Wastewater effluent reuse

Abstract

A method, apparatus and computer program for a wastewater effluent reuse at an industrial plant where process water for the industrial plant is purified from raw water and recycled wastewater effluent in a water purification system. A water quality is determined in reference stream(s), and a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system is defined based on said determining.

Description

[0001] WASTEWATER EFFLUENT REUSE

[0002] TECHNICAL FIELD

[0003] The present disclosure generally relates to water treatment. The disclosure relates particularly, though not exclusively, to a method and apparatus for wastewater effluent reuse at an industrial plant.

[0004] BACKGROUND

[0005] This section illustrates useful background information without admission of any technique described herein representative of the state of the art.

[0006] Many industrial plants, such as pulp and paper mills rely heavily on water. As an example, a typical pulp mill consumes up to 20-40 cubic meters of raw water for each ton of pulp produced. At the same time, significant quantities of wastewater are produced.

[0007] Due to the imperative to conserve scarce water resources, the industry focuses on finding ways to reduce and carefully manage its wastewater. It is equally important to reduce the amount of raw water used and wastewater created.

[0008] As a part of achieving this goal, reusing water stands out as a key solution, urging the industry to come up with new ways to manage water, benefiting both the industry and the environment.

[0009] SUMMARY

[0010] The appended claims define the scope of protection. Any examples and technical descriptions of apparatuses, products and / or methods in the description and / or drawings not covered by the claims are presented not as embodiments of the invention but as background art or examples useful for understanding the invention. It is an object of certain embodiments of the invention to provide solutions for wastewater effluent reuse at an industrial plant or at least to provide an alternative solution to existing technology.

[0011] According to a first example aspect of the invention there is provided a method for a wastewater effluent reuse at an industrial plant where process water for the industrial plant is purified from raw water and recycled wastewater effluent in a water purification system, the method comprising: determining water quality in reference stream(s); and defining, based on said determining, a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

[0012] In certain embodiments, the expression “flow ratio” refers to a flow rate ratio between the flow rate of the recycled wastewater effluent and the flow rate of the raw water to be taken in as an influent into the water purification system. Flow rates can be expressed in suitable units, for example in l / s, m3 / h, or m3 / d.

[0013] In certain embodiments, the recycled wastewater effluent is wastewater effluent produced by a wastewater treatment system of the industrial plant. In other embodiments, the recycled wastewater effluent is wastewater effluent produced by a wastewater treatment system other than that of the said industrial plant, such as a municipal wastewater treatment plant.

[0014] In certain embodiments, said determining water quality in reference stream(s) comprises determining water quality in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

[0015] In certain embodiments, said determining water quality in reference stream(s) comprises determining water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the water purification system.

[0016] In certain embodiments, said determining water quality in reference stream(s) comprises determining water quality in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system and determining water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the water purification system.

[0017] In certain embodiments, said determining water quality in reference stream(s) comprises determining water quality in a stream of chemically treated water in the water purification system. In certain embodiments, the expression “chemically treated water” refers to an outlet stream of the water purification system to be used as the process water.

[0018] In certain embodiments, said determining water quality in reference stream(s) comprises: a. determining water quality in a stream of chemically treated water in the water purification system and determining water quality in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system; or b. determining water quality in a stream of chemically treated water in the water purification system and determining water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the water purification system.

[0019] In certain embodiments, the method comprises: providing an indication (for an operator) or a control signal to control the flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system (e.g., by means of operating an adjustment valve or pump).

[0020] In certain embodiments, the method comprises: determining water quality in reference stream(s) through conductivity of each reference stream.

[0021] In certain embodiments, the method comprises determining water quality in reference stream(s) through an organic compounds indicator of each reference stream. In certain embodiments, the organic compounds indicator indicates the amount or concentration of organic compounds in a stream (here: reference stream(s)). Examples of organic compounds indicators are chemical oxygen demand (COD), UV-absorbance data, color, and the KMnO4 value. These may be obtained through measurements from the reference stream(s) performed by an apparatus implementing the disclosed method, or data reflecting the measurements performed by another apparatus may simply be received by an apparatus implementing the disclosed method.

[0022] In certain embodiments, the method comprises determining water quality in reference stream(s) through a solid matter indicator of each reference stream. In certain embodiments, the solid matter indicator indicates the amount or concentration of solid matter in a stream (here: reference stream(s)). Examples of solid matter indicators are turbidity, light scattering data, and e.g. specific suspended solids (SS) laboratory measurement data. The solid matter indicators may be obtained through measurements from the reference stream(s) performed by an apparatus implementing the disclosed method, or data reflecting the measurements performed by another apparatus may simply be received by an apparatus implementing the disclosed method.

[0023] In certain embodiments, the method comprises determining water quality in reference stream(s) through an organic compounds indicator and through conductivity of each reference stream. In these embodiments, the method comprises taking into account process water quality requirements through the use of conductivity and taking into account the purification system capacity constraints (e.g. to avoid excessive chemical consumption in solid-liquid separation) through the use of the organic compounds indicator.

[0024] In certain embodiments, the method step of defining a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in comprises defining that the flow ratio needs to be changed (here: reduced) in the event the organic compounds indicator exceeds a predefined limit.

[0025] In certain embodiments, the method comprises determining water quality in reference stream(s) through a solid matter indicator and through conductivity of each reference stream. In these embodiments, the method comprises taking into account process water quality requirements through the use of conductivity and taking into account the purification system capacity constraints (e.g. to avoid malfunction in solid-liquid separation, such as flotation (or sedimentation, if in use instead of or in addition to flotation) due to excessive amount of solids) through the use of the solid matter indicator.

[0026] In certain embodiments, the method step of defining a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in comprises defining that the flow ratio needs to be changed in the event the solid matter indicator exceeds a predefined limit.

[0027] In certain embodiments, the method comprises determining water quality in reference stream(s) through an organic compounds indicator, through a solid matter indicator, and through conductivity of each reference stream.

[0028] Further example parameters that may be used in the water quality determination are as follows: pH, the concentrations of dissolved metals, such as Fe, Al, Mn, Ca and Mg, the concentration of ions, such as sulphate and chloride, oxidation reduction potential (ORP), and temperature. It is however noted that some of these parameters already fall within the aforementioned organic compounds or solid matter indicators.

[0029] In certain embodiments, the method comprises: using flow rates in an incoming stream of wastewater effluent and in an incoming stream of raw water into the water purification system in said defining a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in.

[0030] In certain embodiments, the method comprises: defining, based on said determining and based on the flow rate in the stream of recycled wastewater effluent and the flow rate in the stream of raw water, a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

[0031] Accordingly, in certain embodiments, the method comprises: receiving information indicative of flow rate(s) in said reference stream(s); or determining (e.g. by measuring) the flow rate(s) in said reference stream(s).

[0032] More particularly, in certain embodiments, the method comprises: receiving information indicative of flow rate(s) in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system; or determining (e.g. by measuring) the flow rate(s) in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

[0033] In certain embodiments, the method comprises: multiplying conductivity (or another parameter representing water quality, or conductivity and another parameter representing water quality) by the flow rate in the stream of raw water; multiplying conductivity (or another parameter representing water quality, or conductivity and another parameter representing water quality) by the flow rate in the stream of wastewater effluent; and summing the multiplication results.

[0034] Further, in certain embodiments, the result obtained by said summing is used to predict the conductivity (and / or another parameter representing water quality) of the combined stream, and the prediction thus obtained is compared to predefined limit(s) set for the (summed) parameter. In certain embodiments, the desired target flow ratio or a change in flow ratio is defined based on the comparison.

[0035] Herein, it should be noted that measuring the flow rate(s) is however not necessary for the operation of the disclosed method.

[0036] In certain embodiments, the method comprises: providing control of chemical treatment for the water purification system based on water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the water purification system.

[0037] In certain embodiments, the method comprises: providing control of chemical treatment for the water purification system based on water quality in a stream of chemically treated water in the water purification system.

[0038] In certain embodiments, a solid matter indicator and an organic compounds indicator in the stream(s) in question are provided to define said water quality based on which the control of the chemical treatment for the water purification system is provided. According to a second example aspect there is provided an apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the method of the first aspect or any related embodiment.

[0039] According to a third example aspect of the present invention, there is provided a computer program comprising computer executable program code which when executed by a processor causes an apparatus to perform the method of the first aspect or any related embodiment.

[0040] According to a fourth example aspect there is provided a computer program product comprising a non-transitory computer readable medium having the computer program of the third example aspect stored thereon.

[0041] According to a fifth example aspect there is provided an apparatus comprising means for performing the method of the first aspect or any related embodiment.

[0042] Any foregoing memory medium may comprise a digital data storage such as a data disc or diskette, optical storage, magnetic storage, holographic storage, opto- magnetic storage, phase-change memory, resistive random-access memory, magnetic random access memory, solid-electrolyte memory, ferroelectric random access memory, organic memory or polymer memory. The memory medium may be formed into a device without other substantial functions than storing memory or it may be formed as part of a device with other functions, including but not limited to a memory of a computer, a chip set, and a sub assembly of an electronic device.

[0043] Different non-binding example aspects and embodiments have been illustrated in the foregoing. The embodiments in the foregoing are used merely to explain selected aspects or steps that may be utilized in different implementations. Some embodiments may be presented only with reference to certain example aspects. It should be appreciated that corresponding embodiments apply to other example aspects as well. BRIEF DESCRIPTION OF THE FIGURES

[0044] Some example embodiments will be described with reference to the accompanying figures, in which:

[0045] Fig. 1 shows certain parts of an industrial plant in view of certain example embodiments;

[0046] Fig. 2 shows a block diagram embodying operation of certain example embodiments;

[0047] Figs. 3a-3d show methods in accordance with certain example embodiments; and Fig. 4 schematically shows a block diagram of an apparatus according to certain example embodiments.

[0048] DETAILED DESCRIPTION

[0049] In the following description, like reference signs denote like elements or steps.

[0050] Fig. 1 shows certain parts of an industrial plant in view of certain example embodiments. The industrial plant may contain for example a pulp or paper (or board) mill 45.

[0051] Raw water (fresh water) 10 which would typically be taken from a nearby river or lake is purified in a water purification system 30 to produce process water 40 to be used in the mill 45. Produced wastewater is treated in a wastewater treatment system 48 of the plant. Wastewater effluent 49 is released into the nature or directed for further processing, but as a part of the disclosure, at least a part 20 of the treated wastewater is recycled back into the process such that said part 20 of the treated wastewater replaces a part of raw water 10 taken in as an influent into the water purification system 30.

[0052] Fig. 2 shows a block diagram embodying operation of certain example embodiments. Accordingly, Fig. 2 is directed to a method for wastewater effluent reuse at an industrial plant where process water 40 for the industrial plant is purified from raw water 10 and recycled wastewater effluent 20 in a water purification system 30.

[0053] Combined water 12 combined from the raw water 10 and the recycled wastewater effluent 20 is taken in as an influent into the water purification system 30. In certain embodiments, the water purification system comprises a chemical treatment process 31 , followed by at least one solid-liquid separation process. In the example shown in in Fig. 2, the at least one solid-liquid separation process comprises a first solid-liquid separation process 32, which may, e.g., comprise a flotation process or a sedimentation process, and a second solid-liquid separation process 33, which may, e.g., comprise sand filtering.

[0054] The chemical treatment process 31 comprises in many embodiments the addition of chemicals at one or more dosing points 25. Examples of chemicals dosed into the influent incoming into chemical treatment 31 comprise, e.g., coagulant(s) and / or flocculant(s) and / or chemical(s) for adjusting pH and / or disinfectants.

[0055] Treatment with a coagulant typically neutralizes the negative electrical charge on particles and / or dissolved impurities, which destabilizes the forces keeping colloids apart. Flocculation is typically a process of agglomerating destabilized particles into bigger flocs. In treatment by flocculation, colloidal particles are agglomerated in order to aid their removal. Flocculants can be used alone or together with coagulants to make flocs bigger and more resistant to shear forces.

[0056] A flocculant can be a cationic, anionic or nonionic polymer. Said polymers can be synthetic or natural organic polymers. Typical synthetic organic polymers used in flocculation process are different polyacrylamides (cationic, anionic or nonionic polyacrylamides) with a wide range of charge and molecular weight. Synthetic organic polymers comprise polyacrylamide, polyamine, polyDADMAC, polyethyleneimine, dicyandiamide and polyvinyl amine. Natural organic polymers comprise polysaccharide, such as starch, cellulose, guar gum, chitosan, dextran and the like, and polyphenolics, such as tannin and lignin.

[0057] Coagulants comprise iron containing salts, aluminum containing salts, magnesium containing salts, and any derivative thereof, preferably chlorides, sulphates, chlorosulphates, chlorohydrates, silicates, nitrates, and any derivate thereof, more preferably aluminum sulfate, polyaluminum sulfate, aluminum chloride, polyaluminum chloride, polyaluminum chlorosulfate, polyaluminum hydroxychlorosulfate, aluminum chlorohydrate, sodium aluminate, ferric sulfate, polyferric sulfate, ferric chloride, ferric chlorosulphate, polyferric chloride, ferrous sulfate, ferrous chlorosulphate, ferrous chloride, aluminum triformate, polyaluminum formate, polyaluminum nitrate, polyaluminum silicate, magnesium chloride, any derivative thereof, and any combination thereof.

[0058] The control of pH relates to the optimization of pH for coagulation. Sulfuric acid (H2SO4) and sodium hydroxide (NaOH) serve as certain examples of pH control chemicals.

[0059] Disinfection relates to preventing or decreasing microbiological problems and sometimes also deposit problems. Disinfectant is added in certain embodiments upstream of a solid-liquid separation process, in particular upstream of a sand filtering process to keep the related sand filter(s) clean (and to keep the microbial content within predetermined limits).

[0060] In certain embodiments, the method comprises changing (e.g. increasing) a disinfectant dose in the event the flow ratio between the wastewater effluent and the raw water to be taken in is changed (e.g. increased).

[0061] Examples of disinfectants comprise CI2, chlorine dioxide (CIO2), sodium hypochlorite (NaOCI), hypobromous acid (HOBr), stabilized halogens, such as bromochloro dimethyldydantoin (BCDMH) and trichloroisocyanuric acid (TCCA), peracids peracetic acid (PAA) and performic acid (PFA).

[0062] In certain embodiments, water quality in one or more reference streams is determined for the purpose of defining a desired flow ratio between recycled wastewater effluent 20 and raw water 10 to be taken in as an influent into the water purification system 30. The desired flow ratio (or a desired change in the flow ratio in other embodiments) is thus defined based on the determination of the water quality in said one or more reference streams. The flow ratio will have an impact on the quality of the process water (i.e., the quality of the process water is dependent on the flow ratio), and with the aid of defining the flow ratio (or its change) as suggested, a control is enabled for maintaining the quality of the process water within desired limits even though there may be temporal quality variations in the raw water and in the recycled wastewater effluent.

[0063] The reference numeral 50 in Fig. 2 indicates a control apparatus configured to perform the determination(s) of the water quality in the reference stream(s) and configured to define the desired (optimal) flow ratio (or change in flow ratio). The following reference streams may be used: raw water stream, stream of wastewater effluent, combined stream of raw water and wastewater effluent, and stream of chemically treated water in the water purification system 30.

[0064] In the following, certain example embodiments are presented in which one or more of the reference streams are used.

[0065] In a first example embodiment, as shown in Fig. 3a, both the raw water stream and the stream of wastewater effluent are used as reference streams. Accordingly, the water quality both in the raw water stream and in the stream of wastewater effluent is determined. In an embodiment this comprises measuring and / or receiving a respective parameter value indicating water quality in each respective stream. In addition, flow rate both in the raw water stream and in the stream of wastewater effluent is determined in further embodiments. In certain embodiments, a water quality index value is calculated for both streams. In certain embodiments, the water quality index value is obtained by multiplying a parameter value indicating water quality with a factor highlighting its importance (or in the event of more than one parameter, the sum of parameter values multiplied with the factor highlighting their importance). The water quality index value thus combines the impact of the parameters depicting the water quality into a single value.

[0066] A target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 is then defined based on the determined water quality in the reference streams. In practice this may occur by calculating an optimal ratio (or change) for the effluent to be recycled and for the raw water to be taken in, based on their qualities and / or calculated water quality indexes. The optimal ratio (or change) may be used for controlling the flow ratio of recycled effluent and raw water. For example, a control signal to control the flow ratio is produced in certain embodiments (the control signal is provided to valve(s) and / or pump(s) concerned).

[0067] In the first example embodiment, conductivity is preferably used as the parameter whose value indicates quality in each respective stream. Then, a set of control rules may be defined for controlling the flow ratio between the wastewater effluent and the raw water based on conductivity. An example of such a control rule may be defined for example as follows:

[0068] - if conductivity of wastewater effluent exceeds a predetermined limit, then the share of wastewater effluent in the influent into the water purification system 30 is reduced by x percent (where x percent is predefined in control settings)

[0069] In further implementations, in addition to the parameter (or parameters) that indicates (indicate) water quality, the determined flow rates both in the raw water stream and in the stream of wastewater effluent are taken into account (although in all implementations the determination of flow rates is not needed).

[0070] For example, in certain such implementations, conductivity (or another determined parameter representing water quality) is multiplied by the flow rate in the stream of raw water, and conductivity (or another parameter representing water quality) is multiplied by the flow rate in the stream of wastewater effluent, and the multiplication results are summed.

[0071] Further, in certain embodiments, the result obtained by said summing is used to predict the conductivity (or another parameter representing water quality) of the combined stream, and the prediction thus obtained is compared to predefined limit(s) set for the (summed) parameter. In certain embodiments, the desired target flow ratio or a change in flow ratio is defined based on the comparison.

[0072] Similar implementations taking the flow rates into account can be applied also for the remaining example embodiments.

[0073] Further parameters (or indicators) that may be used in determining the water quality in reference stream(s) are an organic compounds indicator and a solid matter indicator. Examples of solid matter indicators are turbidity, light scattering data, and e.g. specific suspended solids (SS) laboratory measurement data. Examples of organic compounds indicators are chemical oxygen demand (COD), UV- absorbance data, color, and the KMnO4 value. These indicators may be obtained through measurements from the reference stream(s) performed by an apparatus implementing the disclosed method, or data reflecting the measurements performed by another apparatus may simply be received by an apparatus implementing the disclosed method. In certain implementations, the method comprises determining water quality in reference stream(s) (here: the raw water stream and the stream of wastewater effluent) through an organic compounds indicator and through conductivity of the reference stream. In these implementations, the method comprises taking into account process water quality requirements through the use of conductivity and taking into account the purification system capacity constraints (e.g. to avoid excessive chemical consumption in solid-liquid separation) through the use of the organic compounds indicator.

[0074] In certain implementations, the method step of defining a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in comprises defining (or concluding) that the flow ratio needs to be changed (here: reduced) in the event the organic compounds indicator exceeds a predefined limit.

[0075] In certain implementations, the method comprises determining water quality in reference stream(s) through a solid matter indicator and through conductivity of each reference stream. In these embodiments, the method comprises taking into account process water quality requirements through the use of conductivity and taking into account the purification system capacity constraints (e.g. to avoid malfunction in solid-liquid separation, such as flotation (or sedimentation, if in use instead of or in addition to flotation) due to excessive amount of solids) through the use of the solid matter indicator.

[0076] In certain embodiments, the method step of defining a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in comprises defining (or concluding) that the flow ratio needs to be changed in the event the solid matter indicator exceeds a predefined limit.

[0077] In certain implementations, the method comprises determining water quality in reference stream(s) through an organic compounds indicator, through a solid matter indicator, and through conductivity of each reference stream.

[0078] Yet further example parameters that may be used in the water quality determination are as follows: pH, the concentrations of dissolved metals, such as Fe, Al, Mn, Ca and Mg, the concentration of ions, such as sulphate and chloride, oxidation reduction potential (ORP), and temperature. It is however noted that some of these parameters already fall within the aforementioned organic compounds or solid matter indicators.

[0079] What has been presented in the foregoing concerning the parameters and indicators and there use can be applied also for the remaining example embodiments.

[0080] In further implementations of the first example embodiment, a prediction of water quality (e.g., in terms of conductivity) for final purified water (i.e., chemically treated water to be used as process water in the mill in question) is calculated. In such embodiments, the target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 may be defined based on the determined water quality in the reference streams and based on the prediction of water quality.

[0081] In a second example embodiment, as shown in Fig. 3b, the stream of combined water 12 is used as the reference stream. Accordingly, the water quality in the combined stream is determined. In an embodiment this comprises measuring and / or receiving a respective parameter value indicating water quality in the combined stream. In certain embodiments, a water quality index value is calculated for the combined stream. In certain embodiments, the water quality index value is obtained by multiplying a parameter value indicating water quality with a factor highlighting its importance (or in the event of more than one parameter, the sum of parameter values multiplied with the factor highlighting their importance).

[0082] A target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 is then defined based on the determined water quality in the reference stream. This may occur by calculating an optimal ratio (or change) for the effluent to be recycled and for the raw water to be taken in, based on the quality of the combined stream and / or calculated water quality index. The optimal ratio (or change) may be used for controlling the flow ratio of recycled effluent and raw water. For example, a control signal to control the flow ratio is produced in certain embodiments.

[0083] In the second example embodiment, conductivity is preferably used as the parameter whose value indicates quality in the combined stream. Further parameters (or indicators) that may be used in determining the water quality in reference stream(s) are an organic compounds indicator and a solid matter indicator. Yet further example parameters that may be used in the water quality determination are as follows: pH, the concentrations of dissolved metals, such as Fe, Al, Mn, Ca and Mg, the concentration of ions, such as sulphate and chloride, oxidation reduction potential (ORP), and temperature. Similar control rules may be defined as for the first example embodiment.

[0084] In further implementations of the second example embodiment, a prediction of water quality (e.g., in terms of conductivity) for final purified water (i.e., chemically treated water to be used as process water in the mill in question) is calculated. In such embodiments, the target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 may be defined based on the determined water quality in the reference stream and based on the prediction of water quality.

[0085] In a third example embodiment, as shown in Fig. 3c, both the raw water stream and the stream of wastewater effluent as well as the stream of combined water 12 are used as reference streams. Accordingly, the water quality both in the raw water stream and in the stream of wastewater effluent as well as in the combined stream is determined. In an embodiment this comprises measuring and / or receiving a respective parameter value indicating water quality in each respective stream. In certain embodiments, a water quality index value is calculated for each stream. In certain embodiments, the water quality index value is obtained by multiplying a parameter value indicating water quality with a factor highlighting its importance (or in the event of more than one parameter, the sum of parameter values multiplied with the factor highlighting their importance).

[0086] A target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 is then defined based on the determined water quality in the reference streams. In practice this may occur by calculating an optimal ratio (or change) for the effluent to be recycled and for the raw water to be taken in, based on the quality of the streams and / or calculated water quality indexes. The optimal ratio (or change) may be used for controlling the flow ratio of recycled effluent and raw water. For example, a control signal to control the flow ratio is produced in certain embodiments.

[0087] In the third example embodiment, conductivity is preferably used as the parameter whose value indicates quality in each respective stream. Further parameters (or indicators) that may be used in determining the water quality in reference stream(s) are an organic compounds indicator and a solid matter indicator. Yet further example parameters that may be used in the water quality determination are as follows: pH, the concentrations of dissolved metals, such as Fe, Al, Mn, Ca and Mg, the concentration of ions, such as sulphate and chloride, oxidation reduction potential (ORP), and temperature. Similar control rules may be defined as for the first example embodiment.

[0088] In further implementations of the third example embodiment, a prediction of water quality (e.g., in terms of conductivity) for final purified water (i.e., chemically treated water to be used as process water in the mill in question) is calculated. In such embodiments, the target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 may be defined based on the determined water quality in the reference streams and based on the prediction of water quality.

[0089] In a fourth example embodiment, as shown in Fig. 3d, the stream of chemically treated water in the water purification system 30 is used as the reference stream. Accordingly, the water quality in the stream of chemically treated water is determined. In an embodiment this comprises measuring and / or receiving a respective parameter value indicating water quality in the stream of chemically treated water. In certain embodiments, a water quality index value is calculated for the stream of chemically treated water. In certain embodiments, the water quality index value is obtained by multiplying a parameter value indicating water quality with a factor highlighting its importance (or in the event of more than one parameter, the sum of parameter values multiplied with the factor highlighting their importance).

[0090] A target for the flow ratio (or a target change in flow ratio) between the wastewater effluent and the raw water to be taken in as an influent into the water purification system 30 is then defined based on the determined water quality in the reference stream. This may occur by calculating an optimal ratio (or change) for the effluent to be recycled and for the raw water to be taken in, based on the quality of the stream of chemically treated water and / or calculated water quality index. The optimal ratio (or change) may be used for controlling the flow ratio of recycled effluent and raw water. For example, a control signal to control the flow ratio is produced in certain embodiments.

[0091] In the fourth example embodiment, conductivity is preferably used as the parameter whose value indicates quality in the stream of chemically treated water. Further parameters (or indicators) that may be used in determining the water quality in reference stream(s) are an organic compounds indicator and a solid matter indicator. Yet further example parameters that may be used in the water quality determination are as follows: pH, the concentrations of dissolved metals, such as Fe, Al, Mn, Ca and Mg, the concentration of ions, such as sulphate and chloride, oxidation reduction potential (ORP), and temperature. Similar control rules may be defined as for the first example embodiment.

[0092] In further example embodiments, the stream of chemically treated water in the water purification system 30 and both the raw water stream and the stream of wastewater effluent are used as reference streams. In yet further example embodiments, the stream of chemically treated water in the water purification system 30 and the combined stream are used as reference streams. The basic operation of these embodiments is similar to those shown in the preceding.

[0093] In further embodiments, in addition to determining water quality in reference stream(s) and defining a target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in, control of chemical treatment for the water purification system 30 is provided based on water quality of the combined water 12 (prior to chemical treatment in the water purification system 30).

[0094] In such embodiments, further control rules may be defined. A solid matter indicator and an organic compounds indicator (see the foregoing) are used as parameters indicating water quality in the stream of combined water 12. These parameters (or indicators) are measured by the control apparatus 50 (or representative data are received by the control apparatus 50). An example of a control rule may be defined for example as follows:

[0095] - If the solid matter indicator or the organic compounds indicator of combined water 12 indicates an increase, then the amount of coagulant or flocculant is increased (based on predefined control settings)

[0096] Another example of a control rule may be defined for example as follows:

[0097] - If the solid matter indicator or the organic compounds indicator of combined water 12 indicates a decrease, then the amount of coagulant or flocculant is decreased (based on predefined control settings)

[0098] The preceding control rule(s) represent an example of feedforward control.

[0099] In further embodiments, in addition to determining water quality in reference stream(s) and defining a target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in, control of chemical treatment for the water purification system 30 is provided based on water quality of the chemically treated water in the water purification system 30.

[0100] A solid matter indicator and an organic compounds indicator (see the foregoing) are preferably used as parameters indicating water quality in the stream of chemically treated water. These parameters (or indicators) are measured by the control apparatus 50 (or representative data are received by the control apparatus 50). An example of a control rule may be defined for example as follows:

[0101] - If the solid matter indicator or the organic compounds indicator of chemically treated water indicates an increase, then the amount of coagulant or flocculant is increased (based on predefined control settings)

[0102] Another example of a control rule may be defined for example as follows:

[0103] - If the solid matter indicator or the organic compounds indicator of chemically treated water indicates a decrease, then the amount of coagulant or flocculant is decreased (based on predefined control settings)

[0104] The preceding control rule(s) represent an example of feedback control. The predefined control settings preferably contain set point values for the solid matter indicator and the organic compounds indicator of the chemically treated water. In preceding embodiments, the determination of water quality in the combined stream indicates whether the flow ratio needs to be changed. Based on the determination of water quality in the incoming streams (i.e., raw water and recycled wastewater effluent streams) it is decided in certain embodiments which of the incoming flows need to be increased or reduced. The disclosed method allows a wide range of flow ratios. Accordingly, the method allows both the raw water stream and the stream of waste water effluent to be the dominant flow depending on the determined water quality in these streams.

[0105] Fig. 4 schematically shows a block diagram of an apparatus according to certain example embodiments. In particular, Fig. 4 shows blocks of a control apparatus 50 capable of performing the aspects and various embodiments of the present disclosure. The apparatus 50 comprises for example a general-purpose computer or server or some other electronic data processing apparatus. The apparatus 50 further comprises an analyser (or analysis equipment) 150 configured to provide water quality information (such as parameter values indicating water quality through measurements performed by the analyser 150), although in other embodiments the apparatus 50 merely receives the said information without the analyser 150 or any other measurement device forming part of the apparatus 50.

[0106] The apparatus 50 comprises a communication interface 55, a processor 51 , a user interface 54, and a memory 52.

[0107] The communication interface 55 comprises in an embodiment a wired and / or wireless communication circuitry, such as Ethernet, Wireless LAN, Bluetooth, GSM, CDMA, WCDMA, LTE, and / or 5G circuitry. The communication interface can be integrated in the apparatus 50 or provided as a part of an adapter, card or the like, that is attachable to the apparatus 50. The communication interface 55 may support one or more different communication technologies. The apparatus 50 may also or alternatively comprise more than one communication interface 55.

[0108] The processor 51 may be a central processing unit (CPU), a microprocessor, a digital signal processor (DSP), a graphics processing unit, an application specific integrated circuit (ASIC), a field programmable gate array, a microcontroller or a combination of such elements. The user interface 54 may comprise a circuitry for receiving input from a user of the apparatus 50, e.g., via a keyboard, graphical user interface shown on the display of the apparatus 50, speech recognition circuitry, or an accessory device, such as a headset, and for providing output to the user via, e.g., a graphical user interface or a loudspeaker.

[0109] The memory 52 comprises a work memory 53 and a persistent (non-volatile, NA / ) memory 56 configured to store computer program code 57 and data 58. The memory 56 may comprise any one or more of: a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a random-access memory (RAM), a flash memory, a data disk, an optical storage, a magnetic storage, a smart card, a solid state drive (SSD), or the like.

[0110] The apparatus 50 may comprise a plurality of memories 56. The memory 56 may be constructed as a part of the apparatus 50 or as an attachment to be inserted into a slot, port, or the like of the apparatus 50 by a user or by another person or by a robot. The memory 56 may serve the sole purpose of storing data, or be constructed as a part of an apparatus 50 serving other purposes, such as processing data.

[0111] A skilled person appreciates that in addition to the elements shown in Fig. 4, the apparatus 50 may comprise other elements, such as microphones, displays, as well as additional circuitry such as an input / output (I / O) circuitry, memory chips, application-specific integrated circuits (ASIC), a processing circuitry for specific purposes such as a source coding / decoding circuitry, a channel coding / decoding circuitry, a ciphering / deciphering circuitry, and the like. Additionally, the apparatus 50 may comprise a disposable or rechargeable battery (not shown) for powering the apparatus 50 if an external power supply is not available. Further, it is noted that only one apparatus 50 is shown in Fig. 4, but certain embodiments may equally be implemented in a cluster of shown apparatuses.

[0112] The apparatus 50 comprises the (at least one) processor 51 and (at least one) memory 52 including computer program code 57, the memory 52 and the computer program code 57 being configured, with the processor 51 , to cause the apparatus 50 to perform the operations as disclosed in the preceding disclosure. These operations include the determination of water quality in reference stream(s), and the definition of a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system based on said determination, preferably with the aid of receiving water quality information (parameters, measurement data) and by performing appropriate calculations.

[0113] In certain embodiments, the apparatus 50 is configured to add color, turbidity, or conductivity into the combined stream 12 by increasing the flow ratio between the wastewater effluent and the raw water in the event their amount is below a predetermined limit however without exceeding the predetermined limit by the addition. In this way, the reuse of effluent can be maximized (and the chemical dosing can be kept substantially constant). This will also produce a stabilizing effect to the quality of the process water 40.

[0114] Without limiting the scope and interpretation of the patent claims, certain technical effects of one or more of the example embodiments disclosed herein are listed in the following. A technical effect is advanced wastewater effluent recycling to raw water and the reduction of pollutants ending up into the nature. A further technical effect is improved control in reusing wastewater at an industrial plant. A further technical effect is the ability to warm raw water with the aid of recycled wastewater effluent (which is typically warmer than raw water). A further technical effect is more stable quality of produced process water.

[0115] Various embodiments have been presented. It should be appreciated that in this document, words comprise, include and contain are each used as open-ended expressions with no intended exclusivity.

[0116] The foregoing description has provided by way of non-limiting examples of particular implementations and embodiments a full and informative description of the best mode presently contemplated by the inventors for carrying out the invention. It is however clear to a person skilled in the art that the invention is not restricted to details of the embodiments presented in the foregoing, but that it can be implemented in other embodiments using equivalent means or in different combinations of embodiments without deviating from the characteristics of the invention.

[0117] Furthermore, some of the features of the afore-disclosed example embodiments may be used to advantage without the corresponding use of other features. As such, the foregoing description shall be considered as merely illustrative of the principles of the present invention, and not in limitation thereof. Hence, the scope of the invention is only restricted by the appended patent claims.

Claims

CLAIMS1 . A method for a wastewater effluent reuse at an industrial plant where process water for the industrial plant is purified from raw water and recycled wastewater effluent in a water purification system, the method comprising: determining water quality in reference stream(s); and defining, based on said determining, a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

2. The method of claim 1 , wherein said determining water quality in reference stream(s) comprises determining water quality in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

3. The method of claim 1 or 2, wherein said determining water quality in reference stream(s) comprises determining water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the water purification system.

4. The method of claim 1 , wherein said determining water quality in reference stream(s) comprises determining water quality in a stream of chemically treated water in the water purification system.

5. The method of claim 1 , wherein said determining water quality in reference stream(s) comprises: a. determining water quality in a stream of chemically treated water in the water purification system and determining water quality in both streams of the wastewater effluent and the raw water to be taken in as an influent into the water purification system; or b. determining water quality in a stream of chemically treated water in the water purification system and determining water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the waterpurification system.

6. The method of any preceding claim, comprising: providing an indication or a control signal to control the flow ratio between the wastewater effluent and the raw water to be taken in as an influent into the water purification system.

7. The method of any preceding claim, comprising: determining water quality in reference stream(s) through conductivity of each reference stream.

8. The method of claim 7, comprising: determining water quality in reference stream(s) through conductivity of each reference stream, and further through an organic compounds indicator and / or a solid matter indicator of each reference stream.

9. The method of any preceding claim, further comprising: using flow rates in an incoming stream of wastewater effluent and in an incoming stream of raw water into the water purification system in said defining a desired target flow ratio or a change in flow ratio between the wastewater effluent and the raw water to be taken in.

10. The method of any preceding claim, further comprising: providing control of chemical treatment for the water purification system based on water quality in a combined stream of the wastewater effluent and the raw water prior to chemical treatment in the water purification system.11 . The method of any preceding claim 1-9, further comprising: providing control of chemical treatment for the water purification system based on water quality in a stream of chemically treated water in the water purification system.

12. The method of claim 10 or 11 , wherein a solid matter indicator and an organiccompounds indicator in the stream(s) in question are provided to define said water quality based on which the control of the chemical treatment for the water purification system is provided.

13. An apparatus, comprising: at least one processor; and at least one memory including computer program code, the at least one memory and the computer program code being configured, with the at least one processor, to cause the apparatus to perform the method of any of claims 1-12.

14. A computer program comprising computer executable program code which when executed by a processor causes an apparatus to perform the method of any of claims 1-12.

Images