted in promoting or utilizing the usage of the membrane in either water reclamation, desalination or POME treatment purpose. Generally, all of the method discussed previously is undoubtedly has shown a great result on a laboratory-scale. Scaling up from laboratory-scale to industrial-scale will be challenging but substantial towards sustaining the environment and ecosystem. References Abdullah, N., Sulaiman, F., 2013. The Oil Palm Wastes in Malaysia. AbdulRahman, A., Latiff, A.A.A., Daud, Z., Ridzuan, M.B., D, N.F.M., Jagaba, A., 2016. Preparation and characterization of activated cow bone powder for the adsorption of cadmium from palm oil mill effluent. IOP Conf. Ser.: Mater. Sci. Eng. 13, 12045. Abdurahman, N.H., Rosli, Y.M., Azhari, N.H., 2011. Development of a membrane anaerobic system (MAS) for palm oil mill effluent (POME) treatment. Desalination 266, 208–212. Adeleke, A.O., Latif, A.A.A., Al Gheeti, A.A., Daud, Z., 2017. Optimization of operating parameters of novel composite adsorbent for organic pollutants removal from POME using response surface methodology. ECSN. Adnan, H., 2013. National Palm Oil Standard Soon. The Star. Kuala Lumpur. Afriyanti, D., Kroeze, C., Saad, A., 2016. Indonesia palm oil production without deforestation and peat conversion by 2050. Sci. Total Environ. 557–558, 562–570. http://dx.doi.org/10.1016/j.scitotenv.2016.03.032. Agamuthu, P., Tan, E.L., 1985. Digestion of dried palm oil mill effluent by cellulomonas species. Microbios Lett. 30, 109–113. Ahmad, A.L., Chong, M.F., Bhatia, S., Ismail, S., 2006a. Drinking water reclamation from palm oil mill effluent (POME) using membrane technology. Desalination 191 (1–3), 35–44. Ahmad, A.L., Ismail, S., Bhatia, S., 2003. Water recycling from palm oil mill effluent (POME) using membrane technology. Desalination 157 (1–3), 87–95. Ahmad, A., Ismail, S., Bhatia, S., 2005a. Ultrafiltration behavior in the treatment of agro-industry effluent: Pilot scale studied. Chem. Eng. Sci. 60 (19), 5385–5394. Ahmad, A.L., Sumathi, S., Hameed, B.H., 2005b. Adsorption of residue oil from palm oil mill effluent using powder and flake chitosan: equilibrium and kinetic studies. Water Res. 39, 2483–2494. Ahmad, A.L., Sumathi, S., Hameed, B.H., 2005c. Residual oil and suspended solid removal using natural adsorbents chitosan, bentonite and activated carbon: a comparative study. Chem. Eng. J. 108, 179–185. Ahmad, A.L., Sumathi, S., Hameed, B.H., 2006b. Coagulation of residue oil and suspended solid in palm oil mill effluent by chitosan, alum, and PAC. Chem. Eng. J. 118, 99–105. Ahmad, Z., Ujang, Z., Olsson, G., Latiff, A., 2009. Evaluation of hybrid membrane bioreactor (MBR) for palm oil mill effluent (POME) treatment. Int. J. Integr. Eng. (Issue Civ. Environ. Eng.) 17–26. Ahmed, Y., Yaakob, Z., Akhtar, P., Sopian, K., 2015. Production of biogas and performance evaluation of existing treatment processes in palm oil mill effluent (POME). Renewable Sustainable Energy Rev. 42, 1260–1278.

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