WO1995011355A1

WO1995011355A1 - Sewage treatment plant

Info

Publication number: WO1995011355A1
Application number: PCT/GB1994/002318
Authority: WO
Inventors: William Storey
Original assignee: Babcock Water Engineering Limited
Priority date: 1993-10-22
Filing date: 1994-10-21
Publication date: 1995-04-27
Also published as: GB9321873D0; AU7945794A

Abstract

Sewage treatment plant receiving an incoming stream of sewage from a sewerage system (2) subject to sudden influxes or storm surges includes a dynamic separator (6) adapted to effect separation of the incoming stream of sewage into a first fraction having a high water content and a low sludge content and a second fraction having a high sludge content and low water content. The first fraction is discharged to effluent treatment plant (36) with sudden influxes being temporarily accumulated in a storm chamber (30) and tank (32). The bulk of the sludge content is carried in the second fraction and removed in screening and degritting apparatus (18). As a result, odours associated with putrescent material in the sludge are largely confined to the dynamic separator (6) and the screening and degritting apparatus (18), which may be roofed over. Additionally, since the relatively clear water of the first fraction may be temporarily accumulated in the storm chamber and tank (30, 32) without producing marked odours, and discharged at a controlled rate, the effluent treatment plant (36) may be sized to a capacity appropriate to accommodate normal sewage flow rather than to accommodate sudden influxes or storm surges, with a consequent saving in capital, and operating costs. One or more additional dynamic separators may be positioned in parallel with the one dynamic separator to accommodate sudden influxes or storm surges.

Description

SEWAGE TREATMENT PLANT

This invention relates to sewage treatment plant and, more particularly, to inlet works of sewage treatment plant subject to sudden influxes and storm sewage from an associated sewerage system.

It is known to provide a sewage treatment plant including biological treatment apparatus discharging treated water to a river or sea and storm tank means arranged to accumulate temporarily sudden influxes of sewage flow and discharge accumulated sewage flow at a controlled rate to the biological treatment apparatus.

It is also known to provide local dynamic separator eguipment located on sewerage systems the eguipment being positioned at locations remote from the sewage treatment plant and adapted to separate putrescent and other solid material from storm sewage prior to discharge to a watercourse. The putrescent and other solid material is discharged intermittently to a mobile tanker or continuously to a suitable closed receiver from which the material is removed at intervals.

According to one aspect of the invention there is provided a sewage treatment plant including a separator adapted to effect separation of an incoming stream of sewage from a sewerage system into a first fraction having a high water content and a low sludge content and into a second fraction having a high sludge content and a low water content.

Preferably, means are provided to adjust and proportion the water content and the sludge content within the first and second fractions depending upon the incoming stream flow rate. Desirably, screening apparatus is positioned on the outlet from the separator for the first fraction and is adapted to remove buoyant material from the first fraction.

Suitably, screening and degritting apparatus is positioned on the outlet from the separator for the second fraction and is adapted to remove off-line screenings and grit from the second fraction.

Advantageously, effluent treatment means are arranged to receive effluent discharge from the first and second screening apparatus.

Additionally, a means of flow control is provided to regulate and adjust the flow rate of the second fraction from the separator to the second screening and degritting apparatus.

Buoyant material removed from the first fraction may be discharged to the screening and degritting apparatus on the outlet from the separator for the second fraction.

The invention also includes the provision of control means arranged to adjust and alter the operational philosophy of the treatment plant depending upon the incoming stream flow rate.

According to another aspect of the invention, there is provided a sewage treatment plant including separators arranged in parallel and each adapted to effect separation of an incoming stream of sewage from a sewerage system into a first fraction having a high water content and a low sludge content and into a second fraction having a high sludge content and low water content, the first fractions being directed for discharge to a river or sea and the second fractions being directed toward a common second screening apparatus. Suitably, one of the separators may be dimensioned to have a capacity to accommodate normal sewage flow and the remaining separator or separators dimensioned to have a capacity to accommodate sudden influxes or storm surges.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:-

Figure 1 is a first arrangement of a sewage treatment plant; and

Figure 2 is an alternative arrangement of a sewage treatment plant.

Referring to Figure 1, a sewerage system 2 discharges to an inlet 4 of a dynamic separator apparatus 6. Within the dynamic separator apparatus the inflow is fractioned into a first, high water content, low sludge content fraction discharging to a first screening apparatus 8 and into a second, high sludge content, low water content fraction discharging to an outlet 10. Discharge through the outlet 10 is effected through a pump 12, the throughput of which may be controlled by means of a signal derived from a flow rate sensor 14 positioned in the inlet 4.

The pump 12 discharges through an outlet 16 to a second screening apparatus 18 arranged to remove off-line screenings and grit and discharge effluent to a pump 20. The pump 20 discharges the effluent through an outlet 22 having a confluence 24 with an effluent outlet 26 from the first screening apparatus 8 to discharge the combined stream through a duct 28 to a storm overflow chamber 30. Overflow from the chamber 30 is accommodated in storm tanks 32 with the chamber 30 having a regulated flow outlet 34 to the effluent treatment plant 36. Screenings of buoyant material from the first screening apparatus 8 are discharged through a line 38 connecting with the outlet 16 from the pump 12 to the second screening apparatus 18, an external source of water 46 being introduced at the first screening apparatus 8, if reguired, to convey the buoyant material to the second screening apparatus 18.

In operation, sewage inflow from the system 2 under all conditions is discharged to the dynamic separator apparatus 6 and separated into first and second fractions with proportioning of the fractions being controlled by the pump 12 in accord with a signal from the flow rate sensor 14 to optimise the performance of the apparatus in removing screenings and grit.

By removing screenings and grit at the inlet works portion of the plant, particularly at times of sudden influx, the remainder of the plant may be designed to have a capacity appropriate to normal operation of the sewerage system rather than having an over-capacity allowing for sudden influxes, thereby giving an economy in land usage and construction costs.

Since the arrangement allows for the provision of compact treatment sites, this enables the sites, such as the dynamic separator apparatus 6 and the second screening apparatus 18, to be roofed over to contain odours and limit access. In addition, since the sources of the odours are thus more predictable they may be specifically targeted to facilitate removal. '

In an alternative embodiment of the invention, a proportioning valve 40 is positioned adjacent the outlet from the pump 20 and serves to divert all or a proportion of the effluent output from the pump 20 to a re-cycling line 42 (shown in chain dotted outline) to return all or a proportion of the effluent to the inlet 4 in order to maintain a flow rate within the separator 6 at an optimum value at times when the flow rate would otherwise be below the optimum value.

It will be understood that non-return means 44 are positioned in the respective lines to prevent undesired backflow.

If reguired, an air and water mixture stream may be introduced from an external source through line 47 for injection through a line 48 discharging adjacent the inlet to the dynamic separator 6 and, or alternatively, through a line 50 discharging into the outlet 10. Discharge of the air and water mixture is controlled by means of a signal derived from the flow rate sensor. Such air and water discharges assist control and separation of the associated, injected streams.

In an alternative arrangement, not shown, two, or more, dynamic separator apparatuses 6 of substantially similar capacity are arranged to receive parallel inputs from the sewerage system 2. The high water content, low sludge content fractions discharged from the apparatuses are combined for discharge to the storm overflow chamber 30. The high sludge content, low water content fractions are discharged through respective pumps 12 and combined for discharge to a common second screening apparatus 18.

Operation of the foregoing arrangement is similar to that described in connection with the arrangement shown in Figure 1, the input sewage stream being divided equally between the dynamic separator apparatuses 6. Arranging the dynamic separator apparatuses in parallel permits the handling of a greater capacity, whilst utilising a common second screening apparatus 18 allows an economy in construction costs.

Referring to the arrangement of Figure 2, there is shown a sewerage system 2 discharging to an initial storm chamber 52 discharging in turn to a composite parallel arrangement of a first dynamic separator apparatus 54 having an inlet 56 and a second dynamic separator apparatus 58 having an inlet 60. The first dynamic separator apparatus 54 is designed to have a capacity sufficient to accommodate an anticipated full treatment flow of sewage and discharges a high water content, low sludge content fraction through first screening apparatus 62 to an effluent treatment plant 64 for biological treatment and discharge to a river or sea. A high sludge content, low water content fraction is discharged from the first dynamic separator apparatus 54 through a pump 66 to a second screening apparatus 68 for removal of the bulk of the sludge content with the remainder of the fraction being returned through line 70 to the inlet 56.

The second dynamic separator apparatus 58 is designed to have a capacity sufficient to accommodate an anticipated sudden influx or storm surge and discharges a high water content, low sludge content fraction through first screening apparatus 72 to a main overflow storm chamber 74 and storm tank 76 arranged to accommodate temporarily the sudden influx and provide for a controlled rate discharge to a river or sea. A high sludge content, low water content fraction is discharged from the second dynamic separator apparatus through a pump 78 discharging to the inlet 56 of the first dynamic separating apparatus 54.

Valves 78, 80 are positioned on the inlets 56,60 and are actuated by means of a signal derived from a flow rate sensor 82 at the outlet from the sewerage system. In operation, under normal conditions, all of the sewage inflow is directed toward the first dynamic separation apparatus 54, which effects a separation of the sewage stream into the two fractions. The high water content, low sludge content fraction is discharged through the first screening apparatus 62 to the effluent treatment plant 64 and the high sludge content, low water content fraction is discharged through the second screening apparatus 68 and the residual water returned to the inlet 56.

Upon a sudden increase in flow from the sewerage system, such as occasioned by a storm, the increased flow is at first accommodated in the initial storm chamber 52 but, upon a relatively steady excess flow being established, the output from the initial storm chamber is directed to both the first and the second dynamic separator apparatuses. Since the excess flow will have a proportionately lower biological content due to the diluting effect of the storm water, it is acceptable to discharge the high water content, low sludge content fraction produced from the second dynamic separator apparatus 58 at a controlled rate to a river or sea with the main overflow storm chamber 74 and storm tank 76 accommodating temporary excesses of flow.

The high sludge content, low water content fraction separated in the second dynamic separator apparatus 58 is extracted through the pump and discharged to the inlet 56 of the first dynamic separator apparatus 54.

This arrangement permits the first and second dynamic separator apparatuses 54, 58 to be dimensioned appropriate to anticipated flows under normal conditions and storm flow conditions to achieve configuration for optimum separation effect at least in the first dynamic separator apparatus 54.

By utilising the initial storm chamber 52 for temporary accumulation of a storm flow, and regulating the flows to the first and second dynamic separator apparatuses, flow rates to the respective separator apparatuses approaching the individual design flow rates for optimum separation effect may be achieved. However, it will be appreciated that, if desired, the first storm chamber may be dispensed with, particularly in situations where space for siting the chamber is not available.

Claims

1. Sewage treatment plant in which effluent treatment apparatus (36,64) is arranged to receive output from an associated sewerage system (2) and to discharge treated water to a river or sea having a storm tank means (30,32,74,76) arranged to accumulate temporarily sudden influxes from the sewerage system and to discharge such accumulated sewage at a controlled rate, characterised in that a separator (6) adapted to effect separation of an incoming stream of sewage into a first fraction having a high water content and a low sludge content and a second fraction having a high sludge content and a low water content is positioned to receive the incoming stream of sewage from the associated sewerage system (2) and to discharge the first fraction for treatment in the effluent treatment apparatus (36) .

2. Sewage treatment plant as claimed in Claim 1, characterised in that means (46,48,50) are provided to adjust and proportion the water content and the sludge content within the first and second fractions depending upon the incoming stream flow rate.

3. Sewage treatment plant as claimed in Claim 1 or Claim 2, characterised in that screening apparatus (8) is positioned on the outlet from the separator (6) for the first fraction and is adapted to remove buoyant material from the first fraction.

4. Sewage treatment plant as claimed in any preceding Claim, characterised in that screening and degritting apparatus (18) is positioned on the outlet (10) from the separator for the second fraction and is adapted to remove off-line screenings and grit from the second fraction.

5. Sewage treatment plant as claimed in Claim 4, characterised in that effluent from the screening and degritting apparatus (18) for the second fraction is arranged to discharge liquid effluent for treatment in the effluent treatment apparatus (36) .

6. Sewage treatment plant as claimed in Claim 4 or Claim 5, characterised in that a means of flow control (4,12) is provided to regulate and adjust the flow rate of the second fraction from the separator (6) to the screening and degritting apparatus (18) .

7. Sewage treatment plant as claimed in Claim 4, Claim 5 or Claim 6 as dependent upon Claim 3, characterised in that buoyant material removed from the first fraction at the screening apparatus (8) positioned on the outlet from the separator (6) for the first fraction is discharged to the screening and degritting apparatus (18) positioned on the outlet (10) from the separator (6) for the second fraction.

8. Sewage treatment plant in which effluent treatment apparatus (36,64) is arranged to receive output from an associated sewerage system (2) and to discharge treated water to a river or sea having a storm tank means (30,32,74,76) arranged to accumulate temporarily sudden influxes from the sewerage system and to discharge such accumulated sewage at a controlled rate, characterised in that separators (54,58) arranged in parallel each adapted to effect separation of an incoming stream of sewage into a first fraction having a high water content and a low sludge content and a second fraction having a high sludge content and a low water content are positioned to receive respective incoming streams of sewage from the associated sewerage system (2) and to direct the first fractions for discharge to a river or sea and to direct the second fractions to a common second screening and degritting apparatus.

9. Sewage treatment plant as claimed in Claim 8, characterised in that one of the separators (54) is dimensioned to have a capacity to accommodate normal sewage flow from the associated sewerage system and discharges the first fraction to effluent treatment apparatus (64) with the remaining separator (58) or separators being dimensioned to have a capacity to accommodate sudden influxes or storm surges from the associated sewerage system, flow control means (78,80,82) being provided to direct the incoming stream to the one (54) of the separators for normal sewage flow conditions and, additionally, to the remaining separator (58) or separators as necessary to accommodate sudden influxes or storm surges.

10. Sewage treatment plant as claimed in Claim 9, characterised in that an initial storm chamber (52) is positioned at an outlet from the sewerage system (2) and discharges to the separators (54,58).