EP0738354B1

EP0738354B1 - Method and apparatus for sewage treatment

Info

Publication number: EP0738354B1
Application number: EP95906584A
Authority: EP
Inventors: Andreas Schelin
Original assignee: VA TEKNIK I BORAS AB
Current assignee: VA TEKNIK I BORAS AB
Priority date: 1994-01-13
Filing date: 1995-01-13
Publication date: 1997-09-17
Anticipated expiration: 2015-01-13
Also published as: SE9400067D0; SE501160C2; AU1469795A; SE9400067L; DE69500734D1; WO1995019471A1; EP0738354A1; ATE158367T1

Abstract

The apparatus comprises a flow passage (10) and a conveyor (14) extending across the flow passage at the bottom thereof. Immediately downstream of the conveyor there are provided flow blocking means (16). Screen means (18) associated with the blocking means are provided with stripper means for cleaning the screen means. According to the method sewage is flown along the flow passage and the flow is blocked under whirling adjacent the bottom of the flow passage over the conveyor and is forced to flow upwards towards the screen means to continue along the flow passage after having passed the screen means. Heavy trash in the sewage is left on the conveyor while light trash is carried onto the screen means to be collected on the inlet side thereof. The collected trash is stripped from the screen means and supplied to the conveyor.

Description

The present invention relates to a method for sewage treatment, wherein the sewage is flown along a substantially linear flow passage to pass through screen means in the flow passage and to continue along the flow passage after having passed said screen means.
The invention also relates to an apparatus for sewage treatment, including a substantially linear flow passage for the sewage, and screen means in said pasage for continued flow of the sewage in the flow passage after having passed through said screen means.
Method and apparatus of this type are disclosed in WO-A-92/21824.
It is common, e.g. in sewage treatment plants, to separate coarse trash from the waste by means of a screen while gravel and sand is allowed to continue with the sewage into the sewage treatment plant to be separated therein by means of aerated grit chambers. This technique involving a two-step separation is disadvantageous because gravel and sand causes great wear on the screen as well as other devices provided in the sewage treatment system such as pumps and valves.
The object of the invention is to eliminate this disadvantage and to separate gravel and sand as well as other heavy trash from the sewage flow at an early stage of the sewage treatment, and in accordance therewith the invention provides a method for sewage treatment wherein the sewage is flown along a substantially linear flow passage, the sewage flow is blocked under whirling adjacent the bottom of said flow passage over a conveyor extending across the flow passage, and is forced to flow upwards towards screen means in the flow passage to continue along the flow passage after having passed said screen means, heavy trash in the sewage being left on the conveyor while light trash is carried onto said screen means to be collected on the inlet side thereof, and trash collected on said screen means is stripped from the screen means and supplied to the conveyor to be conveyed from the flow passage together with said heavy trash.
In the method as proposed according to the invention gravel and sand as heavy trash in the sewage will be separated from the waste at an initial stage of the waste treatment viz from the whirling sewage over the conveyor. The separation of trash including heavy and light trash will be effected in a single stage before the sewage is further processed in the sewage treatment plant. This means that maintenance of the plant will be cheaper due to less wear by gravel and sand and that the investments for sewage treatment can be reduced since no aerated sand traps are necessary.
The invention also provides an apparatus for sewage treatment comprising a substantially linear flow passage for the sewage, a conveyor extending across the flow passage at the bottom thereof, means immediately downstream of the conveyor for blocking the sewage flow under whirling adjacent the bottom of the flow passage over the conveyor for depositing heavy trash in the sewage on the conveyor and for re-direction of the flow onto screen means associated with said blocking means, for continued flow of the sewage in the flow passage after having passed through said screen means, and stripper means for stripping trash from said screen means at the inlet side thereof and transfer of said trash to the conveyor.
According to the invention there is also provided stripper means constructed to move the trash mat formed on the screen means by trash collected thereon, stepwise along the screen means towards said conveyor, a flow passage through the screen means for the sewage then being uncovered at the trailing end of the trash mat. Preferably, the screen means is sloping in the flow direction of the sewage from an upper end adjacent the surface of the flow towards a lower end closer to the bottom of the flow passage so that the trash mat is displaced downwards in the direction of the conveyor and the opening uncovered in the screen at the trailing end of the trash mat is close to the surface of the sewage flow where the content of trash in the flow is at minimum. By this arrangement the content of trash in the sewage flow from the screen means into the sewage treatement plant will be very low as compared with the conditions in sewage treatement systems including screen means wich are cleared by stripping collected trash therefrom upwards in the direction of the surface of the flow.
An illustrative embodiment of the invention will be described below in more detail reference being made to the accompanying drawings in which

FIG. 1 is a longitudinal cross sectional view of one embodiment of the apparatus according to the invention,
FIG. 2 is a plan view of the apparatus in FIG. 1,
FIGS. 3 and 4 are fragmentary side views of the screen and stripper means in two different operational positions of the stripper means, and
FIG. 5 is a fragmentary front view, partly a cross sectional view, of the stripper means.

With reference to FIGS. 1 and 2 there is shown therein a passage 10 for a sewage flow passing through said passage in the direction indicated by an arrow 11. The bottom 12 of the sewage flow passage forms a depression 13 extending transversely across the bottom, and in said depression there is provided a screw conveyor 14 connected to an electric or hydraulic drive motor (not shown) for the operation thereof. Conveyor 14 connects at the discharge end thereof to a screw conveyor 15 externally of flow passage 10 for transporting material forwarded to conveyor 15 from conveyor 14 to external collection means. Also conveyor 15 is connected to an electric or hydraulic motor (not shown) for the operation thereof.
Immediately downstream of conveyor 14 there is provided in flow passage 10 a blocking wall 16 extending over the entire width of the flow passage axially of conveyor 14 and merging by a curved portion 16A into a substantially horizontal portion 16B over conveyor 14 and spaced therefrom.
In the sewage flow passage 10 there is mounted an inclined framework 17 mounting a screen 18. This screen comprises a plurality of flat bars 19 mounted in parallel mutually spaced, FIG 5.
Framework 17 includes two channeled guide rails 20 spaced in the transverse direction of flow passage 10, and in each of these guide rails there is displaceably guided a slide 21 which can be displaced in the longitudinal direction of the guide rail. On each slide two bell cranks including a lever arm 22 and a lever arm 23 are mounted by means of transverse shafts 24. Arms 22 at each side are interconnected by a link 25 and these arms are also connected by a link 26 to a crank 27 rotatably mounted in the framework and connected to an electric or hydraulic drive motor 30 (shown in Fig. 2 only) over suitable gearing for the rotation thereof. Each arm 23 is pivotally connected to a bar 31, and each pair of these bars located opposite to each other on opposite sides of framework 17 are interconnected by a cross bar 32. With reference to FIG. 5 each cross bar is provided with flat irons 33 which are uniformly spaced in the transverse direction thereof to be located in the space between flat irons 19 in parallel therewith. Some or all of flat irons 33 have saw-toothed barbs 34 spaced along the edge thereof, which have the sloping flank facing away from conveyor 14. On bars 31 of one pair of such bars there is fixedly mounted a flange 35 forming a rectangular notch 36, and an abutment 37 fixedly mounted to the associated slide 21 is received by notch 36.
In the apparatus described the method of the invention is practised as follows:
Flow of sewage through flow passage 10 in the direction of arrow 11 and containing trash of different densities will be blocked by element 16 adjacent the bottom 12 of the flow passage. A whirling motion will be imparted to the blocked sewage flow above conveyor 14 and trash which is heavier than water and moves with the sewage along bottom 12 will be separated from the sewage and will be deposited on conveyor 14 so as to be conveyed out from flow passage 10 by conveyor 14 and externally of the flow passage be transported to suitable collector means by conveyor 15. The blocked sewage flow will be re-directed and imparted a flow direction, arrow 11', reversed substantially 180° in relation to the incoming sewage flow and will be directed towards and along screen 18. This sewage flow will pass through the screen and will then continue to flow along flow passage 10. Trash that is lighter than water such as paper, rags, leaves, plant parts etc will be carried along the screen 18 and will be trapped by the screen when the sewage is passing therethrough to form a trash mat on the inlet side thereof. This mat is indicated by a dot-and-dash line 38 in FIGS. 3 and 4. The mat of collected trash on the screen will form a filter for the sewage passing through the screen, and as the thickness of the trash mat is increasing the resistance against flow through the screen will increase. Increasing flow resistance will cause a higher level of sewage at the upstream side of the screen than on the downstream side. It may be assumed that the upstream sewage level is at the dot-and-dash line 39 in FIG. 1 and that the downstream sewage level is at the dot-and-dash line 40 in FIG. 1 and that level 39 represents the highest level that can be permitted in flow passage 10. When this level has been reached it is necessary to clear screen 18 in order to reduce the flow resistance thereof and to allow an increased flow through the screen. At this level motor 30 is energized in order to rotate cranks 27, and this rotation will be transformed to a reciprocating movement of flat irons 33 which form stripper means for cleaning screen 18.
With reference to Figs. 3 and 4 when link 26 is moving in the direction of arrow 41, FIG. 3, bell cranks 22, 23 will initially be pivoted counter-clockwise as seen in FIG. 3. Then flange 35 will be engaged with abutment 37 at the upper side thereof at 42 during downward movement of bars 31 and the flat irons 33 to a position in which at least the barbs 34 are below the lower edges of the flat irons 19 of screen 18 as shown in FIG. 3. Mat 38 will be engaged by barbs 34, and at continued movement of link 26 in the direction of arrow 41 the slides 21 will be displaced along guide rails 20 and irons 33 will be displaced along irons 19. The trash mat 38 will be carried along in this movement so that the trash mat will be slid along irons 19 towards conveyor 14.
When the moving direction of link 26 is reversed and will take place in the direction of arrow 43 in FIG. 4 crank bells 22, 23 initially will be pivoted clockwise, which means that flange 35 will be engaged with abutment 37 at the lower side thereof at 44 as is shown in FIG. 4. By this movement barbs 34 will be withdrawn from trash mat 38 to a position in which barbs 34 are located above the lower edge of irons 19 as is also shown in FIG. 4. Then slides 21 and irons 33 will be displaced along irons 19 in the direction of arrow 43 but due to the fact that barbs 34 are disengaged from trash mat 38 this will remain stationary during this stroke of irons 33 which is thus an idle stroke.
In order to secure the initial pivoting of bell cranks 22, 23 in the stripper means when actuated upon by links 26 in one direction or the other there should exist a certain degree of resistance (friction) against displacement of slides 21, which is not overcome until the bell cranks have been pivoted and flange 35 has been engaged with abutment 37 at the upper and lower side thereof at 42 and 44, respectively. This resistance can be provided by means of guide rails 20 which can have an adjustable spacing in the transverse direction of flow passage 10 to be tightened more or less against the unit moving between the rails.
The movements described will be repeated as long as motor 30 is energized, and as will be understood the trash mat will be moved stepwise downwards in the direction of conveyor 14 and will fall down on this conveyor because the trash mat will be heavier than water due to sand and other small heavy particles having been trapped therein.
When the trash mat is moving towards conveyor 14 an unobstructed opening will be gradually uncovered at the upper end (the right end) of the screen, so that there will be an increased flow of sewage through the screen close to the surface of the flow where the content of trash in the sewage is at minimum. The uppstream sewage level thus will sink, and it may be assumed that motor 30 is de-energized when the level indicated by a dot-and-dash line 45 in FIG. 1 has been reached.
Motor 30 can be energized under the control of a level detector e.g. a float switch when level 39 is reached, and it can be de-energized e.g. by a float switch at level 45 or in dependence of a timer that keeps motor 30 energized substantially for the period necessary in order that level 45 shall be reached. A new filter mat will eventually be formed over the portion of the screen that has been opened up by the operations described and when level 39 is reached again these operations will be repeated as described.
In the embodiment described the apparatus of the invention is provided in a flow passage with sewage continuously flowing along said passage. However, method and apparatus of the invention can be used also for treating sewage sucked from a septic tank or a three-compartment tank into a container truck. In that case the apparatus is mounted in a tank with an inlet for supplying the sewage from the container truck along the bottom of the tank against blocking element 16 in the direction of arrow 11. On the downstream side of screen 18 there is provided an outlet from the tank e.g. at level 40 for delivery of the sewage which has passed through the screen, to a sewage treatment plant.
As will be realized by the man skilled in the art the invention is not limited to the embodiment described. The apparatus can be modified with regard to the technical details thereof and still be suitable for practising the method of the invention. E.g. the drive mechanism for the stripper means including cranks can be replaced by an hydraulic ram for reciprocating movement connected to the bell crank system. Conveyor 15 can be replaced by a belt conveyor, and this conveyor can transport the trash deposited thereon either to an external container or to an apparatus for compressing the trash.
Furthermore, the drive mechanism for irons 33 can be replaced by any other mechanism known in the art which imparts to said irons a longitudinal translation at a lower level in one direction of translation and at a higher level in the other direction of translation, the irons being shifted from one level to the other when the direction is being reversed.

Claims

Method for sewage treatment, wherein the sewage is flown along a substantially linear flow passage (10) to pass through screen means (18) in the flow passage and to continue along the flow passage after having passed said screen means, characterized in
that the sewage flow is blocked under whirling adjacent the bottom (12) of said flow passage (10) over a conveyor (14) extending across the flow passage, and is forced to flow upwards towards said screen means (18) heavy trash in the sewage being left on the conveyor while light trash is carried onto said screen means to be collected on the inlet side thereof, and

that light trash collected on said screen means (18) is stripped from the screen means and supplied to the conveyor (14) to be conveyed from the flow passage (18) together with said heavy trash.
Method as in claim 1 characterized in that a mat formed by trash collected on the screen means (18) is stripped from the screen means downwards in the direction of the conveyor (14), an opening being uncovered in said screen means at the trailing end of the mat near to the surface of the sewage flow.
Method as in claim 1 or 2
characterized in that the sewage immediately before the blocking of the flow adjacent the bottom (12) of the flow passage (10) is flown into a depression in the bottom wherein the conveyor (14) is located.
Method as in any of claims 1 to 3,
characterized in that a re-direction of about 180° is imparted to the flow of sewage adjacent the bottom (12) of the flow passage (10) by blocking of the flow.
Method as in any of claims 1 to 4,
characterized in that stripping of trash from the screen means (18) is initiated at a predetermined the screen means (18) is initiated at a predetermined sewage level in the flow passage (10) upstream of the screen means.
Apparatus for sewage treatment for carrying out the method of the claims 1 to 5, including a substantially linear flow passage (10) for the sewage, and screen means (18) in said passage for continued flow of the sewage in the flow passage (10) after having passed through said screen means (18) characterized by
a conveyor (14) extending across the flow passage (10) at the bottom (12) thereof,

means (16) immediately downstream of the conveyor (14) for blocking the sewage flow under whirling adjacent the bottom of the flow passage (10) over the conveyor for depositing heavy trash in the sewage on the conveyor and for re-direction of the flow into said screen means (18) associated with said blocking means (16), and

stripper means (33) for stripping trash from said screen means (18) at the inlet side thereof and transfer of said trash to the conveyor (14).
Apparatus as in claim 6, characterized in that said screen means (18) is mounted with one end thereof located in the upper part of the flow passage (10) and the other end thereof located in the lower part of the flow passage, and that said stripper means (33) is guided for reciprocation between said ends.
Apparatus as in claim 7,characterized in that said screen means (18) is inclined in the longitudinal direction of the flow passage (10), sloping from said one end to said other end towards said conveyor (14).
Apparatus as in claim 7 or 8,
characterized in that said stripper means (33) is operative for stripping the screen means (18) when moving from said one end to said other end of said screen means and is inoperative in the opposite direction.
Apparatus as in any of claims 6 to 9,
characterized in that said screen means (18) comprises a grid of parallel rails (19) mutually spaced in the transverse direction thereof and that the stripper means comprises rails (33) displaceably mounted between said rails (19) of the screen means (18) in parallel therewith.
Apparatus as in claim 10,
characterized in that the rails (33) of said stripper means are connected to a drive mechanism for imparting to said rails translational movement along the rails (19) of the screen means (18) at a lower level in one direction and at a higher level in the other direction.
Apparatus as in claim 11,
characterized in that the rails (33) of said stripper means are provided with barbs (34) at the edges facing the inlet side of the screen means (18), said barbs projecting beyond the edges of the rails (19) of the screen means facing the inlet side thereof, in the position at said lower level.