WO1994000023A1

WO1994000023A1 - Method and apparatus for processing biologival waste

Info

Publication number: WO1994000023A1
Application number: PCT/NL1993/000133
Authority: WO
Inventors: Josephus Cristianus Johannes Van Ham
Original assignee: Beheermaatschappij 'de Vlietstede' B.V. Tevens Handelende Onder De Naam Green Fish
Priority date: 1992-06-26
Filing date: 1993-06-25
Publication date: 1994-01-06
Also published as: AU4588993A

Abstract

Method and apparatus for processing biological waste, in which: the biological waste is mixed, the waste mixture is chopped, the waste mixture is washed and preheated, the chopped waste mixture is compressed, the compressed mixture is dryed by adding heat and already dryed waste mixture, and the dryed waste mixture is ground to chunks. Preferably prior to the compressing of the waste mixture additives, for example a quantity of fish waste, are added to the waste mixture in order to give the chunks a desired property such as a percentage in weight of protein of approximately 28 %.

Description

Method and apparatus for processing biological waste
The invention relates to a method for processing biological waste such as, for example, processing vegetable, fruit and garden waste (to be called vfg-waste hereafter).

The invention further relates to an apparatus for processing biological waste.

Because separate waste collection is common nowadays, there is the possibility of processing biological waste, such as vfg-waste for reuse.

At present composting waste is most common. Whilst composting, the natural rotting process of the biological waste, which usually takes approximately 1 year, is speeded up by a heating process to approximately 10 days. The costs involved in keeping this heating process going for 10 days are such that composting biological waste is uneconomic.

It is, among other things, an aim of the present invention to provide a method and an apparatus as a result of which processing biological waste is economically more interesting and cost-effective.

For this purpose a method according to the invention for processing biological waste is provided, which is characterized in that it contains the following steps: - mixing the biological waste, - chopping the waste mixture, - compressing the chopped waste mixture, and - drying the compressed waste mixture by adding heat.

For this purpose an apparatus for processing biological waste according to the invention is also provided, which is characterized in that it comprises:
- a mixing apparatus for mixing the biological waste;
- a chopping apparatus for chopping the waste
mixture
- a compressing apparatus for compressing the chopped
waste mixture, and
- a drying apparatus for drying the compressed waste
mixture by adding heat.

In this way biological waste can be processed into animal feed, whereby no operations by which rotting is speeded up are necessary. Apart from that, biological waste can be processed into fertilizer. Although drying the compressed waste mixture preferably takes place at a higher temperature to drastically reduce the liquid content of the waste mixture, the drying time is relatively short (at most a few hours) so that energy use and, as a result, the cost price, is relatively low.

If the mixture is preheated prior to compressing the mixture, preferably in such a way that the cell walls are broken down, then drying can take place more economically and more quickly.

Preferably compressing the mixture takes place by centrifugal compression preferably through a centrifugal riddle.

For processing biological waste this compression appears to be the most economic as regards energy.

In order to provide dryed waste mixture in chunks of the desired size according to an embodiment of the method according to the invention, the dryed waste mixture is ground into chunks.

If the step of compressing takes place until the liquid content of the chopped waste mixture is reduced by approximately 20%, then the total energy consumption of the compressing and drying steps together is found to be minimal.

In order to kill harmful bacteria and such like present in the waste mixture, the step of drying the compressed waste mixture takes place at such an elevated temperature and for such a length of time until the waste mixture is sterilized.

The method and the apparatus according to the present invention are extremely suited for processing biological waste, into, for instance, fish feed.

It has been shown that when adding a quantity of additives, for example fish waste to the waste mixture, prior to the step of compressing the waste mixture, the chunks are especially suited as animal feed, for example fish feed. The additives ensure that the animals for which the processed waste is intended find the processed biological waste agreeable to taste.

By means of the method according to the invention processed biological waste can be obtained without the addition of fish waste as additive chunks with a maximum percentage of protein by weight of approximately 27. Depending on the type of animal for which the processed waste is intended, an optimal protein percentage is desirable as animal feed.

By, for instance, varying the quantity of added fish waste, a higher protein percentage can be obtained.

For fish this protein percentage is about 28.

During the drying process a percentage lower than 27 can be regulated.

Some embodiments of a method and apparatus for biological waste processing according to the invention will hereafter, by way of example, be described on the basis of the drawing.

In the drawing fig. 1 shows a flow diagram of biological waste processing according to the invention, fig. 2 shows a schematic top view of an apparatus for biological waste processing according to the invention, fig. 3 shows a schematic side view of the apparatus according to fig. 2, and fig. 4 shows a schematic perspective view of an alternative apparatus for biological waste processing.

In fig. 1 a quantity of collected biological waste, for example vfg-waste, from which inorganic materials such as metal, plastic etc., which are unintentionally present in the waste, have been removed, are collected in a receiving bin 100 for further processing. For processing into animal feed, for example fish feed, it is preferable if the biological waste used is as fresh as possible.

The biological waste is transported by a conveyor belt to a mixing apparatus 200 to be thoroughly mixed. Before mixing the waste is chopped by a chopping machine (not shown) of a construction known in itself. In addition, it is, however, also possible to chop the waste mixture into chunks during transport by chopping means on the conveyor belt. The waste can, moreover, be washed in order to remove possible remaining non-biological waste. Depending on the ultimately desired percentage of protein by weight of the animal feed or for obtaining other desired properties, a quantity of additives, for example fish waste, can be added in the above mentioned steps to the waste mixture from a bunker apparatus 206. This gives as an extra economic advantage in that possible uneconomical additives, such as fish waste, can be put to efficient use.

After the waste has been mixed, the waste mixture is compressed to reduce the liquid content of the waste mixture, in order to make the following step in the process, drying, more economical energywise. Compressing preferably takes place through a centrifugal riddle 201 but can also take place by hydraulic pressing. It has been shown that if the liquid percentage of the waste mixture has been reduced by 20%, then the compressing step and the subsequent drying use up a minimum of energy.

Drying the compressed waste mixture can take place in indirect steam dryers 300, but also, for example, in rotary (drum) dryers which are used for drying grass or in other indirect, forced dryers. The drying temperature is, for instance, between 650"C and 900"C, and is, for instance, 8000C.

Not only is the largest part of the remaining liquid removed from the waste mixture by the drying process, but by choosing a suitable drying time and temperature,the waste mixture is sterilized at the same time.

In order to further reduce energy consumption the waste is preheated during mixing in the mixing apparatus 200, preferably by hot steam fed from the indirect steam dryer 300 through duct 205 to the mixing apparatus 200. At the same time the cell wall of the cells making up the biological waste are broken down by this, this also being advantageous from a feed technical point of view.

After drying, the waste mixture can be ground to chunks of animal feed in a grinding apparatus, not shown, the size of which depending on the animal sort for which the feed is intended.

In order to be able to vary the liquid content of the waste supplied to the dryer 300, part of the dryed waste, in the form of powder, for example, can be returned and mixed with waste to be dryed in a mixing apparatus.

By this process 2 tonnes of animal feed are obtained in an economic way from, for example, 9 tonnes of biological waste and 1,5 tonnes of fish waste (additives). The weight percentage of protein of the animal feed can be varied by the drying process (the liquid present after the drying process) and by the quantity of fish waste added. Alternatively, the processed waste can be used as fertilizer.

If the processed biological waste is intended as fish feed, then a weight percentage of 28 appears to be desirable.

Vapour released during mixing in the mixing apparatus 200 can be condensed by means of a condenser 302 to be supplied to steam-boiler 400 tending to the indirect heating of the steam dryer 300. Moreover, the vapour can also be treated by a waste water treatment unit (including flocculation/flotation) 500 so that any solid matter which has developped can be led to the mixing apparatus 200 and purified water for, example be discharged through duct b.

In fig. 2 a schematic top view of an apparatus for processing biological waste, for example vfg waste, according to the invention is shown. The apparatus includes a receiving bin 100 for storing biological waste (if necessary purified of inorganic matter). The waste is conveyed to a intermediate collecting bin 102 through a double screw conveyor 101. The screw of the screw conveyor 101 operates as a means for chopping the waste. If another kind of conveyor belt is used, then an extra chopping apparatus should be fitted. A sludger 104 removes waste water coming from the waste on the screw conveyor 101 and guides it, for example, to a waste water treatment plant 500. By way of a second storage bin 800 waste mixture can be conveyed to the intermediate collecting bin through a swivelling conveyor 106 and conveyor 105. The storage bin 800 is also provided with a sludger 802.

The chopped waste is then fed through a conveyor 103, which can be a double screw conveyor, for the possible further chopping of the waste, to the mixing apparatus 200. The waste can be washed during transport on the conveyor 103 to remove inorganic waste. Additives such as fish waste, for example, can be added in the mixing apparatus 200, depending on the eventually desired animal feed through conveyor 207 coming from the additive bunker 206.

The water is preheated in the mixing apparatus 200 by hot steam coming from duct 205. The temperature and the length of stay of the waste in the mixing apparatus 200 are adjusted in such a way that the cell walls of the waste are broken down. Water coming from the mixing apparatus 200 is carried to a waste water treatment unit 500 for further treatment (see description of fig. 1) After mixing, the waste is conveyed to a compression apparatus, preferably a centrifugal riddle 201, through a buffer bin 202 where the waste mixture is compressed to reduce the liquid content of,the waste mixture. Apart from a centrifugal riddle other compression apparatuses can be used, such as a hydraulic press. A water pump 204 is connected to the centrifugal riddle 201 for the removal of waste water.

The compressed waste mixture is conveyed from conveyor 203 to an indirect steam dryer 300 to dry the waste mixture and sterilize it if necessary. Hot steam from the steam dryer 300 is conveyed to the mixing apparatus 200 through duct 205 to provide preheating. A steam-boiler 400 tends to the heating of the steam dryer 300 and receives its water in part through a condenser 302 which condensates steam not conveyed to the mixing apparatus 200. Finally, the dryed waste mixture (if necessary after having been ground to the desired chunk size) is conveyed through conveyor 301 to silos 304 for storage. Apart from that a part of the dryed waste mixture, in powder form, for example, can be returned back up to the dryer 300 to be mixed with the waste mixture which is to be dryed, with the help of a mixing apparatus (not shown).

In this way the liquid content of the waste to be dryed can be adjusted, which can play a part in the efficiency of the dryer process.

In figure 3 a schematic side view of the apparatus is shown, in which there is also an air cooled condenser 305 and in which non-condensatable gases are fed to a bio-bed 603 through a wet washer 600. To this end, use is made of a header 601 for tip extraction and an air discharge duct 602. In this way should any odorous matter be present it can be removed from the apparatus.

In fig. 4 an alternative embodiment of the apparatus according to the invention is schematically shown. Here biological waste 1 is processed into animal feed or fertilizer. The biological waste is on a deposit floor 2 from which, for example by means of a mechanical shovel, it is brought into a feed funnel 3, which is placed directly above a slowly rotating crusher 4 in which the waste is reduced and mixed to a certain extent. An upward conveyor 5 brings the waste to a buffer hopper 6, in which a supply can be stored for three hours. The buffer hopper 6 is provided with a feeding roller 7 which feeds the waste evenly to an upward conveyor 8.

An upper belt magnetic conveyor 9 is fitted above the upward conveyor, which removes all ferriferous materials from the waste and deposits them in an iron container 10.

The waste falls into a hydrocyclone 11 provided with an conditioner 12. Because of the flow of the water and the upward force materials with a larger density than the biological waste are separated. This so-called inert material is removed by an inert conveyor 13 to an inert container 14. The washed waste comes onto a vibration sieve 15 with which the outgoing water is separated from the waste. The water from the vibration sieve falls into a tank 16. From this tank 16 the water is pumped to a water purification 17.

After the water has been removed from the waste, it is conveyed on the vibration sieve to the sorting belt 18 where paper and plastic have, as yet not mechanically removed, are removed. This can be done manually or by socalled "windshifting"
The waste from the sorting belt is deposited into the feed funnel of a reducer 19. A knife roll driven by an electric motor reduces the material to pieces of a maximum dimension of 1,5 to 2 cm.

The waste is brought through conveyor 20 to a preblancher 21. In here the waste is preheated to, for example, approximately 900C as a result of which the waste volume decreases. At the same time sprayed-on pesticides are rinsed out of the waste at this blanching stage, which is facilitated by the high temperature. From blancher 21 the waste falls into blancher 22, in which the waste is heated to approximately 1250C. In this way germs, bacteria and spores are destroyed.

A vibrating trough 23 is placed behind the blancher 22 output, which removes adhering water. At the same time, due to the vibrations the waste mass is dispersed right across the width. In this way a good supply is created for the press roller 24. The press drains to a liquid content of approximately 80%. A feed-through conveyor 25 brings the waste from the roller press to a dryer 26.

In the dryer 26 the material is dryed by the hot walls of the dryer. Heating the walls takes place by means of steam at approximately 1700C. The steam originates from a steam boiler 27. Part of the dryed material is led back through a repulverizing system that is part of the dryer, to avoid sticking.

The dryed material is led by conveyor 28 to container press 29, which presses the end product into exchangeable containers 30.

In the process various streams of water occur, namely: leakage water from the reception, rinse water from the hydrocyclone, leakage water from the reducers, water from the blanchers, water from the press, condensate from the dryer, and other streams of leakage water.

These streams of water are shown on the lower half of fig.

4, by lines which are connected to the water purification 17 or to the steam, boiler 27. The amount of water used can be minimalized by a suitable collection and by recycling.

It is obvious that the apparatuses described in the invention can be of a variety of designs and the invention is therefore not limited to certain specific apparatuses as long as the biological waste is chopped, compressed and dryed.

Claims

1. Method for processing biological waste, characterized

in that the method contains the following steps: - mixing the biological waste, - chopping the waste mixture, - compressing the chopped waste mixture, and - drying the compressed waste mixture by adding heat.

2. Method according to claim 1, characterized in that, prior to compressing the mixture, the mixture is cleansed.

3. Method according to claim 2, characterized in that cleansing takes place prior to chopping.

4. Method according to claim 2 or 3, characterized in that cleansing comprises the step of separating the waste from materials with a larger density than the waste by means of water.

5. Method according to claims 1 or 2, characterized in that, prior to compressing the mixture, the mixture is preheated.

6. Method according to claim 5, charaterized in that preheating contains the step of sterilizing the waste mixture.

7. Method according to claim 5 or 6, characterized in that preheating contains the step of removing chemical agents from the waste mixture by means of water with an increased temperature.

8. Method according to claims 1 or 2, characterized in that for compressing use is made of a centrifugal compression.

9. Method according to claim 1, characterized in that after drying the waste mixture the waste mixture is ground into chunks.

10. Method according to claim 1 or 9, characterized in that a portion of the dryed, compressed waste mixture is led back to and mixed with the chopped waste mixture, which is to be dryed.

11. Method according to claims 1 or 8, characterized in that the step of compressing takes place until the liquid content of the chopped waste mixture is reduced by approximately 20%.

12. Method according to claim 1, characterized in that the step of drying the compressed waste mixture takes place at such an elevated temperature and for such a length of time that the waste mixture is sterilized.

13. Method according claim 1, characterized in that, prior to the step of compressing the waste mixture, additives are added to the waste mixture.

14. Method according to claim 13, characterized in that the additives are an amount of fish waste such that the dryed waste mixture contains approximately 28 % by weight of protein.

15. Apparatus for processing biological waste, characterized in that the apparatus is provided with: - a mixing apparatus for mixing the biological waste; - a chopping apparatus for chopping the waste mixture - a compressing apparatus for compressing the chopped waste mixture, and - a drying apparatus for drying the compressed waste mixture by adding heat.

16. Apparatus according to claim 15, characterized in that the apparatus contains a cleansing apparatus for cleansing the chopped waste mixture.

17. Apparatus according to claim 16, characterized in that the cleansing apparatus contains a hydrocyclone provided with an agitator for separating materials with a larger density than the waste by water flow and upward force.

18. Apparatus according to claim 15, characterized in that the apparatus contains a preheater for preheating the mixture prior to compressing the mixture.

19. Apparatus according to claim 18, charaterized in that the preheater contains a blancher.

20. Apparatus according to claim 15, characterized in that the compression apparatus is a centrifugal riddle.

21. Apparatus according to claim 15, characterized in that the apparatus contains a conveyor belt between the mixing apparatus and the compressing apparatus, whereby the chopping apparatus is formed by chopping means integrated with the conveyor belt.

22. Apparatus according to claim 15, characterized in that the apparatus is provided with a supply apparatus for supplying the waste mixture with additives prior to compressing the waste, mixture.

23. Apparatus according to claim 15, characterized in that the apparatus contains a crushing machine for grounding the dryed waste mixture into chunks.

24. Apparatus according to claim 15, characterized in that the apparatus contains a conveyor for conveying the dryed waste mixture to the chopped waste mixture to be dryed and a mixing apparatus for mixing the dryed and the chopped waste.