NL2012531B1 - Method for dewatering biologically activated sludge and filtering of a waste water influent, and device and system for performing such method. - Google Patents

Description

Method for dewatering biologically activated sludge and filtering of a waste water influent, and device and system for performing such method

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. In such device 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% from the sludge reactor 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 activated sludge of a sludge reactor is collected from the sludge reactor having a dry solid content in the range of 0.04-0.8% and 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 FeCl3 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 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 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 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; 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; 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.

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 m3/hr, a sieve surface of 0.5 m2, and openings in the belts of about 350 pm. 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.

Clauses 1. Method for dewatering activated sludge and filtering of a waste water influent, the method comprising the steps of: supplying the influent to a filter belt device and filtering the influent with the filter belt; providing a filter mat of accumulated solid particles comprising cellulose particles from the influent on a 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% from the sludge reactor and providing the activated sludge to the filter mat. 2. Method according to clause 1, wherein the sludge reactor comprises an aerobic reactor and the activated sludge comprises activated aerobic sludge. 3. Method according to clause 1 or 2, wherein the processing time of the collected activated sludge from collecting to removal from the filter mat substantially is in the range of 1 to 20 minutes, preferably in the range of 2 to 10 minutes. 4. Method according to clause 3, wherein the processing time is such that it is prevented that the collected activated sludge becomes anoxic and/or anaerobic. 5. Method according to one or more of the foregoing clauses, wherein the collecting of activated sludge and providing of activated sludge to the filter mat is such that phosphor and/or phosphate remains incorporated in the sludge. 6. Method according to one or more of the foregoing clauses, wherein a part of the removed filter mat material is supplied as a return flow to the filter belt device for improving the filter mat structure. 7. Method according to one or more of the foregoing clauses, further comprising the step of controlling the inflow of collected activated sludge with a sludge controller. 8. Method according to clause 7, wherein the sludge controller controls the dosing of the sludge to the filter mat. 9. Method according to one or more of the foregoing clauses, further comprising 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. 10. Method according to one or more of the foregoing clauses, further comprising the step of supplying flocculants to the collected activated sludge. 11. Method according to one or more of the foregoing clauses, further comprising the step of supplying a filter mat structure enhancing material to the filter belt device. 12. Method according to clause 11, wherein the material comprises a cellulose comprising fluid and/or coal-dust. 13. Method according to one or more of the foregoing clauses, further comprising the step of providing the material collected in the filter mat to a digester for producing biogas. 14. Filter belt device for dewatering activated sludge and filtering of a waste water influent comprising: a fluid inlet for waste water influent; a filter belt for accumulating solid particles comprising cellulose particles from the influent and achieving a filter mat; 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; and a controller for controlling the belt speed and dosing of activated sludge from the sludge inlet on the filter mat of the belt. 15. Waste water treatment system for dewatering activated sludge and filtering of a waste water influent comprising: a filter belt device according to clause 14; and an aerobic sludge reactor.

Claims (15)

1. Werkwijze voor het ontwateren van actief slib en het filteren van afvalwaterstroom, de werkwijze omvattende de stappen: het toevoeren van de influent naar een filterbandinrichting en het filteren van de influent met een filterband; het voorzien van een filtermat van geaccumuleerde vaste deeltjes omvattende cellulosedeeltjes uit de influent op de band van de filterbandinrichting; het toevoeren van het gefilterde influent naar een slibreactor; en het verzamelen van actief aerobe slib met een vaste stof gehalte in het bereik van 0,04-0,8% uit de slibreactor en het voorzien van het actieve slib aan de filtermat.A method for dewatering active sludge and filtering waste water stream, the method comprising the steps of: supplying the influent to a filter tape device and filtering the influent with a filter tape; providing a filter mat of accumulated solid particles comprising cellulose particles from the influent on the band of the filter band device; supplying the filtered influent to a sludge reactor; and collecting active aerobic sludge with a solids content in the range of 0.04-0.8% from the sludge reactor and providing the active sludge to the filter mat. 2. Werkwijze volgens conclusie 1, waarin de slibreactor een aerobe reactor omvat en het actief slib actief aëroob slib omvat.The method of claim 1, wherein the sludge reactor comprises an aerobic reactor and the active sludge comprises active aerobic sludge. 3. Werkwijze volgens conclusie 1 of 2, waarin de verwerkingstijd van het verzamelde actieve slib vanaf het verzamelen naar het verwijderen vanaf de filtermat in hoofdzaak is gelegen in het bereik van 10 tot 20 minuten, bij voorkeur in het bereik van 2 tot 10 minuten.The method according to claim 1 or 2, wherein the processing time of the collected active sludge from the collection to the removal from the filter mat is substantially in the range of 10 to 20 minutes, preferably in the range of 2 to 10 minutes. 4. Werkwijze volgens conclusie 3, waarin de verwerkingstijd zodanig is dat wordt voorkomen dat het verzamelde actieve slib anoxisch en/of anaerobisch wordt.The method of claim 3, wherein the processing time is such that the active sludge collected is prevented from becoming anoxic and / or anaerobic. 5. Werkwijze volgens één of meer van de voorgaande conclusies, waarin het verzamelen van actief slib en het voorzien van actief slib aan een filtermat zodanig is dat fosfor en/of fosfaat gehouden blijft in het slib.Method according to one or more of the preceding claims, wherein collecting active sludge and providing active sludge on a filter mat is such that phosphorus and / or phosphate remains in the sludge. 6. Werkwijze volgens één of meer van de voorgaande conclusies, waarin een deel van het verwijderde filtermat materiaal wordt toegevoerd als een retourstroom aan de filterbandinrichting voor het verbeteren van de filtermatstructuur.The method of any one of the preceding claims, wherein a portion of the removed filter mat material is supplied as a return flow to the filter belt device for improving the filter mat structure. 7. Werkwijze volgens één of meer van de voorgaande conclusies, verder omvattende de stap van het regelen van de instroom van het verzamelde actieve slib met een slibregelaar.Method according to one or more of the preceding claims, further comprising the step of controlling the inflow of the collected active sludge with a sludge controller. 8. Werkwijze volgens conclusie 7, waarin de slibregelaar het doseren van het slib naar de filtermat regelt.The method of claim 7, wherein the sludge controller controls the dosing of the sludge to the filter mat. 9. Werkwijze volgens één of meer van de voorgaande conclusies, verder omvattende de stap van het regelen van snelheid van de filterband met een bandregelaar gebruikmakend van informatie over de actuele condities van de filtermat en filterbandinrichting.Method according to one or more of the preceding claims, further comprising the step of controlling the speed of the filter tape with a tape controller using information about the current conditions of the filter mat and filter tape device. 10. Werkwijze volgens één of meer van de voorgaande conclusies, verder omvattende de stap van het toevoeren van vlokmiddelen aan het verzamelde actieve slib.Method according to one or more of the preceding claims, further comprising the step of supplying flocculants to the collected active sludge. 11. Werkwijze volgens één of meer van de voorgaande conclusies, verder omvattende de stap van het toevoeren van een filtermatstructuur verbeterend materiaal naar de filterbandinrichting.The method of any one of the preceding claims, further comprising the step of feeding a filter mat structure improving material to the filter tape device. 12. Werkwijze volgens conclusie 11, waarin het materiaal een cellulose omvattende fluïdum en/of koolgruis omvat.The method of claim 11, wherein the material comprises a cellulose comprising fluid and / or coal dust. 13. Werkwijze volgens één of meer van de voorgaande conclusies, verder omvattende de stap van het voorzien van een materiaal verzameld in de filtermat aan een digester voor het produceren van biogas.A method according to any of the preceding claims, further comprising the step of providing a material collected in the filter mat to a digester for producing biogas. 14. Filterbandinrichting voor het ontwateren van actief slib en het filteren van afvalwater influent omvattende: een fluïduminlaat voor aan voer van afvalwater influent; een filterband voor het verzamelen van vaste deeltjes omvattende cellulosedeeltjes uit de influent en het bewerkstelligen van een filtermat; een fluïdumuitlaat voor het toevoeren van het gefilterde influent naar een slibreactor; een filtermat-materiaal uitlaat; een slibinlaat voor het toevoeren van actief slib uit de slibreactor naar de filtermat; en een regelaar voor het regelen van de bandsnelheid en het doseren van actief slib uit de slibinlaat op de filtermat van de band.A filter belt device for dewatering active sludge and filtering waste water influent comprising: a fluid inlet for supplying waste water influent; a filter tape for collecting solid particles comprising cellulose particles from the influent and effecting a filter mat; a fluid outlet for supplying the filtered influent to a sludge reactor; a filter mat material outlet; a sludge inlet for supplying active sludge from the sludge reactor to the filter mat; and a controller for controlling the belt speed and dosing active sludge from the sludge inlet to the filter mat of the belt. 15. Afvalwaterbehandelingssysteem voor het ontwateren van actief slib en het filteren van afvalwater influent omvattende: een filterbandinrichting volgens conclusie 14; en een aerobe slibreactor.A waste water treatment system for dewatering active sludge and filtering waste water influent comprising: a filter belt device according to claim 14; and an aerobic sludge reactor.