GB2474362A

GB2474362A - Waste treatment process and apparatus

Info

Publication number: GB2474362A
Application number: GB1017045A
Authority: GB
Inventors: Jean Pierre Harry; Jean Luc Martel; Bertrand Lepicier; Marco Fontana Giusti
Original assignee: Suez Environnement SAS; Terralys SAS
Current assignee: Vigie Groupe SAS; Suez Organique SAS
Priority date: 2009-10-09
Filing date: 2010-10-08
Publication date: 2011-04-13
Anticipated expiration: 2030-10-08
Also published as: FR2951095A1; AU2010227033B2; GB2474362B; GB201017045D0; PL392607A1; AU2010227033A1; FR2951095B1

Abstract

A waste treatment process features a coarse separator stage 1, and a downstream fine separator stage 2, followed by at least one additional sorting stage, as part of a multi-step process, also involving composting.

Description

PROCESS AND INSTALLATION FOR THE TREATMENT OF HOUSEHOLD

WASTE AND OTHER SIMILAR WASTE.

The invention relates to a process for the treatment of household waste, sewage treatment plant sludge, garden waste and similar waste, in order ultimately to produce a compost, which process comprises a mechanical pre-treatment phase, followed by a biological treatment phase, then by a refining phase.

Household waste deriving from non-selective or even selective collections contains different categories of materials such as putrescible waste io (food waste, green waste), paper, board, glass, plastics, ferrous or non-ferrous metals, woven fabrics, sanitary textiles, toxic products such as batteries or paint pots, etc. The treatment of this household waste with a view to transforming them into reusable compost generally comprises three main stages: -a mechanical waste preparation which aims to optimally separate biodegradable organic materials from other fractions which are not reusable in the form of compost; -a biological treatment (composting preceded or not by a methanization stage) which aims to degrade the materials with a view to their final stabilization and their hygienization; this stage likewise comprises a so-called maturation phase, which aims to reinforce the degree of stability and of hygienization of the compost; -a refining treatment which aims to remove in a complementary manner the contaminants remaining after the two preceding operations and to prepare the compost for a size grading allowing its agronomic reuse.

For the first mechanical waste preparation stage, one at least of the three processes described below is generally used: 1. A preliminary crushing followed by granulometric sorting stages: this process is interesting by virtue of the relative simplicity of the technical means adopted, but has the major drawback of fractionating the contaminants or the reusable materials such as glass, plastic, woven fabric, which generally leads to sorting difficulties and generates a strong risk of contamination of the compost.

2. A rotary pre-fermentation tube followed by granulometric sortings.

This process has the advantage of a fragmentation of the paper and board and a commencement of biological degradation, allowing the composting fraction to then be separated by granulometric sortings. This process nevertheless has the drawback of mixing waste which is reusable and waste which is non-reusable in the form of compost, of soiling recyclable objects such as tins of preserve, plastics containers, and thus increases the risk of contamination by physical or chemical elements.

3. The direct use of crude granulometric sortings: this process has the advantage of directly producing a compostable fine organic fraction, but has the drawback of not integrating the paper-board fraction into this fine fraction and of resulting in a relatively low level of efficiency of the granulometric separation.

The object of the invention is, above all, to provide a treatment process whose mechanical pre-treatment phase no longer has the abovementioned drawbacks, or only to a lesser degree. In particular, it is desirable that the process allows the fragmentation of the contaminant materials to be limited, and thus the risks of physical contaminants being present in the final compost reduced.

According to the invention, the treatment process of the kind previously defined is characterized in that the mechanical pre-treatment phase comprises: -a first granulometric sorting stage for the waste, without prior crushing, with the aid of at least one first drum comprising meshes by which coarse elements having a dimension greater than a value Li can be detained in the drum, these coarse elements being directed towards a manual sorting station; -a second granulometric sorting stage for elements which have passed through the meshes of the first drum, with the aid of at least one second drum comprising meshes by which elements having a dimension greater than a value L2 less than Li can be detained in the second drum, which elements are directed towards the manual sorting station, -and supplementary sortings in respect of elements which have passed through the meshes of the second drum, especially in order to separate light elements and metallic elements.

Preferably, Li ranges between 200 mm and 350 mm, and L2 ranges between 80 mm and 120 mm.

The elements which have passed through the meshes of the second drum can be subjected to an air-based sorting in order to separate light elements, especially of plastics material, which are recovered. The heavier elements are directed towards a sorting station, then are subjected to a magnetic sorting for recovery of ferrous metallic elements, then to a sorting by eddy currents for recovery of non-ferrous metallic elements, in particular elements of aluminium or light metal alloy. A manual sorting can additionally be provided.

Glass elements which have not undergone crushing have dimensions sufficient for an effective manual sorting, and are removed separately.

Non-metallic elements, in particular board and/or paper and vegetable waste, are subjected to a crushing, then to a mixing and humidification stage with non-metallic elements deriving from the sorting by eddy currents.

The mixing and humidification stage is followed by a composting stage for organic fractions.

The invention therefore relates to a mechanical preparation (pre-treatment) system for household waste, prior to a biological treatment combining methanization and composting, or confined to composting, this treatment being intended to ultimately produce a compost which meets the standards applied in the countries affected by the process.

The process additionally allows household biowaste, sewage plant sludge and garden waste (i.e. waste from garden or other green spaces such as grass cuttings, clippings of hedges, shrubs and trees or dead leaves) to be treated.

The process allows an upstream sorting of the waste by an original combination of granulometric and air-based separation techniques, supplemented by at least one manual sorting in respect of certain granulometric fractions, and a final mixture of the different organic fractions pre-purified prior to biological treatment.

In certain situations, it is possible to supplement the apparatus with ballistic equipment (e.g. a ballistic separator) in order to eliminate heavy elements and with optical equipment in order to remove plastics fractions with a view to their reuse.

The invention likewise relates to an installation for the treatment of household waste, sewage treatment plant sludge, green area and similar waste, using the previously defined process, comprising a waste reception zone, characterized in that it comprises, for a mechanical pre-treatment phase, -at least one first drum, for granulometric sorting of the waste without prior crushing, comprising meshes by which coarse elements having a dimension greater than a value Li can be detained in the drum, these coarse elements being directed towards a manual sorting station; -at least one second drum comprising meshes by which elements having a dimension greater than a value L2 less than Li can be detained in the second drum, which elements are directed towards the manual sorting station, -and supplementary sorting stations in respect of elements which have passed through the meshes of the second drum, especially in order to separate light elements and metallic elements.

Advantageously, the installation comprises an air-based sorting station for elements which have passed through the meshes of the second drum, in order to separate light elements, especially of plastics material.

The invention, besides the steps set out above, consists in a certain number of other steps which will be referred to more explicitly below in connection with an embodiment described with reference to the appended drawings, but which is by no means way restrictive. In these drawings: Fig.1 is a logic diagram of the mechanical pre-treatment phase of a process according to the invention, and Fig.2 is a plan diagram of an installation according to the invention for the implementation of the process.

Referring to Figs.1 and 2 of the drawings, it can be seen that the process for the treatment of household and similar waste comprises a first reception stage for the waste in a zone A. The waste is then poured in batches, with the aid of a machine, into a feed hopper D (Fig.2) of a belt conveyor E. A pre-sorting is conducted at a station G, and consists of removing, either manually or with the aid of a machine, bulky objects having a substantial large dimension, for example greater than one metre.

Following this pre-sorting, the waste is dispatched, by the belt conveyor E, to a first coarse granulometric sorting stage I without having undergone prior crushing or mixing likely to heavily pollute the metallic waste or glass waste or plastics material which is intended to be recovered.

This first stage 1 is realized with the aid of at least one first drum or rotary screen TI (Fig. 2) comprising meshes by which coarse elements having a large dimension greater than a value Li can be detained in the drum. This value Li is chosen as a function of several parameters, especially the type of waste, the treatment requirements, etc... Li can range between 200 mm and 350 mm. The drum Ti can be constituted by spaced bars, arranged according to the generating lines of a cylinder and supported by rings in such a way that the peripheral spacing between the bars can be adapted. An adjustment of the meshes of the drum is possible by modifying the spacing of the bars. The considered example corresponds to rectangular meshes, Of course, other shapes of meshes are possible, more particularly: circular, oval, oblong, elliptical.

The coarse elements, that is to say those having a large dimension greater than Li, which have remained in the drum TI are removed upon exit from the drum and are directed, by a belt conveyor El parallel to the axis of the drum, and a conveyor E2 orthogonal to El, towards a manual sorting station MI.

Another drum Ti can be provided, as illustrated in Fig.2, to work in parallel, or possibly in series, with the first. Serial working allows elements having a dimension less than Li yet detained in the first drum to be separated in the other drum TI from elements having a large dimension greater than Li.

Elements which have passed through the meshes of the first drum or drums Ti have a large dimension which, in principle, is less than LI. These elements are gathered on a belt conveyor E3 and are directed towards a secondary granulometric sorting stage 2 with the aid of at least one second drum T2 of structure similar to that of the drum Ti, but comprising smaller meshes. The drum 12 allows elements having a large dimension greater than a value L2 less than LI to be detained inside it. The value L2 generally ranges between 80mm and 120mm and can be chosen equal to 110 mm.

Elements which have passed through the meshes of the second drum 12 are dispatched, by a belt conveyor E4 parallel to the drum and a conveyor E5 orthogonal to the previous such, to a separating station for ferrous and non-ferrous metals.

Elements which have been detained in the second drum T2 exit at one end and are directed towards an air-based sorting stage 3 for separation of the light elements, especially of plastics material, which are recovered in a bin K as reusable materials. Other bins K are provided for other reusable materials or for residue.

Heavier elements, more particularly metallic elements stemming from the air-based sorting 3, are recovered on a belt conveyor, which carries them towards the sorting station H. The other elements, deriving from the sorting, are directed by the belt conveyor towards a sorting stage comprising a magnetic sorting 4, by which ferrous metallic elements can be recovered in another bin, and a sorting by eddy currents 5, for separating the non-ferrous metallic elements, more particularly elements of aluminium or of light metal alloy, and recovering them in a dedicated bin K. The manual sorting stage at the station Ml allows the extraction of glass elements. This operation is facilitated by the fact that the waste has not been subjected to a prior crushing: the glass is not too fragmented and can be located and removed easily. Moreover, the glass is relatively clean, since it has not been contaminated by any such crushing or mixing operation. The glass, following the manual sorting, can be separated by a ballistic sorting (not represented).

At the exit from the manual sorting Ml and from the sorting station H, the elements are substantially constituted by board, paper or vegetable waste, which is directed by a belt conveyor E6 towards a crushing stage 6. The crushing occurs only on that portion of the waste which is constituted by organic elements.

The crushed elements stemming from stage 6, as well as the non-is metallic elements stemming from stage 5, are mixed and humidified in a mixing and humidification stage 7. The humidified mixture is then directed towards a stage 8 comprising composting of the organic fractions. The mixture is received in a zone 8a (Fig.2) and is then introduced into fermentation tunnels 8b.

Following the mechanical preparation, the biological treatment and refining are performed in the usual manner.

The invention therefore relates to a mechanical preparation (pre-treatment) system for household waste or similar, prior to a biological treatment combining methanization and composting or confined to composting. The treatment is intended ultimately to produce a compost which meets the standards applied by the countries affected by this process.

It is likewise possible to treat, in addition, household biowaste, sewage treatment piant sludge and green area waste.

The process allows a sorting upstream of the waste by an original combination of granulometric and air-based separation techniques, supplemented by a manual sorting in respect of certain granulometric fractions, and a final mixture of previously purified different organic fractions, with biological treatment.

In certain situations, it is possible to supplement the apparatus with ballistic equipment in order to eliminate heavy elements, and by optical equipment in order to remove plastic fractions with a view to recycling them.

The fragmentation of contaminant materials is considerably limited by the process. The succession of stages allows maximum extraction of the non-synthetic organic material which is reusable in the form of compost, and the elimination of a majority of physical contaminants in advance of the biological treatment phase.

The invention consists essentially, on the one hand, in the use of an initial separation of coarse elements, then of fine elements contained in the household waste, via two successive tools of the drum or rotary screen type and, on the other hand, in the sequences of sortings and handling realized respectively on the coarse fraction and on the finer fraction, prior to remixing thereof to form the composted fraction. The process of the invention allows the further extraction of material with potential for reuse, more particularly ferrous and non-ferrous metals, certain plastics and sorting residue with high energy value.

The main flows leaving the preparation line are: Reusable organic flows: -large green waste and paper, board, crushed; -small green waste and paper, board, uncrushed; -uncrushed food waste.

Flow of reusable materials: -ferrous metals; -non-ferrous metals; -certain plastics; -residue with energy value.

Flow of materials to be eliminated: -toxic substances, -woven fabrics -sanitary textiles; -bulky objects; -glass; -certain plastics.

The sequence of sorting operations between the initial reception and the pre-composting mixing can vary as a function of the nature of the waste to be received. This sorting sequence is determined within the framework of the realization of pre-realization project studies.

The previously described process can be used industrially to dimension a mechanical pre-treatment line for household waste, maximizing both: -the rate of extraction of non-synthetic organic material initially present in the household waste, according to a minimum residence time limited to a few hours, -the rate of extraction of recyclable elements other than paper, board, namely, more particularly, plastics packagings, ferrous and non-ferrous metals, glass, with a low level of impurities.

The process of the invention, rapid and effective, applied upstream of a treatment by anaerobic digestion, allows a fermentable organic fraction to be introduced into the digester or digesters in the hours following reception of the waste in the plant, and thus the production of methane per tonne of waste entering a plant and per tonne of waste entering into anaerobic digestion to be maximized. In fact, the traditional technique using a revolving tube induces a residence time of several days in the tube and a significant loss of organic carbon linked to a more or less intense onset of aerobic degradation.

The process of the invention applied upstream of a direct treatment by aerobic composting likewise allows more than 80 % of the tonnage of unsorted household waste selectively received at the plant to be composted, and that without recourse to a complementary structuring agent owing to the relatively coarse size grading of the composted fraction.

This process likewise allows the extraction of up to 90 % of the putrescible fraction of the household waste, without recourse to a selective collection dedicated to these materials.

Following controlled composting, maturation and final refining, this process likewise leads to the maximization of the produced quantities of compost and to an optimal quality level owing to the originality and quality of the sortings performed upstream.

Claims

CLAIMSI. A process for the treatment of household waste, sewage treatment plant sludge, garden waste and the like, in order ultimately to produce a compost, which process comprises a mechanical pre-treatment phase, followed by a biological treatment phase, then by a refining phase as defined, the mechanical pre-treatment phase comprising: -a first granulometric sorting stage (I) for the waste, without prior crushing, with the aid of at least one first drum (TI) comprising meshes by which coarse elements having a dimension greater than a value LI which is between 200 mm and 350 mm can be detained in the drum, these coarse elements being directed towards a manual sorting station, -a second granulometric sorting stage (2) for elements which have passed through the meshes of the first drum is provided, with the aid of at least one second drum (12) comprising meshes by which elements having a dimension greater than a value L2 less than LI and ranging between 80 mm and 120 mm can be detained in the second drum, which elements are directed towards the manual sorting station, -and a supplementary sorting stage in respect of elements which have passed through the meshes of the second drum, specifically in order to separate light elements and metallic elements.
2. A process according to Claim 1, wherein the elements which have passed through the meshes of the second drum (T2) are subjected to an air-based or aeraulic sorting (3) in order to separate light elements, specifically of plastics material, which are recovered.
3. A process according to Claim 2, wherein the heavier elements are directed towards a sorting station (H), then are subjected to a magnetic sorting (4), in order to recover ferrous metallic elements, then are sorted (5) by eddy currents for recovery of non-ferrous metallic elements, in particular elements of aluminium or light metal alloy.
4. A process according to Claim 3, wherein a manual sorting is additionally provided.
5. A process according to Claim 3 or 4, wherein non-metallic elements, in particular board and/or paper and organic waste, are subjected to a crushing stage (6), then to a mixing and humidification stage (7) with non-metallic elements deriving from the sorting (5) by eddy currents.
6. Apparatus for the treatment of household waste, sewage treatment plant sludge, garden waste and the like according to the previously defined process, comprising a waste reception zone, for a mechanical pre-treatment phase, comprising: -at least one first drum (TI), for granulometric sorting of the waste without prior crushing, comprising meshes by which coarse elements having a dimension greater than a value LI can be detained in the drum, these coarse elements being directed towards a manual sorting station (Ml); wherein Li ranges between 200 mm and 350 mm, -at least one second drum (12), comprising meshes by which elements having a dimension greater than a value L2 ranging between 80 mm and 120 mm, less than Li, can be detained in the second drum, which elements are directed towards the manual sorting station (Mi), -and supplementary sorting stations in respect of elements which have passed through the meshes of the second drum (T2), in order to separate light elements and metallic elements.
7. The apparatus according to Claim 6, comprising an air-based or aeraulic sorting station (3) for elements which have passed through the meshes of the second drum, in order to separate light elements, specifically of plastics material.
8. A process for treatment of waste substantially as described herein with reference to figures 1 and 2.
9. Apparatus for treatment of waste substantially as described herein with reference to figures 1 and 2.