GB2396348A

GB2396348A - Wastewater treatment plant capable of dealing with heavy inflo

Info

Publication number: GB2396348A
Application number: GB0229362A
Authority: GB
Inventors: Howard Rundle; Julie Hart
Original assignee: SEV TRENT WATER PURIFICATION L
Current assignee: SEV TRENT WATER PURIFICATION L
Priority date: 2002-12-17
Filing date: 2002-12-17
Publication date: 2004-06-23
Anticipated expiration: 2022-12-17
Also published as: GB0229362D0; GB2396348B

Abstract

A wastewater treatment plant comprising an inlet for wastewater which is connected to a primary treatment means 5, the outlet of the primary treatment means being connectable to a downstream submerged aerated filter (SAF) 10. The inlet includes a bypass means 4 to selectively bypass flow form the primary treatment means to the submerged aerated filter. The bypass means being arranged to direct flow to the submerged aerated filter when the inlet flow is particularly higher than normal. Part of the flow may be treated by the primary treatment means and be passed to the environment without contacting the submerged aerated filter. The plant is configured to deal with very high inflow of wastewater, such as in times of heavy rainfall or storms. The primary treatment means may be a sewage works 5 comprising a selection of normal primary and secondary treatments found in sewage/wastewater facilities such as screens, filters, settlement tanks, and biological treatments.

Description

WASTE-WATER TREATMENT PLANT

The present invention relates to a waste-wateror sewage treatment plant and, in particular, to modifications thereof to deal with very heavy inflow of 5 waste-water, such as in times of heavy rainfall.

In conventional sewage or waste-water treatment plants, sewage and other waste-water is treated by a combination of settlement and biological treatment processes. Typical steps in the treatment process would be 10 screening and grit removal, settlement in tanks to remove sludge and then biological treatment to remove organic pollutants. This is normally referred to primary and secondary treatments of the waste-water.

Sometimes the primary and secondary treatments are followed by a 15 tertiary process such as sand filters to remove suspended solids and/or biological processes, for example to remove ammonia.

Most waste-water plants have to treat a combination of sewage and rain water. Normally when the flow increases to a certain value (often three times 20 that received in dry weather) the excess sewage is separated and is usually passed through settlement tanks where suspended solids can be separated.

The supernatant from these tanks is then discharged to the environment without any other treatment.

25 If the increase in flow is greatly above this value (normally above six times that received in dry weather) the excess sewage is separated and discharged to the environment without treatment. At the start of these very heavy inflows, the sewage may contain a lot of pollutants, particularly ammonia. These become diluted as the rain continues and hence high flow 30 continues, but they may still contribute a significant pollution load to the environment.

-2 lt has been suggested to deep bed filters to reduce suspended solids from storm overflows.

The present invention seeks to provide a waste-water treatment plant 5 configured to reduce the output of chemical pollutants in times of unusually heavy water inflow.

According to the present invention there is provided a waste-water treatment plant comprising an inlet for waste-water fluidly connectable to a 10 downstream primary treatment means, the outlet of the primary treatment means being fluidly connectable to a downstream submerged aerated filter, wherein the inlet includes bypass means, the bypass means being arranged to selectively bypass flow from the primary treatment means directly to the submerged aerated filter. It has been found that surprisingly the submerged 15 aerated filter can function and clean wastewater without any prior treatment, when the waste-water has the primary constitution of heavy rainfall. Other types of tertiary filter, such as trickling filters and activated sludge filters, would tend to allow such waste to pass through without significantly treating the waste. The bypass means may be arranged to direct the flow directly to the submerged aerated filter when inlet flow into the plant is three times higher than dry-weather inlet flow, or even when inlet flow into the plant is six times higher than dry-weather inlet flow.

Bypass means is often arranged to divert part of the flow directly to the submerged aerated filter. The remaining flow can be allowed to be treated in normal fashion by the primary and secondary treatment means. In which case the part of the flow not diverted is treated in the primary and secondary 30 treatment means and then diverted directly to the environment without passing through the submerged aerated filter. In this way the total size of the

-3 submerged aerated filter need not be increased despite being used for storm overflow. The invention will now be described with reference to the accompanying 5 drawings, in which: Figure 1: shows a waste-water treatment plant according to the present invention; Figure 2: shows a first submerged aerated filter useful in the 10 embodiment of Figure 1; Figure 3: shows a second submerged aerated filter useful in the embodiment of Figure 1; Figure 4: shows a third submerged aerated filter useful in the embodiment of Figure 1; and 15 Figure 5: shows a fourth submerged aerated filter useful in the embodiment of Figure 1.

Figure 1 shows a waste-water treatment plant generally designated 1.

The main flow of liquid into the plant is through inlet line 2 where it flows into 20 the sewage works 5. These sewage works 5 comprise a selection of the normal primary and secondary treatment means found in sewage/waste-water plant such as screens and grit removal filters, settlement tanks to remove sludge and biological treatments to remove organic pollutants. Flow from the works 5 is through line 8 into a submerged aerated filter (SAF) 10 where 25 tertiary treatment of the waste liquid is normally conducted to remove contaminants such as ammonia. The output from the SAF 10 is flowed through settlement tanks/filters 16 and then out to the environment through line 20.

In times of unusually high inflow of waste liquid, such as in a storm or 30 period of continual heavy rainfall, (hereinafter referred to as "storm flow") bypass means 4 diverts some or all of the flow away from the sewage works

-4 5 through line 20. In the illustrated embodiment, a holding tank 18 is included in line 20. This holds the first volume of the storm flow, which often contains a very high level of solid and biological contaminants. Treatment of this waste can be accomplished after the storm flow conditions revert to normal or dry 5 weather conditions. A further alternative would be to include a settling tank in this line. Waste flowing through bypass line 20 and not retained in holding tank 18, reenters the plant downstream of the sewage works 5 into line 8 and flows into the SAF 10. Surprisingly, the SAF 10 can effectively treat this direct waste with or without previous primary and secondary treatment despite the 10 fact that most biological filters cannot treat this type of discharge due to the fact that biological processes comprise stable operating conditions. However, it seems that due to the particular nature of the SAF 10, it can directly treat this nature of direct waste unlike many other types of biological filters. The SAF 10 can thus treat the storm overflow which then passes via the filter 16 to the 15 outlet 20.

If the bypass means 4 only diverts some of the flow via line 20 and some of the flow passes through the sewage works 5, flow from the sewage works 5 is diverted from the SAF into line 6 in these storm flow conditions in order to 20 prevent overload of the SAF 10. The discharge from line 6 again exits directly to the environment. Alternatively, the SAF 10 (or SAFs) could be increased in size to cope with the total storm flow.

As mentioned above, the use of the SAF 10 to treat the direct inflow into 25 the sewage plant 1 in times of high flow conditions can be done in several ways. Firstly, when overflow occurs the separated sewage bypasses the existing sewage works 5, mixes in line 8 with the effluent from the existing treatment plants and is treated on the tertiary treatment plant SAF 10. The tertiary treatment plant will have to be larger to treat higher flows and loads, 30 but no extension of the sewage works 5 is needed to treat these flows.

Alternatively, when the overflow occurs the separated sewage bypasses the

-5 existing sewage works 5 and is treated solely in the tertiary plant (SAF 10). Al1 or part of the secondary effluent from the existing sewage works 5 is diverted to discharge to maintain near constant load on the tertiary plant. All of the sewage effluent discharge will have to be subject to biological treatment so will 5 be of better overall quality than discharge previously, but the size of the tertiary treatment plant may not necessarily have to be increased. Finally, to deal with the high pollution load at the start of the high load (storm flow event) it is possible to install to retention tank 18, which will hold the first flush which would then be returned to the plant 1 when the storm flow event has finished.

A storm flow filter could be included before or after the SAF 10.

As shown in Figures 2 to 5, the submerged aerated filter SAF 10 is a column filter where the filter media is flooded, i.e. the waste liquid surrounds 15 the media bed 12. Flow through the filter 10 may be upwards or downwards.

Air is pumped through the flooded media bed 12. Of course, it is vital to ensure that the air outlets do not become blocked otherwise oxidation of the waste would cease. The SAF 10 is of a particular filter design where larger media is used in the filter and the design of the media column is such that solids should 20 not be substantially retained in the bed and are consequently removed by settlement tanks 16 following the filter 10.

Back-washing is not required in a SAF, and normally the oxygen/air is forced in the system from the bottom of the bed. The advantages of a SAF 25 over most biological filters are that there is no odour nuisance, there is no fly nuisance and it can be operated at much higher loading rates and so takes a much smaller ground area on site. Existing submerged aerated filters either use plastic media or can use stone e.g. blast furnace, based media. Several different types of media have been used including random fill loose types, 30 loosely filled into the packed media bed which can comprise small hollow tubes or generally large spider- like formations of cries-cross cylindrical shapes. The

-6 more complex shapes provide the advantage of higher surface areas but in time this surface area can be reduced due to local blockaging. Another type of plastic media is block type which is similar in nature to that used in cooling tower media. This again provides high surface area but its disadvantage is that 5 process air can cause it to float in the submerged filter and recorded failures have been occasioned by this type of media.

A simple pump may be included in the SAF to dislodge any solid matter which accumulates therein due to the stormflow or otherwise.

Figures 2 through 4 shows different designs of SAFs 10 which can be used for the present invention. Air is fed into each of these reactors through blowers 14 as shown in more detail in Figure 2. The air in each case enters at the bottom of the filter 10. The media column 12 is supported on base 13.

15 The filter 10 is shown totally flooded with liquid shown above the media column 12. In most cases the media column 12 will be between 2 and 8 meters in height and that depicted in Figure 2 is approximately 3 meters in height. The SAF 10 of Figures 2, 4 and 5 have water flow from the base of the filter flowing through the top where the oxidized waste outflows into line 15 from 20 whence it will pass through settlement tanks 16. In the embodiment shown in Figure 3 the liquid flow is downwardly through the filter and exits via line 15 at the base of the filter 10.

The SAF is particularly used as a stormflow treatment as it is not easily 25 blocked by solid matter in contrast to a biological aerated filter (BAFI. As mentioned before, activated sludge plants and trickling filters do not tend to respond to the storm-flow and so leave the waste water untreated.

Claims

CLAIMS:

1. A waste-watertreatment plant comprising an inlet for waste-water fluidly connectable to a downstream primary treatment means, the outlet of the 5primary treatment means being fluidly connectable to a downstream submerged aerated filter, wherein the inlet include bypass means, the bypass means being arranged to selectively bypass flow from the primary treatment means directly to the submerged aerated filter.

102. The waste-watertreatment plant according to claim 1, wherein the bypass means is arranged to direct the flow directly to the submerged aerated filter when inlet flow into the plant is three times higher than normal inlet flow.

3. The waste-watertreatment plant according to claim 1, wherein the 15bypass means is arranged to direct the flow directly to the submerged aerated filter when inlet flow into the plant is six times higher than normal inlet flow.

4. The waste-water treatment plant according to any one of the preceding claims, wherein the bypass means is arranged to divert part of the 20flow directly to the submerged aerated filter.

5. The waste-watertreatment plant according to claim 4, wherein the part of the flow not diverted is treated in the primary treatment means and then diverted directly to the environment without passing through the submerged 25aerated filter.

6. A waste-water treatment plant as hereinbefore described with reference to, and/or as illustrated by the accompanying drawings.