GB2482286A - Oil spill remediation method - Google Patents

Abstract

The present invention relates to the field of oil spill remediation comprising a first step of a, providing a containment boom which contains oil sorbents, slow release fertilisers, oxygen releasing compounds and optionally laboratory produced bacterial biomass. A second step comprises aerial spraying of nutrients to activate microbial biodegradation. A third step comprises providing oxygen releasing fertilisers to beached oil. The steps may be implemented alone or in combination with either or both of the other steps. The oil sorbent may be polypropylene fibres, the slow release fertilisers may comprise a biodegradable coating of wax esters or long chain fatty acids and a core of water soluble nitrogen and phosphorus salts. The laboratory produced biomass may be Alcanivorax borkumensis. The oxygen releasing compounds may be peroxide salts, preferably calcium or potassium peroxide.

Description

MULTIPLE-APPROACH OIL SPILL REMEDIATION TECHNIQUE.

FIELD OF THE INVENTION.

The present invention relates to the field of oil spill remediation techniques.

DESCRIPTION OF THE RELATED ART.

Biodegradation of oil hydrocarbons has been known for a long time. It was for example disclosed in Sohngen et al. (Sohngen N.L., in Zentr. Bakteriol Parasitenk, 37, 595, 1913). Biodegradation of hydrocarbon is known to be conducted by numerous genera of bacteria, funghi and algae as disclosed for example in Head et al. (Head I.M., Jones D.M., and Roling W.F., in Nat. Rev. Microbiol., 3, 173, 2006).

Several scientists have studied ways of employing this self-cleaning function of the sea, such as for example Atlas and Bartha (Atlas R.M. and Bartha R., in Biotechnol. Bioeng. 14,297,1972; ., in Biotechnol. Bioeng. 14,309, 1972; Can. J. Microbiol.,18, 1851,1972) or Reisfeld et al. (Reisfeld A., Rosenberg E., and Gutnick D., in Appi.

Microbiol., 24, 363, 1972) or Cerniglia and Perry ( CernigliaC.E. and Perry J.J, in Z. AlIg. Mikrobiol., 13, 299, 1973).

Pristine seawater is poor in all nutrients. Most marine bacteria are well-adapted to this state and remain in a "hibernation state" for most of the time. Carbon typically enters seawater via phototrophic algae and is thus always present. Nitrogen and phosphorus are however very limited in marine systems. These vital components are necessary for the production of bacterial protein and DNA and thus constitute the limiting factor for bacterial growth.

When oil enters marine systems, it brings a sudden load of carbon substrate. As it is rich in carbon, but poor in nitrogen, phosphorus and oxygen, it poses a challenge to marine microbes.

A very distinct group of microbes has established strong adaptation to oil degradation. These bacteria have been isolated and characterised by Yakimov et al. (Yakimov M.M., Golyshin P.N., Lang S., Moore E.R. Abraham W.R., Lunsdorf H., and Timmis K.N., in mt. J. Syst. Bacteriol., 48, 339, 1998; Yakimov M.M., Denaro R., Genovese M., Cappello S., D'Auria G., Chernikova T.N., Timmis K.N., Golyshin P.N., and Giluliano N., in Environ. Microbiol., 7, 1426, 2005; Yakimova M.M., Timmis K.N., Golyshin P.N., in Curr. Opin. Biotech., 18, 257, 2007). All these species are closely related and extremely specialised. Recent researches show that they are closely associated to microalgae which produce several compounds, comprising hydrocarbons and fatty acids as a result of photosynthesis. The oil degrading microbes live attached to the microalgae surface and may reduce their metabolism to live solely on this energy source. They are therefore distributed over all oceans and in all climatic zones.

It has been observed that the adaptation of these microbes to oil is absolute. Their metabolism is able to run on an extremely high level, their membranes can tolerate the immense solvent stress of oil by biochemical alterations which only take minutes and their nutrient uptake mechanisms are among the strongest in the microbial world. They produce biosurfactants that are soap-like chemicals consisting of sugars and long-chained fatty acids. Said biosurfactants are connected to their cell surface, and serve as chemical "anchors",to ty them to the oil surface. Marine obligate hydrocarbon degrading microbes (OHCB) may thus get into contact with spilled oil.

After the first contact, OHCB start conversion oxidation of hydrocarbons. The first biochemical reactions, in the processing of potentially toxic hydrocarbons, involve adding oxygen atoms to the hydrocarbon backbone. OHCB are extremely well adapted to carry out this process as they contain up to five different enzymes capable of performing such step. First investigations (Head, Nat Rev Biotechnol, 4, 173-82, 2006) showed that each of the enzymes is capable of oxidising a slightly different range of hydrocarbons, thereby ensuring redundancy and maximum efficiency. Hydrocarbons are quickly turned into alcohols, subsequently into aldehydes, and in a final step into fatty acids. These reactions are extremely quick and dramatically alter toxicity and chemical properties of hydrocarbons. The fatty acids are further metabolised within the cells into carbon dioxide and water and thus into fairly harmless products. A part of hydrocarbons is turned into biomass as well as into biosurfactants. These are released by OHCB and slowly split up the oil slick into small droplets (micelles) thereby providing a larger oil-water interface and thus more space for OHCB to colonise and grow. In contrast to man-made chemical dispersants such as for example Corexit®, these tensides are biomolecules which are non-toxic and fully biodegradable in seawater.

Oil hydrocarbons are partly turned into long-chained polysaccharides, particularly when mineral nutrients are rare. They are excreted by the OHCB as a slimy, protective matrix. This matrix is used to solidify OHCB's position onto oil. They immobilise themselves onto oil and form thin cellular layers on its suface, also known as biofilms. More importantly, they also create a non-toxic "buffer zone" for less adapted bacteria to grow in.

These secondary oil degraders are less specialised than OHCB which can live solely on hydrocarbon and are thus very limited in the degradation of the whole spectrum of oil constituents. The secondary oil degraders take up compounds which cannot be digested by OHCB or those which are excreted by OHCB. Eventually, they also feed on the biofilms and on OHCB. This latter mechanism keeps OHCB in a constant state of growth and activity.

When OHCB have oxidised the majority of their substrates, they suffer from their fast metabolism and begin to starve. Their microbial biomass, excreted by-products and biofilms are slowly attacked by secondary oil degraders or marine nanoplankton or protozoa, such as flagellates. All the nutrients and carbon bound in their biomass thus returns to the seawater or is released as 002 in the atmosphere.

Every species of OHCB uses a very discrete niche. Alcanivorax borkumensis is believed to be the most successful OHCB. It is the most efficient for the degradation of linear alkanes in seawater at temperatures above 50 C and salinity above 0.3%.

Oleispira sp. is prevailing in cold and polar zones, feeding on similar hydrocarbons as Alcanivorax. Cycloclasticus sp. shares a similar global distribution as Alcanivorax, but specialises on aromatic hydrocarbons. Thalassolituus spp. prefer warm waters such as the Mediterranean. Several OHCB species may cooperate in degrading oil due to the complex mixture of hydrocarbons, further assisted by secondary oil degraders. These microbial consortia are formed autonomously and adapt perfectly to oil spilled in seawater. Their growth and activity is controlled and fine-tuned by marine protozoa.

Two basic concepts were typically used in bioremediation: bioaugmentation and biostimulation.

Bioaugmentation is the addition of laboratory-grown bacteria to the polluted environment. This method presented several problems: 1. Microbes grown in laboratory were less adapted to the particular environment than indigenous microbes and required a long time to wake up".

2. Massive introduction of microbes into seawater stimulated the growth of protozoan predators which quickly fed on these microbes thereby nullifying the effect of bioaugmentation.

3. No satisfactory method for delivering microbial cultures into seawater has yet been obtained. If sprayed by an airplane or from a boat, aqueous suspensions rapidly dispersed in the seawater column and high pressures in spraying jets damaged microbial cells.

In order to overcome the rapid dispersal of added bacteria, oil sorbent material was implemented. It was made from products of various origins and compositions such as for example polyethylene or polypropylene cloth or plant fibres as disclosed for example in Wei et al (Wei Q.f., Mather R.R., Fotheringham A.F., and Yang R.D., in Mar. Pollut. Bull., 46, 780, 2003) or in Pasila (Pasila A., in Mar. Pollut. Bull., 49, 1006, 2004) or in Suni et al. (Suni S., Kosunen A.L., Hautala M., and Romantschuk M., in Mar. Pollut. Bull., 49, 916, 2004; Suni S., Koskinen K., Kauppi s., Hannula E. Ryynanen T, Aalto A., Jaanheimo J., Ikavalko J., and Romantschuk M., in Ambio., 36, 173, 2007) or in Gertler et al. (Gertler C., Gerdts G., Yakimov M.M., Timmis K.N., Golyshin P.N., in J. AppI. Microbiol., 107, 590-605, 2009).

Oil containment booms are a common technique applied in oil spill mitigation.

Previous experiments carried out by Gertler et al. (Gertler C, Gerdts G., Timmis K.N., Golyshin P.N., in FEMS Microbiol. Ecol. 69, 288-300, 2009; Gertler C, Gerdts G., Yakimov M.M., Timmis K.N., Golyshin P.N., in J. AppI. Microbiol.,107, 590-605, 2009), demonstrated the feasibility of oil booms combining slow-release fertilisers and oil sorbents. The oil sorbent used in that previous research was a mixture comprising textile and leather and was based on recycled material. That material was environmentally friendly but showed poor floatation capabilities and poor oil absorption capacity, defined as the ratio (oil mass):(sorbent mass). It was of at most 4:1.

Biostimulation is the addition of nutrients, such as nitrate and phosphate, to the polluted environment in order to overcome nutrient limitations of indigenous pollutant-degrading bacteria. A technique has been developed for soils but has not been adapted to seawater. Ideally, tailor-made fertilisers were applied to polluted soils to overcome growth limitations of indigenous bacteria. Excess of nutrients and unlimited growth also minimised predation effect. In addition, predation itself turned into an advantage, as bacteria were forced to continuous growth and thus constant metabolic activity. In marine environment though, the rapid dispersal of aqueous solutions neutralised the effects of aerial spraying of liquid fertilisers.

There is thus a need to find an optimal fertiliser adapted to marine environment and to maintain a constant input of limiting nutrients while preventing eutrophication and, very importantly, to keep the fertiliser in the vicinity of the pollutant.

SUMMARY OF THE INVENTION.

It is an objective of the present invention to produce very efficient absorption/bioremediation oil booms prepared from polypropylene fibres.

It is another objective of the present invention to develop an aerial spray out for in situ bioremediation of oil slick.

It is also an objective of the present invention to produce slow-release fertiliser blends for bioremediation of beach areas and sea sediments.

It is yet a further objective of the present invention to tailor slow-release fertilisers adapted to specific tasks.

In accordance with the present invention, the foregoing objectives are realised as defined in the independent claims. Preferred embodiments are defined in the dependent claims.

DETAILED DESCRIPTION OF THE INVENTION.

Accordingly the present invention discloses a three-step approach to the treatment of oil spills, wherein each step can be implemented either alone or in combination with either or both of the other steps, said steps comprising: a) providing a containment oil boom that includes oil sorbents, slow-release fertilisers, oxygen-releasing compounds and optionally laboratory-produced bacterial biomass; b) aerial spraying of nutrients activating microbial biodegradation; c) providing oxygen-releasing fertilisers to beached oil.

The oil booms of the present invention serve the double purpose of mechanically containing the oil slick and providing sorption and biodegradation capabilities. They further serve as initiators for biodegradation on the edges of the slick.

Oil absorbing boom generally consist of a sorbent material and a permeable but hard-wearing hull material. A major factor of the booms is floatability. The floatability must be ensured for booms that are fully soaked with any type of oil. This is a particularly acute problem for heavy crude/fuel oils, as their density increases when the oil is exposed to seawater due to the formation of water-in-oil emulsions. A boom fully soaked in such oil is likely to sink. To prevent sinking, floatation bodies such as for example empty plastic bottles or air-filled core, must be inserted into the oil boom.

These flotation aids occupy approximately one third of the total boom diameter.

Alternatively, the sorbent boom can comprise a hollow core surrounded by several thin sorbent booms. In most cases, the boom can be cleaned and re-used.

The present invention uses new polypropylene fibres-based sorbents. This material is characterised by a very high absorption capacity, defined as the ratio (oil mass):(sorbent mass), of up to 20:1.

Polypropylene fibres having high bulkiness can be prepared from a blend comprising at least 90 wt% based on the total weight of polypropylene of isotactic polypropylene and up to 10 wt% of syndiotactic polypropylene as disclosed for example in EP- 1299584. Alternatively, polypropylene fibres of reduced density and thus improved absorbency can be used such as for example foamed fibres as described in EP- 2093313 wherein polypropylene is mixed with a chemical foaming agent during extrusion. A blend comprising polypropylene and up to 10 wt% based on the total weight of blend of an incompatible polar rigid polymer such as aromatic or aliphatic polyester can also be used such as described in EP-2096198. Because the polymers are incompatible, micro-domains are formed, associated with voids and thus increased absorbency. Increased roughness and reduced density can also be obtained by using blends of polypropylene and ethylene-propylene rubbers such as described in W0201 0/01 2833.

These new oil booms also present the advantage of keeping an adequate concentration of oxygen at the oil boom core.

The fertiliser combination used for the oil booms is adaptable to the evolving situation, as eutrophication may occur. The solution to eutrophication is the use of slow-release fertilisers which are commonly used in horti-/agriculture. Slow-release fertilisers commonly consist of a biodegradable coating consisting for example of wax esters or long-chained fatty acids, and a core of water soluble nitrogen and phosphorous salts, such as potassium nitrate, ammonium and phosphate salts.

When in contact with water, the coating membranes swell and open pores which allow the nutrients to disperse. The fertilisers are produced in a large variety of nutrient combinations and with a large variety of release rates. The release rates are controlled via the thickness! composition of the membrane. The nutrients can thus be released over different amounts of time or in an exponential scale in order to adjust to the typical growth patterns of microbes. Scotts Osmocote 18:11:10 (3 months release rate) fertilisers have been successfully tested in several independent studies (Xu etal., Mar Pollut Bull 51,1062-70 and 1101 -10; Gertleretal. 2009) and proved to work well in both sediments and oil booms. However, production of toxic nitrite in the booms was detected which strongly suggests an adjustment of fertiliser concentrations and release rates of the prototype oil boom. Due to the short release rate, eutrophication and a significant pH reduction was detected in the prototypes. A customised fertiliser blend specifically adjusted to the needs of bioremediation can be formulated and obtained from major fertiliser producing companies.

Oxygen supply in prior art booms proved to be a problem, as the oxygen concentration sank below 20% saturation at the oil boom's core within a few weeks.

The present invention provides special fertilisers such as for example Agriox® developed by Geoponics or IXPER® developed by Solvay or novel mixtures of fertilisers specifically designed for this purpose and produced exclusively at a major fertiliser production company such as Scotts Ltd. for this application.

The boom can also be supplied with bacterial biomass produced in a laboratory. This step is however optional. The present invention provides a delivery and storage method for such biomass which shows extremely high yields of viable bacteria after 6 months of storage at a temperature of -20 00. As the most common and effective oil-degrading bacterium, Alcanivorax borkumensis, is well known and available in all major bacterial strain collections. This organism can be grown in sterile ONR7a liquid medium (DSM medium 983) on the surface of small portions of oil-spiked sorbent material for seven to 10 days at a temperature of 25°C. The small portions can subsequently be incubated in 20% (vlv) Dimethyl sulfoxide for 30 minutes. The microbial biomass is conserved by initial shock freezing at -80°C and subsequent storage at a temperature of -20°C. Prior experiments showed that biomass treated in this way is viable and capable of oil degradation for at least 6 months. However, naturally occurring oil degrading microbial consortia grown on the sorbent surface showed significantly higher survival rates as disclosed by Gertler (C. Gertler, PhD Thesis).

It is preferred however not to supply bacterial biomass produced in laboratory to the oil boom in order not to interfere with the natural bacteria available on location.

Indeed added bacterial biorriass is less adapted to harsh environmental conditions than indigenous bacteria and they require a long time to become efficient. In addition, massive introduction of microbes into seawater stimulate the growth of protozoan predators which feed on these newly added microbes thereby nullifying their addition. Added microbes can also be detrimental to indigenous population that will view these new bacteria as invaders and fight them rather than feed on the oil spill. In addition, laboratory biomass necessarily contains dead cells that comprise readily available carbon which will be consumed preferably by indigenous biomass.

The second step relates to the aerial addition of nutrients.

The oil slick is sprayed with a realistic amount of compounds that are oleophilic and hydrophobic and can anchor to the oil slick in order to deliver nitrogen and phosphorus in the direct vicinity of the oil. These nutrients are preferably dissolved in a biological solvent such as oil and added to a carrier substance. They thus create optimum growth conditions for OHCB which produce biosurfactants during their growth. These compounds can for example be selected from nitrogen compounds such as paraffin-or sulphur-coated urea, rnethylene urea or more preferably uric acid for the delivery of nitrogen and phospholipids, more preferably Tri-4-(laureth)-phosphate for the delivery of phosphorus.

Uric acid is the chemical of choice for aerial/ship-based spraying, as it has a low molecular weight and can be dissolved in a liquid sprayer. It has furthermore already been tested in field trials but never been transferred in an application for the free market. To increase the bioavailability and improve the distribution of uric acid on the actual oil slick surface, uric acid can be ground in "nanopowders", extremely fine dust of uric acid crystals/particles with diameters ranging between a few nanometers and a few micrometers. This completely novel product offers increased capabilities as hydrophobic nitrogen source.

Tri-4-(laureth)-phosphate also has been tested as component of the successfully applied bioremediation product, Inipol EAP 22, which proved too toxic for large scale applications because of other components. These two components therefore are the most promising candidates for a sprayer. An environmentally friendly alternative to Tri(laureth)sulphate is N-butyl-acid phosphate, or any similar compound, which is non-toxic, biodegradable and further acts as dispersant.

The nutrients can be sprayed either from a ship or from a plane using thin jets in order to be dispersed and deposited at the surface of the oil slick This new technique works synergistically in two ways: it enables microbial oil degradation but also behaves like dispersants such as the Corexit series, but without toxic effects or eutrophication.

In the last step, the present invention addresses the problem of in-situ beach bioremediation. Some attempts have been made but none have been developed.

This is due mainly to the highly variable conditions in sandy soils of beaches. Water logging creates steep gradients of oxygen concentrations that are extremely high at the surface but quickly decrease few inches below the beach surface due to the poor diffusion of oxygen into sand. Anoxic conditions lead to highly problematic situations in bioremediation trials. The rate of fast, aerobic oil degradation quickly disappears a few inches below the beach's surface. Furthermore, the application of nitrate or sulphate containing fertilisers in anoxic conditions leads to the formation of toxic compounds such as nitrite and hydrogen sulphite, intoxicating the beach sediment and killing essential sediment-dwelling organisms such as worms and small crustaceans.

The present invention provides a method for adding oxygen-releasing fertilisers to beaches. A similar method has been applied to terrestrial soils, but it has never been attempted to beaches which present specific problems because they can be waterlogged or dry dependent on the tides Two different fertilisers are available on the market, but preferably, custom ised fertiliser can be used.

Oxygen-releasing fertilisers contain chemically bound oxygen in the shape of peroxide -salts, such as for example calcium peroxide or potassium peroxide.

Peroxides in general are quite stable in dry conditions. When in contact with water, peroxide ions quickly break down into water and elementary oxygen. However, the process of oxygen is very quick, thus the release of the peroxides must be regulated. ii

The exact technique used for this regulation is a corporate secret of companies producing oxygen releasing fertilisers. However it is very likely that this is achieved by coating the peroxides with a hull matrix which slowly decomposes in the environment and releases the peroxides. As mentioned above, two products are available at the moment. As they have never been applied to actual beach sediments, custom ised slow-release fertilisers based on a slow-releasing coating and peroxide salts can be used in parallel to the established products.

Delivery techniques such as tilling with agriculture-based technology can be used.

As the technique for bioremediation should be as simple as possible to be used in short time and on a large scale, primary tilling equipment used for the tilling of fields can be applied, such as for example portable' rotation tillers. This type of machinery is available worldwide and well established. Preferably, a machine which integrates tilling and seeding capabilities in one step is used for the distribution of slow release fertilisers into the subsurface of the beach sediments. Heavy machinery may present problems as the sediments are generally not consolidated and therefore too soft to support the weight of heavy equipment.

Exa in pies.

Two experimental polyvinylchloride basins of 0.8mxO.9mxl.1 m were used. The first basin was filled with 500L of freshly collected seawater. An experimental circular oil boom having a length of 2m and a diameter of 0.2m was prepared from polypropylene tissue from Heliman-Tech as hull material, filled with 10kg of X-OiI® also from Heliman-Tech as oil sorbent material. 4kg of slow-release fertiliser Osmocote Pro® 18+10+11 -i-2MgO+TE from Scotts International B.V. were added as well as 10 polyethylene flotation bottles of 250 mL each from Kautex and 300 gr of inoculum. Two floating cushions of 0.6mxO.7mxO.1 m each were constructed using 4 kg X-OiI®, 1.5kg of Osrnocote Pro® fertiliser, 9 polyethylene bottles and the same polypropylene hull as the boom. The boom and basin were spiked with a total of 2.5L of heat-sterilised and preheated heavy fuel oil IFO 380 from Shell as internal standard. The basin was aerated using compressed air from a central compressor, steriiised tubing and 4 sterilised air stones, and a 0.2 pm membrane filter. The temperature and concentration of dissolved oxygen were measured daily using an oxyscan Graphic electronic oxygen electrode from UMS.

Samples from the sea water and the oil sorbent were taken twice a week over a period of 2 months.

After 6 days an increasing oil emulsification was observed and the viscosity of the oil slick increased within the first 2 weeks. Emulsified oil initially consisted of oil droplets having a diameter ranging between 100 pm and several mm, and bacteria were visualised at the surface of the droplets. The density of the emulsified oil increased between days 7 and 21 and stabilised in the following 7 days.

After 28 days, 250L were removed from the first basin and transferred to the second basin, and both basins were completed to 500L with sea water. A second increase of emulsification appeared in the first basin between days 29 and 35 and the amount of biofilm aggregates decreased steadily thereafter. Similar observations were made in the second basin.

Both basins showed significant amounts of foam during the second half of the experiment.

Oil slicks in the first basin were reduced to small patches ranging between 2 and 5cm which completely disappeared by day 56.

After 56 days, wastewater from both basins was filtered through a sand filter. The presence of residual oil and its toxicity was tested with indicator papers for oil residues from Macherey-Nagel and with an ARTOXKit M from Strategic Diagnostics Inc..

Very little or no biofilm aggregates were observed per litre of mesocosm fluid at the end of the experiment. Both mesocosms showed a strong abundance of marine protozoa and no mortality of Nauplius larvae.

Claims (11)

1. CLAIMS.1. A three step method for the treatment of oil spills comprising: a) providing a containment boom that includes oil sorbents, slow-release fertilisers, oxygen-releasing compounds and optionally laboratory-produced bacterial biomass; b) aerial spraying of nutrients activating microbial biodegradation; c) providing oxygen-releasing fertilisers to beached oil.wherein each step can be implemented either alone or in combination with either or both of the other steps.
2. 2. The method of claim I wherein the containment boom includes oil sorbent prepared from polypropylene fibres.
3. 3. The method of claim 1 or claim 2 wherein the containment boom includes slow-release fertilisers consisting of a biodegradable coating selected from wax esters or long-chained fatty acids and a core selected from water soluble nitrogen and phosphorus salts.
4. 4. The method of any one of the preceding claims wherein the nitrogen and phosphorus salts are selected from potassium nitrate, or ammonium and phosphate salts.
5. 5. The method of any one of claims I to 3 wherein the oxygen-releasing compounds are selected from Agriox® or IXPER®.
6. 6. The method of any one of the preceding claims wherein the optional laboratory-produced bacterial biomass comprises Alcanivorax borkumensis.
7. 7. The method of any one of the preceding claims wherein laboratory-produced bacterial biomass is not added to the boom
8. 8. The method of any one of the preceding claims wherein the compounds used for aerial spraying of step b) are oleophilic, hydrophobic and capable of delivering nitrogen and phosphorus.
9. 9. The method of claim 8 wherein the compounds used for aerial spraying of step b) are selected from paraffin-or sulphur-coated urea, methylene urea, preferably uric acid for the delivery of nitrogen and phospholipids, preferably Tri-4-(laureth)-phosphate or N-butyl-acid phosphate for the delivery of phosphorus.
10. 1O.The method of any one of the preceding claims wherein the oxygen-releasing compounds used in step c) are selected from peroxide salts, preferably calcium or potassium peroxide.
11. 11.The method of claim 8 wherein the oxygen releasing compound are delivered by tilling with agriculture-based technology.