WO2013029615A1

WO2013029615A1 - Method and apparatus for extracting or concentrating carbonaceous compounds from a fluid

Info

Publication number: WO2013029615A1
Application number: PCT/DK2012/050229
Authority: WO
Inventors: Nicolaj Ørskov Olsen; Elaheh Roshani
Original assignee: Horsens Vand Energi A/S
Priority date: 2011-09-02
Filing date: 2012-06-29
Publication date: 2013-03-07
Also published as: EP2751039A1; DK177393B1

Abstract

This invention relates to a method for extracting or concentrating carbonaceous com- pounds from a fluid containing carbonaceous material during wastewater, sludge or biomass treatment using a wastewater plant, which method comprises steps of: -(i) collecting, mixing the fluid in a bio process tank -(ii) subjecting the fluid to clarification in a clarification tank thereby obtaining a clarified fluid, which separates between a treated fluid and a sludge fluid -(iii) subjecting at least one of the clarified fluids and predominantly the sludge fluid to ultrasonic irradiation using an ultrasound system to form a disintegrated fluid -(iv) subjecting the disintegrated fluid to a separation process using a centrifuge to form a rejected fluid and centrifuged fluid -(v) subjecting the centrifuged fluid to digestion in a digester to form a carbon rich gas suitable for further industrial utilization in a gas refiner or in a gas engine.

Description

Method and apparatus for extracting or concentrating carbonaceous compounds from a fluid.

Field of the Invention

The present invention relates to a method for extracting or concentrating carbonaceous compounds from a fluid containing carbonaceous material during wastewater, sludge or biomass treatment using a wastewater plant. The invention further relates to an apparatus for extracting or concentrating carbonaceous compounds from a fluid containing carbonaceous material. Background of the Invention

Treatment of wastewater or sludge is an important part of preserving nature and conserves natural resources in an industrial society being defined in an urban or rural area.

Moreover existing wastewater plants established to treat or process wastewater and waste material to circulate or re-circulate water into the natural water cycle exist.

A disclosure of a treatment of wastewater or sludge is known from patent application WO01/16037, which discloses a method and a system for treating sludge in a wastewater plant and comprising the steps of concentrating the sludge, selecting a desired ho- mogenizing pressure, disrupting a least a portion of the celluar matter in concentrated sludge at the desired homogenizing pressure, digesting the disrupted sludge to produce methane gas.

Although the system and method of treating sludge is a starting point to extract carbo- naceous compounds, the system and method are amongst other things, inferior due to the use of high pressure since this high pressure will disrupt the cell walls of bacteria in the sludge and thus result in a less effective extraction of carbonaceous compounds. Cell disruptions occur at high pressures such as 100 to 200 bars, approximately, where the cell wall disruptions are caused by the extracellular pressure. Even the use of a Super Micro-Gap homogenizing valve to reduce pressure will still result in cell wall cavitation.

A further drawback of the high pressure used in the system and method disclosed, is that it consumes more energy and therefore has a poor energy balance.

Object of the Invention

It is an object of the present invention to improve the absorptive capacity of nutrients such as ammonia ( H₄) from the fluid or matter being treated. Another object of the present invention is to provide means and methods for more efficient and effective extraction of carbonaceous compounds from a fluid in a wastewater or sludge treatment process or plant.

It is a further object of this invention to overcome the deficiencies known in the prior art.

Description of the Invention

At least one object is met according to this invention by a method for extracting or concentrating carbonaceous compounds from a fluid containing carbonaceous material during wastewater, sludge or biomass treatment using a wastewater plant, which method comprises steps of:

-(i) collecting, mixing the fluid in a bio process tank

-(ii) subjecting the fluid to clarification in a clarification tank thereby obtaining a clarified fluid, which separates between a treated fluid and a sludge fluid

-(iii) subjecting at least one of the clarified fluids and predominantly the sludge fluid to ultrasonic irradiation using an ultrasound system to form a disintegrated fluid

-(iv) subjecting the disintegrated fluid to a separation process using a centrifuge to form a rejected fluid and centrifuged fluid

-(v) subjecting the centrifuged fluid to digestion in a digester to form a carbon rich gas suitable for further industrial utilization in a gas refiner or in a gas engine.

In one embodiment the digestion is anaerobic. In another embodiment the digestion is aerobic. In particular the use of an ultrasound system to disintegrate the fluid has improved effect over the prior art since the negative effects of using pressure is eliminated. Fore example the cell walls of bacteria in the fluid are destroyed ultrasonically say at a ultrasonic frequency of about 20 kHz. This in the cell wall-ruptures and thus the release of enzymes that are very actively increases the degradation of biomaterial in the fluid, i.e. sludge, etc. Furthermore as enzymes are only released from minor portions of the cells when using ultrasound, it will over time have the same effect as if all the cells were broken, because of the catalyse effect.

Hence this alternative system using ultrasound at least results in the same disruption of the microorganisms as compared to the use of high pressure or the use of a homogen- iser valve.

Furthermore the use of ultrasound is more energy efficient and thus yields a better energy balance or achieves this at a lower cost.

According to an embodiment of the invention, the method is special in that it further includes a step of subjecting the fluid to clarification in a clarification tank containing aquatic bio plants or weeds such as Duckweed, Azollas or Algae. Thereby increasing the overall efficiency of the method in that the aquatic bio plants to clean the wastewater by removing ammonium.

A further effect is that the aquatic bio plants accumulate carbon thereby reducing or eliminating the need to add pure carbon to the process.

The actual use of Duckweed has shown to be particular effective due to the fast reproduction time of Duckweed in the wastewater plant environment. Several species of Duckweed can be used: Duckweed (Lemna minor), Greater Duckweed Lemna polyrrhiza), Gibbous Duckweed or Fat Duckweed (Lemna gibba), or Star Duckweed (Lemna triscula). According to an embodiment, the aquatic bio plants used are Azollas. Azollas increase the overall efficiency and it has been found that Azollas are beneficial.

Azollas bind Nitrogen thereby producing fertilizers. Azollas are rich on essential amino acids, proteins, vitamins, and minerals thereby providing valuable feed stock for ani- mals. Azollas bind Carbon Dioxide thereby binding Carbon and enhancing carbonaceous content. Azollas can be used to produce biogas due to its carbonaceous content and bio diesel due to the plants high oil content.

Several species of Azollas can be used: Caroliniana, Filiculoides, Mexicana, Mecro- phylla, or Pinnata.

The aquatic pants including Duckweed and Azollas are particularly suited as the have high growth or reproduction rates in the wastewater environment. Thereby aquatic plants increase the absorption of nutrition from the wastewater. A further increased effect is that they bind carbon for bio fuel and/or biogas production. A further increased effect is that they bind carbon and introduce carbon to the process tanks thereby reducing or eliminating the need for feeding external carbon to the process tanks.

It has further shown that aquatic plants such as Duckweed and Azollas are suited for decomposition or disintegration by use of ultrasound. Thereby further enhancing the wastewater plant's biomass entering the wastewater process.

Furthermore it is noted that carbon rich material also can be present in so-called liquid carbon, which includes fluids such as molasses, size, glycerol, whey and alike. Likewise carbon rich receiving food or agricultural products include matters such as corn, reed mace, carrots, plants, root tops, and alike. According to an embodiment of the invention, the method is special in that it further includes a step of feeding back fluid to the bio process tank, which feedback preferably is the rejected fluid from the centrifuge. Thereby the fluid, and here predominantly the rejected fluid from the centrifuge, with nutrition will re-enter the wastewater process in the bio process tank thereby utilizing the process tanks.

According to an embodiment of the invention, the method is special in that it further includes a step of feeding fluid back to the ultrasound system, which feedback preferably is at least part of the centrifuged fluid from the centrifuge.

Thereby the fluid, and here predominantly the rejected fluid from the centrifuge, with nutrition and bio mass and in particular aquatic plant remains will re-enter the decom- position process caused by the ultrasonic system.

According to an embodiment of the invention, the method is special in that it further includes a step of performing a Chemical Oxygen Demand (COD) measurement, a COD-measurement, on a fluid using a COD-meter in at least one process tank and preferably of the rejected fluid from or in the centrifuge.

Thereby obtaining a measurement or indication of the amount of organic compounds in the fluid and preferably the rejected fluid from the centrifuge, which rejected fluid is fed back into an earlier stage of the wastewater plant process.

A person skilled in the art will find different places to perform the measurement and the COD-meter is understood to be a unit configured for performing the COD- measurement more or less automatically although a manual, intermitted or periodic COD- measurement is within the scope of the invention.

Likewise the person skilled in the art will chose a particular COD-measurement method. A starting point could be the ISO 6060, which describes a standard method for measuring chemical oxygen on demand. The person skilled in the art will most likely seek to get a measure expressed in milligrams per liter (mg/L) although the person skilled in the art will know that a relative measure of a value that will imply or from which the absolute COD-measure can be derived will suffice for the purpose of using the COD-measure or indicator to control the feedback process.

The person skilled in the art will according to the invention use a COD-measure to regulate the amount of fluid to be fed back. In a particular embodiment the regulator is a gate or a valve simply opening for the feedback of fluid to occur when the COD- measure or indicator passes a threshold.

In an embodiment the regulator has access to a look-up table with values that for the particular plant have been found to be optimal.

In an embodiment the regulator is implemented on a computer and the control algorithm used to control valves and the amount of fluid to be fed back relies on calculations and optimisations of free variables identified in the feedback loop. According to an embodiment of the invention, the method is special in that it further includes the steps of performing a effect or power measurement of the power consumption of at least one process tank using at least one power meter and preferably in the ultrasound system;

- performing an estimate of the residual energy in the fluid and preferably the rejected fluid based on the COD-measurement;

- performing and projection of the energy needed to reprocess the fluid in the feedback and preferably the rejected fluid

- performing a comparison of the projected energy needed to reprocess the fluid in the feedback and preferably the rejected fluid with the estimated residual energy in the fluid and preferably the rejected fluid based on the COD-measurement to provide an feedback or no feedback decision indicator, which indicator determines if the fluid is to be fed back for reprocessing thereby automating the method. Thereby the regulator can be optimized with respect to energy consumption. Thereby the regulator can be optimized with respect to obtaining as much energy from in the biomass such as biogas as compared to the energy needed to concentrate or extract the biomass or biogas.

Having these measures, a person skilled in the art will find it natural to begin to experiment with standard optimisation or control systems.

According to an embodiment of the invention, the method is special in that it further includes at least one of the steps of:

- parting or chopping the fluid and in particular the

- buffering and/or stirring the fluid by stirring means.

Thereby the matter or materials embedded in the fluid will be parted and a larger sur- face area. Furthermore the chopper willing will allow for material to be added from an external source at this point in the process.

The buffering and/or stirring of the fluid will mix the fluid thereby enhancing the biological process.

According to an embodiment of the invention, the method is special in that it further includes steps of:

- performing a Carbon (C)-Nitrogen (N) measurement, a C/N-measurement, on a fluid using a C/N-meter in at least one process tank of the digester, the centrifuge or the ultrasound system; and preferably in the digester;

- feeding fluid from the centrifuge or the digester back to the ultrasound system or the buffer tank based on a feedback controller to obtain a C/N-ratio of between 4-15; preferably between 7-12.

According to an embodiment of the invention, the method is special in that it further includes a step of: - delivering the products or residue products to receiving tank, and from the receiving tank feeding the products or residue products to the wastewater plant and preferably:

- feeding the agricultural products or residue products to the chopper for chopping the agricultural products or residue products, or

- feeding the food products or residue products to the buffer tank to be blended or stirred with stirring means.

Thereby the previously disclosed process plant can be directly used to process agricultural products or residue products and thereby converting or extracting from these carbonaceous compounds in the form of a carbon rich gas suitable for further industrial utilization in a gas refiner or in a gas engine.

Or thereby extract carbonaceous compounds from food products or residue products added to the process.

The buffer further allows for a controlled feed of material into the system.

A person skilled in the art will during operation and depending on the size of the plant, time constants and so, find at least a suitable feeding point and chopping size. Some times copping or parting of food products will be needed and the chopper is easily modified, altered or changed to facilitate food or agricultural products to enter at a suitable sizes and speed

At least one object is met according to this invention by a method for producing usable energy such as electricity or heat from a carbon rich gas is special in that it includes a step of burning the gas in a in a gas engine, converting the gas in a fuel cell, or any other type of engine or chemical devices configured for converting chemically bound energy to energy in the form of electricity or mechanical energy. At least one object is met according to this invention by a fluid, such as a wastewater or sludge, treatment plant comprising a series of process tanks interconnected by conduits, which process tanks are:

- a bio process tank for collecting, mixing and pre processing a fluid - a secondary clarifier for clarifying the fluid into a treated fluid and a sludge fluid, and a conduct arranged to transfer the sludge fluid to

- an ultrasound system for disintegrating the sludge fluid into a disintegrated fluid

- a centrifuge for centrifuging the disintegrated fluid into a rejected fluid and a centri- fuged fluid

- a digester for digesting the centrifuged fluid and by degassing the centrifuged fluid forming a carbon rich gas

and optionally:

a chopper inserted after the second clarifier for chopping a fluid fed to the chopper, which chopper optionally has means for receiving agricultural products or residue products directly or from a first receiving tank; and/or a buffer tank with stirring means inserted before the ultrasound system for buffering and/or stirring the fluid and optionally has means for receiving food products directly or from a second receiving tank.

Thereby an apparatus is provided to extract or concentrate carbonaceous compounds from a fluid containing carbonaceous material during wastewater, sludge or biomass treatment. In particular the apparatus is to make a carbon rich gas suitable for further industrial utilization in a gas refiner or in a gas engine.

The positive effect is understood by considering a treatment of 50 m³ sludge/d with a solid content of about 8 %. This will give about 4000 kg Ts/d.

For this treatment the energy fed to the ultrasound system is 40 kW/d. This results in an energy consumption of 0,01 kW/Kg Ts, which has a more positive and efficiency energy balance as compared to a homogeniser valve.

Even though both systems can increase the gas production with about 25 %, the ultrasonic system has a better energy balance.

As already mentioned, the ultrasonic system does not require pressure to break down the cell walls. Instead cell wall disruptions are caused by intercellular pressure. According to an embodiment of the fluid treatment plant, it is special in that it further comprises a first feedback conduit connecting the centrifuge back to the bio process tank and allowing a rejected fluid to be fed back to the bio process tank based on signals from a feedback controller with inputs from a COD-meter measuring the COD from the centrifuged fluid and optionally from a power-meter measuring the power consumed by at least the ultrasonic system.

Thereby an apparatus is provided to extract or concentrate carbonaceous compounds from a fluid containing carbonaceous material during wastewater, sludge or biomass treatment. In particular the apparatus is to make a carbon rich gas suitable for further industrial utilization in a gas refiner or in a gas engine. More carbon results in a higher efficiency of microorganisms and these carbons are produced by plant and alga that grow in the secondary clarifiers. It is noted, that eject water from sludge cannot be used as carbon source, because it contains nitrogen, which is toxic for the microorganisms. A treatment of this requires a separate feedback.

There is the case of two separate feedbacks.

The first feedback sends the reject water from the sludge production to the bio process tank. This feedback is always present because the water from the sludge that contains high concentrations of N and cannot be discharged directly into the recipient. A second feedback that supplies carbon to the microorganisms in the bio tank, results in a more optimal removal of N.

The carbon source in the second feedback could come from the degradation of the plants or from the outside, since it is completely clean.

This can be monitored with a C/N-monitor, which measures N from the first feedback and C from the second feedback. It has been found that the optimal C/N-ratio will be about 7 to 10. According to an embodiment of the fluid treatment plant, it is special in that it further comprises a second feedback conduit configured for feeding back the centrifuged fluid from the centrifuge back to the ultrasound system.

With this second feedback, a more homogeneous mixing with the incoming organic matter and the rest of COD can be extracted in order to produce carbon to the first feedback. Alternative this can be adopted to allow for production of biodiesel and/or bioethanol.

According to an embodiment of the fluid treatment plant, it is special in that it further comprises a second feedback conduit configured for feeding back the centrifuged fluid from the centrifuge back to a buffer tank that has stirring means and further is connected to the ultrasound system via a conduit.

According to an embodiment of the fluid treatment plant, it is special in that it further comprises an arrangement or a device configured to measure a Carbon (C) / Nitrogen (N)-ratio, a C/N-meter, and a first feedback conduit connecting the centrifuge or the digester back to the process tank based on signals from a feedback controller with in- puts from a C/N-meter measuring the C/N-ratio of the fluid in the centrifuge or the digester.

The C/N ratio in the digester is important to the optimization of the digestion process and thus the extraction of carbon and the production of biogas.

It is found that an optimal C/N-ratio is between 7-10, which can be obtained by simple control and monitored by installing an online meter that measures the C / N ratio.

C/N ratio can be improved even further by allowing a liquid carbon or carbon supplied as solid matter and included in the production line.

The liquid carbon coming from the receiving tank can be fed to the buffer tank. The solid carbon coming from the second receiver tank is fed to the pre-treatment, and on through the system and ends up in the digester.

By sending a portion of the liquid carbon through the ultrasound system a more homo- geneous mixture can be achieved and simultaneously provides a more accessible source of carbon for microbes, which further enhances the carbon extraction process.

A feedback conduit from the digester either returned to the centrifuge or the ultrasound system is an alternative process. In this case a power meter determines which way the fluid or sludge will go.

Ultrasound treatment alone will provide both a higher COD and a homogeneous mixture of sludge and uses almost no energy in relation to the centrifuge. A person skilled in the art will realize that a fluid, sludge, or plants/algae must go through the system in a certain way.

The sludge must first pass through the centrifuge and then to the ultrasonic treatment and thus be reduced so the sludge can digest better in the digester.

By use of plants/algae a swapped process order is advantageous: first ultrasonic treatment and then centrifugation. In this case the extraction of carbon is to the internal use in the fluid treatment plant or external use or storage. In this case, the sludge production can be stopped so that only one type of biomass production is running through the fluid treatment plant. Alternatively a separate system line could be installed.

16. According to an embodiment of the fluid treatment plant, it is special in that it fur- ther comprises an arrangement or a device configured to measure a Carbon (C) / Nitrogen (N) -ratio, a C/N-meter, and a second feedback conduit connecting the centrifuge or the digester back to the ultrasound system or the buffer tank based on signals from a feedback controller with inputs from a C/N-meter measuring the C/N-ratio of the fluid in the centrifuge or the digester.

Thereby providing an alternative way of providing an optimised extraction of carbon. Description of the Drawing

This invention will be described and exemplified in relation to the drawings, where:

Figure 1 shows a schematic flow chart of a wastewater plant for extracting or concentrating carbonaceous compounds from a fluid, figure 2 shows a schematic flow chart of a wastewater plant for extracting or concentrating carbonaceous compounds from a fluid with feedback conduits for recirculation of fluids based on power consumption and COD-measurements, figure 3 shows a schematic flow chart of a wastewater plant for extracting or concentrating carbonaceous compounds from wastewater added agricultural or food products, figure 4 shows the removal of Ammonia using A Duckwheed and B Azolla, figure 5 shows the growth or doubling time for Duckweed, figure 6 shows a further improved embodiment with a C/N-ratio measurement controlling the feed back of fluids, and figure 7 shows a further embodiment of a C/N-ratio optimised system Detailed Description of the Invention

Embodiments of the present invention are described in the following in terms of technical features as described below.

No Term

1 Wastewater plant

2 Fluid 3 Bio process tank OR Primary clarifier

4 Secondary clarifier

5 Ultrasound system

6 Centrifuge

7 Digester

8 Converter

9 Conduit or Pipe

10 Treated fluid or treated water

11 Sludge fluid

12 Disintegrated fluid

13 Rejected fluid / Treated water

14 Centrifuged fluid / sludge

15 Carbon rich gas OR biogas

16 Gas refiner

17 Gas engine

20 First Feedback conduit or pipe

21 COD-meter

22 Power-meter

23 Second Feedback conduit

24 Buffer tank

25 Stirring means

26 Chopper

27 First Forward conduit

28 Second forward conduit

30 First Receiving Tank

31 Second Receiving Tank

32 Agricultural products or residue products

33 Food products or residue products

34 C/N-meter

35 Carbon Tank

Figure 1 shows a schematic flow chart of a wastewater plant 1, which wastewater plant 1 is a plant suitable for treatment of a fluid 2 that primarily but not exclusively is wastewater.

The shown schematic is a wastewater plant 1 consisting of a series of elements com- prising a bio process tank 3, or a primary clarifier, a secondary clarifier 4, an ultrasound system 5, a centrifuge 6 and digester 7.

The shown wastewater plant furthermore has a converter 8 for handling the gas.

Each of the main elements is connected in series via a conduit 9 between each element. Each conduit 9 is made to according to the nature of the fluid, being a sludge, a gas or combinations thereof. The conduit 9 is a pipe, a channel or any other means for guiding the fluid between two points. A person skilled in the art will find it easy to select the proper material, size, and/or connectors to interconnect different process tanks as needed according to the invention.

In the second clarifier 5 the fluid 2 is parted in a treated fluid 10 and a sludge fluid 11. The treated fluid 10 is generally thinner than the sludge fluid 11. Due to differences in densities of essentially water and other matters in the fluid 2 gravitation will tend to part or to separate the fluid 2 into a treated fluid 10 and a sludge fluid 11. In some cases the separation is very distinct like when oil and water separates and in other cases the separation is not so clear and the separation it more graduate.

The sludge fluid 11, or predominantly the sludge fluid 11, is conducted to the ultra- sound system 12 via a conduit 9.

The ultrasound system 5 disintegrates matters in the sludge fluid 11 by ultrasonic cavitation to a disintegrated fluid 12. The matter being aggregated matter of fibres, organic matter, cellulose etc, depending on the waste product being processed.

The disintegrated fluid 12 is in this embodiment conducted to the centrifuge 6 that separates the disintegrated fluid into a rejected fluid 13 and a centrifuged fluid 14. The centrifuged fluid 14 is conducted to the digester 7 via a conduit 9. In the digester 7 the centrifuged fluid degasses and a carbon rich gas 15 is released.

The carbon rich gas 15 is in this embodiment furthermore shown to be conducted to a converter 8 that has a gas refiner 16 and a gas engine 17 for producing electricity from the refined gas.

Figure 2 shows in a similar vein to figure 1 a schematic flow chart of a wastewater plant 1.

The wastewater plant 1 is a plant suitable for treatment of a fluid 2. The shown schematic has like the plant in figure 1 a series of elements comprising a bio process tank 3, or a primary clarifier, a secondary clarifier 4, an ultrasound system 5, a centrifuge 6, digester 7, and a converter 8 that has a gas refiner 16 and a gas engine 17 for produc- ing electricity from the refined gas.

The wastewater plant 1 further has first feedback conduit 20 configured for feeding back preferably the rejected fluid 13 from the centrifuge 6 to the bio process tank 2. In the first feedback conduit 20 there is a Chemical Oxygen Demand (COD) meter 21 configured to perform measurement of Chemical Oxygen Demand (COD).

In the shown embodiment there is a power-meter 22 measuring the power consumption of the ultrasound system 22. According to a further embodiment there is a second feedback conduit 23 configured for feeding back the centrifuged fluid 14 from the centrifuge 6 back to a buffer tank 24 that has stirring means 25 and further is connected to the ultrasound system 5 via a conduit 9.

According to a further embodiment there is a chopper 26 inserted between the dary clarifier 4 and the buffer tank 24, or the ultrasound system 5. In one variant of the shown embodiment a first feed forward conduit 27 that bypasses the chopper 26 and the buffer tank 24 and connect the secondary clarifier 4 to the ultrasound system 5. In some aspects the first feed forward conduit 27 is like a conduit 9 from figure 1. In other aspects the first feed forward conduit 27 allows for some sludge fluid 11 and treated fluid 10 to be fed forward directly via the feed forward conduit 27 allows for some to be further processed on the chopper 26 and the buffer tank 24.

In another variant of the shown embodiment a second forward conduit 28 connects the centrifuge 7 with the digester 7. In some aspects the second feed forward conduit 28 is much like the conduit 9 from figure 1.

In other aspects the second feed forward conduit 28 allows for part of the centrifuged fluid 14 to be fed directly to the digester 7 and other part of the centrifuged fluid 14 to be fed back via the second feedback conduit 23.

Figure 3 shows in a similar vein to figure 1 and 2 a schematic flow chart of a wastewater plant 1. The wastewater plant 1 is a plant suitable for treatment of a fluid 2. The shown schematic has like the plant in figure 1 a series of elements comprising a bio process tank 3, or a primary clarifier, a secondary clarifier 4, an ultrasound system 5, a centrifuge 6, digester 7, and a converter 8 that has a gas refiner 16 and a gas engine 17 for producing electricity from the refined gas.

In an embodiment building on to the wastewater plant 1 shown in figure 2, the shown embodiment further has a first receiving tank 30 configured for receiving agricultural products or residual products 32, which first receiving tank 30 has a conduit 9 that connects to the chopper 26 or a conduit 9 connected to the chopper 26.

In an embodiment, illustrated in figure 3, there is second receiving tank 31 configured or receiving food products or residue products 33, which second receiving tank 32 has a conduit 9 that connects to the buffer tank 24 or thereto a leading conduit 9. In variants of the embodiments shown in figure 2 and figure 3 there is a direct conduit 9 from the ultrasound system 5 to the digester 7. In between the ultrasound system 5 and the digester 7, there can be a mixer or a macerator.

Thereby this embodiment is suited for effective production of biogas or carbon on the basis of the presence of aquatic plants such as Azolla or Duckweed and received agricultural products or residual products 32 or food products or residual products 33.

Examples:

The invention as disclosed has been tested on a small scale. Amongst a series of tests and experiments used the following are representative. Procedure to remove H₄ from (secondary) clarifier using a H₄-kit (ex. Hack-Lange type LCK 305) as commonly used on wastewater plants is as follows:

- fill aquatic plant (Duckweed) in 1 1 bottle with fluid from the (secondary) clarifier tank whilst stirring;

- gently remove foil from tube

- add 0.5 ml test

- immediately close tube

- shake

- read after 15 min at 600 nm

A procedure to decompose aquatic plants, Duckweed and Azolla, using ultrasound is as follows:

- 30 g Azolla/Duckweed is measured

- these are dissolved in 200 ml water in a blender/mixer for 3 - 6 min to form a fluid

- 2 g taken under stirring for a COD-measurement

- let the fluid settle for about 15 min

- 2 g taken for a COD-measurement

- perform ultrasound treatment on fluid for 30 - 60 min

- let the fluid settle for about 15 min

- 2 g taken for a COD-measurement

The COD-measurement is conducted using a standard Hack-Lange Kit (ex. Type LCK 514), which is commonly used on wastewater plants.

The COD-method used relies on an indirect determination of the total organic material and a few inorganic materials. Oxidizable substances react with sulphuric acid - potas- sium dichromate solution using silver sulphate as a catalyst. Chloride is masked by mercury sulphate and the green coloration (600 nm) from Cr⁺³ is measured.

The results were as follows:

Figure 4 shows the H₄ -removal from the (secondary) clarifier is seen in figure 4. A for Duckweed and for Azolla in figure 4.B. Both figures show the level of ammonium [mg/1] versus time [days]. In the case of Duckweed, a fluid with ammonium-ions were taken from the secondary clarifier tank and Duckweed was added under stirring in a 11 bottle and exposed only to natural laboratory light. In the case of Azolla, concentrated ammonium ions were used.

It is seen that the process reduces the amount of ammonium.

Likewise experiments have been performed to show the removal of Phosphor. In that case P-kit was used.

Figure 5 shows an example of the growth rate of Duckweed. The graph shows an in- crease in leaves of Duckweed (found by counting) over time. The graph shows that Duckweed has a doubling time at about 2.2 days. Azolla was found to have a doubling time at about 2.0 days. Hence aquatic weed, such as Duckweed and Azolla grow fast and thereby efficiently capture and concentrates carbon and introduces carbon into the process.

The positive effect of using ultrasound is exemplified in the following tables. The COD-analysis has been done as described before. Duckweed:

Azolla:

In both cases it is seen that the use of ultrasound has a large impact of the organic matter dissolved. For Duckweed there is an increase from 700 g/ g Dm without ultrasound to 992 k/Kg Dm using ultrasound. For Azolla there is an increase from 977 g/kg Dm without ultrasound to 1400 g/kg Ts using ultrasound.

The production of biogas from aquatic plants in the case of no feedback is estimated in the tables given below. Both tables show the estimated amount of methane gas in kg from the amount of Duckweed and Azolla respectively. From Duckweed to Biogas

From Azolla to Biogas

The production of carbon from aquatic plants is estimated in the tables given below. Both tables show the estimated amount of carbon in kg from the amount of Duckweed and Azolla respectively. The carbon produced in the secondary clarifier is fed back to the bioprocess tank. Carbon from Duckweed to be fed back to bioprocess tank

Figure 6 shows an embodiment of a system according to this invention as disclosed in figures 1 to 3 and further improved by having at least one C/N-meter 34 configured to measure the Carbon (C) and Nitrogen (N) content and in particular the C/N-ratio. Such C/N-meter could be a BIOTECTOR B7000 from HACH LANGE or alternative.

This figure shows an embodiment, with a first feedback conduit 20 and a second feedback conduit 23. In other embodiments either of these first or second feedback con- duits could be absent.

The shown first feedback conduit 20 connects the centrifuge 6 or decanter with the process tank 2. A fluid is fed back based on a control system with input including the C/N-ratio obtained from the centrifuge 6 or the first feedback conduit 20.

The shown second feedback conduit 23 connects the centrifuge 6 or decanter with the buffer tank 24, which in this embodiment is with means for stirring. The fluid fed back is based on a control system with input including the C/N-ratio obtained from the centrifuge 6 or the second feedback conduit 23.

Figure 7 also in continuation of the previous figures shows a variant embodiment, where a C/N-ratio measurement by a C/N-meter is performed in the second receiving tank 31 or in the conduit 9 from the second receiving tank 31 to the digester 7 and to the buffer tank 24. The measured C/N-ratio is fed to the control system that regulates the flow to balance and optimise the output based on the C/N-ratio.

In this case agricultural products or residue products 32 and/or food products or residue products are used to balance and optimise the production or extraction of carbon. A person skilled in the art will understand that the use of the principles outlined here can be combined and the person skilled in the art will recognize that simple experimentation will result in an optimal and efficient extraction of carbon. The person skilled in the art will naturally choose amongst a wide range of available controllers and the person skilled in the art will easily for a given type of agricultural products 32 or food products 33 be able to estimate which feedback conduit 9 pipe to start with.

Claims

1. A method for extracting or concentrating carbonaceous compounds from a fluid (2) containing carbonaceous material during wastewater treatment using a wastewater plant (1), which method comprises steps of:

- (i) collecting, mixing the fluid (2) in a bio process tank (3)

- (ii) subjecting the fluid (2) to clarification in a clarification tank (4) thereby obtaining a clarified fluid, which separates between a treated fluid (10) and a sludge fluid (11)

- (iii) subjecting at least one of the clarified fluids (10, 11) and predominantly the sludge fluid (11) to ultrasonic irradiation using an ultrasound system (5) to form a disintegrated fluid (12)

- (iv) subjecting the disintegrated fluid (12) to a separation process using a centrifuge (6) to form a rejected fluid (13) and centrifuged fluid (14)

- (v) subjecting the centrifuged fluid (14) to digestion in a digester (7) to form a carbon rich gas (15) suitable for further industrial utilization in a gas refiner (16) or in a gas engine (17).

2. A method for extracting or concentrating carbonaceous compounds according to claim 1 characterised in that it further includes a step of:

- (iia) subjecting the fluid (2) to clarification in a clarification tank (3) containing aquatic bio plants or weeds such as Duckweed, Azollas or Algae.

3. A method for extracting or concentrating carbonaceous compounds according to any of claims 1 or 2 characterised in that it further includes a step of:

- feeding back fluid to the bio process tank (3), which feedback preferably is the rejected fluid (13) from the centrifuge (6).

4. A method for extracting or concentrating carbonaceous compounds according to any of claims 1 or 3 characterised in that it further includes a step of:

- feeding fluid back to the ultrasound system (5), which feedback preferably is at least a part of the centrifuged fluid (14) from the centrifuge (6).

5. A method for extracting or concentrating carbonaceous compounds according to any of claims 1 or 4 characterised in that it further includes a step of:

- performing a Chemical Oxygen Demand (COD) measurement, a COD-measurement, on a fluid using a COD-meter (22) in at least one process tank (3, 4, 5, 6, 7) and pref- erably of the rejected fluid (13) from or in the centrifuge (6).

6. A method for extracting or concentrating carbonaceous compounds according to any of claims 1 to 5 characterised in that it further includes the steps of:

- performing a effect or power measurement of the power consumption of at least one process tank (3, 4, 5, 6, 7) using at least one power meter (22) and preferably in the ultrasound system (5);

- performing an estimate of the residual energy in the fluid and preferably the rejected fluid (13) based on the COD-measurement;

- performing and projection of the energy needed to reprocess the fluid in the feedback and preferably the rej ected fluid (13)

- performing a comparison of the projected energy needed to reprocess the fluid in the feedback and preferably the rejected fluid (13) with the estimated residual energy in the fluid and preferably the rejected fluid based on the COD-measurement to provide an feedback or no feedback decision indicator, which indicator determines if the fluid is to be fed back for reprocessing thereby automating the method.

7. A method for extracting or concentrating carbonaceous compounds according to any of claims 1 to 6 characterised in that it further includes at least one of the steps of:

- parting or chopping the fluid and in particular the

- buffering and/or stirring the fluid by stirring means (25).

8. A method for extracting or concentrating carbonaceous compounds according to any of claims 1 to 7 characterised in that it further includes a step of:

- performing a Carbon (C)-Nitrogen (N) measurement, a C/N-measurement, on a fluid using a C/N-meter (34) in at least one process tank (5, 6, 7) of the digester (7), the centrifuge (6) or the ultrasound system (5); and preferably in the digester (7); - feeding fluid from the centrifuge (6) or the digester (7) back to the ultrasound system (5) or the buffer tank (24) based on a feedback controller to obtain a C/N-ratio of between 4-15; preferably between 7-12.

9. A method for extracting or concentrating carbonaceous compounds from agricul- tural (32) or food (33) products or residue products (32, 33) according to any of claims 1 to 8 characterised in that it further includes a step of:

- delivering the products or residue products (32, 33) to receiving tank (30, 31), and from the receiving tank (30, 31) feeding the products or residue products (32, 33) to the wastewater plant (1) and preferably:

- feeding the agricultural products or residue products (32) to the chopper (26) for chopping the agricultural products or residue products (32), or

- feeding the food products or residue products (33) to the buffer tank (24) to be blended or stirred with stirring means (25).

10. A method for producing usable energy such as electricity or heat from a carbon rich gas (15) as produced according to any of the claims 1 to 9 characterised in that it includes a step of:

- burning the gas in a in a gas engine (17), converting the gas in a fuel cell, or any other type of engine or chemical devices configured for converting chemically bound energy to energy in the form of electricity or mechanical energy.

11. A fluid (2), such as a wastewater or sludge, treatment plant comprising a series of process tanks interconnected by conduits (9), which process tanks are:

- a bio process tank (2) for collecting, mixing and pre processing a fluid (2)

- a secondary clarifier (4) for clarifying the fluid (2) into a treated fluid (10) and a sludge fluid (11), and a conduct (9) arranged to transfer the sludge fluid (11) to

- an ultrasound system (5) for disintegrating the sludge fluid (11) into a disintegrated fluid (12)

- a centrifuge (6) for centrifuging the disintegrated fluid (12) into a rejected fluid (13) and a centrifuged fluid (14)

- a digester (7) for digesting the centrifuged fluid (14) and by degassing the centrifuged fluid forming a carbon rich gas (15)

and optionally: a chopper (25) inserted after the second clarifier (4) for chopping a fluid fed to the chopper, which chopper optionally has means for receiving agricultural products or residue products (32) directly or from a first receiving tank (30); and/or

- a buffer tank (24) with stirring means (25) inserted before the ultrasound system (5) for buffering and/or stirring the fluid and optionally has means for receiving food products (33) directly or from a second receiving tank (31).

12. A fluid (2) treatment plant according to claim 10 further comprising a first feed- back conduit (20) connecting the centrifuge (6) back to the bio process tank (3) and allowing a rejected fluid (13) to be fed back to the bio process tank (3) based on signals from a feedback controller with inputs from a COD-meter (21) measuring the COD from the centrifuged fluid (14) and optionally from a power-meter (22) measuring the power consumed by at least the ultrasonic system (6).

13. A fluid treatment plant according to claim 10 or claim 11 further comprising a second feedback conduit (23) configured for feeding back the centrifuged fluid (14) from the centrifuge (6) back to the ultrasound system (5).

14. A fluid treatment plant according to any of claim 10 to claim 12 further comprising a second feedback conduit (23) configured for feeding back the centrifuged fluid (14) from the centrifuge (6) back to a buffer tank (24) that has stirring means (25) and further is connected to the ultrasound system (5) via a conduit (9).

15. A fluid treatment plant according to any of claim 10 to claim 14 further comprising an arrangement or a device configured to measure a Carbon (C) / Nitrogen (N) -ratio, a C/N-meter (34), and a first feedback conduit (20) connecting the centrifuge (6) or the digester (7) back to the process tank (2) based on signals from a feedback controller with inputs from a C/N-meter (34) measuring the C/N-ratio of the fluid in the centri- fuge (6) or the digester (7).

16. A fluid treatment plant according to any of claim 10 to claim 15 further comprising an arrangement or a device configured to measure a Carbon (C) / Nitrogen (N) -ratio, a C/N-meter (34), and a second feedback conduit (23) connecting the centrifuge (6) or the digester (7) back to the ultrasound system (5) or the buffer tank (24) based on signals from a feedback controller with inputs from a C/N-meter (34) measuring the C/N- ratio of the fluid in the centrifuge (6) or the digester (7).