The invention concerns a device for the treatment/purification of sewage-effluent, wherein the effluent is exposed to a filtering process, together with both an aerobic and an anaerobic treatment.

In the biological purification of effluent, the effluent or sewage is brought into contact with micro-organisms, peat, sand and/or material containing cellulose, in order thereby to remove unwanted substances from the effluent, especially nitrogen and phosphorus, but also other substances which are harmful to the environment, thus ensuring that the purified water which is discharged will not harm the natural surroundings, while at the same time the extracted substances can be exposed to natural decomposition and subsequently used in soil management. In this purification treatment the aerobic zone will have a double function, acting both as a part of the nitrification process, i.e. the aerobic part of this process, and in addition as a filter.

There are a number of different known purification processes and plants for the treatment of effluent. One type is the infiltration plant, i.e. a plant in which, after sludge separation, the sewage is infiltrated in loose masses in the ground. This kind of plant can be used only if the soil has a suitable consistency, which permits the natural separation of unwanted substances. A disadvantage of the infiltration plant is that the efficiency and the infiltration in the plant's sand will be reduced with time, which will gradually cause the efficiency to become unsatisfactory, or make it necessary to replace the infiltration mass. This is an obvious disadvantage both from the economic and the practical point of view.

An object of the present invention is to enable a purification to be carried out with which the same advantages are obtained as with an infiltration plant, but which avoids the disadvantages of such plants and in which better purification

can be achieved with substantially simpler means, particularly over a longer period of time than that which is obtained with conventional infiltration plants and which at least corresponds to what is demanded of such plants which are located in the ground.

A further object of the invention is to provide a device which permits effective control of the purification process and its efficiency, a feature which will offer the authorities entirely new opportunities for exercising control over discharge to the environment.

Yet a further object of the invention is to provide the opportunity for considerably more extensive use of biological purification methods than has been possible to date and in addition for returning to nature the resources derived from the purification.

These objects are achieved by a device which is characterized by the features in the claims presented.

The new and crucial feature of the invention consists in the fact that the entire sewage treatment is conducted within a limited, controlled and closed circuit which is located within a totally defined area without any contact with the environment except via the inlet and outlet. It is thereby possible to have full control over both the aerobic and the anaerobic processes, and the treatment process is safeguarded against the effects of any unexpected natural changes.

The invention also provides the possibility of using natural purification processes to a considerable extent, since by using a device of this kind which is independent of positioning it is not necessary to make demands on the quality of the existing soil and it will only be sink water which comes up to the surface.

Another distinct advantage of the device according to the invention- is that it will give resources back to the user in a natural ecological cycle. This is not achieved in normal infiltration plants where the resources pass into the water circuit and constitute a polluting factor in this, instead of passing into the plant circuit where they constitute a resource.

Another important advantage is that the invention does not create methane gas which damages the ozone layer, as happens in traditional septic tanks/sludge separators and in large public purification plants.

The treatment plant will be extremely simple to assemble since it is designed as a closed unit in the form of a container which quite simply can be buried in the ground or in some other way placed in a more or less hidden position.

A further crucial advantage of the device according to the invention is that it enables emptying of both sludge and the materials used during the process to be performed in a very simple manner, and the aerobic material can be allowed to decompose, to be used subsequently as a means for soil improvement. With the special design according to the invention replacement of the material will be a simple matter and not particularly unpleasant for the person performing this task.

Previously known plants operated according to the same basic principles have had the disadvantage that they require a large infiltration area while maintenance has been a relatively complicated procedure.

In the following section the invention will be described in more detail by means of a schematic embodiment which is depicted in the drawing:

Fig. 1 a section through a device according to the invention, and

fig. 2 a cross section of the device in fig. 1, at the lower separation plane

In the illustrated embodiment the device according to the invention is designed as a spherical container with a flat bottom and is indicated on the drawing by reference number 1. Although a spherical container is illustrated in the drawing, it should be obvious that the container could just as easily have been, for example, cylindrical or rectangular or of some other design, since its shape is not important.

The container is equipped with an inlet for effluent or sewage 2, and an outlet for treated water 3 in the lower area. Furthermore, the container has a manhole 4 with a lid for access to the interior of the container for replacement and cleaning purposes.

Thus the biological purification system is located in its entirety inside the container 1 and forms a closed system which is completely under control.

The treatment of the effluent is performed in three stages, which are situated at three levels in the container. These levels are indicated by the reference numbers I, II and III. The levels are separated from one another by separation planes 5 and 6. In separation plane 5 between the top level I and the middle level II, there is integrated a filter device for separation of coarse sludge which accompanies the effluent which is introduced through the inlet 2. The filter device 7 can be designed in many ways, e.g. as a filtering cloth which is attached to hooks which are not illustrated in more detail, or the separation plane 5 can be equipped with removable laths or the like on which can be placed a sieve, filter bag or the like. What is important is that in plane 5 sludge and particulate materials, twigs and the like should be separated and collected in the cloth or bag 7 which can be removed through the manhole 4. By removing any support devices in the plane 5, easy access will then be obtained to the underlying

layer. The filter device 7 should cover the greatest possible area in order to provide the best possible distribution of the through-flow of effluent to the next zone.

The middle level, II, constitutes the aerobic zone in the effluent treatment. For the implementation of this aerobic process, this middle level II is filled with a material suitable for absorbing the effluent flowing from the filter device 7. This material can be ordinary peat, mixed with sand, a cellulose material or another material suitable for this purpose and can also contain enzymes, nitrification bacteria, etc. ; in other words the material can be adapted to suit the purpose or contain the appropriate substances. For easy handling of this material it can be placed in small sacks or bags 12 of a porous or meshed material, which keeps the material 11 in the bags or sacks in place, while at the same time the sacks can fill the entire level II. The sacks 12 can be equipped with cords which are pulled up to the manhole 4 and, e.g., attached together to a step 16 in the manhole. The sacks can thereby be replaced individually or they can all be easily pulled out when the mass in the aerobic zone II is replaced. Other alternatives can be to tie the sacks to one another, thus allowing them to be pulled out in a row. The sacks can, of course, also be handled individually without cords. From the outlet 3 can come air which follows a path close beneath the separation wall 6 and up through holes or gratings in the separation wall 6 and flows through the aerobic material 11 in order to improve its efficiency.

After the aerobic treatment at level II the effluent will flow on through a grating 13 in the bottom, i.e. in the separation plane 6 and down to the anaerobic zone III. This zone can preferably be divided into two or possibly more chambers 14 and 15. The chamber 14 forms an extra sludge filtering zone where the sludge filter can also be a bag, i.e. a filter bag which can be removed through the opening 4 by lifting off the grating 13. Such a filter chamber 14 is not absolutely necessary, however, but it can be appropriate in many cases. From the

chamber 14, which can also be a sedimentation or settling ^' chamber, the effluent will then enter the chamber 15 where it will undergo an anaerobic process as its final treatment, before the water is discharged through the outlet 13. As already mentioned, this outlet can have a double function whereby it also introduces the air necessary for the aerobic process. It is, however, also possible to perform this extra introduction of air separately if this is considered to be advantageous in special cases. Zone III will be filled with water on a level with the outlet 3. In the bottom there is placed a sand layer which is schematically illustrated and indicated by 18.

Fig. 2 illustrates a possible embodiment of the separation plane 6. The separation plane 6 can be designed with plate parts 9 which are connected with the container's 1 walls and leaves free an opening in the middle section on the right-hand side of the drawing. In the area on the right-hand side there is provided a removable grating element 13 which also facilitates access to the underlying zone. The centre of the middle section is covered with a removable plate 10 which is connected with the plate elements 9 by a flange connection, as illustrated in the enlarged section which is illustrated by a circle with an extended line. The entire plane 6 slopes slightly down to the grating element 13, thus causing the water to flow this way and down into the chamber 14. This design is favourable since by simply lifting off the plate 10 and the grating 13, the underlying areas can be reached, the anaerobic chamber can be filled with sand 18 and necessary maintenance can be carried out. The plate 10 preferably has a dimension which enables it to be taken in and out through the manhole 4. Other designs can naturally be envisaged for the separation plane 6, as well as other ways of dividing up the zones.

The effluent which flows out through the outlet 3 is now completely purified and can be freely released into the ground without any demands being placed on the quality of the soil. The effluent can also be conveyed to a recipient.

On the outlet 3 it is advantageous to instal a pipe 19 which leads up above ground level and which, e.g., is terminated with a U-pipe connection 21. The pipe 19 is used for the intake of the air which flows in through the outlet 3 on top of the water level in the anaerobic zone and is led into the aerobic zone II. In the pipe 19 it can be advantageous to place a sampler 20, in the form of a small cup on a cord which is led up through the pipe 19. The cup can be permanently fitted in a pocket in the outlet pipe 3. In this way continuous control can be carried out of the quality of the purified water or the effluent from the device, and by means of spot checks the authorities can thus check whether the purification satisfies requirements, whether maintenance is necessary, etc.

In the illustrated embodiment only one possible embodiment is described for the device according to the invention. As described above, such a container or device can be given many different shapes and designs, all depending on where it is to be placed and what will be the most practical design. It is advantageous for the container to be constructed of fibre glass reinforced plastic, a material which has already been used for a number of containers and these will be able to be modified for this area of application. The container can also be constructed of other suitable materials. With the use of sacks or bags for the sludge filtration and also for location of the aerobic material, a very simple method for the replacement of the material and removal of sludge has been achieved, and in a way which will not be considered unpleasant and which means that, as a result of regular replacement, the aerobic material can also be available on the market as a utility article. However, a replacement of this kind will normally only be necessary once or twice a year. The outlined design with sacks is advantageous, but the invention is not limited to this. A practical solution is to turn the sludge from the filter 7 into compost in a closed container, while the mass from the aerobic zone can be used directly for soil improvement or turned into compost in the open.

There are also many modifications which can be made in connection with the inlet and the outlet of the device according to the invention. There is thereby provided a device for purification of sewage which will prevent fertilizer materials from being included in the actual water circuit and ensure that retained resources enter the correct circuit and can be used for soil improvement. When using the device according to the invention it will not be necessary to connect sparsely built-up areas to the public mains system, and thus the device will provide considerable social savings.