Palm oil milling activities
Palm oil milling has been seen as an agribusiness that brings a good return on investments. The milling activities are those processes and procedures undergone to get an edible SPO (Special Palm Oil) for cooking and other purposes.
During the milling activities to get good quality, edible oil, palm oil mill ‘wastes’ of various forms are usually produced. These wastes which may still be put to a good use include: palm oil mill effluent (POME), empty fruit bunches (EFB), palm fibre and palm kernel.
The palm oil industry contributes 83% of the total pollution in some palm oil producing countries; the situation is probably similar in other palm oil producing countries and so raised the need to look at the effect of palm oil wastes (especially the effluent) on the environment in Nigeria.
The abundance of oil palm trees in Okija, south eastern Nigeria, is responsible for the large production of palm oil. It is the most important crop for the farmers in the area and most households earn their livelihood from it. The majority of palm oil produced in the area comes from individual households and the trade is a true example of a cottage industry.
The production line is basic and traditional, involving rudimentary equipment and the division of labour and tasks is closely integrated with the domestic routine of what is basically an agricultural economy. The only palm oil mill in the study area with a production line involving the use of modern technology was abandoned by the government several years ago (about 15 years).
Palm oil processing is carried out using large quantities of water in mills where oil is extracted from the palm fruits. During extraction of crude palm oil from the fresh fruit, about 50% of the water results in palm oil mill effluent (POME). Each ton of fresh fruit bunches at the extraction mill generates approximately 0.22 tons of empty bunches, and between 800 and 900 litres of effluents and other by products. It is also estimated that for 1 ton of crude palm oil produced, 5 -7.5 tons of water ends up as POME1.
Generally, homesteads in Okija are dotted with processing sites. Thus, while enjoying a most profitable commodity, the adverse environmental impact from the palm oil industry is widespread and cannot be ignored. The study was carried out to determine the effect of palm oil wastes, especially the effluent, on the properties of soil in Okija area of Anambra State, Nigeria.
Palm oil mill wastes
The soil wastes
The solid waste products that result from the milling operation are empty fruit bunches (EFB), palm fibre and palm shell. In both traditional and modern milling settings, these solid waste products are all put to economically useful purposes such as fuel material and mulch in agriculture – despite their high C/N (carbon to nitrogen) ratio. Each ton of fresh fruit bunches at the extraction mill generates approximately 0.22 tons of EFB.
The liquid waste
It is the liquid waste called palm oil effluent (POME) that is usually discharged into the environment, either raw or treated. During the extraction of crude palm oil from the fresh fruits, about 50% of the water results in POME. It is estimated that for 1 ton of crude palm oil produced, 5 – 7.5 tons of water end up as POME. It is critical to examine properly what is added to the soil – that is, wastes – because soil genesis is brought about by a series of specific changes that can be grouped into four broad processes: • Transformations • Translocations • Additions • Losses
Chemical nature of palm oil wastes
The empty fruit bunch and fibre are solid waste products of the palm oil milling process and have a high moisture content of approximately 0.55 – 0.65% and high silica content from 25% of the total palm fruit bunch. The solid wastes contain potentially valuable nutrients, such as nitrogen and phosphorus. EFB increases soil potassium, phosphorus and pH, improves soil structure and produces higher midday relative water content and abaxial stomatal conductance.
Palm oil mill effluent (POME)
The raw or partially treated POME has an extremely high content of degradable organic matter, which is due in part to the presence of unrecovered palm oil.
It also contains high concentrations of free fatty acids, starches, proteins and plant tissues which are non-toxic.
The constituents of raw POME have also been reported to be a colloidal suspension of 95 – 96% water, 0.6 – 0.7% oil and 4 – 5% total solids, including 2 – 4% suspended solids. Raw POME has Biological Oxygen Demand (BOD) values averaging around 25,000 mg/litre, making about 100 times more pollution than domestic sewage. POME from a factory site in India contained about 250,000 mg/litre Chemical Oxygen Demand (COD), 11,000 mg/litre Biological Oxygen
Demand, 65mg/litre Total Dissolved Solutes (TDS) and 9,000 mg/litre of chloroform soluble material2.
Due to the presence of some unrecovered palm oil in the POME, it becomes necessary to look at the chemistry and processing of palm oil.
Chemistry and processing of palm oil
Palm oil and palm kernel oil are composed of fatty acids, esterified with glycerol just like any ordinary fat. Both are high in saturated fatty acids, about 50% and 80% respectively. The predominant portion of all commercial vegetable oils is a mixture of triacylglycerols. The palm oil gives its name to the 16 carbon saturated fatty acid-palmitic acid found in palm oil. Monosaturated oleic acid is also a constituent of palm oil, while palm kernel oil contains lauric acid.
The approximate concentration of fatty acids (FAs) in palm oil is as follows:
Fatty acids are saturated and unsaturated aliphatic carboxylic acid with carbon chain length in the range of C6 up to C24. An example of a fatty acid is palmitic acid. CH3-(CH2)14 –C00H
Splitting of oils and fats by hydrolysis, or under basic conditions saponification, yields fatty acids, with glycerin (glycerol) as a byproduct. The split-off fatty acids are a mixture of fatty acids ranging from C6 to C18 depending on the type of oil/fat.
Palm oil products are made using milling and refining processes; first using fractionation, with crystallisation and separation process to obtain a solid stearin, and liquid olein. By melting and degumming, impurities can be removed and then the oil filtered and bleached. Next, physical refining removes odours and colouration, to produce refined bleached deodorised palm oil (RBDPO), and free pure fatty acids, used as an important raw material in the manufacture of other materials, such as soap.
In the local setting, sometimes the oil in the sludge pit is recovered and mixed with fibre to make a fire starting cake called flint. At other times, the sludge, together with the liquid waste is poured onto the surrounding bushes and soil – an environmental problem. This, no doubt, has effects on soil properties and the surrounding environment when discharged with little or no treatment.
Physico-chemical properties of soils
Soil analysis and testing in soil science are included to define in numerical terms the physico-chemical properties of the major soils in an area 3. Physico-chemical properties here implies physical and chemical properties inherent in the soil. Physical properties can be seen with the naked eye, while chemical properties cannot. The morphological and physico-chemical properties are employed to characterise the soil.
In this article, physico–chemical properties analysed in the soils of the area studied include: particle size distribution, organic carbon and organic matter, total nitrogen, available phosphorous, exchangeable bases, pH, exchangeable acidity, Cation Exchange Capacity, bulk density, gravimetric water content and porosity.
The equipment used in the soil science laboratory to carry out the above listed analyses include: Atomic Absorption Spectrophotometer, UV – visible spectrophotometer, pH meters, electrical balances, distiller, hot plate, ovens, furnaces, hydrometer, glassware, flame photometer, reciprocating shaker, centrifuge and tension plate apparatus.
Breaking down the analysis – processes and terms used
• Particle Size Distribution: the relative distribution of the size group of soil particles and it is analysed using a process called mechanical analysis and measured by using the hydrometer • Soil Organic Matter: consists of a wide range of organic (carbonaceous) substances in various stages of decomposition • Total Soil Nitrogen: Nitrogen is an essential plant macro nutrient in the soil • Available Phosphorous: Phosphorous is an essential plant nutrient in the soil • Exchangeable bases: those usually considered in soil science routine analysis include Calcium, Magnesium, Sodium and Potassium • pH: a measure of hydrogen ion activity of the soil – the soil is tested to determine whether it’s acidic, basic or near neutral • Exchangeable Acidity: the total acidity in the soil which is derived by determining the amount of acidity generated by soil Aluminium and Hydrogen, thereafter, they are summed up to get exchangeable acidity value • Cation Exchange Capacity: derived by the summation of the exchangeable bases and exchangeable acidity defined above • Bulk Density: a measure of mass of the soil relative to its volume • Gravimetric Water Content: the amount of water in a soil – it’s usually determined by getting the weight loss after the soil is oven dried • Porosity: the measure of pore spaces in a soil, calculated from the bulk density values
Affects of wastes on soils
We also observed how physico–chemical properties of soils are affected by wastes from the palm oil milling activities. Inadvertent deleterious anthropogenic activities, in some palm oil mill industries, involving careless disposal of wastes, especially POME, pose a threat to the ‘living soil’. Irrespective of how effective the system of oil recaptured from the sludge may be, the POME discharged from an oil mill is objectionable and could pollute streams, rivers or surrounding land.
The first impression that could be got from the POME soil environment was that of bareness and a wasted land. Often one effect leads to another, so that a complex chain of pros and cons results from the addition of palm oil mill effluent and other mill wastes to soils.
The research that was carried out in Okija was to determine how the palm oil mill wastes have affected the physico-chemical properties of soils around the environment of the mill, after the bareness of vegetation around such mills was noticed. Soils around an abandoned palm oil mill (abandoned for about 15 years) were also tested to understand the resilient nature of soils subjected to treatments/disposals of uncured palm oil mill wastes, especially the POME.
Also, a five year fallow was used as a control in the experiment. The physico-chemical properties of soils of the active palm oil mill, abandoned mill and the fallow were determined by conducting soil tests.
The research showed that although soils around the abandoned palm oil mill and fallow followed the normal trend of decrease in soil bulk density as its organic matter content increases, there was a conspicuous increase in bulk density of soils of the active palm oil mill as its organic matter content increased.
This was because the organic matter materials from the POME were fine materials that blocked the soil pores, resulting in durinodes and then hard pan formation (high bulk density) in the soil.
As can be seen from the table presented above, the soils around the active palm oil mill had the highest bulk density even with its comparable value of organic matter content of soils around the five year fallow. Because of the blockage of soil pore resulting to hard pan on soil surface of the environments where these wastes are disposed, bareness of vegetation is witnessed.
An impenetrable layer of the soil makes it very difficult for vegetative cover to exist. It was also noticed that the soil acidity is increased as raw POME is discharged, but the pH seems to gradually increase as biodegradation takes place.
A traditional method used in the mill for separating the broken palm kernel from the shell (chaff) involves pouring both mixtures of the kernel and its shell into a pit of clay water (Kaoline dissolved in water) so that all the nuts float in the clay water (Kaolinitic), while the shells settle at the bottom. This practice usually leaves the surrounding soil environment with an increased pH due to capillary fringes from the clay dissolved in water.
In most cases, the dissolved clay after a prolonged stay in the pit is lost from the clay-plastered walls and floor through seepage and drainage to the underground water. A cascade effect of the phenomenon results because very high soil calcium usually emanates from the dissolved clay. This is usually not good for the availability of other soil nutrients such as phosphorous.
Having found out that the greatest amount of carbon is sequestered in the soil, bareness of vegetation resulting from the inadvertent deleterious disposal of these wastes poses a great threat not only to our soils for the food sustainance of the nation, but to our soil-water-atmosphere continuum – our environment.
From the research conducted in Okija, it was clear that the physico-chemical properties of soils around the palm oil mills were altered. Moreover, soils around the abandoned palm oil mill confirmed the resilient nature of the soil as it supported vigorous growth of vegetation, and the soil properties were recorded good and optimum for crop production.
It therefore follows that palm oil mill wastes should be well cured before they are disposed of on soils, as research has confirmed their efficiency in use as fertiliser (composting).
1. Ahmad, A; Ismali, S and Bhatia, S (2003). Water Recycling from Palm Oil Mill Effluent (POME) Using Membrane Technology. Desalination, 157:87-95.
2. Oswal, N; Sarma, PM; Zinjarde, SS and Pant, A (2002). Palm Oil Mill Effluent Treatment by a Tropical marine Yeast. In: Bioresearches Technology, Volumes 85, Issue 1, October 2002, Pp 35-37.
3. Esu, I (2010). Soil Characerization, Classification and Survey. HEBN Publishers, Nigeria.
4. Catharina, YW; Keshun Liu and Yao-wen Huang (1999). (eds.). Asian Foods.
Chinedu I Obi is a post graduate student of Pedology at the University of Uyo in Uyo, Nigeria.
He has studied various aspects of soil science, having studied the subject extensively at the Federal University of Technology Owerri (FUTO), Nigeria, where he obtained a first class honours degree as a Bachelor of Agriculture/Agricultural Technology.
Obi was, in addition, awarded the Best Graduating Student in the School of Agriculture/Agricultural Technology, FUTO (2007/2008). At this time he was elected the president of National Association of Soil Science Students, FUTO Chapter, and represented the department of Soil Science, FUTO, at many conferences, seminars and symposiums.
In his career, Obi has worked as a Pedologist at the Federal University of Technology, Owerri, Nigeria, as well as an environmentalist and an adjunct consultant in the field of soil science and land use planning for the Nigerian government.
He is anxious to expand the scope of his knowledge in soil science and seeking a scholarship for a PhD in soil ecosystem dynamics. Obi is prepared to relocate to a new educational establishment to this end and would be happy to hear of any opportunities any readers are aware of in this field.
Chinedu I Obi Department of Soil Science and Technology, Federal University of Technology Owerri, PMB 1526 Owerri, Imo State, Nigeria +2348032687760 [email protected] http://ng.linkedin.com/in/obichineduinnocent
Published: 10th Dec 2011 in AWE International