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Shoreline treatment of spilled vegetable oils
Spill Science & Technology Bulletin, Vol. 5, No. 5/6, pp. 303±304, 1999 Ó 2000 Elsevier Science Ltd. All rights reserved. Printed in Great Britain 1353-2561/00 $ - see front matter
PII: S1353-2561(00)00065-7
Shoreline Treatment of Spilled Vegetable Oils Vegetable oils come from a range of seed plants that are used around the world as both food items and industrial chemicals. It also includes chocolate, cooking oils and margarines that are used in the manufacture of soaps, detergents, toiletries, paints and plastics. There has also been a move towards replacing some mineral oil products such as industrial solvents and greases with vegetable derivatives leading to increased demand. Some drilling muds are now vegetable oil based. There has been a signi®cant increase in annual production with exports expanding from four million tonnes in the mid-1930's to over 20 million tonnes in the mid-1980's. Soya production was signi®cant in the 1950's with palm, sun¯ower and rapeseed oils increasing in the 1970's. World consumption has increased by 4% per year for the last 15 years, and it is estimated that the world production of vegetable oils will reach 85 million tonnes this year. The sites of production and ®nal consumption may not be coincident, with many oils grown in warm tropical regions with usage generally in the northern temperate countries. This necessitates the transportation of either raw oil, processed oil in bulk or ®nished products and wherever there is such transport, there exists the possibility of spills to the marine environment; loading and unloading can lead to chronic contamination and shipping accidents can cause acute pollution. Vegetable oils are comprised essentially of triacylglycerols ± fatty acids esteri®ed to a glycerol backbone. Other lipid compounds may also be present such as cholesterol and tocopherols (Vitamin E). Mineral oils have aliphatic and aromatic hydrocarbons as the primary constituents. By comparison, vegetable oils are much more degradable than mineral oils since the fatty acids can be cleaved from the glycerol by lipase enzymes. These free fatty acids can then be used as food by many marine bacteria. Many species can use these as their sole carbon source. Aliphatic hydrocarbons have no functional groups which makes enzymatic degradation much harder. There are very
few species of bacteria that are able to use hydrocarbons as their sole carbon source. Therefore, it has been generally thought that vegetable oils posed little to no problem in the marine environment. This has now been shown not to be the case and both chronic spills and acute pollution incidents have led to a wide range of deleterious eects. Eects have been reported from the oiling of birds and killing of ®sh through the formation of intractable lumps of oil in subtidal sediments and anoxia in both sediments and water. The loss of the M.V. Kimya on Anglesey, North Wales in Jan 1991 released 1500 tonnes of sun¯ower oil in to the marine environment. Some of this oil is still there now (January, 2000) nine years later; this is longer than most petroleum oil spills. An unforeseen problem was the polymerisation of the oils which form rubber-like strings and clumps in seawater but, if they cover sediments, the sands are used as an aggregate and from very tough, long-lived deposits (see Fig. 1). Bacterial action is still present internally but there is no diusion of oxygen through the outer layer to replenish that used in the degradation. Therefore, bacterial action slows down dramatically and allows these oils to persist. It could be argued that these oils are now benign, as they are having no biological eect although the damage may already have been done. Consider a spill near a salt marsh or other environmentally sensitive site. If the oil polymerizes and eectively cuts of the supply of oxygen to the sediments, the burrowing fauna will not survive. The physical changes may also lead to a change in the erosion pattern and undermine existing terraces and wash them away. With all of these documented eects in mind, the US EPA recently denied petition from the vegetable oil and animal fat trade associations for an exemption under the Oil Pollution Act, 1990. Vegetable oils are considered to be as polluting as mineral oils and an appropriate response strategy must be followed (Federal Register, 1997). Much of the petition
303
STEPHEN M. MUDGE
Fig. 1 Sand bound together with sun¯ower oil nine years after the loss of the MV Kimya on the coast of Anglesey, North Wales. The remaining oil block is approximately 2 m long and very hard. Physical erosion appears to be the prime mechanism for its removal.
focussed on the ``non-toxic'' nature of vegetable oils although toxicity can also be demonstrated in ®sh, birds and invertebrates. However, all is not lost. A bene®cial use of vegetable oils in the cleaning of petroleum oil spills can be demonstrated. For many years, the methyl esters of vegetable oils have been used as a bio-fuel ± biodiesel. In their methyl ester form, these fatty acids are readily degraded in the marine and terrestrial environment and to date no long-term toxicity or damage has been documented. As a replacement fuel, biodiesel can be used in environmentally sensitive regions as spills have less of an ecological impact than marine diesel. No modi®cation is needed to engines in order to use this fuel. The relatively new aspect of biodiesel is in the clean up of crude oil spills on beaches. After crude oils have been spilled at sea, they rapidly lose their volatile compounds to the atmosphere. This can be as much as 50% of the total volume. What is left behind are the non-volatile waxy components, which have a higher viscosity and tend to stick to sediments if washed ashore. In most oil spills, it is usual to keep the oil at sea and use a variety of mitigation methods ranging from burning to pumping on to barges. The ``windowof-opportunity'' for each technology can be narrow and if time or the weather is against you, as it was in the loss of the Erica of Brittany, France, the oil comes ashore. Biodiesel acts as a non-volatile solvent and disolves the waxy compounds making them much more mobile in the environment. Its ®rst use was demonstrated on a
304
spillage in San Juan, Puerto Rico in 1994. Since then, the use of biodiesel has developed and substantially more is known about its behavior. Experiments in my own laboratory have shown that virgin vegetable oil biodiesels are more eective in the removal of oil than recycled waste cooking oils. Application volumes depend on the degree of weathering and type of oil spilled but typically one volume of biodiesel to two volumes of oil are eective. Timings for the application also depend on the degree of weathering and the spraying technique. At present we are working on a ``spray and forget'' methodology for small spills which would greatly reduce the manpower and resources needed to clean such events. Experiments have also demonstrated that the biodiesel can be separated from the oil hydrocarbons ready for reuse. An extra dimension to the clean up with biodiesel is that it stimulates bacterial growth and the biodegradation of crude oil. Many experiments in the bioremediation of oil spills have concentrated on the addition of inorganic nutrients such as nitrates and phosphates. In many cases, however, this has not really helped, as these nutrients were not limiting growth. Experiments have shown that the addition of biodiesel as a solvent for the waxy components of the weathered oil has stimulated the growth of indigenous bacteria by proving a readily degradable carbon source. Water soluble degradation products were seen in the pore waters from arti®cially contaminated sands in as little as three days. This is all good news. The vegetable oil producers, re®ner and users need to recognize that oils themselves can be a problem in the aquatic environment and prevent contamination and pollution events to the best of their abilities. While this may mean extra costs in preventing the loss of their oils, this can be oset by the extra production of biodiesel as a green fuel and oil spill remediation agent. Protection of the environment should be paramount, once it has been degraded it may take years or decades to recover. Let the vegetable oil producers be an example of good practice to others. Stephen M. Mudge School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey. LL59 5EY UK Tel.: +44-0-1248-382879; fax: +44-0-1248-718180 E-mail address: [email protected]
Spill Science & Technology Bulletin 5(5/6)
PII: S1353-2561(00)00065-7
Shoreline Treatment of Spilled Vegetable Oils Vegetable oils come from a range of seed plants that are used around the world as both food items and industrial chemicals. It also includes chocolate, cooking oils and margarines that are used in the manufacture of soaps, detergents, toiletries, paints and plastics. There has also been a move towards replacing some mineral oil products such as industrial solvents and greases with vegetable derivatives leading to increased demand. Some drilling muds are now vegetable oil based. There has been a signi®cant increase in annual production with exports expanding from four million tonnes in the mid-1930's to over 20 million tonnes in the mid-1980's. Soya production was signi®cant in the 1950's with palm, sun¯ower and rapeseed oils increasing in the 1970's. World consumption has increased by 4% per year for the last 15 years, and it is estimated that the world production of vegetable oils will reach 85 million tonnes this year. The sites of production and ®nal consumption may not be coincident, with many oils grown in warm tropical regions with usage generally in the northern temperate countries. This necessitates the transportation of either raw oil, processed oil in bulk or ®nished products and wherever there is such transport, there exists the possibility of spills to the marine environment; loading and unloading can lead to chronic contamination and shipping accidents can cause acute pollution. Vegetable oils are comprised essentially of triacylglycerols ± fatty acids esteri®ed to a glycerol backbone. Other lipid compounds may also be present such as cholesterol and tocopherols (Vitamin E). Mineral oils have aliphatic and aromatic hydrocarbons as the primary constituents. By comparison, vegetable oils are much more degradable than mineral oils since the fatty acids can be cleaved from the glycerol by lipase enzymes. These free fatty acids can then be used as food by many marine bacteria. Many species can use these as their sole carbon source. Aliphatic hydrocarbons have no functional groups which makes enzymatic degradation much harder. There are very
few species of bacteria that are able to use hydrocarbons as their sole carbon source. Therefore, it has been generally thought that vegetable oils posed little to no problem in the marine environment. This has now been shown not to be the case and both chronic spills and acute pollution incidents have led to a wide range of deleterious eects. Eects have been reported from the oiling of birds and killing of ®sh through the formation of intractable lumps of oil in subtidal sediments and anoxia in both sediments and water. The loss of the M.V. Kimya on Anglesey, North Wales in Jan 1991 released 1500 tonnes of sun¯ower oil in to the marine environment. Some of this oil is still there now (January, 2000) nine years later; this is longer than most petroleum oil spills. An unforeseen problem was the polymerisation of the oils which form rubber-like strings and clumps in seawater but, if they cover sediments, the sands are used as an aggregate and from very tough, long-lived deposits (see Fig. 1). Bacterial action is still present internally but there is no diusion of oxygen through the outer layer to replenish that used in the degradation. Therefore, bacterial action slows down dramatically and allows these oils to persist. It could be argued that these oils are now benign, as they are having no biological eect although the damage may already have been done. Consider a spill near a salt marsh or other environmentally sensitive site. If the oil polymerizes and eectively cuts of the supply of oxygen to the sediments, the burrowing fauna will not survive. The physical changes may also lead to a change in the erosion pattern and undermine existing terraces and wash them away. With all of these documented eects in mind, the US EPA recently denied petition from the vegetable oil and animal fat trade associations for an exemption under the Oil Pollution Act, 1990. Vegetable oils are considered to be as polluting as mineral oils and an appropriate response strategy must be followed (Federal Register, 1997). Much of the petition
303
STEPHEN M. MUDGE
Fig. 1 Sand bound together with sun¯ower oil nine years after the loss of the MV Kimya on the coast of Anglesey, North Wales. The remaining oil block is approximately 2 m long and very hard. Physical erosion appears to be the prime mechanism for its removal.
focussed on the ``non-toxic'' nature of vegetable oils although toxicity can also be demonstrated in ®sh, birds and invertebrates. However, all is not lost. A bene®cial use of vegetable oils in the cleaning of petroleum oil spills can be demonstrated. For many years, the methyl esters of vegetable oils have been used as a bio-fuel ± biodiesel. In their methyl ester form, these fatty acids are readily degraded in the marine and terrestrial environment and to date no long-term toxicity or damage has been documented. As a replacement fuel, biodiesel can be used in environmentally sensitive regions as spills have less of an ecological impact than marine diesel. No modi®cation is needed to engines in order to use this fuel. The relatively new aspect of biodiesel is in the clean up of crude oil spills on beaches. After crude oils have been spilled at sea, they rapidly lose their volatile compounds to the atmosphere. This can be as much as 50% of the total volume. What is left behind are the non-volatile waxy components, which have a higher viscosity and tend to stick to sediments if washed ashore. In most oil spills, it is usual to keep the oil at sea and use a variety of mitigation methods ranging from burning to pumping on to barges. The ``windowof-opportunity'' for each technology can be narrow and if time or the weather is against you, as it was in the loss of the Erica of Brittany, France, the oil comes ashore. Biodiesel acts as a non-volatile solvent and disolves the waxy compounds making them much more mobile in the environment. Its ®rst use was demonstrated on a
304
spillage in San Juan, Puerto Rico in 1994. Since then, the use of biodiesel has developed and substantially more is known about its behavior. Experiments in my own laboratory have shown that virgin vegetable oil biodiesels are more eective in the removal of oil than recycled waste cooking oils. Application volumes depend on the degree of weathering and type of oil spilled but typically one volume of biodiesel to two volumes of oil are eective. Timings for the application also depend on the degree of weathering and the spraying technique. At present we are working on a ``spray and forget'' methodology for small spills which would greatly reduce the manpower and resources needed to clean such events. Experiments have also demonstrated that the biodiesel can be separated from the oil hydrocarbons ready for reuse. An extra dimension to the clean up with biodiesel is that it stimulates bacterial growth and the biodegradation of crude oil. Many experiments in the bioremediation of oil spills have concentrated on the addition of inorganic nutrients such as nitrates and phosphates. In many cases, however, this has not really helped, as these nutrients were not limiting growth. Experiments have shown that the addition of biodiesel as a solvent for the waxy components of the weathered oil has stimulated the growth of indigenous bacteria by proving a readily degradable carbon source. Water soluble degradation products were seen in the pore waters from arti®cially contaminated sands in as little as three days. This is all good news. The vegetable oil producers, re®ner and users need to recognize that oils themselves can be a problem in the aquatic environment and prevent contamination and pollution events to the best of their abilities. While this may mean extra costs in preventing the loss of their oils, this can be oset by the extra production of biodiesel as a green fuel and oil spill remediation agent. Protection of the environment should be paramount, once it has been degraded it may take years or decades to recover. Let the vegetable oil producers be an example of good practice to others. Stephen M. Mudge School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey. LL59 5EY UK Tel.: +44-0-1248-382879; fax: +44-0-1248-718180 E-mail address: [email protected]
Spill Science & Technology Bulletin 5(5/6)