Membrane bioreactor wastewater treatment using calcium carbonate

Abstract

The invention relates to a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module, characterized by the following steps: a) providing wastewater, b) contacting the wastewater of step a) with the at least one membrane module in the presence of sludge, c) adding calcium carbonate to the wastewater of step a) before and / or during step b); the use of calcium carbonate in such a process; a method for improving membrane permeability by adding calcium carbonate in a membrane bioreactor (MBR) process using at least one membrane module; and a method for improving membrane flow rate by adding calcium carbonate in a membrane bioreactor (MBR) process using at least one membrane module.

Description

Technical Field

[0001] The present invention relates to a method for treating wastewater in the presence of sludge in a membrane bioreactor (MBR) process using at least one membrane module, the use of calcium carbonate in such a method, a method for increasing membrane permeability in a membrane bioreactor (MBR) process using at least one membrane module, and a method for increasing membrane flux in a membrane bioreactor (MBR) process using at least one membrane module. Background Art

[0002] Membrane bioreactor wastewater treatment is a combination of a membrane process (such as microfiltration or ultrafiltration) and a biological wastewater treatment process (such as an activated sludge process), and is widely used in municipal and industrial wastewater treatment.

[0003] The activated sludge process is a type of process that uses aeration and biological flocs composed of bacteria and protozoa to treat sewage or industrial wastewater. In sewage (or industrial wastewater) treatment equipment, the activated sludge process is a biological process that can be used to oxidize carbon-containing biological matter, oxidize nitrogen-containing substances (mainly ammonium and nitrogen in biological matter), and remove nutrients (nitrogen and phosphorus).

[0004] The process utilizes aerobic microorganisms that digest organic matter in sewage and, as they do so, aggregate into masses (through flocculation). The process thus produces a liquid that is relatively free of suspended solids and organic material, as well as flocculated particles that will readily settle out and can be removed.

[0005] In a membrane bioreactor, separation and further purification are achieved by membranes. When used with domestic wastewater, the membrane bioreactor MBR process can produce high-quality effluents that are sufficient to be discharged into coastal, surface or brackish waterways or recycled for urban irrigation. Other advantages of MBR over conventional processes include a small footprint, easy modification, and upgrading of old wastewater treatment equipment.

[0006] Compared to conventional settling separation systems, the MBR process can be operated at higher mixed liquor suspended solids (MLSS) concentrations, thereby reducing the reactor volume to achieve the same loading rate.

[0007] There are two MBR configurations, namely the immersed / submerged membrane bioreactor configuration (iMBR), in which the membrane is immersed in and integrated with the bioreactor; and the external / side-stream membrane bioreactor configuration (sMBR), in which the membrane is a separate unit process requiring an intermediate pumping step.

[0008] In the submerged membrane bioreactor (iMBR) configuration, the filter element is installed in the main bioreactor container or in a separate tank. The assembly is located above the aeration system and performs two functions: supplying oxygen to the biological process and flushing the membrane surface to minimize the accumulation. The membrane can be a flat sheet or a hollow fiber or a combination of the two, and can be combined with an online backwashing system that reduces membrane surface scaling by pumping the membrane permeate back through the membrane. In a system in which the membrane is in a separate tank relative to the bioreactor, each membrane sequence can be separated for a cleaning solution combined with membrane soaking, however, the biomass must be continuously pumped back to the main reactor to limit the increase in MLSS concentration. Additional aeration is also required to provide air flushing to reduce scaling. In the case where the membrane is installed in the main reactor, the membrane assembly must be removed from the container and transferred to an offline cleaning tank. Typically, a concentration of mixed liquor suspended solids close to 10.000 mg / l is used to ensure good mass transfer of oxygen and good permeate flux.

[0009] In the sMBR technology where the filter assembly is outside the aerobic tank, the aeration system is also used to clean and supply oxygen to the bacteria that degrade organic compounds. Biomass is directly pumped through multiple membrane modules in series and pumped back to the bioreactor, or biomass is pumped to a group of components, and a second pump circulates the biomass from the group of components through the components in series. The cleaning and soaking of the membrane can be carried out on site by using the cleaning tank, pump and piping system installed. The quality of the final product makes it reusable in process applications, which is due to the filtering capacity of microfiltration and ultrafiltration membranes.

[0010] MBR filtration performance inevitably decreases with filtration time. This is due to the deposition of soluble and particulate material onto and into the membranes, which is attributed to the interaction between the activated sludge components and the membranes. This major defect and process limitation has been studied since the early days of MBR and remains one of the most challenging issues facing the further development of MBR.

[0011] Membrane clogging is the most serious problem affecting system performance. When the process is operated under constant transmembrane pressure (TMP) or constant flux conditions, clogging causes a significant increase in hydraulic resistance, which is manifested as a decrease in permeate flux or an increase in TMP. In a system where flux is maintained by increasing TMP, the energy required for filtration is increased. Alternatively, frequent membrane cleaning is therefore required, which significantly increases operating costs due to detergents and production downtime. More frequent membrane replacement is also expected.

[0012] Membrane fouling results from the interaction between the membrane material and the components of the activated sludge liquor, which include bioflocs formed by a wide range of living or dead microorganisms and soluble and colloidal compounds. The suspended biomass has no fixed composition and varies with the feed water composition and MBR operating conditions.

[0013] There are several strategies to reduce clogging and optimize the performance of MBR operations, such as,

[0014] - appropriate pretreatment of the feed water, e.g. reducing the solids loading on the membranes, which reduces membrane fouling but on the other hand also reduces the valuable biology needed to decompose ammonium and other components;

[0015] - Chemical or biochemical modification of the mixed liquor (feed) by adding inorganic coagulants such as ferric chloride, aluminum sulfate, polyaluminum chloride, which improves the settling of solids in the reactor, but on the other hand increases deposition and clogging on the membrane surface, further acidifies the mixed liquor, slows down the biology, and causes additional product consumption;

[0016] - Increased flushing of the membrane surface by cross-flow aeration, which reduces clogging, but on the other hand is energy intensive, has limited impact, and reduces the contact between the mixed liquor and the membrane surface.

[0017] Therefore, there is still a need to optimize the operation of membrane bioreactors in wastewater treatment. Summary of the invention

[0018] It has been found that the use of calcium carbonate surprisingly has a number of positive effects in this respect, in particular with regard to preventing fouling at the membranes.

[0019] Generally, the presence of calcium carbonate in activated sludge processes is known. However, calcium carbonate has not yet been applied in membrane bioreactor systems because it is known that the presence of carbonates may lead to significant and severe scaling problems in membrane bioreactors, i.e., an increase in clogging problems rather than a decrease is more to be expected.

[0020] It is therefore a surprising finding that calcium carbonate can also be used in membrane bioreactor processes and not only reduce fouling but even improve membrane performance.

[0021] When the activated sludge process is combined with a membrane bioreactor for filtering the treated water, the use of calcium carbonate has the particular advantage of improving membrane performance, especially in terms of:

[0022] - Increased flux rates through the membrane, i.e. increased throughput,

[0023] - the total membrane area is reduced,

[0024] - increased permeability, i.e. reduced pumping power,

[0025] - Reduced specific aeration requirements to control clogging,

[0026] - Extended intervals between membrane cleaning cycles,

[0027] - Less chemical cleaning, i.e. increased membrane life.

[0028] Without wishing to be bound by theory, it is believed that this is due to the following effects:

[0029] 1. Dissolved calcium ions "bridge" biomass to produce larger bioflocs that are less likely to clog the membrane surface. It is believed that calcium cations improve floc formation and thereby reduce organic bioclogging, which is known to be the main cause of reduced membrane permeability (see Figure 1 );

[0030] 2. Undissolved calcium carbonate helps provide a "channel" for water to pass through the activated sludge, thereby increasing the permeability of the activated sludge membrane.

[0031] Furthermore, acidification of the wastewater from the nitrification / denitrification process (decomposition of ammonium into nitrogen compounds) and dosing of coagulants lowers the pH. The addition of calcium carbonate stabilizes the pH of the wastewater and provides a natural buffer by dissolving the calcium carbonate into calcium and bicarbonate species.

[0032] The most common chemicals used for pH / alkalinity adjustment in MBRs are sodium hydroxide (NaOH), magnesium hydroxide (Mg(OH) 2 ) and lime (Ca(OH) 2 The most common way to provide calcium ions to wastewater treatment is by adding calcium chloride (CaCl 2 ) or slaked lime (Ca(OH) 2 ). However, for all of the above substances, if the solubility equilibrium of calcium carbonate is exceeded, there is a risk of calcite precipitation. For MBR equipment, calcite scaling is a serious concern because it can greatly reduce the permeability of the membrane.

[0033] Calcite scaling is caused by the precipitation of dissolved calcium cations and carbonate anions rather than by the deposition of solid calcium carbonate particles themselves. Calcite precipitation occurs when the solution is supersaturated with respect to dissolved carbonate anions and calcium cations.

[0034] The solubility equilibrium of calcium carbonate depends mainly on the concentration of carbonate anions and calcium cations. The solubility product K of calcium carbonate sp =[Ca 2+ ]*[CO 3 2- ] is low (about 5*10-9 ). The solubility equilibrium of a dissolved substance can be expressed by the following relationship: Since carbonic acid is a polyacid, the carbonate anion (CO 3 2- ) depends on the concentration of dissolved carbonate (CO 3 2- , HCO 3 - and CO 2,aq ) and pH. At low pH, CO 2,aq is the dominant species, while at high pH, ​​CO 3 2- is the dominant substance. Furthermore, CaCO 3 The solubility of hydroxybenzoic acid decreases greatly with increasing pH.

[0035] Therefore, calcite precipitation can also be carried out by NaOH or Mg(OH) 2 Dosing results from an increase in pH and the movement of bicarbonate to carbonate species. The outstanding advantage of using calcium carbonate for pH / alkalinity adjustment is that product dosage cannot exceed solubility equilibrium. In the case of product dosage exceeding solubility, CaCO 3 will simply not dissolve further. It is important to point out that the formation of calcite scale is caused by the precipitation of dissolved material and not by the deposition of calcium carbonate particles.

[0036] The Langelier Saturation Index (LSI) is a measure of whether water is supersaturated or undersaturated with respect to calcium and carbonate ions. Water containing more calcium and carbonate ions than the solubility limit allows for a positive LSI and is supersaturated with respect to calcium carbonate, while water with less calcium and carbonate ions than the solubility limit is undersaturated and has a negative LSI.

[0037] As used herein, the "Langelier Saturation Index" (LSI) describes the tendency of an aqueous liquid to form scale or corrosive properties, where a positive LSI indicates a tendency to form scale, while a negative LSI indicates corrosive properties. Thus, a balanced Langelier Saturation Index (i.e., LSI = 0) means that the aqueous liquid is in chemical equilibrium. The LSI is calculated as follows:

[0038] LSI=pH-pH S

[0039] Where pH is the actual pH of the aqueous system and pHs is the pH of the aqueous system in the presence of CaCO 3 The pH value at saturation. pHs can be estimated as follows:

[0040] pH S =(9.3+A+B)-(C+D)

[0041] Where A is a numerical indicator of the total dissolved solids (TDS) present in the aqueous liquid, B is a numerical indicator of the temperature of the aqueous liquid, and C is a numerical indicator of the CaCO 3 The numerical index of calcium concentration is calculated, and D is the calcium concentration of the aqueous liquid in terms of CaCO 3 The numerical indicator of the alkalinity of the meter. Parameters A to D are determined using the following equations:

[0042] A=(log 10 (TDS)-1) / 10

[0043] B=-13.12×log 10 (T+273)+34.55

[0044] C = log 10 [Ca 2+ ]-0.4

[0045] D = log 10 (TAC)

[0046] Where TDS is the total dissolved solids expressed in mg / l, T is the temperature expressed in °C, [Ca 2+ ] is based on CaCO 3 The calcium concentration of an aqueous liquid expressed in mg / l. TAC is calculated as CaCO 3 The total alkalinity of an aqueous liquid expressed in mg / l.

[0047] Figure 2a and 2b The LSI is depicted as a function of pH and dissolved carbonate and calcium ions. In scenarios 1, 3 and 4, a positive Langelier Saturation Index (LSI) can be achieved using alkali metal hydroxides, calcium chloride or calcium hydroxide, leading to supersaturation and precipitation reactions. In scenario 2, by increasing the pH using calcium carbonate, supersaturation of calcium carbonate is not possible, and therefore precipitation reactions and scale formation can be excluded.

[0048] Therefore, the use of CaCO in the MBR process 3 The outstanding advantage of pH / alkalinity adjustment is that the product dosage cannot exceed CaCO 3 When the product dosage is higher than the solubility limit, CaCO 3 will simply not dissolve further, and the maximum achievable LSI is 0. Therefore, CaCO 3 Dosages of < 0.05% will not result in calcite scaling on the membrane surface. In contrast, the dosage of NaOH or another alkali metal hydroxide may result in supersaturated conditions (indicated by LSI>0). This will result in calcite precipitation and thus calcite scaling formation on the membrane surface.

[0049] It is therefore an object of the present invention to provide a method for treating wastewater in a membrane bioreactor process which provides improved operation of the membrane bioreactor by, for example, increasing flux rate through the membrane, increasing membrane permeability, reducing clogging, etc.

[0050] The aforementioned and other objects are solved by the subject matter defined in the independent claims. Advantageous embodiments of the invention are defined in the respective dependent claims.

[0051] It should be understood that for the purposes of the present invention, the following terms have the following meanings:

[0052] Where an indefinite or definite article is used when referring to a singular noun such as "a", "an" or "the", this includes a plural of that noun unless otherwise specifically stated elsewhere.

[0053] When the term "comprising" is used in the present description and claims, it does not exclude other elements. For the purpose of the present invention, the term "consisting of" is considered to be a preferred embodiment of the term "comprising". If a group is defined below to include at least a certain number of embodiments, this is also understood to disclose a group that preferably consists of these embodiments only.

[0054] Wherever the terms "including" or "having" are used, these terms are considered equivalent to "comprising" as defined above.

[0055] Terms such as "obtainable" or "definable" and "obtained" or "defined" are used interchangeably. This means, for example, that unless the context clearly indicates otherwise, the term "obtained" is not meant to indicate, for example, that an embodiment must be obtained by, for example, the sequence of steps following the term "obtained", although the term "obtained" or "defined" always includes such a restrictive understanding as a preferred embodiment.

[0056] Thus, in a first aspect, the present invention relates to a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module, characterized by the following steps:

[0057] a) Provide wastewater,

[0058] b) contacting the wastewater of step a) with the at least one membrane module in the presence of sludge,

[0059] c) adding calcium carbonate to the wastewater of step a) before and / or during step b).

[0060] Wastewater is generally defined as used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff / stormwater and any sewer inflow or sewer infiltration.

[0061] The method of the present invention is particularly useful for the treatment of sewage, ie domestic wastewater or municipal wastewater, which is wastewater generated by a community of people.

[0062] However, it can also be used to treat industrial wastewater, aqueous waste generated by various industrial processes, cooling water, leachate, return flow, surface runoff, urban runoff, agricultural wastewater, etc.

[0063] Therefore, the wastewater to be treated may be selected from municipal wastewater, industrial wastewater and mixtures thereof.

[0064] In general, wastewater that can be treated in the process of the present invention is defined as water containing dissolved or suspended matter summarized by the following parameters:

[0065] Chemical oxygen demand 200-10000mg / l Total organic carbon 150-7000mg / l Ammonium 5-500mg / l Total Nitrogen 10-1000mg / l Total suspended solids 50-10000mg / l

[0066] Sludge in the meaning of the present invention refers to any type of sludge contained in wastewater. In this respect, sludge includes any type of sludge initially contained in wastewater before wastewater treatment, sludge added during wastewater treatment, sludge recycled during wastewater treatment, so-called return activated sludge, sludge settled or chemically or biologically modified during wastewater treatment, or mixtures thereof.

[0067] The sludge present in the wastewater according to the present invention may comprise raw sludge, ie untreated non-stabilized sludge.

[0068] In addition, the sludge according to the present invention may include primary sludge, i.e., sludge produced by a mechanical wastewater treatment process. It occurs after the screen and grit chamber and consists of undissolved wastewater pollutants. The sludge accumulated at the bottom of the primary settling tank is also called primary sludge. Primary sludge may consist of a high proportion of organic matter such as feces, vegetables, fruits, textiles, paper, etc.

[0069] In addition, the sludge according to the present invention may include activated sludge. The removal of dissolved organic matter and nutrients from wastewater occurs in a biological treatment step. It is carried out by the interaction of different types of bacteria and microorganisms, which require oxygen to survive, grow and reproduce in order to consume organic matter, as further described below. The resulting sludge from this process is called activated sludge. Activated sludge is usually in the form of flocs, which contain adsorbed, stored and organic and mineral parts in addition to living and dead biomass.

[0070] The settling behavior of the activated sludge flocs is very important for the functioning of the biological treatment. The flocs must be very removable so that the biomass can be separated from the clean wastewater without problems and the required volume of activated sludge can be pumped back into the aeration section.

[0071] Typically, in the first step of wastewater treatment, the wastewater usually undergoes a primary treatment step, which consists in removing a portion of the suspended solids and organic matter from the sewage. It consists in passing the sewage slowly through a basin where the heavy solids can settle to the bottom, while oil, grease and lighter solids float to the surface and are skimmed off. The settled and floating materials are removed and the remaining liquid can be discharged or undergo secondary treatment.

[0072] Secondary treatment is the removal of biodegradable organic matter (dissolved or suspended) from sewage or similar kinds of wastewater. Its purpose is to achieve a certain level of effluent quality in the sewage treatment plant that is suitable for the intended disposal or reuse options. During secondary treatment, biological processes are used to remove dissolved and suspended organic matter measured as biochemical oxygen demand (BOD). These processes are carried out by microorganisms in managed aerobic or anaerobic processes depending on the treatment technology. Bacteria and protozoa consume biodegradable soluble organic pollutants (such as sugars, fats and organic short-chain carbon molecules from human waste, food waste, soaps and detergents) while multiplying the cells that form biosolids.

[0073] Secondary treatment is widely used in sewage treatment and is also applicable to many agricultural and industrial wastewaters.

[0074] The membrane bioreactor process is used in the secondary treatment step and generally involves the introduction of air or oxygen into a mixture of screened, primary treated sewage or industrial wastewater combined with organisms in an aeration tank to produce bioflocs, i.e. activated sludge, which reduces the organic content of the sewage. This material is generally known in the field of wastewater treatment and consists, for example, mainly of saprophytic bacteria, but also has an important protozoan flora component, which consists mainly of amoebae, spirotrichs, peritrichs including vorticellids, and a range of other filter-feeding species. Other important ingredients include mobile and sedentary rotifers. Typically, activated sludge contains bacteria and protozoa that are suitable for the specific wastewater and are able to metabolize the pollutants present in such wastewater.

[0075] The combination of wastewater and biomass is often referred to as mixed liquor as defined in more detail below. The mixed liquor suspended solids in the process of the present invention is preferably 2-20 g / l, more preferably 4-18 g / l, even more preferably 6-15 g / l, most preferably 7-14 g / l.

[0076] The membrane bioreactor process according to the present invention can be operated as an immersed / submerged membrane bioreactor process (i.e. the membrane is immersed in the bioreactor and is integrated with the bioreactor), and / or as an external / side stream membrane bioreactor process (i.e. the membrane is a separate unit as explained above). Thus, the at least one membrane module of step b) can be immersed in the bioreactor (iMBR configuration) or installed in a side stream outside the bioreactor (sMBR configuration).

[0077] For this purpose, any conventional submerged membrane bioreactor configuration or any conventional external / side stream configuration may be used. Schematic configurations of submerged MBR and external / side stream MBR are shown in Figure 3a and shown in b.

[0078] The at least one membrane module can be a flat sheet, a hollow fiber, a tubular or a combination of one or more thereof. It can be any membrane module commonly used in membrane bioreactor processes, and can preferably be made of ceramic, polymer or other synthetic materials.

[0079] The at least one membrane component preferably has a pore size of not more than 5 μm, preferably not more than 2 μm, more preferably not more than 1.5 μm, especially preferably not more than 1.2 μm, most preferably 0.005-1 μm.

[0080] According to the present invention, a plurality of membrane modules having the same or different pore sizes can be combined.

[0081] It is also possible to combine submerged and external / lateral flow membrane configurations.

[0082] In all activated sludge and membrane bioreactor equipment, once the wastewater has been treated sufficiently, the excess mixed liquor is separated from the clean water by a settling tank in a conventional activated sludge treatment or by a membrane in an MBR process. A portion of the settled or filtered material (sludge) is returned to (or left in) the head of the aeration system to contact with the new wastewater entering the tank. This portion of the sludge is called return activated sludge (RAS). The amount of return activated sludge can be different. It can be 0 to a maximum of 100 weight%, preferably 5-95 weight%, more preferably 20-80 weight%, even more preferably 40-60 weight%, for example 50 weight%, based on the total amount of sludge. Typically, 95 weight% of the sludge is returned.

[0083] Activated sludge is also the name given to the active biological material produced by activated sludge and membrane bioreactor equipment. Excess sludge is called waste activated sludge and is removed from the treatment process to maintain a balanced ratio of biomass to food supplied in the wastewater.

[0084] According to the present invention, calcium carbonate is added before and / or during the contact of the wastewater with the at least one membrane module. Calcium carbonate can generally be added at any point in the secondary treatment process of the wastewater treatment, such as in the feed of the secondary treatment, in the secondary treatment, into the aeration tank, in the return activated sludge stream, etc. In a preferred embodiment, calcium carbonate is added to the return activated sludge stream.

[0085] In another preferred embodiment, a portion of the added calcium carbonate is dissolved, while another portion remains undissolved. In applications focused on pH / alkalinity regulation, more than 50% of the calcium carbonate is dissolved. Typically, even 70-100% by weight of the calcium carbonate is dissolved. The solubility can vary significantly because it depends on the pH of the wastewater, the concentration of dissolved calcium and carbonate, and further dissolved anions and cations. In applications focused on adding calcium carbonate primarily as a filtering aid, a significant portion of the calcium carbonate is not dissolved. This is achieved by adding calcium carbonate in an amount exceeding the amount required to achieve a neutral Langelier saturation index (LSI) to the wastewater, or by metering calcium carbonate whose particle size makes the dissolution slow enough to ensure a sufficiently high ratio of undissolved calcium carbonate to dissolved calcium carbonate.

[0086] The amount of calcium carbonate added is such that the pH and / or total alkalinity in the process is controlled. The pH control by adding calcium carbonate is controlled by the following reaction equation:

[0087] 2H + +CaCO 3 =Ca 2+ +H 2 O+CO2

[0088] Therefore, 1 mole or 100 g of CaCO is required 3 To neutralize 2 mol of H + .

[0089] In CaCO 3 In the case of partial dissolution, a higher dose of CaCO may be required in practice according to the following relationship: 3 :

[0090]

[0091] in

[0092] mCaCO3,adjusted is the actual required dose,

[0093] mCaCO3, theoretical is the required dose suggested by stoichiometry, and

[0094] f is the correction factor, defined as follows,

[0095]

[0096] in

[0097] m CaCO3,dissolved is dissolved CaCO 3 amount, and

[0098] m CaCO3,added It is CaCO added to the system 3 The amount.

[0099] With pH controlled by NaOH, the following reaction equation represents the neutralization:

[0100] 2H + +2NaOH=2Na + +2H 2 O

[0101] Therefore, 2 moles or 80 g of NaOH are required to neutralize 2 moles of H + .

[0102] Particularly, calcium carbonate is added in an amount such that the pH value in the mixed liquor comprising sludge and calcium carbonate is 5.5-9, preferably 6-8.5, more preferably 6.2-8, even more preferably 6.5-7.8, most preferably 7-7.3.

[0103] In a further preferred embodiment, calcium carbonate is added in an amount such that the total alkalinity in the effluent is in the form of CaCO 3 30-300 mg / l, more preferably CaCO3 50-275 mg / l, even more preferably in the form of CaCO 3 80-250 mg / l, most preferably CaCO 3 Calculated as 100-200 mg / l.

[0104] The water hardness of the effluent is preferably 0.18 mmol / l to 3.57 mmol / l, more preferably 0.3-3.2 mmol / l, even more preferably 0.4-3.0 mmol / l, most preferably 0.5-2.7 mmol / l.

[0105] Furthermore, preferably, the mixed liquor containing sludge and calcium carbonate has a Langelier Saturation Index (LSI) of -1.5 to +1, preferably -1 to +0.5, more preferably -0.5 to 0.

[0106] According to a preferred embodiment, the maximum Langelier Saturation Index (LSI) of the mixed liquor comprising sludge and calcium carbonate is 0. According to another preferred embodiment, the Langelier Saturation Index (LSI) of the mixed liquor comprising sludge and calcium carbonate is from -1.5 to 0, preferably from -1 to 0, more preferably from -0.5 to 0.

[0107] According to one embodiment, the present invention relates to a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module, characterized by the following steps:

[0108] a) Provide wastewater,

[0109] b) contacting the wastewater of step a) with the at least one membrane module in the presence of sludge,

[0110] c) adding calcium carbonate to the wastewater of step a) before and / or during step b),

[0111] The Langelier Saturation Index (LSI) of the mixed liquor containing the sludge and the calcium carbonate is a maximum of 0, preferably -1.5 to 0, more preferably -1 to 0, and further preferably -0.5 to 0.

[0112] The Langelier Saturation Index (LSI) is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate calcium carbonate, dissolve calcium carbonate, or be in equilibrium with calcium carbonate. The LSI is expressed as the difference between the actual system pH and the saturation pH:

[0113] LSI = pH (measured) - pH s

[0114] For LSI > 0, water is supersaturated and tends to precipitate CaCO 3 scaling layer.

[0115] For LSI = 0, water is replaced by CaCO 3 Saturated (at equilibrium). CaCO 3 The scaling layer neither precipitates nor dissolves.

[0116] For LSI < 0, the water is undersaturated and tends to dissolve solid CaCO 3 .

[0117] If the actual pH of the water is below the calculated saturation pH, the LSI is negative and the water has very limited scaling potential. If the actual pH exceeds pHs, the LSI is positive and the water is CaCO 3 Supersaturated, water has a tendency to form scale. At increasing positive exponential values, the scaling potential increases.

[0118] The calcium carbonate used in the present invention is preferably selected from natural ground calcium carbonate (GCC), mixed natural ground carbonate minerals containing calcium carbonate, precipitated calcium carbonate (PCC) and mixtures thereof.

[0119] The term natural ground calcium carbonate as used herein refers to a particulate material obtained from a natural calcium carbonate-containing mineral which has been processed in a wet and / or dry comminution step (such as crushing and / or grinding) and which has optionally been subjected to further steps such as screening and / or classification (e.g. by means of a cyclone or classifier). Natural ground calcium carbonate (GCC) is preferably selected from marble, chalk, limestone, and mixtures thereof.

[0120] Mixed natural ground carbonate minerals containing calcium carbonate refer to calcium carbonate materials in which a certain portion of the calcium cations are replaced by other cations. A particularly preferred example of such mixed natural ground carbonate minerals is dolomite.

[0121] "Precipitated calcium carbonate" (PCC) in the meaning of the present invention is a synthetic material, which is obtained by the precipitation after reaction of carbon dioxide and calcium hydroxide (slaked lime) in an aqueous environment. Alternatively, precipitated calcium carbonate can also be obtained by reacting calcium salts and carbonates (such as calcium chloride and sodium carbonate) in an aqueous environment. PCC can have aragonite, vaterite or calcite crystal form, wherein any form can be used in the present invention, and their mixture. PCC is described in, for example, the following documents: EP2447213 A1, EP2524898 A1, EP2371766 A1, EP2840065 A1 or WO2013142473A1.

[0122] According to a preferred embodiment of the present invention, the calcium carbonate is in the form of particles having a weight median particle size d 50 The molecular weight (wt) is 0.1-50 μm, preferably 0.2-20 μm, more preferably 0.5-10 μm, and most preferably 1-5 μm.

[0123] According to a further preferred embodiment of the present invention, the calcium carbonate is in the form of particles having a top cut particle size d 98 The molecular weight (wt) is not more than 100 μm, preferably not more than 75 μm, even more preferably not more than 50 μm, most preferably not more than 25 μm, especially 1.2-10 μm, such as 1.6-5 μm.

[0124] Value d x represents the diameter at which x% by weight of the particles have a particle diameter smaller than d x This means that d 98 The value refers to the particle size below which 98% of all particles are smaller than this particle size. 98 Also called "top cut". x Values ​​may be given as volume or weight percent. 50 The (wt) value is thus the weight median particle size, ie the particle size below which 50% by weight of all particles are smaller, and d 50 The (vol) value is the volume median particle size, ie, the particle size below which 50% by volume of all particles are smaller.

[0125] According to one embodiment, the present invention relates to a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module, characterized by the following steps:

[0126] a) Provide wastewater,

[0127] b) contacting the wastewater of step a) with the at least one membrane module in the presence of sludge,

[0128] c) adding calcium carbonate to the wastewater of step a) before and / or during step b),

[0129] The calcium carbonate has a weight median particle size d 50 (wt) is in the form of particles of 0.1-50 μm.

[0130] According to one embodiment, the present invention relates to a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module, characterized by the following steps:

[0131] a) Provide wastewater,

[0132] b) contacting the wastewater of step a) with the at least one membrane module in the presence of sludge,

[0133] c) adding calcium carbonate to the wastewater of step a) before and / or during step b),

[0134] The calcium carbonate has a weight median particle size d50 (wt) is in the form of particles of 0.1-50 μm, and

[0135] The Langelier Saturation Index (LSI) of the mixed liquor containing the sludge and the calcium carbonate is a maximum of 0, preferably -1.5 to 0, more preferably -1 to 0, and further preferably -0.5 to 0.

[0136] In a further preferred embodiment, the calcium carbonate has a BET specific surface area of ​​0.1-100 m 2 / g, preferably 0.2-50m 2 / g, more preferably 0.5-30m 2 / g, even more preferably 0.8-20m 2 / g, most preferably 1-12m 2 / g, for example 5-6m 2 / g.

[0137] Preferably, the calcium carbonate has a purity of at least 70 wt.-%, especially at least 75 wt.-%, more preferably at least 80 wt.-%, even more preferably at least 85 wt.-%, most preferably at least 90 wt.-%, for example 98 wt.-%.

[0138] In the case of mixed natural ground carbonate minerals containing calcium carbonate, the purity refers to the mixed carbonate. For example, if dolomite is used, then dolomite (CaMg(CO 3 ) 2 )) has a purity of at least 70% by weight, in particular at least 75% by weight, more preferably at least 80% by weight, even more preferably at least 85% by weight, most preferably at least 90% by weight, for example 98% by weight.

[0139] Calcium carbonate can be provided in dry form or suspended in water. Preferably, the corresponding aqueous suspension has a calcium carbonate content of 1% to 90% by weight, more preferably 10% to 72% by weight, even more preferably 20% to 70% by weight, especially preferably 30% to 68% by weight, and most preferably 50-60% by weight, based on the weight of the slurry.

[0140] In a particularly preferred embodiment, the calcium carbonate is provided in dry form or in the form of an aqueous suspension having a solids content of at least 60 wt.-%, more preferably at least 68 wt.-%, even more preferably at least 70 wt.-%, most preferably at least 72 wt.-%.

[0141] A "dry (or dry)" material can be defined by its total moisture content, which, unless otherwise stated, is less than or equal to 0.5 wt%, even more preferably less than or equal to 0.2 wt%, and most preferably 0.03-0.07 wt%, based on the total weight of the dried material. The "total moisture content" of a material can be measured by determining the percentage of moisture (e.g., water) that can be desorbed from a sample when heated to 220°C according to the Karl Fischer coulometric titration method.

[0142] A "suspension" or "slurry" within the meaning of the present invention refers to a mixture comprising at least one insoluble solid and optionally other additives in a liquid medium (such as water), and generally containing a large amount of solids and therefore being more viscous (higher viscosity) and may have a higher density than the liquid medium used to form it.

[0143] Calcium carbonate may also be provided in the form of granules which, once in the aqueous phase, disintegrate into a powdery product as described above.

[0144] As explained above, it has been found that the addition of calcium carbonate results in a higher permeability of the at least one membrane module than would be achieved if no calcium carbonate was added or if the same equivalent amount of another base was added.

[0145] The typical achievable permeability of the membrane module is 200-240 l h -1 m -2 bar -1 .

[0146] The permeability that can be achieved by adding calcium carbonate according to the present invention can be 220-600 l h -1 m -2 bar -1 , preferably 250-500 l h -1 m -2 bar -1 , more preferably 300-400 l h -1 m -2 bar -1 , most preferably 330-350l h -1 m -2 bar -1 .

[0147] Thus, by adding calcium carbonate, the permeability of the at least one membrane module may be increased by at least 10%, preferably by at least 25%, more preferably by at least 50%, even more preferably by at least 100%, most preferably by at least 150%.

[0148] It has also been found that the addition of calcium carbonate results in a flux rate through the at least one membrane module that is higher than that achieved if no calcium carbonate is added or if the same equivalent amount of another base is added.

[0149] Thus, by adding calcium carbonate, the flow rate of the at least one membrane at a given pressure may be increased by at least 5%, preferably by at least 10%, more preferably by at least 15%, even more preferably by at least 20%, most preferably by at least 25%.

[0150] Therefore, the use of calcium carbonate in a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module as described above is another aspect of the present invention.

[0151] In addition, a method for increasing membrane permeability in a membrane bioreactor (MBR) process using at least one membrane module by adding calcium carbonate as described above is another aspect of the present invention, wherein the permeability of the at least one membrane module is increased by at least 10%, preferably by at least 25%, more preferably by at least 50%, even more preferably by at least 100%, and most preferably by at least 150% by adding calcium carbonate.

[0152] Yet another aspect of the present invention is a method for increasing the membrane flux rate at a given pressure in a membrane bioreactor (MBR) process using at least one membrane module by adding calcium carbonate as described above, wherein the flux rate of the at least one membrane module is increased by at least 5%, preferably by at least 10%, more preferably by at least 15%, even more preferably by at least 20%, and most preferably by at least 25% by adding calcium carbonate.

[0153] The following examples and tests will illustrate the present invention but are not intended to limit the present invention in any way. BRIEF DESCRIPTION OF THE DRAWINGS

[0154] Figure 1 Schematic diagram showing the effect of sodium cations (scenario 1) and calcium cations (scenario 2) on floc formation and permeability.

[0155] Figure 2a and 2b , 2c and 2d illustrate the Langelier Saturation Index (LSI) as a function of pH and dissolved calcium and carbonate ions: Scenario 1: Dosage of alkali metal hydroxide; Scenario 2: Dosage of calcium carbonate; Scenario 3: Dosage of calcium chloride; Scenario 4: Dosage of calcium hydroxide.

[0156] Figure 3a and 3b A schematic configuration of a membrane bioreactor process is shown. Figure 3a Describe the immersed / submerged membrane bioreactor (iMBR) configuration. Figure 3b Describe the external / side-flow membrane bioreactor (sMBR) configuration.

[0157] Figure 4A more specific configuration of the submerged / immersed membrane bioreactor (iMBR) configuration used in the examples is described. DETAILED DESCRIPTION

[0158] Example

[0159] 1. Analysis methods

[0160] All parameters defined throughout this application and mentioned in the following examples are based on the following measurement methods:

[0161] Particle size distribution

[0162] Volume-determined median particle size d 50 (vol) and volume-determined top cut particle size d 98 (vol) and volume particle size d 90 (vol) and d 10 (vol) was evaluated in a wet cell using a Malvern Mastersizer 2000 or 3000 Laser Diffraction System (Malvern Instruments Plc., UK). If not otherwise stated in the following Examples section, the volume particle size was evaluated in a wet cell using a Malvern Mastersizer 2000 Laser Diffraction System (Malvern Instruments Plc., UK). 50 (vol) and d 98 The diameter value indicated by the (vol) value is such that 50% or 98% of the volume of the particles have a diameter less than this value, respectively. The raw data obtained by the measurement are analyzed using the Mie theory (wherein the particle refractive index is 1.57 and the absorption index is 0.005). The method and the instrument are known to those skilled in the art and are commonly used to determine the particle size distribution of fillers and pigments. The samples are measured under dry conditions without any prior treatment.

[0163] The median particle size determined by weight d 50 (wt) was measured by sedimentation method, which is the analysis of sedimentation behavior in a gravitational field. A Sedigraph from Micromeritics Instrument Corporation, USA TM The method and the instrument are known to those skilled in the art and are commonly used to determine the particle size distribution of fillers and pigments. 4 P 2 O 7 The samples were dispersed using a high-speed stirrer and ultrasound.

[0164] Methods and instruments are known to those skilled in the art and are commonly used to determine the particle size of fillers and pigments.

[0165] BET surface area of ​​the material

[0166] The “specific surface area” (in m2) of a material as used throughout this document is 2 The total surface area (m2 / g) of the material can be determined by the Brunauer-Emmett-Teller (BET) method with nitrogen as the adsorption gas and by using an ASAP 2460 instrument from Micromeritics. This method is well known to those skilled in the art and is defined in ISO 9277:2010. Prior to the measurement, the sample was conditioned at 100°C under vacuum for 60 minutes. 2 ) can be measured by the specific surface area of ​​the material (m 2 / g) and mass (g) to obtain the product.

[0167] Transmembrane pressure

[0168] Transmembrane pressure (bar) measures the pressure drop across the membrane during filtration and is an indicator of the degree of membrane fouling. This is measured by a pressure sensor on the permeate pipeline between the submerged membrane unit and the osmotic pump. The pressure sensor is located as close to the submerged membrane as possible to minimize the impact of pressure losses from pipelines and accessories. The pressure sensor is located at the same height of the water level in the pool to minimize the impact of static pressure differences. For the experiments mentioned below, the transmembrane pressure was continuously measured by a pressure sensor (Vega Grieshaber KG, Schiltach, Germany). Daily averages were calculated.

[0169] flow

[0170] The flow rate (l / h) was measured continuously by a magnetic flowmeter (Endress+Hauser Group Services AG, Reinach BL, Switzerland). Daily average values ​​were calculated.

[0171] Flux

[0172] The flux is calculated by dividing the flow rate value by the membrane surface area (for the filtration step).The flux value is given in liters per square meter of membrane area per hour.

[0173]

[0174] Permeability

[0175] Permeability (lh -1 m -2 bar -1) is calculated based on the following relationship:

[0176]

[0177] The membrane surface area is defined as the membrane surface area per membrane module as indicated by the membrane manufacturer multiplied by the number of modules installed.

[0178] pH

[0179] Any pH value is measured at 25°C using a Mettler-Toledo Seven Easy pH meter and a Mettler-Toledo InLab Expert Pro pH electrode. A three-point calibration of the instrument (according to the step method) is first performed using commercial buffer solutions (from Aldrich) with pH values ​​of 4, 7 and 10 at 25°C. The reported pH value is the endpoint value detected by the instrument (the difference between the signal and the average value in the last 6 seconds is less than 0.1 mV).

[0180] Alkalinity

[0181] As referred to herein, total alkalinity (CaCO 3 ) (sometimes referred to as "TAC") is a measure of the ability of an aqueous solution to neutralize an acid to the equivalence point of carbonate or bicarbonate. This alkalinity is equal to the stoichiometric sum of the bases in the solution and is expressed in mg / l (as CaCO 3 )instruct.

[0182] Total alkalinity was measured using a Mettler-Toledo T70 titrator using the corresponding LabX Light titration software. A DGi111-SG pH electrode was used for this titration according to the corresponding Mettler-Toledo method M415 (water analysis) of Application Note 37. Calibration of the pH electrode was performed using Mettler-Toledo pH standards (pH 4.01, 7.00 and 9.21).

[0183] Water hardness

[0184] Water hardness is the total calcium and magnesium ion concentration in a water sample and is expressed as the concentration of calcium carbonate.

[0185] Water hardness was measured by a colorimetric water hardness cuvette test supplied by Hach Lange GmbH, Düsseldorf, Germany, under product number LCK327.

[0186] LSI (Langelier Saturation Index)

[0187] LSI is expressed as the difference between the actual system pH and the saturation pH:

[0188] LSI=pH-pH S

[0189] pH is the actual measured pH value of the aqueous system

[0190] pH S The solution is Ca 2+ and CO 3 2- The saturation pH value at saturation is calculated by the following formula:

[0191] pH S =(9.3+A+B)-(C+D)

[0192] in

[0193] A=(log 10 (TDS)-1) / 10TDS is the total dissolved solids expressed in mg / l

[0194] B=-13.12×log 10 (T+273)+34.55 where T is the temperature in °C

[0195] C = log 10 [Ca 2+ ]-0.4[Ca 2+ ] is based on CaCO 3 Calcium concentration of aqueous liquid expressed in mg / l

[0196] D = log 10 (TAC), TAC is calculated based on CaCO 3 The total alkalinity of an aqueous liquid expressed in mg / l.

[0197] 2. Equipment

[0198] exist Figure 4 A more detailed setup of an exemplary device is shown in . The following equipment was used in the experiments:

[0199] - Volume 5000m 3 aeration tank.

[0200] - Four 200m 3 A membrane pool with a submerged ultrafiltration (UF) membrane comprising a total of 2000 hollow fiber membrane modules manufactured by Zenon, the hollow fiber membrane modules having a pore size of 0.1 μm and a 75000 m 2 The components are immersed in water and cleaned periodically by reversing the water flow combined with air flushing.

[0201] - Four horizontal centrifugal osmotic pumps with variable speed control to match effluent and influent flow rates.

[0202] - Pressure indicator providing transmembrane pressure (Vega Grieshaber KG, Schiltach, Germany).

[0203] - A magnetic mass flow meter (Endress+Hauser Group Services AG, Reinach BL, Switzerland) providing the flow across the membrane.

[0204] - Pipes and submersible pumps to transfer MLSS(RAS) to membrane tanks and drain membrane tanks to treat waste activated sludge(WAS).

[0205] - pH meter, indicating the pH in the returned activated sludge (pH electrode supplied by Hach Lange GmbH, Düsseldorf, Germany).

[0206] - Pumps to provide base to maintain a constant pH value (diaphragm pump for NaOH and peristaltic pump for calcium carbonate suspension).

[0207] 3. Chemicals

[0208] Base:

[0209] -Caustic soda is added in liquid form as a 25% solution.

[0210] - Stabilized suspension of natural ground calcium carbonate (71% by weight solids, d 50 =1μm; d 98 =5μm; BET specific surface area = 12m 2 / g; purity 98% by weight) was added in liquid form as a 71% suspension.

[0211] 4. Wastewater characteristics:

[0212] The wastewater at the inflow of the plant can be characterized by the following sum parameters: Total suspended solids (TSS) = 150 mg / l, biological oxygen demand (BOD) = 200 mg / l, total nitrogen (TN) = 45 mg / l.

[0213] 5. Procedure

[0214] The urban MBR equipment is operated as normal. The following procedures provide more details on the operating mode and test procedures:

[0215] Municipal wastewater is continuously fed to the wastewater treatment plant via a pressurized sewer pipe. The wastewater undergoes two primary treatment steps consisting of grit removal and a primary sedimentation stage before flowing by gravity to an aeration tank.

[0216] In such Figure 4 In the plant shown, water is continuously treated by an activated sludge process comprising the following steps:

[0217] a) Contacting the wastewater with the recycled activated sludge flocs. The MLSS is kept constant at 10000 mg / l. The water and the return activated sludge are in contact as they enter the aeration tank. The return activated sludge originates from a tank with submerged membranes.

[0218] b)By blowing about 15000m 3 / h of air is fed into the aeration tank to provide oxygen for microbial degradation of organic and inorganic compounds in the wastewater.

[0219] c) The water is transferred via submersible pumps and pipes to a tank with submerged UF membranes.

[0220] d) Separation of treated water and activated sludge by passing them through UF membranes, wherein the transmembrane flow is caused by a pump behind the membrane, which provides a pressure difference across the membrane. The pump controls the flow rate so that the effluent of the wastewater treatment plant matches the flow rate of the influent of the wastewater treatment plant.

[0221] The average daily flow rate to the system pool was kept constant, fluctuating within about 5%.

[0222] The accumulated sludge is recirculated to the aeration tank by a pump immersed in the membrane tank.

[0223] From time to time, excess sludge is discarded to maintain a constant feed (organic matter in the influent) to mass (mixed liquor suspended solids in the system) ratio of approximately 0.1 kg BOD per kg mixed liquor suspended solids per day (in the complete system).

[0224] As a base, calcium carbonate slurry or 25% NaOH solution was added to the system as a comparative sample.By adding the base, a constant pH of 6.5 was maintained.

[0225] In three trials (lasting between 11, 23 and 39 days), a calcium carbonate suspension was added to the system to maintain a constant pH of 6.5.

[0226] In three control trials (lasting between 11, 23 and 39 days), caustic soda was added to the system to maintain a constant pH of 6.5.

[0227] Apart from this, all parameters were kept constant.

[0228] The average amount of alkali added per liter of wastewater in Table 1 refers to the mass weight of the compound added per volume of wastewater treated on that day at a theoretical 100% concentration. The mass weight relates to the weight of the alkali contained in the corresponding solution / suspension, e.g. 41 mg NaOH refers to 164 g of 25% caustic soda solution. 80 mg CaCO 3 Refers to 113g of 71% calcium carbonate suspension, etc.

[0229] Table 1: Test setup

[0230]

[0231] Table 2: Test results

[0232]

[0233] When caustic soda and calcium carbonate were used, system performance and treated water parameters were comparable. However, surprisingly, when calcium carbonate was used to control pH, the average transmembrane pressure at constant flow rate decreased and remained very low.

[0234] This means that the membrane permeability increases. It is believed that calcium cations improve floc formation and thereby reduce organic bio-blocking, which is known to be the main cause of reduced membrane permeability (see Figure 1 The significantly improved permeability also indicates that the addition of calcium carbonate did not lead to any inorganic clogging, which would have resulted in reduced membrane permeability.

Claims

1. A method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module, characterized by the following steps: a) Provide wastewater, b) contacting the wastewater of step a) with the at least one membrane module in the presence of sludge, c) adding calcium carbonate to the wastewater of step a) before and / or during step b).

2. The method according to claim 1, characterized in that A portion of the added calcium carbonate is dissolved and another portion remains undissolved.

3. The method according to any one of the preceding claims, characterized in that The at least one membrane module of step b) is immersed in the bioreactor (iMBR) or installed in a side stream outside the bioreactor (sMBR).

4. The method according to any one of the preceding claims, characterized in that The at least one membrane component has a pore size of not more than 5 μm, preferably not more than 2 μm, more preferably not more than 1.5 μm, especially preferably not more than 1.2 μm, most preferably 0.005-1 μm.

5. The method according to any one of the preceding claims, characterized in that The pH value of the mixed liquor containing sludge and calcium carbonate is 5.5-9, preferably 6-8.5, more preferably 6.2-8, even more preferably 6.5-7.8, most preferably 7-7.

3.

6. The method according to any one of the preceding claims, characterized in that The total alkalinity in the effluent is preferably 30-300 mg / l calculated as CaCO3, more preferably 50-275 mg / l calculated as CaCO3, even more preferably 80-250 mg / l calculated as CaCO3, most preferably 100-200 mg / l calculated as CaCO3.

7. The method according to any one of the preceding claims, characterized in that The mixed liquor containing sludge and calcium carbonate has a Langelier saturation index (LSI) of -1.5 to +1, preferably -1 to +0.5, more preferably -0.5 to 0.

8. The method according to any one of the preceding claims, characterized in that The calcium carbonate is selected from the group consisting of natural ground calcium carbonate (GCC), mixed natural ground carbonate minerals containing calcium carbonate, precipitated calcium carbonate (PCC), and mixtures thereof.

9. The method according to any one of the preceding claims, characterized in that The natural ground calcium carbonate (GCC) is selected from marble, chalk, limestone, and mixtures thereof; the mixed natural ground carbonate mineral is dolomite; and the precipitated calcium carbonate (PCC) is selected from precipitated calcium carbonate having aragonite, vaterite or calcite crystal form, and mixtures thereof.

10. The method according to any one of the preceding claims, characterized in that Calcium carbonate has -Weight median particle size d 50 (wt) is 0.1-50 μm, preferably 0.2-20 μm, more preferably 0.5-10 μm, most preferably 1-5 μm, and / or - Top cut particle size d 98 (wt) is not more than 100 μm, preferably not more than 75 μm, even more preferably not more than 50 μm, most preferably not more than 25 μm, especially 1.2-10 μm, for example 1.6-5 μm, and / or -BET specific surface area is 0.1-100m 2 / g, preferably 0.2-50m 2 / g, more preferably 0.5-30m 2 / g, even more preferably 0.8-20m 2 / g, most preferably 1-12m 2 / g, for example 5-6m 2 / g, and / or The purity is at least 70% by weight, preferably at least 75% by weight, more preferably at least 80% by weight, even more preferably at least 85% by weight, most preferably at least 90% by weight, for example 98% by weight.

11. The method according to any one of the preceding claims, characterized in that The calcium carbonate is provided in dry form or in the form of an aqueous suspension, preferably in the form of an aqueous suspension having a solids content of at least 60 wt.-%, more preferably at least 68 wt.-%, even more preferably at least 70 wt.-%, most preferably at least 72 wt.-%.

12. The method according to any one of the preceding claims, characterized in that By adding calcium carbonate, the permeability of the at least one membrane module is increased by at least 10%, preferably by at least 25%, more preferably by at least 50%, even more preferably by at least 100%, most preferably by at least 150%.

13. The method according to any one of the preceding claims, characterized in that By adding calcium carbonate, the flow rate of the at least one membrane module at a given pressure is increased by at least 5%, preferably by at least 10%, more preferably by at least 15%, even more preferably by at least 20%, most preferably by at least 25%.

14. Use of calcium carbonate in a method for treating wastewater in a membrane bioreactor (MBR) process using at least one membrane module according to claims 1 to 13.

15. A method for increasing membrane permeability in a membrane bioreactor (MBR) process using at least one membrane module by adding calcium carbonate according to claims 1 to 13, Wherein by adding calcium carbonate, the permeability of the at least one membrane component is increased by at least 10%, preferably by at least 25%, more preferably by at least 50%, even more preferably by at least 100%, and most preferably by at least 150%.

16. A method for increasing membrane flux in a membrane bioreactor (MBR) process using at least one membrane module by adding calcium carbonate according to claims 1 to 13, Wherein by adding calcium carbonate, the flow rate of at least one membrane module at a given pressure is increased by at least 5%, preferably by at least 10%, more preferably by at least 15%, even more preferably by at least 20%, and most preferably by at least 25%.

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