Oil Palm Tree Wastes 1: Oil Processing and waste production
Published Date: 5th October 2020
Palms are plants belonging to the family Palmae and are usually of great size having an unbranched trunk crowned by either pinnate or palmate fronds. There are roughly one thousand palm species, with most of them growing in tropical or semi-tropical regions. The most popular species are the oil, date, and coconut palms, which are commodity crops all over east Asia, the Middle East, and the west and central parts of the African continent. The oil palm tree (Elaeis guineensis) is native to the tropical West Africa, where it originally grew semi-wild in grooves. From Africa, it was first introduced to the Asian countries of Malaysia and Indonesia in the 18th century, and from there to other Asian countries. Today, the oil palm is cultivated in 42 tropical countries of the world, over a land area of about 27 million acres. The wood, leaves, sap, and fruit of many species are important to the national economy of many tropical countries. The five major oil palm producing countries are Indonesia, Malaysia, Thailand, Colombia, and Nigeria.
Under plantation management, the crop takes about one year, from the time the seeds germinate and are planted in nursery bags to be transplanted to the field. In the field, however, new improved varieties begin to flower after less than one year of transplantation and produce their first bunches of fruit within two years. At a young age, the tree trunk grows about 35 to 75 cm per year and produces alternate rows of leaves, with the base of the old leaves surrounding the stem. Growth begins to slow down at the age of 12 to 15 years, by which time the fruit production has also slowed down. The semi-domesticated varieties in West Africa are however known to continue growing and producing fruits for more than 40 years. Approximately 60 percent of global palm oil is derived from privately or state-owned oil palm plantations, while the remaining 40 percent is produced by about 3 million smallholders, especially in Africa, who habitually obtain lower yields from poor yielding and wild varieties.
Palm oil and palm kernel oil are extracted from the oil palm fruit flesh and seed respectively. These oils extracted from the palm fruit serve as ingredients for numerous edible and personal care products, as well as feedstock for biofuels. Global production of oil palm has more than doubled in the last three decades to become the world’s leading fruit crop in terms of production. The global production of palm oil was around 72.27 million metric tons in the marketing year, 2019/2020, decreasing from approximately 74.02 million metric tons in the 2018/2019 marketing year. The global production is dominated by Indonesia and Malaysia, which together accounts for 85 – 90 percent of annual production (Figure 1). The palm oil sector is projected to grow further in the coming years, driven by a growing global demand for inexpensive edible oils and fats. This global demand, for its part, is aided by the crop’s superior yields, which are 5 to 10 times that of other vegetable oil crops, and coupled with its long shelf-life, desirable health properties, and versatility of applications. It is predicted that the global market value of the palm oil sector will experience a 5.7 percent compound annual growth rate (CAGR) from 2019 to 2024, reaching a total production of 107.6 million tons by 2024. To drive this growth in Africa, an estimated 3 million hectares (about 7.5 million acres) of land have been acquired by palm oil companies for intensive cultivation of the oil palm.
Nigeria is currently the largest producer of palm oil in Africa, while Benin is the largest exporter of the commodity from Africa in 2018, with Nigeria holding the sixth position on the list of palm oil exporting countries in Africa. The palm oil industry is therefore a major agro-based enterprise in Nigeria, especially in the southern parts where palm trees grow in the wild and in plantations. Approximately 80 percent of the palm oil industry in the country is dominated by smallholders who characteristically use labor-intensive, and semi-mechanized equipment for processing the palm fruits.
The major palm oil producing countries generate large amounts of biomass and liquid wastes, which constitute an environmental problem when disposed of indiscriminately or by the landfilling method. For example, in the big processing units, only the pericarp fiber is used as an energy source for heating the boiler, while the empty fruit bunches and the shell may be disposed of in landfills. Some factories also burn the empty fruit bunches in furnaces, with attendant air pollution. The huge volume of liquid waste generated from palm oil processing is also a major environmental issue, especially when channeled into freshwater bodies. There is an overall surplus of by-products during the palm oil production process, and their utilization rate is currently negligible, especially, the empty fruit bunch, and the liquid effluent. Several studies have however suggested different potential uses of these solid and liquid wastes, which have all been categorized as organic wastes that are environmentally degradable.
Oil palm fruit processing and wastes production
In the automated or semi-automated palm oil mills, oil palm fruit processing involves several steps (Figure 2). The fresh fruit bunches are first sterilized after which the oil fruits can be removed from the bunches. The empty fruit bunches are left as residues, while the fruits are pressed in the oil mills. The palm oil fruits are pressed to generate palm oil, while the kernel is separated from the press cake made up of the mesocarp fibers. The palm kernels are then cracked, and the kernels separated the shell, which also becomes a residue.
The kernels are further pressed in separate mills to produce the palm kernel oil, the remaining meal or cake serving as residue. In many small-scale operations, many of these steps are manually executed. Again, in rural Africa, where families may own just a few oil palm trees, the fruit bunch is usually processed to separate the fruits which are then sold to the village oil mills for further processing. In a typical palm oil mill, almost 70 percent of the fresh fruit bunches are turned into wastes in the form of empty fruit bunches, fibers, and shells, as well as liquid effluent. These by-products can be converted to value-added products or energy to generate additional profit for the palm oil industry. The major lignocellulosic biomass produced from the oil palm industries include the empty fruit bunches (EFB), palm pressed fibers (PPF), palm kernel shells (PKS), and palm oil mill effluent (POME), while wastes obtained from the palm plantation sites include the oil palm trunk (OPT), an oil palm frond (OPF) and pruning oil palm frond (POPF). The typical products generated from palm oil mills and their percentage distributions are shown in table 1, while the breakdown of the products and wastes from each bunch of fresh oil palm fruit is shown in table 2.
These data show that the empty fruit bunch, the palm oil mill effluent, and the pressed fiber are the major wastes derived from oil palm fruit processing. These oil palm fruit biomasses constitute environmental problems when left unutilized, and improperly disposed of, however, a lot of research efforts have been made to create value-added products from them. Presently in many African countries, palm oil mill residues remain unexploited as biomass feedstock even though they are readily available at the oil processing mills, and have low value at the mills.
Types and properties of oil palm wastesOil palm frond (OPF): In big plantations, the palm fronds are regularly obtained during regular pruning and fruit bunch harvesting, and when trees exceeding the economical age are felled. In these plantations, the pruning fronds are mainly used for inter-row mulching or burnt in the palm oil processing plant as fuel. In the West and Central African regions, components of the frond may be processed into household items such as brooms, baskets, woven tray, and fishing gear. The leaf is peeled off to produce the central part which serves as a broom, while all parts of the main frond are stripped and used in weaving baskets, trays, and even battle shields in olden times. The leaves are also important ruminant forage in the West and Central African regions.
Oil palm trunk (OPT): After felling, the OPT is usually left to decompose naturally at the plantation site, where they have been known to encourage the spread of diseases and insects like Rhinocerus beetles and Ganoderma mushroom that are harmful to the plantation. The OPT biomass residue has been used in early times as lumber for building houses in West Africa because of its durability. In Asian countries, however, a lot of commercial products are being developed from the oil palm trunk. For example, the OPT has been used as laminated veneer lumber, pulp for producing paper, bio-compost, and cellulose raw materials for producing panel products such as particleboard, medium-density fiberboards, mineral-bonded particle board, blockboard, and cement board in these countries. A transverse section of the trunk reveals different zones such as the back and cortex, peripheral zone, inner zone, and the central zone, with the characteristic brownish to blackish dots, which are believed to be the main components of the structural strength of the trunk. The fresh trunk is usually heavy due to its high moisture content, while the dry wood is lightweight. When felled, the sap from the trunk is usually tapped as palm wine in many West and Central African countries.
Empty Fruit Bunch (EFB): The empty fruit bunches are abundantly available as fibrous material in palm oil mills. In these mills, the EFB is usually saturated with water (67 percent moisture content) due to their biological nature, in addition to the steam sterilization process, they are subjected to during fruit separation. The EFB is therefore usually air-dried until the moisture content drops to about 40 percent before it is used as fuel in the palm oil processing plant. The ash generated from this process may be used as fertilizer in plantations or discarded in landfills. Open burning of the EFB although discouraged in recent times by environmental authorities, because the process causes air pollution is still practiced in most palm oil mills in Nigeria. Until recently, the ash generated from the burning of the EFB was a very important resource for the production of black soup in rural southern Nigeria. It also serves as edible ash for the preparation of several local dishes. The EFB can be used in oil palm plantations as a mulch, which is subsequently degraded by natural processes to organic fertilizer, which is then directly applied to the field. Malaysian companies have successfully generated power from EFB in small-scale power generation facilities. It also yields excellent pulp for paper production.
Palm Press fiber (PPF): The PPF is a major by-product of the oil press. In modern oil mills, the kernel and fiber are pressed together before separation, meaning that the product may contain some kernels and shells. The PPF is usually burnt in the palm oil processing plant as fuel, while the excess is discarded as waste. It may be blended with palm kernel shells to produce the power needs of the oil mill. Most small-scale oil mills in Nigeria, harness the PPF for their own energy needs. Several studies have reported the production of biochar or activated charcoal from PPF, for agricultural, health, and industrial applications. The fiber contains abundant carotenoids, vitamin E, and sterols. Therefore, minor products like phospholipids, vitamin E, and carotenes have been extracted from it for the production of nutraceutical products.
Palm kernel shell (PKS): Currently most of the press fiber and PKS are used as fuel for the milling process. The amount of energy that is needed for the milling process, both for heating and electricity can be combined with information on the efficiency of heat and power cogeneration at the mill. This gives insight into the amount of fiber and PKS needed for the milling process and the amount of fiber and PKS available for alternative applications. Researchers at the Federal University Owerri, Nigeria, have used PKS to produce feed grade ash as a mineral supplement, and activated charcoal used as additives in poultry feeds. PKS has also been enhanced through the pyrolysis method for conversion into biofuel in the form of manufactured pellets.
Palm oil mill effluent (POME): Large volumes of water are utilized in the processing of the oil palm fruit. This results in the production of large volumes of liquid waste known as palm oil mill effluent (POME). It is estimated that 72 – 80 liters of water is required to process one ton of fresh fruit bunches in the semi-mechanized process, with 72 – 75 percent of this water ending up as POME. The POME constitutes the waste from the final stages of palm oil production in the mill. It is a colloidal suspension comprising 95 – 96 percent water, 0.6 - 0.7 percent oil, and 4 – 5 percent total solids. It is often discarded in disposal ponds, resulting in the leaching of contaminants that pollute the groundwater, and soils, and in the release of methane gas into the atmosphere. When discharged into water bodies, it turns the water brown, smelly, slimy, and reduces the oxygen content of the water body, thereby leading to the death of fishes, and other aquatic organisms. Application of untreated POME on agricultural soils alters their physicochemical properties, causing undesirable decreases in pH, and increases in salinity of the soils.
A number of treatment technologies have been applied to the POME, including ponding, aerobic digestion, anaerobic digestion, and physicochemical treatments among others with varying levels of success. Liquid effluents from palm oil mills can be anaerobically converted into biogas which in turn can be used to generate power through gas turbines or gas-fired engines. The POME has also been used as a carbon source with little or no supplementation to produce feed grade yeast, with a reduction in its pollution potential. In Nigeria, smallholder farmers utilized POME in the feeding of their pigs, especially by mixing it with fibrous feed ingredients to improve their energy values.
Other uses of oil palm wastes: Both the oil palm trunk, frond, empty bunch, and press fiber can serve as substrates for the growth of edible mushrooms. Several Nigerian studies have utilized the empty bunch for the growth of oyster, Volvariella, Lentinus, and Ganoderma mushrooms. Ashes generated from the complete combustion of the empty fruit bunch, and palm kernel shell has been studied as potential mineral sources in animal feeds. Again, the treatment of POME essentially in some big oil mills employ anaerobic digestion of the effluent which is a major production step for biogas production. In Asia, some oil mills capture the biogas from their anaerobic digesters for use in electricity production. The milling of deshelled palm nuts to produce palm kernel oil also generates large quantities of palm kernel cake (PKC) or meal as a by-product. Research outputs on commercial utilization of PKC in animal feeding in Nigeria, and other oil palm producing countries are rich, thus making the product one of the few non-conventional feedstuffs that have been adopted by farmers in the feeding of different classes of livestock. Current literature suggests that several value-added products are being developed from the PKC.
Oil palm is a very important tropical plant that produces a vegetable oil of global importance. A sizable proportion of by-products form of the fresh fruit bunch are discarded as wastes in the form of empty fruit bunches, press fibers, kernel shells, as well as liquid effluent. Palm fronds and occasionally felled trunks are also generated in the oil palm plantation as wastes. Asian studies have shown that some by-products can be converted to value-added products or energy to generate additional profit for the oil palm industry. These studies have suggested different potential uses of solid and liquid wastes, especially in the production of fertilizer, animal feed, lumber, particleboard, and biochar among others.
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