FI113470B - Treatment and utilization of sludge by attaching hydrophilic water binding sludge particles to the surface of hydrophobic organic grains, drying the grains, and circulating back the grains to the first phase - Google Patents

Abstract

Sludge is treated and utilized by attaching hydrophilic water binding sludge particles to the surface of hydrophobic organic grains, e.g. grains of peat in a first phase, drying the grains with a water-bearing layer of sludge particles on the surface in a second phase to hydrophobize the surface layer, and circulating back the hydrophobic grains to the first phase. An Independent claim is also included for the use of the method in biological treatment of waste water for removal of sludge and for providing carbon source and substrate for microorganisms, in the manufacture of fertilizers, and in treating sludge for burning.

Description

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Composting method - Komposteringsmetod

The invention relates to a composting process. The method can be applied especially to the treatment of sludges but also to other compostable waste materials.

Composting can be used, for example, for the treatment of various municipal and industrial sludges, slurry, food industry waste and food waste masses, and is also increasingly used for both small and large-scale purposes. However, there are many disadvantages and problems with the composting methods used. Also, the quality of the products produced by composting has often been moderate or poor.

Field composting, in which the compostable mass sometimes has to be turned to improve oxygen supply, is a tedious retarder. A variety of composting equipment has been developed which provides some form of aeration and control of the mass to be composted, and often also the monitoring and control of temperature, humidity and possibly other parameters of the composting process. For example, there are pool and silo-type composters. Similarly, there are drum composters where, when the drum is rotated, the wings inside it carry the mass forward. For example, in some drum composting applications, it has been reported that the pulp can be composted in the drum in about one week so that it can be transferred to an intermediate storage facility for further composting.

20 To make the mass to be composted suitable for moisture content and porosity for better aeration, and often bio-available carbon; j · 'to add to the pulp a suitable solid is added, such as sawdust, milling peat, * · ·' · '' straw or grass shredding, shredding, etc. The purchase of a suitable solid often results in a substantial * * * cost of composting. .

It is an object of the present invention to provide a composting method which rapidly obtains a. * dry, stable and good quality products for various uses and

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'. · · Which can also bring huge savings in composting costs.

The composting method according to the invention is characterized by

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The other claims define various embodiments of the invention.

: ·. ·. For example, in the process of the invention, the dry matter contained in the slurry. * * *. composting is effected on the surface of a hydrophobic solid granule, such as a hydrophobic • granule, which, for a number of reasons, provides rapid composting and the final grain is easily obtained by drying only a thin layer of · · * 35. The hydrophobic, bioavailable carbon granule first makes the mixture very porous, which ensures a good oxygen supply and

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2 available carbon enhances and accelerates composting of the surface layer. The final granule still contains a large amount of carbon, which makes it very suitable for many applications and also suitable for burning. A very significant advantage of the process is that the granulate can be recycled several times in the process, thus minimizing solids costs.

The invention and some embodiments thereof will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a flowchart generally illustrating a method according to the invention; Figure 2 is a flowchart illustrating a method according to the invention applied to slurry 10; Fig. 4 is a flow chart illustrating an alternative granule further treatment in the process of the invention, Figures 5 (a) to 5 (g) schematically showing a side view of a possible embodiment of a composting reaction in the process of the invention; One possible implementation of a sludge treatment plant applying the method of the present invention.

Figure 1 illustrates the method of the invention in its most common form and Figure 2 as applied to the treatment of sludge. In step 1, the waste to be composted is mixed with hydrophobic granules which, as the name implies, repel water. To implement the invention *. · In the best possible way, the granules must also withstand the damp process, the mechanical stresses and processes resulting from mixing and possibly compressing the mixture: chemical and biological stress, and additionally, the granules should be rich in readily bioavailable carbon. A strongly or permanently hydrophobic turf tree, which is: ': made of a suitable medium to well-decomposed fine quality peat and has a moisture content of between 5% and 20%, is the best material known to the applicant for this purpose. Also, the less hydrophobicized such a peat is about 35% kos; dried granules made from milled peat up to a tin content or in some cases may be *; This is not recommended when the granule is to be recycled several times in the process. It is also conceivable that some slag or coal granules ..; could be at least somewhat suitable for this purpose.

•; For example, the hydrophobic granules are mixed with the slurry in an amount such that the moisture content of the mixture is: · low enough to provide an aerobic state, but at the same time high enough to provide favorable conditions for microbial activity. The recommended range for humidity is thus 45 to 65% by weight of water. In the experiments performed, 3

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because a suitable moisture content of the mixture of slurry and hydrophobic peat granule is about 50%. On the other hand, the granules must have sufficient surface area so that the solids or most of the dry matter of the sludge or other waste material to be composted can be deposited on the surface of the granules. Therefore, the average grain size may be quite small. Good results have been obtained with a hydrophobic turf-5 tongue having a grain size in the range of 0-10 mm. The appropriate amount of granules is also influenced by the nature of the solids (fine or coarse particle size distribution) of the slurry or other waste material, which affects the degree of porosity of the mixture to be obtained by the granules.

The purpose of mixing is also to homogenize the mixture and to make the hydrophobic granules mix as well and uniformly as possible with the compostable waste material.

It may also be necessary to mix other additives, such as lime, to coagulate the slurry or other compostable waste, such as lime to increase the pH, or to improve the microbial function or to obtain certain properties of the final product.

In step 2 of the slurry processing process of Figure 2, the mixture is compressed into suitable size pieces. Compression is effected, for example, by means of a mixing screw which pushes the mixed mass through the die. There may be one or more nozzles, and the mass may be compressed into a piece, rod, ribbon, or sheet. A round die has been used in the tests to produce rod-like pieces about 5 cm thick and about 20 cm long. Mouth-leaching is advantageous in the treatment of sludge because it improves the mixing of the colloidal particles of the sludge in the pulp. The purpose of the compression is to obtain pieces that are so well assembled that they can withstand, for example, transporting on a belt, dropping them into a composting reactor, and stacking the pieces therein into three or four tops of 30 cm to 50 cm thickness. floor.

'. i .: Step 3 provides a composting reaction in which, in short,

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... * 25 temperatures are raised through the mesophilic region, 0-40 ° C, to the thermophilic region, preferably. ·: About 54-60 ° C where it is held until decomposition has progressed to a state where the mixture · · · •. · '· * Consists essentially of hydrophobic granules with a layer of composted slurry or other waste solids on the surface. The composting reaction itself is accomplished and • · »::: controlled in a manner known per se. It is essential to the invention that the hydrophobic granule, especially hydrophobic peat is an excellent composting substrate and as a waste material. is composted as a thin layer on its surface, efficiently and · ·, · · ·. quickly. The hydrophobic granule does not absorb water and therefore the resulting granules having a thin layer of the material composted with the hydrologic granule can also be dried and stabilized rapidly. Composting of the compressed mixture is particularly advantageous because there is ample air space between the pieces, which further enhances and accelerates composting. The above-mentioned 11347Γ4 also makes it possible to carry out the composting reaction as a very advantageous continuous reaction.

The composting reaction and one embodiment thereof are discussed in more detail below with reference to Figures 5 (a) to 5 (g). The reaction can be monitored and controlled in a manner known per se and using known set points and other guidelines, applying temperatures, humidity, oxygen supply, carbon dioxide formation, carbon-nitrogen ratio, pH and microbial strains. In the following discussion of the exemplary embodiment, only the control and control exemplary values that are most relevant to the invention are shown.

Reactor 7, which is schematically described and simplified herein, is an open silo-10-like space having a side wall 8 and a bottom 9. The height of the reactor may be, for example, about 3 meters. Fans 15 are shown near the bottom. A conveyor belt 17 extends above the reactor, which feeds the pieces pressed into the reactor. In practice, the reactor has a plurality of measuring and control devices 15 for controlling reactor conditions as mentioned in the preceding paragraph. In this case, an open reactor has been chosen, for example, because the reaction releases a great deal of moisture, which can be simply removed by blowing it out or condensing it. Similarly, carbon dioxide can be blown straight out or filtered and replaced with oxygen-rich air. By controlling the amount of oxygen, biological combustion can be influenced and thus the temperature of the reactor adjusted.

Figures 5 (a) to 5 (g) illustrate a continuous compost reaction and its initiation. In Figure 5 (a), a first layer 10, 30 to 50 cm thick is introduced into the bottom of the reactor. · · Pieces of a mixture of sludge and peat granulate. Starting the reaction requires an external, · .; half the energy. This is achieved, for example, by blowing blowers 15 of a plurality of pieces of air of about 25 ° C at a temperature of about 30 ° C. Blowing is not needed to supply oxygen to the fires, · · but for the time being there is sufficient air in the intermediate fires. When the temperature of the first layer has risen to about 35 ° C, a second layer 11 of compostable lumps 14 can be introduced into the reactor as shown in Figure 5 (b). The reactor is then allowed to generate further heat (Figure 5 (c)), and 2-3 days after the start of the start, the lowest 30 layer 10 has reached a temperature of 54-60 ° C. Now the reactor has started. You can. '. 4, as shown in Fig. 5 (d), add another layer 12 of compostable pieces 14 fed by conveyor 17. At the same time, pressurized air blowing may be added to the pieces

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microbial oxygen supply.

* · When the temperature in the reactor has risen to the thermophilic region, above 40 ° C, the microbes fall *. · 35 plans also degrade cellulose, hemicellulose and lignin, which are high in municipal sludge, for example. The persistence of the reaction once it is triggered is

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5 away from this particular microbial activity. When the pieces or mixture reach 50 ° C, they begin to decompose vigorously, and as a general rule, after 24 hours at temperatures above 60 ° C, it can be removed from the reactor. When the reactor is fully started, the material disintegrated in the granule is sufficiently hygienized and can be removed from the reactor after 2 to 5 hours of being fed. Even though the reactor is open on top, it produces the heat it needs when it starts, as long as the reaction is maintained by always feeding the reactor with new compostable pieces and ensuring that the temperature never drops too low. The indicative limit is mentioned at about 50 ° C, above which ha-10 solids rich in cellulose, hemicellulose and lignin rich in sludge are strongly drenched. The operation of the reactor is based on the fact that the temperature of the pieces fed to the reactor is raised very rapidly to a thermophilic area where the decomposition is strong.

Figure 5 (e) shows schematically how the lowest layer 10 is broken up into granules. By rotating the carpet conveyor 16, the granular material 18 is removed from the bottom of the reactor, for example to be fed to a dryer. In Figure 5 (f), the granules are removed In Figure 5 (g), a new layer 13 of compostable pieces is again added to the reactor.

It is clear that the composting reaction can be carried out in many ways. It can also be satisfactorily carried out, probably by open composting. A closed composter is an advantageous solution for monitoring and controlling the reaction and, of course, also for temperature control. However, it is relatively expensive to implement one. According to the Applicant's estimate 20, in open composting, where the heat leaking from the reactor to the environment is not actually recovered, the energy resources of the material to be composted are consumed in composting, but only about 10%.

'·' Figure 3 shows schematically how the first part of the granules is recycled: after treatment, back to the process for mixing in the compostable sludge. Second: 25 parts of the granules are recovered, for example, in the interim storage. In order not to increase the amount of granules:: when recycled, they must be removed from the process by the amount of dry matter composted with them: *: The recycling can also be arranged in a continuous process so that 10-20% of the new hydrophobic granule is always added to the circulating granule and excess granules are recovered.

: 'I *; Figure 4 shows in more detail the further processing of the granules, which may include .. '. drying and screening. The surface layer of the granules is moist composted when removed from the reactor; nude substance. Because the granules are warm when taken out of the reactor, they dry considerably * · I t • ·. already by blowing them with cooler air. Their surface layer can also be easily ': * *: reheated and dried with a new cooler air blast. The granules can also be dried using, for example, a flat dryer or a tumble dryer. Initially, the drying of granules is also affected by the continued microbial activity in their surface layer until the surface

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The moisture content of the 6 layers is about 40%. Drying the recyclable granules improves their hydrophobicity and ability to function as desired in the process, i.e. to collect the compostable dry matter on its surface. Well dried hydrophobic granules can be recycled in the process, for example 5 or even 10 times. Large granules appear to have 5 better growth potentials than small ones and can be recycled more often than small granules. Large granules also appear to adhere to larger solids than small particles. Thanks to its hydrophobicity, the grain is rounded in the recycling process. -The more often the granule is recycled, the more it also becomes black due to, for example, the cellulose it contains returns to readily available carbon. At the same time, its properties as a substrate for composting burns as the amount of bioavailable carbon in the surface layer increases. The recycled grain will also be composted and stabilized each time.

After drying, the granules can be screened. For example, a fraction of 0-2 mm, 0-4 mm or 2-4 mm can be recovered. Such grain sizes are suitable for, for example, burning or fertilizer application. The finely divided dusty material, even though it increases the amount of dry solids in the blend, should be removed from recyclable granules from time to time, because very small particles cannot collect the surface to be composted. The screening may be performed, for example, with a mesh, disc or drum screen or with a pneumatic screen.

As required, the screening can also screen all the granules obtained from the reactor into 20 different fractions for different applications. The granules may also be removed without screening or recycled without screening. If only dry composted dry matter is removed from the continuous process:. * the amount of substance, then it is usually removed by screening a particular fraction for what it is intended to be used.

,:. * During recycling, the granules become round and larger in size. • · ·, ..: 25 thicknesses of new surface layers adhering to the granulate in a single turn may be in the order of 0.1-1 mm. :: Also slightly to each other. The resulting oversized granules can also be * · · crushed in the process.

The slurry processing plant shown in Figure 6 is located in a building surrounded by an exterior wall 20. On the left end of the building, there is an open container 24 for receiving the granule: ':': 30 to which the peat can be transported directly from the truck. The bottom of the tank is; V, a first conveyor screw 25 for transferring the granules to conveyor 26, which in turn *. The slurry comes, for example, from the wastewater treatment plant 28, from where it is supplied by screw 29 to the slurry intermediate storage tank 30. The tank 30 is also provided with optional:. * 35 set additives. The screw 32 conveys the slurry and the screw 31 the hydrophobic granule to the mixing box 33 and further through the mixing screw 34 to the mixing and pressing unit 35, where the mixture is further mixed to homogenize. The screw 36 finally compresses the mixture into a press unit 37, whereby an additional blade followered by the screw 36 extracts the mixture out of the tubular nozzles 38. The nozzles press the conveyor belt 39 into rod-shaped pieces about 5 cm thick and about 20 cm long (not shown). The conveyor 39 extends to the upper side of the reactor 40 and the pieces fall from its end into the reactor. Underneath the conveyor is a reciprocating wiper blade 42, which flattens the pieces in the reactor. At the bottom of the reactor is a rotary dropper 41 which removes the granulated material from the bottom and drops it from the openings (not shown) in the conveyor belt 43 below the reactor to the belt. The reactor compartment is separated from the other compartments by partitions 21 and 22. The reactor should have its own well-confined space, since the post-reaction post-10 generates a large amount of moisture and also carbon dioxide and some other gases. The belt 43 conveys the granules into a dryer 44, from which the granules are transferred, after drying, to a screen 45. The recycle fraction is passed from screen 45 to a conveyor belt 46, which transports the granules to intermediate storage 27. Screw 47 conveys the recovered fraction from screen 45 to intermediate storage counter-15 exiting doorways 50.51, 52 and 53.

The recovered granules may also be further post-treated, for example by coating. The coating may be lime, nutrient solution, clay, gypsum, silicon carbonate, etc.

The granules can be used for many purposes, for example as fuel, environmental granules, growing media as aerators, organic carbon sources, various fertilizers, among other sludges, for example to activate anaerobic sludge, or in biofilters.

The invention may vary within the scope of the appended claims.

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Claims (12)

1. A composting process, characterized in that the process comprises: mixing solid granules which are hydrophobic, resistant to damp and mechanically, chemically and biologically degradable and contain bioavailable carbon in a proportion to the compostable material, such as slurry, wherein the granules are mixed with the compostable material in that the mixture is in an aerobic state and that the granules have sufficient surface to bind a substantial portion of the 10 solids contained in the compostable material to their surface; the mixture is subjected to a composting reaction in which the temperature is raised to the thermophilic region through the mesophilic region and continued until the mixture is disintegrated so as to consist essentially of said solid granules having a composted layer of said material on the surface and recirculating the solid granules for mixing with the material to be composted, whereby a new composted layer of said material is formed on their surface during the composting reaction. 1 13471 ' Composting method according to claim 1, characterized in that the solid granules are recycled several times. . Composting method according to claim 2, characterized in that the solid granules are recycled 5-10 times. > · • · '♦ Composting method according to Claim 1, characterized in that the solid granules contain hydrophobic peat granules. V Composting method according to claim 1, characterized in that, after mixing and before the composting reaction is carried out, it comprises the step of compressing the cohesive bodies from the mixture. • · • · _ t Process according to Claim 1, characterized in that the composting reaction is maintained continuously by the addition of the preceding layer at intervals. a new layer of compostable mixture is applied on top and the remaining granular material is removed from the bottom layer from time to time. * 1 * 1 »» 1 · 11347Γ A method according to claim 6, characterized in that there are 3 to 4 overlapping layers. A method according to claim 6, characterized in that the layer has a thickness of 0.3 to 0.5 m. Process according to Claim 6, characterized in that one layer of the compostable mixture per day is added to the reaction. Process according to Claim 1, characterized in that the granules obtained from the composting reaction are dried in order to improve the hydrophobicity of their surface layer. Process according to claim 1, characterized in that the granules obtained from the composting reaction are further screened to separate certain grain size fractions therefrom. 15 Process according to Claim 1, characterized in that the first part of the granules obtained from the composting reaction is recycled and the second part is recovered. »I k t». i »i» »'*» k t »t» 11347Γ ·