Calcium and / or magnesium additives for membrane fouling control, and systems and processes for membrane fouling control using the additives

Abstract

Provided are calcium and / or magnesium additives for membrane fouling control, which particularly comprise particles (6) that, when added to a liquid flowing through a membrane (1), form a flowable protective layer (7) on the membrane (1) for membrane fouling control, wherein the particles (6) comprise calcium and / or magnesium-based synthetic inorganic precipitating particles selected from ultrafine synthetic inorganic precipitating particles and extra-fine synthetic inorganic precipitating particles. A calcium and / or magnesium additive for membrane fouling control, a process, and a system for membrane fouling control are provided.

Description

[Technical Field]

[0001] The present invention relates to a system and process for controlling membrane fouling, and to calcium and / or magnesium additives for controlling membrane fouling. [Background technology]

[0002] Membranes are used for water treatment in many industries, including public drinking water supplies and wastewater treatment, food and beverage processing, pharmaceuticals, oil and gas, and many more.

[0003] The main operational problem with membrane filtration is fouling. Fouling substances contained in the liquid being filtered adhere to the membrane, resulting in degradation of membrane performance. There are different types of fouling. Colloidal / particulate fouling is formed when fouling substances accumulate on the membrane surface and inside the pores, reducing the membrane's permeability. Organic fouling is caused by natural or synthetic organic matter from the feed solution. Biofouling is caused by aquatic organisms such as bacteria or algae that can colonize the membrane surface and cause biofouling. Inorganic fouling or scaling is the formation of hard mineral deposits on the membrane surface due to exceeding the supersaturation limit of sparingly soluble salts. Therefore, fouling control measures are required in most membrane applications to minimize the adverse effects of fouling on membrane operation / life.

[0004] It has been found that fouling in each application is highly dependent on the quality of the feed water, the membrane, and the operating conditions. Therefore, one way to minimize fouling is to properly select the membrane and operating conditions according to the application, i.e., the type of fouling substance in the liquid to be filtered. However, a wide variety of membrane filters are required to deal with a wide variety of different fouling situations. Each application is slightly different, making it difficult to predict filter applications.

[0005] Another solution to fouling is periodic cleaning of the membrane. This can be achieved by physical, biological, or chemical cleaning. Physical cleaning can be backwashing using gas scrubbing, sponges, water jets, or penetrants. Physical cleaning can also include some abrasive cleaning agents added to the liquid being filtered. Chemical cleaning uses chemicals, such as acids, bases, oxidizing agents, enzyme components, surfactants, complexing agents, and formulated detergents, to remove fouling materials and impurities. Chemical cleaning is usually more effective at removing fouling that cannot be removed by physical cleaning. However, chemical cleaning increases waste and therefore has a negative impact on the environment. While physical cleaning is environmentally friendly, it requires more frequent cleaning and may sometimes be insufficient to remove fouling materials from the membrane. Membrane cleaning, also known as membrane recovery, is a method for restoring membrane function after fouling.

[0006] It is also possible to combine physical and chemical cleaning, an example of which can be found in EP 1 920 821, which uses, inter alia, water-insoluble calcium carbonate.

[0007] Another solution is the pretreatment of the water to be filtered. Pretreatment reduces the fouling substances present in the water before it reaches the membrane or changes the properties of the fouling substances so that their interaction with the membrane material and structure is reduced or limited. Examples of pretreatment methods include coagulation, adsorption, oxidation, magnetic ion exchange (MIEX), biological treatment, or some integrated pretreatment. Typically, this is achieved by adding fouling control additives to the water to condition it, i.e., to change or reduce the amount of fouling substances present in the water before it reaches the membrane. However, the efficiency of water pretreatment depends on many factors, such as the type of agent (coagulant, adsorbent, flocculant, oxidant, etc.), dosage, dosage form (continuous or intermittent), dosage point, mixing efficiency, temperature, fouling substance properties (hydrophobicity, charge density, molecular weight and size), and membrane characteristics (membrane charge, hydrophobicity, and surface morphology). Therefore, pretreatment methods are highly sensitive to application conditions and require individual planning, optimization, and monitoring.

[0008] Conditioning by coagulation / flocculation is commonly used in conventional filtration techniques (e.g., media filtration) to prepare the liquid to be filtered so that the media filtration equipment can function properly, particularly by eliminating problems such as clogging of the media bed and surface cake formation or filter plugging.

[0009] Although membrane technology was originally designed as a high-performance, chemical-free alternative to conventional filtration, practical experience has shown that various pretreatment processes (including physicochemical processes) may be required to ensure stable membrane operation. Therefore, coagulation has been applied as a fouling control agent to pretreat water to be filtered through membranes. Adding coagulation additives to the water promotes the aggregation of fouling substances into larger flocs, reducing or eliminating membrane pore blockage. However, because membrane pores are two to three orders of magnitude smaller than those in conventional filtration technologies, microflocs were deemed sufficient. Coagulation agents can be organic or inorganic. Inorganic coagulants include aluminum or iron salts. Coagulation is currently the most widely used fouling control chemical in membrane-based water treatment systems. Here, the coagulation agent acts as a fouling control additive.

[0010] One problem with coagulants is that unreacted coagulant can reach the membrane and react on its surface or within the membrane's porous structure. The membrane can clog the fibers with too much coagulant, or the pores can become blocked by the smaller monomers, dimers, and trimers of the hydrolyzable metal coagulant. This means that the coagulant can cause fouling rather than solve it. Low-quality coagulants can also cause fouling. 2+ and Mn 2+ Fouling by iron may also occur. Iron fouling requires a tailored and thorough cleaning protocol to restore permeability. In addition, the water containing spent coagulants resulting from periodic membrane cleaning may have environmental impacts if it is directly disposed of in the environment without proper treatment.

[0011] While the above pretreatment methods condition the water to be filtered to control fouling, membrane conditioning is also known. For example, International Publication Nos. 2001027036A1 and 2002044091A2 disclose filter aids added to the water to be filtered to condition the membrane during each filter cycle. The filter aids added to the water contain fouling control particles that form a deposit layer on the membrane with the flux of the permeate. The deposit layer protects the membrane from fouling by retaining fouling materials in the deposit layer. At the end of each cleaning cycle, the deposit layer with the retained fouling materials is washed from the membrane, for example, by backwashing. Ion exchange resin particles and suspensions of iron hydroxide, aluminum oxide and aluminum hydroxide, sintered iron oxide particles, crushed activated carbon, clay particles, and other inorganic particles have been proposed as membrane fouling control additives. The use of fouling control particles with sizes between 0.5 and 20 micrometers (μm) has been proposed. However, all of the materials proposed as fouling control particles have been reactive, abrasive, toxic, or environmentally undesirable, and have had significant side effects such as damaging membranes, pumps, and / or causing problems in handling the wastewater resulting from cleaning. Therefore, this technology has not found application on an industrial scale.

[0012] A similar system to the membrane fouling control additive described above is also described in International Publication No. 2017009792A1. Additionally, it is proposed that the membrane and reactive fouling control particles have a stimuli-responsive layer so that the flowable protective layer formed by the fouling control particles remains attached to the stimuli-responsive layer, even during the cleaning step, until a stimulus is formed in the stimuli-responsive layer and the fouling control particles are removed. It is also proposed to use fouling control particles with a particle size smaller than 1 μm, preferably 100-200 nanometers. This technique can somewhat reduce the amount of fouling control particles required. However, it does not solve the problems associated with the suggested fouling control particles, such as being reactive, abrasive, and / or environmentally undesirable. The stimuli-responsive layer creates additional process steps, including waste and handling and disposal, which add to the high cost and complexity of the proposed solution. DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0013] Therefore, the present invention aims to provide a membrane fouling control system and process, and a calcium and / or magnesium additive as a fouling control additive, which avoids the drawbacks of the prior art and / or achieves easy and efficient membrane fouling control. [Means for solving the problem]

[0014] According to the present invention, this object is solved by a process for membrane fouling control, comprising the steps of: directing / filtering a liquid to be filtered through a membrane; and adding fouling control particles upstream of the membrane and / or in the liquid to be filtered to form a flowable protective layer on the membrane. The process is characterized by one or more of the embodiments described below.

[0015] Furthermore, according to the present invention, this object is also solved by a system for membrane fouling control, comprising: a first guiding section; a second guiding section; a membrane arranged between the first guiding section and the second guiding section and / or configured to filter a liquid by guiding the liquid from the first guiding section to the second guiding section; and a fouling control means filled with fouling control particles and / or configured to add fouling control particles to the first guiding section, wherein the fouling control particles and / or the fouling control means are configured such that the fouling control particles added by the fouling control means form a fluid protective layer on the membrane to protect the membrane from fouling substances. This system is characterized by one or more of the following embodiments.

[0016] According to the present invention, this object is further solved by a calcium and / or magnesium additive (for membrane fouling control), preferably comprising particles which, when added to a liquid flowing through a membrane, form a flowable protective layer on the membrane for membrane fouling control.

[0017] Calcium and / or magnesium additives (for membrane fouling control) are used to control the amount of particles in the membrane. 50 , d less than 10 μm 90 , and d of 50nm to 500nm 10 Calcium and / or magnesium based ultrafine synthetic inorganic precipitated particles having a particle size distribution of 5 μm or less, and 50 , d less than 15 μm 90 , and d of 200 nm to 3 μm 10 The calcium and / or magnesium-based synthetic inorganic precipitated particles are characterized by containing calcium and / or magnesium-based synthetic inorganic precipitated particles selected from calcium and / or magnesium-based ultrafine synthetic inorganic precipitated particles having a particle size distribution of

[0018] The additive of the present invention is therefore a calcium and / or magnesium-based synthetic inorganic precipitate with a tightly controlled particle size distribution, which is suitable for membrane fouling control applications, as membrane permeability is nearly fully restored after each cleaning of the flowable protective layer without causing damage to the membrane. The calcium and / or magnesium additive of the present invention is capable of allowing high initial liquid flow rates, providing pore space to capture and accommodate fouling substances, and in particular, tailoring the particle size distribution of the calcium and / or magnesium-based synthetic inorganic precipitate to provide maximum flow rates through the membrane, without adversely affecting membrane permeability due to the formation of a coating layer with layer-level properties.

[0019] According to the present invention, the particle size distribution (PSD) is measured by laser light scattering (commonly also called laser diffraction) of calcium and / or magnesium additives dispersed in water in accordance with standard ISO 13320:2020(E), item 5. Preferably, the PSD is analyzed / measured by laser light scattering using 450 nm, 600 nm, and 900 nm light with two polarizations for each wavelength for the range below 0.4 μm, and by a 780 nm laser for the range above 0.4 μm. The PSD is generated by the Mie scattering model in accordance with standard ISO 13320:2020(E), item 5. Water is used as the dispersing liquid. Before measurement by laser diffraction, ultrasonic treatment is used to obtain a complete dispersion of the calcium and / or magnesium additives in water. In the measurement method used to obtain PSDs below 0.4 μm, a white light-emitting diode (LED) is used with three different filters to obtain optical measurements at three wavelengths: 450 nm, 600 nm, and 900 nm, and with two polarizers to obtain two (orthogonal) polarizations for each of the three wavelengths (resulting in a total of six optical measurements). In the measurement method used to obtain PSDs above 0.4 μm, a 780 nm laser light (red laser) is used. No polarizer is used for the red laser. For the range below 0.4 μm, the PSD is generated by a Mie dispersion model based on six measurements obtained from three wavelength measurements at 450 nm, 600 nm, and 900 nm, each measured with two orthogonal polarizations. For the range above 0.4 μm, the PSD is generated by a Mie dispersion model based on measurements with the red laser.

[0020] As explained below, the particle size distribution value d y is the distribution of y% of the diameter d y The value d in this application refers to a size that is less than y is the number of particles that is y% of the total number of particles. y and / or (100%-y%) of the number of particles is less than d y Super (just d yThe particle size distribution value d is a number-based particle size distribution that means that particles with a particle size of d are ignored. y is determined from the PSD determination by laser light scattering described above.

[0021] Synthetic inorganic precipitates based on calcium and / or magnesium are inorganic precipitates whose production is controlled to achieve certain characteristics associated with synthetic precipitates, such as particle size distribution, BJH porosity, and BET specific surface area. While natural inorganic precipitates typically have very broad particle size distributions due to unconstrained and often slow crystallization, such synthetic inorganic precipitates are typically distinguished from natural inorganic precipitates by constraints applied during the production process, which typically result in synthetic inorganic precipitates with narrower particle size distributions due to the controlled production process.

[0022] Synthetic inorganic precipitated particles are disclosed, for example, in U.S. Patent Application Publication No. 20150044469 or U.S. Patent Application Publication No. 20180170765.

[0023] The process, system and / or additive are characterized by one or more of the following embodiments.

[0024] In one embodiment, the fouling control particles are precipitates, preferably inorganic or metallic precipitates. The class of precipitate particles, particularly inorganic and metallic precipitate particles, allows for the properties of the fouling control particles, such as their size or size distribution, to be tailored during production.

[0025] In one embodiment, the calcium and / or magnesium particles are / include calcium and / or magnesium carbonate-based synthetic inorganic precipitates. Preferred examples of this category are precipitated calcium carbonate and precipitated hydromagnesium. This is a versatile inorganic material that can be tailored in terms of morphology, particle size, and polydispersity to provide a range of functions for different applications. For the purpose of membrane fouling control, the inventors have found this material to be surprisingly effective, nearly completely restoring membrane permeability each time the flowable protection layer is cleaned. In addition, this material does not damage membrane materials or other system components (it is not abrasive or corrosive) and is environmentally friendly (it can be disposed of with minimal processing). Ultrafine and / or extra-fine precipitated calcium carbonate or / and precipitated hydromagnesium are chemically inert and can form a porous filter cake that allows high initial liquid flow, provides pore space to capture and accommodate fouling substances, and does not adversely affect membrane permeability. The particle size distribution of the precipitates of this material can be adjusted to form a coating layer that provides maximum flow rate through the membrane.

[0026] In one embodiment, the fouling control particles are composite particles (composed of a composition) of a first material and a second material. The composite particles preferably comprise a core of the first material and a shell of the second material. The first material is preferably an inorganic substance and / or an inorganic precipitate, preferably a calcium-based inorganic substance (precipitate), preferably calcium carbonate, preferably primarily calcite with a trace of aragonite. The second material is preferably an inorganic substance and / or an inorganic precipitate, preferably a magnesium-based inorganic substance (precipitate), preferably hydromagnesium, preferably hydromagnesium with (some trace of) nesquehonite. These composite particles can be easily sized based on the core material and / or the first material and / or easily functionalized based on the shell material and / or the second material. This allows for functionalization of the fluidic protective layer, for example, to enhance adhesion of fouling substances to the fluidic protective layer, thereby further improving the filtration function of the fluidic protective layer. Preferably, the shell material has different properties than the core material, and will adsorb different types of fouling substances and different surfaces. In addition, the shell material can be porous, allowing absorption into the pores, thereby leaving the interparticle voids (pores) open. On the other hand, this group of composite particles is much more environmentally friendly than the reactive fouling control particles used in the prior art.

[0027] In one embodiment, the fouling control particles are inert. Within the meaning of the present invention, the term "inert" means that the fouling control particles do not change their properties in the flowable protective layer on the membrane during the operation mode. Prior art has suggested that only reactive fouling control particles react with fouling substances, which has a negative impact on the environment and requires special disposal procedures. Often, reactive fouling control particles are, for example, abrasive or corrosive, damaging the membrane and other system equipment, such as pumps.

[0028] In one embodiment, the fouling control particles are reactive or functionalized. Within the meaning of the present invention, the term "reactive or functionalized particles" preferably means that the surface of the fouling control particles has specific charges or groups that absorb fouling substances and / or bind to the membrane surface.

[0029] In one embodiment, the calcium and / or magnesium-based synthetic inorganic precipitated particles have a polydispersity value of 0.1 or greater and / or 1.5 or less. Preferably, the polydispersity value is 0.2 or greater, preferably 0.3 or greater, preferably 0.4 or greater, preferably 0.5 or greater. Preferably, the polydispersity value is 1.4 or less, preferably 1.2 or less, preferably 1.1 or less, preferably 1.0 or less. Preferably, the ultrafine synthetic inorganic particles have a polydispersity value in the range of 0.3 to 1.2, preferably 0.5 to 1.0. Preferably, the ultrafine synthetic inorganic particles have a polydispersity value in the range of 0.7 to 1.5, preferably 0.9 to 1.3. The polydispersity value of the synthetic inorganic precipitated particles of the present invention allows for the characterization of the distribution width (often referred to as the uniform polydispersity of a particle population of inorganic precipitated particles), and the particle size d 90 ~d 10 d 50 The polydispersity value of the calcium and / or magnesium particles, considered as the particle size divided by the particle size, is preferably 0.1 or more, preferably 0.15 or more, preferably 0.2 or more. The polydispersity value of the calcium and / or magnesium particles is preferably 1.5 or less, preferably 1.2 or less, preferably 1.0 or less, preferably 0.8 or less, preferably 0.6 or less, preferably 0.4 or less, preferably 0.35 or less, preferably 0.3 or less, preferably 0.25 or less. The term "polydispersity value" is used within the meaning of the present invention to mean d 90 ~d 10 d 50 The polydispersity value is calculated according to the following formula:

[0030]

number

[0031] In the formula, d 90 , d 10 , d 50 The value is the d of calcium and / or magnesium based synthetic inorganic settling particles. 90 , d 10 , d 50 As defined above, d 90 , d 10 , d 50 is obtained from a number-based distribution. Such polydispersity values ​​obtained from number-based distributions are used to characterize the narrow particle size distribution of the synthetic inorganic precipitating particles according to the present invention and are disclosed in the literature. Although polydispersity values ​​can also be obtained from volume-based distributions, the polydispersity values ​​calculated according to the present invention are obtained from number-based distributions. It has been recognized in practice that the polydispersity value plays an important role in the formation of a flowable protective layer by fouling control particles, on the one hand, due to the risk of pore blockage by excessively small fouling control particles, and on the other hand, due to poor and uneven membrane coverage by large fouling control particles.

[0032] In one embodiment, the fouling control particles have an absolute value of the zeta potential of less than 50 mV, preferably less than 45 mV, and preferably less than 40 mV. This has the advantage that the fouling control particles can form a sacrificial layer, i.e., a layer that can be easily peeled off from the membrane. In one embodiment, the particles have a positive zeta potential of 50 mV or less, preferably 45 mV or less, and preferably 40 mV or less. In another embodiment, the particles have a negative zeta potential of more than -50 mV, preferably -45 mV or more, and preferably -40 mV or more.

[0033] According to the present invention, the zeta potential of particles was measured according to the following experimental procedure. A suspension of synthetic inorganic precipitated particles was subjected to magnetic stirring for 30 minutes before each zeta potential measurement. The suspension was then subjected to a dispersion step for 30 seconds with a Hielscher-UP4005 ultrasonication probe (50% amplitude and 0.5 cycles), followed by another 30 minutes of magnetic stirring, after which a new series of measurements was performed. Zeta potential measurements were performed with an electroacoustic spectrometer DT-1200 (Dispersion Technology). The electroacoustic probe for measuring the zeta potential was calibrated with a colloidal silica suspension exhibiting a zeta potential of -38 (±1) mV. Five zeta potential measurements were performed for each sample.

[0034] In one embodiment, the fouling control particles are measured by nitrogen adsorption manometry and calculated according to the BET method. 2 / g, preferably above 15m 2 / g, preferably more than 20m 2 / g or more, which results in better deposition on the membrane surface as well as a higher affinity for fouling substances to capture them from the liquid being filtered.

[0035] In one embodiment, the Scherrer diameter of the fouling control particles is greater than 20 nm, preferably greater than 30 nm, preferably greater than 40 nm, preferably greater than 50 nm, preferably greater than 60 nm. In one embodiment, the Scherrer diameter of the fouling control particles is less than 150 nm, preferably less than 140 nm, preferably less than 130 nm, preferably less than 120 nm, preferably less than 110 nm, preferably less than 100 nm. Preferably, the Scherrer diameter of the fouling control particles is 50 nm to 100 nm. The Scherrer diameter indicates the average diameter of ordered (crystalline) domains and is calculated according to the Scherrer equation, preferably based on measurements by X-ray diffraction.

[0036] Powder X-ray diffraction (XRD) is an analytical technique used for phase identification and crystallite size (Scherrer diameter) of crystalline materials. Diffraction is based on the generation of X-rays in an X-ray tube. These X-rays are filtered and collimated to produce focused monochromatic radiation that is irradiated onto the sample. This analysis is performed using a Bruker-D8 advance instrument. Copper K-alpha is an X-ray energy frequently used in laboratory-scale X-ray instruments. The energy is 8.04 keV, which corresponds to an X-ray wavelength of 1.5406 Å.

[0037] In crystalline materials, scattered X-rays undergo constructive and destructive interference. This diffraction process is described by the Bragg equation (nλ=2d sinθ). The diffracted X-rays are detected, processed, and counted.

[0038] Because the possible diffraction directions depend on the size and shape of the crystals that make up the sample, and the intensity of the diffracted waves depends on the type and arrangement of atoms in the crystal structure, this method allows the determination of the chemical composition of the sample. By applying the Scherrer equation to the peak width of the crystal structure, it is also possible to determine the size of the crystals in the sample.

[0039] Typically, we use a Lorentzian fit (for the diffraction peaks) to calculate the Scherrer diameter, which we apply to the peaks at approximately 29.45°, 39.46° and 43.21° in the diffraction pattern.

[0040] In one embodiment, the fouling control particles and / or additives are in the form of a slurry having a solids content and / or fouling control particle content of preferably 20% by weight or less, preferably 15% by weight or less, preferably 12% by weight or less, preferably 11% by weight or less, preferably 10% by weight or less. In one embodiment, the fouling control particles and / or additives are in the form of a slurry having a solids content and / or fouling control particle content of preferably 1% by weight or more, preferably 1.5% by weight or more, preferably 3% by weight or more, preferably 5% by weight or more, preferably 6% by weight or more, preferably 7% by weight or more. The higher the solids content of the fouling control particles, the lower the volume and weight of the additive and / or fouling control particles required for storage and transportation.

[0041] In one embodiment, the calcium and / or magnesium based ultrafine synthetic inorganic precipitated particles have a d of 1 μm or less. 50 , d less than 10 μm 90 , and d of 50nm to 500nm 10 The ultrafine inorganic precipitated particles according to the present invention are particularly suitable for ultrafiltration.

[0042] In one embodiment, the calcium and / or magnesium based ultrafine synthetic inorganic precipitated particles have a d of 5 μm or less. 50 , d less than 15 μm 90 , and d of 200 nm to 3 μm 10 The ultrafine inorganic sedimenting particles according to the present invention are particularly suitable for microfiltration.

[0043] Typically, according to the present invention, the particle size distribution of calcium and / or magnesium particles is 10 is greater than the specified pore size of the membrane. Preferably, the d of the size distribution of the fouling control particles 10is 3 times, preferably 5 times, preferably 7 times, preferably 9 times, preferably 10 times larger than the specified pore size. It has been shown that selecting a lower limit for the size of calcium and / or magnesium particles in accordance with the specified pore size of the membrane significantly improves the performance of the fouling control method. By selecting calcium and / or magnesium particles larger than the specified pore size of the membrane, the calcium and / or magnesium particles are prevented from entering the membrane, thereby preventing the membrane pores from narrowing. This likely explains the positive effect of this measure. In the prior art, only the average particle size was controlled, and the average particle size was not selected in accordance with the specified pore size of the membrane. This explains the limited effectiveness of membrane fouling control using fouling control particles that form a fluid protective layer on membranes in the prior art. Additionally, the fact that only the average particle size is controlled in prior art fouling control particles ignores the often very wide size distribution of fouling control particles at these smaller dimensions, which for average particle sizes above the specified pore size still results in a large amount of fouling control particles smaller than the specified pore size, thus narrowing the pores. This measure is particularly advantageous in the following embodiments.

[0044] In one embodiment, the d of the size distribution of calcium and / or magnesium particles is determined depending on the microfiltration membrane. 90 is 15 μm or less, preferably 10 μm or less, preferably 5 μm or less, preferably 1 μm or less, preferably 0.7 μm or less, preferably 0.5 μm or less.

[0045] In one embodiment, the d of the size distribution of calcium and / or magnesium particles depending on the ultrafiltration membrane 90 is 10 μm or less, preferably 5 μm or less, preferably 1 μm or less, preferably 0.7 μm or less, preferably 0.5 μm or less.

[0046] It has been shown that the main effect of the upper size limit of calcium and / or magnesium particles on the performance of fouling control methods is the uniformity of calcium and / or magnesium particle deposition. The uniformity is primarily dependent on the absolute particle size and less dependent on the specified pore size of the membrane. It has been proven that the above upper size limit significantly reduces the non-uniformity of the deposited calcium and / or magnesium particles, thus providing a high performance flowable protective layer to the membrane. As mentioned above, it is not only the average particle size that is important to select, but also the size distribution of the calcium and / or magnesium particles. 90 It was further found that it is more important to select the particle size. There may also be some upper particle size effects depending on the specified pore size, such as complete pore blockage. However, these effects depending on the specified pore size have been shown to be less influential than the previously mentioned homogeneity, which depends on the absolute particle size.

[0047] In a preferred embodiment, the particle size distribution of the calcium and / or magnesium particles is 10 is selected depending on the defined pore size, while d of the size distribution of calcium and / or magnesium particles 90 is chosen as an absolute value. This combination significantly improved the performance of membrane fouling control compared to that known in the prior art.

[0048] In one embodiment, the particle size distribution of calcium and / or magnesium particles for ultrafiltration is 10 is 50 nm or more, preferably 70 nm or more, preferably 100 nm or more, preferably 200 nm or more.

[0049] In one embodiment, the particle size distribution of calcium and / or magnesium particles for ultrafiltration is 10 is 500 nm or less, preferably 400 nm or less, preferably 350 nm or less, preferably 320 nm or more.

[0050] In one embodiment, the particle size distribution of calcium and / or magnesium particles for microfiltration is 10 is 200 nm or more, preferably 250 nm or more, preferably 300 nm or more, preferably 500 nm or more.

[0051] In one embodiment, the particle size distribution of calcium and / or magnesium particles for microfiltration is 10 is 1000 nm or less, preferably 900 nm or less, preferably 800 nm or less, preferably 750 nm or less.

[0052] In one embodiment, the process comprises the further step of forming calcium and / or magnesium particles in situ and / or the fouling control means comprises fouling control particle forming means for forming fouling control particles in situ or in the fouling control means, preferably the fouling control particles are formed prior to adding the fouling control particles to the liquid to be filtered.

[0053] The calcium and / or magnesium particles are preferably formed by a physical action and / or a chemical reaction. The chemical reaction preferably uses at least one raw material or substance, preferably at least two raw materials or substances, to obtain the calcium and / or magnesium particles. The chemical reaction is preferably precipitation. The chemical reaction is preferably carbonation, preferably carbonation of calcium hydroxide and / or magnesium hydroxide. Preferably, precipitated calcium carbonate is obtained by the chemical reaction. By generating the calcium and / or magnesium particles in situ, some stability issues related to the size distribution of some calcium and / or magnesium particles can be reduced, and the raw materials used in the chemical reaction can be easier to handle and process. The physical action can be size reduction and / or classification.

[0054] In one embodiment, in the process of the present invention, the flowable protective layer is formed directly on the membrane.

[0055] In one embodiment, in the process of the present invention, the flow protection layer formed on the membrane is a porous layer that allows liquid to pass through the membrane and retains fouling substances.

[0056] In one embodiment, in the process according to the invention, the fluid protective layer is formed and / or maintained on the membrane by transmembrane pressure generated through the membrane by directing the liquid to be filtered through the membrane and / or by permeate flux, i.e., by permeation resistance or fluid pressure that carries particles to the membrane surface.

[0057] In one embodiment, the process of the present invention includes the further step of washing the flowable protective layer together with the filtered / retained fouling material from the membrane, and / or the system of the present invention is configured to achieve this.

[0058] In one embodiment, the process of the present invention performs a plurality of filtration cycles and / or the system of the present invention is configured to perform a plurality of filtration cycles, wherein one or more or all of the filtration cycles in the plurality of filtration cycles: adding fouling control particles to the liquid to be filtered to form a fluid protective layer on the membrane; filtering the liquid to be filtered guided through the membrane while retaining the fouling substances by the fluid protective layer; and Washing the flowable protective layer together with the retained fouling material from the membrane. Includes.

[0059] In the process according to the invention, the membrane fouling control additive is the calcium and / or magnesium additive described above.

[0060] In one embodiment, the membrane of the process of the invention and / or the system of the invention is a microfiltration membrane or an ultrafiltration membrane.

[0061] In one embodiment, in the process according to the invention, the liquid guided through the membrane is an aqueous liquid, preferably public wastewater, seawater, industrial process water and wastewater, source water for public drinking water, brackish water, fresh underground water, fresh surface water.

[0062] In one embodiment, in the process according to the invention, calcium and / or magnesium particles added to the liquid to be filtered form a fluidic protective layer on the membrane such that, if the liquid to be filtered contains fouling substances, the fouling substances are retained in the fluidic protective layer before the liquid to be filtered is guided through the membrane.

[0063] Other embodiments of the present invention are described in the accompanying claims and in the following description of the drawings. [Brief explanation of the drawings]

[0064] [Figure 1] FIG. 1 shows a system for controlling fouling. [Figure 2] FIG. 2 shows steps in a method for fouling control in which a membrane fouling control additive is introduced into the liquid to be filtered. [Figure 3] FIG. 3 shows steps in a method for fouling control that forms a flowable protective layer on a membrane. [Figure 4] FIG. 4 illustrates steps in a method for fouling control that retains fouling materials in a flowable protective layer. [Figure 5] FIG. 5 illustrates steps in a method for fouling control for cleaning the flowable protective layer from the membrane. [Figure 6] FIG. 6 shows an embodiment of the size distribution of calcium and / or magnesium particles. [Figure 7] FIG. 7 shows an ideal membrane with fouling control particles of a first size. [Figure 8]FIG. 8 shows an ideal membrane with fouling control particles of a second size. [Figure 9] FIG. 9 shows the pressure over different filtration cycles for membrane fouling control using coagulants. [Figure 10] FIG. 10 shows the pressure over different filtration cycles for membrane fouling control using precipitated calcium carbonate as the fouling control particle. [Figure 11] FIG. 11 shows a conversion table of specified pore sizes and MWCOs. [Figure 12] FIG. 12 shows the pressure over different filtration cycles for membrane fouling control with precipitated calcium carbonate as the fouling control particle and without the fouling control particle.

[0065] In the drawings, the same or similar components are designated by the same reference numerals. DETAILED DESCRIPTION OF THE INVENTION

[0066] Other characteristics and advantages of the invention will emerge from the non-limiting description that follows, with reference to the drawings and examples.

[0067] 1 shows a system for membrane fouling control comprising a membrane 1, a first guide 2, a second guide 3 and a fouling control means 4. Preferably, the system further comprises a cleaning outlet 9 and / or a cleaning outlet control means.

[0068] The membrane fouling control system is configured to filter a liquid to be filtered through the membrane 1 to obtain a filtrate while controlling fouling of the membrane 1. The membrane fouling control system can be used for public drinking water, public wastewater, water desalination or reclamation, industrial wastewater such as oily water, sludge, or water containing chemicals, etc. However, the system can also be applied to industrial process water in the beverage industry, etc.

[0069] The liquid to be filtered is the liquid in the first guide 2 or the liquid upstream of the membrane 1 in the operating mode. The filtrate is the liquid in the second guide 3 or the liquid downstream of the membrane 1 in the operating mode. The filtrate obtained by guiding the liquid to be filtered through the membrane 1 is also called permeate. The liquid to be filtered and the filtrate are usually aqueous liquids. However, it is also possible that the liquid to be filtered is not aqueous but is another liquid.

[0070] The liquid to be filtered is usually a liquid containing contaminants (contaminated liquid). The contaminants are intended to be filtered out by the membrane 1. The filtrate is a liquid with a reduced amount of contaminants, preferably substantially depleted of contaminants. Naturally, the liquid to be filtered can also be a clean liquid, i.e., a liquid free of contaminants, due to certain operating modes or simply because the filtrate is not always contaminated. The liquid to be filtered is usually an aqueous liquid, i.e., contaminated water or water containing contaminants, and the filtrate is usually clean water or water with a reduced amount of contaminants, preferably free of contaminants. The contaminated water can be a source of public drinking water, and / or the filtrate can be public drinking water or pretreated public drinking water. The contaminated water can be public wastewater containing biological or other contaminants, or wastewater such as industrial wastewater containing chemicals, inorganic or other contaminants, or wastewater such as sludge, and / or the filtrate can be filtered wastewater or clean water. The contaminated water can be salt or seawater, where the contaminants are salts, inorganic and / or biological contaminants. The contaminated water can be industrial process water.

[0071] Contaminants are typically unwanted particles in the liquid being filtered, and the filtrate (also called permeate) is the desired product of the membrane process. However, in some applications, the contaminants retained by membrane 1, or the retentate, i.e., the liquid containing the retained contaminants, can be the desired product of the process. Preferably, the contaminants are particles that can and / or should be retained by membrane 1.

[0072] The liquid to be filtered further comprises fouling substances 10. Fouling substances are contaminants that form membrane fouling. The fouling substances can be in solid form (fouling particles) in the liquid to be filtered and / or in dissolved form in the liquid to be filtered. Different types of fouling substances 10 and different types of membrane fouling have already been described in the introduction and will not be repeated here. All or some of the fouling substances 10 can be contaminants. All or some of the contaminants can be fouling substances 10. This depends on the application, the liquid to be filtered, the membrane 1 and the process conditions. The following description mainly focuses on the fouling substances 10, without specifying whether the fouling substances are contaminants or not.

[0073] The membrane 1 is configured to filter contaminants from the liquid to be filtered as it passes through the membrane 1, thereby obtaining a filtrate. Filtration of contaminants means that the amount of contaminants in the filtrate is less than the amount of contaminants in the liquid to be filtered, preferably by more than 50%, preferably more than 60%, preferably more than 80%, preferably more than 90%. Most preferably, all contaminants are retained by the membrane 1 as the liquid to be filtered passes through the membrane 1. The membrane 1 has a first side 1.1 and a second side 1.2. The first side 1.1 is connected to the second side 1.2 through pores 5 in the membrane 1. The first side 1.1 provides the membrane surface of the membrane 1. The first side 1.1 or membrane surface can be provided depending on the design of the membrane 1, such as a tube, hollow fiber, or other geometry.

[0074] Preferably, membrane 1 has a specified pore size that determines the retention capacity of membrane 1. The specified pore size is a value obtained from the pore size distribution of membrane 1 and / or a value obtained from a particle size at which particles having a certain size are retained at a certain rate X%. An example of a pore size obtained from a pore size distribution is the most common pore size in the distribution, or the average pore size, or the d value of the pore size distribution. 90 The diameter distribution d z z% of the distribution is z The specified pore size of some membranes 1 refers to the particle size at which particles are retained by the membrane 1 (with a certain probability). The specified pore size of a membrane 1 preferably refers to the particle size at which X% of particles of this size are retained. The percentage X is preferably 50% or more, preferably more than 60%, preferably more than 70%, preferably more than 80%. A preferred definition of the specified pore size is X=90%. Some membranes 1 define the specified pore size as a molecular weight cut-off (MWCO) in Daltons (Da). This is defined as the minimum molecular weight of spherical molecules that are retained by the membrane 1 at 90%. For the purposes of the present invention, the MWCO can be converted to a specified pore size according to the table shown in FIG. 11. The second column shows the MWCO in kilodaltons (kDA), and the first column shows the corresponding specified pore size converted to nanometers (nm). The third column shows the corresponding membrane type: reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. Any MWCO value of Membrane 1 can be converted to its corresponding specified pore size of Membrane 1 according to the present invention by linear interpolation between the next higher and next lower MWCO values. While this conversion method may not always be accurate, it is sufficient for the present invention to unambiguously define the specified pore size of Membrane 1 based on its MWCO value when Membrane 1 is defined by its MWCO value rather than pore size.

[0075] The present invention is particularly advantageous for membrane 1 having a pore size greater than 5 nm, preferably greater than 10 nm, preferably greater than 50 nm, and in some embodiments, greater than 100 nm. The present invention is particularly advantageous for membrane 1 having a pore size less than 50 μm, preferably less than 20 μm. Membrane 1 is preferably a microfiltration membrane or an ultrafiltration membrane. Microfiltration membranes are considered to have pore sizes between 150 nm and 20 μm. Ultrafiltration membranes are considered to have pore sizes between 5 nm and 150 nm. However, the present invention is not limited to these pore sizes and is applicable to other membrane types, including larger nanofiltration membrane pore sizes. In a preferred embodiment, membrane 1 is not suitable for removing monovalent and / or divalent ions.

[0076] Membrane 1 can be any membrane type, such as a monolith, a tube, a flat sheet (plate, frame, or spiral wound), a hollow fiber, or any other membrane type. Membrane 1 can be made of any material, such as ceramic, polymer, or others. Membrane 1 shown in FIG. 1 is arranged in a dead-end configuration. However, membrane 1 can also be arranged in a cross-flow filtration configuration. This membrane preferably operates in low-pressure membrane technology.

[0077] The first guide 2 is configured to store or guide the liquid to be filtered so that it can be guided through the membrane 1. The first guide 2 therefore has a contact surface with the first side 1.1 of the membrane 1. The first guide 2 can be a container, a pipe, a tank, or any other means for storing or guiding liquid. The first guide 2 can generate transmembrane pressure between the first side 1.1 of the membrane 1 and the second side 1.2 of the membrane 2 and / or can be equipped with a pump for generating a hydraulic pressure that drives the liquid to be filtered to the membrane 1 and / or the membrane surface. The generated liquid flow is preferably perpendicular to the membrane surface. The transmembrane pressure is the resulting pressure generated in the system from the flow through the membrane according to Darcy's law. The first side 1.1 and the second side 1.2 of the membrane 1 do not necessarily depend on the geometry of the membrane 1, but rather on its function.

[0078] The second guide 3 is configured to store or guide the filtrate. Thus, the liquid to be filtered passes through the membrane 1 and becomes the filtrate, which flows into the second guide 3. The second guide 3 therefore has a contact surface with the second side 1.2 of the membrane 1. The second guide 3 can be a container, a pipe, a tank or any other means for storing or guiding a liquid. The second guide 3 can include a pump that pumps the filtrate away from the membrane 1 and / or creates transmembrane pressure between the first side 1.1 of the membrane 1 and the second side 1.2 of the membrane 1.

[0079] Preferably, the system or the first guide 2, the membrane 1 and / or the second guide 3 (in operation mode) is configured to create a transmembrane pressure or a liquid flow that guides the liquid to be filtered from the first guide 2 through the membrane 1 to the second guide 3, resulting in filtrate. The transmembrane pressure can be achieved by a pump in the first guide 2 or the second guide 3. The transmembrane pressure or the liquid flow can also be created by gravity or any other force on the liquid. In some embodiments, the system or the first guide 2, the membrane 1 and / or the second guide 3 (e.g., in a cleaning mode) is preferably configured to create a reverse transmembrane pressure or a reverse liquid flow that guides the filtrate or liquid in the second guide 2 through the membrane 1 to the first guide 2. This reverse transmembrane pressure or reverse liquid flow can be applied in the cleaning mode to backwash the membrane 1 and clean it from the flowable protective layer 7, calcium and / or magnesium particles 6 and / or fouling substances.

[0080] The fouling control means 4 is configured to add calcium and / or magnesium particles 6 and / or membrane fouling control additive to the liquid to be filtered and / or the first guiding section 2. The fouling control means 4 preferably includes a container or vessel for storing the calcium and / or magnesium particles 6 and / or membrane fouling control additive. The fouling control means 4 includes an opening or a connection to the first guiding section 2 for adding the calcium and / or magnesium particles 6 and / or membrane fouling control additive to the liquid to be filtered and / or the first guiding section 2. The opening or connection is preferably openable or closable to control the amount of opening or connection to the first guiding section 2 for adding the calcium and / or magnesium particles 6 and / or membrane fouling control additive. Preferably, the fouling control means 4 contains calcium and / or magnesium particles 6 and / or membrane fouling control additive.

[0081] The membrane fouling control additive is an additive that prevents or controls membrane fouling by conditioning the membrane, in particular by forming a flowable protective layer 7 of calcium and / or magnesium particles 6 on the membrane 1. The membrane fouling control additive is an additive that is added during the operating mode of the system / method (rather than during the cleaning mode). The membrane fouling control additive comprises calcium and / or magnesium particles 6 that are configured to form a flowable protective layer 7 on the membrane 1 when the calcium and / or magnesium particles 6 are added to the liquid to be filtered.

[0082] The membrane fouling control additive and / or calcium and / or magnesium particles 6 are preferably in the form of a slurry. The slurry preferably contains a liquid, preferably water, and solid particles (solids). The solids include calcium and / or magnesium particles 6, and preferably consist of at least 50% by weight of calcium and / or magnesium particles, preferably at least 60% by weight of calcium and / or magnesium particles, preferably at least 70% by weight of calcium and / or magnesium particles, preferably at least 80% by weight of calcium and / or magnesium particles, and preferably at least 90% by weight of calcium and / or magnesium particles. Most preferably, the solids are calcium and / or magnesium particles 6. The solids content and / or calcium and / or magnesium particle 6 content of the slurry is preferably less than 20 weight percent (wt%), preferably less than 15 wt%, preferably less than 12 wt%. The solids content and / or calcium and / or magnesium particle 6 content of the slurry is preferably greater than 1 wt.%, preferably greater than 2 wt.%, preferably greater than 4 wt.%, preferably greater than 5 wt.%, preferably greater than 6 wt.%, preferably greater than 7 wt.%.

[0083] In an alternative embodiment, the membrane fouling control additive and / or calcium and / or magnesium particles 6 are delivered to, loaded into, stored in the fouling control means 4 and / or added to the first guiding part 2 and / or the liquid to be filtered as a dry blend, i.e., powder. In order to add the membrane fouling control additive and / or calcium and / or magnesium particles 6 to the first guiding part 2 and / or the liquid to be filtered as a slurry, it is also possible to mix the powder with the liquid between the above steps, for example before or during loading the powder into the fouling control means 4, to obtain a slurry.

[0084] In the above embodiment, the membrane fouling control additive and / or calcium and / or magnesium particles 6 are loaded into the fouling control means 4 in the same form as they enter the first guiding part 2 and / or the liquid to be filtered. In an alternative embodiment, one or more raw materials are added to the fouling control means 4 so as to obtain the membrane fouling control additive and / or calcium and / or magnesium particles 6 as they enter the first guiding part 2 and / or the liquid to be filtered. This can simply be a mixing step, for example, mixing the membrane fouling control additive and / or calcium and / or magnesium particles 6 as a powder with a liquid to obtain said membrane fouling control additive and / or calcium and / or magnesium particles 6 as a slurry.

[0085] In one embodiment, the membrane fouling control additive contains calcium and / or magnesium particles 6 and a dispersant. The dispersant prevents the calcium and / or magnesium particles 6 from agglomerating. The dispersant can be a polyether-polycarboxylate dispersant, a polyacrylate dispersant, or other dispersant.

[0086] In one embodiment, the fouling control means 4 includes a calcium and / or magnesium particle production device for in-situ formation of calcium and / or magnesium particles 6 or membrane fouling control additive by chemical reaction. Therefore, one or more raw materials are introduced into the fouling control means 4, particularly the calcium and / or magnesium particle production device, and the membrane fouling control additive and / or calcium and / or magnesium particles 6 are obtained in-situ by chemical reaction. The membrane fouling control additive and / or calcium and / or magnesium particles 6 are further supplied to the first guiding section 2 and / or the liquid to be filtered. Preferably, the chemical reaction includes a gas-liquid reaction. Preferably, the chemical reaction includes precipitation to obtain synthetic precipitation particles as calcium and / or magnesium particles.

[0087] Preferably, the chemical reaction and / or precipitation is carbonation. Preferably, a synthetic inorganic precipitate is obtained by carbonation. Preferably, the chemical reaction is achieved by introducing gaseous carbon dioxide into a calcium / magnesium hydrate suspension under controlled conditions to obtain the final calcium and / or magnesium particles. In this way, a synthetic inorganic precipitate can be produced. The controlled conditions include the carbon dioxide flow rate, temperature, pressure, and / or other conditions. The calcium and / or magnesium particles 6 and / or additives can be produced before being added to the fluid to be filtered.

[0088] For example, one embodiment for in situ production of precipitated calcium carbonate will be described. In a calcium and / or magnesium particle production apparatus, milk of lime (slaked lime or calcium dihydrate) having a solids content of 1 to 15% by weight is heated to a temperature of 0 to 20°C. A gas mixture containing gaseous carbon dioxide at a volumetric rate of 5 to 40% by volume is injected under a pressure of 0.1 to 0.5 MPa at a gas flow rate of 1 to 5 (typically) liters of CO2 / min / liter of suspension. The supply of gaseous carbon dioxide is stopped when the pH reaches 8.3 or less. The resulting suspension contains at least 5 to 20% by weight of precipitated calcium carbonate relative to the total weight of the slurry and 95% by weight of the total solids content. The resulting suspension is a slurry of calcium and / or magnesium particles, which is then further supplied to the first flow path 2.

[0089] The system is preferably configured to operate in different modes.

[0090] In the operating mode, a transmembrane pressure is created across the membrane 1 and / or a liquid flow of the liquid to be filtered is created from the first guide 2 through the membrane 1 to the second guide 3, thereby obtaining a filtrate.

[0091] In the cleaning mode, the membrane 1 is cleaned from the flowable protective layer 7, the calcium and / or magnesium particles 6 and / or the fouling substances 10. Preferably, cleaning is achieved by backwashing (also called backflushing), i.e. by reversing the transmembrane pressure and / or the flow direction across the membrane 1. Preferably, the filtrate is guided back through the membrane 1 to clean it. However, it is also possible to use different cleaning mechanisms to clean the membrane 1 from the flowable protective layer 7, the calcium and / or magnesium particles 6 and / or the fouling substances 10. This can be other cleaning mechanisms such as those described in the introduction. Preferably, the cleaning outlet 9 is opened during the cleaning mode, so that the cleaning liquid comprising the flowable protective layer 7, the calcium and / or magnesium particles 6 and / or the fouling substances 10 is guided through the cleaning outlet 9 and flows out of the first guide part 2. The cleaning outlet control means preferably closes the membrane 1 from the source of the liquid to be filtered to prevent further contamination of the liquid to be filtered. Preferably, the cleaning outlet control means is configured to close the cleaning outlet 9 during the operating mode. However, in other embodiments, it is also possible to direct the cleaning liquid back into the first directing part 2 during the cleaning mode, in which case the cleaning outlet 9 and cleaning outlet control means are not required.

[0092] The system is preferably configured to perform different filtration cycles, each of which includes an operating mode and a cleaning mode.

[0093] The process for membrane fouling control will be described below with the exemplary steps shown in Figures 2 to 5, which represent one exemplary filtration cycle. In the following, for the sake of brevity, the calcium and / or magnesium particles 6 and the membrane fouling control additive will not be explicitly stated as options in each case, but it will be clear that in the following text they are always synonymous.

[0094] FIG. 2 shows the step of adding calcium and / or magnesium particles 6 to the first guide 2 and / or the liquid to be filtered. During this step, the system is preferably in the operating mode. During this step, the liquid to be filtered is preferably guided through the membrane 1. During this step, the liquid in the first guide 2 is preferably guided through the membrane 1 to the second guide 3. Preferably, the calcium and / or magnesium particles 6 are added so that they are well-dispersed, preferably evenly dispersed, in the liquid to be filtered when they reach the membrane 1. This can be achieved by adding the calcium and / or magnesium particles 6 where laminar flow is not established, for example, in or near a pump, or where turbulence is present. As mentioned above, the calcium and / or magnesium particles 6 are preferably added in the operating mode, i.e., when the liquid to be filtered is being guided through the membrane 1. However, it may also be possible to add the calcium and / or magnesium particles 6 partially or completely before flow through the membrane 1 is initiated. Preferably, the calcium and / or magnesium particles 6 are added at the beginning of the filtration cycle, preferably at the beginning of the operating mode, so that a fluid protective layer 7 is formed on the membrane 1 immediately, before fouling substances can contact the membrane 1 more than necessary. The calcium and / or magnesium particles 6 are preferably added during the first 120 seconds (sec), preferably the first 90 seconds, and preferably the first 60 seconds of the filtration cycle. Preferably, the addition of the calcium and / or magnesium particles 6 and / or membrane fouling control additive is discontinued after a sufficient amount of calcium and / or magnesium particles 6 has been added to form the fluid protective layer 7, for example, after 30 to 120 seconds, depending on the concentration of calcium and / or magnesium particles 6 added to the liquid to be filtered. For some applications, it has been shown to be advantageous to resume the addition of calcium and / or magnesium particles 6 during the operating mode after a period of interruption (not shown), for example, at the end of the operating mode. This has been shown to aid in the removal of the fluid protective layer 7 from the membrane 1 during the cleaning mode in some applications.In some applications, it has been shown to be beneficial to add calcium and / or magnesium particles 6 continuously throughout the operating mode.

[0095] FIG. 3 illustrates the step of forming a fluid protective layer 7 on a membrane 7. The fluid protective layer 7 is formed by calcium and / or magnesium particles 6 added to the liquid to be filtered. The flow of the liquid to be filtered delivers the calcium and / or magnesium particles 6 to the membrane 1, where they are retained so as to form the fluid protective layer 7, similar to a filter cake (see also FIG. 8 ). The flow of the liquid to be filtered through the membrane 1 generates transmembrane pressure, which forms and / or maintains the fluid protective layer 7. The calcium and / or magnesium particles 6 are configured to form a porous fluid protective layer 7 on the membrane 1, allowing the liquid to continue to flow through the fluid protective layer 7 to the membrane 1 and then through the membrane 1.

[0096] Preferably, the step of adding calcium and / or magnesium particles 6 and the step of forming the fluid protective layer 7 at least partially overlap. While the calcium and / or magnesium particles 6 are being added to the flow of the liquid to be filtered, the fluid protective layer 7 is formed on the membrane 1 by the liquid flow and / or transmembrane pressure. The fluid protective layer 7 is formed on the first side 1.1 of the membrane 1. The time during which the calcium and / or magnesium particles 6 are added and the time during which the fluid protective layer 7 is formed can be divided into three periods. In the first period, the calcium and / or magnesium particles 6 are added to the liquid to be filtered and are delivered to the membrane 1. In the second period, the calcium and / or magnesium particles 6 are continuously added to the liquid to be filtered and the fluid protective layer 7 begins to form on the membrane 1 with the calcium and / or magnesium particles 6 that reach the membrane 1. During this second period, the fluid protective layer 7 continues to grow with the newly added calcium and / or magnesium particles 6. During the third period, the addition of calcium and / or magnesium particles 6 is stopped and the formation of the fluid protective layer 7 is completed while the calcium and / or magnesium particles 6 remaining in the liquid to be filtered are sent to the membrane 1 and deposited on the fluid protective layer 7. It is clear that this third period can be omitted if calcium and / or magnesium particles 6 are added continuously throughout the entire operating mode. It is also understood that calcium and / or magnesium particles 6 can deposit not only on the membrane 1 but also on the walls of the first guide 2. However, how this can optimally be avoided or reduced is described below.

[0097] The liquid to be filtered and / or the liquid in the first guide section 2 to which the calcium and / or magnesium particles 6 are added is preferably the same liquid to be filtered containing fouling substances and / or contaminants filtered in the step shown in FIG. 4 . This has the advantage that clean liquid does not need to be discarded for the deposition / formation of the flowable protective layer 7. However, in certain cases, such as very harmful contaminants and / or fouling substances that should never come into contact with the membrane 1, it is also possible to use a liquid to be filtered that is different from the liquid to be filtered in the step of adding the calcium and / or magnesium particles 6 and / or during the step of forming the flowable protective layer 7 on the membrane 1, as shown in FIG. 4 . This has the advantage that a very clean flowable protective layer 7 can be formed without any fouling substances and / or contaminants in between. However, this increases the complexity of the membrane fouling control system, increases the waste of clean liquid, and therefore, in many cases, reduces the amount of clean liquid produced by the process.

[0098] FIG. 4 illustrates the steps of filtering a liquid to be filtered through the membrane 1 to obtain filtrate and / or guiding the liquid to be filtered from the first guiding section 2 through the membrane 2 to the second guiding section 3. Before passing through the membrane 1, the liquid to be filtered must first pass through the fluid protective layer 7. Fouling substances 10 in the liquid to be filtered are retained by the fluid protective layer 7 before reaching the membrane 1, thereby preventing membrane fouling of the membrane 1. While it may be apparent that a certain percentage of fouling substances 10 may pass through the fluid protective layer 7, in any case, the amount of fouling substances reaching the membrane 1 is significantly reduced, thereby reducing or preventing membrane fouling. The fluid protective layer 7 can also retain liquid contaminants. Therefore, the fluid protective layer 7 can be considered a filtration aid that assists the membrane 1 in filtering the liquid to be filtered. The longer the operating mode, the greater the amount of fouling substances 10 and / or contaminants retained in the fluid protective layer 7. Therefore, the filter cake formed by the flowable protective layer 17, fouling material 10 and / or contaminants grows over time, which reduces the flow rate of the filtrate through the membrane 1 and / or increases the amount of energy required to maintain the same flow rate.

[0099] FIG. 5 shows a cleaning step in which the fluid protective layer 7, along with the retained fouling materials 10 and / or contaminants, is cleaned. In the cleaning step, the filter cake formed by the fluid protective layer 17, the fouling materials 10, and / or contaminants is removed / cleaned. Preferably, the cleaning step involves forming a cleaning flow of liquid in the first guide section 2 to carry the filter cake from the first guide section 2 to the cleaning outlet 9. This cleaning flow is preferably achieved by a backwashing or backwashing operation, as shown in FIG. 5, in which the filtrate is guided from the second guide section 3 back to the first guide section 2 through the membrane 1. One selection criterion for the calcium and / or magnesium particles 6 is their easy cleanability from the membrane 1. Preferably, the cleaning operation is performed by physical cleaning, such as backwashing. However, a chemical cleaning step can also be used. Most preferably, the cleaning step of the filtration cycle is a physical cleaning step, and a chemical cleaning step is used at appropriate times to remove any irreversible fouling that has formed despite the fluid protective layer 7. Before the cleaning step / mode is started, it is preferred to end the operating mode and no longer guide the liquid to be filtered from the first conducting part 2 to the second conducting part 3. After the cleaning step / mode is finished, the cleaning outlet 9 is closed. In another less preferred embodiment, instead of sending it to the cleaning outlet 9, it is also possible to guide the filter cake back to the first conducting part 2. In this case, the cleaning outlet 9 is not necessary, but the quality of the liquid to be filtered in the first conducting part 2 would be deteriorated. After the cleaning step / mode, a new filtration cycle can be started.

[0100] Preferably, the system or process includes multiple subsequent filtration cycles as described above.

[0101] In one embodiment, the process may include an optional step of forming calcium and / or magnesium particles in situ before adding them to the liquid to be filtered, which may be achieved by chemical reaction, as explained in more detail above.

[0102] In one embodiment, the calcium and / or magnesium based ultrafine synthetic inorganic precipitated particles have a d of 1 μm or less. 50 , d less than 10 μm 90 , and d of 50nm to 500nm 10 The ultrafine inorganic precipitated particles according to the present invention are particularly suitable for ultrafiltration.

[0103] In one embodiment, the calcium and / or magnesium based ultrafine synthetic inorganic precipitated particles have a d of 5 μm or less. 50 , d less than 15 μm 90 , and d of 200 nm to 3 μm 10 The ultrafine inorganic sedimenting particles according to the present invention are particularly suitable for microfiltration.

[0104] In one embodiment, the particle size distribution of calcium and / or magnesium particles for ultrafiltration is 10 is 50 nm or more, preferably 70 nm or more, preferably 100 nm or more, preferably 200 nm or more.

[0105] In one embodiment, the particle size distribution of calcium and / or magnesium particles for ultrafiltration is 10 is 500 nm or less, preferably 400 nm or less, preferably 350 nm or less, preferably 320 nm or more.

[0106] In one embodiment, the particle size distribution of calcium and / or magnesium particles for microfiltration is 10 is 200 nm or more, preferably 250 nm or more, preferably 300 nm or more, preferably 500 nm or more.

[0107] In one embodiment, the particle size distribution of calcium and / or magnesium particles for microfiltration is 10 is 1000 nm or less, preferably 900 nm or less, preferably 800 nm or less, preferably 750 nm or less.

[0108] The smaller the particles, the more homogeneous the deposition of the calcium and / or magnesium particles 6 forming the flowable protective layer 7. Preferably, the average particle size of the calcium and / or magnesium particles 6 is greater than 0.05 μm, preferably greater than 0.1 μm, preferably greater than 0.15 μm. However, the average particle size in practice is determined by the d 10 and d 90 This has been found to be less important than the size distribution boundaries, such as 0.05 mm, ... 10 and d 90 1 shows an exemplary size distribution of

[0109] The calcium and / or magnesium particles 6 are larger than the specified pore size of membrane 1, preferably 2 times the specified pore size of membrane 1, preferably 3 times the specified pore size of membrane 1, preferably 5 times the specified pore size of membrane 1, preferably 7 times the specified pore size of membrane 1, preferably 9 times the specified pore size of membrane 1, preferably 10 times the specified pore size of membrane 1. 10 For illustrative purposes, Figures 7 and 8 show a schematic membrane 1 with a single, defined pore size and a single fouling control particle 6 size, i.e., a Dirac distribution of pore sizes and a Dirac distribution of fouling control particle sizes, respectively. Figure 7 shows what happens when the fouling control particle 6 size is smaller than the defined pore size. Calcium and / or magnesium particles 6 penetrate the pores 5 of the membrane 1 and accumulate therein. This narrows the pores 5 of the membrane 1, negatively impacting the flow of the liquid to be filtered through the membrane 1. This is also referred to as standard clogging in membrane technology. Figure 8 shows a schematic flowable protective layer 7 on the membrane 1 in which the calcium and / or magnesium particles 6 do not cause standard clogging in the pores 5 and therefore do not clog the pores 5.

[0110] The calcium and / or magnesium particles 6 have a d of less than 10 μm, preferably less than 5 μm, preferably less than 1 μm, preferably less than 0.5 μm 90 It is preferred that the particle diameter has a size distribution having the following formula:

[0111] More preferably, in one embodiment, the d of the size distribution of calcium and / or magnesium particles depending on the microfiltration membrane 90 is 15 μm or less, preferably 10 μm or less, preferably 5 μm or less, preferably 1 μm or less, preferably 0.7 μm or less, preferably 0.5 μm or less.

[0112] In one embodiment, the d of the size distribution of calcium and / or magnesium particles depending on the ultrafiltration membrane 90 is 10 μm or less, preferably 5 μm or less, preferably 1 μm or less, preferably 0.7 μm or less, preferably 0.5 μm or less.

[0113] This helps ensure that the calcium and / or magnesium particles 6 form a uniform, flowable protective layer 7 on the membrane surface. 90 If d becomes too large, the deposition of calcium and / or magnesium particles 6 will be too uneven. This may disrupt the function of the fluidic protective layer 7 and reduce the effective membrane surface. For example, a hollow fiber membrane 1 or tubular membrane 1 provides a membrane surface 1.1 in a long hollow fiber or tube with pores 5 in the fiber or tube wall. If the calcium and / or magnesium particles 6 have a d larger than that mentioned above, 90, the larger particles will be concentrated mainly at the end of the tube or fiber, resulting in a non-uniform deposition of calcium and / or magnesium particles 6. This will result in an insufficient flow protection layer 7 at the beginning of the tube or fiber for effective fouling control, and an excessively thick flow protection layer 7 at the end of the tube or fiber, blocking flow through the tube or fiber and / or through the flow protection layer 7 to the pores 5. A small average particle size of calcium and / or magnesium particles 6 alone will not ensure uniform deposition. If calcium and / or magnesium particles have a wide size distribution or a large d 90 , these tend to result in non-uniform deposition of calcium and / or magnesium particles 6. The flowable protective layer 7 formed by the non-uniformly deposited calcium and / or magnesium particles 6 will block the pores 5 of the membrane 1, reducing the efficiency of fouling control. Therefore, a d smaller than the above value is preferred. 90 The calcium and / or magnesium particles 6 having the above properties significantly improve the quality and performance of the flowable protective layer 7 for membrane fouling control of the membrane 1.

[0114] The calcium and / or magnesium particles 6 are preferably synthetic precipitated particles, which have the advantage that characteristics such as size, thermal stability, mechanical stability, polydispersity index, zeta potential, BET surface, and / or possibly others, can be well controlled during their manufacture.

[0115] Preferably, the calcium and / or magnesium particles 6 and / or synthetic precipitate particles are / comprise metallic and / or inorganic precipitate particles. Preferably, the calcium and / or magnesium particles 6 and / or synthetic inorganic precipitate particles are calcium and / or magnesium based. This class of inorganic precipitates provides tunable and environmentally compatible particles.

[0116] In one embodiment, the calcium and / or magnesium particles 6 and / or synthetic inorganic precipitated particles are / comprise precipitated calcium carbonate (PCC).

[0117] In one embodiment, the calcium and / or magnesium particles 6 and / or synthetic inorganic precipitated particles are / comprise precipitated hydromagnesium.

[0118] In one embodiment, the calcium and / or magnesium particles 6 and / or synthetic inorganic precipitated particles are / comprise inorganic composite particles containing a mixed solid phase of two minerals, preferably calcium and magnesium, preferably synthetic calcium carbonate and synthetic magnesium carbonate, preferably (synthetic precipitated) calcium carbonate and (synthetic) hydromagnesium carbonate.

[0119] Synthetic calcium / magnesium carbonate is derived from natural calcium / magnesium carbonate, which is calcined to produce calcium / magnesium oxide by removing CO2 during calcination. Natural calcium carbonate is commonly called limestone. Natural magnesium carbonate is commonly called magnesite, but can exist in a variety of hydrate forms. Natural calcium-magnesium carbonate is commonly called dolomite. When calcium / magnesium oxide is produced by calcination, it can be further hydrated to form a hydrate or slaked lime form, which can be further carbonated to form calcium / magnesium carbonate precipitate (with or without pressure). Typically, the molar ratio of calcium to magnesium in natural dolomite is 0.8-1.2. This ratio can be modified to about 0.1-10 by slaking the oxide in the presence of magnesium hydroxide or calcium hydroxide.

[0120] The precipitated calcium / magnesium carbonate may also contain impurities derived from the natural forms, in particular clays of the aluminosilicate type, silica, iron or manganese based impurities, all of which are found in natural limestone and dolomite, in amounts of up to 10% by weight, preferably up to 5% by weight, preferably up to 1% by weight.

[0121] In general, the CaCO3, MgCO3, Ca(OH)2 and Mg(OH)2 contents in calcium-magnesium compounds can be readily determined by conventional methods.

[0122] The composite particles preferably comprise a core of a first inorganic material and / or a shell of a second material. Preferably, the first inorganic material is an inorganic precipitate, preferably a calcium-based mineral, preferably PCC.

[0123] The PCC core preferably comprises primarily calcite with trace amounts of aragonite, which are two crystalline forms of calcium carbonate, CaCO3.

[0124] In other embodiments of the present invention, the PCC core may further contain calcium hydroxide, Ca(OH)2, for example in the form of portlandite. It should be noted that in any PCC core, calcite, aragonite or a mixture of both will always account for more than half by weight.

[0125] PCC can be obtained by controlled carbonation of quicklime as previously mentioned, and there are several reports in the literature of the carbonation of milk of lime in the presence of additives, e.g. for papermaking (see US Patent Application Publication No. 20189170765).

[0126] Preferably, the second inorganic material is a magnesium-based material, preferably comprising hydromagnesium, preferably hydromagnesium with a trace amount of nesquehonite. Hydromagnesium, also known as basic magnesium carbonate, has the formula Mg5(CO3)4(OH) 2·4H2O or 4MgCO3·Mg(OH)2·4H2O. At the International Center for Diffraction Data (ICDD), hydromagnesium corresponds to data sheets with reference 00-025-0513 (monoclinic) or 01-070-1177 (orthorhombic). In one embodiment, monoclinic hydromagnesium is used. In another embodiment, orthorhombic hydromagnesium is used. Hydromagnesium should not be confused with magnesite, a magnesium carbonate with the formula MgCO3, or nesquehonite, a hydrated magnesium carbonate with the formula MgCO3.3H2O, which are to be avoided in this invention.

[0127] In one embodiment of the present invention, the second inorganic material may further contain periclase MgO and / or brucite Mg(OH)2. The proportions of these different components in the second inorganic material of the present invention, in addition to synthetic calcium carbonate and hydromagnesium, may be related to the operating conditions used in the carbonation process and the properties of the hydrated dolomite, which allow obtaining a mixed solid phase in the second inorganic material of the present invention as described below. With fully hydrated dolomite (hydrated under pressure to prevent the residual presence of MgO in the hydrated dolomite), the content of Mg(OH)2 in the mixed solid phase of the second inorganic material of the present invention will be higher than when partially hydrated dolomite is used, the latter likely resulting in the presence of MgO in the mixed solid phase of the second inorganic material of the present invention.

[0128] An example of a method for producing inorganic composition particles containing a mixed solid phase of calcium carbonate and magnesium carbonate is detailed in WO 2013 / 139957 and WO 2015 / 039994, both of which are incorporated herein by reference. According to these prior art documents, the synthetic inorganic precipitates do not exhibit the particle size distribution that makes them suitable for membrane fouling control and provides the aforementioned advantages. However, according to the present invention, the production process does not 50 <5 μm, d 90 <15 μm and d between 200 nm and 3 μm 10The particle size distribution is adjusted by controlling the growth of the mixed solid phase of calcium carbonate so as to exhibit a particle size distribution characterized by: Optionally, a grinding or sieving step can be carried out to remove oversized particles or to concentrate the product to very fine particles.

[0129] Preferably, the calcium and / or magnesium particles containing a mixed solid phase (of calcium carbonate and magnesium carbonate) comprise one of the two minerals or PCC as one of the two minerals.

[0130] Preferably, the calcium and / or magnesium particles containing a mixed solid phase (of calcium carbonate and magnesium carbonate) comprise hydromagnesium as one of the two minerals or as the other of the two minerals.

[0131] Such a mixed solid phase is 4 to 15 m 2 In one advantageous embodiment of the present invention, the mixed solid phase has a specific surface area of ​​about 15 m / g. 2 / g or more, more specifically 20m 2 / g and preferably 25m 2 / g or more, in some cases 35m 2 The "specific surface area" used in the present invention means the specific surface area measured by manometric nitrogen adsorption after degassing at 190°C and calculated using the Brunauer, Emmett and Teller model (BET method).

[0132] The mixed solid phase is 250 kg / m, measured according to standard EN459.2. 3 and below 80 kg / m 3 It is preferable that the bulk density of the cellulose acylate is equal to or greater than 1000 vol.

[0133] In one embodiment, the calcium and / or magnesium particles are inert, such as PCC or precipitated magnesite, or other inert inorganic precipitates. In another embodiment, the calcium and / or magnesium particles are reactive or functionalized. The composite particles described above are preferably functionalized.

[0134] The proposed solution aims to enhance the hydraulic performance and rejection of membrane 1 by applying a flowable protective layer to the surface of membrane 1, preferably at the start of each filtration cycle. The flowable protective layer acts as a filtration aid, helping to control the flow through the membrane. The flowable protective layer is preferably composed of ultrafine precipitated calcium carbonate particles (i.e., nano-PCC). The flowable protective layer forms a porous layer on the membrane surface, providing a filtration medium that captures solids and prevents them from fouling the membrane surface and pores. Flowable protective layer filtration is primarily mechanical, not chemical, in nature, with particles interlocking and overlapping to provide a large network of interstitial spaces that can allow water flow.

[0135] The proposed membrane pretreatment invention was tested against a water pretreatment based on a coagulation solution (i.e., using FeCl3 to pretreat the liquid to be filtered). For all experiments, canal water collected in Arquennes was used as the liquid to be filtered. A laboratory-scale membrane module based on ultrafiltration membrane 1 was used for the tests. The molecular weight cut-off (MWCO) of the membrane 1 used was 150 kDa, i.e., a defined pore size of 0.02 μm. The surface area of ​​the filtration was approximately 0.08 m 2 Filtration was carried out in dead-end mode with 10 consecutive cycles of filtration and backwashing. The filtration flux was 190 dm for 15 min / cycle. 3 / (m 2 .h)(dm 3 / m² / hour). After each filtration cycle, a backwash step was performed at a rate of 250 dm 3 / (m 2The process was carried out at a flux of 0.5 sq. m / s (0.05 sq. ft.) for 1 minute. Figure 9 shows the results for the coagulation solution, while Figure 10 shows the results for the solution proposed by the present invention. The transmembrane pressure (TMP) was recorded throughout the successive cycles as an operational indicator of membrane performance and is plotted in Figures 9 and 10. The second Y-axis on the right shows TMP in bar (lower curve). After 10 successive cycles of filtration and backwashing, a chemically enhanced backwashing step was carried out using caustic soda, oxidizing agent and acid, followed by a rinse with demineralized water. Each chemical was applied to the membrane system at 250 dm 3 / (m 2 The first Y-axis on the left is dm 3 / h (or litres / hour - l / h upper curve).

[0136] The solution obtained by coagulation contains 1 mg Fe at an equal concentration. 3+ / dm 3 This was achieved by treating the liquid to be filtered with a hydraulic backwash. The coagulant was placed in a feed tank and mixed at 350 rpm for 1 minute to rapidly disperse the coagulant and destabilize colloidal / particulate matter in the liquid to be filtered. A slow mixing intensity of 50 rpm was then applied for the remainder of the test period. The results are shown in Figure 10. The TMP started at 0.35 bar at the beginning of the experiment and rose to a value of 0.85 bar after 10 consecutive cycles of filtration and backwashing. The hydraulic backwashing was not sufficient to restore the TMP at the end of each cycle.

[0137] Experiments based on the solution according to the present invention were carried out using calcium and / or magnesium particles 6 with a diameter distribution of 0.08 μm. 10 , and d of the size distribution of 0.15 μm calcium and / or magnesium particles 6 90This experiment was performed using ultrafine PCC. The PCC stock solution was diluted to a solids concentration of 0.5% and continuously stirred at 50 rpm to prevent settling. Calcium and / or magnesium particles 6 were introduced into the liquid to be filtered via the feed line at the beginning of each filtration cycle. Canal water was then filtered through the membrane for 15 minutes, and the cycle was terminated by backwashing to remove the PCC fluid protective layer 7 and fouling material 10. Chemically enhanced backwashing was performed after 10 filtration cycles. The results are shown in Figure 10. The TMP remained nearly constant at 0.45 bar throughout the experiment. There was minimal pressure increase during the filtration cycle, and permeability was almost fully restored at the end of the cycle. This allows for extremely long filtration cycles and significantly increases the number of filtration cycles with physical cleaning before chemical cleaning is required. This reduces the power required to establish TMP, extends the operation time of the membrane 1, and reduces the amount of chemicals required for cleaning.

[0138] Other experiments were carried out with the following experimental protocol: Surface water membrane filtration experiments were carried out on an automated pilot where the feed, permeate, concentrate and backwash valves and pumps were automatically switched. Continuous readings of flow rate and pressure were taken. 2 An ultrafiltration membrane module with a total area of ​​1000 μm, with a defined pore size of 30 nm, was used in these experiments. The surface water quality used was pH 8, conductivity 670 μS / cm, DOC 9 mg / L, TOC 12 mg / L, Ca 97 mg / L. 2+ , 10 mg / L Mg 2+ The PCC samples were characterized by a pH of 1.0, a pH of 1.0, and an alkalinity of 5 mmol / L. A total of seven cycles (315 min) were performed per PCC product. From the pressure readings, the transmembrane pressure (TMP) and the water permeability K (for these experiments, flux = 82.5 L / m 2 The change in permeability (dK / dt) during the test was measured over six cycles (270 minutes) using the permeability at the start of cycles 1 and 7. Each filtration cycle included approximately 45 minutes of operation followed by a cleaning mode. The critical permeability value (K 臨界) (below which chemical backwashing is required for continued operation) to 150 L / m 2 h, and the chemical strengthening backwash frequency (CEB F The higher this value, the better the filtration performance.

[0139]

number

[0140] These parameters were used in the following four measurements.

[0141] In the first measurement, a PCC suspension with a solids content of 0.6 wt. % was prepared, stirred, and injected onto the membrane surface at a rate of 25 mg solids per liter of filtrate water at the beginning of the operating mode of the filtration cycle, resulting in a 0.58 μm thick PCC flowable protective layer 7 (first half of the operating mode). This was followed by a 45-minute surface water filtration cycle (second half of the operating mode), at the end of which the membrane was backwashed with permeate water (cleaning mode). At this point, the PCC layer (sacrificial layer) was washed away along with any contaminants. The PCC particles used had a d10 of 0.05 μm, a d50 of 0.07 μm, and a d90 of 0.12 μm.

[0142] In the second measurement, the same PCC suspension was initially mixed into the feedwater, corresponding to the same amount of membrane fouling control additive added at a lower concentration and more continuously throughout the entire operating mode, as is done in the prior art for purposes of coagulation or feedwater conditioning (not shown).

[0143] In a third measurement, the same experiment was performed without the addition of fouling control particles.

[0144] In the fourth measurement, a prior art PCC was injected into membrane 1 as in the first measurement (not shown).

[0145] Figure 12 shows the TMP16 over time for the first measurement and the TMP15 over time for the third measurement. It can be clearly seen that without the PCC flowable protective layer 7, the TMP15 for the third measurement increases more with each cycle than the TMP16 for the first measurement with the flowable protective layer 7. CEB F For the frequency measurement 16, it was calculated as 29 hours, while for the third measurement 15 it was 8-9 hours. Also, the CEB for the second measurement F The CEB of the conventional PCC was only 11 hours. This means that continuous injection of fouling control particles was less effective than concentrated injection at the beginning of the operation mode. F , and therefore much worse than the PCC within the value range of the particle distribution according to the present invention.

[0146] It should be understood that the invention is not limited to the described embodiments and modifications are possible without departing from the scope of the claims.

Claims

1. A calcium and / or magnesium additive for membrane fouling control, comprising particles (6) that, when added to a liquid flowing through a membrane (1), form a fluid protective layer (7) on the membrane (1) for fouling control of the membrane (1), characterized in that the particles (6) comprise calcium and / or magnesium-based synthetic inorganic precipitate particles selected from ultrafine synthetic inorganic precipitate particles and extra-fine synthetic inorganic precipitate particles, wherein the ultrafine synthetic inorganic precipitate particles have a diameter of 1 μm or less. ５０ , d less than 10 μm ９０ , and d between 50 nm and 500 nm １０ and wherein the ultrafine synthetic inorganic precipitated particles are based on calcium and / or magnesium having a particle size distribution of d ５０ , d less than 15 μm ９０ , and d between 200 nm and 3 μm １０ 1. A calcium and / or magnesium additive for membrane fouling control, the calcium and / or magnesium additive being based on calcium and / or magnesium having a particle size distribution of:

2. 10. The additive of claim 1, wherein the calcium and / or magnesium based synthetic inorganic precipitated particles comprise precipitated calcium carbonate.

3. 3. The additive according to claim 1, wherein the calcium and / or magnesium based synthetic inorganic precipitated particles comprise precipitated hydromagnesium.

4. 4. The additive of claim 1, wherein the calcium and / or magnesium based synthetic inorganic precipitated particles comprise composite particles comprising a first mineral based on calcium and a second mineral based on magnesium.

5. The additive of claim 4 , wherein the composite particle comprises a core of the first inorganic material and a shell of the second inorganic material.

6. The additive according to any one of claims 1 to 5, wherein the calcium and / or magnesium based synthetic inorganic precipitate particles are inert.

7. The additive according to any one of claims 1 to 6, wherein the calcium and / or magnesium based synthetic inorganic precipitated particles have a polydispersity value obtained from a number-based distribution of 0.1 or more and 1.5 or less.

8. The additive according to any one of claims 1 to 7, wherein the calcium and / or magnesium based synthetic inorganic precipitated particles have an absolute value of the zeta potential of 50 mV or less.

9. The synthetic inorganic settling particles are measured by nitrogen adsorption manometry and calculated according to the BET method. ２ The additive according to any one of claims 1 to 8, having a specific surface area of ​​1 / g or more.

10. The additive of any one of claims 1 to 9, wherein the additive is in the form of a slurry having a synthetic inorganic precipitated particle content of 1.5% to 15% by weight.

11. The additive according to any one of claims 1 to 9, wherein the additive is in the form of a powder.

12. The ultrafine synthetic inorganic precipitated particles have an average particle size distribution d of 0.8 μm or less and 0.1 μm or more. ５０ The additive according to any one of claims 1 to 11, which is an ultrafiltration fouling control particle having the following structure:

13. The ultrafine synthetic inorganic precipitated particles have an average particle size distribution d of 5 μm or less and 0.6 μm or more. ５０ The additive according to any one of claims 1 to 11, which is a microfiltration fouling control particle having the formula:

14. 1. A process for controlling membrane fouling, comprising: - guiding the liquid to be filtered through the membrane (1); - adding a membrane fouling control additive containing fouling control particles (6) to the liquid to be filtered upstream of the membrane (1), the fouling control particles (6) added to the liquid to be filtered form a fluid protective layer (7) on the membrane (1), whereby if the liquid to be filtered contains fouling substances (10), the fouling substances (10) are retained in the fluid protective layer (7) before the liquid is guided through the membrane (1); Including, A process for controlling membrane fouling, characterized in that the membrane fouling control additive is a calcium and / or magnesium additive according to any one of claims 1 to 13.

15. 15. The process of claim 14, further comprising the step of forming the additive in situ by carbonation of calcium hydroxide and / or magnesium hydroxide prior to the step of adding the additive to the liquid.

16. 1. A system for membrane fouling control comprising: a first guide part (2); - second guide part (3); a membrane (1) arranged between the first guide part (2) and the second guide part (3) for filtering the liquid by guiding the liquid from the first guide part (2) to the second guide part (3); and a fouling control means (4) configured to add a membrane fouling control additive containing fouling control particles (6) to the first guide portion (2) so that the fouling control particles (6) form a flowable protective layer (7) on the membrane (1) to protect the membrane (1) from fouling substances (10); A membrane fouling control system comprising: a membrane fouling control additive; and a membrane fouling control additive according to any one of claims 1 to 13.

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