EP1454019A1

EP1454019A1 - Method and plant for purification of water

Info

Publication number: EP1454019A1
Application number: EP01274690A
Authority: EP
Inventors: Robert Henriksen
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-11-15
Filing date: 2001-11-15
Publication date: 2004-09-08
Also published as: WO2003042465A1

Abstract

The invention provides a modular facility for purifying water, in particular sewage water from one or more residences in an area with dispersed buildings, the facility comprising a partly or completely buried container (20), the container comprising a number of tank sections (A,B,C) which are mutually connected, and that the container (20) at the top exhibits an opening (24) from which there is access to all tank sections (A,B,C), and where one tank section (C) is a pre-sedimentation, collection and equalising tank divided into two or more chambers, and that another tank section (A) is a process tank for batchwise biological treatment and that the facility has a separate sludge tank (B) only for storing excess sludge. The process performed in the facility corresponds to the purification cycle known from larger purification plants.

Description

METHOD AND PLANT FOR PURIFICATION OF WATER

Background of the invention.

The present invention concerns a facility for purifying water, in particular a mini purifying plant for biological purification of sewage water from one or more residences in an area with dispersed buildings, the facility comprising a number of completely or partly buried tank sections which are mutually connected by means of pump and process means and are provided with inlet and outlet pipes for supplying sewage water and discharging purified water, respectively.

Mini purifying facilities are used for biological purification of domestic sewage water from 5 to 30 population equivalents (P.E.) and are thus particularly suited for cleaning sewage water from one or more habitations in dispersed buildings in open land.

Today, mini purification plants for biological sewage water cleaning by bacterial de- composition are known in connection with one or more residences in an area with dispersed buildings. Prior art facilities comprise a container construction in which aeration and subsequent final sedimentation of the supplied sewage water, which is supplied to this container structure from a septic tank, such as double or triple chamber sedimentation tank, connected to the container, are performed. Mini purification plants of such kinds are known e.g. from DK utility model DK 96 00416 U4 and DK patent application no. 0865/96.

Both the facility container and the septic tank of the installation are buried, implying that process equipment fitted in the facility container may be difficult to supervise. The prior art mini purification plants presuppose that a separate septic tank is mounted in addition to the mini purification plant itself. Furthermore, the excess sludge from the biological process chamber is pumped back to the septic or sedimentation tank, a fact making it difficult to keep the strict cleaning requirements as recycling sludge to the receiving/sedimentation tank causes the efficiency and the purifying action of the facility to be drastically reduced. The prior art mini purification plants furthermore has the drawback that they are sensitive toward fluctuating loads. They are so-called through-flow plants where the cleaning effect varies with variations in the amount of supplied sewage water. Furthermore, they have a biological film acting by bacteriae placed on a large surface by which the water is led past, whereby biological purification occurs. If the mini purification plant is thus not supplied with sewage water in a period, such as a holiday period, there is, however, the risk that bacterial growth becomes strongly reduced or even becomes extinct, whereby the efficiency of the plant is drastically reduced.

From large purification plants processes are known for sewage water purification which is based on active sludge, as well as it is known to perform a batchwise treatment (SBR-technology) in such large purification plants. These plants consist of several process tanks where in each of the tanks different purification processes are performed. Before the process tank there is installed a receiving tank for the unclean sew- age water which functions both as coarse separator and as buffer in periods with extra great supply of unclean sewage water. This implies that the purifying effect of a SBR- plant is approximately constant, also in periods with very great sewage water loads.

From DK utility model no. DK 98 00135 U3 is known a mini purification plant based on SBR- technology where the sedimentation and the biological water purification is performed in one integrated unit. This plant is characterised in that the first chamber is a sedimentation chamber for pre-sedimenting and storing of excess sludge, that the second chamber is a pumping and equalising chamber for collecting drainage water during a cleaning cycle, and the third chamber is a process chamber, and that the water circulates between all three chambers in a circuit from chamber 1 to chamber 2 and further on to chamber 3.

From patent application PA 1999 01202 there is also known a mini purification plant based on SBR-technology, where the first tank section is a double or triple chamber sedimentation tank which is used for sedimenting the supplied unclean sewage water and for storing excess sludge from the process chamber. Also, in these plants the excess sludge is pumped from the biological process back to the septic or sedimentation tank, making it difficult to keep the strict purification requirements, as this reduces the cleaning effect of the plant.

The present invention indicates a modular mini purification facility for performing the biological purification process. The facility consists of several tank sections or facility containers for complete or part burying, which, unlike the prior art, is peculiar in that the basic module of the plant is a container consisting of two tank sections: a process tank in which the biological purification occurs, and a separate sludge tank which is only intended for storing excess sludge from the biological process tank. From here, the excess sludge may either be collected in a sludge drying unit or be removed by normal sludge emptying.

The construction is different from prior art plants by having a separate sludge storage so that the excess sludge is not conducted back to the sedimentation tank. This opti- mises the purifying effect and operational stability of the plant and leads to minimising the need of sludge emptying for the plant.

The tank for excess sludge may according to the invention be equipped with a sludge drying unit, e.g. by inserting a filter cartridge where the excess sludge may be dewa- tered. After that, the sludge may e.g. be composted, and the fertiliser value be utilised.

In the present invention, the facility has the advantage that it may be connected to existing sedimentation tanks where the existing sedimentation tank will then act as receiving tank from which the sewage water, by means of a mammoth pump or tradi- tional sewage water pump is pumped to the process tank, after which the biological purification process may be initiated. Decisive for the choice of pump type is the content of coarse impurities of the sewage water and the distance between the biological mini purification plant and the existing sedimentation tank. In such facility types it is necessary to install level sensors in the existing sedimentation tank which is connected to the programmable control unit associated with the facility.

In the present invention, allowance is made for cases where the existing sedimentation tank is old and obsolete and unwanted to use. Here, the facility may be provided in a further facility module, a so-called integrated facility, where the biological process tank and the separate sludge tank are integrated with a receiving tank. This receiving tank may either consist of one single, large chamber, or of several chambers, e.g. designed according to the conditions in the Danish guide for double or triple chamber sedimentation tanks, which then may serve as receiving chamber for the supplied sewage water.

Unlike other known mini purification plants for complete or part burying where only pre-sedimented sewage water without sludge from the sedimentation tank is pumped to the biological purification part, in the facility according to the invention both sewage water and sludge may be pumped into the process tank in which the biological purification process occurs. This has the advantage that the sedimentation tank may be emptied completely whereby anaerobic conditions are avoided and that the buffer capacity of the sedimentation tank is considerably increased. For this either a mammoth pump or a traditional sewage water pump may be utilised. Decisive for the choice of pump type is inter alia the content of coarser contaminants of the sewage water.

Hereby is achieved a compact mini purification facility that fulfils the norms and requirements according to law, which is easy to inspect, maintain and empty, and which is well suited for batchwise treatment of sewage water, as sewage water and sedi- mented sludge may be pumped to the desired tank sections for performing a purification cycle corresponding to the purification cycle known from larger purification plants. In the preferred embodiment of the invention of the integrated mini purification facility, the first tank section is a receiving tank constituting a combined sedimenting and buffer tank section, the second tank section is a process section for biological treatment of the sewage water, and the third tank section is a separate sludge storage place so that the excess sludge from the process tank is always retained and stored in a closed sludge storage place - and is not, like other mini purification plants for burying, are recycled to the sedimentation tank and thereby mixed with unpurified sewage wa- ter and sludge from the sedimentation tank. The separate sludge storage place according to the invention may possibly comprise means for disinfection/hygienisation. In the present invention, in the described facility module where the sedimentation tank is integrated in the mini purification facility, it will thus be possible to design the sedimentation tank according to the rules for sedimentation tanks in force at any time in any country. In Denmark, this means that the sedimentation tank may be designed according to the latest guide issued by the Environmental Authority concerning double and triple chamber sedimentation tanks. Therefore, the sedimentation tank in the embodiment with two chambers is adapted so that the first chamber constitutes about 70- 90% of the tank volume in the first tank section.

Alternatively, the sedimentation tank may include three chambers so that the first chamber constitutes about 50-70% of the tank volume in the first tank section, and that the remaining tank volume is equally distributed between the two other chambers. The chambers in the sedimentation tank in the container according to the invention may be provided by one or more partitioning walls from the centre line to the outer wall in the container. Alternatively, one of the chamber may be provided by a pipe, e.g. a corrugated pipe with suitable diameter. The partitioning walls between the individual chambers in the sedimentation tank are provided with through holes which at least have the same dimensions/area as the inlet pipe.

The facility according to the invention operates by an active sludge process which by batchwise treatment performs a bacterial decomposition of the sewage water. The facility is notable in that it may be buried in such a way that only the upper opening is accessible. Process, pump and stirring means interact with control means, such as a programmable control unit for regulating and transporting sewage water and excess sludge in the tank sections and for discharging the purified sewage water. In the preferred embodiment, all process, pump and stirring means are arranged readily accessible under the opening of the container which may be covered by a cover. With this arrangement, process, pump and stirring means and overflow pipes together with possible sensors and the like are all disposed in such a way that they may be inspected and serviced, including dismounted one by one through the opening in the aperture of the container. Also, all tank section are supervised through the opening in the container, which means that it is possible to supervise the efficiency of the mini purification plant according to the invention while the facility is operating. The system is preferably rotationally symmetric, and the tank sections in the integrated mini purification plant module are separated by wall elements, where two of the wall elements are made in one wall plate, and that this, or the other wall elements, is arranged so that the wall elements extend about from the centre line of the container to the container wall. In a preferred embodiment, the container is approximately cylindri- cally shaped, which is a particularly simple shape in connection with manufacture, transport and installation. Furthermore, the container may be substantially cylindri- cally shaped and provided at the bottom with a buoyancy safety device upon which e.g. a reinforced concrete plate is poured with dimensions for the actual buoyancy calculation. Hereby possible buoyancy of the buried container is counteracted.

In the following, the invention is described more closely with reference to the accompanying drawing material, where:

Fig. 1 shows the basic module of the mini purification facility system viewed from above, Fig. 2 show a top view of the integrated module of the mini purification facility, Fig. 3 shows the basic module of Fig. 1 in sectional view I-I, Fig. 4 shows the integrated module of Fig. 2 in sectional view II-II,

Fig. 5 a shows the integrated module of the mini purification facility as seen from above, consisting of only one large receiving tank C, Fig. 5b shows the integrated module of the mini purification facility as seen from above, consisting of a receiving tank C with a wall element 27, Fig. 5c shows an embodiment with three separate tank sections installed,

Fig. 5d shows an alternative embodiment, Fig. 5e shows an alternative embodiment, Fig. 6 and 7 shows two embodiments of a facility with a triple chamber sedimentation tank.

Fig. 1 shows the arrangement of the basic module A + B of the biological mini purification facility according to the invention which is intended for connection to already existing sedimentation tanks. The basic facility module A + B consists of a container 20 which is divided into two tank sections A and B at the wall element 21.

Fig. 2 shows the arranging of a further module, the integrated module of the mini puri- fication facility according to the invention. The basic module A+B is here enlarged with an integrated receiving and sedimentation tank C exhibiting a volume which is about the same as that of the two tank sections A + B of the basic module. The tank section C is separated from the basic module A + B by wall elements 22 and 23. The tank section C is divided into at least two chambers, and between the two chambers there are at least one through hole, the dimension of which has at least the same size as the inlet pipe 10.

In the tank section C, the second chamber 25 on Fig. 2 is shown as an inlet pipe with minimum 10% and maximum 30 % of the total volume of tank section C. The volume of the second chamber may be regulated by suitable choice and diameter of the inserted pipe 25 or by inserting a further wall element 27 as shown on Fig. 5b.

In an alternative embodiment, the tank section C may only consist of a large compartment as shown on Fig. 5 a.

In other versions, the embodiment may be either three separate tank sections as shown on Fig. 5c, or alternative embodiment as shown on Figs. 5d and 5e.

Subsequently, the function of basic module A+B of the biological mini purification facility intended for installation after already existing sedimentation tanks is described. Prior to connecting basic module A + B, it is necessary that level sensors or pressure sensors are installed in the existing sedimentation tank.

When these level sensors or pressure sensors are actuated, pulses are sent to the pro- grammable control unit of the facility, after which the sewage water, either by means of mammoth or sewage pump, is pumped to the basic module Fig. 1 of the mini purification facility through the inlet 10 of the facility into the biological process tank A. When the process tank is filled, a previously programmed amount of sewage water is furthermore pumped into the process tank A, whereby floating objects, contaminants and floating sludge runs back through the return pipe 11 and back to the sedimentation tank, after which the aerating pump 6 is activated and the biological purification process is initiated in the process tank A by the sewage water being aerated in a pre- programmed period of time. Hereby, the bacterial decomposition process is accelerated which is taking place as a consequence of the active part of active sludge which is always occurring in tank section A after a purifying cycle.

If the mini purification facility is installed in an area where there is need for adding chemicals and therefore has both biological/chemical purification for keeping more stringent purification requirements, the facility may be equipped with chemical sedimentation functioning by the programmable control unit activating a dosing pump after which chemicals are introduced from the chemicals container 16 in the facility. Subsequently, the programmable control unit activates the aerating pump 6 for stirring the added chemicals in the process tank A.

After finished aeration and stirring, the programmable control unit provides for calm in the process tank A, after which the biological sludge is sedimented.

After the finishing of the purification process, the purified water is pumped by means of the outlet pump 2 through the outlet pipe 14 to the recipient.

In the container, a little amount of purified sewage water from the last discharging to recipient is retained for monitoring the discharged water 15, so that the purifying ef- feet of the facility may be controlled at any time.

The sedimented excess sludge is pumped over into the sludge tank B by means of the sludge pump 3, where the excess sludge is sedimented and stored. The surplus water runs back via the return pipe 12 and back to the sedimentation tank.

The process tank A then changes to pause function until the level sensors in the sedimentation tank indicates via the programmable control unit that there is sufficient sewage water again in order that a new purification cycle may be commenced. During this this pause function, the process tank A is pulse aerated for keeping the bacteriae active until the next purification cycle is commenced.

As a further safeguard, the biological mini purification facility is equipped with an overflow pipe 13 which, in case the facility is overloaded or due to prolonged power failure or by other defects in the facility, allows the water to be led out through the outlet pipe 14 without biological purification. A pressure sensor 9 for high level in the process tank will simultaneously activate the alarm of the facility.

Subsequently, the function of the integrated module of the biological mini purification facility shown in Fig. 2, intended for installation without already existing sedimentation tank, is described, as this facility module has the sedimentation tank C which is an integrated unit.

The sewage water runs into the facility through the inlet pipe 10 to the double chamber sedimentation tank C of the facility, into the first chamber and subsequently into the second chamber 25, wherefrom the sewage water, by means of the pump 1, is pumped into the biological process tank A. When the process tank is filled, a further amount of sewage water is pumped into the process tank A, if necessary, whereby contaminants and surface sludge returns through the return pipe 11 back to the sedimentation tank C, after which the aerating pump 6 is activated and the biological purification process is initiated in the process tank A by the sewage water being aerated in a pre-programmed period of time. Hereby, the bacterial decomposition process, which is taking place as a consequence of active part of active sludge which is always occur- ring in tank section A after a purifying cycle, is accelerated.

If the mini purification facility is installed in an area where there is need for keeping more stringent purification requirements, the facility may be equipped with chemical sedimentation functioning by the programmable control unit activating a dosing pump after which chemicals are introduced from the chemicals container 16 in the facility. Subsequently, the programmable control unit activates the aerating pump 6 for stirring the added chemicals in the process tank A. After finished aeration and stirring, the programmable control unit provides for calm in the process tank A, after which the biological sludge is sedimented.

In the container, a little amount of purified sewage water from the last discharging to recipient is retained for monitoring the discharged water 15, so that the purifying effect of the facility may be controlled at any time.

The sedimented excess sludge is pumped over into the sludge tank B by means of the sludge pump 3, where the excess sludge is sedimented and stored. The surplus water runs back via the return pipe 12 and back to the sedimentation tank C.

The process tank A then changes to pause function until the level sensor 8 in the sedimentation tank C indicates via the programmable control unit that there is sufficient sewage water again in order that a new purification cycle may be commenced. During this pause function, the process tank A is pulse aerated for keeping the bacteriae active until the next purification cycle is commenced.

All pump and process means 1-9 are arranged centrally in the container 20 immediately under the centre positioned cover and opening 24. In Figs. 3 and 4, the facility according to the invention is shown rotationally symmetric. However, the facility may have other designs without departing from the inventive principle.

All pump and process means 1-9 are connected to an not shown control unit specified for the process, such a programmable computer control developed for the facility, or a traditional PLC-control so that the process in the facility may be regulated and adapted to the operational and functional demands required at any time. The container is, as shown in Figs. 3 and 4, provided with a relatively long cylindrical pipe 28 in connection with cover and opening 24. This implies that the container may be made with a riser tube 28 with cover and the opening 24, the length of which may be adjusted according to the burying depth and/or how far it is desired for the opening 24 to protrude up over the ground surface.

At the bottom, the container 20 is provided with an annular buoyancy safety flange 26 on which there may be poured e.g. a reinforced concrete plate which is dimensioned for the actual buoyancy calculation. Hereby the container 20 is provided sufficient weight in order to prevent tendencies of buoyancy, particularly when the container is empty or only filled to a small extent.

As shown in Figs. 6 and 7, the sedimentation tank in the first tank section may alternatively be divided into three chambers I_a, I_b, I₀. The first chamber I_a here constitutes minimum 50%, preferably 50-70%. The partitioning may either be as shown in Fig. 6 with two partitioning walls 17, or, as shown in fig. 7, as a combination of a partitioning wall 17 and a pipe 18. The single chambers in the sedimentation tank C are con- nected with through-going holes.

The number of chambers in the sedimentation tank is determined in relation to the tank capacity so that it, inter alia in case of large capacity, is easy to empty and inspect the tank.

At the same time, the first tank section C may furthermore be used alone, i.e. without putting the other tank sections into use. Hereby one may provide and use the facility according to the invention as a usual septic tank/sedimentation tank, after which one may later upgrade it to a biological/chemical mini purification plant.

A test plant installed in connection with the development of the invention shows purification results that are significantly below the figures expected in other known plants, and values substantially (up to 250 times) below the values required by the Danish Environmental Authority. This is illustrated in the table below:

SOP Strict Organic Phosphorus

SO Strict Organic

OP Organic Phosphorus

O Organic

1. according to DS/R 254 (EN 1899-1)

2. according to DS 224

3. according to DS 292 In a further embodiment of the invention, the container 15 is divided into two chambers. In a first chamber, means e.g. in the shape of vertical tubes are arranged, or alternatively a screw. When the sewage water specimen is led into the container 15, the first water (5-15 1) will be caught and retained in the tubes, after which the succeeding water will land in the second chamber from which a purification specimen may be taken. The water from which the purification specimen is taken is thus more representative for the purifying effect as possible sedimented sludge or other remains in the supply tubes from the process chamber will be caught in the first chamber.

After finishing taking specimens, the water is conducted from the container 15 back into the process chamber, and a new specimen may be led into the container, and a subsequent specimen may be taken.

DESCRIPTION OF COMPONENTS

1. Inlet pump - (with basic module, pump is installed in receiving tank - mammoth or common sewage pump pumping to process tank) 2. Outlet pump - mammoth

3. Sludge pump - mammoth

4. Stirring pump for sludge tank - aeration

5. Stirring pump receiving tank (poss. septic tank) - aeration

6. Aerating pump - oxidation in process tank - stirring of chemicals 7. Pressure sensor - process tank full

8. Pressure sensor - start pumping into the unit (with basic module level regulation in external sedimentation tank)

9. Pressure sensor - alarm high level

10. Inlet pipe/pumping pipe in the facility with external sedimentation tank 11. Return pipe from process tank

12. Return pipe from sludge storage place

13. Overflow pipe - overload - or power failure

14. Outlet pipe - purified water to recipient

15. Container for controlling discharged water (to recipient) 16. Container for chemicals

20. Container - container opening

21. Wall element

22. Wall element

23. Wall element 24. Cover

25. Inserted pipe - chamber 2 in sedimentation tank

26. Buoyancy safety flange

27. Extra wall element

28. Riser tube of container 30. Filter cartridge for sludge drying unit for dewatering excess sludge

Claims

1. A facility for purifying water, in particular a mini purifying plant for biological purification of sewage water from one or more residences in an area with dispersed buildings, the facility comprising a number of completely or partly buried tank sections (A,B,C) which are mutually connected by means of pump and process means (1- 9) and are provided with inlet and outlet pipes for supplying sewage water and discharging purified water, respectively, and that one or more of the tank sections are arranged in a container (20) which at the top exhibits an opening (24) from which there is access to all tank sections (A,B,C) in the container (20), and where at least one of the completely or partly buried tank sections constitutes a separate sludge storing place, and that the tank section (C) of the facility functions as pre-sedimentation, equalisation and buffer tank.

2. A facility according to claim 1, characterised in that the sedimentation tank

(C) comprises two chambers of which the first chamber constitutes about 70-90% of the tank volume in the first tank section.

3. A facility according to claim 1, characterised in that the sedimentation tank (C) comprises three chambers, where the first chamber constitutes about 50-70% of the tank volume in the first tank section, and that the remaining tank volume is evenly distributed between the two other chambers.

4. A facility according to claim 1 to 4, characterised in that the pump and process means comprise aerating and stirring means (4,5,6) and pump means (1,2,3) and level sensors (7,8,9) which interact with control means, such as a programmable control unit for controlling the processes between the tank sections (A,B,C) for batch- wise treatment of sewage water and sludge.

5. A facility according to claim 4, characterised in that the pump means mainly consist of mammoth pumps (1,2,3) and that all mechanical components except possible sewage water pumps are arranged in a cabinet above ground level.

6. A facility according to any preceding claim, characterised in that the sedimentation tank (C) is equipped with stirring and aerating pump (5) so that both nitrification and denitrification can be performed for initiating the biological purification process in the sedimentation tank (C).

7. A facility according to claim 6, characterised in that chemicals may be added and simultaneously stirred in the sedimentation tank (C).

8. A facility according to any preceding claim, characterised in that tank section (A) is a process tank for pumping in, aerating, sedimenting, pumping out of excess sludge to sludge storage in tank section (B) and pumping out of purified water to recipient through the outlet (14).

9. A facility according to claim 1, characterised in that the container (20) lowermost is provided with a buoyancy safety flange (26) for use in counteracting undesired buoyancy of container (20), such as an aimular weight arranged on the buoyancy safety flange (26).

10. A method for cleaning water, particularly for biological purification of sewage water from one or more residences in an area with dispersed buildings, the method comprising a process tank (A) in which the biological purification occurs, and a separate sludge tank (B) in which excess sludge from the biological process tank (A) may be stored and where pulse aeration may be performed with an aerating pump (4).

11. A method according to claim 9, where the excess sludge is dewatered with a sludge drying unit in the sludge tank (B).