The present invention relates to the treatment of waste organic material. More specifically, the present invention provides a method and apparatus for the treatment of waste organic material, which enables heat and other useful products to be extracted from an otherwise waste material in a clean and efficient manner.

The disposal or treatment of waste material, such as human or animal effluent and other by-products of food processing, puts a large burden on the farm or facility to dispose of in an environmentally acceptable manner, often requiring large amounts of land to be provided to allow the waste material to be spread sufficiently thinly to meet legislation relating to the products contained therein.

In Denmark, for example, every pig farmer must have enough land to spread the pig effluent (containing mostly urea and ammonia) to prevent the phosphorus and nitrogen compounds also contained in the effluent from getting into streams and surface water. This puts quite a large burden on the farmer since if the farmer distributes nitrogen-containing material from the pig slurry on to land according to its apparent content a problem is created in that, because a high quantity of phosphorus is contained in the slurry, spreading the slurry to disperse the nitrogen causes a very high excess of phosphorus to be introduced into the environment.

Most of the phosphorus is in the form of orthophosphate (P2O ₅ ) which means it is bound to organic material in the slurry and not easily available for plants to uptake. Indeed, a portion of the nitrogen content is also bound to organics, albeit to a lesser degree. Hence, spreading the slurry to distribute the nitrogen introduces excess phosphorus into the environment, causing pollution. In addition, there is considerable transport cost in distributing the pig slurry during the year and storing it during periods where the land is frozen and cannot take up the nutrient. There is a paradox in the problem presented by the excess phosphorus in that whilst there may be excess phosphorus in the soil, there is not enough available for the plants that need it because too much phosphorus in the soil is bound to organics. Consequently farmers often use fertilizers containing phosphorus in the needed form, which introduces further cost and environmental issues.

Another example of where problems might be caused by excess phosphorus is fish farming, wherein fish are generally raised in an environment where they spend most of their life swimming in varying concentrations of their own excrement, which contains the same phosphorus and nitrogen compounds described above. A number of diseases and problems are specifically attributed to the practice including infection by Flavobacterium as well as giving unwanted "taste of mud" caused by waste (Geosmin and Methylisoborneol) from bacteria metabolism. A further problem is caused when clean water, which is occasionally added to dilute the environment in which the fish are farmed, causes overspill of the contaminated water into streams.

In the prior art, DK200800645 (Purliq) teaches a method of filtering much of the fibers and organic material from organic waste material, in this case pig effluent ("slurry"). As mentioned above, such organic waste material typically contains high levels of nitrogen, phosphorus and ammonia. Since much of the phosphorus and some of the urea and ammonia are bound to the organics, by using the Purliq method, a farmer can solve some of the problems relating to waste effluent disposal by removing these fibers and organic materials from the slurry and hence reduce the amount of land required to dispose of the remaining waste.

A problem with the above-mentioned Purliq method is that a filtered "biomass" containing a large quantity of Nitrogen (N), Phosphorus (P) and Potassium (K), is obtained, which poses a separate problem in that, if left untreated, the biomass will rot. An obvious solution to this problem is to burn the biomass, but this introduces a further problem in that burning of organic waste is regulated due to the harmful nitrogen compounds that are created when organic material is burnt in air, commonly referred to as NO _x .

If the Purliq method is used the problem is partially solved but there is still a requirement to dispose of the fibers. One solution is to truck the fibers to an offsite incinerator but this incurs additional cost and environmental impact. Alternatively, the slurry can also be transported to a facility/farm further away, which is typically what is done. In addition to the cost of transportation, however, there is the attendant problem of the potential for spreading sickness from one farm to another.

It is well known that the level of NO _x gases released into the atmosphere can be controlled by scrubbing flue gases with ammonia (NH ₄ ), as described in US- B-3900554, for example. Advantageously, if the flue gases can be scrubbed to reduce the harmful NO _N gases to an acceptable level, burning of the waste material can provide useful energy to the farm or facility, in the form of heat.

Unfortunately, sourcing the ammonia required for scrubbing introduces additional cost both in terms of purchasing it and transportation. In addition, transportation of ammonia has an undesirable carbon footprint. Hence, the cost of sourcing the ammonia typically negates the savings that could otherwise be made from capturing and using heat from burning the waste material. According to the present invention there is provided a method of treating flue gases emanating from burning organic waste material from scrubbing them using ammonia captured from waste material during a prior drying step, during which sufficient heat is applied to waste material to fractionally distil the ammonia from the waste material. Preferably, before the drying step, the waste material is pressed using sufficient force to remove a majority of fluid contained within. An apparatus for performing the method is also provided.

By performing in situ combustion there is a large saving in energy consuming transportation. Only the residual ash must be transported, and this ash has a value in the form of phosphorus that can be exploited commercially. Furthermore, a farmer can obtain authorization to use the liquid fraction to complete fertilization of its cultivation (without application of fertilizer) that is a substantial financial saving for the farmer and an environmental benefit to society. In the same vein, the farmer can often be allowed a larger pig production in Denmark, for example, an increase of 40%.

In the drawings:

Figure 1 shows an example of an apparatus suitable for performing the method of the present invention; and

Figure 2 shows a flow diagram representing the process steps of the present invention. Figure 1 is a schematic diagram showing an apparatus in accordance with the invention, which can perform the method of invention. The apparatus receives pressed organic waste material, such as pig effluent, into a hopper 1. The material passes through a first preheating chamber 2 on conveyor belt, screw or other driving mechanism. The heating in this example, is at around 70 °C to vaporize ammonia present in the material. The connecting chamber 3 allows material to pass from the first chamber 2 into a second chamber 4 which has a temperature in the region of 150 °C which further heats the material and ensures removal of water from the material.

A second connecting chamber 5 then allows material from the second collecting chamber 4 to pass into a burning chamber 6. The material is burnt within the chamber 6 unit until it has been reduced to ashes and passed out into ash collection region 7. Waste gas from the burning process is collected via pipe 8 and then passed up into the atmosphere via flue 9. A scrubbing unit 10 is positioned within the flue 9 so that the waste gasses from the burning can be scrubbed to remove the NO _x compounds within the gas. The scrubbing unit 10 requires a supply of ammonia gas and can be aided by the presence of water vapour.

This is collected by blowers 1 1 , 12 which are connected to the first and second collecting chambers 2, 4, the blowers create potential vacuums across their respective chambers to create efficient flow of ammonia and moisture to the blowers 1 1 , 12. Sensors may be provided at the scrubber to ensure that there is an appropriate ratio of ammonia to NO _x compounds to ensure efficient scrubbing. If it is detected that the amount of ammonia is insufficient then additional ammonia can be added through an increase in the input of material via the hopper 1 , or optionally by the supply of liquid that was obtained during the pressing of the organic material prior to its delivery to the hopper 1 .

The system may also optionally be arranged such that the liquid collected during pressing, or water from a separate supply, can be applied to the burning chamber 6 via spray 15 to ensure that the temperature in the chamber does not exceed levels which causes the generation of excess NO _x in the exhaust gases that pass to the flue line.

It will be readily appreciated that the apparatus of the invention can be used as a heat source that can be used as a source of energy for electrical generator, for example, or can be used to heat farm buildings or domestic buildings as appropriate.

Figure 2 shows the operating steps for the apparatus. Organic waste material, such as pig effluent, is pressed, ideally using around 500MPa pressure, to remove the majority of excess fluid contained in the organic waste material. This excess fluid can be collected for further treatment as the fluid itself may contain useful material. The remaining pressed fibres and material, which contain nitrogen, phosphorus, and ammonia, are then heated to a temperature that is sufficient to cause vaporization of ammonia from the moisture contained in the organic faction, the boiling point of ammonia being -33.34 °C (or 240 K). The removal of ammonia from moisture is controlled by temperature and pressure. If a simple turbine is driven by the steam coming from a second, water chamber it could be used to create a partial vacuum in the ammonia extraction chamber, increasing the efficiency. Ammonia "sucked" out of the chamber is then blown into the flu gas.

An advantageous effect of heating the fibres and waste material to distil the ammonia is that it reduces the amount of energy required to burn it, thus allowing more energy to be generated through burning it. Also, burning the waste material removes a significant amount of phosphorus from the total amount of organics that the farmer has to account for in otherwise untreated organic waste slurry.

Once sufficiently dried, the remaining fibres and material can then be burnt to dispose of them while generating heat energy, which can be captured and used. Although it is well know that organic sludge can be burned to capture phosphorus and other useful material contained therein, existing methods require the process to take place in a, typically offsite, processing facility where the ashes are laden with heavy metal due to the content of the municipal sludge. Much organic material, including that in pig slurry, is coagulated with chemicals such as iron chloride, leaving chemical residues in the sludge which are undesirable and, once all of the materials are mixed together, the process of separating them is highly complicated.

In addition to containing phosphorus, the ashes resulting from the burnt fibers also contain potassium which, when the ashes are spread on farm land, reduces the cost of lime that is otherwise typically required by farmers to raise the pH of the soil being fertilized. The ashes from the farmer are free from contamination from other waste streams.

To eliminate NO _x compounds in the flue gases emitted as the fibres and waste material are burnt, previously distilled and captured ammonia is sprayed into flue gasses with the concentration of ammonia having, ideally, a stoichiometric ratio of 1 :1 with the ΝΟχ compounds. As the ammonia molecule is covalent, it donates the hydrogen atoms to stabilize the NO _x compounds. The ammonia is, preferably, sprayed across a ceramic-based diffuser, positioned in a chimney through which the flue gases are directed. It is well known from selective reduction (SRC) processes that if ammonia is vaporized and sprayed across various catalytic materials, the NO _x remediation will take place at lower temperatures and hence the process is more efficient. A disadvantage with existing SRC processes, however, is that they require a complicated method for storing and delivering the ammonia used to knock the NO _x compounds.

An advantage of the present invention is that since the flue gases are scrubbed using ammonia obtained from the waste material to be burnt, there is no need to source ammonia elsewhere. This holistic approach can considerably reduce transport and other costs relating to the ammonia to allow usable heat and power to be generated during the treatment process in a cost-effective way.

In addition to the extraction of "clean" heat, a further advantage of the above- described process is that, although the bulk of the biomass material is greatly reduced, the phosphorus contained therein is not destroyed but remains present in the burnt ashes, along with the potassium. This high concentration of phosphorus can itself have a commercial value. If the resulting ashes are used as fertilizer, in addition to the benefits of the phosphorus to the soil it is spread on, the potassium contained in the ash will increase the pH of the land on which it is spread and hence reduce the amount of calcium otherwise required to be spread to achieve a desired pH balance needed by the plants.

In addition, if the ashes were used as they are generated, the phosphorus would be made more basic due to the potassium of the pig slurry, thereby reducing the amount of lime a farmer would have to spread.