Oil spill pollution, a severe environmental problem which persists in marine environment or in inland water across the world, has grown to an alarming magnitude with increased levels of oil production and transport. Its causes are either accidental or due to operation wherever oil is produced, transported, stored and used on sea or land. Hence, it is almost impossible for marine life to be free from the danger of an oil spill, though the discharge of oil is controlled by international convention. Prime concern for marine health life has created an instinct for undertaking this type of study by the authors. Objectives of the present work include testing of four different materials in separating oil from water having different oil concentrations along with its efficiency of removal. The work focuses on effect of time of contact and dosage of materials used for oil removal. Corchorus depressus, which is locally available, has proven to be more effective in addressing this problem and at the same time its byproduct does not give rise to unwanted hazards to the marine life.
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Oil has long been used as a source of heat and light but due to the advent and innovations in automobile technology it has become a source of power for transport. Developments in the petrochemical industry warrants increased oil supply carried through pipelines and ships from places where it is found to the most convenient sites for refineries and chemical manufacturing plants. The quantity of oil transported over the sea has enormously increased in volume, encompassing tankers from capacity of 100,000 to 500,000 tonnes, resulting in increased possibility of spillage by accident or due to operation. In the event of an accident, oil pollution will be encountered in the marine environment or in inland water.
Sources of Oil Pollution
The major sources of oil spill pollution are the following:
Tanker accidents: Large tankers carrying oil over the sea increase the possibility of more oil spillage in the event of an accident.
Ballast water: When unloaded, returning tankers fill sea water as ballast to be carried in the compartments previously occupied by oil. The walls of compartments are cleaned with dinging oil by powerful seawater jets hence ballast water inevitably acquires a considerable quantity of oil, which when discharged causes unacceptable oil spill pollution.
Moller (1997) studied the Nakhodka oil spill and suggested improvements with respect to shippers' perspective defining the role of industry in dealing with oil spill pollution. Dicks (1998) summarized impact of oil spills on different components of the marine environment as well as potential for natural recovery and manmade restoration/re-instatement measuresÂ envisagedÂ accordingÂ toÂ internationalÂ compensationÂ conventions. KerambrunÂ andÂ ParkerÂ (1998) dealt with shorelines inundated with thick black oil pollutants. Results of the study focus on the society to accept responsibility for repair of damage to environment through human intervention and carefully targeted clean-up activities. Wadsworth, Dicks & Lavigne (1999) stated that oil spills contaminate both agricultural facilities and livestock, which can be prevented by innumerable self-help response options like relocation of cages, transfer of stock and early harvest. He elucidated cooperation between ship owners, government and private bodies involved in addressing hassles due to oil spillage. Moller, Dicks, Whittle & Girin (1999) explored approaches for managing activity bans in fisheries and aquaculture sectors following oil spills.
White (1999, 2000, 02) stated that considerable improvement is desired in spill response technology, highlighting technical and organizational problems associated with major marine oil spills. Also he reported that cost of incidence in coastal waters, shorelines and seas depends on factors like type of oil coupled with physical, biological and economic characteristics of spill locations, other factors being rate of spillage, weather, time of year and effectiveness of clean-up. Purnell (1999, 2002) examined costs associated with low technology shoreline clean-up methods that were used in response to Sea Empress incident. At the same time he categorized incidents according to their cause, type of ship, oil spilt and location. He also highlighted Amorgos incident in Taiwan.
Dicks, Parker, Moller, Purnell & White (2000) examined a wide range of technical, organizational, logistic and financial problems faced by the people managing shoreline clean-up operations due to oil spills around the world. Anderson (2001) sketched the characteristics of black oils that normally do not break down readily after spills and remain long enough in the environment to necessitate response. Ansell, Dicks, Guenette, Moller, Santner & White (2001) concluded that lessons learnt from the past provide a basis for the selection of more effective response techniques and equipment. White & Molloy (2001, 03), while discussing accidental oil spills, reported that incidents provide a good basis for examining technical factors giving rise to cost variations. Dicks, Parker, Purnell & Santner (2002) explained aggressive cleaning techniques like hot water washing and use of chemicals to remove viscous oils or weathered residues from rocks and commented that environmental sensitivity of the shore has to be borne in mind during such operations.
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Brien (2002) compared effectiveness of state-of-the-art equipment with non-specialized equipment such as mechanical grabs. It is concluded that while heavy oils often warrant special attention, large investment in specialized equipment and R&D is likely to be less beneficial than improved planning and preparation with locally available resources. Moller, Molloy & Thomas (2003) reviewed partnership between government and industry for dealing with oil spills arising from transportation of oil by sea in the event of risk of spills, environmental sensitivity and capabilities for dealing with oil spills in different regions of the world.
The following observations were made reviewing the literature:
It is inappropriate to make cost comparisons between fundamentally different oil spill events referring to a single parameter, such as total amount of oil spilled.
Various response techniques such as booms and skimmers, chemical dispersion, protective booming and shoreline cleanup has many limitations.
Marine health life was not properly addressed due to adverse effects of oil spill pollution.
Many at times locally available materials were not used for removing oil spilled in seawater.
Major marine oil spills were rarely dealt with as effectively as current technology should allow due to lack of shortcomings in the organization, management and equipment of spill response.
There has been no dramatic reasonable reinstatement measures for oil spills in past.
Most of the methods adopted were rather heuristic/ adhoc in nature in the past.
Need for the study
Around 5 million tonnes of petroleum hydrocarbons reach the world's seas and oceans each year and 140 incidents of oil spills were reported in 75 countries. These incidents throw light on shortcomings of the organizations, employment of equipment and management of spill response and contingency planning for improving the usage of locally available materials. It is almost impossible to say that the marine life is likely to be free from the danger of an oil spill, though the discharge of oil is controlled by international convention. Therefore the environmental authorities must be aware of this particular risk and must have enough knowledge to deal with priority to remove the oil as quickly as possible. This is to reduce the dangers caused by oil spill pollution, which affect economic development of a country. Hence this work is aimed to achieve the following tasks.
To test naturally available local materials in removing the oil spill from water having different oil concentrations and its associated oil removal efficiency.
To study effect of time and dosage on oil removal efficiency and compare with standard adsorbents.
Oil tends to form insoluble layers with water as a result of its hydrophilic characteristics, which can be easily separated from seawater by gravity and skimming. When it forms emulsion with water as a result of turbulent mixing it becomes difficult to break, hence there are a number of methods which may apparently be used to deal with oil spills in seawater. Some options used for marine protection from oil pollution include:
*Mechanical collection *Chemical dispersants *Natural removal.
Setting fire to the oil spill: Frequently crude oil is set on fire in a wrecked ship when an accident occurs. The problem of burning surface oil is very difficult due to less thickness of the layer and large surface area. The volatile fraction evaporates quickly and makes it impossible to ignite without doping special measures.
Skimming: It can be performed by employing devices for collecting oil from a large area of water to make it a thicker layer in harbour sheltered places.
Gelling: Spraying gelling agents with a certain amount of mixing energy into the oil spill causes formation of gel or coagulation. The resulting lumps can be collected easily in the vicinity of a wrecked ship.
Sinking: Mixing small fine granular solids of fairly high density (sand) culminates into slurry, sinking the oil spill to the bottom of the seabed.
Absorbing: Floating oil can be separated due to absorbsion applying chemicals.
However, many of the methods described above have limited usage and at times prove to be expensive in view of regional conditions and other influencing parameters. But in reality to achieve cost effectiveness in prevention of oil spill pollution, the selection of materials should be based on the following factors:
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* Efficiency in removing oil * Local availability
* Relatively cheap cost * Ability to regenerate and reuse.
*Environment friendly byproduct.
Naturally available local materials utilized for removing oil spills from seawater in the present work are Corchorus depressu and Arachis hypogea.
Corchorus depressus: This plant, whose Arabic name is Mulukhia EI Bar (Desert queen), is embossed of a flat prostrate compact perennial pink herb 25 cm long. The leaves are small elliptic crenate 0.3 -1 x 2.0 -0.5 cm, flowers are yellow, calyx 5 lobed, 7 mm long, corolla S-lobed. The plant has stamens 10 and capsule is oblong cylindrical 1-2 x 0.2 mm, curved, beaked with dark green seeds. It is commonly available in Oman whereever compact sandy soil is present. It is used for grazing animals. Powdered Corchorus depressus sieved on No. 40 sieve contains AlCl3 40-70 %, NaSo4 0 to +8, H3Bo3 +13 (band 11) and considerable amount of ethanol, which gives the plant the ability to coagulate. This material acts as a sinking material when used in the powder form for removal of oil from seawater by absorbing oil and settling to the bottom.
Arachis hypogaea: This plant, 450- 600 mm high with short branches known as groundnut, has golden-yellow pentads about 10mm long. The pods are long with 2 or 3 seeds oblong, roughly cylindrical with rounded ends. The solid pulp that remains after edible oil is extracted from it as a high protein live stock feed which enables it to absorb the oil spill from sea water which gets collected on the surface.
Materials used for comparison
Some materials good for removing oil from water were tested with the same restraint to compare their efficiency with naturally available local materials.
Bentonite clay: It acts as a sinking material when added to oil spill polluted water sample.
Activated carbon: This material causes the oil spill to form a gel or coagulate, however due to its chemical composition it may have negative side effects on marine health life environment.
A standard partition-gravimetric method was applied for extracting dissolved or emulsified oil from seawater having volatile hydrocarbons that otherwise would have lost in solvent-removal operation of the gravimetric procedure.
Oil spilled seawater with predetermined levels of oil concentration was collected for the experimentation employing Datasonde hydrolab equipment with data logger. This sample was thoroughly mixed with the powdered locally available material by varying dosages and time of contact. The material in this case reacted with the mixture by adsorbing oil and settling at the bottom of the water (sedimentation). Hydrochloric acid (HCL) was used with dilute amount of 4 ml and 30 ml of trichlorotrifluoroethan to separate the remaining amount of oil, which was not removed by the material. Trichlorotrifloroethan extracts unsaturated fats and fatty acids and oxidizes the sample but precaution has to be taken to control temperature and solvent vapor displacement. It has the ability to dissolve not only the oil and grease, but also other organic substances. Hence as a result oil is separated from the seawater. The results help in determining the optimum usage of the material and its associated efficiency in separating oil from the seawater.
However in order to establish the effectiveness of the locally available materials (Corchorus depressus and Arachis hypogaea), the results obtained are compared with the other adsorbents (Bentonite clay and Activated carbon).
Tests Results and Conclusions
The set of experiments carried out helps to compute the oil removal efficiency by above mentioned selected materials and the effect of time and dosage on it.
Details of quantity of oil separated from seawater having 90, 160 and 360 mg/l oil concentrations when Corchorus depressus was used are presented in Table-1 and Fig-1. The following formula was used for the computations:
Oil remained = (total gain in weight * 1000) /sample in 'ml'
Oil removed = initial oil concentration - oil remained.
Details of results obtained adopting the above procedure for removing oil from seawater having 90, 160 and 360 mg/l oil concentrations when other locally available material (Arachis hypogaea) and the materials used for comparison (Bentonite clay and Activated carbon) were used are presented in Table-2, 3 & 4 and Fig-2, 3 & 4 respectively.
The following conclusions were drawn analyzing the test results:
The optimum removal efficiency of oil from the sample when Corchorus depressus was used yielded 99.4% at 160mg/l oil concentration and 20g of material, contact time being 20 min. The results show that removal efficiency increases at the beginning and subsequently decreases with increase in dosage quantity and time of contact.
The optimum removal efficiency of oil from the sample when Arachis hypogaea was used yielded 70.3 % at 360mg/l oil concentration and 20g of material, contact time being 20 min. The results show that removal efficiency increases at the beginning and subsequently decreases with increase in dosage quantity and time of contact.
The optimum removal efficiency of oil from the sample when Bentonite clay was used yielded 85.5% at 90mg/l oil concentration and 20g of material, contact time being 20 min. The results show that removal efficiency increases at the beginning and subsequently decreases with increase in dosage quantity and time of contact.
The optimum removal efficiency of oil from the sample when Activated carbon was used yielded 66.87% at160mg/l oil concentration and 20g of material, contact time being 20 min. The results show that removal efficiency increases at the beginning and subsequently decreases with increase in dosage quantity and time of contact.
It has been deduced that locally available herb Corchorus depressus used for separation of oil from seawater was the most effective and efficient and at the same time proved to be economical, Results conclude optimum dosage as 20g of it having a contact time of 20 min. Finally comparison of oil removal efficiency for all the four materials with their individual dosage and the time of contact are presented through Table-5 and Fig- 5, 6 and 7 respectively.
Scope for further study
The following points can be considered for undertaking future research work. More experiments can be conducted by selecting appropriately locally available natural materials employing innovated experimental techniques. Further these materials may be used in combination with chemical reagents, in order to achieve economy in experimentation. It is felt appropriate to consider the chemical composition of materials employed and consumption of by products formed addressing oil spill pollution.