NO140927B - PROCEDURE AND APPARATUS FOR THE TREATMENT OF SPECIAL HOUSEHOLD WASTE - Google Patents

Description

The present invention concerns a method and an apparatus for an integrated, local treatment of biodegradable waste, e.g. household waste such as kitchen waste, paper and faeces, and waste from barns and stables.

With regard to the rapidly increasing costs of the now common methods of centrally collecting and destroying all household waste, it is likely that in the future we will have to count on a greater and greater extent of decentralization of waste treatment, which means that all biodegradable waste is treated lo- called close to the source and that only non-degradable residual products are collected at central waste facilities.

Previously proposed devices for the biological decomposition of household waste have almost without exception worked according to the principle of aerobic dry decomposition, which has greatly limited the possibilities of supplying liquid waste beyond the amounts of urine that go with the faeces. The dry molding reaction is so sensitive to external disturbances that it can almost come to a complete halt when the liquid supply is periodically increased beyond the maximum amount for which the apparatus is process-technically dimensioned. The aerobic forming reaction usually only starts after a sufficient amount of liquid has had time to evaporate. During the time that the aerobic fermentation slows down due to a too high liquid content, an anaerobic fermentation can begin, which i.a. causes the development of foul-smelling gases.

In order, if possible, to optimize the dry formulation reaction, many of these previously proposed devices have been provided with thermostatically controlled heating coils for evaporation of excess liquid, and organs for the forced supply of air, but despite this there is quite a small difference between the breakdown achieved in this way and the decomposition achieved in a conventional compost pile, although the rate of decomposition in the above-mentioned devices is normally higher than in the compost pile. The formation rate for faeces and food waste is relatively satisfactory in such a device during normal operation, while the device's possibilities to break down paper and other cellulose at the desired speed are limited. The course of the molding reaction also becomes uneven, as a mixture of dry household waste and faeces constitutes a very heterogeneous material, the components of which generally come to be mixed in layers. The uneven formulation makes it difficult to achieve a complete breakdown of all degradable material, and the resulting residual waste will therefore be able to contain disease-causing bacteria (pathogens) as well as worm eggs and weed seeds. Such residual waste cannot therefore be deposited; anywhere.

However, it has also been found that practically homogeneous liquid waste of the type putrefactive sludge and e.g. chicken and pig manure under certain special conditions can be reduced to a liquid phase with the help of aerobic, thermophilic microorganisms, whose optimal living conditions lie at temperatures of approx. 50 - 70

°C. In order for the aerobic decomposition not to turn into an anaerobic decomposition, a relatively efficient mixing of the liquid waste is required at the same time as air or oxygen is added to it. If the decomposition treatment takes place in sufficiently well-insulated containers, the intrinsically exothermic reaction can be utilized to maintain the desired reaction temperature.

The decomposition carried out in the liquid phase by aerobic, thermophilic micro-organisms is even so heat-generating that in its most active phases it develops significantly more heat than that involved in replacing the heat losses', and as long as the reaction takes place there is therefore nothing problem of maintaining the required reaction temperature.

The present invention has, to a certain extent, opened up new areas of application for the aerobic thermophilic wet molding process, as it has now become possible to utilize this process also for the biological degradation of very heterogeneous waste mixtures, the original consistency of which can be allowed to vary within very wide limits. With the invention, it has been shown that you can make yourself independent of the original consistency of the waste by finely dividing the waste and slurping it in water in a sufficient quantity for the mixture to form a flowable slurry (slurry, a term used here for a -retention of solid waste particles in the liquid part of the waste and added water). The solids content that can be achieved in such a slurry without it losing its flowability can vary between approx. 1 and approx. 15% by weight, preferably between 5 and 10% by weight, depending on the content of the waste. The low dry matter content, i.e. the consistency, applies primarily to cellulose-rich waste. The required degree of fine distribution is not absolutely critical, but as an increased particle size extends the necessary decomposition time, the particle size of the finely divided waste should only in exceptional cases be allowed to exceed 1 - 2 mm diameter. Particles with a small cross-sectional area, but significantly greater length, e.g. paper and other fibres, however, may be permitted.

When breaking down normal household waste of a daily life nature, i.e. food waste, food packaging residues, etc. as well as faeces, it must be assumed that approx. 1/5 of the waste is completely inert to biological degradation, and this residual waste must therefore, regardless of the treatment method, also be dealt with centrally in the future. Local decomposition of all degradable material can therefore reduce household waste by 4/5. As the residue obtained by carrying out the method according to the invention is also completely harmless to humans and animals in that it does not contain any live disease-causing bacteria, live worm eggs or the like, it can, after it has been appropriately freed from metal, glass and preferably also plastic scraps, are used e.g. as a soil conditioner. The killing effect of thermophilic decomposition is partly explained by the relatively high temperature that prevails during the decomposition, and partly by the antibiotics produced by the thermophilic bacteria during the decomposition process.

After the water-containing waste slurry has been prepared in the previously described manner, the dppslurry is mixed during the continued treatment either continuously or intermittently to a sufficiently high degree to prevent its solid components from sedimenting or the slurry from settling. At the same time, the slurry is supplied with heat in a sufficient quantity to raise its temperature to the thermophilic temperature range. Thermophilic bacteria with the ability to break down organic matter into carbon dioxide and water are normally available in larger or smaller quantities in any type of biodegradable waste material, and such bacteria therefore generally do not need to be supplied. However, the desired decomposition reaction can be accelerated if the waste slurry is inoculated with a suitable bacterial culture. As there are a number of different types of thermophilic bacteria with different properties, one can choose a bacterial culture with a documented good ability to break down the main constituents of the waste material in question by such inoculation. Especially when treating such waste which is difficult to break down, e.g. waste with a high cellulose content, it may be appropriate to inoculate the slurry.

After the temperature of the slurry has been raised to the thermophilic range, the heat supply is interrupted while the mixing is continued at the same time that oxygen-rich gas, suitably in the form of ordinary air, is supplied to the slurry either in the form of fine bubbles, which are distributed in the slurry, or by giving the slurry a large contact surface against the surrounding air, e.g. in that the slurry is finely divided into droplets or spread into a thin flowing layer. The amount of oxygen added to the slurry that is sought must be such that the aerobic thermophilic bacteria's oxygen needs are met. An oxygen supply corresponding to 0.2 - 2.0 g of air per liters of waste slurry and hour will generally be suitable. No absolute critical limits for the oxygen supply can be established, but an oxygen content in the slurry that is too low leads to a gradual transition to anaerobic decomposition, while an air supply that is too high causes heat loss and leads to an overly unstable contact between the oxygen in the air and the aerobic bacteria. Furthermore, the only possibility of adding too large amounts of air (oxygen) is to force it into the slurry, and too high an air (oxygen) supply will therefore also lead to excessive bubbling in the slurry. A pure oxygen poisoning of the thermophilic aerobic bacteria can only be achieved by supplying pure oxygen gas in an excessively large quantity.

As previously mentioned, the aerobic thermophilic decomposition results in a temperature rise in the slurry if the excess heat is not carried away. By condensing evaporated water from the slurry in a reflux cooler, this surplus heat can easily be taken care of. The calculation shows that the overflow heat that can be used e.g. for space heating by breaking down household waste from a normal family, corresponds to approx. one to two radiators. The return of condensed water from the return cooler to the slurry is regulated so that the slurry's consistency and temperature remain within appropriate limits. Among other things, the fluidity of the slurry must be maintained, so that it is almost as easy to re-mix and add oxygen. The temperature of the slurry is suitably kept during the course of the decomposition within the interval 50 - 70°C and then preferably between 55 and 60°C.

By raising the temperature of the slurry to the thermophilic range already before the addition of oxygen begins, the decomposition reaction can be brought to start with high intensity already at an early stage. This has made it possible to break down the main part of all biodegradable material into carbon dioxide and water already within the first day. After 5-7 days, all biodegradable material has been consumed and at the same time the disease-causing bacteria have been killed. What remains can be easily broken down into biologically inert water and non-degradable residual products. This division can e.g. happen by sedimentation, filtration or centrifugation. If the filtration takes place in disposable filters, these can be used as transport packaging for the solid residual products.

It appears from the above that an important purpose of the invention is to enable relatively fast wet formulation of the waste from individual households using a relatively cheap and compact, but effective device, which takes up relatively little space, but has sufficient capacity for batch processing of the waste from households' of normal size.

This is achieved by a method and an apparatus as specified in the patent claims.

In practical tests with an apparatus of a preferred embodiment according to the invention, by means of which a mixture of household waste, faeces and water (dry matter content 8%) was broken down over the course of six days at an average temperature of 57°C, one obtained after separation -"of the solid waste residues, a residual water with a weak yellow color and a weak smell, which almost reminded of the smell of an old earthen cellar. In a regular coli test (i.e. water test) of the remaining waste slurry after complete decomposition, the coli content turned out to be zero (0) cultures per 100 ml This can be compared with the hygienic requirements for drinking water of 0 - 7 cultures/100 ml and for bathing water 1000 cultures/100 ml.

The method and apparatus according to the present invention shall be described in more detail below with reference to the attached drawings.

Fig. 1 shows schematically and in simplified form an apparatus according to the invention, which is mostly intended for the treatment of waste from individual households, fig. 2 shows an advantageous embodiment of a stirrer in the apparatus of fig. 1 and fig. 3 shows a modified embodiment of an apparatus according to the invention.

The apparatus according to fig. 1 comprises two separate formulation reactors 1, 2, each of which has a preferably mainly cylindrical receiving chamber 3 or 4 with an upper inlet 5 or 5' and a lower drain 6 resp. 6'. The two inlets 5, 5' are arranged to be connected via a multi-way valve 7 alternately to the drainage system 8 from a toilet 9 and a kitchen waste grinder 10 and the two drains 6, 6', which are each equipped with a shut-off valve 11 or 11', can lead to a common (not shown) drain.

A stirrer 12, 12' is mounted in each reactor chamber. Each stirrer has a vertical shaft 13, which is supported at its upper end part, e.g. in the reactor's upper wall, as shown at 14 and the two stirrers' 12, 12' shafts 13 can be driven by means of a common motor 15 via a suitable transmission, e.g. a belt transmission 16 and a coupling 17, which is operated by means of the motor and is arranged to allow separate operation of the stirrers 12, 12' and possibly also simultaneous operation of these.

To the two reactor chambers 3, 4 is connected a device for blowing in air at a level below the surface of the in resp. chambers from the toilet 9 and kitchen waste grinder 10 received slurry of solid substances and liquid. This air blowing device is shown in the form of an air compressor 18, whose pressure line 19 is connected via two branches 20, 20' to the two reactor chambers. The branch lines 20, 20" each have their own shut-off valve 21, 21'.

In fig. 1, the valve 7 is shown set for delivery of liquid-slurried waste from the devices 9, 10 to the left reactor chamber 3. The right chamber 4 is already filled to a certain level and shut off from the devices 9, 10. The air injection valve 21 to the left reactor chamber 3 is closed and the air injection valve 21' to the right reactor chamber 4 is open, and air is blown into the slurry through this valve. Furthermore, it is assumed that the motor 15 drives the stirrer 12' in the right reactor chamber 4, while the stirrer 12 in the left reactor chamber 3 can

be stationary.

In the case of a system with two or, if desired, more reactors 1, 2, a smoother, faster treatment and breakdown of the waste is made possible than if the system only includes one reactor.

The stirrers 12, 12' in the two reactor chambers 3, 4 can be of the type shown in fig. 2, where the stirrers are denoted by 12. This stirrer 12 in fig. 2 partly comprises two stirring means 23 mounted at a distance from each other on the shaft 13 with paddle blades 24, and a foam-breaking means 25, which is mounted on the shaft 13 above the upper stirring means 23 and at an appropriate level for influencing the foam on the surface of the slurry in the working reactor chamber (see right chamber 4 in fig. 1). The foam breaker 25 may consist of a number of inclined wings 26, which may have relatively thin or sharp edges.

To make the stirring effect even more intense in resp. reactor chamber, one or possibly more rails 28, 28' can be mounted on the vertical chamber wall, which have the task of influencing the vortex produced by the stirrers 12, 12' in the slurry and, more specifically, breaking a completely regular vortex pattern. A combination of a double paddle agitator of the one in fig. 2 shown type, and fixed rails 28, 28' in resp. chamber has been shown to provide a particularly good mixing effect in the slurry.

The wings 26 on the foam breaking member 25 can be attached to resp. shaft in such a position that the wings 26 lie a little above the normal liquid level in resp. chamber during operation, e.g. about. 5 - 10 cm above this level. The vanes 26 have the task of breaking up the excess foam and pushing it back into the slurry. A foam layer of limited thickness may, however, be of some value due to its heat-insulating ability, but it must not be allowed to grow too thick. The wings shown can have a propeller blade-like shape with varying pitch.

The fixed rails 28 can extend from a point up to or below the normal surface level of the slurry when resp. chamber is filled to a point some distance from the bottom of the chamber.

At the bottom of each reactor chamber is arranged a heating element 30, 30' which is intended to be used for raising the temperature in the slurry in resp. reactor chamber during an introductory stage of the treatment and therefore with some reason can be called starting element. There may also be devices (not shown) for temperature regulation.

The two reactors 1 and 2 can be provided with double drains 6, 6', 6" at different heights, whereby a relatively clean water after a shorter period of sedimentation in the respective chamber can be diverted through the upper drain, while the sludge-rich fraction of the slurry can be discharged through the lower drain.

The flushing water from the toilet 9 and the waste grinder 10 is used for the preparation of the aqueous sludge. Kitchen waste is finely distributed in the waste grinder, while the agitators are responsible for a fine distribution of the faeces. The flushing water for the waste grinder and the toilet is supplied via a water pipe system 31.

Instead of the one in fig. 2 shown stirrers, which consist of two flat, circular disks on a shaft and a number of radial flat vanes 21 distributed around the circumference, of course stirrers of the propeller type, paddle type or the like can be used.

As shown in fig. 1, each reactor chamber can have a gas outlet 32 at its upper end, resp. 32', which can optionally be shut off by means of a damper (not shown).

In the modified embodiment in fig. 3, the two reactors 1, 2 are found with the reactor chambers 3, 4, the distribution valve 7 for alternate connection of the reactor chambers to the water closet and the kitchen waste grinder 9 resp. 10, the gas outlets 32, 32' and the starting element 30, 30'. In fig. 3 is shown, similarly to fig. 1, the left reactor chamber during filling and the right during operation for the waste treatment.

In the embodiment in fig. 3 is, however, used instead of the stirrers in fig. 1 a dividing mud pump 35, e.g. of the inclined disc or so-called vane disc rotor type, whose inlet is connected to each reactor chamber 3, 4 near the bottom of the chamber via a shut-off valve 36 or 36' and whose outlet 37 is connected via two branch lines 38, 38' to an injection nozzle 39, 39' arranged in each chamber. Under the nozzle in each chamber is mounted an organ, e.g. in the form of a cone 40, 40' with an upwardly pointed tip, which is arranged to split up the injected slurry and the air in the upper part of the reactor. The two branch lines 38, 38' each contain a shut-off valve 41, 41'.

In fig. 3, the shut-off valve 36' in the pump inlet line and the shut-off valve 41' in the pump outlet branch line 38' are shown open, as it is assumed that the right reactor chamber 4 is in operation, while the corresponding left valves 36 and 41 are closed. The distribution valve 7 is open to the left chamber for grinding waste slurry into it, while the right chamber is working.

In the embodiment in fig. 3 have the two reactor chambers 3, 4

a common drain 42 with a shut-off valve 43, which under those in fig. 3 shown work phases are closed.

The mud pump's 35 four valves can, as indicated with

dashed lines in fig. 3, be arranged for pairs

ring.

The sludge pump 35 can also be used for optional emptying

reactor chambers 3, 4 through the central drain 42. By using a pump 35, which produces a grinding effect, a continuous

current division of the waste in connection with the circulation pump

the ping of the slurry for mixing and aeration.'

As shown in fig. 3 it can be advantageous in each case

reactor chamber 3, 4 to connect a reflux cooler 44 for re-

condensation of in resp. reactor chamber vaporized liquid and return

leading the liquid to the slurry as well as to take care of the liquid's excess heat. Gases, such as formed carbon dioxide and excess air, can be carried out through the ventilation drains 32,

32'.

Claims (7)

1. Procedure for treating solid and liquid waste waste materials including household waste, such as food waste, paper and/or faeces, which comprise a significant proportion of biodegradable components, for the production of an aerobic, thermophilic wet formulation of the biodegradable components, where a) the solid components of the waste material are broken down into relatively small particles, preferably under 2 mm in diameter and the amount of liquid is adjusted to produce a well-homogenized, easy-flowing slurry with a solids content with a dry weight of no more than 15% and preferably below approx. 10%, and b) the slurry is inoculated with a mixture of different types of aerobic, thermophilic microorganism cultures suitable for the particular case, characterized by" c) that the temperature of the slurry in the initial stage of the treatment is raised to a range of 50 - 70°C for optimal activation of the aerobic, thermophilic microorganisms originally present and formed during the treatment and the heat input is interrupted as soon as the naturally exothermic treatment reaction develops sufficient heat to keep the temperature of the slurry within the said thermophilic range, until the treatment is completed, d) that the composting is carried out in a container in which the slurry is stirred with sufficient intensity to prevent layer formation or sedimentation of the slurry's constituents, and while the stirring is carried out, the slurry in the container is forcibly brought into intimate contact with oxygen-rich gas in sufficient quantity to satisfy the oxygen demand of the aerobic microorganisms which is-present in the slurry from the beginning of and develops during the course of the treatment, e) and that the above-mentioned conditions in the container with stirring, addition of oxygen and temperature conditions within 50 - 70°C are maintained until essentially all biodegradable material in the slurry has been consumed, after which the treatment in the container is interrupted and, if necessary, a division of the slurry into hygienically acceptable fractions of essentially liquid and essentially solid components is carried out. 2. Method as specified in claim 1, characterized in that at least part of the necessary mixing water for preparation of the slurry is made up of flushing water from a connected waste grinder. 3. Apparatus for carrying out the method as stated in claim 1, characterized in that it consists of at least one formulation reactor (1, 2) in the form of a preferably heat-insulated, ventilated, stationary container (3, 4) provided with an run (5, 5') in the upper part of the container for the waste to be treated, organs, e.g. a grinder (10), for dividing the waste into a finely divided state, means (31) for adding slurry water (a) to the waste before it is introduced into the container, means (12, 12', 13, 15) for stirring the the waste slurry collected in the container consisting of finely divided waste and water, means (20 or 35, 37 - 40) for adding oxygen to the slurry, at least one outlet opening (6, 6') arranged in the lower part of the container which can be opened for emptying the finished treated slurry and a heating device (30, 30') arranged preferably adjacent to the container (3, 4) for raising the temperature of the slurry. 4. Apparatus as set forth in claim 3, characterized in that said oxygen addition means comprises a compressed air source (18) and a connected air inlet nozzle (20) which opens into the container (3, 4) below the slurry level, and which is arranged to spread and distribute as evenly as possible the blown air in the slurry. 5. Apparatus as stated in claim 3, characterized in that the formulation reactor comprises at least two containers (3, 4) which are arranged to work alternately for batch treatment of the waste material. 6. Apparatus as specified in claims 4 and 5, characterized in that the two containers (3, 4) are each connected to a closable circulation line (36 or 36'), which is operated by a common circulation pump (35). 7. Apparatus as stated in claims 4 and 5, characterized in that the two containers (3, 4) each have their own shut-off air blowing device (20, 20') and that these air blowing devices are connected to a common air source (18, 19) .