The present invention relates to dewatering of activated sludge and filtering of a waste water influent. Dewatering of sludge in waste water treatment is important to reduce the amount of sludge and to reduce the costs for handling the sludge and/or to increase the caloric value per ton of dry solids. Such waste water may involve municipal and industrial waste water.

Conventional waste water treatment involves a pre-treatment filtering of the influent with screens and sieves. For example, this may involve a settling/sedimentation tank and/or a screen for removing (large) items from the fluid. In further steps the water is treated to reduce the level of contaminants in the water to acceptable limits. This may involve the use of one or more sludge reactors, including aerobic, anaerobic and anoxic sludge or bio-reactors.

Some of the conventional pre-treatment systems include a filter belt device. For example, WO 2012/105847 Al discloses such device wherein a filter mat structure is created on a filter belt from solid particles accumulated from the influent. The filter belt with the filter mat structure thereon filters contaminants from the influent, while the liquid passes through the belt. The use of such filtering device contributes to the reduction of the expenses and complexity of the further treatment steps. Such further treatment steps often involve the use of sludge reactors to achieve a purified water flow. The sludge reactors produce an amount of excess sludge that needs to be removed and/or exposed to a post-treatment involving one or more drying, dewatering and/or thickening steps, for example. All further treatment steps increase the complexity and costs of handling waste water influent.

The present invention has for its object to provide a method for treating waste water that enables an effective purification process.

Therefore, the present invention provides for its purpose a method for dewatering activated sludge and filtering of a waste water influent, the method according to the invention comprising the steps of:

supplying the influent to a filter belt device and filtering the influent with a filter belt;

- providing a filter mat of accumulated solid particles from the influent on the belt of the filter belt device;

supplying the filtered influent to a sludge reactor; and

collecting activated aerobic sludge with a dry solids content in the range of 0.04- 0.8% and providing the activated sludge to the filter mat.

By supplying the waste water as an influent to a filter belt device and filtering the influent with a filter belt, solid particles are collected and accumulated on the surface of the filter belt in a filter mat structure or filter matrix. The filter mat that is provided on the belt surface of the filter belt device according to the invention comprises a substantial amount of cellulose particles. These cellulose particles may originate from toilet paper in municipal waste water, for example. In the next step the filtered influent, the filtrate, is supplied to a sludge reactor. In the context of this description a sludge reactor may also relate to a bioreactor for treating biologically activated sludge.

According to the invention the method involves providing a filter mat onto a filter belt, with the filter mat particularly originating from cellulose feed material. The collected activated sludge is preferably dosed onto the matured filter mat, preferably at a location further down on the filter belt in the direction of movement of the filter belt and filter mat thereon. This provides a serial type filtering that renders the dewatering more effective and efficient as compared to conventional methods. In fact, in a presently preferred embodiment according to the invention the filter mat is provided on the filter belt at a first location and the activated fresh sludge is supplied to the filter matrix at a second location further down the filter belt in the direction of movement of the filter matrix. This achieves that the fresh sludge is matured on the belt and the sludge is will be trapped in the filter mat matrix. Preferably, the activated fresh sludge is collected from the sludge reactor.

According to the invention the activated sludge of a sludge reactor is preferably collected from the sludge reactor, has a dry solid content in the range of 0.04-0.8% and is supplied to the filter mat of the filter belt device in the pre-treatment step. Adding surplus activated sludge to the filter mat provides a dewatering step of the sludge as water in the sludge moves through the filter belt while solid particles are maintained in the filter mat structure. More contaminants are being removed from the influent thereby rendering further treatment steps more effectively and efficiently. Preferably, the activated sludge specifically relates to biologically activated sludge.

In addition, providing the activated sludge to the filter matrix achieves a dewatering of this activated sludge. Especially having cellulose particles being included in the filter mat improves the dewatering of the sludge material. Filter mat material leaving the filter mat device comprising the collected contaminants from both the influent and the sludge particles typically has a dry solid content of about 25-45%. It will be understood that a dry solid content depends on a number of parameters, however, especially the combination of the use of activated sludge with a filter mat comprising cellulose particles achieves a good dewatering result. This reduces the amount of sludge that would require post-treatment, often involving a number of drying, dewatering and/or thickening steps requiring the use of a lot of energy and/or chemicals. This renders the process more efficient.

In a presently preferred embodiment according to the invention the activated sludge originates from an aerobic sludge reactor and is activated aerobic sludge. It was shown that the use of activated aerobic sludge improves the processing of waste water while at the same time the efforts related to post-treatment of the activated sludge can be significantly reduced.

A further advantage of performing the pre-treatment step as a combination of dewatering activated sludge and filtering a waste water influent is the collecting of cellulose particles in the filter mat. The cellulose particles that are collected from this influent can be anaerobically treated such that biogas is produced. This renders the dewatering and filtering step even more effective as the cellulose particles can be removed from the influent at an early stage of the treatment with an enhanced biogas production in the post-treatment step. It is shown that a significant amount of the cellulose particles that are collected in the pre-treatment step can be transformed in biogas in an anaerobic post-treatment step. As compared to conventional waste water treatment this is an improvement of over 30% as compared to the conventional decomposing of cellulose particles under aerobic conditions and/or anaerobic conditions. Furthermore, such conventional treatment requires a significant amount of energy that can be reduced in the post-treatment step as described earlier.

In a further advantageous preferred embodiment according to the present invention the processing time of the collected activated sludge between collecting the activated sludge from the preferably aerobic sludge reactor to the removal of the collected activated sludge from the filter mat is in the range of 1 to 20 minutes, preferably in the range of 2 to 10 minutes.

Conventional water treatment operations make use of so-called biological phosphate removal. Phosphate is collected in the sludge to achieve a fluid that is substantially free of phosphate. A problem that occurs in water treatment is that under anaerobic conditions the sludge returns the phosphate to the liquid phase. To (again) bind the phosphate the use of chemicals is required, such as FeCl ₃ to remove the phosphate from the liquid waste. This results in a ferric phosphate, for example, that has to be removed as waste.

Through the use of aerobic sludge, that preferably originates from the aerobic sludge reactor, in the filter belt device, the sludge that is provided to the filter mat behaves as an aerobic sludge without a significant amount of phosphate being removed from the sludge. This is preferably achieved by keeping the sludge toxic. This provides an advantageous removal of the phosphate from the influent in an energy efficient manner. As a further advantage the sludge that is used in the filter mat comprising the phosphate and/or phosphor components can optionally be treated further in a post-treatment step. This renders dewatering activated sludge and filtering of a waste water influent according to the invention more efficiently.

In a further advantageous preferred embodiment according to the present invention part of the removed filter material is supplied as a return flow to the filter belt device for improving the filter mat structure. The use of at least a part of the removed filter mat material from the filter belt as a return flow to the filter belt device further enhances the filter mat structure thereby improving the filtering of the influent. This enables a higher throughput of influent through the filter mat device.

In a further advantageous preferred embodiment according to the present invention the method further comprises the step of controlling the inflow of collected activated sludge onto the filter mat on the filter belt with a sludge controller.

The sludge controller controls the inflow of collected activated sludge. Preferably, the controller controls the amount of inflow depending on the conditions of the filter mat, filter mat structure, influent characteristics, amount of throughput through the device and/or the conditions of the collected activated sludge. Preferably, the sludge controller controls the dosing of the sludge to the filter mat. By directly controlling the dosing of the sludge to the filter mat the effect of the sludge on this filter mat can be directly manipulated. This further improves the efficiency of providing the preferred activated aerobic sludge to the filter mat and enables dealing with the variations that occur in the waste water influent.

Preferably, the method according to the invention further comprises the step of controlling the speed of the filter belt with a belt controller using information about the actual conditions of the filter mat and filter belt device. In addition, the belt controller may use information about the incoming influent such as the dry solids content and/or information about the activated sludge that is fed back to the filter belt device. Preferably, the sludge controller and belt controller cooperate and/or are combined in one filter belt device controller to optimise the overall performance of the dewatering and filtering step.

In a presently preferred embodiment the feed cellulose concentration is measured with a first sensor, for example involving an indirect measurement on the basis of insoluble solids concentration. Depending on variations in the concentration the activated sludge is dosed by the sludge controller to achieve an optimal cellulose/activated sludge ratio. Controlling the activated sludge supply on basis of cellulose concentrations of the influent showed optimal dewatering performance.

In a further preferred embodiment according to the present invention the method further comprises the step of supplying flocculants to the collected activated sludge.

By supplying flocculants to the collected activated sludge the effect of the sludge on the filter mat can be enhanced. The flocculants may comprise polyelectrolyte, for example, however, the use of the flocculants can be significantly reduced by the use of aerobic sludge as compared to conventional treatments. Flocculants use is however limited, if compared to flocculants dosages in conventional sludge handling processes.

In a preferred embodiment according to the present invention a filter mat structure enhancing material is supplied to the filter belt device. This further improves the filtering effect and in addition further improves the incorporation of the aerobic sludge into the filter mat structure. This material may comprise a cellulose comprising fluid and/or coal-dust. It is shown that these materials further improve the efficiency of the filtering and the following step.

In a presently preferred embodiment the material collected in the filter mat is provided to a biogas reactor. As mentioned earlier this renders the biogas production more efficiently as compared to conventional treatments of waste water.

The invention further relates to a filter belt device for dewatering activated sludge and filtering of a waste water influent, and a waste water treatment system comprising such device, with the device comprising:

- a fluid inlet for waste water influent;

a filter belt for accumulating solid particles from the influent and achieving a filter mat at a first location on the filter belt;

a fluid outlet for supplying the filtered influent to a sludge reactor; a filter mat material outlet;

- a sludge inlet for supply of activated sludge from the sludge reactor to the filter

Mat at a second location on the filter belt; and

a controller for controlling the belt speed and dosing of activated sludge from the sludge inlet on the filter mat of the belt.

Such device and system provide the same effects and advantages as those in respect of the method. Preferably, the controller also controls the supply of flocculants through a flocculants inlet. Optionally, the filter belt device can be used in combination with a biogas reactor. The sludge that is supplied preferably originates from an aerobic sludge reactor.

According to the invention the device and system provide a filter belt on which a filter mat is provided at a first location, particularly from the cellulose feed material. Incoming sludge is dosed onto the matured filter mat at a second location further down on the filter belt in the direction of movement of the filter belt and filter mat thereon. This provides a serial type filtering that renders the dewatering more effective and efficient as compared to conventional systems. This enables simultaneous treatment of the influent and the collected sludge.

Preferably, the sludge inlet provides sludge from an activated sludge treatment process, with the sludge not being pre-treated by settling, storage etc. In fact, the sludge is dosed directly onto the filter mat of the belt at the second location. The second location is further down the filter belt as seen in the moving direction of the filter belt as compared to the first location. In such embodiment the sludge that is dosed onto the filter mat may be flocculated in-line. Furthermore, the sludge that is dosed onto the filter mat is matured on the belt and the sludge will be trapped in the filter mat matrix. This provides an effective and efficient dewatering of the sludge. Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the drawings, in which:

figure 1 shows a filter belt device according to the invention;

figure 2 shows a conventional treatment process; and

- figure 3 shows the treatment process according to the present invention involving the filter belt device of figure 1.

Filter belt device 2 (figure 1) comprises a housing 4 with an influent inlet 6. Influent inlet 6 comprises inlet valve 8 and sensor 10 to measure the characteristics of influent 12 that is supplied to device 2. Filter belt device 2 comprises a continuous belt 14 with rollers 16 that act as drive for belt 14. In the illustrated embodiment filter, and to be interpreted as an example only, belt device 2 has a maximum capacity of 120 m ³ /hr, a sieve surface of 0.5 m ² , and openings in the belts of about 350 μπι. It will be understood that other dimensions are also possible according to the invention. In fact, the actual dimensions may depend on the actual application of the filter belt device 2.

Belt 14 collects solid particles 18 that are present in influent 12 on its belt surface.

Particles 18 built a filter mat structure 20 with effective filter openings that are often smaller than the openings in belt 14. The thickness of filter mat 20 can be manipulated with the belt speed, for example. Air nozzle 22 can be used to blow air to the inside surface of the belt to collect dry solids/sievings from the belt. The removed material from filter mat 20 is collected in buffer 24 and removed from filter belt device 2 at outlet 26 for further processing of the sievings. The filtered influent is collected as filtrate 28 and exits filter belt device 2 at filtrate outlet 30.

In the illustrated embodiments filter belt device 2 is provided with level sensor 32 for measuring the level of fluid in the device, and optional level sensor 34 for determining the level of filtrate 28. Furthermore, optionally, filter structure sensor 36 is provided to determine the thickness and/or structure of filter mat 20.

Filter belt device 2 is further provided with sludge distributor 38 that distributes sludge material as additional material 40 to filter mat structure 20. Structure providing material 40 originates from activated sludge inlet 42 and/or additional inlet 44 that may receive material from an external source, such as coal-dust and/or sievings from outlet 26. Controller 46 collects level measurement information 48 from sensor 32, level measurement information 50 from optional sensor 36, structure measurement information 51 from sensor 34, sensor information 52 from roller 16 and/or measurement information 53 from distributor 38. In addition, characteristic or relevant influent information 54 from sensor 10 can also be collected by controller 46. Controller 46 determines the optimal settings for filter belt device 2 trying to achieve the objectives 56 as set by user 58. Controller 46 provides control signal 60 to roller 16, control signal 62 to knife 22, control signal 64 to distributor 38, and control signal 66 to inlet valve 8. Optionally, also other control actions can be taken, such as controlling outlet valves in one or more of outlets 26, 30. It will be understood that controller 46 may relate to an integrated central controller and/or a number of decentralised controllers.

Influent 12 is provided to filter belt device 2 and forced through filter mat structure 20 at belt 14. Particles 18 are accumulated on filter mat structure 20 and the filtrate will be supplied to filtrate outlet 30. Outlet 30 can be provided as an overflow. The collected particles 18 in structure 20 can be supplied to sievings outlet 26. By providing additional material to structure 20 the filter mat structure is significantly improved, thereby improving the entire filtering operation in filter belt device 2. This has the result that the filtrate 28 can be further processed in a more efficient manner.

Conventional waste water treatment process 68 (figure 2) starts with an influent 70 having a dry solids content of about 0.04%. In the waste water treatment plant 72 the dry solids content is increased. Further processing step 74 increases the dry solids content to about 2.5%. Further steps include mixing iron chloride 78 in an amount of 20 kg/ton ds for example, and polyelectrolyte 80 in an amount of 3 kg/ton ds, for example. From thickening belt 82 the dry solids content is further increased to 5-8%. From fermentation step 86, biogas 84 can be removed, the resulting fluid can be provided with an additional iron chloride 90 in an amount of 65 kg/ton ds and polyelectrolyte in an amount of 7.5 kg/ton. Press 94 increases the dry solids contents to about 26%. In evaporator 96 the dry solids content is further increased to 92% and the resulting products can be used as a fuel in other processes. It will be understood that process scheme 68 is an example of a conventional process scheme that would involve further processing steps.

In process 100 involving the device and/or method according to the present invention, the processing scheme 100 (figure 3) starts with receipt of influent 70. Influent 70 is provided to filter belt device 2. Optionally, filter belt device 2 is provided with activated aerobic sludge originating from the waste water treatment plant 72 to which polyelectrolyte 78 can be added. The resulting product from waste water treatment plant 72 is provided to fermentation process 102. The resulting product can be used in further processes 106, including the use as fuel for electric energy production. The sievings of filter belt device 2 can be provided to further process steps 104. It will be understood that other applications would also be possible in accordance with the present invention.

The present invention is by no means limited to the above described preferred

embodiments thereof. The rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.