Technical field

The present invention relates to an after-treatment system for after-treatment of waste water from a treatment plant.

Background

A number of different types of purification systems exist for treating sewage based on biological, chemical, radiation-based or other treatment principles. In these purification systems solid materials (sludge etc.) are removed and the treated waste water can be released into the environment if they fulfil the existing criteria for purity.

The criteria for purity may, for example, stipulate that the number of bacteria (typically TKB (coliform thermotolerant bacteria)) per volume unit of waste water should be below a given level and/or that the phosphorus content per volume unit of waste water should be below a given level. The permitted levels for TKB and phosphate content are often determined by national or local regulations, and may vary.

There are a number of challenges associated with such treatment plants. In areas with a great many holiday homes, for example mountain or forest areas with cabins, the decision is often made to build treatment plants for groups of cabins located close together. However, there is considerable variation in the use of a holiday home throughout a year. During some periods the holiday homes are very little used and there is therefore very little sewage. The result may be that the micro-organisms in the treatment plants do not receive the nourishment they require in order to function optimally. During other periods the holiday homes are in regular use, thereby causing the amount of sewage to increase substantially. It can take time for the number of micro-organisms to increase to the desired level, with the result that during these intervals the treatment plant does not function optimally. On account of the sudden increase in sewage during such periods, the treatment plant may therefore release waste water in which the criteria for purity are not fulfilled.

Another challenge may arise where there is a wish to build treatment plants in areas where the local regulations state that the level of TKB and phosphate content should be extremely low or almost zero, which is not possible with present day treatment plants.

The object of the present invention is to provide an after-treatment system for after- treatment of waste water from a treatment plant, where by means of such an after- treatment system the purity of the waste water is increased, i.e. the level of TKB and/or phosphate content in the waste water is reduced. Summary of the invention

The present invention relates to an after-treatment system for after-treatment of waste water from a treatment plant, comprising:

- a container device with a main chamber;

- a filter device provided inside the main chamber;

- a first pipe arrangement comprising an outlet, where the first pipe arrangement conveys the waste water from the treatment plant via the outlet to a first area in the container device;

- a second pipe arrangement comprising an inlet, where the second pipe

arrangement conveys the waste water from a second area in the container device via the inlet and out of the container device;

where the filter device, the first pipe arrangement and the second pipe arrangement are configured so that the waste water has to pass through the filter device in order to get from the first area to the second area;

where the filter device is alkaline; and

where the size of the after-treatment system is dimensioned according to the expected amount of waste water per time unit so that the residence time T for the waste water in the main chamber is greater than 20 hours.

In an aspect of the invention the filter device is continuously submerged in the waste water.

In an aspect of the invention the outlet is placed at a height lower than the inlet in the container device.

In an aspect of the invention the first area and the second area are provided in the main chamber.

In an aspect of the invention the container device comprises a sedimentation chamber, where the waste water flows from the main chamber to the sedimentation chamber and where the inlet is provided in the sedimentation chamber.

In an aspect of the invention the main chamber and the sedimentation chamber are separated from each other by means of a wall, and the waste water flows from the main chamber over a threshold in the upper part of the wall to the sedimentation chamber. In an aspect of the invention the outlet in the first pipe arrangement comprises a plurality of smaller openings for distributing the waste water to the filter device in the main chamber.

In an aspect of the invention the filter device comprises a perforated bag filled with filter mass and where the outlet is in the form of a substantially upwardly directed spear for penetrating the perforated bag.

In an aspect of the invention the bag comprises a fastening device for fastening to a lifting device.

In an aspect of the invention the residence time T for the waste water in the main chamber is greater than 20 hours, thereby giving the waste water a pH > 10.

In an aspect of the invention the first pipe arrangement comprises a controllable pump device or a controllable valve for controlling the residence time T for the waste water in the main chamber.

The after-treatment system according to the invention lowers the level of the TKB content to approximately 0 and the phosphorus content to 0.2-0.1 mg/litre, i.e. a total of approximately 97-98% including the pre-treatment plant, or approximately 80-90% in addition to the pre-treatment plant/the treatment plant arranged before the plant/the wetlands tank. This will also be apparent in the detailed description below.

Detailed description

Embodiments of the present invention will now be described in detail with reference to the attached drawings, in which:

Fig. 1 illustrates a first embodiment viewed from the side;

Fig. 2 illustrates a second embodiment viewed from the side; and

Fig. 3 illustrates a third embodiment viewed from the side.

We now refer to fig. 1, which illustrates a first embodiment of an after-treatment system 1 for after-treatment of waste water from a treatment plant. Sewage and other types of water which have to be purified therefore arrive first at an ordinary treatment plant (not shown), whereupon the waste water is conveyed from the treatment plant to the after-treatment system 1 for after-treatment.

The after-treatment system 1 comprises a container device 10. The container 10 is normally a tank made of plastic, glass fibre or other suitable materials, with a circular, rectangular, polygonal or other suitable basic shape. In the first

embodiment the container device comprises a chamber, called a main chamber 12. Inside the main chamber 12 a filter device 18 is provided. The filter device is alkaline, i.e. aqueous liquid becomes alkaline during residence in the filter device.

The filter device 18 is provided in such a manner that waste water can pass through it. The filter device 18 may, for example, be porous.

The filter device 18 may be homogeneous, i.e. the filter device 18 is made of only one material. Alternatively, the filter device 18 may comprise an outer membrane filled with a filter mass. In such cases the membrane may be a cloth or a bag of a suitable material. The filter mass may, for example, comprise calcareous materials, for example Filtralite P (trademark - http://www.filtralite.com ), shell sand or other suitable materials. Such materials are considered to be known to a person skilled in the art and are available on the market.

A first pipe arrangement 20 conveys waste water from the treatment plant to the after-treatment system 1. The pipe arrangement 20 comprises an outlet 21 , where the first pipe arrangement 20 conveys the waste water from the treatment plant via the outlet 21 to a first area 14 in the container device 10.

A second pipe arrangement 30 discharges the after- treated waste water from the after-treatment system 1. The second pipe arrangement 30 comprises an inlet 31 , where the second pipe arrangement 30 conveys the waste water from a second area 16 in the container device 10 via the inlet 31 and out of the container device 10. The outlet of the second pipe arrangement may, for example, discharge the after-treated waste water into a shallow infiltration or earth mound infiltration or the like, or into an all-year water-carrying stream or river. The way in which this can or must be done may be governed by national or local regulations.

As illustrated in fig. 1 the filter device 18, the first pipe arrangement 20 and the second pipe arrangement 30 are configured so that the waste water has to pass through the filter device 18 in order to get from the first area 14 to the second area 16.

In the embodiment in fig. 1 both the first area 14 and the second area 16 are provided in the main chamber 12.

Fig. 1 shows that the outlet 21 is placed at a height lower than the inlet 31 in the container device 10. This means that the first area 14 is lower in the main chamber 12 than the second area 16. The arrows in fig. 1 , which indicate the direction of flow of the waste water through the after-treatment system 1 , show that the direction of flow of the waste water through the filter device 18 is substantially upwardly directed from the first area 14 to the second area 16.

By configuring the after-treatment system in this manner, the additional object is achieved that the filter device 18 is continuously submerged in the waste water. This can be an advantage for some types of filter devices, since their effect may be substantially reduced if they become dry after having been submerged in water or exposed to moisture in another way.

Thus it is the filter device 18 which divides the main chamber 12 into the first area 14 and the second area 16. Fig. 1 illustrates that the volume of the first area of the main chamber 12 is greater than the second area 14 of the main chamber 12.

The outlet 21 in the first pipe arrangement 20 comprises a plurality of smaller openings 22 for distributing the waste water to the filter device 18 in the main chamber 12. In the embodiment in fig. 1 the pipe arrangement 20 comprises a pipe provided along the bottom of the main chamber 12, where the outlet 21 is provided as perforations or openings 22 in this pipe. Alternatively, the pipe arrangement 20 may comprise several such perforated pipes beside one another in order to further distribute the waste water to the filter device 18.

In order to achieve the desired effect, the residence time T for the waste water in the main chamber 12 should be greater than 20 hours, thereby giving the waste water a pH > 10. Since the filter device 18 is provided in the main chamber 12, the result is that the residence time T for the waste water in the filter device 18 also becomes greater than 20 hours.

When the waste water obtains a pH > 10, the result is that the environment in the after-treatment system 1 becomes such that the amount of bacteria is reduced.

Furthermore, phosphorus will be precipitated and the amount of phosphorus in the water will be reduced. A further benefit is that the amount of virus in the water will be reduced.

The residence time T can be achieved by determining the size of the after-treatment system according to the expected amount of waste water per time unit.

Alternatively, the residence time T may be controlled by means of a controllable valve in the first pipe arrangement 20, with the result that only a specific amount of waste water is permitted into the main chamber 20 per time unit. In such cases a measuring device and a control unit should be connected to the controllable valve for control thereof. Alternatively, a buffer tank may be provided between the treatment plant and the after-treatment system 1 in order to ensure that the residence time T is long enough. In this case a controllable pump device may be employed for controlling the residence time T for the waste water in the main chamber 12. In this case too a measuring device and a control unit should be employed for controlling the controllable pump device.

It should be noted that the filter device 18 in fig. 1 is replaceable. Solid materials entering the after-treatment system 1 and passing the filter device 18 will fall down as sediment in the main chamber 12.

We now refer to fig 2, which illustrates a second embodiment of an after-treatment system 1 for after-treatment of waste water from a treatment plant. The same reference numerals are used for the same elements as in fig. 1 , and only the differences between figs. 1 and 2 will be described in detail here.

In fig. 2 the container device 10 comprises two chambers, the main chamber 12 and a sedimentation chamber 42. The main chamber 12 and the sedimentation chamber 42 are separated by means of a wall 43, where the upper end of the wall 43 forms a threshold 44. The waste water will therefore flow from the main chamber 12 over the threshold 44 to the sedimentation chamber 42. The inlet 31 for the second pipe arrangement 30 is provided in the sedimentation chamber 42.

Solid materials entering the after-treatment system 1 and passing the filter device 18 will fall down as sediment in the sedimentation chamber 42.

In this embodiment the first area 14 where the water flows out of the outlet 21 is also arranged under the filter device 18, and the water flows in an upward direction in order to get through the filter to the second area 16. The second area 16 may be considered here to be upper parts of both the main chamber 12 and the

sedimentation chamber 42.

Alternatively, water may flow from the main chamber 12 to the sedimentation chamber 42 through an opening in the wall 43. Such an opening is preferably placed in the upper part of the wall 43. The object is to avoid a flow pattern in the after- treatment system 1 which will result in a very long residence time for one volume of waste water, while another volume of waste water spends too short a residence time in the after-treatment system 1.

We now refer to fig. 3, which illustrates a third embodiment of an after-treatment system 1 for after-treatment of waste water from a treatment plant. The same reference numerals are employed for the same elements as in fig. 1 and only the differences between fig. 3 and fig. 1 will be described in detail here.

In fig. 3 the container device 10 comprises one chamber, the main chamber 12.

In this embodiment the outlet 21 is in the form of a substantially upwardly directed spear 23. The filter device 18 comprises a perforated membrane or bag 40 filled with filter mass 41. The filter device 18 can therefore be lowered down over the spear-shaped end of the pipe arrangement 20, thereby penetrating the bag 40. The openings 22 forming the outlet 21 of the pipe arrangement 20 are provided in such a manner that they land in a central area inside the filter device 18. The interior of the bag therefore forms the first area 14. Consequently the waste water here also has to pass through the filter in order to get from the first area 14 to the second area 16.

In this embodiment the lid of the container 10 is removable or it can be opened in a simple manner for access to the main chamber 12. The bag 40 may comprise a fastening device 42 for fastening to a lifting device in order to simplify the task of lifting the bag 40 in and out of the main chamber 12. A simple method is

consequently achieved for replacing the filter device.

An after-treatment system 1 as illustrated in fig. 1 has been tested together with several treatment plants. Water samples were taken of the after-treated waste water discharged from the second pipe arrangement 30.

The table below shows the results of the water tests. The maximum permitted TBK content in waste water is 1000 per 100ml. The maximum permitted phosphorus content in waste water is 1 mg/1. The treatment plants together with which the after- treatment system 1 was tested had TBK and phosphorus content for their outlets approximately at these maximum permitted levels.

Table 1 : Water samples of after-treated waste water.

The water samples show that when an after-treatment system according to the invention is employed, the result is achieved that the TBK content and the phosphorus content of the waste water are reduced to far below the maximum permitted levels.