Liquid purification or separation – Structural installation – Flume stream type
Reexamination Certificate
2000-03-10
2001-09-25
Upton, Christopher (Department: 1724)
Liquid purification or separation
Structural installation
Flume stream type
C210S158000, C210S160000, C210S400000
Reexamination Certificate
active
06294085
ABSTRACT:
The invention relates to a sewage screening apparatus, for removing solid materials from a sewage flow.
It is recognised that the effluent flow entering a sewage treatment plant contains solid materials, such as rags, paper, polythene and other plastic sheeting, and the like, which cannot be processed by the treatment plant. Solids can be removed from the flow by screens or sieves which capture the solids. The screens or sieve are then periodically or continuously operated for cleaning to remove the captured solids, commonly referred to as screenings, for disposal. One such screening apparatus known in the art is the “continuous-belt screen” which includes a continuous driven belt screen presenting a continuous, moving screening area to the input sewage flow to effect removal of screenings within the sewage flow.
It is inevitable that faecal materials from the effluent flow entering the sewage treatment plant will become entrapped with the screenings. In order to improve the working environment of personnel handling the extracted screenings and to minimise potential health hazards, it is desirable that screenings removed from the flow are as free as possible from any faecal material.
A solution to the problem of cleaning screenings is described in EP 0 557 030. Using this technique, screenings are passed through a washing apparatus following their removal from the main sewage flow. The washing apparatus includes a tank into which screenings removed from the effluent flow are introduced along with aqueous liquid. A rotating impeller generates turbulence within the aqueous liquid in the tank resulting in a break down of the faecal contaminants.
EP 0 592 508 describes an alternative apparatus for cleaning screenings to be removed from a sewage flow. In this apparatus, removal of the screenings is effected by means of a screw conveyor having a perforated trough through which sewage in the liquid phase passes. An agitator, in the form of an impeller device, is used to create a turbulent effect in the sewage flow. The turbulence effect causes faecal contaminants to be washed from the screenings prior to their entry to the screw conveyor and their subsequent removal from the flow. The screenings cannot pass through the perforated trough and are compacted by the screw conveyor for subsequent disposal from the apparatus.
A disadvantage of the apparatus is that it has a relatively low sewage flow capacity and, typically, the apparatus can only be used with sewage flow rates of less than 300-400 liters per second. Thus, the apparatus is not well suited for use as a primary sewage screening system. In particular, the apparatus cannot be employed in a sewage treatment plant serving areas where it is necessary to process a large sewage flow, such as areas of high population. Furthermore, the washing action is effected by repeatedly removing and reintroducing screenings into the region of turbulence by periodically reversing the direction of the screw conveyor during operation. Repeatedly reversing the direction of the screw conveyor in this way is mechanically inconvenient.
It is an object of the present invention to provide an apparatus for removing washed screenings from a sewage flow which has an increased sewage flow capacity. It is a further object of the invention to provide such an apparatus in which washing of the screenings can be achieved in a more convenient manner.
According to the present invention there is provided a sewage screening apparatus comprising;
a screen arrangement having a continuous belt screen for capturing screenings contained within the sewage flow to enable their subsequent removal therefrom; and
impeller means for generating a turbulence effect within the sewage flow to effect washing of the screenings contained within the sewage flow prior to their removal therefrom,
wherein the impeller means is located within the screen arrangement.
The apparatus has a large flow capacity by virtue of the large screening area presented by the continuous belt screen. The apparatus therefore provides the advantage that it can be used for screening a high volume sewage flow. It is therefore particularly suitable for use in a sewage treatment plant serving highly populated areas. Furthermore, owing to the increased sewage flow capacity, the apparatus is suitable for use as a primary sewage screening apparatus, where screenings are washed in the main sewage channel prior to their removal therefrom.
The screen arrangement has a base region at its lower part and a head space at its upper part. The apparatus may include one or more rotary impeller for generating a turbulence effect within the sewage flow. Preferably, the impeller is arranged within the base region of the screen arrangement.
On introduction of the sewage flow into the screen arrangement, the base region of the arrangement becomes flooded with liquid sewage. The screenings to be removed from the sewage flow remain waterborne within the sewage flow for a period of time, prior to their removal from the flow, during which time they are continuously subjected to the turbulence action generated by the rotary impeller. The containment of the screenings within the turbulence region in this way results in an effective washing action.
In addition to the separation of faecal contaminants from the screenings by washing, the turbulence created by the impeller has a liquefying effect on the separated contaminants such that, when liquefied, they can pass through the belt screen with the liquid phase of the sewage to the subsequent processing stages. The retention of faecal contaminants within the liquid sewage flow ensures that the biological loading for the treatment plant is sustained.
The present invention also provides the advantage that, should the impeller fail, operation of the screen arrangement can continue. In conventional systems, in which the screen arrangement delivers unwashed screenings to a separate washing apparatus, failure of the washing apparatus can lead to prolonged system down-time as operation of the screen arrangement has to cease whilst the washing apparatus is repaired or replaced.
Preferably, the rotary impeller is driven by a motor located outside the screen arrangement.
Screenings removed from the input sewage flow are washed prior to their removal from the screen arrangement by the turbulence generated by the impeller. The screenings can therefore be handled more safely by operating personnel following removal of the screenings from the apparatus without the need for a second, subsequent stage for washing the removed screenings. The screenings to be removed from the sewage flow may include rags, papers, plastic materials and stones which cannot be processed by the subsequent processing stages of the sewage treatment plant.
The screen arrangement includes a back plate, at the rear of the arrangement, on which the impeller may be mounted such that the impeller is located within the screen arrangement. One or more impellers may be located within the screen arrangement.
The belt screen passes through the head space of the screen arrangement. The apparatus also includes a drive mechanism for driving the belt screen, the drive mechanism being mounted externally of the screen arrangement. It is usual in conventional continuous belt screen arrangements for the drive mechanism to take the form of a driving wheel located within the head space of the screen arrangement. Mounting the driving mechanism externally of the screen arrangement provides the advantage that brushing means, such as a rotary brush, may be housed within the head space to effect removal of screenings from the belt screen as it is passed therethrough. Additionally, by mounting the drive mechanism externally, contamination by the sewage flow is avoided.
According to another aspect of the invention, two or more screen arrangements may be employed within the main sewage channel to provide an increased sewage flow capacity, each screen arrangement having a continuous belt screen for capturing screenings to be removed from the sewage flow. Impel
Andrus Sceales, Starke & Sawall
Jones and Attwood Limited
Upton Christopher
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