WO2004076082A1

WO2004076082A1 - Process for treatment of an organic waste material

Info

Publication number: WO2004076082A1
Application number: PCT/DK2004/000132
Authority: WO
Inventors: Lars Henrik Riisager; Thomas Andreas Skoven
Original assignee: Bioenergi Danmark A/S
Priority date: 2003-02-28
Filing date: 2004-02-27
Publication date: 2004-09-10

Abstract

The present invention relates to a process for treatment of an organic waste material, the process comprising the steps of subjecting said organic waste material to a heat treatment process, where the bio-availability of a resulting hydrolysed product is increased for later treatment, and of subjecting said hydrolysed product to at least one anaerobic fermentation process whereby biogas is produced and an organic residue is formed, wherein said process furthermore comprises a first step of providing said organic waste material in a solid form to said heat treatment process. The present invention furthermore relates to a process for treatment of an organic waste material wherein the aforementioned process furthermore comprises a fourth and a fifth step of separating said organic residue into a liquid phase and a solid phase, and combusting said solid phase of said organic residue at a maximum temperature of 900°C resulting in liberation of thermal energy and concentrated combustion residue, and the formation of flue gasses.

Description

Process for treatment of an organic waste material

Scope of the invention

The present invention relates to a process for treatment of an organic waste material, the process comprising the following steps: (b) . subjecting said organic waste material to a heat treatment process, where the bio- availability of a resulting hydrolysed product is increased for later treatment, and

(c) subjecting said hydrolysed product for at least one anaerobic fermentation process whereby biogas is produced and an organic residue is formed.

Background of the invention

One of the main problems of livestock breeding today is an increasing amount of waste f om each livestock farm due to intensive livestock breeding. Intensive breeding of animals, in particular pigs, leads to the production of huge amounts of manure representing an increasing environmental issue to be dealt with.

The trend towards more and more intensive livestock breeding will undoubtedly continue in the future. While providing important benefits in terms of increased yield and a more efficient production process, intensive livestock breeding has negative environmental consequences due to the large amounts of organic waste material that are produced.

Especially the content of nutrients in organic waste material in solid form contributes to the negative environmental impacts. It has traditionally been difficult to dispose of this part of the organic waste in an environmentally acceptable manner. The situation exists in several areas, such as agriculture, manufacturing industries, processing industries, fisheries, institutions and households.

It is well-known in the art that liquid organic waste can be converted to compost, fertilizers, water and biogas. The conversion process involved may include a filtration process for separating fibrous and particulate material from the liquid, a fermentation process for the production of biogas, and a separation process for separating solid matter from liquid. Traditionally, removal of organic waste has been focused on liquid organic waste material. One object of the prior art may be to divide the liquid organic waste in as many constituents as possible for proper discharge of the non- wanted constituents and for useful utilisation of other constituents serving as fertilizers.

Another object of the prior art may be to reduce the number of viable microbial organisms in order to decrease the risk of diseases when subsequently utilising the organic waste in one way or the other.

Thus, all methods of the prior art deal with the treatment of liquid organic waste, and none of the prior art methods suggests only treating the solid form organic waste which provides new opportunities for utilising only the solid form of the organic material contained in manure.

Object of the invention

It is the object of the present invention to obtain a more efficient energy balance in the treatment of organic waste material, thereby more efficiently utilising the source of energy in the organic waste material in solid form.

A further object of the present invention is to obtain a more efficient mass balance in the treatment of organic waste materials, thereby separating the nutrients in the organic waste material more efficiently.

A further object of the present invention is to focus on other fractions of the organic waste than those traditionally focused on.

A further object of the present invention is to reduce the unpleasant odour resulting from the decomposition of organic material.

A further object of the present invention is to improve the water environment that has been severely affected by accumulation and disposal of organic waste material. A further object of the present invention is to improve producers' possibilities for removal of organic waste material, for example from livestock breeding, industries, fisheries, institutions and households.

A further object of the present invention is to offer producers of organic waste material an economically favourable deposit alternative.

A further object of the present invention is to increase production such as livestock breeding, as a consequence of economically favourable and more environmentally safe deposit of the organic waste material.

A further object of the present invention is to eliminate the presence of pathogenic elements in the organic waste material in solid form.

A further object of the present invention is to reduce the discharge of nitrogenous harmful gasses to the environment during combustion of the organic residue.

A further object of the present invention is to limit the problems related to applying organic waste in solid form having a high content of nutrients during combustion.

A further object of the present invention is to convert the organic waste material in solid form into harmless organic residues applicable for combustion.

A further object of the present invention is to concentrate the difficultly degradable part of the organic waste material applicable for combustion.

A further object of the present invention is to reuse the water content of the organic waste material in other processes.

One or more of all these objects may be obtained by a process for treatment of an organic waste material according to the preamble. of claim 1, wherein said process furthermore comprises a first step of: (a) providing said organic waste material in a solid form to said heat treatment process. Additionally, one or all of these objects may furthermore be obtained by a process for treatment of an organic waste material according to the preamble of claim 1 and wherein said process furthermore comprises a fourth and a fifth step of (d) separating said organic residue into a liquid phase and a solid phase, and (e) combusting said solid phase of said organic residue at a maximum temperature of 900°C resulting in liberation of thermal energy and concentrated combustion residue, and the formation of flue gasses.

Summary of the invention

The term "waste" in relation to organic material should be very broadly interpreted, meaning organic material that is left after any kind of treatment, leaving a part of organic material that could more beneficially be processed by way of the process of the present invention. In the description below, the term "source" is often used to reflect that multiple organic waste materials in solid form can be applied in the present invention.

Waste which could be used in the present invention is e.g. waste from animal husbandry, manure, domestic waste, or animal waste material.

In the following, "organic waste material" is understood as the waste material treated by the process according to the present invention, but said organic waste material comprises different components during the separate steps of the process. For example, said organic waste material is understood in the following ways: - before the heat treatment process, as a solid waste material, after said heat treatment process, as a hydrolysed product, after the anaerobic fermentation process, as an organic residue, after separation of said organic residue, as a solid phase, and after combustion of said solid phase of said organic residue, as a concentrated combustion residue containing nutrients, such as phosphor and calcium.

The first step of the process is to provide said organic waste material in a solid form to said heat treatment process. "Solid form" should be understood as a material consisting of dry matter and any liquid, where the Hquid is associated with the dry matter and perhaps contained in the material, so that a person skilled in the art would regard the material as being in solid form.

To avoid processing a large amount of organic waste in the processes according to the present invention and thereby causing high energy consumption in these processes, the organic waste material is provided in a solid form to said heat treatment process.

The solid form of the organic waste material, e.g. manure, is obtained by a pre- separation process, which can be performed on site or in a process installation connected to the necessary installation provided to perform the present invention.

The pre-separation of the waste, e.g. manure, separates the waste into a solid part and a liquid part, where the solid part is processed according to the present invention. One advantage of pre-separation is that the energy consumption required for performing an efficient heat treatment is reduced significantly when only the solid part of the waste has to be heat treated because it is energy-demanding to heat liquids, e.g. water.

Another advantage is that the liquid part of the waste, e.g. manure, only contains the amount of nutrients, e.g. ammonium, phosphor, potassium, sulphur, calcium, and the like, which can easily be absorbed in the environment when the liquid part of the manure is dispersed as a fertilizer. The excess amounts of nutrients, especially phosphor, are tied up in the separated solid part of the waste and will thus be converted into organic residue which can be combusted.

The pre-separation of nutrients, e.g. ammonium, tied up in the liquid part of the waste will provide a lower level of nitrogen to be processed in the subsequent processes, which will be an advantage because high levels of ammonium can reduce the efficiency of a bioreactor.

Due to the fact that a smaller amount of waste has to be heat treated before entering the bioreactor, it is possible to process waste, e.g. manure, together with a large amount of e.g. animal waste products. Furthermore the pre-separation will ensure that the organic residue for combustion will have a higher calorific value, because it has a higher content of the solid part of the waste, which contains difficultly degradable parts, such as straw, wood or other bio-fuels, while the easily degradable part of the solid part of the waste will be processed in a bioreactor or the like.

The organic waste material comprises 1 to 30 wt. percent dry matter. In one embodiment of the present invention the dry matter content of an organic waste material in solid form is preferably understood as being between 20-30% wt. In another embodiment of the invention, the dry matter content may be between 1-10% wt, alternatively between 10-20% wt. If at least 21% wt of an organic waste material in solid form is dry matter content, this will be preferred for the present invention.

One of the great advantages of the present invention is that the organic waste material in solid form is provided with a limited presence of liquid, according to the above definition of organic waste material in solid form. As the energy in manure is bound in the organic matter, the present invention accordingly benefits from treating the solid matter in manure. The present invention offers numerous advantages:

Firstly, a more efficient energy balance in the treatment of organic waste material is achieved, whereby the energy in the organic waste material in solid form is utilised more efficiently. Additionally, a more efficient mass balance in the treatment of organic waste material is obtained, whereby the separation of the nutrients in the organic waste material is more efficient.

Secondly, the unpleasant odour, which is a consequence of the decomposition of organic material, is limited in the present invention. The present invention also solves the problem of accumulation and disposal of organic waste material to the environment, such as the water environment.

The organic waste material in solid form originates from livestock production and/or animal waste product, for example from manure from livestock production. Alternatively, the organic waste material in solid form is from deep bedding originating from livestock production, poultry production, such as poultry litter and dung. It should be understood that the source of the organic waste material in solid form could be other wastes from agricultural production.

In a preferred embodiment of the invention the organic waste material in solid form is a mixture of manure, waste from animal husbandry, and/or animal waste product, which are provided to separate heat treatment processes.

In one presently preferred embodiment, organic waste material is separated into liquid and a solid form prior to treatment according to the present invention. This separation may be in the form of manure separation techniques, by which the manure is separated into a liquid and a solid form. Other techniques may be applied, such as centrifugation and membrane separation techniques.

If the content of liquid in the organic waste material in solid form lies within the interval according to the definition in the present invention, and depending on the source of organic waste material in solid form, separation may not be necessary, for example if poultry dung is used.

As an alternative, the separation of the source into a liquid phase and a solid phase prior to the heat treatment process is physically connected to the subsequent treatment equipment. If the treatment equipment for instance is placed near the source, this physical connection could be an advantage.

The second step of the process is to subject said organic waste material to a heat treatment process, whereby the bio-availability of a resulting hydrolysed product is increased for later treatment, and the bacteriological culture in the bioreactor is maintained as a clean culture.

The laws and regulations governing the area of waste disposal require that a heat treatment process is performed for reasons of hygiene and health because the wastes are used further for other products, processes, or they are disposed of: The term "hydrolysed product" relates to the organic waste material after the heat treatment process including the decomposed organic material and the organic acids formed during the process.

During the heat treatment process, the organic waste material in solid form is hereby sterilised and/or hygienised, the cell structure of said organic waste material in solid form is degraded, the organic constituents of said organic waste material are dissolved giving improved viscosity for later processing, and at least a fraction of said organic waste material in solid form is converted into organic acids, after which the bio- availability of the resulting thermally hydrolysed product is increased for later processing

Because of the heat treatment process, it is possible to separate ammonia, and any pathogenic elements in the organic waste material are eliminated.

Because of the different types of organic waste material that can be used in the treatment process, the heat treatment process may differ. For example said heat treatment process is either: - a heat treatment process under elevated pressure, or a heat treatment process without elevated pressure, or a heat treatment process by hygienisation.

When using the wording "heat treatment process under elevated pressure", it should be understood that "heat treatment process" means heat treatment above ambient temperature, and "elevated pressure" relates to a pressure above 1 Pa.

For animal waste products, the two first mentioned types of heat treatment processes are used, typically in a sterilisation unit where the heat treatment process under elevated pressure is performed at a temperature above 133°C, a pressure of at least 3 bar, and over a period of at least 20 minuets. . , For manure from livestock production a heat treatment process by hygienisation is used, where the temperature is above 70°C over a period of at least 60 minuets. The organic waste material in solid form is heated to ensure that harmful bacteria are killed.

Another type of organic waste material that is processed by hygienisation is waste from animal husbandry where the waste has a high content of solids like straw, sawdust and the like.

One of the advantages of subjecting the organic waste material in solid form to heat treatment is that the organic material is sterilised, whereby the anaerobic microorganisms in the subsequent formation process are not subjected to foreign microorganisms and thereby external contamination. This facilitates the growth and specialisation of the anaerobic microorganisms present during the fermentation process.

As a consequence, the production of biogas in the fermentation process increases, giving an increased energy yield. Furthermore potential pathogenic microorganisms are eliminated during the treatment, as well as potential pathogenic viruses and other pathogenic elements, such as BSE, giving the final hydrolysed product multiple applications.

Bio-availability in the fermentation process is furthermore increased when the organic waste material in solid form is degraded by heat treatment resulting in a hydrolysed product.

By hydrolysis the cell structure is disrupted and the organic constituents present in the cells and the organic constituents that are part of the cell membranes and cell walls are decomposed, and the smaller the organic constituents the easier is the decomposition for the microorganisms in the fermentation process. This decomposition furthermore means that the organic waste material is dissolved giving improved viscosity for later treatment. Additionally, heat treatment results in an increased content of organic acids for later treatment, and thus the fermentation process is further supported. It should be understood that the content of organic acids formed during the heat treatment may vary depending on the conditions in the treatment, but at least a fraction of said organic acids should be formed.

Another advantage of applying heat treatment prior to the fermentation process is that gases such as ammonia are released during the process. Ammonia will act as a poison to the anaerobic fermentation microorganisms; thus, by removal of ammonia prior to fermentation, the fermentation process is further accelerated.

For example pre-separation of the liquid part of manure will reduce the amount of ammonium in the fermentation process. Thus it is possible to mix the solid part of the manure with a large amount of animal waste products without causing congestion to the anaerobic fermentation microorganisms.

Still another advantage of using heat treatment prior to the fermentation process is that the organic residue left after the fermentation process is reduced compared to traditional fermentation plants due to increased bio-availability. Thus, the deposition of sludge after the fermentation process is reduced if this organic residue is not used for further processing.

It is furthermore possible to use gases, such as ammonia, for the control of said heat treatment process during which measurements of the content of gases, such as ammonia, is performed during release in said heat treatment process.

It is also possible to use heat from cooling of said heat treatment process with a heat exchange with water connected to district heating.

The third step of the process is to subject said hydrolysed product to at least one anaerobic fermentation process whereby biogas is produced and an organic residue is formed. After cooling of the hydrolysed product to an acceptable temperature for fermentation, the hydrolysed product is led to a conventional biogas reactor, wherein anaerobic fermentation processes occur. A person skilled in the art will be aware of a suitable reactor for the treatment according to the present invention.

According to the present invention, it is preferred that the anaerobic fermentation takes place in one process only, but it may also take place in more than one process, such as two processes. The residence time may be about 1-7 days, for example about 3-6 days, such as about 3-4 days, but depends on factors such as bio-availability for the microorganisms in the reactor.

The temperature in the reaction vessel can be varied, but will preferably be from 39°C to 55°C, alternatively about 30°C-39°C. The use of higher or lower fermentation temperatures is possible, if appropriate.

Biogas produced by the anaerobic fermentation processes is removed from the reactor via an outlet at the top of the reactor vessel. The resulting biogas contains predominately methane and some carbon dioxide, and only very small amounts of other gasses, and therefore it is highly suitable for use in for example gas motors or generators for the production of heat and/or electric power. The organic residue from the anaerobic fermentation processes sediments at the bottom of the reactor and is optionally further treated in the form of a solid phase.

The result, of the heat treatment is that at least 60-80% of the energy contained in the organic waste material can be used in the formation of biogas by the anaerobic fermentation process. This conversion of organic material is in fact increased significantly compared to conventional methods. One great advantage is that the organic residue produced in the anaerobic fermentation process is decreased similarly, being a great economic advantage.

Reduction of the dry matter content of said organic waste material after said anaerobic fermentation process is at least 50%, preferably 50-70%, such as around 60%, whereas reduction of the organic residue after fermentation using conventional methods at the most is up to 50%. Furthermore, the invention is more advantageous in relation to a de- watering process of the organic residue after the fermentation process.

Furthermore the result of the heat treatment process is a reduction of the nitrogen content of said organic waste material after said heat treatment process by at least

30%, such as 30-35%, such as 35-40%, depending on the treatment in the first step of the process.

It should be understood that the process can be halted at this point, and the organic residue from the fermentation process can be disposed of, for example distributed as a fertilizer, or deposited at a waste deposit.

In a preferred embodiment of the invention the organic residue is further treated, and the fourth step of the process is to separate said organic residue into a liquid phase and a solid phase.

The separation process may include centrifugation, an ultra-centrifugation step, a stripping step, an evaporation step and a reverse osmosis step. These separation steps may be used individually or together in any combination and any order.

In one embodiment, both centrifugation, ultra-centrifugation, stripping and reverse osmosis are applied in the mentioned order. In addition, any other separation processes may be. applied, including other membrane separation techniques, evaporation, centrifugation, such as decanter centrifugation, etc.

Ultra-filtration separates the organic residue from the fermentation process into a liquid phase and a solid phase. The liquid phase is substantially sterile and particle- free and may be treated further. In a preferred embodiment, the solid phase retained by ^■ ultra-filtration, containing bacteria and suspended organic material, is used as fuel in a combustion process. In another embodiment, the solid phase is used as fertilizer. In yet another embodiment, the solid phase s deposited. Although the liquid phase from the ultra-filtration step in principle can be treated directly by reverse osmosis, the liquid phase after ultra-filtration may preferably be stripped. Efficient removal of ammonium is critical for the success and economical operation of the subsequent reverse osmosis step. The precise nature of the ammonia stripper used is not critical.

The reverse osmosis step includes separation of nutrient salts in the liquid to result in a fertilizer concentrate fraction, such as ammonia concentrate and P/K fertilizer concentrate, and a water fraction. The nutrient salts removed in this step are in particular salts of phosphorus and potassium, and the water that remains after the reverse osmosis step is clean, perhaps potable water that fulfils the WHO requirements for drinking water.

In one embodiment of the invention the clean water is reused in either the heat treatment process or the fermentation process for watering the organic waste in solid form, thereby making it possible to convey/pump the organic waste between process installations.

The fifth step of the process is to combust said solid phase of said organic residue at a maximum temperature of 900°C resulting in liberation of thermal energy and concentrated combustion residue, and the formation of flue gasses.

The flue gasses contain only a limited amount of NO_x due to the low combustion temperature.

A great advantage is that energy left in the organic residue from the anaerobic fermentation process is liberated in the combustion process. Thus, in the present invention an optimal amount of energy contained in the organic waste material in solid form is liberated during the treatment process. An increased energy yield is of great economic importance.

In one presently preferred embodiment, a reduction of the dry matter content of said organic waste material after said combustion is at least 90%. Preferably the reduction in the content of organic dry matter may be higher, such as 90-95%o, or such as 95-

97%. In any circumstances, the content of dry matter in the present invention is considerably decreased compared to traditional treatment processes.

Another advantage, of combining the fermentation process with a combustion process is that draining conditions are improved. Traditionally, the organic residue from the fermentation process has been applied, as fertilizer in agriculture. Due to the fact that the. nitrogen. in the organic residue is tighter bound than free nitrogen, the crops will assimilate a minor part of the nitrogen in the organic residue.

It is generally accepted that the crops assimilate around 30% of the nitrogen in the organic residue, whereas 70% of the nitrogen is bound in the organic residue, and leached, causing environmental damage.

According to the present invention, the organic residue undergoes combustion, whereby all of the organic nitrogen contained is removed. The resulting concentrated combustion residue contains phosphorus, which after combustion is more tightly bound in the soil, and thereby functions as a deposit for later use, giving, a great advantage as fertilizer.

Another important advantage according to the present invention is that a relatively low combustion temperature such as temperatures below 900°C implies that formation of

NO_x is limited.

In the combustion process ammonia is released from the organic constituents contained in the solid phase from separation. Ammonia gases react with the NO_x formed in the process according to the following reaction resulting, in free nitrogen, which is considered clean in an environmental aspect:

NH, + NOv →-H,O ^'+ N, If the temperature is too high such as 1200°C during the combustion, a relatively high amount of NO_x is formed, making the availability of ammonia a critical factor for the conversion of NO_x to free nitrogen, according to the reaction above.

In the present invention, the temperature is below 900°C. Control of the inlet of air and the inlet of the organic constituents contained in the solid phase from separation makes it possible to minimise the outlet of NO_x.

In one preferred embodiment, a reduction of the nitrogen content of said organic waste material after said combustion is at least 95%, such as 95-99%, or such as 99-99,9%. In the present invention the content of NO_x is below 250 ppm, preferably below, or at least as low as, 70-150 ppm.

Resulting from this consideration, organic constituents contained in the solid phase from separation and said constituents, being rich in nitrogen, may be an advantage in limiting the amount of NO_x released from the combustion process. In one embodiment, the content of nitrogen of said solid phase of said organic residue to be combusted (e) is at least 25%, such as 25-30%.

In one embodiment, these organic constituents contained in the solid phase originate from separation. In another embodiment, the organic constituents from organic waste material in a solid form, according to the definition in the present invention, originate from an external source, such as poultry dung and litter. The nitrogen content of poultry dung and litter may be relatively high.

In one presently preferred embodiment the temperature is between 650°C and 850°C during the combustion process such as between 650°C and 700°C. Due to regulations, the temperature in the present invention must, for a short period of at least 2 seconds be 850°C. In another embodiment this short period of at least 2 seconds of a temperature of 850°C may be omitted.

In yet another embodiment, the combustion temperature may be up to 1200°C, primarily to eliminate the content of malodorous compounds. It should be understood that other temperatures may be applied for combustion of the organic constituents contained in a solid phase.

The residence time during combustion may in a preferred embodiment be 220-250 s. In the present invention additional combustion steps may be applied, using a step with reducing conditions.

Another advantage of the present invention is that the combustion leaves a part being concentrated combustion residue. It should be understood that this concentrated combustion residue includes essential inorganic compounds, such as phosphorus and calcium. The concentrated combustion residue may be treated further to purify the inorganic compounds for use as fertilizers.

By using the rest of organic waste material as fuel in a subsequent combustion process the usability of the organic waste material is nearly 100%.

To obtain a constant flow of material into the combustion process or ensure a full combustion, the combustion of said solid phase of said organic residue is effected by adding other combustible products, preferably waste products or other fuels.

Other combustible products, preferably waste products, could for example be poultry dung and litter, biomass such as wood chips, hay or the like. Other fuels could be biogas, natural gas, oil or the like.

In one embodiment of the invention a mechanical drying unit is arranged prior to the combustion process, whereby it is possible to evaporate further moist/water from the organic residue.

The drying unit can be heated by bio gas from the fermentation process or from the combustion of the organic residue. The flue gases containing the evaporated moist or water can be conducted through a condenser unit, whereby water can be recuperated and used in either the heat treatment process or the fermentation process. In general, the present invention is not limited to treatment of an organic waste material in solid form originating from agricultural production. The present invention is suitable for treatment of any organic waste material in solid form including wastewater from households and industries, sewage from institutions such as hospitals, waste from fish industries as well as organic waste material in solid form from livestock production, meat and bone meal, and slaughterhouse waste.

The use of the present invention will have the advantage of:

- lower waste treatment costs, - lower initial cost for the installation for the waste treatment,

- more environment-friendly waste treatment,

- hygienic and health secure waste treatment,

- higher energy yield from the waste treatment, and

- lower energy consumption for waste treatment.

Short description of the drawings

The invention will be explained in more detail below with reference to the drawings, where

Fig. 1 is a diagram illustrating the full process from step (a) - (d) according to the invention,

Fig. 2 . is a diagram illustrating the heat treatment process (b) according to the invention,

Fig. 3 is a diagram illustrating the process from step (a) to (e) according to the invention, and

Fig. 4 is a diagram illustrating the combustion (e) according to the invention. Detailed description of the invention

Fig. 1 shows a situation where the organic waste material in solid form is provided in step (a), as organic animal waste product and manure.

The organic animal waste product is ground and added water so as to be in a form suitable for being pumped from the intake to the heat treatment process.

The manure is separated into a liquid and a solid part, where the solid part is pumped to the hygienisation unit.

In step (b) the manure is hygienised, and the animal waste product is heat treated under elevated pressure where ammonium is released.

The hydrolysed product formed under the heat treatment process (b) undergoes at least one fermentation process in step (c), and the organic residue formed is separated in step (d) into a solid phase and a liquid phase.

It should be understood that separation prior to the treatment in step (b) and step (c) of the organic waste material provided in step (a) may be omitted, and that separation in step (d) may be omitted too.

Fig. 2 shows the heat treatment process (b) of the "heat treatment under elevated pressure" and the process is further described below.

In a presently preferred embodiment the "heat treatment under elevated pressure" includes preheating of the organic waste material in solid form, for example at a temperature of around 133°C.

Preheating of the organic waste material according to the present invention is preferably associated with heat exchange with liquid from a later treatment, such as from the separation of steam from the liquid in a container. The organic waste material in solid form is heated in a first container (V) at around 133°C. The heating leads to evaporation of gases (IN), such as ammonia and organic odour gases. These gases are preferably eliminated in a subsequent plant.

The gases, such as ammonia, may in a preferred embodiment be used to control the heat treatment under elevated pressure comprising measurements of the content of gases such as ammonia during release from the containers (V, NI) by use of a regulation valve.

Alternatively, the gases, such as ammonia, may be used as control means, including measurements of the content of gases such as ammonia during release from the first container (N), the second container (NI), and/or from the fermentation process (XII) by use of a regulation valve.

The source of steam may preferably be excess steam from a combustion process, from a steam boiler or exhaust from a motor generator and preferably has a temperature of about 160°C.

The organic waste material may hereafter be led to a container (N), where the temperature preferably is 130-180°C, such as 145-170°C, preferably 160-170°C. The pressure in the container (V) is preferably between 3-10 Pa, such as 5-8 Pa, preferably 6-7 Pa. The treatment in the container (N) may preferably take 5-60 rnin. In the process, at least a fraction of organic acids is formed.

After this treatment the organic waste material is subjected to a decompression period, wherein an instant pressure reduction takes place.

The instant pressure reduction decomposes the cells, thereby releasing cell-bound water and dissolving solids. The bio-availability of the organic constituents is hereafter increased, which is an advantage for the anaerobic fermentation process in step (c). The pressure is 4-1 Pa in the depressurising period and the steam is separated and reused in the condenser (III) with the incoming water from commercial use such as in district heating.

The hydrolysed product is used in heat exchanger (I) to preheat the incoming organic waste material (manure) before it is lead though the heat treatment to the fermentation container (XII).

After the hydrolysed product from container (VI) has preheated the organic waste material in heat exchanger (I), the hydrolysed product is preferably further cooled in a heat exchanger (II). In a preferred embodiment, this cooling in the heat exchanger (II) is associated with heating of water for commercially use, such as in district heating.

The temperature of the incoming water from district heating may be 35-40°C, and after heat exchange, the temperature may be 40-50°C. Furthermore, the water heated to preferably 40-50°C may undergo heat exchange in the condenser (III), whereby the outgoing water has a temperature in the range of 65-85°C.

This condenser (III) may be connected to a turbine and/or generator (XI) driven by biogas from the fermentation process in step (c). The temperatures may vary, and the temperatures mentioned should be understood as preferred temperatures for illustrating the concept.

Fig. 3 shows a situation where organic residue formed during the fermentation process (c) is separated in step (d) into a liquid phase and a solid phase, which undergoes combustion in step (e). The combustion forms heat, flue gases and combustion residue.

Fig. 4 shows the combustion process (e) where organic waste material (solid phase of the organic residue from the fermentation process (c)) is fed to a combustion chamber. The flue gas is led through a filter unit. The combustion residue can be mixed with fly ash from the filter unit and used as e.g. a fertilizer (due to a high content of phosphor), road surface material, or as a component in building materials like concrete or the like.

The heat from the combustion chamber is used in a steam boiler for producing steam to a turbine/generator whereby electricity and heat are generated or to generate heat for the drying unit.

Claims

1. Process for treatment of an organic waste material, the process comprising the following steps: (b) subjecting said organic waste material to a heat treatment process, where the bio- availability of a resulting hydrolysed product is increased for later treatment, and (c) subjecting said hydrolysed product for at least one anaerobic fermentation process whereby biogas is produced and an organic residue is formed, characterisedin that said process furthermore comprises a first step of: (a) providing said organic waste material in a solid form to said heat treatment process.

2. Process according to claim l,characterisedin that said process furthermore comprises a fourth and a fifth step of: (d) separating said organic residue into a liquid phase and a solid phase,

(e) combusting said solid phase of said organic residue at a maximum temperature of 900°C resulting in liberation of thermal energy and concentrated combustion residue, and the formation of flue gasses.

3. Process according to claim 1, eharaeterϊsed in that said heat treatment process (b) furthermore comprises separation of ammonia.

4. Process according to any of the claims 1 or 3, characterised in that said heat treatment process (b) includes: (i) sterilising and/or hygienising said organic waste material,

(ii) degrading the cell structure of said organic waste material, (iii) dissolving the organic constituents of said organic waste material, (iv) converting at least a fraction of said organic waste material into organic acids.

5. Process according to any of the claims 1, 3 or 4, characterisedin that said heat treatment process (b) is either: - a heat treatment process under elevated pressure, or - a heat treatment process without elevated pressure, or

- a heat treatment process by hygienisation.

6. Process according to any of the claims 1 or 4, characterised in that said organic waste material is waste from livestock production andor animal waste product.

7. Process according to claim 2, characterised in that combusting (e) said solid phase of said organic residue is effected by adding other combustible products, preferably waste products or other fuels.

8. Process according to any of the claims 1,4 or 6, characterised in that said organic waste material comprises 1-30 wt percent dry matter.

9. Process according to claim 1, characterised in that a reduction of the dry matter content of said organic waste material after said anaerobic fermentation process (c) is at least 50%.

10. Process according to any of the claims 2 or 7, characterised in that a reduction of the dry matter content of said organic waste material after said combustion (e) is at least 90%.

11. Process according to any of the claims 1, 3, 4 or 5, characterisedin that a reduction of the nitrogen content of said organic waste material after said heat treatment process (b) is at least 30%.

12. Process according to any of the claims 2, 7 or 10, characteris ed in that a reduction of the nitrogen content of said organic waste material after said combustion

(e) is at least 95%.

13. Process according to claim 2, 7, 10, or 12, ch racterised in that the content of nitrogen of said solid phase of said organic residue to be combusted (e) is at least 25%.