Study on the use of banana peels for oil spill removal

1. Introduction

Oil spill is now considered one of the most important concerns of the world, because it causes a great risk for the environmental and marine life. Spills have many sources, such as oil transport, energy sources, waste disposal, accidents and the production of oil. These sources are linked to human activities. More than 5 million tons of crude oil are transported annually around the world by the sea, putting the ecosystem in danger. Subsequently, the environmental and marine lives are affected by spills, particularly birds, shorelines, shell fishes, mosses and sea creatures. On the other hand, a chemical dispersant is one of the most common techniques used to remove oil spill. However, these methods may be harmful and a reason for killing fishes [1], [2].

Crude oil consists of a wide range of hydrocarbons from very light oil to heavy oil, where hydrocarbons proportions range from 50 to 98%. When oil is spilled into the sea, it leads to several processes which are known as weathering processes that include evaporation, dissolution, oxidation, emulsification, sedimentation, spreading, dispersion and finally biodegradation. The evaporation process changes the physical characteristics of oil and leads to an alteration of its density and pour point due to the loss of volatile components. In addition, emulsification affects oil composition and cause a decrease in oil density and an increase in pour point. Spreading occurs at varying rates according to the oil properties as light oil spreads faster than heavy oil. Among all factors affecting spreading, water temperature and wind speed have an intense effect on pollutants. In the case of a motionless surface, oil spreading may occur, but in the case of rivers, spills are moved along the stream. Tidal currents have an intense impact on pollutants in the sea, especially in open seas and in parts. All these processes help in the choice of an appropriate way for oil spill treatment [3].

Environmental scientists face a serious challenge in oil spill treatment from produced water [4]. With regards to the processing of the oil spill removal, there are different methods that can be used separately or with each other. These technologies are classified into three groups: first, chemical methods, such as solidifiers, dispersion and in-situ burning, second, biological methods, finally, mechanical methods, such as booms, skimmers and adsorbent [5]. Mechanical and chemical treatment commonly used to remove oil spill, the main limitation of these methods are their high cost and inefficient trace level adsorption. Mechanical treatment can’t be applied under rough sea waves and high wind velocity but it suitable for completely oil removal. As for the chemical treatment such as dispersion to be effective must be applied soon after a spill and can affect marine organism due to high toxicity [6]. Adsorption is considered the most preferred technique for oil spill clean-up, because it is an easy method, environmentally-friendly and of low cost. In recent years, the interest of many researchers is drawn to using agriculture wastes or by-products materials. It offers many advantages, including being a low cost alternative material and the ability to biodegrade [7], [8]. It is important to note that cleaning-up with a sorbent is one of the most effective technologies among all oil removal methods that give good results in oil removal from contaminated water [9]. Table 1 shows the classification of sorbents such as inorganic mineral, organic synthetic and organic vegetable [10], [11]. Despite the fact that polymer products (polypropylene, polyethylene and polyurethane) are the most widely used, one of their main disadvantage is their non-biodegradability [12]. Nowadays, there is a growing interest in sorbent production from natural organic sorbents for oil spills removal, such as barley straw, rice straw, rice husk, pith bagasse, banana trunk, garlic and onion peel. The direction of interest in developing alternative materials, such as agriculture wastes, is the result of the restrictions of other types of sorbent products [13], [14].

Table 1. Types of oil spill sorbents.

Categories	Inorganic mineral	Organic synthetic	Organic vegetable
Sorbent types	Glass-Wool-Sand-Graphite-Silica-Zeolites	Polypropylene-Polyurethane	Cotton fiber-Straw-Feathers-Sawdust-Wood fiber

Sorbents can remove oil from produced water by using a suitable method without oil draining out because it can collect and transform liquids to the semi-solid or solid phase. With regards to the advantages of the sorbent material produced from agriculture wastes, besides being biodegradable and of low cost, it is a high oil sorption, with low water pickup, high buoyancy and good reusability [15], [16]. Sorbents are most commonly used for final stage to remove oil from marine environment. Sorbents may be applied to an oil spill manually or chemically by using blowers and fans. The selection of sorbents application method various according to location and size of the spill. Also sorbents can be used in different forms such as loose, roll, sheet, pad, allow and booms, these forms various with their composition. The disposal options available for oiled sorbent materials are disposal by certain routes for example, incineration by burning contaminated sorbent, disposal of oiled sorbents as landfill and biodegradation [17].

The focus of the present study is to assess the ability of banana peel as natural sorbents, of low cost and a commonly available waste material for oil spill removal water across various factors. The effect of variable parameters, such as surface properties, oil type, oil film thickness, sorption time, temperature, salinity and the morphology of banana peel surface, are also studied.

2. Materials and methods

2.1. Materials

2.1.1. Sorbent materials

Banana peel was obtained from an available local fruit market as solid waste. Then, banana peel was cleaned with water to remove undesired materials. Banana peel was next left to dry under sun light for 7-days, then it was dried in a drying oven at 70 °C for 4 h. Big particles were crushed in a willy mill and sieved into particles with an average size of 0.225, 0.3625, 0.5125 and 0.725 mm.

2.1.1.1. Characterization techniques of banana peel

For studying the morphology of banana peel surface, a scanning electron microscope (SEM) model (JEOL JSM-5300, Japan) was used. The sample was prepared by coating double sided conductive adhesive tapes with gold. SEM recorded an accelerating voltage at 20 KV and a magnification of 2000×.

FTIR Spectroscopy: Fourier Transformation Infrared Spectroscopy (FTIR) was recorded to identify a number of peaks and an organic functional group on the surface of the banana peel. The sample was mixed at a ratio of 1/100 and the wave numbers ranged from 4000 to 400 cm1.

2.1.2. Tested oil

Three types of crude oil were investigated to represent a wide variation in the ability of banana peel in oil spill cleanup. The oils employed in this study, namely: gas oil, were obtained from a benzene station and (1-day & 7 day) Almein crude oil was obtained from Amreya Petroleum Refining Company.

The gas oil was used without modification; it had a specific gravity of 0.82 at 15 °C, viscosity of 4.8Cs at 25 °C and flash point at 55 °C. While crude oil had a density equal 0.8180 g/cm3 at 15 °C (ASTMD-1298), API gravity 41.38 and kinematic viscosity 2.29 CST at 40 °C.

With regards to more volatile components, they evaporated quickly after spreading oil spill. At the beginning of an oil spill, less volatile fractions evaporate and, as a result, the oil viscosity increases. So, in order to simulate the same situation of an oil spill and to reduce sorption procedure, the crude oils were put on trays for one and seven days in open air [18].

2.2. Experimental procedure

By apply a common method for oil sorption capacity that related to the American Society for Testing Materials ASTM standard [19].

Five hundred milliliters of seawater (3.5% NaCl) were placed in a 1 L beaker filled with a 5 mm layer of oil to form a specific layer of oil and a mesh screen was depressed at the bottom of the beaker before adding the oil sample. One gram of dried sorbent banana peel was put in a pad, then spread over the surface of the system.

The beaker content was set up in a Digital Precise Shaking water bath for 15 min at 115 cycle/min and temperature was kept constant at 25 ± 1 °C. After 15 min, the sorbent was taken away with the mesh screen and the sorbent was left to drain for 5 min. The weight of the sorbent was determined and recorded, after that the sorbent was transferred to the piston to extract the oil.

During the pressing stage, a small amount of n-hexane (10–20 mL) was added to the mechanical stage to help in the extraction of the oil in order to separate it from the water. After the oil was collected in a graduated centrifuge tube, the centrifuge tubes were placed in a water bath at 60 °C for 20–30 min to break any emulsion presence. The final stage for water content was determined by the centrifuge technique described in ASTM D4007-81 (ASTM, 1998). The final sorption capacity of the adsorbent was determined by the following equation: $S_{O} = S_{T} - S_{W} - S_{I}$ where ST is the total weight (g/g sorbent) of oil water and sorbent material, SWis the water weight (g/g sorbent), and SI is the initial sorbent material weight (g/g sorbent) and SO is the oil sorption capacity of the fiber which is calculated as grams of oil per grams of sorbent.

3. Results and discussions

3.1. Scanning Electron Microscope of banana peel

The SEM images of banana peel are shown in Fig. 1. It was found that it has an irregular morphology and a porous surface. These pores can make oil entrance into the internal parts of the material easier and helpful in the sorption process.

3.2. FTIR spectroscopy of banana peel

As shown in Fig. 2, this is the FTIR spectrum of a natural banana peel. The bands in the region of 3400.49 cm−1 indicate the presence of a stretching of strong hydroxyl groups. The band at 2925.34 cm−1 is assigned to C single bond H stretching. Also, the band at 1735.83 cm−1 corresponds to the stretching of a carbonyl group C double bond O (hemicellulose band). The band at 1633.14 cm−1 represents absorbed water and the band at 1385.21 cm−1 assigned to –CH bending. In addition, the band at 1258.75 cm−1 corresponds to C single bond O stretching (lignin band) and the band at 1063.28 cm−1 represents C-OR stretching.

3.3. Effect of particle size

The effect of different particle sizes on the oil sorption capacity is illustrated in Fig. 3. It can be seen that there is a gradual increase in oil sorption capacity with a decrease in particle size till it reaches a maximum value at 0.3625 mm. A 5.31, 6.35, 6.63 g/g sorbent for gas oil, 1-day and 7-day weathered respectively. Then, it declines with the particle size decrease. The increase in the oil sorption capacity, with the decreasing particle size, may be due to the increase in surface area which allows the increase in sorption capacity.

On the other hand, with the decrease in particle size, the oil sorption decreases. The reason for that might be due to the accumulation of small particles on each other, which results in plugging the pores and capillaries present between fibers and the reverse [20].

3.4. Effect of sorption time

Fig. 4 shows the effect of sorption time on the oil sorption capacity of banana peel at different times of 5, 10, 15, 30, 45 and 60 min. The Figure shows that oil sorption increases gradually as sorption time increases from 5 up to 15 min, when the maximum value is reached at 15 min, its might be due to adsorption of crude oil on the surface of the sorbent before the oil beginning to break through the inside microscopic voids [21]. Then, these values decrease, regardless of soaking time for 1-day and 7-day weathered crude oil and for gas oil. These result may be due to formation of water in oil emulsion that cause increases in water pickup and decreases in oil sorption capacity [21].

3.5. Effect of temperature

The result of different temperatures at 20, 25, 30, 35, 40 and 45 °C on the oil sorption capacity of banana peel was investigated.

As shown in Fig. 5, it is immediately apparent that adsorption capacitydecreases gradually with the temperature increase. With regards to the maximum sorption capacities, they are 4.33, 7.94 and 7.14 g/g sorbent of gas oil, 1-day and 7-day weathered at 20 °C respectively. This result may be due to the solubility of crude oil which increases in water and its decreasing viscosity, making it drain off the sorbent’s surface easily.

Some researchers have noticed that with the temperature increase, the Brownian motion of oil particle is accelerated and increased, therefore the energy required attaching oil particle to the sorbent surface increases [22], [23], [24].

3.6. Effect of film thickness

The graph in Fig. 6 illustrates changes in the oil sorption capacity at different film thickness 1, 2, 3, 4 and 5 mm. Over all, it can be seen that oil sorption rose gradually with film thickness increasing in all three oil types.

There was a moderate rise over the period. It is observed that the maximum oil sorption of gas oil, 1-day and 7-day weathered are about 5.31, 5.83 and 6.63 g/g sorbent at 5 mm film thickness respectively. The capacity of the crude oil removal is related to the chemical composition and surface properties of the fibers. In contrast, it is clearly observed that for gas oil, 1-day weathered water pick up remained constant at zero, but it increased gradually with the rise of the film thickness.

These results indicates that with increasing oil film thickness, large amount of oil are removed as predictable and may be related to the chemical composition and surface properties of the fibers as well as the concentration, specific gravity and temperature of the crude oil [25].

3.7. Effect of salinity

The result of salinity on the sorption capacity was experimentally investigated. Fig. 7 illustrates that the oil sorption capacity of banana peel firstly increases with increasing salinity, till it reaches its maximum values at 3.5% salinity, then it declines with the salinity rising.

The reason for increasing sorption capacity with increasing salinity might be due to the effect of electrostatic interaction and salting out, the oil sorption capacity of banana peel becomes large and more hydrophobic. In contrast, the decline with the salinity rise is due to the decrease in the solubility of crude oil and physical and the chemical properties of fiber which were influenced by higher salinity [23].

3.8. Effect of sorbent weighs

As shown as in Fig. 8, this graph illustrates that sorption capacity for gas oil, 1-day and 7-day weathered increased steadily with sorbent weigh rising from (0.5 to 2.5 g). For gas oil and 7-day weathered, the sorption capacity continues to increase while increasing sorbent dose, whereas for 1-day weathered, the sorption capacity is approximately constant.

On the other hand, for water pick up, it is observed that water pick up remained constant for solar and 1-day weathered which approach to zero, that means sorbent weigh does not affect water pick up. While for 7-day weathered crude oil with increasing sorbent weight, water sorption capacity increases.

These results indicate that while increasing the amount of sorbent, large amounts of oil are removed. Thus, the interface between oil and water nearly disappeared allowing the sorbent to absorb high values of water [18].

3.9. Effect of reusability

The reusability is one of the major factors for selection fibers materials. The graphs below give information about the number of cycles for banana peel reused by removing oil from sorbent by mechanical action and n-hexane extraction to reuse sorbent for several times.

Firstly, for gas oil sorption capacity, it is observed that in Fig. 9, the sorbent is reused by a mechanical action to remove oil 20 times. Also, approximately 90% of the initial sorption capacity remained after 10 cycles. Then, about 1-day weathered crude oil sorption capacity, fluctuated, then declined gradually from 9.25 to 4.25 g/g sorbent after 15 times. Finally, the figure illustrates the varying values of sorption capacity of 7-day weathered crude oil that showed a slight decrease in sorption capacity, before falling significantly till it reached less than 50% of the initial sorption capacity after 10 cycles in which the sorbed amount was 6.63 g/g sorbent before it declined to 3.13 g/g sorbent.