WO2001049615A1

WO2001049615A1 - Wastewater treatment plant operating procedure

Info

Publication number: WO2001049615A1
Application number: PCT/AU2001/000007
Authority: WO
Inventors: Derek Richard Wilson
Original assignee: Water Corporation
Priority date: 2000-01-07
Filing date: 2001-01-05
Publication date: 2001-07-12
Also published as: AUPQ496600A0

Abstract

A method of treating wastewater in a plant (10) operating a plurality of basins (14, 16, 18, 20) in a sequential fill and draw system. The method includes a procedure for diverting excess incoming wastewater from a fill basin to a basin which is filling without altering the cycle times.

Description

TITLE

" WASTEWATER TREATMENT PLANT OPERATING PROCEDURE"

FIELD OF THE INVENTION

The present invention relates to a wastewater treatment plant operating procedure.

In treatment of wastewater a problem that is encountered is that the rate of water flow varies considerably during a daily cycle. Typically, there is a peak flow around mid morning. Any wastewater treatment plant has to be able to deal with the peak flow.

As a result there is a tendency to construct the plant large enough to cope with peak flows and this has the disadvantage that for most of the day the plant is under-utilized.

If the plant is not sufficiently large, the known solution to the event of a peak flow above the capacity of the plant is to reduce the time period in which the waste water is treated. This can result in the discharge of poor quality effluent.

The present invention provides a method of operation which enables a wastewater treatment plant to handle peak flows whilst being constructed at a smaller size than is normal.

SUMMARY OF THE PRESENT INVENTION

In accordance with one aspect of the present invention there is provided a method of operation of a wastewater treatment plant comprising a plurality of basins arranged in series and arranged to be operated on a sequential fill and draw system wherein when a first basin is full before the end of a fill cycle excess water is diverted into a second basin.

Substitute Sheet (Rule26) RO/AU BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure I is a schematic view of a wastewater treatment plant;

Figures 2 to 5 illustrate schematically operation of the plant of Figure 1 through a complete cycle of stages; and

Figures 6 and 7 illustrate schematically a modified method of operation of the plant of Figure 1 for increased efficiency during peak flow periods.

DESCRIPTION OF THE INVENTION

In Figure 1 of the accompanying drawings, there is shown an intermittent wastewater treatment plant 10 comprising an outflow channel or pipe 12, a plurality of basins 14, 16, 18 arid 20, a main inflow conduit 21 and a splitter box 22 from which extend a plurality of inflow conduits 24 extending to respective basins 14, 16, 18 and 20. The basins 14, 16, 18 and 20 are all of equal capacity. Each basin 14, 16, 18, and 20 includes a plurality of decanters 26.

In operation, the plant 10 operates on a sequential fill and draw system. In this type of system wastewater is treated in the basins 14, 16, 18 and 20. Each basin is in turn filled with wastewater through the main inflow conduit 21, the splitter box 22 and an inflow conduit 24.

The wastewater in each basin is aerated usually during all or part of the filling process. Suspended solids in the aerated wastewater are then allowed to settle and after a period clean water is decanted from the basin.

The process is repeated continually as wastewater flows into the plant 10. The plant of the present invention must have at least three basins but preferably has four or more basins. With a four basin plant one mode of operation is to fill and aerate each basin for a first time period, to allow settling for a second time period and to decant for a third time period. The length of each time period is determined primarily by process requirements. The length of the first time period is typically equal to the combined length of the second and third time periods.

Typically, with a four basin plant, when a first basin has completed its filling and aerating period, a second basin will be halfway through its filling and aerating period, a third basin will have completed its settling period and the fourth basin will have finished decanting.

The capacity of the basins is typically determined by the amount of wastewater expected to enter the plant 10 at daily peak flow periods. Thus, all of the basins have a capacity reflecting peak flow rates although in a normal mode of operation only one or two may actually be filled to capacity even at peak flow rates.

It has now been discovered that the plant 10 may be made more efficient by a modification of the operating procedure.

Assuming that the peak hourly flow enters the basin 14 then, providing the basin 14 was large enough, the fill and draw of the basin 14 would be equal to the inflow volume. If the basin 14 was made smaller it would begin to overflow at certain times of the day. This could result in discharge of poor quality effluent.

However, it has been found that this problem may be alleviated by managing excess flow in a modified way. Assume that flows to the plant 10 are such that the basin 14 is filled before it has completed its normal fill and aerate cycle, then in accordance with the present invention the flow to the basin 14 is shut off as soon as the basin 14 is full. Any excess wastewater is allowed to spill into the basin 16 which is already partway through its own fill and aerate cycle. It should be noted that basins of the type shown in Figure 1 typically have a nominal capacity which is generally below the top of the basin. Thus, a basin is regarded as being full when its nominal capacity has been reached.

Even after it is full, the basin 14 continues to be aerated until the end of its normal fill and aerate cycle is reached. Further, it is possible that the basin 16 will also fill before its fill and aerate cycle is completed. In this case, any excess wastewater is allowed to spill into the basin 18 which itself is a partway through its own fill and aerate cycle. The process of spilling over to the next basin continues for as long as required until the inflow through the conduit 21 drops.

In light of the above, it will be seen that it is most important that the fill and draw capacity of a basin is not exceeded until the following basin has begun its fill and aerate cycle. Once it is established what the capacity requirement is in a particular situation then fill and draw volumes of the basin can be determined to ensure that if the basin does fill it is after the following basin has begun its fill and aerate cycle.

The above procedures will now be discussed in relation to Figures 2 to 7 of the accompanying drawings.

Figure 2 shows the state of the wastewater treatment plant 10 not experiencing peak flow at a time part way through a time period during which the first basin 14 is towards the end of the time period of filling and aerating, the second basin 16 is towards the start of the period of filling and aerating, the third basin 18 is decanting and the fourth basin 20 is settling.

The plant 10 is shown partway through the next time period in Figure 3 in which the first basin 14 is settling, the second basin 16 is filling and aerating, the third basin 18 is filling and aerating and the fourth basin 20 is decanting.

In Figure 4 the plant 10 is shown partway through the next time period in which the first basin 14 is decanting, the second basin 16 is settling, the third basin 18 is filling and aerating and the fourth basin 20 is filling and aerating. The state of the plant 10 during the final time period of this example is shown in Figure 5. The first basin 14 is filling and aerating, the second basin 16 is decanting, the third basin 18 is settling and the fourth basin 20 continues to fill and aerate. The cycle continues in this pattern, with the next time period returning the plant to the state shown in Figure 2.

The present invention is primarily concerned with the operation of the plant 10 during peak flow periods. In such a case the basin being filled is filled before the end of the period during which it is required to fill and aerate. Such a situation is shown in

Figure 6. In this case the first basin 14 is filled with wastewater before the end of the current fill and aeration time period.

In accordance with the present invention incoming wastewater is diverted to the basin which is near the start of a filling and aerating period (in the example of Figure 6 this is the second basin 16). However, aerating continues in both the full and the filling basins.

The increased burden on the filling basin during this period may well result in it in turn reaching capacity before the end of the filling period. This situation is depicted in

Figure 7. The same procedure is followed, and inflow is diverted to the next basin in turn (the third basin 18 in Figure 7). The diversion of inflow to the next basin which is filling and aerating is continued for as long as the amount of inflow exceeds basin capacity. In practice, the amount of diverted flow decreases as the plant 10 recovers from the peak flow period.

As the inflow rate reduces from its peak, the amount of extra wastewater introduced into a basin during the filling cycle will decrease until the basin is no longer filled. The plant 10 will then operate again as shown in Figures 2 and 3.

The method of operation described above has the effect of distributing peak flows of wastewater more evenly about the available basins. This reduces the required capacity The method of operation described above has the effect of distributing peak flows of wastewater more evenly about the available basins. This reduces the required capacity of each individual basin. The process also ensures that full treatment of wastewater is performed during peak flow periods.

The same method is applicable to management of wet weather events whereby the normal inflow is augmented by rain water. If such an event causes the inflow to the plant 10 to be excessive, then it may be necessary to reduce the length of each time period as well as operating the plant in accordance with the present invention. The inflow in such a case is generally extremely diluted, and reduced aeration times are sufficient for adequate water treatment. Further, the amount of reduction of the time period may be calculated from measurement of flow rates upstream of the plant 10.

The particular description above has applied the present invention to a four basin treatment plant. It should be appreciated that the same process could be applied to an plant with more than four basins. It should also be appreciated that minor variations could be made to the cycle such as the introduction of idle periods following a decanting phase, whilst remaining within the scope of the present invention.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

1. A method of operation of a wastewater treatment plant comprising a plurality of basins arranged in series and arranged to be operated on a sequential fill and draw system characterised in that when a first basin is full before the end of a fill cycle excess water is diverted into a second basin.

2. A method of operating a wastewater treatment plant according to claim 1, characterised by the steps of, for each basin,

(i) introducing incoming waste water into the basin during a first time period; (ii) allowing the waste water to settle in the basin during a second time period; and

(iii) decanting water from the basin during a third time period,

and wherein the plurality of basins is arranged to perform these steps in a sequential manner such that at all times, in use, there is at least a first basin having waste water introduced thereinto and a second basin having waste water introduced thereinto.

3. A method of operating a wastewater treatment plant according to claim 2, characterised in that if the first basin is filled before the end of the first time period of the first basin incoming waste water is diverted from the first basin to the second basin for the remainder of the time period.

4. A method of operating a wastewater treatment plant according to claim 3, characterised in that if a subsequent basin to the first basin is filled before the end of the first time period of the subsequent basin incoming wastewater is diverted from the subsequent basin to a further basin which is in a first time period.

5. A method of operating a waste water treatment plant as claimed in any one of claims 2 to 4, characterised in that waste water in each basin is aerated during the first time period of the basin.

6. A method of operating a waste water treatment plant as claimed in claim 5, characterised in that if a basin is filled before the end of the first time period of the basin then the basin continues to be aerated until the end of the first time period.

7. A method of operating a waste water treatment plant as claimed in any one of claims 2 to 5, characterised in that the first time period is equal in length to the second and third time periods combined.

8. A method of operating a wastewater treatment plant as claimed in any one of claims 1 to 7, characterised in that the plant comprises at least 3 basins.

9. A method of operating a waste water treatment plant as claimed in claim 8, characterised in that the plant comprises 4 or more basins.

10. A method of operating a waste water treatment plant as claimed in any one of claims 1 to 9, characterised in that the length of the first, second and third time periods can be adjusted during wet weather events.

11. A method of operating a waste water treatment plant as claimed in any one of claims 1 to 10, characterised in that the wastewater treatment plant is an intermittent plant.