GB2553357A - Method and system for treatment of produced water - Google Patents

Abstract

A method of treating oily water comprises the introduction of oily water into a system comprising a subsea bioreactor in which microorganisms biodegrade oil from the oily water. Preferably, the bioreactor is a membrane bioreactor (MBR), which may be operated with a hydraulic retention time of 15-40 hours. The method may comprise a step of filtering the oily water through an adsorption medium. The bioreactor can be a biofilter, preferably a trickle filter or a fluidized bed filter. The system may comprise a second bioreactor, wherein the first bioreactor can be operated under aerobic conditions and the second bioreactor can be operated under anaerobic conditions. In another aspect, a system for treating oily water is claimed, wherein the system comprises a bioreactor configured to operate in a subsea location. The bioreactor may receive the output of an oil-water separator, such as a three-phase separator, a gas flotation vessel, an in-line separator or the output of a concentration vessel. The bioreactor may be configured to facilitate plug-flow of the oily water.

Description

(54) Title of the Invention: Method and system for treatment of produced water Abstract Title: Treatment of produced water in a subsea bioreactor (57) A method of treating oily water comprises the introduction of oily water into a system comprising a subsea bioreactor in which microorganisms biodegrade oil from the oily water. Preferably, the bioreactor is a membrane bioreactor (MBR), which may be operated with a hydraulic retention time of 15-40 hours. The method may comprise a step of filtering the oily water through an adsorption medium. The bioreactor can be a biofilter, preferably a trickle filter or a fluidized bed filter. The system may comprise a second bioreactor, wherein the first bioreactor can be operated under aerobic conditions and the second bioreactor can be operated under anaerobic conditions. In another aspect, a system for treating oily water is claimed, wherein the system comprises a bioreactor configured to operate in a subsea location. The bioreactor may receive the output of an oil-water separator, such as a three-phase separator, a gas flotation vessel, an in-line separator or the output of a concentration vessel. The bioreactor may be configured to facilitate plug-flow of the oily water.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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Method and System for Treatment of Produced Water

Field of the Invention

The present invention relates to a method and/or system of treating oily water, comprising biodegradation of oil from the oily water in a subsea bioreactor. The aim is to reduce the oil content of the water, preferably to less than 30 ppm.

Background

Oil and gas reservoirs have a natural water layer, called formation water. In addition, to achieve maximum oil recovery, further water is often injected into a reservoir to help force the oil out of the reservoir. Consequently, water containing oil is a by-product of oil and gas recovery and this is referred to in the oil industry as “produced water” or “oily water”. There is a need to treat such oily water to reduce the oil content thereof, to allow the treated water (effluent) to be discharged into the sea or to be used for further applications.

The treatment of produced water is distinct from the treatment of oil spills. In particular, oil spills tend to be caused by a specific event and the clean-up can be carried out over a long period of time. By contrast, produced water is typically generated continuously and there is a need to treat it quickly. The treatment of oil spills also typically takes place in situ, rather than inside a bioreactor. Oil spills may also have a different chemical composition from produced water. For example, certain chemicals such as corrosion inhibitors or surfactants may be used during oil production and such chemicals may be present, or present in a higher concentration, in produced water compared to oil spills.

Mechanical options for treating produced water include gravity oil-water separators; filtration through a granular medium, such as sand; membrane filtration; hydrocyclones; and/or induced gas flotation. Whilst a few subsea systems have been developed to allow for some of these processes to be carried out subsea, produced water is still predominantly treated topside or on shore. Details are described, e.g., in “Advanced Produced Water Treatment” by Daigle et al. 2012, 1^st Annual Upstream Engineering and Flow Assurance (UEFA) Conference, which can be accessed, e.g., at http://www.rpsea.org/media/files/project/cf672196/09121-3100-01-PA-

Advanced_Produced_Water_Treatment-Daigle-02-02-12.pdf and which is incorporated herein by reference. Examples of subsea oil-water separation systems include the Norwegian Troll C subsea separation system, which has a horizontal gravity-based separation vessel; the Vertical Annular Separation and Pumping System (VASPS); and the Statoil Tordis, which uses a gravity based separator.

There is a need for further methods, particularly subsea methods and systems. Description of invention

The present invention provides a method of treating oily water, said method comprising introducing oily water into a system comprising a subsea bioreactor in which microorganisms degrade oil from the oily water.

The invention also provides a system for treating oily water, the system comprising a bioreactor configured to operate in a subsea location. Preferably, the system is configured to perform any of the methods provided herein. Any reference herein to a “system” may be considered to mean an “apparatus” or a “combination of apparatuses”.

It should be understood that the methods of the invention may comprise a step of using/operating any of the systems or system components disclosed herein. Thus, any discussion of a feature in the context of a system applies mutatis mutandis to the method, and vice versa.

The method or system may advantageously allow enhanced oil and/or gas production; less energy consumption; and/or reduce operating costs with regard to the treatment of produced water.

The method or system of the invention may be used in conjunction with conventional methods and systems, so it may be part of a tie-back to an on shore or topside host, e.g. a floating vessel or platform, i.e. be connected thereto via risers. The tie-back may, e.g., be about 10-100 kilometres. The system may include all of the necessary components to provide a complete subsea factory for oil, gas and water processing, to eliminate the need for platform topside or onshore processing systems.

At least part of the method is performed subsea, i.e. at a subsea location, which may be contrasted with onshore or topside locations. Thus, by subsea is meant below the surface of the sea, such as at a depth of at least around 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1500, 2000, 2500 or 3000 m and preferably no more than 3500, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, or 20,000m, preferably around 70 to 3000, 2000 or 1000m, e.g. about 500m or more. Preferably, the subsea location is on the seabed, e.g. one or more of the components of the system, preferably at least the bioreactor, are located on the seabed. It will be understood that when a system component is located “on” the seabed, it may be partially embedded within the seabed, e.g. have foundations within the seabed, and/or be anchored to the seabed.

In some embodiments, the entire oily water treatment method is carried out subsea, but in other embodiments the method may include one or more steps that are carried out at a non-subsea location. At least one bioreactor is configured to operate in a subsea location and is located subsea when the method is in operation, so at least one biodegradation step is carried out at a subsea location. One or more further components of the system may also be configured to operate in a subsea location, and/or be located subsea.

The method comprises a step of introducing oily water into a system comprising a bioreactor, which may preferably be a step of introducing oily water, or oil derived therefrom, into a bioreactor. The oily water may, e.g., be derived directly from one or more oil-water separators, or have been subjected to one or more pre-processing steps. The method may comprise one or more steps of processing the oily water before introducing it into the system comprising the bioreactor, or into the bioreactor. For example, the method may comprise a step of concentrating the oily water prior to introducing it into the bioreactor. Alternatively or in addition, the method may comprise a step of filtering the oily water through an adsorption medium and washing said adsorption medium, and/or incubating said adsorption medium in a bioreactor. Details of any of these steps are provided elsewhere herein.

Thus, the biodegradation may be the biodegradation of oil that is present in the oily water. Alternatively or in addition, the biodegradation may be the biodegradation of oil that has been removed from the oily water, e.g. through adsorption onto an adsorption medium as discussed elsewhere herein. Thus, the biodegradation may be used to regenerate an adsorption medium that has oil adsorbed thereon. The term “oil from the oily water” is used herein to encompass oil present in the oily water and/or oil that have been removed from the oily water. Alternatively or in addition, the biodegradation may be the biodegradation of oil and/or microbes present in sludge, e.g. sludge derived from the treatment of oily water. As discussed in more detail below, oil in or from oily water may, e.g., be treated in a first bioreactor and sludge may be removed from said first bioreactor and introduced into a second bioreactor to biodegrade oil and/or microbes present in the sludge.

The bioreactor is configured, and preferably operated, to allow biodegradation of oil from the oily water to take place, e.g. to allow microorganisms to biodegrade said oil and preferably to survive and/or grow. Thus, when the bioreactor is in operation (in bioreactor mode), biodegradation takes place in the bioreactor, which is preferably carried out by microorganisms. The bioreactor is thus configured/operated to allow the cultivation of microorganisms that can biodegrade oil.

The biodegradation may result in a decrease in the total oil content of the bioreactor, particularly if oily water is introduced into the bioreactor in a semi-continuous or batch-flow manner. Depending on the bioreactor configuration, the biodegradation may result in oily water in a first area of the bioreactor having a lower oil content than oily water in a second area. The first area may, e.g., be in closer proximity to the bioreactor effluent outlet than to the bioreactor oily water inlet, and the second area may, e.g., be in closer proximity to the bioreactor oily water inlet than to the bioreactor effluent outlet. For example, if the bioreactor allows plug flow, then the second area may be a plug that is closer to the bioreactor oily water inlet than the first area.

In this context, a “decrease in the total oil content” or a “lower oil content” is preferably a decrease in the oil content by, or a difference in the oil content of, at least 10,

20, 30, 40, 50, 60, 70, 80, 90, 95 or 99%, e.g. by 30-90%.

The rate of biodegradation inside the bioreactor(s) may be at least 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3300, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 11000, 12000, 13000, 14000 or 15000 kg oil per day, preferably about 600-1000 kg oil/day, 3000-5000, or 800012000 kg oil/day . This may be the rate of biodegradation inside a single bioreactor, or the combined rate of all of the active bioreactors in operation in the system; for example, if the system comprises 10 bioreactors which are operated to yield a rate of biodegradation of 500 kg oil/day each, then the total rate of biodegradation inside the system will be 5000 kg oil/day. Hence, the bioreactor(s) may be configured/operated to allow such a rate of biodegradation to take place.

The biodegradation may rely solely or partly on microorganisms that are naturally present in the oily water, e.g. they may be indigenous to one or more of the oil, formation water, seawater and/or other water that yielded the oily water. For example, they may be indigenous to the oil reservoir. In any of these cases, the microorganisms may be referred to as being indigenous to the oily water.

Alternatively or in addition, the biodegradation may rely solely or partly on a microbial inoculum that is added to the bioreactor as part of the method of the invention.

Enzymes may be added to the bioreactor to aid the biodegradation.

The biodegradation takes place in a bioreactor, so in one embodiment microorganisms are (only) introduced into the bioreactor insofar as they are (naturally) present in the oily water and/or or in any other materials that are introduced into the bioreactor, such as seawater and/or nutrients. Thus, in this embodiment, the method does not comprise a step of adding a microbial inoculum to the bioreactor.

By relying solely on naturally present microorganisms is meant that the method does not necessitate, and preferably does not include, a step of adding a microbial inoculum to the bioreactor. Thus, the method involves biodegradation (only) by microorganisms that are naturally present in the oily water. By relying partly on naturally present microorganisms is meant that the method involves biodegradation by microorganisms that are naturally present in the oily water, but may also include a step of adding a microbial inoculum to the bioreactor.

By relying solely or partly on a microbial inoculum is meant that the method includes a step of adding a microbial inoculum to the bioreactor. Indeed, in such an embodiment the method may necessitate such a step. Thus, the method involves biodegradation by microorganisms from a microbial inoculum.

The skilled person will appreciate that microorganisms are present in almost any material, particularly aqueous material, such as seawater or produced water. Therefore, a step of adding, e.g., seawater would inevitably add indigenous microorganisms to the bioreactor. However, such a step must be contrasted with a step of adding a microbial inoculum.

A microbial inoculum is a material containing microorganisms in concentrated form, which may be added to a bioreactor to start or replenish a microbial culture. The microbial inoculum will typically have a high concentration of microorganisms, e.g. at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 500, 1000, 2000, 5000, 8000, 10000, 50000 or 100000 times higher than seawater and/or produced water. The microbial inoculum may, e.g. have a microbial concentration of at least 10⁴, 10⁵, 10⁶, 10⁷, 10⁸, 10⁹, 10¹°, 10¹¹,10¹²,

10¹³, 10¹⁴, 10¹⁵, 10¹⁶, 10¹⁷, 1Ο¹⁸,10¹⁹,10²°, 10²¹,10²²,10²⁵,1Ο³⁰,10³⁵,10⁴° microorganisms per millilitre or mg of inoculum.

The microbial inoculum may comprise or consist of a pure microbial species, or of a mixture of at least 2 or more microbial species, and/or it may, e.g., be activated sludge, which may preferable comprise or consist of biomass that was previously removed from a or the bioreactor and/or from another part of the oily water treatment system, e.g. a biomass storage vessel.

The microbial inoculum may be fully characterised, i.e. the identity of each microbial species present therein may be known; or it may be partially characterised, i.e. the identity of a proportion of the species present therein, e.g. one or more, may be known, but one or more species of unknown identity may also be present; or it may be uncharacterised, i.e. the identities of none of the species present therein may be known.

The microbial inoculum may be used to increase the concentration in the bioreactor of one or more microbial species that are already present in the oily water, e.g., that are indigenous to the oily water. Alternatively or in addition, the microbial inoculum may be used to introduce one or more microbial species into the bioreactor that were not previously present in the oily water, e.g. that are not indigenous to the oily water.

In embodiments in which a microbial inoculum is used, it may be introduced into the bioreactor at one or more discrete time points, and/or in a continuous fashion. Different microbial inoculums may be used at different time points, if desired. The inoculum may be added at one or more predetermined time points, and/or if and when a determination is made that the addition of a (further) inoculum is desirable or required. The growth and/or activity of the microbes in the bioreactor may be monitored and the results of such monitoring may be used to determine whether and at what time point a (further) inoculum should be introduced into the bioreactor. Thus, the bioreactor is preferably provided with a system for monitoring microbial activity and/or biomass levels, and/or a system for introducing an appropriate inoculum into the bioreactor.

The microbial inoculum may be introduced directly into the bioreactor, and/or it may be added indirectly to the bioreactor, e.g. by adding it to the oily water before it is introduced into the bioreactor.

The terms “microorganism” and “microbe” are used interchangeably herein. Unless otherwise stated, any reference herein to a microbial population should be understood to refer to a pure or mixed population of microbes, e.g. in the inoculum and/or bioreactor. Unless otherwise stated, any reference herein to a microbe should be understood to refer to a microbe present in the microbial population.

The microbe or microbial population may comprise or consist of microbes that are naturally present in oil-containing environments, such as oil reservoirs/wells. Suitable examples are listed below, but the skilled person will be aware of other examples of microbes that are naturally present in oil-containing environments.

The microbe or microbial population may be aerobic or anaerobic. More particularly, the microbe may be, or the microbial population may comprise or consist of, an obligate aerobe, an obligate anaerobe, a facultative anaerobe, a microaerophile, and/or an aerotolerant anaerobe. The microbial population present in the inoculum and/or bioreactor may comprise or substantially consist of aerobic microbes, anaerobic microbes, or a combination thereof.

Thus, the bioreactor may be operated, and/or configured to be operated, under conditions that allow or favour the growth and/or activity of certain microbes, such as aerobes, anaerobes, and/or any of the subclassifications mentioned above. For example, the conditions may be oxic, which may allow or favour the growth and/or activity of aerobes; or anoxic, which may allow or favour the growth and/or activity of anaerobes. As a shorthand, a bioreactor that is operated, and/or configured to be operated, under conditions that allow growth and/or activity of aerobes may be referred to as an “aerobic bioreactor”, whereas a bioreactor that is operated, and/or configured to be operated, under conditions that allow growth and/or activity of anaerobes may be referred to as an “anaerobic bioreactor”, and so on.

The wording “operated/configured” is used herein as a shorthand to mean “operated, and/or configured to be operated”. Similarly, the wording “arranged/operated” is used herein as a shorthand to mean “operated, and/or arranged to be operated”.

Oxic conditions may be achieved and/or maintained by supplying free oxygen (O₂) to the bioreactor, preferably in gaseous form. Unless otherwise stated, any reference herein to “oxygen” is meant to be free oxygen (O₂). Oxygen may be supplied e.g. in the form of air and/or in the form of a gas mixture comprising oxygen. The amount of oxygen that may be added may be related to the amount of oil that is introduced into the bioreactor (as part of the oily water). Thus, oxygen may preferably be added as at least 1,2, 3, 4 or 5 mg per mg of oil, and preferably no more than 10, 8, or 6 mg per mg of oil.

Anoxic conditions may be achieved and/or maintained by excluding free oxygen (O₂) from the bioreactor.

The microbial population may preferably comprise or consist of one or more methanogens, i.e. a microbe that produces methane as a metabolic byproduct in anoxic conditions; denitrifying microbes; syntrophs; and/or sulfate reducing microbes.

For example, the microbial population may preferably comprise or consist of one or more methanogens and one or more syntrophs. Such a microbial population may preferably be used under anoxic conditions.

The microbial population may comprise or consist of one or more different microbial types selected from bacteria, fungi, archaea, algae, protozoa, and/or viruses. Preferably, it comprises one or more different species of bacteria.

The bacteria may optionally be selected from the phylum Actinobacteria, Bacteroidetes, Clamydiae, Deinococcus, Firmicutes, or Proteobacteria. .The bacteria may optionally be selected from the order Actinomycetales, Flavobacteriales, Sphingobacteriales, Verrucomicrobia, Thermales, Bacillales, Lactobacillales, Clostridiales, Caulobacterales, Kordiimonadales, Rhizobiales, Rhodobacterales, Rhodospirillales, Sphingomonadales, Burkholderiales, Hydrogenophilales, Nitrosomonadales, Rhodocyclales, Aeromonadales, Alteromonadales, Enterobacteriales, Methylococcales, Oceanospirillales, Pasteurellales, Pseudomonadales, Thiotrichales, Vibrionales, Xanthomonadales, Desulfobacterales, Desulfovibrionales, Desulfuromonadales, or Syntrophobacterales.

The microbial population may preferably comprise or consist of one or more members of the Pseudomonadaceae family, e.g. one or more members of the Pseudomonas genus, such as Pseudomonas aeruginosa. Such a microbial population may preferably be used under oxic conditions.

The system may comprise 2 or more bioreactors, e.g. at least a first and a second bioreactor, which may be arranged/operated in parallel and/or sequentially. Any discussion herein regarding a bioreactor applies independently to any of the bioreactors that the system may comprise. The plurality of bioreactors may all be of the same type, or include at least 2 different types, e.g. one or at least one anoxic (anaerobic) bioreactor and one or at least one oxic (aerobic) bioreactor. By a “sequential” arrangement is meant that a first bioreactor is arranged/operated upstream of a second bioreactor, such that oily water is first introduced into the first bioreactor and subsequently introduced into the second bioreactor. For example, an anoxic (anaerobic) bioreactor may be arranged/operated upstream of an oxic (aerobic) bioreactor, or vice versa. Examples of suitable arrangements of a plurality of bioreactors are shown in Fig. 5, Fig. 8, Fig. 10 and Fig. 11 and discussed in connection with the fifth and eighth embodiment.

Thus, for example, oily water, of oil therefrom (for example, on an adsorption medium) may be introduced into a first bioreactor. A discharge from the first bioreactor may then be introduced into a second bioreactor. For example, the first bioreactor may be configured/operated under aerobic conditions and the second bioreactor may be configured/operated under anaerobic conditions, or vice versa. Some of the contemplated configurations are illustrated in Fig. 10 and Fig. 11, but it must be appreciated that these are for illustrative purposes only. The “discharge” from the first bioreactor may be oily water and/or sludge.

The system may, e.g., comprise a first bioreactor with an inlet for oily water, an outlet for effluent water and/or sludge, and an outlet for transferring oily water and/or sludge into a second bioreactor. As illustrated in Fig. 10, the first bioreactor may be configured/operated under aerobic conditions and the second bioreactor may be configured/operated under anaerobic conditions. Preferably, in this embodiment, the discharge that is transferred from the first bioreactor to the second bioreactor is, or comprises, sludge.

As illustrated in Fig. 11, the first bioreactor may be configured/operated under anaerobic conditions and the second bioreactor may be configured/operated under aerobic conditions. Preferably, in this embodiment, the discharge that is transferred from the first bioreactor to the second bioreactor is, or comprises, oily water.

Microbes may aggregate together to form floes, biofilms or granules that comprise living and/or dead microbes. This may particularly happen in a bioreactor. Floes may also contain further materials, such as any of the constituents of the oily water, and/or any of the by-products of the biodegradation.

The system may comprise a settling vessel, which may also be referred to as a clarifier. A settling vessel may preferably be arranged/operated downstream of a bioreactor. For example, the effluent of the bioreactor may be passed through a settling vessel, in which any floes are allowed to settle out, i.e. to sink to the bottom of the settling vessel. However, in some embodiments, the method advantageously does not require, and/or does not involve the use of a settling vessel. Thus, the system may optionally not comprise a settling vessel.

A mass of floes may be referred to as “sludge” or “activated sludge”. The method may involve the removal/discharge of biomass, e.g. such sludge, from the bioreactor and/or any from other equipment, such as a settling vessel and/or a membrane. The sludge may comprise oil and in some embodiments the sludge may comprise at least 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or 200 ppm of oil. In such embodiments, the sludge may optionally be treated to reduce the oil content, e.g. treated in a further bioreactor. In other embodiments, the sludge may comprise no more than 30, 25, 20, 15, 10, 5, or 1 ppm of oil.

Any removed/discharged sludge may be used in a number of different ways, as discussed elsewhere herein.

In some embodiments, the oily water, which may be produced water, may be treated in a bioreactor without a prior concentration step. In other embodiments, the method may comprise a step of concentrating the oily water prior to the biodegradation step. The unconcentrated oily water may be referred to as a “first” oily water, and the concentrated oily water may be referred to as a “concentrate” or “second oily water”.

The oily water may be introduced into the system, or into one or more components thereof, in a continuous or semi-continuous manner, or in batches. Preferably, it is introduced into the bioreactor in a manner that allows plug-flow of the oily water. To treat produced water the system must be capable of dealing with a continuous flow of a large volume of oily water. Whilst oily water may thus be introduced into the system in a continuous manner, the system may be configured/operated to allow oily water to be introduced into one or more components of the system in a semi-continuous or batch-flow manner. For example, the system may comprise a plurality of vessels, e.g. bioreactors, and the system/method may be configured/operated such that at a given time the oily water is only introduced into a proportion of the vessels. In particular, oily water may be introduced into a first bioreactor, but not a second bioreactor for a first period of time, and for a second period of time oily water may be introduced into the second bioreactor but not the first one. Such a configuration/operation may allow the operation of appropriate retention times within each bioreactor. The flow of oily water may be controlled, e.g. via valves and/or pumps.

Concentrating the oily water may involve a step of filtering the oily water through a membrane and/or an adsorption medium. Preferably, such a step is upstream ofthe bioreactor, in which case it is the concentrate generated via such a step that is treated in the bioreactor. However, in some embodiments, such a step may alternatively or in addition be downstream of a bioreactor, e.g. downstream of a first bioreactor but upstream of a second bioreactor.

Thus, the system may comprise a membrane configured to allow the concentration of oily water. For example, it may comprise a vessel containing a membrane, which may be configured to allow the filtration of oily water. Said vessel may be referred to as a “concentration vessel”. It may comprise one or more transfer means to allow the transfer of oily water into said vessel; the transfer of effluent water out of said vessel; and/or the transfer of a concentrate out of said vessel, e.g. into a bioreactor. The transfer means may comprise a conduit leading from an oil-water separator to the concentration vessel; a conduit leading from the concentration vessel to a bioreactor; and/or a conduit leading from the concentration vessel to the sea or to a further vessel. An Example of a suitable membrane vessel is shown in Fig. 8 and discussed in connection with the eighth embodiment.

Alternatively or in addition, the system may comprise an adsorption medium. The adsorption medium is preferably in a vessel, which may be referred to as an adsorption vessel. It may comprise one or more transfer means to allow the transfer of oily water into said vessel; the transfer of effluent water out of said vessel; and/or the transfer of a concentrate out of said vessel, e.g. into a bioreactor. The transfer means may comprise a conduit leading from an oil-water separator to the adsorption vessel; and/or a conduit leading from the adsorption vessel to the sea or a further vessel. Optionally, it may also comprise a conduit leading from the adsorption vessel to a bioreactor.

An adsorption vessel may e.g. be a cylinder and preferably have a diameter of about 10 m, and/or a height of about 6 meters. The vessel, or more typically a plurality of vessels, may e.g. have a total weight of about 230 tonnes, plus about 50 tonnes of foundation

The adsorption vessel(s) may be configured to hold a volume of at least 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1200, 1500, 1800, 2000, 2200, 2500, or 3000 m³, e.g. 100-1000 m³, preferably 500-1000 m³. If the system comprises a plurality of vessels, then each vessel may be configured to hold such a volume individually, or the plurality of the vessels present in the system may be configured to hold such a volume between them.

Thus, for example, if the system comprises 10 adsorption vessels which are configured to hold a volume of at least 200 m³ each, then the total volume that the system may hold within the adsorption vessels is at least 2000 m³.

A plurality of adsorption media may be used, e.g. a plurality of vessels each comprising an adsorption medium may be used. The vessels may be arranged, e.g., as shown in Fig. 2B. Suitable Examples of methods comprising the use of adsorption media are discussed in connection with the second and third embodiments.

The adsorption vessel may be operated/configured in an adsorption mode and preferably also in a regeneration mode, as discussed in more detail below.

As explained in more detail below, the oily water may be filtered through a membrane to yield a permeate and a retentate, wherein the retentate is the “concentrate” or “second oily water”. The permeate may be, or may form part of, the effluent. Such a filtration is preferably carried out before introducing the oily water into the bioreactor.

Alternatively or in addition, as also explained in more detail below, the oily water may be filtered through an adsorption medium to yield an effluent. The adsorption medium may be washed to yield a back-wash, which is the “concentrate” or “second oily water”. The terms “back-wash” and “back-flush” and variations thereof like back-washing and backflushing are used interchangeably herein.

Concentrating the oily water results in oily water having a smaller volume and/or a higher oil concentration that the first oily water, which may advantageously allow the use of a smaller bioreactor. Preferably, the step of concentrating the oily water results in an at least 1.5, 2, 2.5, 3, 3.5 or 4 fold reduction in the volume of oily water. Thus, the concentrate may have a volume fraction of no more than about 70, 60, 50, 40, 30, 20 or 10% of the first oily water, e.g. a volume fraction of about 30-50% or 20-40%. The oil content in the concentrate may be in the range of 1000-10000 ppm. Thus, the step of concentrating the oily water results in an at least 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25 or 30 fold increase in the oil content of the resulting concentrate., e.g. the oil content increase by at least 50, 100, 200, 500, 1000 or 5000%.

In embodiments in which the oily water is concentrated prior to being introduced into a bioreactor, it is preferred to introduce a microbial inoculum into the bioreactor. In addition, it is preferred to add nutrients and/or to adjust and/or maintain the culture conditions within the bioreactor such that biodegradation of the oil by the microbial population of the microbial inoculum is optimised.

The system may comprise a membrane integral to, or downstream of, the bioreactor. Preferably, the bioreactor is a membrane bioreactor (MBR).

The membrane may be in an immersed set up, i.e. inside the bioreactor, in which case it may be referred to as being “integral” to the bioreactor. If the membrane is integral to the bioreactor, then the bioreactor may be considered to have a biodegradation chamber, where biodegradation takes place, and a membrane chamber, where water is filtered through a membrane.

Alternatively or in addition, the membrane may be in a sidestream set up, i.e. outside of the bioreactor. Thus, the bioreactor may comprise a membrane, or be in fluid communication with a membrane. The membrane may preferably be a separate unit with redundancy and/or be configured to allow chemical cleaning and/or replacement of the membrane.

The method may preferably comprise a step of filtering water from the bioreactor, e.g. from the biodegradation chamber, through a membrane. This filtering may occur at or near the bioreactor effluent outlet, so the water/effluent may be filtered as it leaves the bioreactor, or as it leaves the biodegradation chamber of the bioreactor.

A suitable membrane may be one that is permeable at least to water and rejects particles on the basis of size and/or charge. Preferably, it substantially rejects oil and/or microbes, such as bacteria. Such a step may help to retain most of the microorganisms and oil, as well as any carriers, in the bioreactor, thus yielding an effluent that has a low oil content.

In some embodiments, the microbial concentration within the bioreactor may be fairly low, but in other embodiments it may be fairly high. The membrane is preferably selected to be capable of maintaining the desired biomass concentration in the bioreactor. It may, for example, be capable of maintaining a biomass of at least 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15 or 20 g TS/I in the bioreactor.

The membrane is preferably a microfiltration membrane or an ultrafiltration membrane. It may e.g. have a pore size of 0.001 to 10 pm, preferably 0.1 - 10 pm, e.g. about 0.5 pm. It may, e.g., be ceramic or polymeric, e.g. a synthetic polymer. For example, it may be made of ceramic materials,e.g. silicate carbide, or of graphene, polyacrylonitrile, polyethylene, polyethylsulphone, polysulphone, polytetrafluoroethylene or polyvinylidine difluoride.

Preferably, the bioreactor is operated/configured to have a hydraulic retention time of about 15-40 or 15-30 hours, preferably less than 30 or 24 hours but more than 1, 2, 5 or 10 hours. This is particularly preferred if the bioreactor is an MBR.

The method may involve a step of adding seawater to the bioreactor. Thus, oily water and seawater may be introduced into the bioreactor, for example at a ratio of oily water:seawater of from about 50:10, 10:1, or 5:1 to about 1:5, 1:10 or 1:50, e.g. about 1:10, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1 or 10:1, preferably about 2:1 to 1:2 or about 1:1.

The method may involve a step of filtering the oily water through an adsorption medium. The adsorption medium must be capable of adsorbing oil from the oily water.

Thus, the oily water may be filtered through the adsorption medium to yield effluent water as defined elsewhere herein. The adsorption medium may be referred to as an adsorption filter.

The adsorption medium may be natural or synthetic. For example, it may comprise or consist of a polymer, (organo) clay, resins, preferably anionic ones, zeolite, graphene, anthracite, garnet, and/or walnut shell, e.g. activated carbon such as granular activated carbon (GAC). It preferably has a high surface area to volume ratio. It preferably has an oil adsorption capacity of at least 1,2,3, 4, 5, 6, 7, 8, 9 or 10 w%.

The adsorption medium, e.g. adsorption filter, preferably has a size of at least about 100, 200, 300, 400, 450, 500, 550, 600 or 700 m³ and preferably no more than 2000, 1000, 900, 800 or 700 m³. It preferably has an adsorption capacity of at least 500, 1000, 2000, 3000, 4000, 4500, 5000, 5500, 6000, 7000, 8000, 9000 or 10000 kg. This may be the size/capacity of an individual adsorption medium, or the combined size/capacity of the plurality of adsorption media present in the system.

The density of the adsorption medium may, e.g. e about 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2 kg/m³.

The filtration rate through the adsorption medium may be at least 5 m/h, preferably at least 10, 15, 18 or 20 m/h, more preferably at least 22, 24, 26, 28, 29, 30, 31,32, 33, 34, 35, 40 or 45 m/h. Thus, the adsorption vessel may be configured to be operated at such a filtration rate. This may be the filtration rate through an individual adsorption medium, or the combined filtration rate through the plurality of adsorption media present in the system.

The volume of oily water that may be filtered through an adsorption medium during an adsorption cycle may be at least 200, 300, 400, 450, 500, 550, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, 18,000, 19,000, 20,000, 21,000, 22,000, 23,000, 24,000 or 25,000 m³. This may be the volume filtered per adsorption medium or the total volume filtered through the plurality of adsorption media present in the system that is/are operated in adsorption mode.

The adsorption medium may be regenerated at suitable intervals, preferably when it has reached at least 30, 40, 50, 60, 70, 80, 90, 95 or 99% of its adsorption capacity, e.g. when it is saturated, or at least partially saturated, with oil. Thus, the method may include a step of regenerating the adsorption medium.

The regeneration of the adsorption medium may involve incubating the adsorption medium in a bioreactor. Thus, the adsorption medium may be incubated with microorganisms. This may be referred to as direct bioregeneration of the adsorption medium. Suitable incubation times may be at least 1,2, 3, 4 or 5 days, and no more than 40, 30, 20 or 15 days, e.g. 7-10 days, but preferably less than 6, 5, 4 or 3 days.

Alternatively or in addition, the regeneration of the adsorption medium may involve back-flushing said adsorption medium, for example back-flushing with an aqueous solution and/or steam to remove oil from the adsorption medium and yield an oily back-flush, which may be introduced into a bioreactor. This may be referred to as indirect bioregeneration of the adsorption medium.

The aqueous solution and/or steam used for back-flushing may, e.g. comprise or consist of sea water, fresh water, and/or effluent water as defined elsewhere herein. It may comprise additives, e.g. one or more detergents, to aid the removal of oil from the adsorption medium. The volume of aqueous solution/steam used to back flush the adsorption medium to remove oil therefrom will typically be significantly smaller than the feed volume (i.e. volume of oily water that deposited the oil on the adsorption medium when it was filtered through the adsorption medium). Thus, by filtering a first oily water through adsorption medium and subsequently back-flushing said adsorption medium it is possible to generate a second oily water of a smaller overall volume and/or a higher oil concentration than the first oily water. Preferably, the back-flushing volume will be less than 20, 15, 10, 9, 8, 7, 6, or 5% of the feed volume, more preferably less than 4, 3, 2, 1 or 0.5%.

The second oily water, which may also be referred to as the “back-flush”, may be introduced into a bioreactor for biodegradation of the oil by microorganisms as discussed elsewhere herein.

Once regenerated, the adsorption medium will be ready for re-use, i.e. further oily water may be filtered through it.

A step of filtering the oily water through an adsorption medium may also be referred to as an “adsorption cycle”. The method may include 2 or more adsorption cycles, but preferably, a single cycle will yield an effluent water as defined elsewhere herein, so preferably the method only includes a single adsorption cycle.

A step of regenerating the adsorption medium may also be referred to as a “regeneration cycle”.

The adsorption medium is preferably in a vessel, which may be a horizontal or a vertical vessel. The flux (m³/m²h) may, e.g. be in the range of 1-100, 5-50, or 10-30, and the filter bed retention time may be in the range of 3-15 min, preferably less than 10 min.

Such a vessel may be operated, or configured to be operated, in at least 2 different modes selected from adsorption mode and regeneration mode. During the adsorption cycle, the vessel is configured/operated in adsorption mode, whereas during the regeneration cycle, the vessel is configured/operated in regeneration mode. The vessel may have one or more inlets and/or outlets, which may be controlled, e.g. via valves. For example, to operate the vessel in adsorption mode, the oily water inlet may be opened to introduce oily water into the vessel. To configure/operate the vessel in regeneration mode, the oily water inlet may be closed to stop or prevent the introduction of oily water into the vessel. Thus, such a vessel may be switched from adsorption mode into regeneration mode, and vice versa. The method may comprise switching a first vessel from adsorption mode into regeneration mode, and switching a second vessel from regeneration mode into adsorption mode. Such switching steps may be carried out simultaneously or sequentially.

If and when a vessel is configured/operated in direct bioregeneration mode, the vessel may be configured/operated as a bioreactor. Any discussion provided herein regarding a bioreactor applies mutatis mutandis to the vessel comprising an adsorption medium when it is configured/operated in bioreactor mode.

In other embodiments, the adsorption medium may be back-flushed as described elsewhere herein, and the back-flush may be introduced into a bioreactor, which may be in fluid connection with the vessel comprising the adsorption medium.

The method may include one or more adsorption cycles and/or one or more regeneration cycles in parallel. This may advantageously allow the continuous or semicontinuous treatment of oily water. For example, the system may comprise a plurality of vessels containing adsorption media, e.g. at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or 20, preferably no more than 50, 40, 30 or 25, e.g. about 6-20 or 8-14, or about 12, although 2-10 is preferred. The flow of oily water into said vessels may be controlled, e.g. via valves, such that some vessels are used for adsorption cycles and others are used for regeneration cycles. Thus, the system may be configured/operated such that at any given time whilst the system is in operation a proportion, e.g., no more than 5, 10, 20, 30, 40 or 50%, of the vessels may be in adsorption mode, whilst another proportion, e.g., at least 50, 60, 70, 80, 90 or 95%, of the vessels may be in regeneration mode. For example, the system may comprise about 12 of said vessels, of which at any given time whilst the system is in operation e.g. 2 may be configured/operated in adsorption mode and 10 may be in regeneration mode.

The oily water may comprise compounds that are non-desorbable and/or nonbiodegradable. The method may therefore optionally include a step of non-biological regeneration of the adsorption medium. Such a step may involve one or more processes that are well known in the art, such as the use of detergent, acid, and/or steam. Such a step may be carried out at predetermined time points, e.g. regular intervals, and/or as and when needed. The need to carry out a step of non-biological regeneration of the adsorption medium may be determined by determining whether the adsorption capacity of the adsorption medium has declined.

The term “bioreactor” is used herein to mean a vessel in which microorganisms can biodegrade oil. The bioreactor is configured to contain microorganisms, and to allow the survival and/or growth thereof, e.g. to allow the cultivation thereof. It is configured to allow or encourage the biodegradation of oil to take place. The bioreactor comprises the necessary inlet(s) and outlet(s) to allow the biodegradation of oil from oily water by microorganisms. In particular, the bioreactor is configured to receive oily water and to have an output for effluent water. Preferably, the bioreactor is also configured to receive a microbial inoculum, nutrients, gas, and/or seawater; and/or to have an outlet for gas, biomass, and/or other waste products.

Any reference herein to a “vessel” should be understood to mean a structure that can contain liquid. The vessel may, e.g. be a container or tank, or it may be a cylindrical structure, such as a pipe. Thus, it may, e.g., be a horizontal or a vertical vessel. Preferably, the vessel creates an enclosed space without any openings other than any inlet(s) and outlet(s) discussed elsewhere herein.

The vessel, e.g. cylindrical structure, may, e.g., have an outer diameter of at least or about 10, 12, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 45 or 50 cm, preferably less than 60, 50, 40 or 30 cm. It may have a length of at least or about 1,5, 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 km, preferably less than 500, 200 or 150 km, e.g. 1-5 or 20-40 km.

A cylindrical bioreactor is illustrated in Fig. 9, but it should be understood that a cylindrical bioreactor may be used in any method or system of the invention.

If the bioreactor is in the form of a pipe, then it may be used to transport and treat oily water, preferably simultaneously. For example, oily water, e.g. produced water, may be introduced into the bioreactor pipe at a location at or near an oil reservoir/oil well and transported to another location, which may be a distant location, e.g. 10, 50, 100 m or km away. During said transport, biodegradation of the oil may take place, preferably in a plug flow mode as discussed elsewhere herein. The effluent may then be used or discharged at the distant location.

The bioreactor is preferably configured to allow the adjustment and/or maintenance of the bioreactor conditions/parameters, as discussed elsewhere herein.

The bioreactor may comprise a membrane and/or adsorption medium, as discussed elsewhere herein. It may comprise a “biodegradation chamber”, by which is meant a chamber in which biodegradation can take place. For example, an MBR may be considered to have a biodegradation chamber and a membrane downstream thereof.

According to the present invention, the bioreactor must also be configured to operate subsea. Details of subsea configurations are provided elsewhere herein.

As explained elsewhere herein, a vessel may be configured to operate in at least two different modes, at least one of which may be a biodegradation/bioreactor mode.

Preferably, the bioreactor contains microorganisms, e.g. at a biomass concentration mentioned elsewhere herein.

The bioreactor may be configured to facilitate plug flow, e.g. it may comprise one or more baffles and/or chambers, or it may have a long cylindrical shape. Thus, the bioreactor may be configured to maximise the distance that the oily water must travel through the bioreactor to reach the effluent outlet, and this may be particularly effectively achieved via a cylindrical shape in which the ratio of the length to the inner diameter is very high. By “plug flow” is meant that longitudinal mixing of the oily water within the bioreactor is minimised.

The oily water can be imagined to flow as a plug from the bioreactor inlet towards the bioreactor outlet. Thus, the parameters/conditions in each “plug” may be different, e.g. one or more parameters/conditions in close proximity to the bioreactor oily water inlet may be different to one or more parameters/conditions in close proximity to the bioreactor effluent outlet. For example, the oily water may have a high oil concentration at/near the oily water inlet and a lower oil concentration at/near the effluent outlet. Thus, there may be an oil concentration gradient throughout the bioreactor, and the bioreactor may be configured to facilitate this.

Similarly, there may be differences, e.g. a concentration gradient, in the levels of gas, nutrients, microbes, waste products and so on. Different types of microbes may be more prevalent in different parts of the bioreactor, e.g. a first microbial type may be present at the highest level at/near an inlet, e.g. the oily water inlet, and/or a second microbial type may be present at the highest level at/near an outlet, e.g. the effluent outlet.

The size, i.e. volume capacity, of the bioreactor may be between about 100 and 400,000 m³, depending on the desired method. For example, if the method does not include a step of concentrating the oily water, then the bioreactor may preferably have a size of at least 5000, 8000, 9000 or 10,000 m³, and preferably no more than 500,000 or 400,000 m³, e.g. about 10,000-35,000, preferably 10,000-25,000 m³ or 5000-25,000 m³. For example, if the bioreactor is an MBR, it may have such a size. It may have a (vertical) cylindrical shape with a diameter of e.g. at least 20, 25, 30, or 35 m, e.g. about 36m and a height of e.g. at least 20, 25, 30, or 35 m, e.g. 36 m. It may weigh at least 5000, 6000, 7000, 8000 or 9000 tonnes, e.g. about 10000 tonnes.

If the bioreactor is a vessel comprising an adsorption medium, then it may preferably have a size of at least 100, 200, 300, 400, 500, or 600 m³, and preferably no more than 2000 or 1500 m³, e.g. be about 500-1000 m³.

If the bioreactor is a biofilter, then it may have a size of 50,000 - 300,000 m³. If the system comprises a bioreactor configured for oxic conditions (“aerobic bioreactor”) and a bioreactor configured for anoxic conditions (“anaerobic bioreactor”), then the size of the anaerobic bioreactor may be about 5000-25,000 m³ and the size of the aerobic bioreactor may be about 2000-10,000 m³.

The bioreactor(s) may be configured/operated to support or cause microbial biomass growth of at least 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8 kg volatile suspended solid (VSS) per kg of oil. Biomass production in the bioreactor(s) may preferably be about, or at least about, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 2600, 2700, 2800, 2900 or 3000 kg/day. The microbial biomass concentration in the bioreactor(s) may e.g. be about, or at least about, 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or 10000 ppm. The total microbial biomass in the bioreactor may e.g. be about, or at least about, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, 170,000, 180,000, 190,000, 200,000, or 300,000 kg.

In some embodiments, the bioreactor may be or comprise a biofilter. A biofilter comprises media to which microorganisms can attach and grow, e.g. in the form of a biofilm. Thus, a biofilter is a bioreactor configured to allow the microorganisms to be cultured in an essentially immobilised manner. The media may comprise or consist of inorganic media, e.g. sand, gravel, plastic, glass, and/or ceramic; and/or organic media, e.g. wood chips, and/or nut or coconut shell fragments. The oily water may be applied via upflow or downflow.

The biofilter may e.g. be a trickle filter or a fluidized bed filter. The biofilter may, e.g., be of the fixed bed type.

The oily water and/or any seawater, nutrient supplement, microbial inoculum and the like may be added into the bioreactor, e.g. biofilter, through different inlets into different zones of the bioreactor, e.g. biofilter, e.g. to favour optimal distribution of the oil, microbes, and/or nutrients, and/or optimal oxygenation and/or hydrodynamic conditions.

The retention time in the biofilter is preferably determined by the type of biodegradation that takes place therein. In particular, for aerobic biodegradation, the retention time is preferably no more than a day, whereas for anaerobic degradation, the retention time is preferably several days. Thus, the retention time may be 1-24 hours or 124 days. More specifically, e.g. for an aerobic process, it may preferably be at least about 1, 1.5 or 2 hours, and no more than about 20, 15, 10, 9, 8, 7, 6 or 5 hours, e.g. e.g. about 2-6 or 3-5 hours. E.g. for an anaerobic process, it may preferably be at least about 1, 2, 3, 4 or 5 days, and no more than about 20, 15, 10, 9, 8, 7, or 6 days, e.g. about 5-15 days.

The oily water will preferably be produced water, so it will typically and preferably have a temperature of about 50 to about 200, 160 or 100 °C when it enters the system, e.g. the bioreactor. The method may preferably involve adjusting and/or maintaining a temperature in the bioreactor of about 10-95 °C, e.g., about 10-20, 30-40, 50-60, or 60-80°C, preferably about 15, about 35 or about 55 °C. Thus, the bioreactor may preferably be configured/operated to achieve and/or maintain such a temperature as the internal operating temperature, e.g. it may have a temperature control.

The microbes, e.g. the microbial inoculum, may comprise or consist essentially of psychrophilic, mesophilic or thermophilic microbes, in which case the internal operating temperature of the bioreactor is preferably adjusted and/or maintained at about 15, 35 or 55°C respectively.

Produced water typically has a pH of 5-8, so the oily water may have a pH of 5-8 when it is introduced into the bioreactor. The method may involve adjusting and/or maintaining the pH of the oily water, e.g. at about 3, 4, 5, 6, 7, 8, or 9, e.g. about 4-7, 7-9, 56, 6-7, 7-8 or 8-9. Thus, the bioreactor may preferably be operated/configured to achieve and/or maintain such a pH, e.g. it may have a pH control. Controlling the pH may comprise a step of adding a suitable buffer, and/or an acid or a base to the bioreactor.

The method may involve a step of adding freshwater and/or seawater to the bioreactor. Seawater contains nutrients such as carbon, nitrogen and phosphorus, typically in a ratio of about 100:15:1, e.g. 106:16:1. Seawater also contains dissolved free oxygen (O₂), typically about 1 mg/L to about than 20 or 30 mg/L. Freshwater typically also contains nutrients and oxygen. Thus, seawater and/or freshwater may be a source of one or more nutrients and/or oxygen, so the addition of seawater and/or freshwater will typically inherently add some nutrients and oxygen to the bioreactor.

Alternatively or in addition, the method may include a step of adding a nutrient supplement to the bioreactor. By a “nutrient supplement” is meant a material consisting of one or more nutrients, or comprising a high concentration of one or more nutrients. The nutrient supplement may have a defined nutrient composition, i.e. the nature and concentration of each nutrient may be known; or it may have a partially defined nutrient composition, i.e. the nature and/or concentration of at least one nutrient may be known; or it may have an undefined nutrient composition, as may e.g. be the case for yeast extract.

Thus, the method may involve the addition of a nutrient supplement comprising or consisting of one or more nutrients to aid the growth of the microorganisms. The nutrients may most preferably include nitrogen and/or phosphorus. Preferably, sulphur may also be added. The method may also involve the addition of one or more trace elements and/or minerals.

One or more detergents and/or enzymes, such as oil degrading enzymes, may be introduced into the bioreactor.

The bioreactor may comprise carriers that may provide a support for the microorganisms. By “support” is meant that the microorganisms may preferably colonise the carrier and/or form a biofilm on and/or within the carrier. The carriers may be immobilised, but preferably they are non-immobilised (except in a biofilter). Most preferably, they are floating in suspension within the oily water. The method may, e.g., comprise the use of a stream of gas and/or liquid which causes the carriers to be in suspension. Alternatively or in addition, the suspension may be mechanically stirred. The carriers may comprise or consist of an adsorption material, such as activated carbon (e.g. GAC), a plastic, and/or a ceramic, preferably a polymer such as polyethylene or polypropylene. The carriers preferably have a lower density than water. If carriers are used, the bioreactor is preferably a “Moving Bed Biofilm Reactor”.

Within the bioreactor, the microbes may grow in suspension culture and/or form a biofilm. For example, if a carrier is used, then the microbes may preferably form a biofilm on and/or within the carrier. If an adsorption medium is present within the bioreactor, then the microbes may form a biofilm on and/or within the adsorption medium.

As mentioned elsewhere herein, one or more different gases may be supplied to the bioreactor. Preferably, the gas is supplied in a manner that facilitates fluidization of any membrane and/or adsorption medium that is used within or in connection with the bioreactor.

The present invention concerns the treatment of oily water. Where required to aid clarity, reference is made to a first oily water and a second oily water. Any reference herein to “oily water” without further reference to a “first” or “second” oily water should be understood to apply equally to a first oily water and a second oily water. By “oily water” is meant water containing oil. The oil may be in the form of large droplets referred to in the art as “free oil”; dissolved in the water; and/or dispersed in the water. Preferably, at least 20,

30, 40, 50, 60, 70, 80, 90 or 95% of the oil present in the oily water is dissolved in the water.

API gravity is calculated using the specific gravity of an oil, which is the ratio of its density to that of water (density of the oil/density of water). Specific gravity for API calculations should be determined at 60 degrees Fahrenheit. Though API values do not have units, they may be referred to as degrees. The API gravity may be used to classify oils as light, medium, heavy, or extra heavy. The API values for each “weight” are as follows: Light - API >31.1; Medium - API between 22.3 and 31.1; Heavy - API between 22.2 and 10.0; Extra Heavy - API < 10.0. Thus, the oil in or from the oily water may have an API of at least 5 or 10, preferably of at least 12, 15, 18, 20, 21,22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 or 40. Alternatively, it may have an API of less than 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 2, 26, 25, 24, 23, 22, 21, 20, 18, 15, 12, 10 or 5.

Oil comprises hydrocarbons, so any reference herein to “oil” should be understood to encompass a reference to hydrocarbons. The oil may optionally also comprise other organic molecules, such as carboxylic acids, e.g. fatty acids. The carboxylic acids may be saturated, monounsaturated or polyunsaturated. The hydrocarbons may comprise or consist of alkanes, e.g. higher alkanes up to C25, naphthenes, aromatics and/or asphaltics. For example, they may comprise or consist of BTEX (benzene, toluene, ethylbenzene and xylene), NPD (naphthalene, phenanthrene, and dibenzothiophene),PAHs (polyaromatic hydrocarbons) alkyl benzenes, phthalates, phenols, and/or non-phenolic aromatics .

Thus, as an alternative or in addition to measuring the total oil content of the water, one or more other parameters that take into account such other organic molecules may be used. Such parameters may, e.g. be selected from BOD (biochemical oxygen demand), COD (chemical oxygen demand), and/or TOC (total organic carbon). The BOD indicates the content of oxygen needed to decompose organic compounds in the oily water by microbes. The COD is a parameter that indicates the amount of oxygen which would be needed to oxidise all organic ingredients completely. The TOC reflects the organic pollution on the basis of a direct carbon determination. Methods of measuring any of these are known.

The biodegradation may therefore reduce the oil content of the water and/or reduce the BOD, COD and/or TOC of the water. Thus, the method may preferably yield an effluent having a lower BOD, COD and/or TOC than the oily water that was introduced into the system, e.g. the bioreactor. The reduction may, e.g. be by at least or about 10, 20, 30, 40, 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99%.

The method involves the biodegradation of oil, which is preferably the biodegradation of one or more different hydrocarbons. As mentioned above, the method may also involve the biodegradation of non-oil organic compounds. Biodegradation of organic compounds by microbes is substrate-specific, so any particular microbial species is typically only able to biodegrade a certain organic compounds, e.g. certain hydrocarbons. Thus, any particular microbial species will typically biodegrade a least a proportion of the oil, or more specifically a least a proportion of the various hydrocarbons.

The oily water may, for example, be what is referred to in the oil industry as “produced water”, which may e.g. be introduced into the system, preferably the bioreactor, from an oil-water separator, preferably a subsea one, with or without any pre-processing steps. Pre-processing steps, which may optionally form part of the method of the invention, may include the removal of gas, solid particles, salt, and/or chemicals.

Thus, the oily water may optionally contain, inter alia, solid particles, and/or chemical additives, such as corrosion inhibitors, oxygen scavengers, scale inhibitors, biocides, emulsion breakers, cross linkers, hydrate inhibitors, clarifiers, coagulants, flocculants, and/or solvents. The corrosion inhibitor may e.g. comprise or consist of amide and/or imidazoline compounds, the scale inhibitor may e.g. comprise or consist of phosphate and/or phosphate ester compounds, the biocide may e.g. be a brominated nitrilopropionamide, the cross linker may e.g. be ethylene glycol, the hydrate inhibitor may e.g. be methanol.

Preferably, the method of the invention also reduces the concentration of one or more of these chemical additives. Thus, preferably, the effluent water will have a lower concentration of one or more of these chemical additives than the oily water that is introduced into the system. For example, the concentration may be reduced by at least 10,

20, 30, 40, 50, 60, 70, 80, 90, 95 or 99%. The method may include a step of modulating one or more of these chemical additives in the oily water, preferably prior to introducing the oily water into a bioreactor. Such modulation may include reducing the concentration thereof, and/or physically and/or chemically modifying said chemical(s). Such a step may include diluting the oily water, e.g. with seawater; adding a chemical, such as a buffer; and/or a step of removing one or more of the chemicals, e.g. selective removal.

The solid particles may be sand and/or silt. The oily water will preferably have less than about 50, 40, 30, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11 or 10 ppm of such solid (nonliving) particles, more preferably less than about 9, 8, 7, 6, 5, 4, 3, 2, or 1 ppm.

The oily water may have an oil content of about 50-2000 ppm, preferably at least 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800 or 900 ppm, but preferably no more than 2000, 1000, 800 or 500, e.g. about 50-1000, 100-800, 40-100, 100-500 and the like.

The water that has been treated via the method of the invention may be referred to as “treated water” or “effluent”. The effluent preferably has an oil content of less than 35, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21,20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5,

4, 3, 2, or 1 ppm. It preferably has a BOD, COD and/or TOC of less than 1000, 800, 500, 400, 300, 250, 200, 150, 100, 90, 80, 70, 60, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5 or 1 ppm.

The effluent preferably has less than about 50, 40, 30, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11 or 10 ppm of solid (non-living) particles, more preferably less than about 9, 8, 7, 6, 5, 4, 3, 2, or 1 ppm. The percentage of solid particles present in the oily water may be reduced using known methods, e.g. down-hole sand screens and/or in-line sand separators on the well stream upstream separators. In this context, reference is made to non-living solid particles, so microbes are not encompassed by the term “non-living solid particles”.

The effluent may comprise a microbial population, or it may be substantially free of bacteria, fungi, archaea, algae, protozoa, and/or viruses.

The oil content of water, e.g. the oily water and/or the effluent water, may be measured using known processes, which may be carried out in situ, or samples may be taken subsea and transported to a topside on onshore site where the measurements may be carried out. Processes for analysing oily water may involve, for example, inductance and capacitance measurements, Microwave sensors, Near Infra Red Absorption methods, Photometry, Gravimetric and/or GC-FID (gas chromatography with flame ionisation detection) and/or Ultrasonic Frequency Measurements.

In some embodiments, the microorganisms added to/present in the bioreactor are capable of producing extracellular biopolymers and/or bio-surfactants. The method may comprise a step of adding microorganisms capable of producing such compounds into the bioreactor; thus, the microbial inoculum may comprise or consist of such microorganisms. The method may comprise a step of adjusting and/or maintaining the bioreactor conditions to cause the production of extracellular biopolymers and/or bio-surfactants by the microorganisms in the bioreactor. Details of adjusting and/or maintaining the bioreactor conditions are discussed elsewhere herein. The biopolymers and/or bio-surfactants may preferably be recovered, e.g. they may be present in the effluent water. The recovered biopolymers and/or bio-surfactants may preferably be used in a method of enhanced oil recovery, e.g. they may be injected into an oil reservoir for enhanced oil recovery.

The biopolymer or bio-surfactant may be an amphiphilic compound that may e.g. be selected from glycolipids, phospholipids, lipopeptides, fatty acids, mycolic acids, lipopolysaccharides and the like. It may, e.g. be a surfactin, a sophorolipid, a mycolate, ora rhamnolipid, e.g. a mono or di-rhamnolipid, which may e.g. be produced by a Pseudomonas species such as Pseudomonas aeruginosa.

The bioreactor and preferably one or more further components of the system are preferably configured for the treatment of produced water, preferably in situ. Produced water is typically generated continuously and in large quantities. Thus, the bioreactor and preferably one or more further components of the system are preferably configured to accept and process large volumes of oily water that may be introduced into the system in a continuous or semi-continuous manner. Consequently, the bioreactor and preferably also any other vessels that form part of the system must be of a sufficiently large size to accept large quantities of oily water.

The method of the invention involves the use of at least a bioreactor in a subsea location. Thus, at least the biodegradation of oil takes place subsea. Other steps of the method may also be carried out subsea, so in addition to the bioreactor, other components of the system may be located subsea. However, in some embodiments, some steps of the method may be carried out at a non-subsea location, so some components of the system may be located at a non-subsea location. Preferably, all of the steps of the method of treating oily water, and therefore all of the relevant components of the system, are subsea. The subsea treatment of oily water, such as produced water, may be part of a method and system of oil production. The oil and gas treatment steps and system components may be at a topside location, e.g. on a floater host. In such a scenario, the host is preferably manned. Alternatively, the oil treatment steps and system components may also be at a subsea location, whereas the gas treatment steps and system components may be at a topside location, e.g. on a floater host. In such a scenario, the host is preferably unmanned. Alternatively, the oil and gas treatment steps and system components may also be at a subsea location. Thus, the subsea oily water treatment may be part of a subsea factory.

Thus, the bioreactor and preferably one or more further components of the system are configured to operate in a subsea location. By “configured to operate in a subsea location” is meant that the bioreactor and any other subsea components are configured to withstand subsea conditions, such as subsea pressures, temperatures, salinity and the like.

The bioreactor and any other subsea components are preferably configured to withstand the internal operating temperatures that arise during oily water treatment, e.g. 1150 °C. Further details on internal operating temperatures are provided elsewhere herein. The bioreactor and any other subsea components are preferably configured to withstand the external temperatures that exist in a subsea location, e.g. about 0-20, 0-10 or 0-5 °C.

For example, the subsea components of the system must be able to withstand an external hydrostatic pressure of at least about 5, 7, 10, 12, 14, 16, 18, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 650, 690 or 700 bar and/or an internal operating pressure of at least 5, 7, 10, 12, 14, 16, 18, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 650, 690 or 700 bar. The external pressure will be determined primarily by the depth of the subsea location. The internal pressure may be regulated and although the internal pressure may be the same as the external pressure, it is preferable to adjust and/or maintain the internal pressure at a selected pressure, e.g. a pressure that is optimal for the process that is operated inside any given vessel. Thus, for a bioreactor, the internal pressure may be adjusted and/or maintained to be optimum for biodegradation to take place. For example, the internal operating pressure may be about 5, 50, 100, 200, 340 or 690 bar.

As mentioned elsewhere, any of the vessels of the system may comprise various inlets and outlets. Any of the inlets, outlets, conduits and the like mentioned herein may be controlled by a pump and/or a valve.

The system may comprise one or more of the following components:

Subsea bioreactor, preferably with a multi-chamber design, preferably with a membrane and/or filter; feed-pump; discharge-pump; check valve; pressure release-valve for gas discharge; level transmitter; pressure transmitter; sensors and instruments; and/or subsea control module. For example, the system may comprise a check valve and pump to introduce seawater into the bioreactor.

The system may comprise an umbilical line that may supply nutrients to the bioreactor from shore, from a platform/floater, and/or from a buoy and a riser.

The system may comprise a control module configured to operate any valves, pumps, sensors and the like remotely, e.g. from a topside or onshore location.

The system may comprise fiber optic cables, which may allow lightning fast data transfer rates, high data volume and/or the ability to transmit data over distances exceeding 100 miles without a repeater (amplifier).

The system may comprise one or more sensors for Oxygen, pH, Nutrients, particularly nitrogen and phosphorus, oil content, and/or temperature. Standard sensor technologies are available for subsea monitoring of any of these variables.

Thus, one or more parameters may e.g. be read by a detection system and the reading may be fed back via a fibre-optic communication system to a process controller that may be at a topside or on shore location.

The system, or at least one or more components thereof, preferably the bioreactor, may comprise corrosion-resistant material, e.g. be corrosion-resistant. For example, it may have a coating, such as bitumastic or epoxy coating.

The method and system is suitable for use with any subsea oil production processes, so the system may be configured to be used with any subsea oil production processes. The subsea oil production process may e.g. have the following parameters:

Oil production, Sm3/d	6000- 10000
Water production, Sm3/d	7000 - 20000
Gas production, Sm3/d	500000- 1000000
API	30-40
Reservoir temperature, deg C	50-100

Flowing well head pressure, bar	15-60
GOR, Sm3/Sm3	100-200
Oil in produced water, ppm	100-500
Freshwater	N/A
Solid particles in produced water, BS&W, %	~ 0,5

Optionally, one or more processing steps may be performed prior to introducing the oily water into a bioreactor. In particular, the oily water may optionally be passed through, or be derived from, an oil-water separator, such as a 2-phase separator, 3-phase separator, an in-line separator, and/or a gravity separator, such as a long-retention time gravity separator

For example, a gravity separator may be used with a hydraulic retention time of about 5-24 hours, preferably less than 10 hours. The gravity separator may be either a horizontal vessel with inlet (e.g. guided vanes) and outlet arrangements (e.g. V-notch), or a vertical vessel designed for enhanced separation using dissolved or induced gas. The size of the vessel may be in the range of 10 000-20 000 m³.

For example, a 3-phase separator with a length of about 12-13 meters, e.g. 12.3 meters, a diameter of about 3 meters, e.g. 3.1 meters, and/or a weight of about 140-160 tonnes may be suitable. The 3-phase separator may preferably have a retention time of about 1-10 or 1-5 minutes, e.g. about 3 minutes. Oily water derived from a 3-phase separator may preferably have an oil content of about 100-500ppm.

The oil-water separator may be configured to operate in a subsea location, and may indeed be in a subsea location. For example, the system may comprise a coalescer, or a pipesep m/dialectric material.

The method may include a step of processing oily water through one or more of these separators, or may involve the use of oily water that has been subjected to one or more of these as a starting material. Thus, an oil-water separator may be configured/operated upstream of the bioreactor and preferably upstream of any concentrator or adsorption medium, details of which are discussed elsewhere herein.

Produced water typically has a temperature of 50-100 °C and the heat from this water may preferably be used to power one or more of the apparatuses used in oil production and/or oily water treatment. In particular, it may, e.g., be used to power an inline oil/water separator, which may reduce the need for large oil/water separators.

The oily water may contain one or more different gaseous compounds, such as CO₂, H₂S, N₂, methane, and/or other volatile hydrocarbons, so the introduction of oily water into the bioreactor may introduce gas into the bioreactor. The biodegradation of oil may also result in the formation of gases, such as methane, CO₂, hydrogen (H₂), H₂S, N₂ and the like. Gases may also be introduced into the bioreactor to provide oxygen, to keep any carriers in suspension, and/or to aid the fluidization of any membranes. Gases that are introduced into, and/or that form within, the bioreactor may be removed from the bioreactor. Once removed from the bioreactor, any gas may be released, i.e. discharged into the environment; injected into the oil reservoir; and/or used for other applications, e.g. in an oil recovery and/or produced water process. For example, CO₂ may be used to re-fill cooler turbines.

Any gas that is removed from the bioreactor may, e.g., be used in a gas flotation process, which may be upstream of the bioreactor. For example, gas flotation may be used to separate some oil from oily water, yielding oily water that may, e.g. be introduced into a bioreactor of the invention. An example is illustrated in a non-limiting manner in Fig. 9. It should be understood that any system/method of the invention may be configured/operated to introduce gas from a bioreactor into a gas flotation vessel. The system of the invention may thus comprise a gas flotation vessel.

Gas flotation technology is widely used for the treatment of produced water. This process uses fine gas bubbles to separate suspended particles that are not easily separated by sedimentation. When gas is injected into produced water, suspended particulates and oil droplets are attached to the air bubbles as it rises. This typically results into the formation of foam on the surface of the water which may be skimmed off as froth. By using gas from the bioreactor for gas flotation, the overall process is made more efficient, as fewer resources are used and less waste is produced.

The salinity of produced water is typically 5000-60000 mg TDS/I, but it can be as high as 150,000 or 200,000 mg TDS/I. Microbes can typically adapt to a wide range of salinity, but stable salinity conditions are preferred. Thus, the method preferably involves adjusting and/or maintaining the salinity of the oily water at a particular level, which may be a predetermined level, e.g. about 5000-60000 mg TDS/I, e.g. at least 5000, 6000, 7000, 800 or 9000 but no more than 60000, 50000, 40000, 30000, 20000, 15000 or 10000 .

Preferably, the salinity is controlled such that the variation range is max +/- 5000 mg/l TDS, more preferably max 4000, 3000, 2000, 1000, 500 or 1100 mg/l TDS.

Adjusting and/or controlling the salinity may preferably be achieved through dilution with seawater and/or freshwater e.g. aquifer water, and/or through the use of a buffer.

In some embodiments, the method may comprise a step of adding the effluent water into a bio-polishing vessel. Thus, the system may comprise a bio-polishing vessel. In some embodiments, method may also comprise a step of adding seawater to the bio-polishing vessel, for example at a ratio of effluent:seawater of from about 50:10, 10:1, or 5:1 to about 1:5, 1:10 or 1:50, e.g. about 1:10, 1:5, 1:4, 1:3, 1:2, 1:1,2:1, 3:1, 4:1, 5:1 or 10:1, preferably about 2:1 to 1:2 or about 1:1. The bio-polishing vessel advantageously contains planktonic organisms, which may be introduced into the vessel through the addition of seawater, which typically contains such organisms, and/or through the addition of an inoculum of planktonic organisms. Preferred planktonic organisms include algae and protozoa. The planktonic organisms consume microorganisms present in the effluent water, so by passing the effluent water through a bio-polishing vessel, the microbial load of the effluent water may be reduced.

The method may yield microbial biomass or sludge, which may be removed and optionally used in a number of different ways. For example, it may be introduced or reintroduced into the bioreactor; stored in a storage vessel; used as a biofuel; used as a feed in sea farming; used for pharmaceutical production; retained for other applications; and/or discarded.

For example, the effluent water, microbial biomass, nutrients, oxygen, CO₂ and/or heat generated during, or available in excess from, the method ofthe invention can be utilized in a sea farming system, e.g. for production of macro/micro algae, mussels, algae, and/or fish.

One or more ofthe effluent water, microbial biomass, nutrients, oxygen, CO₂ and/or heat may be introduced into a sea farming vessel or system, which may e.g. be located on the seabed or be a floating system. Thus, the system may comprise a sea farming vessel, or be in communication with a sea farming system.

The term “sea farming” is used herein to refer to aquaculture, preferably mariculture.

The system may preferably be operated remotely. Thus, the method may comprise operating one or more, or all, components ofthe system remotely, particularly the bioreactor and any inlets and outlets thereof, as well as any sensors. Thus, for example, one or more or all valves are preferably configured to be controlled remotely, so the method preferably comprises controlling one or more or all valves.

The system preferably comprises one or more sensors to monitor and/or control one or more parameters selected from the temperature, pH, free oxygen levels, nutrient levels, oil levels, Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and/or Total Organic Carbon (TOC) in one or more components ofthe system, preferably at least in the bioreactor. Such sensors may be configured for subsea operation and standard technologies are available.

The system may comprise one or more sensors to monitor one or more parameters relating to the microbial population in the bioreactor, e.g. the microbial growth, microbial concentration, microbial identities, microbial activity, particularly biodegradation activity and the like. In particular, the metabolic activity of the microbial population may be monitored, e.g. by monitoring the production of gas, such as CO₂ and/or methane. The biomass density, and/or properties such as fluorescence of cells and/or genetic features may be monitored. For example, a flow-through system may be used, which may e.g. include a microfluidic chip.

Thus, the method may comprise the use of one or more such sensors to measure one or more of these parameters, e.g. of the oily water prior to the introduction thereof oily water into the bioreactor; of the oily water inside the bioreactor at one or more different time points; and/or of the effluent water.

The system, e.g. bioreactor, may comprise an outlet for biomass and/or an outlet for effluent water. Any outlet may preferably have a discharge pump and preferably a check valve upstream of the discharge pump.

Any of the components of the system, particularly any vessels, may comprise steel and/or concrete, e.g. reinforced concrete. Suitable systems or components may be obtained from manufacturers such as Kongsberg Gruppen ASA (Kirkegardsveien 45, NO-3616 Kongsberg, Norway).

Any of the components of the system, particularly the subsea components such as the bioreactor, should be configured/operated to require minimal maintenance; have a lifespan of at least 20 years; and meet safety requirements, in particular avoid or minimise any leakage, particularly of oil or oily water.

The invention will now be described in more detail by reference to the following nonlimiting Figures and Examples.

Figs. 1A-1B show an example of a first embodiment of the method and system of the invention; Fig. 1A shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle; Fig 1B shows a membrane bioreactor;

Figs. 2A-2B show an example of a second embodiment of the method and system of the invention; Fig. 2A shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle; Fig 2B shows a plurality of vessels containing adsorption media; an embodiment is shown in which 2 vessels are in adsorption mode and the remainder (12 vessels) are in a bioregeneration mode;

Fig. 3 shows an example of a third embodiment of the method and system of the invention; It shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle; It shows a cluster of 4 vessels containing adsorption media and 1 bioreactor vessel and illustrates various inlets and outlets;

Fig. 4 shows an example of a fourth embodiment of the method and system of the invention; it shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle;

Fig. 5 shows an example of a fifth embodiment of the method and system of the invention; it shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle;

Fig. 6 shows an example of a sixth embodiment of the method and system of the invention; it shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle;

Fig. 7 shows an example of a seventh embodiment of the method and system of the invention; it shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle;

Fig. 8 shows an example of an eighth embodiment of the method and system of the invention; it shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle;

Fig. 9 shows an example of a ninth embodiment of the method and system of the invention; it shows the method and system in the larger context of oil exploration, wherein the key elements of the invention are shown in a rounded rectangle;

Fig. 10 is a schematic of one embodiment of a system according to the present invention, wherein oily water is treated in an aerobic bioreactor and sludge from the aerobic bioreactor is treated in an anaerobic bioreactor; and

Fig. 11 is a schematic of one embodiment of a system according to the present invention, wherein oily water is first treated in an anaerobic bioreactor and then in an aerobic bioreactor.

Further details of embodiments ofthe invention, particularly the various embodiments shown in the Figures, are discussed below. The skilled person will appreciate that some or all of the features of each of these embodiments may be combined with some or all features of any of the other embodiments. For example, any system/method of the invention may comprise a 3-phase separator, e.g. as shown in Fig. 1A or Fig. 2A; any system/method of the invention may comprise an in-line separator, e.g. as shown in Fig 4; any system/method of the invention may comprise a cooler turbine configured/operated to use CO₂ produced in a bioreactor, e.g. as shown in Fig. 4; any system/method ofthe invention may comprise a bio-polishing vessel, e.g. as shown in Fig. 5; any system/method ofthe invention may comprise a sea farm vessel, e.g. as shown in Fig. 7; any system/method ofthe invention may comprise a membrane vessel to concentrate the oily water, e.g. as show in Fig.8; any of the bioreactors ofthe system/method ofthe invention may incorporate an aerobic and an anaerobic bioreactor as shown in Figure 8; and any system of the invention may comprise a gas flotation tank configured/operated to use gas released from a bioreactor as shown in Fig. 9.

In a first embodiment, the method comprises a step of introducing oily water into a bioreactor where microorganisms degrade oil present in the oily water, and a step of filtering water from the bioreactor through a membrane to yield an effluent that has a low oil content.

An example of the first embodiment and individual features thereof is shown in Figs. 1A-1B. Preferably, one or more conditions may be optimised to allow or cause maximum biodegradation of the oil to take place. The conditions may for example include one or more of temperature, pH, nutrient levels, trace element levels, mineral levels, enzyme levels, detergent levels and the like, as discussed elsewhere herein.

The method may be carried out under oxic conditions to cause aerobic biodegradation to take place. Thus, free oxygen may be introduced into the bioreactor. Alternatively, the method may be carried out under anoxic conditions to cause anaerobic biodegradation to take place, in which case the method preferably does not comprise a step of adding free oxygen to the bioreactor.

The biodegradation may be carried out by microbes that are naturally present in the oily water. As required, seawater and/or a microbial inoculum may be added to the bioreactor.

The oily water that may be introduced into the bioreactor may, e.g. have an oil content of about 500 ppm. The biodegradation reduces the oil content of the oily water. The method may comprise a step of filtering the content of the bioreactor through a membrane located downstream of the bioreactor. Thus, the bioreactor may preferably be a membrane bioreactor (MBR). The bioreactor may comprise carriers, as discussed elsewhere herein.

An example MBR is shown in Fig. 1B. The filtration through the membrane yields a permeate, which may be referred to as the effluent water and which should have an oil content of no more than 10ppm.

The effluent water, any excess biomass, any gases, such as CO₂, methane and/or air, may be removed from the bioreactor.

For example, the following parameters shown in Table 1 may be used. This is a nonlimiting Example for a design with a flow of oily water of 20 000 m³ with 500 ppm oil.

Table 1

	Example range	Example value
Biomass concentration	3000-8000	5000	PPm
Degradation rate	0.05-0.2	0.1	kg oil per kg biomass
Minimum hydraulic retention time	5-25	24	hours
Minimum reactor volume	10,000-30,000	20,000	m3
Biomass production	700-1800	1200	kg/d
Total amount of biomass	70,000-130,000	100,000	kg
Volume excess biomass removal	150-350	250	FrTTd
Oxygen for degradation	20,000-50,000	35,000	kg/d
Gas production (CO2)	10,000-50,000	30,000	kg/d

In a second embodiment, the method comprises a step of filtering oily water through an adsorption medium and a step of bio-regenerating the adsorption medium. An example of the second embodiment and individual features thereof is shown in Figs. 2A-2B.

A plurality of vessels comprising adsorption media may be used. 10 vessels are shown in Fig. 2A, and 14 are shown in Fig. 2B; this is for illustrative purposes only, as any suitable number of vessels may be used. The method may comprise introducing the oily medium into one or more vessels comprising adsorption media. The adsorption media may be allowed to adsorb oil and the effluent may typically have an oil content of less than 30 ppm, e.g. no more than 10 ppm.

During the adsorption cycle, the vessel may be operated in adsorption mode. The introduction of oily water into the vessels may be controlled, such that oily water is introduced into a particular vessel when that vessel is operated in adsorption mode, but not when it is in regeneration mode. As shown in Fig. 2 B, the flow of oily water into the vessels may be controlled via valves.

During the regeneration cycle, the vessel may be operated as a bioreactor. Thus, microbes and preferably nutrients may be introduced into the vessel. The bioreactor conditions may be adjusted and/or maintained as discussed elsewhere herein. In particular, free oxygen may be supplied, e.g. in the form of air, e.g. from an air compressor. The gas flow may be configured to aid fluidization.

The system may be operated such that a proportion of the vessels are in adsorption mode, e.g., 2, whilst the remainder of the vessels are in regeneration mode.

For example, the following parameters shown in Table 2 may be used. This is a nonlimiting Example for a design with a flow of oily water of 20 000 m³ with 500 ppm oil

Table 2

	Example range	Example value
Adsorption capacity	0.5-5	1	wt%
Oil load	5,000-15,000	10,000	kg/d
Media density	0.5-1.5	1	kg/m3
Volume one filter	100-1000	500	m3
Adsorption capacity per filter	3000-7000	5000	kg
Regeneration time	3-10	6	days
Size of one filter	300-700	500	m3
Number of filters needed	6-18	14
Biomass growth	0.05-0.25	0.125	kg VSS per kg oil
Total bioimass in reneration fluid	1000-6000	3000	kg
Void volume filter	20-70	50	%
Total volume regeneration fluid	1000-5000	3000	m3
Total biomass in regeneration fluid	1000-5000	3000	kg
Slipstream regeneration fluid	200-700	500	rrFd
Concentration of biomass in slipstream	500-1500	1000	mg/l
Oxygen for degradation	20,000-50,000	35,000	kg/d
Gas production (CO2)	10,000-50,000	30,000	kg/d

In a third embodiment, the method comprises a step of filtering oily water through an adsorption medium, a step of back-flushing the adsorption medium to regenerate it and a step of biodegrading the back-flush in a bioreactor.

An example of the third embodiment and individual features thereof is shown in Fig.

3. A plurality of vessels comprising adsorption media may be used. 4 vessels are shown in Fig. 3; this is for illustrative purposes only, as any suitable number of vessels may be used.

The method may comprise introducing the oily medium into one or more vessels comprising adsorption media for an adsorption cycle, as described for the second embodiment.

During the regeneration cycle, the vessel may be operated in regeneration mode. An appropriate solution may be used to back-wash the adsorption medium, e.g. is filtered through the adsorption medium, to remove the oil from the adsorption medium. The oily back-wash may be introduced into a bioreactor. The bioreactor may e.g. be an MBR as shown in Fig. 1B.

In a fourth embodiment, the method comprises introducing oily water, microbes and nutrients into a high concentration bioreactor where microorganisms degrade oil present in the oily water, and a step of filtering water from the bioreactor through a membrane to yield an effluent that has a low oil content. The method may be considered to be based on embodiment 1, with some additional features. An example of the fourth embodiment is shown in Fig. 4.

A microbial inoculum may be introduced into the bioreactor to achieve a high microbial concentration in the bioreactor. The system may comprise a biomass storage vessel and the method may comprise transferring microbial biomass from the storage tank to the bioreactor, and/or vice versa.

The system may comprise a nutrient storage vessel and the method may comprise transferring nutrients from the storage tank to the bioreactor. The biomass and nutrients may be stored separately, or in the same storage vessel.

The bioreactor may e.g. be an MBR as shown in Fig. 1B. The membrane is preferably selected to be capable of maintaining the desired biomass concentration in the bioreactor, e.g. at least 10 g TS/I.

CO₂ produced in the bioreactor may be used to fill a cooler turbine.

Heat, e.g. heat of the produced water, and/or generated during the biodegradation, may be used to run an in-line oil-water separator upstream of the bioreactor.

In a fifth embodiment, the method comprises a mechanical (non biological) step of oil-water separation, e.g. via an oil-water separator, introducing the oily water from this separation into a biofilter and introducing the effluent thereof into a bio-polishing vessel.

An example of the fifth embodiment is shown in Fig. 5.

The method may comprise introducing oily water into an oikwater separator, such as a gravity separator, which may be a long-retention-time vessel. The oil outlet may be combined with the three-phase separator oil outlet. The oily water outlet may have a reduced oil content, e.g. less than 50 ppm. This oily water may be introduced into a biofilter, which may, e.g., be operated/configured with a retention time of about 2-24 hours, in the case of an aerobic biofilter, or 2-15 days, in the case of an anaerobic biofilter.

The method may comprise introducing seawater into the biofilter. Thus, the oily water may be mixed with seawater, for example in a ratio of 1:1. Seawater contains essential nutrients such as nitrogen and phosphore (typical C:N:P ratio close to 106:16:1) and brings in nutrients and oxygen.

Oxygen may be added, for example 3 mg per mg of oil entering the biofilter.

In orderto limit the amount of seawater added and the volume of the vessel, the concentration of oxygen of the seawater may be increased artificially through pressurization of surface air into an inlet chamber. The oxygen-rich seawater may be added into the biofilter through different inlets into different zones of the biofilter in order to favour optimal oxygenation and hydrodynamic conditions. Additional nutrients may also be added from an umbilical or mixed with the seawater, if desired.

The effluent of the biofilter may be introduced into a bio-polishing vessel. The method may comprise introducing seawater into the bio-polishing vessel. Thus, the biofilter effluent may be mixed with seawater, for example in a ratio of 1:1.

In the bio-polishing vessel, microorganisms may be consumed by larger planktonic organisms, which may result in a significant reduction of the total biomass produced.

Finally, the bio-polishing tank effluent may be discharged from the system.

In a sixth embodiment, the microbes in the bioreactor are stimulated to produce extracellular biopolymer and/or bio-surfactants. The objective is to increase the viscosity or wettability of the treated water for enhanced oil recovery (EOR). The production of extracellular biopolymer and/or bio-surfactants may be stimulated by using special genotypes of bacteria (e.g. Pseudomonas aeruginosa) in combination with special nutrients and operating conditions (e.g. nutrient concentrations, N/P ratio, temperature, oxygen, pH, agitation, etc.).

The production of such substances may be maintained through periodic addition of a microbial inoculum and/or nutrients.

The sixth embodiment is shown in Fig. 6 in connection with embodiment 5, but the sixth embodiment may alternatively be combined with any of the other embodiments.

In a seventh embodiment, the effluent water, excess biomass, nutrients, oxygen, CO₂ and/or heat may be utilized in sea farming concept for production of e.g. macro/micro algae, mussels, algae, and/or fish. The effluent water excess biomass, nutrients, oxygen, CO₂ and the like may be introduced into large sea farming vessels, which may be located on the seabed or on floating systems. The produced biomass may be applied for e.g. biofuel, feed, pharmaceutical production.

The sixth embodiment in shown in Fig. 7 in connection with embodiment 5, but the seventh embodiment may alternatively be combined with any of the other embodiments.

In an eighth embodiment, the oily water is concentrated through membrane filtration before being introduced into a bioreactor. An example of the eighth embodiment is shown in Fig. 8.

The oily water may be filtered through a membrane. In order to reduce fouling, the recovery rate may be limited to less than 90, 85 or 80%, e.g. to 50-70%, to reduce the load on the membrane.

The retentate, which may be referred to as a “concentrate” may e.g. have a volume fraction of 30-50%. It may be introduced into a bioreactor. For example, it may be treated in a two-step bioreactor combining anaerobic and aerobic metabolism. The anaerobic stage may degrade a proportion of the oil and produce methane, which may be captured, while the aerobic stage may be used for bio-polishing. Alternatively, a single step bioreactor may be used, e.g. an MBR as shown in Fig. 1B.

Excess biomass may be pumped to shore via an umbilical where it may be cultivated and reused, or utilized in other applications (e.g. oil spill bioremediation). Nutrients, biomass (new or recycled) and oxygen for optimal degradation rate may be supplied via an umbilical from the shore or a topside platform.

The oil concentration in retentate may be in the range 1000-10000 mg/l. The hydraulic retention time in the anaerobic reactor may be in the range 1-5 days, preferably <2 days. The hydraulic retention time of the aerobic step may be in the range 10-30 hours, preferably less than 20 hours.

In a ninth embodiment, the system may comprise a gas flotation vessel. This embodiment is shown in Figure 9. Gas from the bioreactor, which may, e.g., be gas provided during the biodegradation, may be removed from the bioreactor and introduced into the gas flotation vessel. The bioreactor may, e.g., be operated/configured as an aerobic bioreactor or as an anaerobic bioreactor.

Claims (32)

Claims

1. A method of treating oily water, said method comprising introducing oily water into a system comprising a subsea bioreactor in which microorganisms biodegrade oil from the oily water.

2. A method according to claim 1, comprising introducing said oily water into said bioreactor.

3. A method according to any preceding claim, wherein said system comprises a membrane integral to or downstream of the bioreactor, preferably wherein the bioreactor is a membrane bioreactor (MBR), and/or preferably wherein the bioreactor is operated with a hydraulic retention time of 15-40 hours.

4. A method according to claim 3, wherein said method comprises a step of filtering water from the bioreactor through said membrane.

5. A method according to any preceding claim, comprising a step of concentrating said oily water prior to introducing it into said bioreactor, preferably to reduce the volume of the oily water by at least 20% and/or to increase the oil content of the oily water by at least 100%.

6. A method according to claim 5, wherein said step of concentrating said oily water comprises (i) Filtering said oily water through a membrane; or (ii) Filtering said oily water through an adsorption medium and back-flushing said adsorption medium

7. A method according to any preceding claim, comprising a step of filtering said oily water through an adsorption medium and preferably comprising a subsequent step of incubating said adsorption medium in a bioreactor.

8. A method according to any preceding claim, comprising adjusting and/or maintaining the bioreactor conditions to create and/or maintain an oxic environment, or to create and/or maintain an anoxic environment.

9. A method according to any preceding claim, wherein said method comprises transferring microbial biomass between a biomass storage vessel and said bioreactor.

10. A method according to any preceding claim, comprising introducing seawater into the bioreactor, preferably at a ratio of oily water:seawater of 10:1 to 1:10, most preferably 1:1.

11. A method according to any preceding claim, wherein said bioreactor is a biofilter, preferably a trickle filter or a fluidized bed filter, and preferably is operated with a retention time of 2-24 hours or 2-15 days.

12. A method according to any preceding claim, wherein the microorganisms in the bioreactor produce extracellular biopolymers and/or biosurfactants.

13. A method according to any preceding claim, wherein the oily water that is introduced into the system has an oil content of about 40-1000 ppm, preferably about 100500ppm.

14. A method according to any preceding claim, wherein said method yields an effluent water having an oil content of less than 30ppm, preferably less than 5 or 1ppm.

15. A method according to any preceding claim, wherein said microorganisms are indigenous to the oily water and/or wherein said method comprises a step of adding a microbial inoculum to said bioreactor.

16. A method according to any preceding claim, wherein said oily water is introduced into said bioreactor in a continuous manner, or in a semi-continuous manner, or wherein said oily water is batch-fed into said bioreactor.

17. A method according to any preceding claim, further comprising introducing nutrients, enzymes and/or gas into the system, preferably into the bioreactor.

18. A method according to any preceding claim, wherein said system comprises at least a first and a second bioreactor.

19. A method according to claim 18, wherein said method comprises adjusting and/or maintaining the bioreactor conditions to create and/or maintain an anoxic environment in the first bioreactor and an oxic environment in the second bioreactor, or vice versa.

20. A method according to claim 18 or 19, wherein said second bioreactor is a biopolishing vessel, preferable comprising planktonic organisms.

21. A method according to any one of claims 18-20, wherein said method comprises introducing the oily water into a first bioreactor and introducing sludge from said first bioreactor into a second bioreactor, wherein preferably the first bioreactor is operated under aerobic conditions and said second bioreactor is operated under anaerobic conditions.

22. A method according to any one of claims 18-20, wherein said method comprises introducing the oily water into a first bioreactor and introducing oily effluent from said first bioreactor into a second bioreactor, wherein preferably the first bioreactor is operated under anaerobic conditions and said second bioreactor is operated under aerobic conditions.

23. A method according to any preceding claim, wherein effluent water, microbial biomass, nutrients, oxygen, CO2 and/or heat are discharged from the system and/or introduced into an aquaculture vessel or system.

24. A system for treating oily water, the system comprising a bioreactor configured to operate in a subsea location.

25. A system according to claim 24, wherein said system is configured to perform a method according to any one of claims 1-23.

26. A system according to claim 24 or 25, wherein said system, preferably said bioreactor, is configured to receive the output of an oil-water separator, such as a three-phase-separator, a gas flotation vessel and/or an inline separator, and/or the output of a concentration vessel.

27. A system according to any one of claims 24-26, wherein said system, preferably said bioreactor, is configured to facilitate plug-flow of the oily water.

28. A system according to any one of claims 24-27, wherein said system, preferably said bioreactor, is configured (i) to receive oily water, and preferably a microbial inoculum, nutrients, a gas such as oxygen, and/or seawater; and (ii) to have an output for effluent water, and preferably biomass and/or gas.

29. A system according to any one of claims 24-28, wherein said system comprises one or more adsorption media, preferably one or more vessels comprising an adsorption medium.

30. A system according to claim 29, wherein said vessels are configured to switch between adsorption and regeneration mode.

31. A system according to any one of claims 24-30, wherein said system comprises one or more of (i) a vessel configured to allow filtration of oily water through a membrane; (ii) a vessel configured to allow storage of microbial biomass; (iii) a vessel configured to allow the settling of microbial biomass; and/or (iv) a vessel or system configured to allow aquaculture.

32. A method of treating oily water, comprising using the system of any of claims 24-31 to perform the method.

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Application No: GB 1615023.7 Examiner: DrAlunOwen