A process of producing soil amendment from organic waste, and a fertilizer produced from same

Description

[0002] A process of producing soil amendment from organic waste, and a fertilizer produced from same

[0003] The present invention is related to a process of producing soil amendment from organic waste, in particular a process of producing semi-finished products which can be mixed and matched to form specified fertilizer and soil improvement products from organic waste as raw materials.

[0004]

[0005] Background

[0006]

[0007] The traditional way of handling waste has in large been a result of viewing waste handling as a process to mitigate the problems related to the waste, with processes primarily designed to mitigate the negative aspects. The more modern philosophy of viewing the waste as raw materials introduces new ways of thinking, and thereby designing processes with a goal of value-added end-products.

[0008] Organic waste, such as municipal waste, waste from fish industry or breweries is today treated in numerous ways, traditional depositing, and combustion to produce energy for example in the form of hot water, anaerobic digestion or composting. The term composting is often viewed as a collective concept of a range of different biological processes, both aerobic and anaerobic, naturally occurring when organic / bio-waste has been left to decompose by nature itself. Among people more into the craft composting is mainly viewed as a process dominated by aerobic processes in contrast to anaerobic more commonly known as biogas or anaerobic digestion.

[0009]

[0010] The lack of precise definition of the process is closely linked to the fact that only a low percentage of microorganisms involved are known and even less scientifically mapped out. As a result, composting as treatment method of organic waste has been dominated by practical craftsmanship rather than scientific research.

[0011]

[0012] Composting is a technology for treatment of biodegradable (organic) waste. The main advantages of successful composting are a decrease in waste volume; the elimination of most organic toxic compounds, pathogens and pests (potentially present in the original waste) and a transformation of organic matter and nutrients into a stable product that acts as a soil amendment.

[0013]

[0014] Composting is a biological aerobic process in which microorganisms convert organic materials and utilize primarily N and C compounds to grow and convert the biomass to a more stable earthy organic material. It is an exothermic process (self-heating), and commonly encompasses three phases: (i) the mesophilic (< 40 °C), (ii) the thermophilic (> 40 °C) and (iii) the maturation / mesophilic curing / cooling (< 40 °C)

[0015] The dominating industrial-scale approach to composting is open windrow composting on hard surface, with or without cover or roof. Feedstocks are normally treated and mixed to obtain desirable properties of carbon-nitrogen ration, moisture levels and size distributions to speed up the process. Some facilities also have an aeration system of perforated pipes at the bottom of the windrows to ensure aerobic conditions, but must be closely monitored to avoid excessive drying with need of adding water as a result. As the process is exothermal the temperature rises as microorganisms thrive resulting in a temperature gradient from core to surface of the windrow. Other conditions like moisture and oxygen levels also vary across the windrow. As a consequence, turning of the windrow is variably introduced to mix the mass and increase the chance of all mass being subjected to the moist, warm zone. Two continuous days of over 60°C is desired to kill unwanted bacteria.Temperatures over 65 °C is normally not recommended, most commonly rationalized claiming that it also kills the desired bacteria wanted for an effective composting process.

[0016]

[0017] In-vessel composting is to some degree introduced to ensure hygienization (two days above 60 °C) and to kick-start the composting process. In-vessel residence time varies from a few days to a month, followed by weeks to months of maturing at lower temperatures, typically in windrows.

[0018]

[0019] The end-product, commonly known as compost, is then normally applied directly to use without further processing as the negative aspects of organic waste has been mitigated. Compost is considered fully converted when it is stable, and the exothermic processes has stopped increasing the temperature of the material.

[0020]

[0021] Britannica defines ‘fertilizer’ as “natural or artificial substance containing the chemical elements that improve growth and productiveness of plants. Fertilizers enhance the natural fertility of the soil or replace the chemical elements taken from the soil by previous crops.”

[0022]

[0023] The use of manure and composts for fertilizing purposes is probably as old as agriculture itself. Organic fertilizer like these have traditionally been defined by the processing, or lack thereof, and to little degree the end-product need. Consequently, organic farming has had challenges with replacing the nutrients removed by crops in a balanced manner.

[0024]

[0025] Chemical fertilizer on the other hand, made for an agricultural revolution by making fertilizer with balanced amounts of nutrients available in the end-product. The content of nutrients is designed in accordance with the needs required for different crops and soil, and in a repeatable manner. By combining different salts chemical fertilizer can easily replace the amount of nutrients removed by crops.

[0026] In contrast to organic fertilizer the chemical ones contain low to none amounts of carbonaceous material. As crops, and some soil with them are removed, the levels of organic matter in the soil have dropped significantly the last decades. The ability of the soil for storing and buffering the nutrients from chemical fertilizer is reduced, leading to eutrophication and high run-off levels. As a consequence, more and more attention is given to soil degradation as a big, future challenge within agriculture. Low levels of soil organic matter is correlated to bad soil health and higher need for fertilizing. The complex ecological interactions in soil are poorly understood from a scientific perspective, but calls for increasing the soil organic contents as a means to restore soil health and crop yields are gaining attention.

[0027]

[0028] WO 2010 / 139028 A1 describes a method of producing electric power and fertilizer from combustion of biomass, e.g. straw from cereal crops, by producing a liquor from compounds extracted from the exhaust gas, and a fertilizer by composting organic materials in the presence of the liquor.

[0029]

[0030] Object

[0031]

[0032] The main object of the invention is to provide a process of treating organic waste to produce valuable products that can be recycled to increase plant growth with high degree of efficiency.

[0033] The invention

[0034]

[0035] The object above is achieved by a process in accordance with the characterizing part of claim 1, and a fertilizer in accordance with claim 8. Additional advantageous features appear from the accompanying dependent claims.

[0036]

[0037] Definition

[0038]

[0039] The term “wet organic waste” is meant to include wet waste (e.g. dry matter (DM) 2-50 %) as such, but also dry waste obtained through some drying process.

[0040]

[0041] The term “structural material” is meant to include a carbon-rich bulking material which serves as carbon source for microorganisms, providing porosity and air movement through the mass as well as high level of gas diffusion and is typically wood chips preferably in a dry state.

[0042]

[0043] “The term “biochar” is meant to include carbonaceous material of biological origin converted to char by a pyrolytic process, typically shredded, wooden material.

[0044]

[0045] “Third generation composting” is meant to describe an aerobic microbial process in a closed reactor where decisive parameters (e.g. composition of feedstock mix, retention time and speed through drum, addition of other substances such as oxygen and gas exchange rate) are monitored and adjusted to obtain desired output in a predictable and repeatable way.

[0046]

[0047] The term “compost” is used to describe the wet mass coming from the drum outlet after the composting process, excluding the gaseous phase.

[0048]

[0049] General description

[0050]

[0051] The present invention is related to a process of producing fertilizers and soil amendments from organic waste, ideal feedstocks typically have 55 – 65 % moisture, high nutrient levels, well balanced C / N ratio and functional structure material size distribution, said process comprising the steps of:

[0052] feeding wet organic waste including added biochar together with structural discontinuous shredded or similarly treated wooden material to form a feed mixture in conduit to a composting drum,

[0053]

[0054] subjecting the mixture in said composting drum to a controlled process of microbial aerobic conversion for a prolonged period of time and at an elevated temperature to produce:

[0055]

[0056] a solid phase comprising wet compost with biochar, and

[0057]

[0058] a gaseous phase comprising substantially humid air with elevated levels of CO2 and ammonia.

[0059] The process further comprises the steps of:

[0060]

[0061] feeding the solid phase to a dryer to remove water from the solid phase and produce dry compost in conduit,

[0062]

[0063] feeding the dry compost to a solid-solid separator to extract the structural material from the dry compost fine fraction having a desired maximum diameter range, and then:

[0064]

[0065] feeding dry compost substantially free from structural material in conduit to a mixer,

[0066] feeding separated structural material in conduit to a structural material reception,

[0067] feeding said gaseous phase from the composting drum to an ammonia absorber to perform gas scrubbing producing:

[0068]

[0069] a gaseous phase substantially free from ammonia, and

[0070]

[0071] a liquid phase comprising ammonia salts,

[0072] feeding the liquid phase comprising ammonia salts the mixer, and

[0073]

[0074] feeding ammonia enriched compost from mixer to a fertilizer reception.

[0075]

[0076] The scrubbing step is advantageously performed by means of an acidic fluid, e.g. an aqueous solution of nitric acid HNO3 (aq), an aqueous solution comprising sulfuric acid H2SO4 (aq), or an aqueous solution of phosphoric acid H3PO4 (aq).

[0077]

[0078] In a preferred embodiment, the process further comprises the steps of feeding structural material, ideal feedstocks have 10 – 20 % moisture and high lignin content, such as field residues or woody biomass, to a pyrolysis reactor to produce:

[0079]

[0080] a solid carbonaceous material in conduit, and feed the solid carbonaceous material to said mixer as a carbon supply to the fertilizer end product in fertilizer reception, and

[0081]

[0082] a gaseous phase, and feeding the latter to the dryer, serving as a heat source to the dryer.

[0083]

[0084] At least a part of the solid carbonaceous material (biochar) can be used in a filter to extract ammonia from the gaseous phase from composting drum. Suitable amounts of biochar is added to the composting process, as it contribute positively to the composting process and binds up more nitrogen in the solid phase and the biochar itself gets activated.

[0085]

[0086] The invention is also related to a fertilizer for use in agriculture, produced by the process according to the process steps above as well as a product-by-process stemming from separating the fine fraction of the solid phase, for example <2 mm.

[0087]

[0088] Detailed description

[0089]

[0090] The invention is in the following described in further detail by means of an illustration, where

[0091] Fig.1 is an overall process flow diagram of the process in accordance with the present invention.

[0092] Fig. 1 illustrates a simplified flow sheet of the process in accordance with the present invention, indicated by reference numeral 100. Wet organic waste 101 together with of structural material 102 and biochar from 118 or other source is fed to a composting drum 107 via a hopper 103 and a screw conveyor 104. The wet organic material should ideally be pre-treated by size reduction to a Dmax of 12mm for sanitation purposes.

[0093] The structural material is typically shredded wood material with several purposes: Large pieces increase stirring / cavitation and gas distribution, smaller units has large relative surface and serves as good carbon sources for microbial activity in the composting drum 107. Particle size distribution of structural material is ideally of a wide range, from dust particles to larger material. The carbonaceous material commonly known as biochar has an overall positive impact on the composting process as well as retention of nitrogen. Addition of 2 – 10 % dry substance mix have significantly positive properties, with typically 5 % of DS giving good results. The biochar added should ideally be in particle size range Dmin 0,5 mm to Dmax 2,0 mm for optimal separation and effect.

[0094] In the composting drum 107, the mixture of wet organic waste with biochar and structural material is subjected to microbial aerobic conversion to form compost in a manner known per se. While feeding and unloading is typically done batchwise (e.g daily) the composting process conditions are of a more continuous nature with a steady movement from loading side to unloading end of the reactor. While expertise in the field normally advise against temperatures over 65C a desirable process parameter here is a relatively steep increase in temperature to reach 70-75°C in a section of the reactor. Contrary to common practice present method facilitate for such high temperature conversion until the microbial population change and temperature is reduced.

[0095]

[0096] Following this step a gradual reduction in temperature to about 40-45°C will take place, whereupon a near complete microbial conversion will have taken place, typically in about 12 – 17 days. An optional, additional sequential step for slow drying and / or maturation may be applied, and the same may be achieved with e.g. longer drums. The composting drum 107 is typically a rotating (inclined) drum with flights, preferably equipped with sensors, at least for temperature control, and with possibility for forced ventilation to ensure aerobic conditions.

[0097]

[0098] When the conversion process of the mixture in the composting drum 107 has been completed, the resulting compost in conduit 108 is fed to a dryer 109 where remaining humidity is evaporated and rejected to the surrounding air via a purification device, e.g. a cyclone (not shown). The resulting dried mixture in conduit 110 is then fed to a solid-solid separator 111, e.g. in the form of a sieve, where the majority of structural material, having relatively coarser structure than the compost fines fraction, is separated from the dry compost in separator 111 and fed to a structure material reception 117 via conduit 116.

[0099]

[0100] Typically, a separation of D<2 mm gives a fine fraction which includes the majority of biochar. As a consequence of the composting process the biochar has new and improved properties. The mixture of fine fraction (FF) from composting and activated biochar (aB) has unique properties, and FFaB is the main ingredient in the products from the present process.

[0101]

[0102] FFaB may be applied as a standalone soil amendment product. FFaB also serves as a highly efficient base / intermediate for composing a wide range of nutrient specific organic based fertilizers; thus competing with the flexible product range of chemical (“mineral”) fertilizers but substantially more sustainable. A substantial part of the nitrogen in such products may come from the ammonia recovery in the process (120).

[0103]

[0104] The desired fraction> more than about 2 mm will mainly be structural material. From its origin (shredded wood) this fraction also has changed properties as a consequence of the process: More stable, reduced carbon content and with changes in the relative amounts of lignin, hemicellulose and cellulose. Based on its positive effects in soil (e.g. water retention ability, stimulating soil life and more) this fraction is an important ingredient in peat replacing products which also includes FFaB. It should be emphasized that the desired maximum diameter range will vary with the desired goal.

[0105]

[0106] In summary: This fine fraction (FFaB) and the post composting structural material (typically <2 mm) serves as excellent intermediates to form an organic based soil amendment and fertilizer product line. Mixtures of converted wet organic waste, some sufficiently degraded structural material and biochar is characterized by high carbon and humus content with good soil amendment properties and as an intermediate product for producing organic fertilizer with high NPK-content.

[0107]

[0108] Dry compost in conduit 112 is fed to a mixer 113, where the compost is mixed with additives to enrich the compost in view of fertilizing purposes.

[0109]

[0110] The gaseous phase from the composting drum 107 is discharged in conduit 119 by means of fan and can be fed to an optional nitrogen absorber 120 to enrich the resulting end product (fertilizer) with nitrogen compounds. The nitrogen absorber 120 is advantageously a gas scrubber, where the gaseous nitrogen containing discharge 118 from composting drum 107 is subjected to nitrogen absorption by a liquid solution of sulfuric acid or nitric acid, producing a gaseous outlet (not shown) which is subjected to purification before being discharged to the surrounding air, and a liquid outlet in line 121 comprising water and solvated ammonium salts, e.g. sodium nitrate NH4NO3. The ammonium containing water solution 121 from absorber 120 is then fed to a mixer 113, where the dry compost from solid-solid separator 111 is enriched by ammonia to produce a more valuable fertilizer.

[0111] However, it is also conceivable to recover ammonia by other methods known per se, e.g. adsorption or condensation.

[0112]

[0113] Structural material from conduit 122, or other carbon-rich materials, is advantageously fed to a pyrolysis reactor 123, with the purpose of producing carbonaceous material in line 126 to enrich the fertilizer end product with carbon in mixer 113. The carbonaceous product from pyrolysis reactor 123 can also preferably be supplied to the composting reactor via structural material reception 117 or otherwise in the mixture. The structural material should ideally have dry substance level >80% for efficient processing in the pyrolysis reactor and 30mm max diameter and length. Several carbonrich feedstocks may be used, but shredded wooden materials from The gaseous phase from the pyrolysis reactor 123 in conduit 125 is optionally cooled in heat exchanger 124 and fed to dryer 109 to recover energy in the process. In this embodiment, carbon from the structural material is in the fertilizer end product reception 115 instead of being combusted to carbon dioxide and released to the environments.

[0114]

[0115] The solid phase product from pyrolysis reactor 123 may also be used to capture nitrogen from composting drum 107, where gaseous ammonia in conduit 116 can be captured (not shown) within micro pores in the carbonaceous discharge, and hence further enrich the desired fertilizer end product.

[0116]

[0117] The fertilizer end product can also be supplied with other additives to further enrich the fertilizer.

[0118]

[0119] Summary

[0120]

[0121] The present invention provides a process of recovering valuable chemical compounds from wet organic waste to produce fertilizer, contrary to depositing of waste or combustion of the same to produce energy and releasing carbon dioxide to the environments.

[0122]

[0123] Technical Effects

[0124]

[0125] The invention in total presents several technical effects:

[0126]

[0127] · A very energy-efficient process of treating wet organic waste with low GHG-emissions · Very high recovery of nutrients normally lost to the atmosphere or washed out at sea, saving chemical fertilizer use extracted from limited sources

[0128]

[0129] o Ammonia (nitrogen) normally lost in composting processes is recovered (>95%) and utilised for plant growth

[0130] o Phosphorus is recycled into soil amendments / fertilizers and utilised for plant growth

[0131]

[0132] o Potassium is recycled into soil amendments / fertilizers and utilised for plant growth · Carbon often lost to the atmosphere is converted to chemical forms like humus and biochar beneficial for plant growth efficiency

[0133] · The recycling of nutrients save GHG-emissions by saving use of chemical fertilizers with high GHG-emissions

[0134]

[0135] The fines fraction with activated biochar (FFaB) serves as an excellent soil amendment as well as intermediate for organic fertilizers with nutrient content competing with traditional chemical fertilizers. This mix is high in humus content and with substantial levels of activated biochar and cellulose / hemi-cellulose-reduced structural material, which can be seen as a ‘concentrate’ of compost, with several beneficial properties when applied to soil:

[0136]

[0137] · Reduced leaching of nitrogen and a lower need for nitrogen application for crops

[0138]

[0139] · Possible reduced emissions of nitrous oxide

[0140]

[0141] · Increased cation-exchange capacity resulting in improved soil fertility

[0142]

[0143] · Moderating of soil acidity

[0144]

[0145] · Increased water retention

[0146]

[0147] · Increased number of beneficial soil microbes

[0148]

[0149] Combined with additives for higher levels of nutrients (NPK) the FFaB-mix makes for a sustainable alternative to chemical fertilizers, but with several other beneficial properties other than the purely nutrient addition of chemical fertilizer.

Claims

Claims1. A process of producing soil amendment from organic waste, said process comprising the steps of: feeding wet organic waste (101) together with structural discontinuous wooden material (102) and a solid carbonaceous material (118) to form a feed mixture in conduit (106) to a composting drum (107),subjecting the mixture in said composting drum (107) to microbial aerobic conversion for a period of approximately two weeks and at a temperature profile rising to 70-75°C followed by a gradual reduction to 40-45 °C to produce:a solid phase (108) comprising compost with biochar, anda gaseous phase (119) comprising substantially humid air and elevated levels of CO2 and ammonia,characterized infeeding said solid phase (108) to a dryer (109) to remove water from the solid phase (108) and produce dry compost in conduit (110),feeding said dry compost in conduit (110) to a solid-solid separator (111) to extract a majority of said structural material having a desired maximum diameter range from the dry compost, and then:feeding dry compost substantially free from structural material in conduit (112) to a mixer (113),feeding separated structural material in conduit (116) to a structural material reception (117), feeding said gaseous phase (119) from the composting drum (107) to an ammonia absorber (120) to perform gas scrubbing producing:a gaseous phase substantially free from ammonia, anda liquid phase comprising ammonia salts in conduit (121),feeding the liquid phase comprising ammonia salts in conduit (121) to said mixer (113), and feeding ammonia enriched compost from mixer (113) to a fertilizer reception (115).

2. The process of claim 1, wherein the scrubbing is performed by means of an acidic fluid.

3. The process of claim 2,wherein acidic fluid is an aqueous solution of nitric acid HNO3 (aq).

4. The process of claim 2, wherein the acidic fluid is an aqueous solution comprising sulfuric acid H2SO4 (aq).

5. The process of claim 2, wherein the acidic fluid is an aqueous solution of phosphoric acid H3PO4 (aq).

6. The process of any one of the claims above, wherein the process further comprises the steps of feeding structural material (101) to a pyrolysis reactor (123) to produce:a solid carbonaceous material in conduit (126), and feed the solid carbonaceous material (126) to said mixer (113) as a carbon supply to the fertilizer end product in fertilizer reception (115), and a gaseous phase in conduit (125) and feeding the same to the dryer (109), serving as a heat source in dryer (109).

7. The process of claim 6, wherein using a multilayer batch filter, including as filter layer at least a part of solid carbonaceous material in conduit (126), and a layer of dry compost in conduit (113),used as an ammonia absorber to extract ammonia from the gaseous phase (119) from the composting drum (107) and use the filter material loaded with ammonia in end products.

8. A fertilizer for use in agriculture, produced by the process the soil amendment of any one of the claims 1-7 as an intermediate product, for then supplying additives to achieve a designed level of plant nutrients, typically in the form of a pellet when advantageous for distribution.

9. A product, high in carbon content, rich in humus, with biochar (typically 5-10 %) and structural material having a maximum diameter Dmax in the range of about 1-3 mm, in particular less than about 2 mm, produced by the process described by claim 1.,