Keywords

1 Categories and Types of Biomass Resources in Malaysia

Biomass is extremely valuable for the generation of new, structurally complex, bioactive compounds, and clean energy sources. Biomass-dendromass and phytomass of lignocellulose is a natural material consisting of complex heterogeneous cell-structured macromolecules (lignin, hemicellulose, and cellulose) and various organic and inorganic structures of low molecular weight [1]. Biomass can be considered into several main types; agricultural biomass (phytomass grown on agricultural land), forest biomass (firewood, residual from forestry and wood industry), and residual biomass (by-products of agriculture and manufacturing industry) [2]. Malaysia is a tropical country (warm and wet weather year-long) that has large areas of natural arable land for crop production. The annual production of important crops including the plantation in Malaysia is presented in Table 1. Major biomass resources in Malaysia can be categorized into different sectors: residues from agriculture (palm oil mill waste, paddy straw, rice husk, banana stems, sugarcane bagasse, etc.), forestry (wood from pulp, paper industries, and logging activities), and municipal waste (Fig. 1). In line with the major crop produced in Malaysia, oil palm biomass contributes the largest amount of biomass. Each year about 168 million tonnes of biomass is generated in Malaysia as a prospective bioenergy resource and long-term solution to the nation’s energy demand [3].

Table 1 Production and planted area of important crops in Malaysia 2019
Full size table
Fig. 1
figure 1

Biomass availability in Malaysia [9]

Full size image

Palm oil is majorly produced in Malaysia and served as a long-term agriculture investment in Malaysia [8]. Substantial total agricultural wastes in Malaysia are derived from oil palm plantations [9]. The lignocellulose of oil palm wastes can be converted into value-added products, for example, glucose which could be further fermented into biofuel. Presently, feedstocks of cellulose-based biomass for conversion into biofuels are larger in volume than any other carbohydrate source. Lignocellulose biomass refers to plant materials that are mainly composed of cellulose and hemicellulose that are bound together by lignin (Fig. 2). Each year, the production of rice in Malaysia (Kedah, Penang, Perak, Kelantan, Selangor, and Terengganu) is approximately up to 75% to supply local demand with the remaining sourced out from Southeast Asia countries such as Thailand, Vietnam, and Indonesia [11]. Rice cultivation activities are expected to grow due to increased demand and population. Rice producing industry generates three main by-products: rice straw, rice husk, and rice bran. When the grain had been harvested, the rice straw became the vegetative residue. Rice husk is the hard-protecting coating of grains that is broken up from the brown rice grain. Rice bran is the residues from the milling process that has been the profitable vegetative waste as a protein supplement in livestock farms. In contrast with rice straw and rice husk wastes remain unutilized. On the other hand, sago is also deemed to be one of the most potential feedstocks for the production of value-added products. In brief, sago hampas is a solid by-product resulting from the sago starch extraction process. It is made up of 58% of starch, 32% of cellulosic materials as well as 4% of lignin [12, 13]. It is interesting to mention that the considerably low amount of lignin content in sago hampas suggests no pretreatment process is required before fermentation. Several studies identified sago hampas as a substrate for the production of sugars [14, 15], bioenergy, and biofuels, including biohydrogen [12], bioethanol [16], biobutanol [17], and bioelectricity [18, 19].

Fig. 2
figure 2

The simplified general plant cell wall structure [10]

Full size image

1.1 Palm Oil Industry

The commercial oil palm (Elaeis guineensis) cultivated in Malaysia originated from Africa. It was introduced into Malaya (later named Malaysia) in 1875 as an ornamental plant and only in 1917; it was first cultivated for commercial purposes in Tennamaran Estate, Kuala Selangor [20]. Since the 1960s, oil palm plantings in many parts of the world including Malaysia have seen significant expansion (Fig. 3). Over the past 50 years (1970–2018), the production of palm oil on the world market has been 35 times higher and the consumption in producing countries themselves has also increased dramatically [21]. Malaysia is the world’s second-largest palm oil producer and the largest exporter in the international market [22]. Malaysia’s palm oil production is almost 50% of the world’s total production (crude palm oil and palm kernels oil) and the industry also produces millions of tonnes of residues or by-products which contain valuable resources yet to be fully utilized. Currently with about 5.9 million hectares of oil palm are cultivated in Malaysia, these plantations produce over 11.9 million tonnes of oil and more than 100 million tonnes of biomass residues per year [23]. This huge quantity of biomass includes the empty fruit bunch (EFB), pressed fruit fibre (PFF) or mesocarp fibre (MF), palm kernel shell (PKS), palm oil mill effluent (POME), oil palm trunks (OPT), and fronds (OPF). Until now the major portion of resources used is mesocarp fibre and kernel shells as main thermal energy sources in generating process steam and electricity in the palm oil mill. However, only 60% of these resources are used as fuel in boilers [24].

Fig. 3
figure 3

World major producers of oil palm (1960–2018)

Full size image

More than 10 million tonnes of EFB are generated from more than 30 million tonnes per annum of fresh fruit bunches (FFB) [23]. Only 10% of the EFB is used as mulching material to protect the soil surface, conserve soil water and nutrients and the rest are burnt in incinerators in the palm oil mills to produce bunch ash or dumped in areas adjacent to the mill which generate environmental problems such as air and odour pollution in the nearby localities [25]. Another barrier that hindered the use of EFB as mulching material is their bulkiness with high moisture content resulting in transportation difficulties [26]. OPF and OPT are other biomass generated in oil palm plantations. OPF is available daily during harvesting of ripe fruit bunches by pruning of fronds and is traditionally used as mulching materials in plantations. OPT becomes available during the felling of old trees and replanting of the oil palm trees every 25 years. Previously, the burning of the OPT was carried out for fast disposal until stringent open burning regulations prevented this method of trunk disposal. The OPT is shredded and left in the field to decompose naturally. Overall, much of palm biomass remains as waste and awaits commercial exploitation. The total production and possible uses of the palm biomass are presented in Table 2. Oil palm biomass enriched with holocellulose can be converted into fermentable sugars and subsequently used for various bioproducts (bioethanol, biomethanol, biohydrogen, polyhydroxyalkanoates, polylactic acid, and others).

Table 2 Production and potential uses of palm biomass for biofuels
Full size table

1.2 Rice Biomass

Malaysia has contributed 3.1 million tonnes of rice straw and 0.48 million tonnes of rice husk annually [27]. Rice straw is separated from the grains after being threshed either manually, using stationary threshers, or combined harvesters. The rice husk or rice hull is the coating on a seed or grain of rice. It is formed by hard materials comprising silica and lignin to protect the seed during the growing season. Each kilogramme of milled white rice resulted in approximately 0.2 kg of rice husk during milling and 1–1.5 kg rice straw depending on varieties, cutting height of the stubbles, and moisture content during harvest [28, 29]. Common products from rice husks are solid fuel (loose form, briquettes, and pellets), carbonized rice husk produced after burning, and the remaining rice husk ash after combustion.

1.3 Sago

Sarawak, Malaysia is known to be one of the largest sago starch exporters in the world which accounted for 55,000–65,000 tonnes/year [56]. With that matter, it has generated approximately 50–100 tonnes per day of sago hampas, especially in Sibu and Mukah division [57] and it is expected to exponentially increase over the year due to the demand. It is fascinating to note that due to the presence of lignocellulosic fibrous components in the sago hampas, it has been used as animal feed [58], mushroom culture’s medium [59, 60] as well as particleboard manufacture [61].

2 Biomass Characteristics and Compositions

In general, about 30–60% cellulose, 20–40% of hemicellulose, and 10–30% of lignin are available in different kinds of lignocellulosic biomass sources [62]. These differences within this range either for the same species or between different biomass would depend on the growing location, season, harvesting methods as well as analytical procedures used [63]. Cellulose and hemicellulose are carbohydrate polymers that are built up by long chains of sugar monomers. Therefore, they are potential sources of fermentable sugars but are not readily available for hydrolysis without pretreatment [64]. Lignin is a phenolic polymer in the plant cell walls. This compound binds cellulose and hemicellulose, imparts further strength, offers rigidity, and provides resistance against pests and diseases [65]. Besides these major constituents, the plant cell wall also contains pectic substances, proteins, waxes, cutin, suberin, and sporopollenin in smaller portions [66].

2.1 Cellulose

Cellulose is a linear polymer of homopolysaccharide (an unbranched polymer) composed of repeating glucose monomers that are linked together by β-1-4-glycosidic bonds or in short it is a highly crystalline polymer of glucose. The basic structure of cellulose is (C6H10O5)n. Based on structural characteristics, cellobiose is the repeating subunit in cellulose, in which each glucose unit is rotated 180º relative to its neighbour [67]. The individual cellulose chains are packed together and weakly bound through hydrogen bonding into ‘elementary fibrils’ [68, 69]. These ‘elementary fibrils’ about 3–4 nm wide (about 36 chains) are bundled together into organized parallel cellulose-fibrils called crystalline microfibrils which make up the core of a cellulose microfibril and are difficult to degrade [69]. Within the microfibrils, cellulose in plants is also found in the form of an amorphous structure, where the elementary fibrils are attached or cross-linked together by hemicelluloses, with the amorphous polymers of different sugars as well as other polymers such as pectin and covered by lignin [67, 69]. Generally, hydrolysis can reduce the cellulose to a cellobiose repeating unit (C12H22O11) and ultimately to a glucose (C6H10O5) unit by cellulase. The partial structure of a cellulose molecule is illustrated in Fig. 4.

Fig. 4
figure 4

Partial structure of cellulose molecules showing the β-linkage of glucose units [70]

Full size image

2.2 Hemicellulose

Hemicellulose, non-cellulosic structural polysaccharides, or sometimes also called polyose are branched heteropolysaccharides that exist in association with cellulose and lignin in the plant cell wall [62, 67]. Hemicellulose is composed of shorter chain polysaccharides which act as a linkage between lignin and cellulose. In general, hemicellulose may contain pentoses (β-D-xylose, α-L-arabinose), hexoses (β-D-mannose, β-D-glucose, α-D-galactose) and/or uronic acids (α-D-glucuronic, α-D-4-O-methylgalacturonic and α-D-galacturonic acids) [65, 69, 71, 72]. It is a low molecular weight compound that is much easier to hydrolyze than cellulose [62]. According to Miller et al. [67], hemicelluloses are typically composed of main-chain backbones of xylan which consists of β-1,4-linked-D-glucopyranose and β-D-mannopyranose units with α-1,6 galactose residues. Other non-cellulosic structural polysaccharides like arabinogalactan are also commonly found in the plant cell wall. Many side-chain constituents namely arabinofuranosyl, acetyl, feruloyl, and methylglucoronyl groups branch off the main backbone. The most important hemicelluloses are xylans and glucomannans, with xylans being the most abundant component of hardwoods and herbaceous plants [71]. Xylose is one of the major building blocks of hemicellulose or fermentable sugars present in lignocellulosic biomass and the second most abundant carbohydrate polymer in nature after glucose [73, 74]. Within the plant cell wall structure, the hemicelluloses are thought to coat the cellulose-fibrils resulting in reduced accessibility of the cellulose-fibrils. Therefore, pretreatment and enzymatic hydrolysis of the hemicellulose component is essential to facilitate complete cellulose degradation [65]. The sugar units of hemicelluloses are illustrated in Fig. 5.

Fig. 5
figure 5

Schematic illustration of sugar units of hemicelluloses [75]

Full size image

2.3 Lignin

Lignin is a phenolic aromatic macromolecule that is primarily formed by free-radical polymerization of ρ-hydroxy cinnamyl alcohol units with varying methoxyl contents commonly known as phenylpropane units [65]. The three monomeric unit precursors of lignin are based on: coniferyl alcohol, sinapyl alcohol, and ρ-coumaryl alcohol, and they vary among species [76] (Fig. 6). Lignin, in general, is an important structural component serving as a supporting agent and gives strength to the cell biomass. It glues together the other fractions in the complex phenolic polymers and assists in the resistance of biomass against microbial attack and decay [77, 78]. Therefore, lignin is considered an important barrier to polysaccharide utilization such as hydrolysis by cellulases. It is believed that the existence of strong carbon–carbon \(\left( {C - C} \right)\) and ether \(\left( {C - O - C} \right)\) linkages in lignin affect its susceptibility to chemical disruption.

Fig. 6
figure 6

Schematic illustration of building units of lignin [79]

Full size image

2.4 Empty Fruit Bunch: Production, Structural Characteristics and Uses

The EFB is abundant solid biomass or residue from the palm oil industry which are produced in large amounts from the FFB of oil palm. According to Tan et al. [39], FFB comprises 21% palm oil, 7% palm kernel, 14% PPF, 7% PKS, and 23% EFB. It has been estimated that for every kilogramme of palm oil produced roughly 4 kg of dry biomass is generated [80]. Hence, every year approximately 15 million tonnes of EFB are produced in Malaysia and about 37.7 million tonnes are produced globally [34]. In short, EFB is the largest residual product of the palm oil milling process. EFB is the residual bunch remaining after the reddish palm oil is removed from the FFB by the thresher during oil extraction [39]. The process flow of the palm oil mill demonstrates the types of oil palm biomass available and the EFB generated (Fig. 7) [54, 55, 80, 81]. The typical palm oil milling process in Malaysia is the wet process which uses a lot of water in the sterilization and extraction process.

Fig. 7
figure 7

Process flow diagram of fresh fruit bunch processing and biomass generation in palm oil mills

Full size image

The milling process generates vast amounts of wastewater effluent (POME) which are from three main sources, namely sterilizer condensate, sludge separator, and the hydro-cyclone [53]. Sterilization of FFB at high temperature (140 °C) under pressurized steam (0.28 MPa) for 75–90 min is the beginning stage of the milling process. The sterilization process introduces moisture into the nuts, causes the detachment of the kernel from the shell wall, and loosens kernels within their shells. The sterilized FFB is then fed into a rotary drum thresher for stripping the fruits and conveying the empty wet bunches called EFB to the dumping ground. EFB is categorized as fibrous crop residue or known as the lignocellulosic residue. EFB consists of almost 70% of water and 30% solids which comprise lignocellulosic materials [82]. Based on composition EFB is comparable to those of hardwoods (Table 3). The main components of EFB are cellulose, hemicellulose, and lignin. It is estimated that EFB is composed of 43–60% cellulose, 19–34% hemicellulose, and 12–24% lignin. Cellulose is a polymer of the hexose sugar glucose, while hemicellulose is a pentose sugar-containing mainly xylose.

Table 3 Chemical composition of empty fruit bunch, hardwood, and softwood
Full size table

These sugars can be used as substrates for the production of a wide variety of compounds by chemical and biochemical processes. Since the solid EFB bunches are rich in cellulose and hemicellulose that are cross-linked with lignin which is not easily decomposed, degraded, or hydrolyzed into their monomers, these bunches must be subjected to pretreatment involving physical, chemical, or biological processes to cleave the chains or dissolve the lignin before production of useful chemicals and biofuels.

2.5 Rice Husk and Rice Straw: Production, Structural Characteristics and Uses

A low bulk density rice husk is produced off-site during grain processing and is normally 20–25% of the overall weight of milled paddy [29]. A rice husk is yellowish in colour, convex shape, and consists of rigid materials such as opaline silica and lignin acting as seed protection. Rice husk has become a source for many silicon compounds, including silica (SiO2), silica carbide (SiC), silicon (Si), silica nitride (Si3N4) meanwhile for the chemical composition contains 74% organic and 26% of inorganic [88]. When rice husk is burned or carbonized rice husk is formed, it generates 17–26% of rice husk ash which is another important product that can be obtained from rice husk [89]. Table 4 shows the chemical composition of rice husk and Table 5 shows the composition of organic compounds in rice husk. Rice husk has a global potential as a renewable feedstock for the generation of biofuels. Moreover, the estimated additional revenue can also be improved by high calorific value lignin after the production of biofuels. Thus, rice husk is an excellent potential raw material, economical, and abundant source for future biofuels production and has the potential to provide a high yield of biofuels [90].

Table 4 Lignocellulosic composition of rice husk
Full size table
Table 5 The composition of the rice husk organic compound [95]
Full size table

Rice straw is a waste from the collection of rice grains. A substantial large quantity of waste and the fact that it is non-food, this lignocellulosic waste was promoted as a possible source of material for global ethanol production [96]. The quantity of straw that can be collected from year to year, such as the annual variability in straw production, the yield of straw varies greatly between regions and countries, the modern grain harvesting method, and also the cereal breeding directly towards the development of short stem varieties [97]. The processing of rice straw sugars by enzymatic reaction attracts manufacturing attention due to the light reaction conditions used and the fairly pure formulation of products [98]. The important components of the rice straw are cellulose, lignin, hemicellulose, phenol fraction, and silica [99]. Table 6 shows the composition of rice biomass and Table 7 is the characterization of monomers of each component. Components of lignocellulosic biomass are the polysaccharides that are built up by different types of monomers. To alter the structure of the polysaccharides, a pretreatment method is required to improve the accessibility of hemicellulose and cellulose in enzymatic hydrolysis or fermentation.

Table 6 Chemical composition of rice straw [100]
Full size table
Table 7 Characterize monomers of each component in rice straw [101]
Full size table

2.6 Sago Hampas: Production, Structural Characteristics and Uses

Generally, based on Table 8, sago hampas is made up of 58% of starch, 32% of cellulosic materials as well as 4% of lignin [12, 13]. The considerably low amount of lignin content in sago hampas and valued as energy feedstock since no pretreatment is needed before the fermentation process.

Table 8 Chemical composition of sago hampas
Full size table

3 Potential of Biomass Utilization as a Feedstock for Renewable Energy in Malaysia

Renewable energy alternatives in Malaysia are primarily solar, biogas, biomass, and mini-hydro. In the recent decades, the utilization of biomass as renewable feedstock increased as the Malaysian government implemented national policies and strategies such as the National Green Technology Policy (2009), National Renewable Energy Policy and Action Plan (2010), New Energy Policy (2010), Renewable Energy Act (2011) and National Biomass Strategy 2020 (2011) [102]. The objectives of these policies are to reduce the national dependency on fossil fuel and promote renewable energy initiatives to meet the national energy requirement that increases yearly which is projected will be 103 million tonnes of oil equivalent (Mtoe) by 2035 [103].

3.1 Government Assistance

Malaysia also pledged and assured to reduce its greenhouse gas emissions of Gross Domestic Product by 45% by 2030 under the Paris Agreement as compared to intensity in 2005 at the 2015 United Nations Climate Change Conference (COP 21) [104]. The recent report from IPCC [105] indicates that the global mean surface temperature which ranged from 1.8 to 4.0 °C would rise sharply in the next century and beyond if existing patterns of human activity are left unchecked. To achieve this voluntary target, an agency in Malaysia such as the Sustainable Energy Development Authority (SEDA) is responsible to execute the action plan to enhance the activity and project related to renewable energy by managing the implementation of the Feed-in Tariff (FiT) mechanism. Figure 8 exhibits that renewable energy generation from biomass is the second-highest contributor after solar photovoltaic from 2012 until 2018. This remarkable potential of biomass utilization in Malaysia should be increased in the coming years as Malaysia has abundant biomass resources that can be utilized to generate electricity.

Fig. 8
figure 8

Renewable energy generation projects that have achieved commercial operations since 2012 in Malaysia [106]

Full size image

3.2 Environmental Sustainability

In the eco-awakening era, the dramatic rise of concern towards the environment drives the Malaysian government to reduce its greenhouse gas (GHG) emissions from the palm oil industry through the Malaysian Sustainable Palm Oil (MSPO) certification scheme. Figure 9 shows the annual carbon dioxide emission reduction from the commercial operation of solar photovoltaic energy, biomass, biogas, and small hydro in Malaysia. A promising option for renewable energy from biomass is vividly seen as it records the second-highest carbon dioxide reduction after solar photovoltaic energy. The entire oil palm industry (plantation and mill operators) is mandatory to apply the MSPO scheme starting from 31 December 2019 [107]. Currently, 437 out of 455 palm oil mills (96.04%) in the country have been certified as MSPO compliant [108]. MSPO-certified palm oil mills are required to generate renewable energy sources to reduce national GHG emissions. With the vital principle of protecting the environment, the MSPO certification helps to promote and encourage all palm oil millers to generate electricity by their own produced solid biomass. This sustainable certification scheme should be extended to other agricultural sectors in Malaysia to initiate renewable energy from other crops such as rice straw, rice husk, landscape waste, and others.

Fig. 9
figure 9

Annual CO2 emissions reduction from renewable energy projects that have achieved commercial operations (2012–2018) in Malaysia [106]

Full size image

3.3 Biomass Availability and Logistic Facilities

The agricultural sector contributed 7.1% to the national Gross Domestic Product (GDP) in 2019 with oil palm being the largest contributor at 37.7% [109]. Hence, biomass from the agricultural sector is abundantly produced at the mill and available all year round. The main challenges to utilizing Malaysian biomass as a feedstock for biofuel are collection, transportation, and storage issues. For instance, OPF is the largest biomass produced during pruning in the oil palm plantation area. However, the OPF is not collected and transported out of the oil palm plantation [110]. Eventually, the OPF biomass is left for the plantation nutrient recycling purpose. Another case example is EFB which has a high moisture content of around 50–60%. The biomass undergoes a sterilization step in a digester at the beginning of the FFB processing in the palm oil mill. The water molecule from the steam is locked by oil residue and this contributes to the high moisture content of EFB. Consequently, this condition is very favourable for fungal degradation which caused a serious issue in further exploration of EFB utilization. The EFB is produced abundantly at the palm oil mill and needs to be transported rapidly to the operator or buyer. Some of the palm oil millers have shredded the EFB and increased their opportunity to sell the EFB to other parties. By referring to the module of other developed countries on this issue, for example in the United States, the facility of biomass drying, grinding and briquetting is centralized for a certain number of mills [111]. Therefore, the facility can be shared by the mills and it is considered a cost-effective strategy. This collective effort is essential to achieve the ideal cost of feedstock, quantity, and quality for the future of renewable energy from biomass.

3.4 Technology Feasibility

Lignocellulosic biomass is directly incinerated from the source as solid biofuel for electricity. The biomass power plant at Prolific Yield Palm Oil Mill in Sandakan, Sabah uses EFB as primary fuel with oil palm shells and mesocarp fibres as secondary fuels. The biomass power plant is capable of generating 12 Megawatt of electricity [112]. Meanwhile, liquid biofuel production requires a pretreatment step, saccharification, and fermentation. An efficient pretreatment method is required to release all monomers from lignocellulosic biomass for conversion into biofuels. The inefficiency of pretreatment conversion facility, core technology, and equipment shortage may hinder the production of biofuel. The pretreatment step and hydrolytic enzyme possess a domino effect on the subsequent steps in biofuel production, technically and economically [113]. Moreover, high energy consumption and high capital cost in the pretreatment process lead to the high risk of investment. In the Malaysian scenario, most of the small and medium enterprises (SMEs) in the oil palm industry are operating at a small financial budget and hardly venture into value-added bioproduct from the biomass [114]. Nevertheless, OPF juice exhibited a promising potential as a feedstock for bioethanol production as the OPF only required a pressing machine to obtain the juice and directly can be fermented into bioethanol [115].

4 Conclusion

The utilization of renewable bioresources has become a more promising technology due to the main concern of high dependency on non-sustainable resources. Biomass is one of the best potential candidates to be an alternative source for renewable energy. Hence, Malaysia is blessed with abundant biomass resulting from agricultural sectors, including oil palm, rice, and sago. The biomass generated from each sector has it is before fermentation which is further used in different applications. In this chapter, we have critically summarized each biomass produced from the oil palm, rice, and sago industry in Malaysia. Furthermore, we have details about individual biomass from respective agricultural industries, related to their production, structural characteristics as well as uses. In addition, we also have critically discussed other potential factors contributing to the utilization of biomass in renewable energy production in Malaysia. All in all, Malaysia is deemed to have a strong platform in implementing the biomass utilization strategy and further developing the next new era in renewable energy development.