The invention relates to apparatus and methods for remediating biological trickling filters, especially those used in wastewater treatment for the removal of dissolved organic material from water, Backgrs i^ I i ca n

The treatment of wastewater is crucial for the maintenance of the health of communities, and for the provision of fresh water supplies. Sewage treatment works, often referred to as domestic wastewater treatment works, are installations for the removal of contaminants from wastewater, and especially from household sewage and commercial waste streams.

Once solid contaminants have been removed from the water stream., a biological filter is typically used to remove remaining dissolved organic components. One such system is referred to as a "trickling filter". Such trickling filters are not filters in the conventional sense of a mechanical removal of suspended solids, but operate by the presence of a microbial biofilm immobilised on the surface of a packing material typicaliy in the form of a bed of relatively small rocks, especially granite. Other bed material used includes coke, gravel, slack, ceramic or even plastic media. The wastewater is sprinkled over the surface of a bed of such packing material where it flows downwards in intimate contact with the layer of microbial biofiim, which grows, attached to the bed of media. The filter bed is kept aerobic by the presence of air gaps between the support media with air flowing upwards through the bed by either natural or forced convection, Growth of the organisms (typically a mixed aerobic bacterial population, often with other organisms such as protozoa and rotifers) in the biofiim leads to the removal of organic components dissolved in the water. Nitrifying bacteria are also often present in some lower regions of the bed of material, which leads to the removal of dissolved nitrogenous material from the water as well. Over time, the microbial biofiim grows, and portions of the film are sloughed off and entrained in the water flow to be removed downstream, typically by a sedimentation process.

Such trickling filters have been in use in water treatment works for many years. However, it is known that after several tens of years the efficacy of the trickling filters can reduce, often caused by excessive build up of biofiim on the support material, This leads to sub- optimal removal of dissolved contaminants from the water stream, often evidenced by an increase in ammonia concentration in the outlet water. Strict environmental controls prevent the release of such water into watercourses, and operators of such wastewater treatment plants maybe forced to divert water, often transported by road, in tankers, to alternative treatment facilities.

It is possible to renew or remediate such trickling filter beds by removing some or all of the support medial from the beds and replacing it with new material or by removing the material and washing it and returning it to the bed, Such major disruption to the beds requires the use of mechanical diggers to remove the packing material which can damage the relatively fragile support structures and can result In the trickling filter bed being offline for several days leading to an expensive and disruptive requirement to transport water to alternative treatment plants whilst the remediation work is underway.

It is among the objects of the present invention to provide apparatus and methods to facilitate the remediation of such trickling filter beds. SuniOiar of £he Inyemiaa

According to a first aspect, the invention comprises filter bed remediation apparatus comprising an auger, the auger having a shaft, said auger being mounted for reversible axial displacement and for rotation, and the auger having a channel providing fluid communication from a point adjacent a first (proximal) end of the shaft of the auger to a side discharge hole adjacent the other (distal) end of said shaft and wherein said channel further provides fluid communication to an end discharge hole at the distal end of said shaft and oriented to discharge fluid substantially parallel to the axis of said shaft. Fluid, such as water, may be passed through the channel whilst the rotating auger is lowered into the filter bed support material, thereby mixing and cleaning the support material it is thought that the efficiency of operation of this type of trickling filter is gradually reduced over the years by excessive built-up of biofilm on the bed material. This might not affect the operation of the filter bed for perhaps 10 or 20 years, but when the beds are no longer capable of removing organic material and nitrates to the required degree, then the operation difficulties for the water treatment works are severe.

The provision of a discharge hole at the end of the shaft further enhances the removal of excess biofilm, aids in keeping the material In suspension, and also aids penetration of the auger assembly into the bed of support material.

In preferred embodiments, said channel provides fluid communication to a plurality of side discharge holes, said side discharge holes located in the shaft of the auger between the auger flights. Having multiple discharge holes located on the side of the auger shaft improves the efficiency of partial removal of excess biofilm, and further aids keeping the sloughed-off biofilm in suspension in the wash water.

in any such embodiment, it is especially preferred to further provide a fluid discharge nozzle arranged to discharge a jet of fluid adjacent said auger, in a direction substantially parallel to the axis of the auger and towards the distal end of said auger. Such a nozzle can deliver a high flow rate (in the order of 20-40 litres/second) of water adjacent the operating auger. This additional flow further helps in cleaning of the filter support media and maintaining the sloughed-off biomass in suspension. In any aspect of the invention the apparatus further comprises a pump, to pump water through said channel at a rate of between 10 and 40 litres per second.

Where a discharge nozzle is provided, said apparatus preferably further comprises a further pump to pump water through said discharge nozzle at a rate of between 10 and 40 litres per second, although the flow from a single pump may be split to feed both the auger channel and the discharge nozzle.

The fluid discharge nozzle may be separately positionable relative to the auger, but in preferred arrangements, said fluid discharge nozzle is mounted on said auger for vertical displacement therewith.

In a second aspect, the inventors provide a method of remediating a biological filter bed comprising the use of apparatus described herein. Preferably, said method comprises the steps of: interrupting the normal operational fluid flow to said filter bed; sequentially using said apparatus to redistribute and wash filter bed material in regions of said filter bed; and restoring the fluid flow to said filter bed.

In preferred embodiments of the method, water is passed through said apparatus at a rate of between 10 and 80 litres per second.

Preferably said water is taken from a point downstream of adjacent like filter beds. In this way, the environmental impact of the remediation regime is minimised. More preferably, water and material washed from said filter bed is collected and returned to a point upstream of adjacent like filter beds. Again, this further minimises the environmental impact of the process, which is carried out in an essentially self-contained fashion. In an aspect of the method, grit is preferably removed from said collected water before being returned to said upstream point. This prevents clogging of sedimentation tanks with gritty material, or return of gritty material to the trickle filters, which might interfere with the essentially open structure of the filter beds, thereby reducing oxygen transfer rates to the water and biofi!m.

Also included within the scope of the invention is apparatus substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings, except figures 1 and 2.

Also included within the scope of the invention is a method substantiall as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings, except figures 1 and 2. Brijei&es ript;sn.9l.†be Pa in

The invention will be described with reference to the accompanying drawings, in which:

Figures 1 -2 illustrate augers which fall outside of the claims as amended,

Figure 3 illustrates an auger of the present invention;

Hgure 4 illustrates an embodiment of the invention incorporating an additional fluid discharge nozzle;

Figure 5 illustrates apparatus of the invention in use; and

Figures 6 and 7 illustrate schematic flow diagrams of a waste water treatment works during trickle bed remediation. esc!iption.oLEm eiF M

Figure 1 shows in a schematic side view of filter bed remediation apparatus generally indicated by 1 and comprising an auger 2 having a shaft 3 and helically-mounted flights 4 surrounding the shaft 3. The shaft 3 is mounted for rotation, as indicated. In a typical arrangement, the shaft 3 would be cylindrical and have a diameter of approximately 100mm, typically in the range 75-200mm. The outer diameter of the flights 4 is typically in the range of 200-SOOmm, for example approximately 300mm. The shaft 3 is provided with a fluid -conducting channel, or conduit, 5 running from a point adjacent a versed

(proximal) end 6 of the shaft 3 to a side discharge hole 7 adjacent the other brackets distal end 8 of the shaft 3. A fluid-tight bearing is provided to allow fluid, such as water, to be introduced into the channel 5 for discharge through the side hole 7 located in the side of the auger shaft 3 between an adjacent pair of flights 4. In preferred embodiments, the channel 5 is located within the body of the shaft 3, i.e. the shaft is hollow, In use, the auger is rotated, typically at a rate of approximately 60rpm, water is pumped through the channel 5 and out of the discharge hole 7, and the auger is gently lowered into a portion of a trickling filter bed to be remediated. The action of the auger lifts a redistributes packing material within the bed, whilst the flow of water through the discharge hole 7 removes at least a proportion of excess biofilm on the filter bed material The inventors have found that a water exit velocity of approximately 4m per second from the discharge hole is ideal for removing excess biofilm. The auger is typically left to rotate in the bed for a dwell time of approximately 30-60 seconds to allow the support material to be mixed and cleansed before the auger is moved to another region of the filter bed, During this dwell time, the state of the packing material may be observed as it is brought to the surface of the bed by the auger, and the treatment period adjusted, as necessary, depending on the degree of cleaning required.

Figure 2 shows a device with the same element numbering as figure 1. This device has a plurality of side discharge holes 7 on the side of the shaft 3, again in fluid communication with the channel S, Such discharge holes are ideally distributed radially around the shaft, for example on opposite sides of the shaft It is particularly preferred that the discharge holes are located only in the distal region of the auger, up to a height corresponding to the depth of a typical trickle filter bed, in the region of 2m, Figure 3 illustrates a further particularly preferred embodiment of filter bed remediation apparatus, again having like elements numbered as figure 1 -2. in this embodiment there is further provided an end discharge hole 9 located at the distal end 8 of the auger shaft 3, and again in fluid communication with the channel 5, This arrangement allows water to be pumped through the channel 5, to exit both through the side discharge hcle(s) 7 and through the end discharge hole 9. The inventors have found that the provision of multiple discharge holes in this manner greatly facilitates both the removal of excess biofilm from the filter bed media, and the maintenance of the sloughed biofilm in suspension in the water.

Figure 4 illustrates a yet further preferred embodiment of filter bed remediation apparatus according to the present invention. This apparatus again comprises an auger 2 mountabie for rotation about its axis as indicated, and for reversible axial displacemen as indicated by the two-headed arrow. In this embodiment, the apparatus further comprises a fluid discharge nozzle 10 arranged to discharge a jet of fluid 1 1 adjacent the auger 2, and in a direction substantially parallel to the axis of the auger and towards the distal end 8 of the auger.

Pumps 12 are provided to pump water both through the channel 5 running through the auger shaft 3 and via a watertight coupler 13. A second pump pumps water through the discharge nozzle 10, It is also possible to use a single pump to feed both the auger channel 5 and the discharge nozzle 10 by splitting the flow,

In use, water maybe pumped through the discharge nozzle 10 at a rate of between 10-50 litres per second, and preferably about 20 litres per second ±5 litres per second. At the same time, water is pumped through the auger channel 5 at a similar rate. The side discharge holes 7 and end discharge hole 9 _; each hole typically having a diameter of 25mm ±5mm, leading to approximately one third of the flow being through the end discharge hole 9, with the balance through the side discharge holes 7,

In use, the fluid jet 1 1 from the fluid discharge nozzle 10 is arranged to be located between 200- 000mm from the axis of the shaft, typically around 300mm away. The jet from the discharge nozzle 0 is directed onto the surface of the trickling filter bed as the auger assembly is rotated and gently lowered into the bed causing the redistribution and washing of the bed material In envisaged embodiments, the fluid discharge nozzle 10 is located at an approximately fixed distance above the bed surface, in other preferred embodiments the fluid discharge nozzle 10 is mounted for vertical reversible displacement with the auger assembly 2. Figure 5 illustrates an embodiment of filter bed remediation apparatus in use during remediation of a filter bed. The auger assembly 1 is located above the filter bed 1 , and the auger rotated as indicated. Water is then pumped through the channel 5 in the auger shaft 3 to discharge through the side and end discharge holes as jets 1 1 of water. The fluid discharge nozzle 10 similarly has water passed through it creating a jet 1 adjacent to the auger 2. The trickling bed support media 13 Is drawn upwards by the rotating auger and a portion of the filter bed 12 is thereb turned over and washed by the jets of water. The filter bed support media 3 is Illustrated schematically in figure 5 in a spaeed-apart configuration for clarity. In reality, of course, the media 13 is packed in close contact, with air gaps between it Water from the auger and from the discharge nozzle 10 passes through the bed, keeping the sloughed-off biofllm material in suspension, and passes into the drain 14 located at the bottom of the bed 2 where it can be collected.

Figure 6 is a schematic process diagram illustrating how filter bed remediation may be carried out on a waste water treatment plant. The diagram shows three elements from a typical plant: an initial settling tank 15 to separate suspended solids, the trickling filter 1 and a further settling tank 16. Arranged above the trickling filter 12 are the sprinkler bars 17 that, under normal operating conditions, rotate and discharge water onto the surface of the trickling bed. These bars 17 are typically suspended by cables 18. Water for use in the remediation process described above maybe drawn from downstream of the trickling filter, for example from the clear water discharge from the settling tank 16. Ideally, the water is drawn from the site's FE (final effluent) washwater system, collected from the supernatant liquors taken from the discharge weirs around the site's humus tank(s). This is passed through the remediation apparatus 1 whilst the bed is being cleaned. The water containing the sloughed-off material, often with a small amount of grit from broken packing material 13 is removed from the bottom of the trickling filter 12 by means of a further pump 9. This stream may then be passed through a separator 20 to remove gritty material before being returned to the water treatment works upstream of the trickling filter, for example into a primary settlement tank 15 in which the suspended sloughed-off biofilm can be made to settle out for disposal Some waste water treatment works are able to cope with suspended gritty material in the inlet stream., and in these cases an additional grit separator 20 is not required.

One particular advantage of this remediation scheme is that the auger and discharge nozzle can be mounted on the end of an articulated arm to allow precise positioning auger assembly over the trickling filter bed to sequentially wash and turn over small regions of the bed. In this way, the operation can be carried out without disturbing the sprinkler distribution arms 17 and their associated cables 18. The flow to the sprinkler arms merely needs to be switched off, and the rotation of the arm assembly halted during the process.

Figure 7 illustrates a schematic flow diagram of part of a typical water treatment installation having four trickling filter beds 1 arranged in parallel and fed from one or more settlement tanks 15 and discharging into a further one or more settlement tank 16. During the remediation process one of the trickling filter beds (labelled 12 A) may be taken out of the process (indicated by the X in figure 7} during remediation. Water is drawn from the exit of the settlement tank 16 and pumped to the remediation apparatus (not illustrated) by flow path 21. Water containing sloughed-off biomass and grit is collected from the bottom of the filter bed 1 a, passed through a separator 20 to remove the gritty material and then returned, by way of flow path 22 to the settlement tank 1 S. In this way, the water treatment plant maybe kept in operation, using the 3 remaining trickling filter beds. The water quality at the outlet maybe periodically monitored, for example for ammonia levels, and if this or the biochemical oxygen demand (BOD) threatens to exceed the discharge limits of the site, then the trickling filter bed being remediated (12a) maybe quickly brought back on stream to maintain the outlet within the environment discharge limits, in this way, transient load increases on the plant may readily be accommodated™ a feature that is not possible if all or some of the packing material was being replaced or removed. Confidential trials of the apparatus and method were carried out on four trickling filter beds thai had been installed and operated in a waste water treatment facility for several decades. Average ammonia concentration in the outlet of the filter beds was measured daily over an approximately three-week period before and after remediation of the filter beds using apparatus and methods described herein. Results from trials are shown in Table

Table 1 - Ammonia Concentration Before and After Treatment

The results demonstrate a significant improvement in the operation of the filter beds following treatment.