WO2008148942A1

WO2008148942A1 - Process tank of small sewage treatment plant

Info

Publication number: WO2008148942A1
Application number: PCT/FI2008/050341
Authority: WO
Inventors: Pekka Koskelo
Original assignee: Ecolator Finland Oy
Priority date: 2007-06-07
Filing date: 2008-06-09
Publication date: 2008-12-11

Abstract

A process tank of a small, sewage treatment plant which process tank essentially consists of a well part (1) and a cover (2), is characterized in that operating and control devices (6, 15, 18, 21, 32, 34, 37) of the process tank are integrated with and/or suspended on the cover (2) and the well part (1) is generally formed to contract towards the bottom, at the mouth (42) without any contraction opening and in the inside completely open and unobstructed, whereby the well parts (1) may be packed one inside the other for saving space in transport and storage.

Description

PROCESS TANK OF SMALL SEWAGE TREATMENT PLANT

FIELD OF THE INVENTION

The invention is related to a process tank of a small sewage treatment plant.

BACKGROUND OF THE INVENTION

Small sewage treatment plants are applied for cleaning wastewater in areas of dispersed settlement. A small sewage treatment plant cleans typically the wastewater of one or a few residential houses and is dimensioned according to the amount of residents producing wastewater so that small sewage treatment plants are generally dimensioned for wastewater of 5, 10, 15, 20 or 25 persons.

The invention is primarily related to a batch type small sewage treatment plant the central part of which is a process tank. In batch type cleaning, wastewater gathered in a gathering well or tank is charged at certain times, e.g. once, twice or tree times in a day, to the process tank in which a controlled cleaning process is run through, after which the cleaned water is led off from the process tank. The same is repeated in due course for the next wastewater batch and so on.

In addition to the charging of the process tank and the removal of the cleaned water, basic functions of the cleaning process include aeration, dosing and addition of the flocculation chemicals to the wastewater to be cleaned, settling and recirculation or removal of the sludge gathered in the process tank. For aeration, a controlled compressor and a membrane plate or equivalent device for producing bubbles from pressurized air are needed. For feeding the flocculation chemical, a flocculation chemical container and a controlled dosing pump are needed. Additionally, a controlled pump is needed in the tank for the removal of the cleaned water and another Controlled pump for the recurrent removal of the sludge gathered on the bottom of the tank. Also the charging of the tank, which is made by means of a pump or equivalent device placed in the septic tank or gathering well or equivalent, is controlled by means of the same control arrangement which controls the cleaning process. Furthermore, a fluid level detector or equivalent device is needed in the process tank by means of which it is assured that the level of the water in the tank is not rising too high.

A general way of realizing the process tank of a small sewage treatment plant seems to be such that an expanded round or horizontally extending cylindrical tank space is combined with a thin neck extending to the ground surface, the opening of said neck being closed by a hatch. In some cases, on the other hand, the process tanks are solutions including several parts, various functions being placed in the separate parts of the tank. In many solutions,

i operating devices have been placed in the neck part or the upper part of the tank which is kept empty in the process. It is also known to put operating devices in a separate box which includes an electrical and control unit.

In view of the use of a small sewage treatment plant it is very important that as little maintenance as possible is needed, and if needed, the maintenance should be as easy as possible.

It seems also that the planning of the process tanks of small sewage treatment plants in the market has taken very little into account that the tanks would be also advantageous in view of transport and storage. In view of the manufacture and delivery to customers it would also be desirable that the plants made for different capacities include as many common parts as possible.

SUMMARY OF THE INVENTION

An object of the invention is to present such a process tank of a small sewage treatment plant which realizes the above desires and advantages set for small sewage treatment plants better than the known solutions.

To achieve this object, a process tank of a small sewage treatment plant according to the invention which essentially consists of a well part and a cover is characterized in that which is defined in the characterizing part of the independent claim 1. Other claims define some advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in further detail in the following with reference to the accompanying drawings, in which: Fig. 1 presents schematically in side view a possible realization of a cover of a process tank according to the invention and a well part with which the cover forms the process tank; Fig. 2 presents schematically in side view a process tank provided with the cover of Fig. 1 and including all the devices which are essential for the operation of the tank;

Figs. 3 and 4 present in further detail the realization of the cover of Fig. 1, and Fig. 3 is a section of Fig. 4 along line IH - DI;

Figs. 5 to 8 present the use of the cover according to the invention in various process tank solutions; and

Fig. 9 depicts the advantageousness of the process tank of Figs. 1 and 2 in view of the transport and storage of the tanks. DETAILED DESCRIPTION OF THE INVENTION

A process tank of Figs. 1, 2 and 9 consists essentially of a well part 1 and a cover 2. The well part 1 has a general form of a truncated cone provided with a bottom. An aim is to make the wall 39 of the well part as thin as possible in view of the manufacturing costs, and the construction is therefore strengthened by circular and vertical reinforcement structures 40 and 41 (Fig. 9). For attachment of an exhaust pipe, the well part comprises a stub 13 which is cut at a suitable point for either a larger or smaller exhaust pipe.

There is no contraction at the mouth of the well part but it is confined by the truncated edge 42 of the conically expanding wall. Below in Fig. 2 and in Fig. 9, the well part is presented as a simplified section cut in front of the reinforcement structure 41 so that the wall 39 is indicated by a thickened line. Inside the well part there is no additional walls or other structures. The diameter of the mouth opening may be e.g. of the order of 150 centimeters.

Accordingly, the well part in the solution of the invention is as simple as possible and completely open and unobstructed in the inside. It has been possible to concentrate the planning of the well part to the technical design of it in view of the advantageousness in the manufacture, transport and storage and, on the other hand, its functionality in the desired process. Due to the wide mouth opening and the downward tapering form, the well parts may be packed one inside the other, whereby the transport and storage costs are reduced essentially (Fig. 9). In view of the functionality of the process, an important detail is the round form of the bottom which promotes the circulation of water and at the same time sludge particles in the tank and so intensifies biological activities in the process.

In the following, the functions of the process tank of the invention are described with reference to Fig. 2 and at the same time a possible realization of the cover 2 with reference to Figs. 3 and 4.

In the solution of the invention, the following operating devices: a flocculation chemical container 37, a flocculation chemical pump 34 and a compressor 32, have been integrated in the cover. Also an electrical and control unit 6 has been combined with the cover, and the distribution of electricity and control connections pass through the cover. The electrical and control unit 6 comprises all the electrical and control means needed for the operation of the process tank and cleaning process: a main switch, fuses, relays and a computer controlling the operation. Additionally, all the devices to be placed in the well part have been suspended on the cover, and the cover is provided with a maintenance opening 24 through which the devices may be lifted up for maintenance at need and then lowered again down into the tank. The cover is comprised of a basic part 3 and an additional lid 4 by which the devices of the basic part are covered and shielded and which is set on the slightly recessed part 3' of the basic part. At the same time, the additional lid 4 closes the maintenance opening 24 in the basic part 3, and it is also possible to close the access to the devices and the tank itself by providing the additional lid with a lock (not presented). The basic part 3 of the cover has been dimensioned to be wide and thick enough, and inside it there remains a hollow space confined by the upper and lower walls of the cover and, respectively, the walls S of the openings and recesses, the space forming the flocculation chemical container. The cover is manufactured of e.g. polyethene plastic, and the thickness of the walls S may be e.g. of the order of 6 millimeters. The volume of the container may be e.g. 50 to 80 liters, and an aim is that it can take at one time the amount of chemical needed for one year. The filling opening of the container and the cap 28 are under the additional lid in a recess 27. The flocculation chemical may be e.g. a liquid flocculant based on ferric sulfate.

The flocculation chemical pump 34 (presented here only schematically) is placed in a recess 33. A suitable pump is e.g. so called hose pump which is designed especially for accurate dosage. The compressor 32 (presented here only schematically) is placed in a recess 31 comprising enough space for a more effective compressor at need. The compressor is a conventional device suitable for this kind of use, and its capacity may be e.g. within 2 to 5 m³/h. In connection with the recess 31 there is also a duct 30 through which necessary pipes and wires needed for power feed and control operations are led into the tank. The duct 30 is provided with a gasket 9 through which said pipes and wires are led. The electrical and control unit 6 is supported by means of a tube 7 on the recess 29 from which a groove 38 is led into the space 31, another groove 36 being led from it further on to the space 33. The grooves 38 and 36 are provided for pipes and wires. Additionally, a duct 25 is led through the basic part 3 for ventilation of the tank, an extension 26 of the duct coming above the basic part and a ventilation pipe 5 being connected to said extension and coming through the additional lid 4.

Fig. 2 presents in further detail other devices needed in the process tank. An aeration device suspended by means of a cord 16 on a lug 12 on the lower surface 8 of the cover is lowered down into a recess on the bottom of the tank, the aeration device comprising a weight 14 and a membrane plate or equivalent device 15 for forming fine bubbles from the air pumped by the compressor. A pipe 17 is led from the compressor to the aeration device through the duct 30 and the gasket 9.

An exhaust pump 18 is suspended by means of a cord 20 on a lug 10. The pump pumps the cleaned water into the exhaust pipe by means of a hose or pipe connected to it, which hose or pipe is not presented here but the removal is indicated by arrow P. Wires 18' feed electricity to the pump 18.

In connection with the pump 18 there is also a fluid level detector 19 the electrical and control wires of which are indicated by reference sign 19'. Sludge settled and gathered in the process tank is removed from time to time by a pump

21 suspended by a cord 22 on a lug 11. The removal is made e.g. back to the gathering tank or equivalent, and for that there is a hose or pipe led respectively from the pump, which hose or pipe is here indicated only by arrows L.

Via the duct 30 in the cover also electrical and control connections C are led into the gathering well, septic tank or equivalent which is in front of the process tank and into which the wastewater is conducted first for being pumped therefrom from time to time according to the control. The electrical and control connections C are needed both for controlling the pumping and the pumping itself and for monitoring the height of water in the gathering tank or equivalent. A pipe 23 comes from the flocculation chemical pump 34 via the groove 36 into the space 31 and from there through the duct e.g. some centimeters below the cover. In practice, the chemical pipe must be placed so that the corrosive chemical drops directly into the water and not on the pipes, wires or other devices.

The solution of integrating the operation devices in the cover of the process tank is as such very advantageous. It becomes more advantageous by realizing the cover so that the same cover may be used for a wide range of process tank capacities. The lower surface 8 of the basic part 3 of the cover 2 is formed especially for this purpose, and likewise the spaces for various devices in the cover have been dimensioned so that there are room also for more efficient devices at need. Figs. 5 to 8 depict the operation of the cover of the invention in this respect. Figs. 5 to 7 indicate how the cover 2 may be combined to operate with the well parts IA, IB and 1C dimensioned for various capacities.

Additionally, the cover 2 is dimensioned and designed so that it works also in renovation solutions in which an existing sewage well ID is used as a well for the process tank. As indicated by Fig. 2, the integration and suspension of the devices with and, respectively, on the cover cause that a process tank may be realized with essentially the same easiness when using an existing sewage well as the well part as when using the well part truly meant for this solution.

The invention is not restricted to the above examples. What is essential in the solution of the invention is on the other hand the integration and/or suspension of the operation and control devices with and, respectively, on the cover and, on the other hand, that the inside of the well part is completely open and unobstructed and the well part is at the mouth opening widely and without any contraction and designed so that the well parts may be packed one inside the other for saving space in transport and storage.

The invention may vary within the scope of the accompanying claims.

Claims

1. Process tank of a small sewage treatment plant which process tank essentially consists of a well part (1) and a cover (2), characterized in that: operating and control devices (6, 15, 18, 21, 32, 34, 37) of the process tank are integrated with and/or suspended on the cover (2); and the well part (1) is generally formed to contract towards the bottom, at the mouth (42) without any contraction opening and in the inside completely open and unobstructed, whereby the well parts (1) may be packed one inside the other for saving space in transport and storage.

2. Process tank of a small sewage treatment plant according to claim 1, characterized in that the well part (1) has a general form of a truncated cone provided with a bottom.

3. Process tank of a small sewage treatment plant according to claim 1, characterized in that the operating and control devices integrated with the cover (2) comprise a container (37) for flocculation chemical.

4. Process tank of a small sewage treatment plant according to claim 1, characterized in that the operating and control devices integrated with the cover (2) comprise a dosing pump (34) for flocculation chemical and means (23) for leading the chemical into the process tank.

5. Process tank of a small sewage treatment plant according to claim 1, characterized in that the operating and control devices integrated with the cover (2) comprise a compressor (32) for producing pressurized air and leading said air into the process tank for aeration.

6. Process tank of a small sewage treatment plant according to claim 1, characterized in that the operating and control devices integrated with the cover (2) comprise an electrical and control unit (6).

7. Process tank of a small sewage treatment plant according to claim 1, characterized in that the operating and control device (14, 15, 21, 18) placed in the tank is suspended (12, 16; 11, 22; 10, 20) on the cover so that the device may be lifted up and lowered down through a maintenance opening (24) in the coyer.

8. Process tank of a small sewage treatment plant according to claim 1, characterized in that the cover (2, 3) and its lower surface are dimensioned and designed so that the cover (2) is adapted for use with several various well parts (IA, IB, 1C, ID) for realizing a process tank.