WO2001038259A2

WO2001038259A2 - Method for recycling the organic fraction of municipal solid waste and the like

Info

Publication number: WO2001038259A2
Application number: PCT/EP2000/011594
Authority: WO
Inventors: Luciano Zoia; Fabio Piasentin
Original assignee: BIOENERGY Srl
Current assignee: BIOENERGY Srl
Priority date: 1999-11-26
Filing date: 2000-11-21
Publication date: 2001-05-31
Anticipated expiration: 2002-05-26
Also published as: WO2001038259A3; AU3154701A; IT1306696B1; ITPD990266A1

Abstract

A method for recycling an organic fraction of municipal solid waste which derives from separate or sorted collections, comprising the steps of: shredding (12) the organic fraction, breaking up the cell membrane of the organic fraction; crushing (13) the shredded organic fraction in order to separate a liquid part (14) from the first solid part (15); subjecting to an anaerobic process the liquid part (14) in order to obtain a second solid part (25) and biogas (21).

Description

METHOD FOR RECYCLING THE ORGANIC FRACTION OF MUNICIPAL SOLID WASTE AND THE LIKE Technical Field

The present invention relates to a method for recycling the organic fraction of municipal solid waste and the like. Background Art

The source of the organic fraction is municipal solid waste derived from separate collection or sorted collection.

Italian legislative Decree no. 22 of February 5, 1997, in defining a new waste management strategy, introduces its priority in terms of reuse, recovery and disposal under safe conditions.

The application of the biological fermentation process, which converts municipal solid waste or biomasses into mixtures of microorganisms which derive from the increase in the number and quality thereof, using the waste as a nutrient mix, raises some severe practical problems in terms of reuse and transformation determined by the lack of qualitative uniformity of the waste and of the biomasses.

The facilities that process the organic material arriving from the moisture-containing fraction of separate collection encounter considerable problems arising from naturally occurring release and percolation, which is particularly conspicuous in the summer months, of the liquid drainage fraction that originates from the organic matter.

The produced amount of liquid fraction, owing to its intrinsic characteristics, is the source of unpleasant odors, considerable processing and/or disposal costs, etcetera.

The impurities that notoriously accompany the material make it hardly usable for transfer to the anaerobic process also due to the poor quality of the feed, which does not allow to assign the final solid product of fermentation for all kinds of recovery. Moreover, the presence of metallic and stone-like objects in the mass to be sorted and processed causes severe drawbacks and damage to the grinding and sorting equipment. Disclosure of the Invention

The aim of the present invention is to provide a dense organic liquid which is of excellent quality and is separate from the remaining fibrous part.

A consequent object is to provide such an organic liquid through simple and safe operations.

Another object is to provide sterilization of the residual products.

A further object is to provide a low-cost apparatus for sorting the resulting product.

A still further object is to increase disposal volumes for an equal fermentation plant.

Another object is to use insufficiently sorted fractions with good process results. Another object is to expand the categories of waste that can be processed by means of a fermentation-based recovery process.

Another object is to obtain a higher quality and a larger amount of biogas.

Another object is a possible increase in the supply load, with a consequent increase in the specific potential of fermentation plants.

These and other objects which will become better apparent hereinafter are achieved by a method for recycling a pre-screened organic fraction of municipal solid waste and the like derived from separate or sorted collections, characterized in that it comprises the steps of: shredding the pre-screened organic fraction, breaking up the cell membrane of the organic fraction; crushing the shredded organic fraction in order to separate a liquid part from a first solid part; subjecting to an anaerobic process said liquid part in order to obtain a second solid part and biogas. Brief Description of the Drawings Further characteristics and advantages of the invention will become better apparent from the detailed description of the method and of the apparatus for providing it, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

Figure 1 is a block diagram of the layout of a method according to the invention;

Figure 2 is another more detailed block diagram of an operating step of the method of Figure 1. Way of carrying out the Invention

As shown in Figures 1 and 2, the method comprises a first step 10 for opening bags, since the material arrives loose and contained in bags which must be opened in order to allow the discharge of the organic material.

The material is then subjected to a screening process 11, which consists in cleaning by separating out plastics, various containers, metals, etcetera. The organic material is then shredded, step 12, undergoing comminution and breaking the plant cell walls so as to facilitate the release of the cell sap, and is then crushed, step 13.

During step 13, separation occurs between a liquid-dense part 14 on one side and a woody-fibrous solid part 15, with the remaining impurities, on the other. Advantageously, the steps 12 and 13 are provided by means of various types of apparatus, such as variable-pitch screw feeders, press heads, pressing systems using shock waves produced by explosion or air or gas pressure, accompanied by a series of perforated grids or membranes which allow drainage of the dense liquid 14 and retain the solid fraction or fiber 15 and/or the impurities inside the pressure region.

The resulting liquid part 14 has a light brown color, a density approximately equal to that of oil, a pungent acrid odor, a percentage of total solids on the dry substance of 7-15%, a percentage of volatile solids on the dry substance of 70-75%, a C/N (carbon/nitrogen) ratio of 1/12 ± 2%, a percentage of impurity of less than 0.5% and a pH of 4-5. The steps 10, 11, 12 and 13 sort the organic fraction of municipal solid waste and the like, achieving a degree of cleaning of the material with particle size and uniformity adapted for feeding anaerobic reactors 20, opening a new frontier in the use of this biological process in the field of recovery and reuse.

In order to achieve good fermentation and thus maximize the yield in biogas production, the material to be fermented must in fact be as much as possible dispersed and solubilized in a liquid, so as to increase the efficiency of the breakdown of carbon compounds on the part of methane- generating bacteria.

The steps 10, 11, 12 and 13 provide an extremely fine dispersion of the liquid.

In this manner, foreign matters, such as plastics of any kind, paper, wood, inert materials, metals and other various materials are eliminated. Moreover, the fibrous organic fraction that is scarcely putrescible and therefore useless in the subsequent anaerobic fermentation process is also eliminated from the useful nutrient component, such as carbohydrates (starch, sugars, etcetera), proteins, fats, alcohols, organic acids, etcetera.

The end result is a dense organic liquid 14 which is separate from the remaining fibrous part 15.

The organic liquid 14 is used for a subsequent step which is constituted by an anaerobic process 16 for producing biogas 21, while the fibrous part 15 is sent to the aerobic process 28.

Practical tests have shown that this liquid 14 is excellent for the fermentation yield of the process 16.

The liquid part 14 is thus destined for the anaerobic fermentation process 16, collecting into a discharge region 17 and, by means of a pump 18, into a homogenization tank 19, from which it then enters an anaerobic reactor 20.

Biogas 21 exits from the reactor 20 and can be advantageously utilized to obtain heat 22 and/or electric power 23. In addition to the biogas 21, a spent substance (second solid part), i.e., a substance which can no longer be subjected to a fermentation process, also leaves the reactor 20; sludge 25 and a supernatant liquid part 26, destined for biological conditioning 27, are obtained by means of a belt press 24 which is per se known.

The sludge 25, together with the solid part 15 obtained from the crushing 13 and the shredding 12 of the organic fraction of the waste, is subjected to an aerobic process 28 in order to obtain a compost 29.

In practice, it is a matter of utilizing the fermentation potential of the drainage material of the organic fraction currently obtained from conventional composting methods and which, despite being currently produced in limited quantities, is the cause of considerable problems and of high treatment and/or disposal costs.

In addition to solving the problem of the management of the drainage material, which is currently produced in an incidental and unwanted step in a very small percentage, in practice it is possible to obtain a material which has excellent yields both in quantitative terms and in qualitative terms.

The extraction of the liquids, achieved by breaking up the cell membrane, allows to accelerate and optimize the fermentation process and to select only the part that is useful for anaerobic fermentation, at the same time releasing a residue which is sanitized and is to be used, in the composting process, as organic material with a high nitrogen content (5-6%) in a mixture with the woody-fibrous part in order to obtain a biological organic fertilizer. The system is provided as an alternative to current waste disposal systems, demonstrating that it integrates perfectly in the recovery of biomasses as a renewable and alternative energy source.

The present invention is susceptible of modifications and variations, all of which are within the scope of the inventive concept. The constructive details may be replaced with other technically equivalent means.

The materials and the dimensions may be any according to requirements.

The disclosures in Italian Patent Application No. PD99A000266 from which this application claims priority are incorporated herein by reference.

Claims

1. A method for recycling a organic pre-screened fraction of municipal solid waste and the like derived from separate or sorted collections, characterized in that it comprises the steps of: shredding the pre-screened organic fraction, breaking up the cell membrane of the organic fraction; crushing the shredded organic fraction in order to separate a liquid part from a first solid part; subjecting to an anaerobic process said liquid part in order to obtain a second solid part and biogas.

2. The method according to claim 1, further comprising the step of: separating said second solid part into sludge and a supernatant liquid part by means of a belt press.

3. The method according to claim 2, characterized in that said supernatant is subjected to biological conditioning.

4. The method according to claim 2, comprising the step of: subjecting to an aerobic process said first solid part and/or said sludge in order to obtain a compost.

5. The method according to claim 1, characterized in that said liquid part, before undergoing the anaerobic process, is collected in a homogenization tank.

6. The method according to claim 5, characterized in that said liquid part is collected into a discharge region and, by means of a pump, into said homogenization tank.

7. Use of a liquid part obtained from a process for shredding and crushing a pre-screened organic fraction of municipal solid waste and the like deriving from separate or sorted collections in order to perform an anaerobic process.