WO2001012573A1

WO2001012573A1 - Process for supplying gas to a plant for the anaerobic and/or aerobic microbial degradation of organic wastes

Info

Publication number: WO2001012573A1
Application number: PCT/EP2000/007539
Authority: WO
Inventors: Carsten Frobel
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 1999-08-17
Filing date: 2000-07-26
Publication date: 2001-02-22
Also published as: DE19938853B4; DE19938853A1; AU6834900A

Abstract

The present invention relates to a process for supplying gas to a plant (10) according to the invention for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost. By oxygen being generated directly on site in an air separation plant (1), advantageously, each time the correct mixture can be generated of oxygen (O2)-enriched air which is required according to, for example, acceleration of composting in a composting system (12), control purposes of the plant (10), for blowing free gas-supply lines (13, 14) or the like. By means of nitrogen (N2) also generated by the air separation plant (1) being utilized in particular for rendering a fermentation system (11) inert, advantageously, the air separation plant (1) is utilized optimally and, in particular, the otherwise necessary extraction of the air or the rotting gases from the fermentation system (11) is reduced. The present invention is equally suitable for the fermentation and composting of organic wastes which can also take place in a joint system. In addition, it is suitable, in particular, for sewage sludge processing, biological residual refuse treatment, biological decontamination of polluted soil, storage of quality soils prior to bagging and aeration of agricultural goods.

Description

PROCESS FOR SUPPLYING GAS TO A PLANT FOR THE ANAEROBIC AND/OR AEROBIC MICROBIAL DEGRADATION OF ORGANIC WASTES

5 The present invention relates to a process for supplying gas to a plant for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost, comprising at least one fermentation system and/or one composting system, with the composting system being fed with oxygen (O₂)-enriched air via a first gas-

10 supply line; the invention also relates to an associated plant. The invention further relates to a process for supplying gas to a plant for the anaerobic and subsequent aerobic microbial degradation and conversion of organic wastes to form fermentation residue or compost in one and the joint system facility; as well as an associated plant.

15 Anaerobic degradation is taken to mean the conversion of organic substances by microorganisms (anaerobes) in the absence of oxygen (anaerobic conditions), and aerobic degradation the opposite.

Known processes for biological waste treatment are composting and fermentation. Suitable for composting are especially highly structured

20 and thus readily aeratable wastes, for example dry biowastes and green wastes, whereas high-water-content and pasty-pulpy materials are primarily accessible to fermentation.

The composting process, i.e. the aerobic microbial degradation or conversion of organic wastes to form compost with simultaneous formation of

25 carbon dioxide, water and heat, is controlled, inter alia, by the factors oxygen availability, moisture and temperature. Biomass and humic substances are formed in this case from the compost raw materials, in particular lignin, cellulose, hemicellulose, fats, waxes, proteins and starch due to the enzyme activity of bacteria, fungi and higher organisms with use of the degrading

30 microorganisms. The mean degree of degradation of the compost raw materials is about 50%, i.e. the organic matter is not completely oxidized, for example in contrast to waste incineration. Due to partial degradation of the organic material and water loss, the weights and volumes of the rotting material decrease to approximately half (rotting loss). The water present in 35 the starting material and formed during composting is released in part as leachate water, but due to the prevailing rotting temperatures, predominantly as water vapour. The energy given off in this case as heat is, despite the relatively low temperature level, conditionally utilizable.

In the various composting process techniques, care must be taken especially to ensure an adequate oxygen supply, moisture content and temperature. An insufficient oxygen content especially leads to anaerobic rotting processes (what is termed fermentation) and to the formation of foul- smelling volatile metabolites.

Therefore, to increase the O₂ partial pressure, the organic wastes are force-ventilated. In a simplest form, compressed air is fed to these. This, i.e. the use of blower air, increases the O₂ partial pressure only slightly, however. It is therefore known to feed oxygen (O₂)-enriched air to the wastes. The oxygen (O₂) comes either from tank facilities or from gas cylinders. The increased O₂ partial pressure improves the composting and, especially owing to its savings in time, effects a more inexpensive composting process. However, in addition to the expenditure of a constant new supply with oxygen (O₂), mixing air with oxygen (O₂) to, for example, 30% 0₂ content is relatively expensive. In addition, controlling the composting process is only possible with limitations, especially if the pressure at the supply orifices, i.e. outlet orifices of the gas-supply line, is only about 200 mbar, so that the outlet orifices can plug.

The customary process sequence of composting in large-scale plants may be subdivided into the partial sectors setting-up, intensive rotting, final rotting and formulation. The core and differentiating feature of each composting process is the control and duration of the first rotting phase, what is termed the intensive rotting (preliminary rotting, hot rotting). In this the readily biologically digestible constituents are degraded, which is accompanied by intensive multiplication of biomass and a high rotting temperature, due to its waste heat, of from 50 to over 70°C. Sanitation of the compost takes place at these temperatures. The intensive rotting processes may be divided into static, semistatic (semidynamic) and dynamic processes. The processes most frequently used in practice are static. These include clamp composting without turning, box/container composting and Brikollare composting.

Clamp composting is the process which has been operated for longest. The material for rotting is layered to form a heap (clamp) which can have different shapes. In addition to relatively small triangular clamps, in particular, space-saving trapezoid clamps are known. The oxygen is supplied either by diffusing into the clamp interior or by forced aeration. In the latter case, for example, aeration elements are let so as to be passable into an asphalt or concrete floor and are covered with specifically perforated metal sheets. Using measuring lances, the 0₂ content and the temperature are measured. The aeration blower is controlled, for example, by means of a computer. This visualizes and documents the entire rotting process. To protect the rot material from climatic effects and for further emission control, it is known to cover the clamps with a vapour-permeable but water-tight, preferably textile, tarpaulin.

Mobile clamps are also known which are not bound to clamp mounting systems or axle bearings. After completion of the rotting phase, such mobile clamps can rapidly be disassembled and made ready in a few minutes for the next clamp. In the box process and container process, composting takes place in sealed force-ventilated stationary (box) or mobile (container) spaces with complete collection of exhaust air.

In the Brikollare process, the compost raw materials are compressed to form shaped pieces having aeration boreholes and, stacked on pallets, are subjected to the rotting. The semistationary processes include clamp composting with turning and also line and tunnel and composting. In all cases, the rotting material is periodically turned over for improved ventilation and homogenization, the material in the case of the line and tunnel composting being situated in rotting lines separated from one another by partitions open at the top (lines) or covered (tunnel). In the case of the dynamic processes, the compost raw materials are continuously agitated either by forced discharge over individual stages (rotting tower) or by displacement (rotting drum) and in the course of this simultaneously aerated, mixed and comminuted. Common to all intensive rotting processes is the requirement of a final rotting phase, generally for several months, if a stable plant-acceptable finished compost is to be produced. The final rotting stage takes place virtually exclusively as clamp composting, during which the less readily decomposable substances are degraded. Following this there is generally also a formulation, for example screening or air classification, before the compost is marketed. In contrast to composting, in fermentation which has been used since antiquity, but is currently predominantly limited to uncontrolled processes, the biodegradation of the organic matter takes place using microorganisms or enzymes in the absence of air. The air or the rotting gases are removed by suction here.

Similarly to composting, however, before the fermentation process, i.e. the anaerobic microbial degradation, there is frequently also a thorough, in particular mechanical, preparation of the input material to be fermented.

Depending on the solids content, various reactor types can then be used. During the residence time in the reactor, the material successively flows through the phases hydrolysis, acidification and methanation. The products formed are biogas and fermentation residue. The biogas can be used as energy source. The fermentation residue is dewatered and fed to a downstream intensive aerobic process, in which case closed systems are especially advantageous for reliable sanitation.

In systems having aeration elements, the material then matures within a few weeks to form a finished compost which smells of soil and has high plant compatibility.

It is an object of the present invention to specify a process for supplying gas to a plant for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost, as well as an associated plant, in which the rotting of biomass is accelerated. In addition, the rotting of biomass is to be able to be better controlled. This object is achieved by a process having the features according to Claim 1 ; by a process having the features according to Claim 2; by a plant having the features according to Claim 7 and by a plant having the features according to Claim 8. Advantageous embodiments and developments are specified in the respective dependent claims. The novel process according to Claim 1 , preferably for supplying gas to a novel plant according to Claim 7, for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost, comprising at least one fermentation system and/or one composting system, with the composting system being fed with oxygen (O₂)-enriched air via a first gas-supply line, is distinguished in that, by means of an air separation plant, an essentially nitrogen (N₂)-containing retentate and an oxygen-containing permeate are generated on site, the retentate being fed to the fermentation system via a second gas-supply line to render it inert; and/or in that the permeate is fed to the composting system via the first gas-supply line. In the novel process according to Claim 2, preferably for supplying gas to a novel plant according to Claim 8, for the anaerobic and subsequent aerobic microbial degradation and conversion of organic wastes to form fermentation residue or compost in one and the same joint system, by means of an air separation plant, an essentially nitrogen (N₂)-containing retentate and an oxygen-containing permeate are generated on site, the essentially nitrogen (N₂)-containing retentate being fed to the joint system via a shared gas-supply line during the anaerobic process, and the permeate being fed during the aerobic process.

By the oxygen being generated directly on site in an air separation plant, advantageously, each time the correct mixture can be generated of oxygen (O₂)-enriched air which is required according to, for example, acceleration of composting, control purposes of the plant, for blowing free the gas-supply line or the like.

By means of the nitrogen (N₂) generated by the air separation plant also being utilizable, in particular for rendering the fermentation system inert, advantageously, the air separation plant is utilized optimally and, in particular, the otherwise necessary extraction of the air or rotting gases from the fermentation system is decreased. In addition, the fermentation process is improved, if the nitrogen (N₂) is also used for control purposes of the plant, for blowing free the gas-supply line or the like.

Means for switching over from a feed of retentate to a feed of permeate and vice versa via the shared gas-supply line into the joint system advantageously enable the utilization of one and the same space-saving system for the fermentation process and subsequent composting process, as a result of which owing to abolished reaction times, in addition to a further acceleration of the degradation of the organic wastes, in particular, capital costs are saved.

Preferably, the air separation plant has a membrane which comprises a plastic which, in particular, promotes the diffusion of oxygen (O₂) through the membrane. For temporary storage of the retentate and/or permeate generated on site, it is proposed to provide, if appropriate, a buffer in each case, which buffer advantageously makes possible, for example, more flexible control of the respective process or blowing-free of the lines if appropriate at a higher pressure, for which purpose separate means can be provided. In particular, for permeate and/or retentate, means can be provided for compression to higher pressures.

The gas-supply lines preferably have outlet orifices via which the retentate and/or the permeate are fed to the fermentation system, the composting system and/or the community facility. The gas-supply lines advantageously introduce sufficient retentate or permeate precisely to where it is required most urgently by the microorganisms, that is to say into the centre of the corresponding system.

For further improvement of the process control and/or blowing-free of blocked lines, preferably the retentate, i.e. essentially nitrogen (N₂), and/or the permeate are/is fed at an outlet pressure or at least 0.4 bar per outlet orifice. In comparison with pure compressed air, especially nitrogen (N₂) has the advantage of being very dry and dust-free.

For pressure generation, it is proposed to provide at least one compressor which preferably provides sufficiently large amounts of compressed air for the air separation plant, so that advantageously, despite the not greatly differing diffusion factors of nitrogen and oxygen, separation at the membrane is ensured.

So that the system in which the fermentation process proceeds can be rendered as inert as possible, it is proposed that the retentate comprises at least 95% nitrogen (N₂), preferably 99.9%.

To increase an O₂ partial pressure it is proposed that the permeate contains at least 30% of oxygen (O₂), preferably at least 35%.

By means of the present invention, inter alia, foul-smelling fermentation zones are prevented right in the initial stage, the rotting performance is improved and, in particular, the compost maturing is accelerated.

Additional details and other advantages are described below with reference to preferred illustrative examples, to which, however, the invention is not restricted, in connection with the accompanying drawings. In the drawings:

Fig. 1 shows diagrammatically a first illustrative example of a plant according to the invention;

Fig. 2 shows diagrammatically a second illustrative example of a plant according to the invention; and

Fig. 3 shows diagrammatically a third illustrative example of a plant according to the invention.

Fig. 1 shows a first illustrative example of a plant 10 according to the invention for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost. The plant comprises at least one fermentation system 11 and/or one composting system 12. In addition the plant 10 comprises an air separation plant 1 by means of which an essentially nitrogen (N₂)-containing retentate and an oxygen-containing permeate can be generated on site. The permeate is fed to the composting system 12 via a first gas-supply line 13; the retentate is fed via a second gas-supply line 14 for rendering the fermentation system 11 inert.

The air separation plant 1 has a membrane 2 which comprises a plastic which promotes in particular the diffusion of oxygen O₂ through the membrane. For pressure generation, at least one compressor 3 is assigned to the air separation plant 1 , which compressor provides sufficiently large amounts of compressed air for the air separation plant 1 so that advantageously, despite the not greatly differing diffusion factors of nitrogen and oxygen, separation at the membrane 2 is ensured.

For temporary storage of the retentate and/or permeate generated on site in the air separation plant 1 , an N₂ buffer 4 and an O₂ buffer 5 are respectively disposed at the corresponding outlet connections 6, 7 of the air separation plant 1. Downstream of these the first gas-supply line 13 leads to the fermentation system 11 and the second to the composting system 12.

Fig. 2 shows a second illustrative example of a plant 20 according to the invention for the anaerobic and subsequent aerobic microbial degradation and conversion of organic wastes to form fermentation residue or compost. In contrast to the plant 10 according to Fig. 1 , fermentation and composting now take place successively in one and the same joint system 21 , in which, again, by means of an air separation plant 1, an essentially nitrogen N₂-containing retentate and an oxygen-containing permeate are generated on site. The retentate is fed during the anaerobic process to the joint system 21 via a shared gas-supply line 22 to render the system inert and the permeate is fed during the aerobic process.

In particular if the plant 20 of the second type is operated individually, this has means 23 for changing over the feed of retentate to the feed of permeate and vice versa via the shared gas-supply line 22 to the joint system 21. In this case, the element not fed in each case to the joint system

21 should be stored temporarily in a corresponding N₂ buffer 4 or 0₂ buffer 5.

Alternatively, it has proved to be particularly advantageous to operate plants 20 of the second type in pairs in each case and in an alternating manner between fermentation and composting. In this case, as shown in Fig. 3, advantageously an air separation plant 1 supplies the joint system 21 filled with the substances intended for fermentation with the nitrogen-containing retentate and the joint system 21 filled with substances intended for composting with the oxygen-containing permeate. Corresponding buffer apparatuses can - the same as in plants 10 of the first type - be dispensed with in this case or, for example, to equilibrate small pressure fluctuations, can likewise be provided (not shown).

All gas-supply lines 13, 14, 22 have outlet orifices 15, 24 in the region of the systems 11 , 12, 21 , which outlet orifices are preferably constructed as nozzles. In the long-term operation, both the retentate and the permeate exit from the nozzles at a pressure of at least 0.4 bar in order to prevent plugging of the outlet orifices 15, 24. To blow the lines 13, 14, 22 free, both retentate and permeate can also exit from the outlet orifices 15, 24 at times at a higher pressure. The retentate supplied to the plants 10, 20 comprises at least 95% of nitrogen (N₂), preferably 99.9%; the permeate comprises at least 30% of oxygen (O₂), preferably at least 35%.

By the oxygen being generated directly on site in the air separation plant 1 , advantageously, each time the correct mixture can be generated of oxygen (O₂)-enriched air which is required according to, for example, acceleration of composting, control purposes of the plant 10, for blowing free the gas-supply line 13, 14, 22 or the like. By means of the nitrogen (N₂) generated by the air separation plant 1 also being utilizable, in particular for rendering inert the fermentation system 11 or the joint system 21 , advantageously, the air separation plant 1 is utilized optimally and, in particular, the otherwise necessary extraction of the air or rotting gases from the fermentation system 11 or the joint system 21 is decreased.

The present invention is equally suitable for the fermentation and composting of organic wastes. In addition, it is suitable, in particular, for sewage sludge processing, biological residual refuse treatment, biological decontamination of polluted soil, storage of quality soils prior to bagging and aeration of agricultural materials.

Claims

1. Process for supplying gas to a plant (10) for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost, comprising at least one fermentation system (11) and/or one composting system (12), with the composting system (12) being fed with oxygen (O₂)-enriched air via a first gas-supply line (13), characterized in that, by means of an air separation plant (1), an essentially nitrogen (N₂)-containing retentate and an oxygen-containing permeate are generated on site, and in that the retentate is fed to the fermentation system (11) via a second gas- supply line (14) to render it inert; and/or in that the permeate is fed to the composting system (12) via the first gas- supply line (13).

2. Process for supplying gas to a plant (20) for the anaerobic and subsequent aerobic microbial degradation and conversion of organic wastes to form fermentation residue or compost in one and the same joint system

(21), wherein, by means of an air separation plant (1), an essentially nitrogen (N₂)- containing retentate and an oxygen-containing permeate are generated on site, and wherein via a shared gas-supply line (22) during the anaerobic process the essentially nitrogen (N₂)-containing retentate to render the system inert, and during the aerobic process the permeate is fed to the joint system (21).

3. Process according to Claim 1 or 2, characterized in that the retentate and/or permeate are/is stored temporarily in a buffer (4,5) after its on-site generation.

4. Process according to Claim 1 , 2 or 3, characterized in that the gas- supply lines (13, 14, 22) have outlet orifices (15, 24) via which the retentate and/or the permeate are/is fed to the fermentation system (11), the composting system (12) and/or the joint system (21) at an outlet pressure of least 0.4 bar per outlet orifice (15, 24).

5. Process according to one of the preceding claims, characterized in that the retentate comprises at least 95% of nitrogen (N₂), preferably 99.9%.

6. Process according to one of the preceding claims, characterized in that the permeate comprises at least 30% of oxygen (O₂), preferably at least 35%.

7. Plant (10), preferably for carrying out the process according to Claim 1 , for the anaerobic and/or aerobic microbial degradation and conversion of organic wastes to form fermentation residue and/or compost, comprising at least one fermentation system (11) and/or one composting system (12), with the composting system (12) being fed with oxygen (0₂)- enriched air via a first gas-supply line (13), characterized in that, by means of an air separation plant (1), an essentially nitrogen (N₂)-containing retentate and an oxygen-containing permeate can be generated on site, and in that the retentate can be fed to the fermentation system (11) via a second gas-supply line (14) render the system inert; and/or in that the permeate can be fed to the composting system (12) via the first gas-supply line (13).

8. Plant (20), preferably for carrying out the process according to Claim 2, for the anaerobic and subsequent aerobic microbial degradation and conversion of organic wastes to form fermentation residue or compost in one and the same joint system (21), wherein, by means of an air separation plant (1), an essentially nitrogen (N₂)- containing retentate and an oxygen-containing permeate can be generated on site, and wherein via a shared gas-supply line (22) during the anaerobic process the retentate to render the system inert, and during the aerobic process the permeate can be fed to the joint system (21).

9. Plant (2) according to Claim 8, characterized in that means (23) are provided for switching over from a feed of retentate to a feed of permeate and vice versa via the shared gas-supply line (22) into the joint system (21).

10. Plant (10, 20) according to Claim 7, 8 or 9, characterized in that the air separation plant (1) has a membrane (2).

11. Plant (10, 20) according to Claim 10, characterized in that the membrane (2) comprises plastic.

12. Plant (10, 20) according to one of Claims 7 to 11 , characterized in that a buffer (4, 5) is provided for the temporary storage of the retentate and/or permeate generated on site.

13. Plant (10, 20) according to one of Claims 7 to 12, characterized in that the gas-supply lines (13, 14, 22) have outlet orifices (15, 24) via which the retentate and/or the permeate can be fed to the fermentation system (11), composting system (12) and/or the joint system (21) at an outlet pressure per outlet orifice (15, 24) of at least 0.4 bar.

14. Plant (10, 20) according to Claim 13, characterized in that, for pressure generation, at least one compressor (3) is provided.

15. Plant (10, 20) according to one of Claims 7 to 14, characterized in that the retentate comprises at least 95% of nitrogen (N₂), preferably 99.9%.

16. Plant (10, 20) according to one of Claims 7 to 15, characterized in that the permeate comprises at least 30% of oxygen (O₂), preferably at least 35%.