MICROBIOLOGY, BIOCHEMICAL CHANGES AND BIOGAS PRODUCTION DURING BIODEGRADATION OF OIL PALM EMPTY FRUIT BUNCH
Oil palm is a tropical plant that grows in warm climate at altitudes below 500 meters above sea level. It came from the Gulf of Guinea in West Africa, which explains its scientific name, Elaeis guineensis Jacq. and its popular name, the African oil palm. In Nigeria, oil palm tree is widely grown and is a valuable economic crop that provides a source of employment and revenue to farmers.. It allows many small landholders to participate in the cash economy. Oil palm is a major source of edible oil which is extracted from fruits (Lua and Gua, 1998). However, palm oil mills produce a large amount of solid wastes. The remainder of the oil palm consists of huge amount of lignocellulosic materials such as oil palm fronds, trunks, palm kernel and empty fruit bunches. The residues contain 7.0 million tonnes of oil palm trunks, 26.2 million tonnes of oil palm fronds and 23% of Empty Fruit Bunch (EFB) per tonne of Fresh Fruit Bunch (FFB) processed in oil palm mill. Palm oil is a source of income and is also used as food. Palm kernel produces palm kernel oil and palm kernel shell when processed. The palm kernel oil is a source of income while the palm kernel shell can be used as a source of heat energy. The leaves are used for the production of brooms and for the construction of local fence. The trunk can be used as fire wood and can be sewn into planks for use in roofing.
The Oil Palm EFB is a suitable raw material for recycling because it is produced in large quantities in localized areas. In the past, it was often used as fuel to generate steam at the mills (Ma, Cheah and Chow, 1993). The empty fruit bunch can also be used as local fertilizer.
The ash produced from empty fruit bunches is sprayed on crops to prevent insects from destroying the crops, it is also used for washing of plates and pots. The ash, with a potassium content of about 30% was used as fertilizer. The filtrate obtained from the filtration of the mixture of this ash and water normally has a brown colour can emulsify oil, thus producing an emulsion with it. It is slippery to touch, giving an impression that it is alkali. In Akwa Ibom State, Nigeria, this filtrate is used in preparing a local delicacy known as “Otong” which is used in eating meat, drinking of palm wine and can be used to spice soup. Otong, which looks like an emulsion is also slippery to touch just like soap, suggesting that the reaction that produced it may have been a saponification reaction. Saponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base (usually caustic soda NaOH) hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate (Ababio, 1993).
Oil palm empty fruit bunch is one of the byproducts left in the palm oil mill. This residue cause environmental pollution problems and spread diseases. Burning of EFB is now prohibited by regulations to prevent air pollution (Hamdan, Tarmizi and Mohd, 1998). The EFB is now used mainly as mulch materials placed around young palms, to control weeds, prevent erosion and maintain soil moisture. However, due to the current labor shortage, the transportation and distribution of EFB in the field is becoming more expensive. There is a growing interest in composting EFB, in order to add value and also to reduce the volume to make application easier (Thambirajah, Zulkifli and Hashim, 1995). Other researches stated that oil palm empty fruit bunch is a lignocellulosic source which is available as a substrate in cellulase production (Rajoka and Malik, 1997).
The incorporation of empty fruit bunch (EFB) into polymers to obtain cost reduction and reinforcement has been reported by various workers. Rozman, et al. (2001) investigated the mechanical properties of polypropylene/EFB composites and found that EFB has high tensile modulus, but low tensile strength. Abdul, Siti, Mohd and Omar ( 2006) reported that modified EFB has improved the mechanical properties and water resistance of the polyester/EFB composites. Ridzuan, Shaler and Jamaludin (2002) reported that EFB is possibly suitable for medium density fibreboard (MDF). Pre-treatment of the fibre to remove its residual oil significantly improved the MDF properties and eliminated the delamination during consolidation of the panels. For removing the oil, sodium hydroxide (NaOH) is more effective than water, but a poorer fibre was obtained with a higher bulk density which also reduced the mechanical and physical properties. Ismail, Rosnah and Rozman (1997) reported that the adhesion between oil palm fibre and rubber matrix is poor but it can be modified by a treatment at high temperatures and various bonding agents. According to Aznizam and Azman (2003), there were reductions of the impact strength from the incorporation of EFB into the unmodified and modified unplasticised poly (vinyl chloride).
Biodegradation is the process by which organic substances are broken down into smaller compounds by the enzymes produced by micro-organisms. The micro-organisms transform the substance through metabolic or enzymatic processes. Biodegradation processes vary greatly, but frequently the final product of the degradation is carbon dioxide or methane. Organic material can be degraded aerobically, with oxygen, or anaerobically, without oxygen. Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms, or artificial materials that are similar enough to plant and animal matter to be put to use by microorganisms. Some microorganisms have the astonishing, naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge range of compounds including hydrocarbons, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radionuclides and metals (Gross and Kalra, 2002).
Biogas typically refers to a gas produced by the biological breakdown of organic matter in the absence of oxygen. Organic waste such as dead plant and animal material, animal dung and kitchen waste can be converted into a gaseous fuel called biogas. The gas is produced by anaerobic digestion of fermentation of biodegradable materials. Anaerobic decomposition occurs when the anaerobic microbes are dominant over the aerobic microbes. Biodegradable wastes are degraded in the absence of oxygen through the process of anaerobic digestion. The anaerobic decomposition of organic substances may be classified into four steps: hydrolysis, acid formation, acetate formation and methane formation. In the first two steps the organic substances are liquefied and decomposed (O’Loughlin, Traina and Sims, 2000). Their proper conversion into methane takes place in the last two steps of decomposition. The individual steps do not only differ from each other as regards the microorganisms participating and the products formed but also essentially by the environmental conditions required.
Biogas is practically produced as landfill gas or digester gas. A biogas plant is a name often given to an anaerobic digester that treats these biodegradable materials. The oil palm EFB is a non wood lignocellulosic material, which can be utilized as a renewable energy source for biogas production. The gas comprises primarily of methane (CH4) and carbon dioxide (CO2), and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes (Wieland, 2011). These gases can be combusted or oxidised with oxygen, releasing energy which allows biogas to be used as fuel. Biogas can be used in any country for any heating purpose, such as cooking. It can also be used in anaerobic digester where it is typically used in a gas engine to convert the energy in the gas into electricity and heat. Biogas can be compressed, much like natural gas, and used to power motor vehicles. In the UK, for example, biogas is estimated to have the potential to replace around 17% of vehicle fuel. Biogas is a renewable fuel, so it qualifies for renewable energy subsidies in some part of the world (Richards, et al., 1994).
Since empty oil palm fruit bunches are extensively used in the rural communities of Akwa Ibom State as fertilizers (or soil conditioners), especially in pineapple and oil palm tree plantations, the analysis of its NPK value and the microbiology of its decomposition may help to recommend its use as fertilizer.
1.2 Objectives of Study
This work was aimed at investigating the types of microorganisms found at different stages of the biodegradation process of EFB of oil palm. To achieve this, some specific objectives were extensively assessed. They included:
- To ascertain the microbial content of EFB at each stages of decomposition process for ten months at three weeks interval.
- To assess the physicochemical composition of the EFB of oil palm
- To assess the nutritional composition of the EFB of oil palm
- To assess the gas production potentials of EFB using bio-digester.