Control System of Wastewater Treatment Plant

Abstract

The control system of the present invention can be constructed using different measurement units and control units. Which units are used to construct the control system depends on the wastewater treatment plant. This system structure enables the construction of a control system suitable for a specific wastewater treatment plant. Therefore, the present invention enables the construction of control systems for different wastewater treatment plants to operate the wastewater plants more effectively.

Description

Technical Field

[0001] The present invention relates to a control system for a wastewater treatment plant. Background Art

[0002] Wastewater treatment plants are used to purify municipal sewage and / or industrial wastewater. The implementation of the treatment plant depends on the size of the community and the quality of the wastewater to be treated as well as the quality requirements of the treated water. Industrial wastewater can be treated in a separate industrial wastewater treatment plant or introduced into a municipal wastewater plant, for example, potentially pretreated if environmental permit requirements so dictate. Rainwater can also be introduced into the sewage, which affects the quality of the wastewater pumped to the wastewater treatment plant.

[0003] Figure 1 A simple example of a known wastewater treatment plant is shown. Wastewater 1 first flows to mechanical preliminary treatment 2, where different objects are removed from the wastewater. Larger objects are removed by using a coarse screen. Smaller objects (such as matches, etc.) are removed by a fine screen. Some other wastewater treatment plants may have only one screen. Preliminary treatment usually has at least one chamber to remove gravel / grit. There may be separate chambers to remove gravel and grit. The removed objects, gravel, and grit are not reusable due to their high pollution.

[0004] After preliminary treatment, the wastewater flows into a primary treatment tank 3, also known as the primary treatment process. Primary treatment is usually based on the sedimentation of particles in the wastewater. Sediment forms sludge at the bottom of the tank, which is called primary sludge, and is separated from the tank for further processing. The secondary treatment process 4 is based on a biological process 5. It uses bacteria that consume pollutants, especially biodegradable organic matter, carbon, and phosphorus as well as some nitrogen. Biomass with organic and / or inorganic residues forms sludge. To enable the biological process to operate properly, the sludge (and bacteria) is pumped to a secondary sedimentation tank 6 that is part of the biological process. The sludge sediments at the bottom of the secondary sedimentation tank 6.

[0005] The main part of the sludge is pumped back to the biological process. The remaining sludge, excess sludge, and primary sludge are transported to further processing, such as thickening, anaerobic digestion 7, and sludge dewatering, where biogas is produced. The anaerobic digester can be at the wastewater treatment plant or another location. The digested and dewatered sludge 8 can be transported to a final use, such as composting, incineration, or for agriculture. The effluent from the secondary sedimentation tank 6 is usually clean enough to be released to a receiver, but there may be one or more additional processes 10 to further purify the treated water. The additional process can be, for example, a disinfection process using chlorine, ozone, peroxide, peracetic acid, or UV (ultraviolet).

[0006] For controlling the process of a wastewater treatment plant, there are some online measurements, such as the influent wastewater flow rate, the oxygen content in the aeration zone during the biological process, and the mixed liquor suspended solids (MLSS), which is the concentration of suspended solids in a typical aeration zone, more precisely the concentration of activated sludge. However, biological treatment can also be carried out without an aeration zone. There can also be other online measurements. The online measurements are used for monitoring, and the monitored values are mainly used to manually or semi-automatically change the operating parameters. Only a few parameters (the oxygen content and the excess sludge from the biological process to keep the MLSS uniform) are usually automatically controlled. Summary of the Invention

[0007] The object of the present invention is to improve the operation of a wastewater treatment plant. This object is achieved in the manner described in the independent claims. The dependent claims illustrate different embodiments of the present invention. The present invention is based on the idea that a control system according to the present invention can be constructed using different measurement units and control units. What units are used to construct the control system depends on the wastewater treatment plant. Such a system structure enables a control system suitable for a specific wastewater treatment plant to be constructed. In other words, the present invention enables a control system to be constructed for different wastewater treatment plants so that the wastewater plants can operate more efficiently.

[0008] The control system of the wastewater treatment plant of the present invention is for a wastewater treatment plant that at least includes a primary treatment process 3 and a secondary treatment process 4. The plant may also include other processes. The control system includes a measurement unit 12 arranged to measure the turbidity or suspended solids of the wastewater before or during the primary treatment process 3, and a second measurement unit 13 arranged to measure the nitrate level or the oxidation-reduction value in the denitrification zone of the secondary treatment process 4.

[0009] The control system further includes a control unit 14, which is arranged to receive the measurement values (measurements) from the measurement unit 12 and the second measurement unit 13. The control unit is also arranged to form a control signal for dispensing at least one chemical before the primary treatment or into the influent of the primary treatment process 3 or into the primary treatment process 3 based on the measurement value from the measurement unit 12. The control unit is further arranged to adjust the dispensing based on the measurement value from the second measurement unit 13. Brief Description of the Drawings

[0010] Hereinafter, the present invention will be described in more detail with reference to the drawings, in which

[0011] Figure 1 an example of a known wastewater treatment plant is shown,

[0012] Figure 2 an example of the control system of the present invention is shown,

[0013] Figure 3shows Figure 2 an example of a control unit in the system of

[0014] Figure 4 shows another example of the control system of the present invention,

[0015] Figure 5 shows Figure 4 an example of a control unit in the system of

[0016] Figure 6 shows yet another example of the control system of the present invention,

[0017] Figure 7 shows Figure 6 an example of a control unit in the system of Detailed Description of the Invention

[0018] Figure 2 shows an example of the control system according to the present invention. The control system of the wastewater treatment plant of the present invention is used for a wastewater treatment plant including at least a primary treatment process 3 and a secondary treatment process 4. The plant may also include other processes. Figure 2 Also shown as Figure 1 is also shown the mechanical preliminary treatment 2.

[0019] The control system includes a measuring unit 12 arranged to measure the turbidity or suspended solids of the wastewater before or during the primary treatment process 3, and a second measuring unit 13 arranged to measure the nitrate level or redox value in the denitrification zone 4A of the secondary treatment process 4. In addition, the control system may further include a flowmeter 11 arranged to measure the wastewater flow rate 1 entering the wastewater treatment plant.

[0020] The control system further includes a control unit 14 which is arranged to receive measurement values from the measuring unit 12 and the second measuring unit 13. The control unit is also arranged to form a control signal for dispensing at least one chemical before the primary treatment 3 or into the inflow to the primary treatment process 3 or into the primary treatment process 3 based on the measurement values from the measuring unit 12. The control unit is further arranged to adjust the dispensing based on the measurement values from the second measuring unit 13. The control unit 14 may also be arranged to receive measurement values from the flowmeter 11 for use when forming a control signal for dispensing at least one chemical before the primary treatment 3 or into the inflow to the primary treatment process 3 or into the primary treatment process 3. The dispensing position of at least one chemical before the primary treatment 3 or into the inflow to the primary treatment process 3 may be before the preliminary treatment 2 or just before the end of the inflow channel / pipeline leading to the primary treatment process 3, or at the start of the primary treatment process 3, or at any suitable position between before the preliminary treatment 2 and the start of the primary treatment process 3. And as described above, the dispensing may also be carried out during the primary treatment process 3.

[0021] As Figure 2 can be seen, the control unit 14 can be a unit separate from the monitoring / control system 15 of the factory. If all sensors and dosing devices are in direct contact with the control unit 14, the separate unit can even be completely independent of the monitoring / control system 15 of the factory. This applies to other embodiments such as Figure 2 , Figure 4 and Figure 6 . However, as an alternative embodiment, the control unit can also be incorporated into the monitoring / control system of the factory. Thus, the control unit 14 can be in a server at another location, in which case it can be implemented as a cloud service, and the communication with the factory (for receiving measurement data and transmitting control-related signals) can be arranged via a communication network (such as a wireless network and / or a fixed network).

[0022] In the present invention, at least one chemical is dosed before the primary treatment 3 or into the inflow to the primary sedimentation tank 3 or into the primary sedimentation tank 3. Thus, there are at least one chemical tank / reservoir 17, 19 and dosing devices 16, 18 for supplying the chemical from the tank / reservoir to the inflow to the primary sedimentation tank 3 or directly into the primary sedimentation tank. Figure 2 The embodiment of

[0023] shows two chemical tanks and dosing devices. In many cases, appropriate wastewater treatment can be achieved by using one or two chemicals, but additional chemicals can also be used if required or preferred.

[0024] Suitable dosing devices (such as pumps) can be used to supply one or more chemicals before the primary treatment 3 or into the inflow to the primary treatment 3 or directly into the primary treatment 3. Thus, the wastewater treatment plant has at least one dosing device for supplying chemicals.

[0025] The chemicals used can be inorganic coagulants, which typically consist of Al salts or Fe salts. These salts coagulate small particles, so they precipitate easily in primary treatment and thus improve the removal of solid matter in the wastewater, more specifically the suspended solid concentration. This has the effect of removing more primary sludge 3A from the bottom of the primary sedimentation tank 3. The more primary sludge is produced, the more material is supplied to the anaerobic digester 7, where biogas 7A is produced. In other words, when having the control system of the present invention, the wastewater treatment plant can produce more biogas and thus operate more efficiently. The primary sludge 3A has a high energy content, so it is a good material for producing biogas. It can be seen that there can also be a sensor 70 to measure the biogas production. The control unit 14 ( Figure 4 and Figure 6 14A, 14B in the embodiments of

[0026] The inorganic coagulants also precipitate dissolved phosphorus (mainly in the form of phosphates). Typically, the higher the dose, the better the removal effect of phosphates. However, over-dosing is not preferred because it can interfere with secondary processes.

[0027] In a few cases, organic coagulants are used. Organic coagulants consist of polymeric substances (such as polyamines, polyDADMAC, chitosan, etc.). When these are used, the removal of dissolved phosphates does not occur.

[0028] The chemicals used can also be polymers (such as polyamines, polyDADMAC, chitosan, which can also be coagulants). Additionally, polyacrylamide, Mannich polymers, starch-based polymers, and other polymers can be used. The polymers can carry a cationic or anionic charge, or can be uncharged. The purpose of using the polymers is to aggregate the particles into larger particles so that they are easier to separate. The separation occurs in the primary treatment process 3. Thus, the use of polymers also improves the production of primary sludge 3A, which means more biogas 7A can be produced.

[0029] Any combination of one or more coagulants and / or one or more polymers optionally together with another chemical can be used. The other chemicals can include but are not limited to acids, bases, carbonates, nutrients (phosphorus, nitrogen), and carbon sources. The chemicals used depend on the needs of the wastewater treatment plant. In the present invention, the combination of coagulants and polymers is used effectively, which is considered to give a very good possibility of achieving the best treatment results. In Figure 2In the illustrated embodiment, the dosing device 16 and the tank 17 can be used for polymers, and the dosing device 18 and the tank 19 are for the coagulant. In another embodiment, similar dosing devices and tanks / reservoirs can be used for other combinations of chemicals. Thus, the chemicals used improve the sedimentation in the primary treatment 3, and thereby form more primary sludge 3A, which in turn can generate more biogas 7A in the digester 7. Regarding the function of the secondary treatment 4, it is beneficial to remove as much of the primary sludge 3A as possible. The effluent wastewater from the primary treatment still contains nutrients for the biological treatment in the secondary process 4.

[0030] After the primary treatment, the wastewater is treated in a biological treatment (secondary treatment). The secondary treatment 4 comprises a denitrification zone 4A and an aeration zone 4B, or multiple denitrification zones and aeration zones. The drawings of this specification are schematic and illustrate the activated sludge process. However, other biological processes can be used for the secondary treatment.

[0031] Denitrification is the process in which nitrate is reduced to gaseous nitrogen. Denitrification is based on the ability of denitrifying bacteria to reduce nitrogen in the form of nitrate to free nitrogen gas and release it into the atmosphere. In the aeration zone 4B of the activated sludge process, the ammonium nitrogen contained in the wastewater is oxidized to nitrate NO3 (more specifically, the wastewater is oxidized to nitrite and then further oxidized to nitrate), which is reduced to nitrogen gas N2 in the denitrification zone. In other words, the aeration zone is a nitrification zone, where typically most of the nitrogen in the form of ammonium NH4+ is converted to nitrate NO3- by nitrifying bacteria (nitrification). The aeration zone also degrades biodegradable substances. This is done before nitrification occurs. In some cases, nitrification is limited to nitrite NO2-, which is then denitrified to N2 by denitrifying bacteria or by bacteria that react with nitrite and ammonium to form nitrogen gas and biomass. In the secondary treatment, nitrogen is removed, and the BOD / COD ratio is also reduced. BOD is the biological oxygen demand, and COD is the chemical oxygen demand. The reduced BOD / COD ratio can be used as an indicator of the treated water. The biological process 4 can also remove phosphate using polyphosphate-accumulating bacteria. The biological process 4 can be an activated sludge process (AS) or a moving bed biofilm reactor (MBBR), a trickling filter, or a membrane bioreactor (MBR) or a combination thereof. The most common are AS and MBBR.

[0032] The wastewater is arranged to flow from the biological treatment (denitrification zone 4A and nitrification zone 4B) to the secondary sedimentation tank 6 which is part of the biological process. The sludge settles at the bottom of the secondary sedimentation tank 6. In this way, the biomass (containing live and dead bacteria as well as organic and / or inorganic residues) is removed from the secondary treatment. The main part of the sludge is pumped back to the biological process to activate it. The remaining sludge (i.e., the excess sludge) is conveyed to another process such as an anaerobic digester 7 where biogas is produced. The effluent from the secondary sedimentation tank 6 is usually clean enough to be discharged to a receiver, but there may be one or more additional processes as Figure 1 shown.

[0033] Figure 3 shown in the control unit 14. The control unit 14 is arranged to receive the measured values 121, 131 from the measuring unit 12 and the second measuring unit 13. The control unit is also arranged to form a control signal 37 for dosing at least one chemical before the primary treatment 3 or into the influent to the primary treatment process 3 or into the primary treatment process 3 based on the measured value from the measuring unit 12. The control unit is further arranged to adjust the dosing based on the measured value from the second measuring unit 13. As described above, the measuring unit 12 is arranged to measure the turbidity or suspended solids of the wastewater before the primary treatment process, and the second measuring unit 13 is arranged to measure the nitrate level or the redox value in the denitrification zone of the secondary treatment process. Redox is an electrical measurement showing the tendency of a chemical to gain or lose electrons. When electrons are lost, the chemical is oxidized. When electrons are gained, the chemical is reduced. In addition, the control unit 14 may also be arranged to receive the measured value 111 from the flowmeter 11, in which case the control unit is also arranged to form a control signal 37 for dosing at least one chemical before the primary treatment 3 or into the influent to the primary treatment process 3 or into the primary treatment process 3 also using the measured value from the flowmeter 11.

[0034] The function of the control unit 14 may be formed in several sub-units. Figure 3 shown in an example where at least two or three sub-units are used, namely, the primary control unit 30, the regulating control unit 31 and possibly the signal conversion unit 32. Figure 3 The embodiment of Figure 2 can be used in the system of

[0035] The primary control unit 30 forms a control signal 35 in order to keep the chemical dosing at a setpoint. Due to the changing wastewater flow and wastewater quality, the setpoint follows the measured values 111 and 121, and thus the setpoint is arranged to change in order to represent the correct chemical dosing for the current wastewater conditions.

[0036] Figure 3 The goal of the control system 14 is to reduce the suspended solids as much as possible in the primary process, but not too much. Therefore, the load of organic substances on the biological process 4 is controlled.

[0037] A second measuring unit 13 that measures the nitrate level or the redox value gives an indication of whether too much is removed. The regulating control unit 31 is arranged to be responsible for the measured value 131 from the second measuring unit. The regulating control unit 31 is arranged to receive or have an initial setpoint for the nitrate level or the redox value 34, and is also arranged to receive the control signal 35. The regulating control unit 31 uses the measured value of the nitrate level or the redox value to regulate the control signal 35 and forms a regulated control signal 36.

[0038] If the nitrate level is too high, the regulation increases the value of the control signal 35 to obtain a higher chemical dose and forms a regulated control signal 36. If the nitrate level is too low, the regulation decreases the value of the control signal 35 to obtain a lower chemical dose and forms a regulated control signal 36. The redox potential is a cheap and indirect reading value for the denitrification process and the nitrate level. If the redox drops, there is less nitrate and the dose is reduced, and vice versa. The control unit 14 can be arranged to dose at least two chemicals. In some embodiments, the dosing of at least two chemicals is independent of each other. The two chemicals can be one or more coagulants and / or one or more polymers, optionally together with another chemical, or any combination thereof.

[0039] Since the regulated control signal 36 may not be in a form suitable for the dosing devices 16, 18, the control unit 14 can have a signal conversion unit 32 for converting the regulated control signal 36 into a suitable form, which is the final control signal 37 for the dosing devices. Alternatively, the function of the signal conversion unit 32 can be arranged to be performed in the plant monitoring / control system 15.

[0040] Figure 4 Another example of the control system of the present invention is shown. The phosphorus level after the primary treatment and / or the secondary treatment can also be controlled. In addition to Figure 2 the measuring units shown in Figure 4The system further includes third measurement units 20, 21 arranged to measure the phosphorus level in the effluent of the secondary treatment process 4 or in the effluent of the primary treatment process 3. Accordingly, the third measurement units 20, 21 are phosphorus measuring devices 20, 21. There may also be two phosphorus measuring devices placed as described above. The measuring device may measure dissolved phosphorus or total phosphorus.

[0041] The control unit 14A is further arranged to receive measurement values from the third measurement units 20, 21 and to use these measurement values when forming a control signal for dosing at least one chemical before or into the influent of the primary treatment 3 or into the primary treatment process 3. Figure 5 Shown in Figure 4 the system is the controller 14A.

[0042] The control unit 14A may be arranged to dose one or more coagulants and / or one or more polymers, optionally together with another chemical. Polymer dosing may utilize measurement values from the measurement unit 12 and / or the second measurement unit 13. Coagulant dosing may utilize measurement values from the measurement unit 12 and / or the second measurement unit 13 and / or the third measurement units 20, 21. The control unit may further be arranged to set threshold values for the maximum and minimum doses based on the phosphorus level in the effluent of the secondary treatment process. The maximum and minimum doses may be related to the coagulant or the polymer or both. In addition, the control unit 14A may also be arranged to dose at least two chemicals using measurement values also from the flowmeter 11, the two chemicals being one or more coagulants and / or one or more polymers, optionally together with another chemical.

[0043] Figure 6 Shown is another example of the control system of the present invention. In this example, the load of the biological treatment is more accurately controlled by more accurately measuring and analyzing the wastewater entering the biological treatment 4. According to Figure 6 the system ensures that well-balanced wastewater enters the biological treatment. Well-balanced water means water having a suitable ratio between TOC / COD / BOD, nitrogen, and phosphorus such that none of these substances is lacking or in excess in the biological treatment.

[0044] In addition to Figure 4 the measurement units shown in Figure 6 the system further includes a fourth measurement unit 22 arranged to measure the suspended solids or turbidity level in the effluent of the primary treatment process 3, or a fifth measurement unit 23 arranged to measure the COD, BOD, or TOC (total organic carbon) value in the effluent of the primary treatment process 3, or both the fourth measurement unit 22 and the fifth measurement unit 23.

[0045] The control unit 14B is further arranged to receive measurement values 221, 231 from the fourth measurement unit 22 or the fifth measurement unit 23 or both the fourth measurement unit 22 and the fifth measurement unit 23. The control unit is also arranged to use these measurement values when forming a control signal for dosing at least one chemical before the primary treatment 3 or into the inflow to the primary treatment process 3 or into the primary treatment process 3, and for regulating said dosing. Figure 7 An embodiment of the control unit 14B used in the Figure 6 system is shown.

[0046] The control unit 14B is arranged to provide sufficient carbon for denitrification. Accordingly, the TOC or COD or BOD value / level, nitrogen value / level, and phosphorus value / level of the measurement values are arranged to be maintained within a range that preferably enables the process to operate properly. The control unit 14B may be arranged to dose one or more flocculants and / or one or more polymers, optionally together with another chemical. Polymer dosing may utilize measurement values from the measurement unit 12 and / or the second measurement unit 13 and / or the fourth measurement unit 22 and / or the fifth measurement unit 23. Flocculant dosing may utilize measurement values from the measurement unit 12 and / or the second measurement unit 13 and / or the third measurement units 20, 21 and / or the fourth measurement unit 22 and / or the fifth measurement unit 23.

[0047] There are also other embodiments of the invention. It can be noted that the present invention enables the construction of control systems for a large number of different wastewater treatment plants. Embodiments of the present invention produce more primary sludge, which means that the secondary process is more stable and thus operates more efficiently. Due to the increase in the amount of primary sludge, more biogas can be produced.

[0048] For example, in addition to the units mentioned above, the control of the present invention may further include a sixth measurement unit 25 arranged to measure the ammonium nitrogen level in the effluent of the primary treatment process, and the control units 14A, 14B are further arranged to receive the measurement value 251 from the sixth measurement unit 25. The control unit is also arranged to use these measurement values when forming a control signal for dosing at least one chemical before the primary treatment 3 or into the inflow to the primary treatment process 3 or into the primary treatment process 3, and for regulating said dosing.

[0049] The control system of the present invention may further include a seventh measurement unit 24 arranged to measure the ammonium level in the aeration zone of the secondary treatment process, and the control units 14A, 14B are further arranged to receive the measurement value 241 from the seventh measurement unit 24, and are also arranged to use these measurement values when forming a control signal for dosing at least one chemical before the primary treatment 3 or into the inflow to the primary treatment process 3 or into the primary treatment process 3, and for regulating said dosing.

[0050] The control units 14, 14A, 14B may further comprise at least one further measuring unit, and the control unit 14A is further arranged to receive measurement values from at least one further measuring unit, and is also arranged to use these measurement values when forming a control signal for dosing at least one chemical before the primary treatment 3 or into the influent of the primary treatment process 3 or into the primary treatment process 3, and for regulating the dosing.

[0051] With regard to the different measured values of the sensor, it is worth mentioning that all measured values indicated in this description can be used in any combination or even alone for dosing coagulant or regulating the dosing of coagulant, and all measured values in this description except measured values 20 and 21 can be used in any combination or even alone for dosing polymer or regulating the dosing of polymer. The examples of this description only show some possible embodiments.

[0052] The dosage of chemicals (such as coagulants or polymers) can be determined by the results (measured values) of the treatment. The dosage of chemicals (such as coagulants or polymers) can also be determined by the amount of chemicals per cubic meter or the amount of chemicals per mass unit of impurities. The measuring units and instruments are online measuring devices. In order to verify energy saving and increased biogas production, the energy consumption of the blower and / or the air flow to the secondary treatment and the biogas flow can also be tracked. Another suitable measuring device can also be used to monitor the biogas production. Tracking of MLSS content is also useful because the control system of the present invention can reduce the generation of excess sludge and prevent the sludge age from being unnecessarily increased too much.

[0053] Figure 3 , Figure 5 and Figure 7 Some embodiments of the control unit of how the invention can be implemented are shown. The primary control unit 30 provides a control signal 35 which can be regulated by the regulation control unit. If necessary, regulation takes place. However, the primary control unit and the regulation control can also be a single unit, in which case all functions or the primary control unit 30 and the regulation control unit 31 are formed in the same unit. If there is no conversion unit 32, the control signal (regulated or unregulated) can be the output of the control unit 14, 14A, 14B. When a conversion unit is used, the output control signal can also be in a converted form.

[0054] Any suitable control algorithm can be used to calculate the dose of the chemical and can also be used to adjust the calculated dose. The dose calculation mainly or entirely provides the control signal to the dosing device. If necessary, the adjustment is more like a fine-tuning of the dose and can provide a faster response in cases where the measured value indicates that the dose should be changed. Since there can be several measurement units, an algorithm that can handle many variables is preferred, such as language equations, neural networks, fuzzy logic, etc. Additionally, the control system can be arranged to utilize feedforward and / or feedback measured values and other algorithms, such as P, PI, PID, etc. The control unit can be implemented as software, hardware, or a combination thereof. The hardware implementation can be based on a printed circuit.

[0055] It can be noted that the design of the wastewater treatment plant depends on the water quality, treatment requirements, available space, flow rate, etc., and thus also depends on the control system. In some embodiments, for example, the wastewater treatment plant can further include a tertiary treatment process for improving the removal of phosphorus. Other additional processes can also be included.

[0056] Depending on what is measured in the plant, the control of the present invention can be used at different levels. As more online analyzers become available, the accuracy of the control is improved and more parameters can also be controlled. The control of the present invention controls the chemically supported separation to the correct level. If the chemical is in excess, there is a risk that the biological treatment will be disturbed. If the dosing is too small, more energy is consumed than necessary and less biogas is produced than possible. The algorithm sets the correct treatment level in any case.

[0057] Embodiments of the present invention can be carried out in several ways. The examples described above are some possible embodiments, but there can also be other embodiments. One or more chemicals dosed before the primary treatment or into the inflow to the primary treatment process or into the primary treatment process can be inorganic or organic. One or more coagulants can be used, or one or more polymers can be used, or any combination thereof can be used. Other chemicals, such as acids or bases, can also be used to control the pH.

[0058] At least one dosing device is used to supply the chemical from one or more tanks / reservoirs before the inflow to the primary treatment process or into the inflow to the primary treatment process or into the primary treatment process. The dosing device can be a chemical-specific pump or a dosing device suitable for non-liquid chemicals, or it can be a device suitable for supplying several chemicals. Therefore, many dosing devices can be any of the one and more chemicals used. The tanks / reservoirs are chemical-specific. Therefore, the dosing device and the tanks / reservoirs can be used for any combination of chemicals.

[0059] Additionally, the embodiments described above illustrate examples of different measurement arrangements. However, in other examples not shown in these examples or in this specification, there may also be other measurement units. The additional measurement units can provide more data from the wastewater treatment plant, which enables even more accurate chemical dosing.

[0060] It is evident from the foregoing that the invention is not limited to the embodiments described herein, but can be implemented in many other different embodiments within the scope of the independent claims.

Claims

1. A control system for a wastewater treatment plant, wherein the wastewater treatment at least includes a primary treatment process (3) for removing solid substances and a secondary treatment process (4) as a biological treatment, characterized in that, The control system includes a measuring unit (12) arranged to measure the turbidity or suspended solids of the wastewater before or during the primary treatment process, and a second measuring unit (13) arranged to measure the nitrate level or redox value in the denitrification zone of the secondary treatment process. And a control unit, the control unit being arranged to receive measurement values from the measuring unit (12) and the second measuring unit (13), and further being arranged to form a control signal for dosing at least one chemical before the primary treatment process (3) or into the influent of the primary treatment process (3) or into the primary treatment process (3) considering the wastewater conditions based on the measurement values from the measuring unit (12) to reduce the suspended solids in the primary treatment process, and adjusting the control signal for dosing based on the measurement values from the second measuring unit (13) to control the load of organic matter on the secondary treatment process.

2. The control system according to claim 1, characterized in that, The control unit is arranged to dose at least two chemicals.

3. The control system according to claim 1 or 2, characterized in that, The control unit is arranged to dose a coagulant or a polymer or any combination thereof.

4. The control system according to claim 1, characterized in that The control system further includes a third measuring unit (20, 21) arranged to measure the phosphorus level in the effluent of the secondary treatment process or in the effluent of the primary treatment process, and the control unit is further arranged to receive the measurement values from the third measuring unit (20, 21), and use these measurement values when forming a control signal for dosing at least one chemical before the primary treatment process (3) or into the influent of the primary treatment process (3) or into the primary treatment process (3).

5. The control system according to claim 4, wherein The control unit is arranged to dose at least two chemicals, the two chemicals being a coagulant or a polymer or any combination thereof, the dosing of the polymer being based on the measurement values from the measuring unit (12), and the dosing of the coagulant being based on the measurement values from the third measuring unit (20, 21) or the measurement values from the third measuring unit (20, 21) and the measurement values from the second measuring unit (13).

6. The control system according to claim 5, wherein The control unit is arranged to set thresholds for the maximum and minimum doses for dosing the two chemicals based on the phosphorus level in the effluent of the secondary treatment process.

7. The control system according to claim 4, wherein The control system further includes a fourth measuring unit (22) arranged to measure the suspended solids or turbidity level in the effluent of the primary treatment process, or a fifth measuring unit (23) arranged to measure the COD or BOD or TOC value in the effluent of the primary treatment process, or both the fourth measuring unit (22) and the fifth measuring unit (23). And the control unit is further arranged to receive the measurement values (221, 231) from the fourth measuring unit (22) or the fifth measuring unit (23) or both the fourth measuring unit (22) and the fifth measuring unit (23). and is also arranged to use these measurement values when forming a control signal for dispensing at least one chemical before the primary treatment process (3) or into the inflow to or into the primary treatment process (3), and for adjusting the dispensing.

8. The control system according to claim 1, characterized in that, The control unit is arranged to provide sufficient carbon for denitrification.

9. The control system according to claim 4, characterized in that the control unit is arranged to dispense at least two chemicals, the two chemicals being a coagulant or a polymer or any combination thereof, the dispensing of the polymer being based on at least the measurement values from the second measurement unit (13), and the dispensing of the coagulant being based on the measurement values from the third measurement units (20, 21).

10. The control system according to claim 7, characterized in that, The control system further comprises a sixth measurement unit (25) arranged to measure the ammonium nitrogen level in the effluent of the primary treatment process. and the control unit is further arranged to receive the measurement values (251) from the sixth measurement unit (25), and is also arranged to use these measurement values when forming a control signal for dispensing at least one chemical before the primary treatment process (3) or into the inflow to or into the primary treatment process (3), and for adjusting the dispensing.

11. The control system according to claim 10, wherein, The control system further comprises a seventh measurement unit (24) arranged to measure the ammonium level in the aeration zone of the secondary treatment process. and the control unit is further arranged to receive the measurement values (241) from the seventh measurement unit (24), and is also arranged to use these measurement values when forming a control signal for dispensing at least one chemical before the primary treatment process (3) or into the inflow to or into the primary treatment process (3), and for adjusting the dispensing.

12. The control system according to claim 11, wherein The control system further comprises at least one additional measurement unit. and the control unit is further arranged to receive the measurement values from the at least one additional measurement unit, and is also arranged to use these measurement values when forming a control signal for dispensing at least one chemical before the primary treatment process (3) or into the inflow to or into the primary treatment process (3), and for adjusting the dispensing.

13. The control system according to claim 1, wherein The control system further comprises a flow meter (11) arranged to measure the wastewater flow rate (1) entering the wastewater treatment plant. The control unit is arranged to also receive the measurement values from the flow meter (11), and is also arranged to form a control signal for dispensing at least one chemical before the primary treatment process (3) or into the inflow to or into the primary treatment process (3) using the measurement values from the flow meter (11).

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