Method for treating wastewater

Abstract

The embodiment relates to a method for treating wastewater with enhanced efficiency of wastewater treatment, which comprises preparing wastewater; and adding a cationic inorganic coagulant and silica (SiO2) to the wastewater.

Description

Method for Treating Wastewater

[0001] Embodiments relate to a method for treating wastewater and specifically relate to a method for enhancing the efficiency of wastewater treatment by adding a specific additive to wastewater.

[0002] When wastewater is discharged in an amount exceeding the designated wastewater discharge amount in an industry, the discharged water pollutants are required to meet the discharge allowance standards or effluent water quality standards. The pulp and paper industries, which are representative examples of water-intensive industries, generate large amounts of wastewater per ton of paper or cardboard produced. The chemical oxygen demand (COD) in such wastewater is also generally high.

[0003] In the pulp and paper industries, due to the strengthening of wastewater discharge regulations in some countries in addition to recent increases in production, pulp or paper companies may have difficulties in treating wastewater to meet the wastewater standards. For example, the “Enforcement Decree and Enforcement Regulations of the Water Environment Conservation Act” was promulgated in 2019 in Korea, which mainly focuses on changing the management indicators for organic substances in wastewater. Starting around 2021, the water quality standards for organic substances in wastewater were changed from the conventional chemical oxygen demand (COD) to total organic carbon (TOC).

[0004] In response thereto, technologies that can reduce chemical oxygen demand (COD) and total organic carbon (TOC) in wastewater, such as Fenton treatment and use of activated carbon, have been used. As a similar advanced treatment, the AOP (advanced oxidation process) system has been studied. In these technologies, however, there is a problem in that processing costs increase, and new investments in facilities are required.

[0005] Accordingly, there is a need for research on technologies that can reduce chemical oxygen demand (COD) and total organic carbon (TOC) in wastewater through chemicals at low costs while using conventional facilities without additional equipment.Technical Problem

[0006] The embodiments provide a method for treating wastewater with improved efficiency of wastewater treatment.Solution to Problem

[0007] The method for treating wastewater according to embodiments comprises preparing wastewater; and adding a cationic inorganic coagulant and silica (SiO2) to the wastewater.Advantageous Effects of Invention

[0008] As a cationic inorganic coagulant and silica (SiO2) are added to wastewater in the method for treating wastewater according to an embodiment, they not only facilitate the coagulation and flocculation of suspended solids in the wastewater but also adsorb organic substances dissolved in the wastewater, thereby improving the efficiency of wastewater treatment. In addition, if the cationic inorganic coagulant and silica are added prior to a biological treatment step, the cationic inorganic coagulant and silica can preemptively remove confounding substances that interfere with the biological treatment step from wastewater, thereby maximizing the efficiency of the biological treatment step as well.

[0009] is a schematic flow diagram of a method for treating wastewater according to an embodiment.

[0010] is a schematic flow diagram of a method for treating wastewater according to another embodiment.

[0011] is a schematic flow diagram of a method for treating wastewater according to still another embodiment.

[0012] is a photograph showing the test results according to Test Examples A1 to A6.

[0013] is a photograph showing the test results according to Test Examples B1 to B6.

[0014] is a photograph showing the test results according to Test Examples C1 to C6.

[0015] is a photograph showing the test results according to wastewater E, Test Example E5, and Test Example E8, respectively, observed under a microscope.

[0016] is a photograph showing the test results according to Test Example F.

[0017] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains may easily practice them. However, the embodiments may be implemented in many different ways. The present invention is not limited to the embodiments described in the present specification. In addition, the sizes of individual elements in the drawings may be exaggeratedly depicted or omitted for the sake of description, and they may differ from the actual sizes.

[0018] In the description of the present invention, if it is determined that a detailed description of a relevant known constitution or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

[0019] In the present specification, when a part “comprises” a certain element, it is intended to specify a particular characteristic, region, step, process, element, and / or component. It does not exclude the presence or addition of any other characteristic, region, step, process, element and / or component, unless specifically stated to the contrary.

[0020] In the present specification, in the case where an element is mentioned to be formed, connected, or combined on or under another element, it means all of the cases where one element is directly, or indirectly through another element, formed, connected, or combined with another element. In addition, the criterion for the terms on and under of each component may vary depending on the direction in which the object is observed.

[0021] In the present specification, a singular expression is interpreted to cover a singular or plural number that is interpreted in context unless otherwise specified.

[0022] In addition, all numbers and expressions related to the quantities of components, reaction conditions, and the like used herein are to be understood as being modified by the term “about,” unless otherwise indicated.

[0023] The terms first, second, and the like are used herein to describe various elements, and the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one element from another.<Additive>

[0024] The method for treating wastewater according to an embodiment comprises preparing wastewater; and adding a cationic inorganic coagulant and silica (SiO2) to the wastewater.

[0025] The silica may have an average particle diameter of 1 to 100 nm. Specifically, the average particle diameter of the silica may be 5 to 90 nm, 10 to 80 nm, or 20 to 60 nm, but it is not limited thereto.

[0026] In an embodiment, at least a portion of the silica may be added in a colloidal state. For example, at least a portion of the silica may be added in the form of silica sol. Specifically, 80% or more, 90% or more, 95% or more, or 99% or more of the silica may be added in the form of silica sol. The silica sol may be an anionic inorganic colloidal material, but it is not limited thereto.

[0027] The silica sol may mean that silica particles are stably dispersed in water or an organic solvent without precipitating or flocculating. The silica sol may be an aquasol, or the silica sol may be an organosol.

[0028] If silica satisfying the above average particle size and / or condition is added to wastewater together with a cationic inorganic coagulant, it not only facilitates the coagulation and flocculation of suspended solids in the wastewater, but also adsorbs organic substances dissolved in the wastewater to form flocks and removing them from the wastewater, thereby improving the efficiency of wastewater treatment.

[0029] Specifically, when a cationic inorganic coagulant and silica are added to wastewater, suspended solids in the wastewater are adsorbed, coagulated, and flocculated, thereby improving the turbidity of the wastewater. As organic substances dissolved in wastewater are adsorbed, coagulated, and / or flocculated, the chemical oxygen demand (COD) and total organic carbon (TOC) in the wastewater can be reduced.

[0030] In an embodiment, the silica may have an unmodified surface. For example, the surface of the silica may not have been subjected to acidification treatment and / or alkalization treatment. Specifically, the silica may have an unmodified and unactivated surface, but it is not limited thereto.

[0031] When the surface of the silica is not modified, the coagulation of suspended solids in wastewater can be facilitated more efficiently, or dissolved organic materials can be adsorbed more effectively, as compared with the case where surface-modified silica is added. In addition, when the surface of the silica is not modified, there may be additional advantages in that it has a long shelf life, which makes it convenient to store, and it is inexpensive, as compared with surface-modified silica.

[0032] In another embodiment, the silica may have a modified surface. For example, the surface of the silica may have been subjected to acidification treatment and / or alkalization treatment.

[0033] The effect of improving water treatment due to the surface and structural characteristics of silica may vary depending on the properties of the raw wastewater. Silica may be selected in various ways depending on the nature and treatment conditions of the raw wastewater.

[0034] In an embodiment, at least a portion of the silica may be added in the form of silica sol, and the silica sol may be added to wastewater at a concentration of 10 to 1,000 ppm. Specifically, the silica sol may be added to wastewater at a concentration of 10 to 800 ppm, 10 to 600 ppm, 10 to 500 ppm, 10 to 300 ppm, 100 to 1,000 ppm, 100 to 800 ppm, 100 to 600 ppm, 100 to 500 ppm, or 100 to 300 ppm, but it is not limited thereto.

[0035] In an embodiment, the silica sol may have a total solids content of 3% to 30%. Specifically, the total solids content of the silica sol may be 5% to 25%, 7% to 20%, or 10% to 15%, but it is not limited thereto. In an embodiment, the silica sol may further comprise aluminum oxide and / or sodium oxide in addition to silica (SiO2), but it is not limited thereto.

[0036] In an embodiment, the content of silica (SiO2) in the silica sol may be 3% to 30%. Specifically, the content of silica (SiO2) in the silica sol may be 3% to 25%, 5% to 20%, or 7% to 15%, but it is not limited thereto.

[0037] In an embodiment, the silica (SiO2) may be added to wastewater at a concentration of 10 to 100 ppm. Specifically, the silica (SiO2) may be added to wastewater at a concentration of 10 to 80 ppm, 10 to 60 ppm, 10 to 50 ppm, 10 to 300 ppm, 20 to 100 ppm, 20 to 80 ppm, 20 to 60 ppm, 20 to 50 ppm, or 20 to 30 ppm, but it is not limited thereto. For example, the concentration of silica added may be measured by the concentration of SiO2present in wastewater.

[0038] When the amount of silica sol added, the solids content of silica sol, and / or the content of silica each satisfy the above ranges, not only can organic substances in wastewater be more effectively removed, but the turbidity of wastewater can also be improved more efficiently.

[0039] In an embodiment, the cationic inorganic coagulant may be one or more types. Specifically, the cationic inorganic coagulant may be two or more types, but it is not limited thereto.

[0040] In another embodiment, the cationic inorganic coagulant may be one type.

[0041] In an embodiment, the cationic inorganic coagulant may comprise an aluminum-based coagulant, an iron-based coagulant, or a combination thereof.

[0042] For example, the aluminum-based coagulant is at least one selected from the group consisting of aluminum sulfate and polyaluminium chloride, and the iron-based coagulant may be at least one selected from the group consisting of iron(I) sulfate, iron(II) sulfate, iron(III) sulfate, iron(I) chloride, iron(II) chloride, iron(III) chloride, and polyiron sulfate, but they are not limited thereto.

[0043] In an embodiment, the cationic inorganic coagulant may comprise an aluminum-based coagulant comprising polyaluminium chloride. Specifically, the cationic inorganic coagulant may be composed of an aluminum-based coagulant comprising polyaluminium chloride. More specifically, the cationic inorganic coagulant may be composed of polyaluminium chloride, but it is not limited thereto.

[0044] In an embodiment, the cationic inorganic coagulant may be added to wastewater at a concentration of 100 to 1,500 ppm. Specifically, the cationic inorganic coagulant may be added to wastewater at a concentration of 100 to 1,000 ppm, 100 to 800 ppm, 100 to 600 ppm, 100 to 500 ppm, 100 to 300 ppm, 200 to 1,500 ppm, 200 to 1,000 ppm, 200 to 800 ppm, 200 to 600 ppm, or 200 to 500 ppm, but it is not limited thereto.

[0045] Specifically, polyaluminium chloride as the cationic inorganic coagulant may be added to wastewater at a concentration of 100 to 1,500 ppm. Specifically, polyaluminium chloride as the cationic inorganic coagulant may be added to wastewater at a concentration of 100 to 1,000 ppm, 100 to 800 ppm, 100 to 600 ppm, 100 to 500 ppm, 100 to 300 ppm, 200 to 1,500 ppm, 200 to 1,000 ppm, 200 to 800 ppm, 200 to 600 ppm, or 200 to 500 ppm, but it is not limited thereto.

[0046] In an embodiment, the cationic inorganic coagulant and the silica sol may be added to wastewater at a weight ratio of 10:1 to 1:5. Specifically, the cationic inorganic coagulant and the silica sol may be added to wastewater at a weight ratio of 5:1 to 1:5, 3:1 to 1:5, 1:1 to 1:5, 1:2 to 1:5, 10:1 to 1:3, 5:1 to 1:3, 3:1 to 1:3, 1:1 to 1:3, 10:1 to 1:1, 5:1 to 1:1, or 3:1 to 1:1.

[0047] When the cationic inorganic coagulant and the silica sol are added to wastewater at the above weight ratio, not only can the coagulation and flocculation of suspended solids in wastewater be effectively facilitated, but the adsorption of organic substances dissolved in wastewater can also take place more efficiently.

[0048] In an embodiment, a supplement may be further added to the wastewater. For example, at least one selected from the group consisting of sodium aluminate, an alkali flocculant, an organic flocculant, and an emulsion polymer may be further added to wastewater, but it is not limited thereto.

[0049] When a supplement is added to wastewater, it may play a role in controlling the pH of wastewater or promoting adsorption, flocculation, or coagulation. The supplement may be selected in various ways depending on the nature and treatment conditions of the raw wastewater.<Method for treating wastewater>

[0050] The method for treating wastewater according to an embodiment may comprise preparing wastewater (S100); adding a cationic inorganic coagulant and silica (SiO2) to the wastewater (S200); and removing flocks from the wastewater (S300).

[0051] For example, as shown in, the method for treating wastewater may sequentially comprise preparing wastewater (S100); adding a cationic inorganic coagulant and silica (SiO2) to the wastewater (S200); and removing flocks from the wastewater (S300).

[0052] -Step of preparing wastewater

[0053] In the step of preparing wastewater (S100), the wastewater may comprise domestic wastewater, industrial wastewater, or a combination thereof.

[0054] Specifically, the wastewater may comprise wastewater from the pulp industry, wastewater from the paper industry, or a combination thereof.

[0055] The wastewater may be wastewater comprising dissolved organic compounds. Specifically, the wastewater may be wastewater comprising dissolved organic compounds and suspended solids.

[0056] In the step of preparing wastewater, the wastewater may have a pH of 4 to 10. Specifically, the pH of the wastewater may be 5 to 9, 6 to 8, or 6.5 to 7.5, but it is not limited thereto.

[0057] In an embodiment, if the pH of the wastewater is outside the above range, the method for treating wastewater may further comprise adjusting the pH of the wastewater. Specifically, the pH of the wastewater may be adjusted to 5 to 9, 6 to 8, or 6.5 to 7.5.

[0058] In the step of preparing wastewater, the wastewater may have a turbidity of 500 NTU or more. For example, the turbidity of the wastewater may be 1,000 NTU or more, 3,000 NTU or more, 5,000 NTU or more, or 10,000 NTU or more.

[0059] In the step of preparing wastewater, the wastewater may have a chemical oxygen demand (COD) of 100 ppm or more. For example, the chemical oxygen demand (COD) of the wastewater may be 500 ppm or more, 1,000 ppm or more, 2,000 ppm or more, or 3,000 ppm or more.

[0060] In the step of preparing wastewater, the wastewater may have a total organic carbon (TOC) of 300 ppm or more. For example, the total organic carbon (TOC) of the wastewater may be 1,000 ppm or more, 2,000 ppm or more, 3,000 ppm or more, 5,000 ppm or more, or 7,000 ppm or more.

[0061] -Step of adding a cationic inorganic coagulant and silica to the wastewater

[0062] In an embodiment, the step of adding a cationic inorganic coagulant and silica to the wastewater may comprise adding a cationic inorganic coagulant to the wastewater and adding silica to the wastewater. Specifically, in the step of adding a cationic inorganic coagulant and silica to the wastewater, a cationic inorganic coagulant and silica may be added simultaneously or sequentially to the wastewater.

[0063] For example, the step of adding a cationic inorganic coagulant and silica to the wastewater may sequentially comprise adding a cationic inorganic coagulant to the wastewater and adding silica to the wastewater, or it may sequentially comprise adding silica to the wastewater and adding a cationic inorganic coagulant to the wastewater.

[0064] For example, as shown in, the method for treating wastewater of the present invention may sequentially comprise adding silica (e.g., silica sol) to the wastewater; adding a cationic inorganic coagulant (e.g., polyaluminum chloride); and removing flocks from the wastewater.

[0065] In an embodiment, the step of adding a cationic inorganic coagulant and silica to the wastewater may be a step in which a cationic inorganic coagulant, silica, and a supplement may be added simultaneously or sequentially to the wastewater.

[0066] Specifically, the step of adding a cationic inorganic coagulant and silica to the wastewater may be a step in which a cationic inorganic coagulant, silica, and a supplement may be added sequentially to the wastewater, but it is not limited thereto.

[0067] When a cationic inorganic coagulant and silica are separately added to the wastewater, a step of removing flocks from the wastewater as described below may be carried out between the step of adding a cationic inorganic coagulant and the step of adding silica.

[0068] In another embodiment, the step of adding a cationic inorganic coagulant and silica to the wastewater may be characterized in that a cationic inorganic coagulant and silica are added simultaneously to the wastewater, but it is not limited thereto.

[0069] Descriptions of the cationic inorganic coagulant and the silica are as described above. The amount, timing, and order of adding the cationic inorganic coagulant and the silica may be adjusted depending on the characteristics of the wastewater, such as the type of wastewater, the amount of wastewater, and the content of organic substances in the wastewater, and the specific process of treating wastewater.

[0070] In an embodiment, the ratio of the turbidity (TB) of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater to the turbidity (TA) of the wastewater in the step of preparing the wastewater (TB / TA) may be 0.98 or less. Specifically, the ratio of the turbidity (TB) of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater to the turbidity (TA) of the wastewater in the step of preparing the wastewater (TB / TA) may be 0.94 or less, 0.9 or less, 0.85 or less, or 0.8 or less.

[0071] In an embodiment, the ratio of the total organic carbon (TOCB) of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater to the total organic carbon (TOCA) of the wastewater in the step of preparing the wastewater (TOCB / TOCA) may be 0.98 or less. Specifically, the ratio of the total organic carbon (TOCB) of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater to the total organic carbon (TOCA) of the wastewater in the step of preparing the wastewater (TOCB / TOCA) may be 0.96 or less, 0.94 or less, 0.92 or less, 0.9 or less, 0.85 or less, or 0.8 or less.

[0072] In an embodiment, the chemical oxygen demand (CODB) of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater may be less than the chemical oxygen demand (CODA) of the wastewater in the step of preparing the wastewater by 10 ppm or more, 20 ppm or more, 30 ppm or more, 50 ppm or more, or 100 ppm or more.

[0073] In an embodiment, the change in pH of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater may be 1 or less, 0.7 or less, or 0.5 or less. Specifically, the pH of the wastewater after the step of adding a cationic inorganic coagulant and silica to the wastewater may be 5 to 9, 6 to 8, or 6.5 to 7.5, but it is not limited thereto.

[0074] -Step of removing flocks from the wastewater

[0075] In an embodiment, the method for treating wastewater may comprise removing flocks comprising organic substances from the wastewater. Specifically, it may further comprise removing flocks from the wastewater subsequent to adding a cationic inorganic coagulant and silica (SiO2) to the wastewater, but it is not limited thereto.

[0076] The method for treating wastewater according to an embodiment may comprise preparing wastewater comprising dissolved organic compounds; adding a cationic inorganic coagulant and silica (SiO2) to the wastewater; and removing flocks comprising dissolved organic compounds from the wastewater.

[0077] For example, the method for treating wastewater may sequentially comprise preparing wastewater comprising dissolved organic compounds; adding a cationic inorganic coagulant and silica (SiO2) to the wastewater; and removing flocks comprising the dissolved organic compounds from the wastewater.

[0078] In an embodiment, the step of removing flocks from the wastewater may comprise removing flocks precipitated in the wastewater.

[0079] In another embodiment, the step of removing flocks from the wastewater may comprise removing flocks suspended in the wastewater.

[0080] A conventional process for removing flocks may be used to remove precipitated flocks or suspended flocks from the wastewater.

[0081] In an embodiment, the step of removing flocks from the wastewater may be carried out through a purification device. Specifically, the step of removing flocks from the wastewater may be carried out through a solid-liquid separation unit.

[0082] For example, the flocks may be removed from the wastewater through a disc filter, a sedimentation tank, or a membrane filtration device, but it is not limited thereto.

[0083] In an embodiment, the ratio of the turbidity (TC) of the wastewater after the step of removing flocks from the wastewater to the turbidity (TA) of the wastewater in the step of preparing the wastewater (TC / TA) may be 0.98 or less. Specifically, the ratio of the turbidity (TC) of the wastewater after the step of removing flocks from the wastewater to the turbidity (TA) of the wastewater in the step of preparing the wastewater (TC / TA) may be 0.94 or less, 0.9 or less, 0.85 or less, or 0.8 or less.

[0084] In an embodiment, the ratio of the total organic carbon (TOCC) of the wastewater after the step of removing flocks from the wastewater to the total organic carbon (TOCA) of the wastewater in the step of preparing the wastewater (TOCC / TOCA) may be 0.98 or less. Specifically, the ratio of the total organic carbon (TOCC) of the wastewater after the step of removing flocks from the wastewater to the total organic carbon (TOCA) of the wastewater in the step of preparing the wastewater (TOCC / TOCA) may be 0.96 or less, 0.94 or less, 0.92 or less, 0.9 or less, 0.85 or less, or 0.8 or less.

[0085] -Step of biological treatment

[0086] In an embodiment, the method for treating wastewater may further comprise a step of biological treatment to remove dissolved organic substances from the wastewater.

[0087] Specifically, the method for treating wastewater according to an embodiment may comprise preparing wastewater (S100); adding a cationic inorganic coagulant and silica (SiO2) to the wastewater (S200); removing flocks from the wastewater (S300); and biological treatment to remove dissolved organic substances from the wastewater (S400).

[0088] In an embodiment, the method for treating wastewater may further comprise biological treatment to remove dissolved organic substances from the wastewater subsequent to adding a cationic inorganic coagulant and silica (SiO2) to the wastewater.

[0089] In another embodiment, the method for treating wastewater may further comprise biological treatment to remove dissolved organic substances from the wastewater subsequent to removing flocks from the wastewater.

[0090] For example, as shown in, the method for treating wastewater may sequentially comprise preparing wastewater (S100); adding a cationic inorganic coagulant and silica (SiO2) to the wastewater (S200); removing flocks from the wastewater (S300); and biological treatment to remove dissolved organic substances from the wastewater (S400).

[0091] According to an embodiment, when the step of adding a cationic inorganic coagulant and silica to the wastewater (S200) is carried out prior to the step of biological treatment (S400) to remove dissolved organic substances from the wastewater, the addition of a cationic inorganic coagulant and silica reduces the amount of confounding substances present in the wastewater that interfere with the biological treatment step, whereby it is possible to maximize the efficiency of the biological treatment step.

[0092] Specifically, in the biological treatment step, microorganisms (bacteria) play a role in removing dissolved organic substances. However, since microorganisms are also consumed by confounding substances such as various suspended substances, if the amount of confounding substances is large, the efficiency of the biological treatment step may be deteriorated. As the step of adding a cationic inorganic coagulant and silica to the wastewater is further carried out prior to the step of biological treatment of the wastewater, it not only facilitates the flocculation of suspended solids in the wastewater, but also preemptively removes colloidal and / or dissolved confounding substances, whereby it is possible to maximize the efficiency of the biological treatment step. More specifically, materials that are not biodegradable but are soluble in wastewater are present in the materials used in the papermaking process (especially, the papermaking process that recycles waste paper). These materials significantly reduce the efficiency of the biological treatment step of wastewater. As the step of adding a cationic inorganic coagulant and silica to the wastewater is further carried out prior to the step of biological treatment of the wastewater, it is possible to further enhance the efficiency of the biological treatment step and to further reduce the COD and TOD of the wastewater.

[0093] In an embodiment, the ratio of the turbidity (TD) of the wastewater after the step of biological treatment to remove dissolved organic substances from the wastewater to the turbidity (TA) of the wastewater in the step of preparing the wastewater (TD / TA) may be 0.9 or less. Specifically, the ratio of the turbidity (TD) of the wastewater after the step of biological treatment to remove dissolved organic substances from the wastewater to the turbidity (TA) of the wastewater in the step of preparing the wastewater (TD / TA) may be 0.8 or less, 0.7 or less, 0.6 or less, or 0.5 or less.

[0094] In an embodiment, the ratio of the total organic carbon (TOCD) of the wastewater after the step of biological treatment to remove dissolved organic substances from the wastewater to the total organic carbon (TOCA) of the wastewater in the step of preparing the wastewater (TOCD / TOCA) may be 0.95 or less. Specifically, the ratio of the total organic carbon (TOCD) of the wastewater after the step of biological treatment to remove dissolved organic substances from the wastewater to the total organic carbon (TOCA) of the wastewater in the step of preparing the wastewater (TOCD / TOCA) may be 0.9 or less, 0.8 or less, 0.7 or less, 0.65 or less, 0.6 or less, or 0.5 or less.

[0095] According to an embodiment of the present invention, when the step of biological treatment to remove dissolved organic substances from the wastewater is carried out subsequent to the step of adding a cationic inorganic coagulant and silica (SiO2) to the wastewater, the efficiency of the biological treatment step can be improved by 10% or more as compared with the case where the step of adding a cationic inorganic coagulant and silica (SiO2) to the wastewater is not carried out.

[0096] In an embodiment, the step of biological treatment may be carried out by microorganisms. Specifically, the step of biological treatment may comprise digesting organic substances contained in the wastewater using microorganisms; and solid-liquid separation.

[0097] In another embodiment, the step of biological treatment may be carried out by aerobic microorganisms present in an aeration tank. Specifically, the step of biological treatment may comprise digesting organic substances contained in the wastewater using aerobic microorganisms; and solid-liquid separation.

[0098] In another embodiment, the step of biological treatment may be carried out by anaerobic microorganisms present in an anaerobic tank. Specifically, the step of biological treatment may comprise digesting organic substances contained in the wastewater using anaerobic microorganisms; and solid-liquid separation.

[0099] In an embodiment, the step of biological treatment may be carried out by aerobic microorganisms and anaerobic microorganisms present in an aeration tank. Specifically, the step of biological treatment may comprise digesting organic substances contained in the wastewater simultaneously or sequentially using aerobic microorganisms and anaerobic microorganisms; and solid-liquid separation.

[0100] In an embodiment, activated sludge may be separated from the wastewater through the step of solid-liquid separation.

[0101] -Tertiary treatment step

[0102] In an embodiment, the method for treating wastewater may further comprise a step of tertiary treatment to remove residual organic substances from the wastewater, but it is not limited thereto.

[0103] Specifically, it may further comprise a step of tertiary treatment to remove residual organic substances from the wastewater subsequent to the step of biological treatment to remove dissolved organic substances from the wastewater.

[0104] In an embodiment, the tertiary treatment step may comprise coagulating colloidal particles in the wastewater and flocculating the particles into larger clusters. Specifically, the tertiary treatment step may comprise coagulating colloidal particles in the wastewater, flocculating the particles into larger clusters, and removing flocks from the wastewater.

[0105] For example, the tertiary treatment step may comprise a step of dissolved air flotation (DAF) and sedimentation, and it may comprise transferring wastewater to a DAF flotation tank and / or a sedimentation tank, but it is not limited thereto.

[0106] In an embodiment, the tertiary treatment step may comprise adding a cationic inorganic coagulant and silica.

[0107] Descriptions of the cationic inorganic coagulant and the silica are as described above.<Facility for treating wastewater>

[0108] The facility for treating wastewater according to an embodiment may comprise a reactor (10) in which wastewater and additives are mixed; a primary purifier (20) to remove suspended solids and particulate matter from the wastewater; a biological treatment unit (30) in which organic substances contained in the wastewater are digested; and a secondary purifier (40) for separating activated sludge. Specifically, the facility for treating wastewater may sequentially comprise a reactor (10) in which wastewater and additives are mixed; a primary purifier (20) to remove suspended solids and particulate matter from the wastewater; a biological treatment unit (30) in which organic substances contained in the wastewater are digested; and a secondary purifier (40) for separating activated sludge.

[0109] The facility for treating wastewater according to another embodiment may comprise a reactor (10) in which wastewater and additives are mixed; a primary purifier (20) to remove suspended solids and particulate matter from the wastewater; a biological treatment unit (30) in which organic substances contained in the wastewater are digested; a secondary purifier (40) for separating activated sludge; and a tertiary treatment unit (50) for further removing residual organic substances from the wastewater. Specifically, the facility for treating wastewater may sequentially comprise a reactor (10) in which wastewater and additives are mixed; a primary purifier (20) to remove suspended solids and particulate matter from the wastewater; a biological treatment unit (30) in which organic substances contained in the wastewater are digested; a secondary purifier (40) for separating activated sludge; and a tertiary treating unit (50) for further removing residual organic substances.

[0110] -Reactor

[0111] In an embodiment, in the reactor (10) for mixing wastewater and additives, wastewater and silica may be mixed. Specifically, wastewater, silica, and a cationic inorganic coagulant may be mixed in the reactor.

[0112] In an embodiment, the reactor may comprise a stirrer. When the reactor comprises a stirrer, the mixing of wastewater and additives is facilitated, and the reaction between wastewater and the additives may be more actively carried out.

[0113] In an embodiment, a cationic inorganic coagulant and silica may be added to a tertiary treatment unit, a biological treatment unit, a primary purifier, or a reactor. Specifically, a cationic inorganic coagulant and silica may be added to the primary purifier or may be added to the reactor. Preferably, a cationic inorganic coagulant and silica may be added to the reactor, but it is not limited thereto. For example, raw wastewater containing silica sol is charged to the reactor, and a cationic inorganic coagulant may be further added to the reactor.

[0114] When a cationic inorganic coagulant and silica are added to any reactor prior to a biological treatment unit, for example, when a cationic inorganic coagulant and silica are added into a primary purifier or the reactor (10), the addition of a cationic inorganic coagulant and silica preemptively reduces the amount of confounding substances present in the wastewater that interfere with the biological treatment step, whereby it is possible to maximize the efficiency of the biological treatment unit.

[0115] -Primary purifier

[0116] In an embodiment, the primary purifier (20) for removing suspended solids and particulate matter from the wastewater may comprise a solid-liquid separation unit. Specifically, the solid-liquid separation unit may be used in a step to remove flocks from the wastewater. For example, the primary purifier may be a settling tank, but it is not limited thereto.

[0117] In an embodiment, the primary purifier may serve to remove total suspended solids and other particulate matter from the wastewater.

[0118] -Biological treatment unit

[0119] In an embodiment, the biological treatment unit (30) for digesting organic substances contained in the wastewater may comprise an aerobic treatment tank. Specifically, the biological treatment unit (30) for digesting organic substances contained in the wastewater may comprise an aeration tank. For example, the biological treatment unit (30) for digesting organic substances contained in the wastewater may comprise an aeration tank containing aerobic microorganisms, and air and / or oxygen may be injected into the wastewater, but it is not limited thereto.

[0120] In another embodiment, the biological treatment unit (30) for digesting organic substances contained in the wastewater may comprise an anaerobic treatment tank.

[0121] In another embodiment, the biological treatment unit (30) for digesting organic substances contained in the wastewater may comprise an aerobic treatment tank and an anaerobic treatment tank.

[0122] -Secondary purifier

[0123] In an embodiment, the secondary purifier (30) for separating activated sludge may comprise a solid-liquid separation unit. Specifically, the solid-liquid separation unit may be used in a step to remove organic substances sludge resulting from the biological treatment step from the wastewater. For example, the secondary purifier may be a settling tank, but it is not limited thereto.

[0124] In an embodiment, the secondary purifier may serve to remove activated sludge from the wastewater.

[0125] -Tertiary treatment unit

[0126] In an embodiment, the tertiary treatment unit (40) for further removing residual organic substances may comprise a solid-liquid separation unit. Specifically, the solid-liquid separation unit may be used to remove organic substances through a conventional coagulation-flocculation process, but it is not limited thereto.Examples

[0127] Hereinafter, the present invention will be described in more detail with reference to the following examples. But the following Examples are intended to further illustrate the present invention, and the scope of the present invention is not limited thereto.<Preparation Example>

[0128] An aqueous solution of sodium silicate with a molar ratio of SiO2:Na2O of about 3:1 and a content of silica (SiO2) of 5% by weight was subjected to ion exchange using a cation exchange resin to prepare a silica sol precursor. Stirring the silica sol precursor with the aqueous solution of sodium silicate was repeated to adjust the pH of the mixture to about 10. The mixture was concentrated to have a silica content of about 12% by weight. An aqueous solution of sodium silicate with a molar ratio of SiO2:Na2O of about 3:1 and a content of silica (SiO2) of 24% by weight was added to prepare a silica sol precursor with a molar ratio of SiO2:Na2O of about 12:1. Deionized water was added thereto to prepare silica sol (FennoCat) with a final silica content of 12% by weight.

[0129] The silica sol (FennoCat) thus prepared had a total solids content of 13% by weight and a pH of 11, and it contained silica particles with a specific surface area of 950 m2 / g.<Test Examples A to C>Test Examples A1 to A6

[0130] Wastewater A generated from a paper mill was stirred for 20 seconds at a speed of 400 rpm. Polyaluminum chloride (PAC), an alkali flocculant, and A-PAM (organic flocculant) were added, bentonite was optionally added as an additional additive, and they were then stirred for 15 minutes at a speed of 40 rpm. Thereafter, stirring was stopped and waited for about 5 minutes to allow the flocks to settle. The supernatant, approximately 3 cm below the liquid level, was collected using a pipette, and turbidity, COD, pH, and conductivity were measured, respectively. The results are shown in Table 1 below. Here, the test was carried out using a flocculation sedimentation machine Flocculator 2000. Turbidity was measured using a turbidity meter 2100Q from Hach, COD was measured according to method 8000 from Hach, and pH and conductivity were measured using an instrument HQ40d from Hach.

[0131] Test Ex.Polyaluminum chlorideAlkali flocculantAdditional additiveA-PAMTurbidity (NTU)COD (ppm)pHConductivity (ms / cm)NameAdded amount (ppm)NameAdded amount (ppm)NameAdded amount (ppm)NameAdded amount (ppm)A1Mill PAC217Alkali flocculant67--Mill APAM1.51965687.845.13A2Kemira PAC217Alkali flocculant67--K-120V1.51785677.885.12A3Kemira PAC217Alkali flocculant67Bentonite50K-120V1.51905657.95.10A4Kemira PAC217Alkali flocculant67Bentonite100K-120V1.51965687.925.08A5Kemira PAC217Alkali flocculant67Bentonite150K-120V1.51765537.935.06A6Kemira PAC217Alkali flocculant67Bentonite200K-120V1.51745697.935.04Test Examples B1 to B6

[0132] Tests were conducted using wastewater B generated from a paper mill. The tests were conducted in the same manner as in Test Examples A1 to A6, except that ground calcium carbonate was optionally added instead of bentonite as an additional additive. The results are shown in Table 2 below.

[0133] Test Ex.Polyaluminum chlorideAlkali flocculantAdditional additiveA-PAMTurbidity (NTU)COD (ppm)pHConductivity (ms / cm)NameAdded amount (ppm)NameAdded amount (ppm)NameAdded amount (ppm)NameAdded amount (ppm)B1Mill PAC217Alkali flocculant67--Mill APAM1.51794877.893.77B2Kemira PAC217Alkali flocculant67--K-120V1.51614797.833.75B3Kemira PAC217Alkali flocculant67Prefloc GCC50K-120V1.51624857.813.76B4Kemira PAC217Alkali flocculant67Prefloc GCC100K-120V1.51644727.793.75B5Kemira PAC217Alkali flocculant67Prefloc GCC250K-120V1.51574747.763.73B6Kemira PAC217Alkali flocculant67Prefloc GCC500K-120V1.51554717.773.69Test Examples C1 to C6

[0134] Tests were conducted using wastewater C generated from a paper mill. The tests were conducted in the same manner as in Test Examples A1 to A6, except that silica (FennoCat) was optionally added instead of bentonite as an additional additive. The results are shown in Table 3 below.

[0135] Test Ex.Polyaluminum chlorideAlkali flocculantAdditional additiveA-PAMTurbidity (NTU)COD (ppm)pHConductivity (ms / cm)NameAdded amount (ppm)NameAdded amount (ppm)NameAdded amount (ppm)NameAdded amount (ppm)C1Mill PAC217Alkali flocculant67--Mill APAM1.51674787.763.77C2Kemira PAC217Alkali flocculant67--K-120V1.51484547.773.76C3Kemira PAC217Alkali flocculant67FennoCat100K-120V1.590.84587.773.75C4Kemira PAC217Alkali flocculant67FennoCat250K-120V1.556.84377.763.75C5Kemira PAC217Alkali flocculant67FennoCat500K-120V1.536.64367.753.73C6Kemira PAC217Alkali flocculant67FennoCat1000K-120V1.531.04317.753.70

[0136] As shown in Table 1 above, when bentonite was added to wastewater as an additional additive in addition to polyaluminum chloride, which is a cationic inorganic coagulant, there was no significant improvement in turbidity, COD, and the like of wastewater. Referring to, which shows the test results according to Table 1 as a photograph, it was difficult to see that the coagulation or flocculation effect of organic substances in wastewater was improved despite the addition of the coagulant and additive.

[0137] As shown in Table 2 above, when ground calcium carbonate was added to wastewater as an additional additive in addition to polyaluminum chloride, which is a cationic inorganic coagulant, there was no significant effect although the turbidity of wastewater was slightly improved. Referring to, which shows the test results according to Table 2 as a photograph, it was difficult to see that the flocculation effect of organic substances in wastewater was improved despite the addition of the coagulant and additive.

[0138] In contrast, as shown in Table 3 above, when silica sol (FennoCat) was added to wastewater as an additional additive in addition to polyaluminum chloride, which is a cationic inorganic coagulant, the turbidity of wastewater was significantly improved, while COD in wastewater was significantly reduced as well. Specifically, referring to, which shows the test results according to Table 3 as a photograph, turbidity was improved in Test Example C3 in which 100 ppm of FennoCat was added as compared with Test Examples C1 and C2 in which FennoCat was not added. In Test Examples C4 to C6 in which 250 to 1,000 ppm of FennoCat was added, not only was the flocculation of organic substances facilitated to significantly improve the turbidity of the wastewater, but COD in the wastewater was also reduced.<Test Example D>Test Examples D1 to D6

[0139] Wastewater D generated from a paper mill was stirred for 20 seconds at a speed of 400 rpm. Polyaluminum chloride (PAC) and CPAM (organic flocculant) were added, and sodium aluminate and FennoCat were optionally added as an additional additive, and they were then stirred for 15 minutes at a speed of 40 rpm. Thereafter, stirring was stopped and waited for about 5 minutes to allow the flocks to settle. The supernatant, approximately 3 cm below the liquid level, was collected using a pipette, and pH, concentration, turbidity, and TOC were measured, respectively, and the change in TOC in the solution of each Test Example relative to TOC in wastewater D was calculated. The results are shown in Table 4 below. Here, the test was carried out using a flocculation sedimentation machine Flocculator 2000. Turbidity was measured using a turbidity meter 2100Q from Hach, and pH and conductivity were measured using an instrument HQ40d from Hach.

[0140] Wastewater DTest Ex. D1Test Ex. D2Test Ex. D3Test Ex. D4Test Ex. D5Test Ex. D6Polyaluminum chloride (ppm)-5005001000500700700Sodium aluminate (ppm)-300500100300300-FennoCat (ppm)----100300300CPAM (ppm)-454545454545pH6.997.127.506.847.017.006.73Conc. (%)4.414.444.404.534.484.424.47Turbidity (NTU)52.972.276.995.573.262.065.9TOC (mg)2,172.82,0902,087.62,2242,000.81,936.41,765.2Change in TOC (%)--3.81-3.922.36-7.92-10.88-18.76

[0141] As shown in Table 4 above, wastewater D used was wastewater with relatively low turbidity but high TOC. In Test Examples D1 to D3, in which polyaluminum chloride and sodium aluminate were added, there was no significant change in TOC of wastewater.

[0142] In contrast, in Test Examples D4 to D6, in which silica (FennoCat) was added together with polyaluminium chloride, a cationic inorganic coagulant, TOC decreased by about 7% to 18% even though the turbidity of the wastewater did not change significantly. Thus, it was confirmed that the cationic inorganic coagulant and silica adsorb dissolved organic substances having an impact on TOC from wastewater to form them into flocks, thereby producing the effect of reducing the dissolved organic substances in the liquid.<Test Example E>Test Examples E1 to E8

[0143] Wastewater E containing excessive wood powder was stirred for 20 seconds at a speed of 400 rpm. A QIP polymer, an emulsion polymer, was added, FennoCat was optionally added, and they were then stirred for 15 minutes at a speed of 40 rpm. Thereafter, stirring was stopped and waited for about 5 minutes to allow the flocks to settle. The supernatant, approximately 3 cm below the liquid level, was collected using a pipette, and the total content of nitrogen (N) was measured, and the change in the total content of nitrogen (N) in the solution of each Test Example relative to the total content of nitrogen in wastewater E was calculated. The results are shown in Table 5 below. Here, the test was carried out using a flocculation sedimentation machine Flocculator 2000. Turbidity was measured using a turbidity meter 2100Q from Hach, and the total content of N was measured according to method 10071 from Hach.

[0144] Wastewater ETest Ex. E1Test Ex. E2Test Ex. E3Test Ex. E4Test Ex. E5Test Ex. E6Test Ex. E7Test Ex. E8Added amount (%) of QIP-0.20.20.20.20.40.40.40.4Added amount (%) of FennoCat--0.250.51.0-0.250.51.01Turbidity (NTU)15525.910.36.666.3118.75.122.742.38Total N content (ppm)158149143130127143139127122Chang in N content--5.70-9.49-17.72-19.62-9.49-12.03-19.62-22.78

[0145] As shown in Table 5 above, wastewater E used was wastewater having not only high turbidity due to wood powder but also a high total content of nitrogen. In Test Examples E2 to E4 and E6 to E8 in which silica (FennoCat) was added, the effect of improving turbidity and reducing the total content of nitrogen was significant as compared with Test Examples E1 and E5 in which the emulsion polymer alone was added without adding silica (FennoCat). It was confirmed from the above that silica (FennoCat) can adsorb colloidal substances and / or dissolved impurities from wastewater.

[0146] In addition, referring to, which shows the solutions according to Wastewater E and Test Examples E5 and E8 under a microscope, much fewer particulates per unit area were present in the solution according to Test Example E8 in which silica (FennoCat) was added as compared with Test Example E5 in which the emulsion polymer alone was added. That is, it was confirmed that silica (FennoCat) adsorbs particulates from wastewater and causes them to flocculate together into flocks, thereby reducing particulates in the wastewater.<Test Example F>

[0147] Wastewater F containing excessive wood powder was stirred for 20 seconds at a speed of 400 rpm. A QIP polymer, an emulsion polymer, was added in various concentrations, FennoCat was optionally added, and they were then stirred for 15 minutes at a speed of 40 rpm. Thereafter, stirring was stopped and waited for about 5 minutes to allow the flocks to settle. The photograph taken is shown in.

[0148] Referring to, when a QIP polymer, an emulsion polymer, was added, clear precipitation separation was achieved as compared with when a QIP polymer was not added (wastewater F in). It was confirmed that clearer separation was achieved when FennoCat was added as compared with when a QIP polymer alone was added.

[0149] That is, it was confirmed that the addition of silica (FennoCat) not only has the effect of improving turbidity but also adsorbs particulates such as nitrogen in wastewater and causes them to flocculate together into flocks, thereby reducing particulates in the wastewater.<Example>

[0150] Example: Addition of polyaluminum chloride and silica (FennoCat)

[0151] Experiments were carried out in a wastewater treatment unit comprising a primary purifier, a biological treatment unit, a secondary purifier, and a tertiary treatment unit as main equipment.

[0152] As depicted in, silica sol (FennoCat) was added to wastewater before it was charged to the reactor so as to be charged to the reactor together with the wastewater. Polyaluminium chloride was added to the point where raw wastewater was charged to the reactor. A-PAM (organic flocculant) was added just before discharge from the reactor to the primary purifier.

[0153] On Day 1 of the experiments, the silica sol (FennoCat) was added at a concentration of 150 ppm relative to the total wastewater. Polyaluminium chloride (PAC) and A-PAM were added at concentrations of 700 ppm and 5 ppm, respectively, to conduct the treatment of wastewater.

[0154] On Day 3 of the experiments, the silica sol (FennoCat) was added at an increased concentration of 200 ppm relative to the total wastewater in order to increase the efficiency of turbidity improvement in the primary purifier. PAC and A-PAM were maintained at concentrations of 700 ppm and 5 ppm, respectively.

[0155] Upon completion of the experiments on Day 6, flock slurry was removed from the effluents from the first purifier, second purifier, and third treatment unit, respectively, to obtain liquids. Turbidity and COD were then measured for the liquids. The results are shown in Table 6 below.

[0156] Comparative Example: Addition of polyaluminum chloride and sodium aluminate

[0157] Experiments were carried out in the same manner as in the Example, except that the same amount of sodium aluminate was added in the same step instead of silica sol (FennoCat).

[0158] Upon completion of the experiments on Day 6, flock slurry was removed from the effluent wastewater from the first purifier, second purifier, and third treatment unit, respectively, to obtain liquids. Turbidity and COD were then measured for the liquids. The improvement rate of the turbidity and COD according to the Example relative to the turbidity and COD according to the Comparative Example was calculated and shown in Table 6 below.

[0159] Turbidity (NTU)COD (ppm)Type of wastewaterEffluent from the primary purifierEffluent from the secondary purifierEffluent from the tertiary treatment unitEffluent from the primary purifierEffluent from the secondary purifierEffluent from the tertiary treatment unitExample1217377328200160Comparative Example645030298144112Improvement rate (%)46.731.760.69.228.030.1

[0160] According to Table 6 above, in the Example, in which polyaluminum chloride as a cationic inorganic coagulant and silica (FennoCat) were added together, the turbidity of the effluent from the primary purifier was improved by about 47% relative to the Comparative Example, in which silica was not added. In addition, in the Example, the improvement in COD in the effluent from the primary purifier was about 9%, while the improvement in COD in the effluent from the secondary purifier upon the biological treatment step was as high as 28%. Thus, it was confirmed that the cationic inorganic coagulant and silica added in the process of the Example preemptively removed confounding substances that interfered with the biological treatment step from the wastewater, thereby maximizing the efficiency of the biological treatment step.

[0161] That is, as a cationic inorganic coagulant and silica are added to wastewater, they not only facilitate the coagulation and flocculation of suspended solids in the wastewater but also adsorb organic substances dissolved in the wastewater, thereby further enhancing the efficiency of wastewater treatment.

Claims

A method for treating wastewater, which comprises preparing wastewater; and adding a cationic inorganic coagulant and silica (SiO2) to the wastewater.The method for treating wastewater of claim 1, wherein the silica (SiO2) has an average particle diameter of 1 to 100 nm.The method for treating wastewater of claim 1, wherein at least a portion of the silica (SiO2) is added in the form of silica sol.The method for treating wastewater of claim 1, wherein the silica (SiO2) has an unmodified surface.The method for treating wastewater of claim 3, wherein the cationic inorganic coagulant and the silica sol are added at a weight ratio of 10:1 to 1:5.The method for treating wastewater of claim 3, wherein the silica sol is added to the wastewater at a concentration of 10 to 1,000 ppm.The method for treating wastewater of claim 1, wherein the cationic inorganic coagulant comprises an aluminum-based coagulant, an iron-based coagulant, or a combination thereof.The method for treating wastewater of claim 7, wherein the aluminum-based coagulant is at least one selected from the group consisting of aluminum sulfate and polyaluminium chloride, andthe iron-based coagulant is at least one selected from the group consisting of iron(I) sulfate, iron(II) sulfate, iron(III) sulfate, iron(I) chloride, iron(II) chloride, iron(III) chloride, and polyiron sulfate.The method for treating wastewater of claim 1, wherein the wastewater comprises wastewater from the pulp industry, wastewater from the paper industry, or a combination thereof.The method for treating wastewater of claim 1, wherein the step of adding the cationic inorganic coagulant and silica (SiO2) to the wastewater is a step in which the cationic inorganic coagulant, silica, and a supplement are added simultaneously or sequentially to the wastewater.The method for treating wastewater of claim 1, which further comprises, after the addition of the cationic inorganic coagulant and the silica (SiO2) to the wastewater, removing flocks from the wastewater.The method for treating wastewater of claim 1, which further comprises, after the addition of the cationic inorganic coagulant and the silica (SiO2) to the wastewater, biological treatment to remove dissolved organic substances from the wastewater.

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