Method for promoting biofilm formation on carrier, promoter for biofilm formation on carrier, and wastewater treatment apparatus

Abstract

To provide a method for forming a biofilm on a carrier in an early stage in wastewater treatment adopting biological treatment, an additive used for the method, and a wastewater treatment apparatus SOLUTION: In the method for promoting the formation of the biofilm on the carrier, a surfactant having a low HLB value is added to a reaction tank of a fixed bed or a fluidized bed having the carrier at least the surface part of which is hydrophobic or the upstream position of the reaction tank in the place of biological treatment in wastewater treatment for biologically treating wastewater. According to this, the surfactant having a low HLB value added to the wastewater in the reaction layer of the fixed bed or the fluidized bed having the carrier or at the upstream position thereof covers the surface of the carrier, whereby the formation of a conditioning film on the surface of the carrier is promoted, and as a result, a biofilm can be formed on the carrier at an early stage.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for promoting biofilm formation on a carrier, a promoter for biofilm formation on a carrier, and a wastewater treatment device, and in particular to a method for promoting biofilm formation on a carrier that is added to a reaction tank or an upstream position in wastewater treatment for biologically treating wastewater, the promoter for biofilm formation on this carrier, and the wastewater treatment device. [Background technology]

[0002] In wastewater treatment, biological treatment using a biological treatment tank is known as an economically advantageous wastewater treatment method because it does not require special facilities or complex equipment and the treatment is carried out primarily by microorganisms, compared to physical and chemical wastewater treatment methods.

[0003] One of the most common biological treatment methods is the fluidized bed method, which is a type of biofilm treatment method. The fluidized bed biological treatment system has a fluidized bed reactor in its equipment configuration, and carriers (also called fillers) that serve as habitats for microorganisms are added to this fluidized bed reactor. In the fluidized bed reactor, air is blown in by aeration to activate the microorganisms living on the carriers, which then decompose and assimilate the organic matter contained in the inflowing wastewater.

[0004] Organic matter contained in wastewater includes starch, protein, and fats and oils, and the mechanism for their removal depends heavily on the activity of microorganisms (especially aerobic bacteria) living in activated sludge. Microorganisms in activated sludge secrete a wide variety of enzymes, such as starch-degrading enzymes (amylase), protein-degrading enzymes (protease), and fat-degrading enzymes (lipase), to break down the organic matter. Starch, a typical organic matter, is broken down into monosaccharides (glucose), proteins into amino acids, and fats and oils into glycerin and fatty acids.

[0005] The decomposition products of organic matter, such as monosaccharides, amino acids, glycerin, and fatty acids, are relatively low molecular weight and are quickly taken up by microorganisms to serve as an energy source for the bacterial body. The microorganisms that grow using these energy sources are then eaten by protozoans such as Vorticella that live in activated sludge. These microorganisms and protozoans are then eaten by metazoans such as Bdelloid rotifers that also live in activated sludge. In other words, organic matter becomes food for microorganisms, microorganisms become food for protozoans, and microorganisms and protozoans become food for metazoans. Therefore, a unique ecological pyramid is constructed within activated sludge, and it is known that the food chain continues to progress.

[0006] As mentioned above, it is the enzymes secreted by microorganisms that break down organic matter in wastewater into smaller molecules, and the microorganisms then consume the decomposition products broken down into smaller molecules by the enzymes. In other words, it is important to attach a large number of microorganisms to the carrier in a fluidized bed reactor.

[0007] The state in which microorganisms and microbial products adhere to a carrier is called a biofilm. The process of biofilm formation is as follows: (i) Formation of a conditioning film by the attachment of organic matter to the support surface; (ii) microbial adhesion to the conditioning film; (iii) production of extracellular polymers by attached microorganisms, and (iv) Biofilm growth, including other microorganisms It is said to consist of:

[0008] Furthermore, these formation processes are known to take a long time because they depend on the rate at which organic matter adheres and the rate at which microorganisms grow.

[0009] As mentioned above, it is important to quickly attach a large number of microorganisms to the carriers to form a biofilm, for example, when starting up a new fluidized bed reactor (new installation) or replenishing the carriers. In the biofilm formation process, the rate-limiting factor is thought to be the adhesion of organic matter to the carrier surface (i), i.e., the slow formation of the conditioning film.

[0010] Patent Document 1 discloses a method for promoting biofilm formation by spraying an environmental pollution purification aid made by mixing bromelain enzyme extracted from fruit, black vinegar mash, water, yeast of the genus Saccharomyces, vitamin B, and glucose into contaminated water or soil to multiply extracellular polymers produced by microorganisms.

[0011] According to the technique of Patent Document 1, by promoting the formation of a biofilm, microorganisms in the biofilm can be efficiently cultivated and multiplied, and the decomposition of pollutants can be promoted.

[0012] Patent Document 2 describes a method for removing nitrate nitrogen from the water being treated by adding sludge, which is a naturally occurring organic matter, as well as higher fatty acids such as stearic acid to the water being treated, to promote anaerobic conversion of the water to be treated, and forming a biofilm at the interface between the higher fatty acids and the water, thereby creating anaerobic conditions with little oxygen within the biofilm, and promoting and activating the cultivation of denitrifying bacteria with the phosphorus contained in the sludge.

[0013] According to the technique of Patent Document 2, nitrogen and phosphorus can be effectively removed, particularly from closed water areas, and the amount of higher fatty acids added can be reduced compared to conventional methods. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2023-128215 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-142810 Summary of the Invention [Problem to be solved by the invention]

[0015] However, the method of Patent Document 1 improves the productivity of extracellular polymers by attached microorganisms (iii) by supplying raw materials that become the material for biofilms, but does not promote the formation of conditioning films (i).Furthermore, there is no description of biofilm treatment methods or surfactants.

[0016] Furthermore, the higher fatty acids added by the method of Patent Document 2 are classified as normal hexane extractable substances, which is one type of wastewater standard, and are also difficult to decompose, so adding higher fatty acids is an extremely risky act due to the impact on the quality of the treated water. Therefore, adding higher fatty acids to wastewater treatment would not be adopted by a person skilled in the art.

[0017] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a method for quickly forming a biofilm on a carrier in wastewater treatment that employs biological treatment, an additive to be used in the method, and a wastewater treatment device. [Means for solving the problem]

[0018] The present inventors have conducted extensive research to achieve the above object, and as a result, have found that the combination of a hydrophobic carrier and a surfactant with a low HLB value promotes the formation of a conditioning film due to the adhesion of organic matter to the carrier surface, thereby accelerating the formation of a biofilm on the carrier, thereby completing the present invention.

[0019] That is, it has been found that the above-mentioned object can be achieved by a method for promoting the formation of a biofilm on a carrier in wastewater treatment, which is characterized by adding a surfactant with a low HLB (Hydrophile Lipophile Balance) value to a fixed-bed or fluidized-bed reaction tank or a position upstream of the reaction tank, which is a site of biological treatment in wastewater treatment where wastewater is biologically treated and which has a carrier at least the surface of which is hydrophobic.

[0020] A preferred embodiment of the method for promoting biofilm formation on a carrier according to the present invention is as follows. (1) The surfactant has a low HLB value of 1 or more and 6 or less. (2) The surfactant is added in an amount of 0.1 to 20% (w / w) based on the weight of the carrier. (3) At least the surface portion of the hydrophobic carrier is made of plastic.

[0021] The above object can also be achieved by a biofilm formation promoter on a carrier, which is added to a fixed-bed or fluidized-bed reaction tank or an upstream position thereof, at least the surface of which is hydrophobic, in a wastewater treatment site for biologically treating wastewater, and which is characterized by being a surfactant with a low HLB (Hydrophile Lipophile Balance) value.

[0022] Furthermore, the above object is to provide a wastewater treatment device that biologically treats wastewater, This can also be achieved by a wastewater treatment device comprising: a wastewater tank into which the wastewater is introduced; a fixed-bed or fluidized-bed reaction tank having a carrier whose surface is hydrophobic and which serves as a site for the biological treatment; and an addition means for adding a surfactant with a low HLB value at an addition rate of 0.1 to 20% (w / w) relative to the weight of the carrier to the fixed-bed or fluidized-bed reaction tank or to a position upstream of the fixed-bed or fluidized-bed reaction tank. [Effects of the Invention]

[0023] According to the method for promoting biofilm formation on a carrier, the promoter for biofilm formation on a carrier, and the wastewater treatment device of the present invention, a surfactant with a low HLB value added to the wastewater in the reaction layer of a fixed bed or fluidized bed having a carrier or at a position upstream thereof covers the surface of the carrier, promoting the formation of a conditioning film on the surface of the carrier, and as a result, allowing a biofilm to form on the carrier at an early stage. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram illustrating a wastewater treatment device 10 according to one embodiment of the present invention. [Figure 2]1 is a micrograph of the surface of the carrier 7 days after the start of aeration in a test plot in which the surfactant addition rate was 0% (w / w) in an example. [Figure 3] 1 is a micrograph of the surface of a carrier 7 days after the start of aeration in a test plot in which the surfactant addition rate was 1% (w / w) in an example. DETAILED DESCRIPTION OF THE INVENTION

[0025] <Method for promoting biofilm formation on a carrier> The method of promoting biofilm formation on a carrier of the present invention is characterized by adding a surfactant with a low HLB value to a fixed-bed or fluidized-bed reactor or an upstream position thereof, which is a biological treatment site in wastewater treatment where wastewater is biologically treated and which has a carrier whose surface portion is at least hydrophobic.

[0026] The wastewater (raw water) to be treated contains at least organic matter, and may be, for example, but not limited to, wastewater from various manufacturing factories such as food manufacturing factories, chemical manufacturing factories, equipment manufacturing factories, and pharmaceutical manufacturing factories, or wastewater from slaughterhouses, water purification plants, sewage treatment plants, human waste treatment plants, farms, etc.

[0027] The wastewater treatment method for biologically treating wastewater, which can be used with the method of the present invention, is not particularly limited as long as it is a biofilm treatment method using a carrier. Biofilm methods such as an aerobic biofilm method, a fixed-bed submerged filter method, a fluidized-bed submerged filter method, a fluidized carrier method, and a rotating disk method can be used as appropriate, as well as anaerobic treatment tanks, methane fermentation tanks, nitrification / denitrification tanks, and anammox tanks.

[0028] In the present invention, a carrier having at least a hydrophobic surface is a carrier having at least a surface made of plastic, and from the viewpoint of cost, a carrier made entirely of plastic, not just a surface, is preferred. Note that a carrier made entirely of plastic, not just a surface, also includes a carrier whose surface is further coated with another resin or the like.

[0029] In the present invention, plastic refers to synthetic resin and / or natural resin, and in the present invention, the plastic is preferably a synthetic resin. Examples of synthetic resins include polyethylene (including high density polyethylene (HDPE) and low density polyethylene (LDPE)), polypropylene, polystyrene, polyurethane, polyvinyl alcohol, and polyethylene glycol, regardless of whether they are thermoplastic or thermosetting. Plastics may be hard plastics or soft plastics like sponges.

[0030] Natural resins include natural rubber.

[0031] Furthermore, these raw materials may be processed by ultraviolet irradiation or the like.

[0032] In the present invention, a lipophilic surfactant with a low HLB value is used. HLB (Hydrophile Lipophile Balance: a value that represents the balance between the hydrophilic and hydrophobic properties of an emulsifier) ​​is an index that indicates the balance between the hydrophilic and hydrophobic properties of a surfactant, and the smaller the HLB value, the less soluble it is in water.

[0033] Generally, the HLB value is set at 7 as the reference value, with values ​​of 7 or higher indicating hydrophilicity and values ​​of 7 or lower indicating lipophilicity, but based on the examples described below, in the present invention, a surfactant with a low HLB value refers to one with an HLB value of 9 or lower. The surfactant of the present invention preferably has a low HLB value of 1 or higher and 6 or lower, and particularly preferably 1 or higher and 3 or lower.

[0034] Examples of surfactants having a low HLB value according to the present invention include glycerin fatty acid esters, sorbitan fatty acid esters, propylene glycol fatty acid esters, sucrose fatty acid esters, lecithin, and enzymatically decomposed lecithin.

[0035] Examples of glycerin fatty acid esters include glycerin fatty acid esters (monoglycerides), organic acid monoglycerides, polyglycerin fatty acid esters, polyglycerin condensed ricinoleic acid esters, etc. Note that these are not limited to monoglycerides, but also include diglycerides.

[0036] Examples of sorbitan fatty acid esters include sorbitan monostearate, sorbitan monooleate, and sorbitan monolaurate, and they may be diesters or triesters.

[0037] An example of the propylene glycol fatty acid ester is propylene glycol monostearate.

[0038] Examples of sucrose fatty acid esters include sucrose stearate, sucrose palmitate, sucrose myristate, sucrose oleate, and sucrose behenate, and include not only monoesters but also mixtures of monoesters with diesters, triesters, and polyesters.

[0039] Examples of lecithin and enzymatically decomposed lecithin include soybean lecithin, egg yolk lecithin, and enzymatically decomposed lecithins obtained by enzymatically decomposing these.

[0040] Commercially available surfactants with a low HLB value can be used. For example, surfactants with an HLB value of 1 to 3 include condensed polyglyceryl ricinoleate (Sunsoft® No. 818DG, manufactured by Taiyo Kagaku Co., Ltd., HLB = 2), polyglyceryl-6 polyricinoleate (Sunsoft® No. 818R, manufactured by Taiyo Kagaku Co., Ltd., HLB = 3), sucrose stearate (S-270, manufactured by Mitsubishi Chemical Corporation, HLB = approximately 2), glycerin monodibehenate (Poem® B-200, manufactured by Riken Vitamin Co., Ltd., HLB = 2.8), and sorbitan tribehenate (Rikemal® B-150, manufactured by Riken Vitamin Co., Ltd., HLB = 2.5).

[0041] Furthermore, the surfactant with a low HLB value of the present invention can be used as a food additive grade from the viewpoint of safety management for facilities and users. Being food additive grade makes it easier to obtain approval for the introduction of the agent into wastewater treatment facilities such as food factories, which have strict hygiene management.

[0042] Furthermore, chemical substances that fall under the category of food additives are guaranteed to be safe for humans and biodegradable in the body to a certain extent, so they are expected to have low toxicity to the microorganisms that are used in biofilm treatment methods, or to be highly biodegradable by microorganisms. Surfactants generally used in food are also called emulsifiers.

[0043] As described above, in the method of the present invention, a surfactant is added to a fixed-bed or fluidized-bed reaction vessel having a carrier with at least a hydrophobic surface, or to a position upstream thereof. Here, the upstream position includes an adjustment vessel (see FIG. 1 described later) and a pipe connecting the adjustment vessel and the reaction vessel.

[0044] Among these, it is preferable to add the surfactant in the reaction tank from the viewpoint of dispersing the surfactant to some extent in the wastewater before contact with the carrier and from the viewpoint of preventing the surfactant from adhering to the upstream position.

[0045] Furthermore, the order of adding the carrier to the reaction vessel and the low HLB surfactant is not particularly limited. For example, the carrier may be added first, and then the low HLB surfactant may be added directly on top of the carrier. Alternatively, the surfactant and carrier may be sandwiched in the order of adding half the carrier, adding half the surfactant, adding the remaining half of the carrier, and adding the remaining half of the surfactant, or the low HLB surfactant may be added first, floating it on the interface of the fluidized bed reaction vessel (see Figure 1), and then adding the carrier and blending it.

[0046] Furthermore, if the carrier has a low specific gravity and poor sedimentation properties, it is possible to first add the carrier and let it soak in water for several hours to several days to allow it to settle to a certain extent below the interface, and then add a surfactant with a low HLB value.

[0047] The timing of adding the surfactant with a low HLB value in the present invention is not particularly limited, and the surfactant may be added when adding carriers to a newly installed tank, or when replenishing carriers in an existing tank, or when carrier sludge is peeled off from an existing tank.

[0048] The addition rate of the surfactant with a low HLB value of the present invention is preferably within a range that does not affect the COD of the treated water. COD is determined by oxidizing oxidizable substances in water with an oxidizing agent and calculating the amount of oxygen required for oxidation from the amount of oxidizing agent used, and is used as an index to measure pollution by organic matter in water. In this specification, COD is determined by using potassium permanganate as an oxidizing agent (COD Mn )

[0049] By adding the low HLB surfactant of the present invention, most of it adheres to the plastic carrier and becomes part of the conditioning film, but some remains, peels off, dissolves, and is transferred to the COD of the treated water. The surfactant addition rate may be any, but from the viewpoint of promoting biofilm formation, it is 0.1% (w / w) or more based on the weight of the carrier. Furthermore, from the viewpoint of suppressing an increase in the COD of the treated water, the surfactant addition rate is 0.1 to 50% (w / w) based on the weight of the carrier, preferably 0.1 to 20% (w / w), and particularly preferably 0.1 to 10% (w / w).

[0050] That is, at sites with strict effluent standards, the addition rate can be set low at 0.1% to take into account the possibility of an increase in COD of the treated water, while at sites with relatively looser regulations, the addition rate can be increased to 10-20% (w / w).Adjustments can be made as appropriate depending on the site.

[0051] Generally, plastic carriers have poor affinity (compatibility) with water. For example, in the case of a fluidized bed system, the carrier tends to float to the interface immediately after addition, then gradually sinks below the interface over several days, coming into contact with organic matter and initiating the formation of a biofilm. By adding the low-HLB surfactant proposed in this invention, the surfactant firmly adheres to the carrier, increasing its specific gravity, allowing a certain amount of the carrier to sink below the interface immediately after addition, thereby shortening the initial contact period with organic matter. While the primary purpose of adding a low-HLB surfactant is to form a conditioning film, the increased specific gravity of the carrier also contributes to a certain extent to promoting biofilm formation.

[0052] The addition of the surfactant with a low HLB value used in the present invention makes the carrier surface viscous, which not only makes it easier for microorganisms to adhere, but also allows the microorganisms to further grow using the surfactant as a nutrient source, enabling them to rapidly form a biofilm on the carrier surface. The attached microorganisms are not limited to specific microorganisms, but also promote the formation of biofilms of many microorganisms that adhere to plastic carriers in biofilm treatment methods using plastic carriers.

[0053] For example, any microorganism that is expected to adhere to a plastic carrier, such as microorganisms of the genus Bacillus used in aerobic treatment, nitrifying bacteria with nitrification activity, microorganisms of the genus Pseudomonas responsible for denitrification, anammox responsible for anaerobic ammonium oxidation, methanogens responsible for methane fermentation, and microorganisms of the genus Thiobacillus used in biological deodorization, can be appropriately attached.

[0054] Furthermore, the substances or organisms that can adhere are not limited to microorganisms, but can be of any type that contributes to biofilm formation, such as sludge such as seed sludge, organic or inorganic matter in raw water, or protozoa and metazoa that appear in the later stages of biofilm formation.

[0055] Generally, surfactants have both hydrophilic and hydrophobic groups. It is believed that the hydrophobic groups of the low-HLB surfactants used in this invention primarily adhere to the plastic carrier, leaving the hydrophilic groups exposed to the aqueous system. In other words, when a plastic carrier is used alone, only the plastic portion (the hydrophobic portion) is exposed. However, by adding this agent, part of the carrier surface becomes hydrophilic due to the hydrophilic groups, making it possible for various microorganisms and organic matter to adhere to the carrier.

[0056] The surfactant with a low HLB value used in the present invention is not limited to water treatment processes such as biofilm treatment methods, etc. For example, it can be used appropriately in any field where promotion of biofilm formation is expected, such as addition as a bioremediation material for the purpose of removing persistent substances in soil, application to ship hulls to form biofilms on the hulls and suppress barnacle adhesion, and formulation components for improving the intestinal environment to promote the formation of biofilms consisting of useful microorganisms such as lactic acid bacteria.

[0057] Therefore, according to the method of promoting biofilm formation on a carrier of the present invention, a surfactant with a low HLB value added to the wastewater in the reaction layer of a fixed bed or fluidized bed containing the carrier or at a position upstream thereof covers the surface of the carrier, thereby promoting the formation of a conditioning film on the surface of the carrier, and as a result, allowing a biofilm to form on the carrier at an early stage.

[0058] <Biofilm formation promoter on carrier> The biofilm formation promoter on a carrier of the present invention is characterized in that it is added to a fixed-bed or fluidized-bed reaction tank or an upstream position thereof, at a site of biological treatment in wastewater treatment where wastewater is biologically treated, and is a surfactant with a low HLB value, with at least the surface portion having a hydrophobic carrier.

[0059] Since wastewater, wastewater treatment, carriers having at least a hydrophobic surface, fixed-bed or fluidized-bed reactors or their upstream positions, and surfactants with low HLB values ​​have already been explained, their explanation will be omitted.

[0060] The biofilm formation promoter on the carrier of the present invention can contain, in addition to a surfactant with a low HLB value, a substance containing microorganisms, a substance that serves as a nutrient source (BOD) for microorganisms, a substance that promotes the activity of microorganisms, a substance that promotes floc formation or biofilm formation, etc.

[0061] For example, substances containing microorganisms include microbial preparations containing beneficial microorganisms such as Bacillus bacteria, and activated sludge (seed sludge) collected from other water treatment sites; substances that serve as nutrients (BOD) for microorganisms include raw industrial wastewater, blackstrap molasses, liquid sugar, amino acid solutions, and amino acid waste liquid; substances that promote microbial activity include Al, Ca, Cl, Co, Cu, Fe, Mg, Mn, Mo, N, Na, Ni, P, S, Se, Zn, and their salts; and substances that promote floc formation and biofilm formation include inorganic coagulants, polymer coagulants, and quorum-sensing substances (e.g., acyl homoserine lactone).

[0062] The agent for promoting biofilm formation on a carrier of the present invention may be added to a biofilm treatment method in the form in which it is produced, or may be mixed with an appropriate solvent before being added.

[0063] It is also possible to prepare a mixture in advance by mixing the biofilm formation promoter of the present invention with a carrier having at least a hydrophobic surface. In this case, it is preferable to dilute the biofilm formation promoter with an appropriate solvent before mixing with the carrier, from the viewpoint of evenly coating the carrier surface with the surfactant.

[0064] <Wastewater treatment equipment> 1 is a schematic diagram illustrating a wastewater treatment device 10 according to one embodiment of the present invention. As shown in the figure, the wastewater treatment device 10 is a device that biologically treats wastewater, and includes an adjustment tank (wastewater tank) 12, a reaction tank 14, and an addition means 20.

[0065] The wastewater and wastewater treatment have already been described, and therefore a detailed description thereof will be omitted here.

[0066] The adjustment tank (wastewater tank) 12 is a raw water tank into which wastewater (raw water) is introduced. The size of the wastewater tank 12 can be determined appropriately depending on the amount of wastewater treatment per day by the wastewater treatment device and the amount of wastewater generated.

[0067] For example, if 10 kg of wastewater is generated per day and the wastewater treatment device 10 treats 10 kg of wastewater per day, then if the storage capacity of the wastewater tank 12 is 10 kg of wastewater, the device must be able to handle wastewater with different concentrations every day. However, if the storage capacity of the wastewater tank 12 is set to, for example, 100 kg of wastewater, it will be able to store 10 days' worth of wastewater, adjusting for changes in the wastewater concentration over the 10 days and enabling stable treatment every time.

[0068] The adjustment tank (drainage tank) 12 may be used to dilute the wastewater, adjust the pH, homogenize the wastewater by stirring, etc. In this case, the adjustment tank (drainage tank) 12 has an agitator and is also provided with a means for adding a pH adjuster such as an acid or alkali, and a means for adding dilution water, as appropriate.

[0069] Furthermore, the adjustment tank (drainage tank) 12 may be configured as a plurality of tanks, or may be configured as a raw water tank and an adjustment tank separated from each other.

[0070] The reaction tank 14 is a fixed-bed or fluidized-bed reaction tank having a hydrophobic carrier at least on the surface thereof, and serves as the site of the biological treatment. In this embodiment, since the aerobic biofilm method is employed, a fluidized-bed reaction tank 14-1 is disposed on the upstream side of the reaction tank 14, and a flocculation reaction tank 14-2 is disposed on the downstream side. The carrier has already been described, and its description will be omitted here.

[0071] The fluidized bed reactor 14-1 has carriers with microorganisms attached to the surface and a biofilm formed, and decomposition of organic matter in the wastewater is carried out in an aerobic environment through aeration. The coagulation reactor 14-2 is a tank that performs the coagulation reaction as a preliminary step to the downstream coagulation and sedimentation treatment. After the organic matter is decomposed in the fluidized bed reactor 14-1, a coagulant is added in the coagulation reactor 14-2, promoting the formation of flocs. The coagulant can be any combination of inorganic coagulants and polymer coagulants. The liquid after the coagulation reaction is sent to the downstream coagulation and sedimentation tank 16.

[0072] In the coagulation settling tank 16, the liquid sent from the coagulation reaction tank 14-2 is left to stand and undergoes solid-liquid separation. The sludge that settles at the bottom is sent to the fluidized bed reaction tank 14-1 or is dehydrated and then discarded. The supernatant becomes treated water 2.

[0073] The addition means 20 is an addition means for adding a surfactant with a low HLB value at an addition rate of 0.1 to 20% (w / w) based on the weight of the carrier to the fixed-bed or fluidized-bed reaction vessel 14 or a position upstream thereof. Note that the low HLB value surfactant has already been explained, so its explanation will be omitted here.

[0074] The reaction tank 14 or a position upstream thereof may be any position in the adjustment tank (drainage tank) 12, the reaction tank 14, or the piping between them. In this embodiment, examples include a position upstream of the adjustment tank (drainage tank) 12 (arrow A in FIG. 1), a position in the middle of the adjustment tank (drainage tank) 12 (arrow B in FIG. 1), a position in the rear of the adjustment tank (drainage tank) 12 (arrow C in FIG. 1), a position upstream of the fluidized-bed reaction tank 14-1 (arrow D in FIG. 1), a position in the middle of the fluidized-bed reaction tank 14-1 (arrow E in FIG. 1), and a position in the rear of the fluidized-bed reaction tank 14-1 (arrow F in FIG. 1).

[0075] The surfactant with a low HLB value may be added at one or more of the locations indicated by arrows A to F in FIG. 1 . However, if the surfactant with a low HLB value is added at the locations indicated by arrows A, B, or C in the adjustment tank (drainage tank) 12, which is the tank before the fluidized-bed reactor 14-1, which is the tank to which the carrier is added, the surfactant may adhere to the wall or piping of the adjustment tank (drainage tank) 12. Therefore, it is preferable to add the surfactant directly to the fluidized-bed reactor 14-1 at the locations indicated by arrows D, E, or F.

[0076] The adding means 20 is, for example, a chemical injection pump. The adding method may be a single addition, a plurality of intermittent additions, or a continuous addition.

[0077] Furthermore, although the wastewater treatment device 10 according to the above embodiment is a wastewater treatment device used in the aerobic biofilm method, the wastewater treatment device of the present invention is not limited to a wastewater treatment device used in the aerobic biofilm method.

[0078] For example, the wastewater treatment device of the present invention may be configured as a wastewater treatment device having an anaerobic treatment tank or a wastewater treatment device having a methane fermentation tank. In this case, for example, the reaction tank 16 in Fig. 1 becomes an anaerobic reaction tank, and the coagulation reaction tank is not required.

[0079] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. [Example]

[0080] 1) Test to confirm adhesion of surfactant to carrier A test was conducted to examine the adhesion of surfactants with various HLB values ​​to a plastic (polyethylene) carrier (BIO WHEEL (registered trademark), manufactured by Mizun Engineering Co., Ltd.) (hereinafter referred to as the carrier). Note that the same carrier was used in all of the examples.

[0081] The surfactant used was an emulsifier used in food, taking into consideration user safety. 200 ml of tap water was placed in a 500 ml Erlenmeyer flask, and one carrier and surfactant were added at 10% (w / w) per carrier weight. Since the carrier weight is approximately 0.6 g per carrier, if the specific gravity of the surfactant is 1, a 10% (w / w) addition would be 60 mg, or 60 μl, so 60 μl was added directly using a syringe.

[0082] As a control, sodium alginate, a type of water-soluble viscous substance, was also tested. The concentration of sodium alginate added was the same as that of the surfactant.

[0083] The surfactant test group and the sodium alginate control group were then rotary shaken overnight at 150 rpm and room temperature using a medium-sized shaker (Bioshaker (registered trademark) BR-40LF, manufactured by Taitec Co., Ltd.), after which the carriers were removed and it was confirmed whether the drug adhesion was maintained.

[0084] The confirmation method was as follows. That is, in addition to visual observation, because all medications were viscous, the spoon was turned upside down and pressed against the surface of the carrier, and then the spoon was moved upward. At this time, if the carrier adhered to the spoon due to its viscosity and the medication rose up together with the spoon, this was considered to be "adhered," and adhesion was evaluated on a four-point scale (◎: firmly adhered, ○: somewhat adhered, △ slightly adhered, ×: not adhered at all).

[0085] The test results are shown in Table 1.

[0086] [Table 1]

[0087] As shown in Table 1, it was found that there is a correlation between the HLB value of a surfactant and its adhesion to a medicine spoon. The smaller the HLB value (i.e., the more hydrophobic the surfactant), the easier it is to adhere to the carrier. Conversely, the larger the HLB value (i.e., the more hydrophilic the surfactant) or sodium alginate, the more likely it is to elute into the aqueous system and adhere to the carrier less easily. In other words, surfactants that can adhere to the carrier and act as a conditioning film have an HLB value of 1 to 9, preferably an HLB value of 1 to 6, and more preferably an HLB value of 1 to 3.

[0088] 2) Confirmation test of the effect of adding surfactants on COD of treated water The impact on COD of treated water was investigated using a product (Sunsoft (registered trademark) No. 818DG, Taiyo Kagaku Co., Ltd.) of condensed polyglyceryl ricinoleate, which had the highest evaluation of adhesion to the carrier in the above 1) surfactant carrier adhesion confirmation test, and which has an HLB of 2.

[0089] The test was conducted under the same conditions as in 1) Test to confirm the adhesion of surfactants to carriers, except that the addition rate of condensed polyglyceryl ricinoleate was 0 (no addition), 0.1, 1, 10, 20, 50, and 100% (w / w) per carrier weight in each test group. Therefore, the water initially poured into the Erlenmeyer flask was tap water.

[0090] After rotary shaking at 150 rpm and room temperature overnight, the COD of the supernatant was measured as the COD of the treated water. COD measurements were performed using the potassium permanganate method specified in JIS K 0102, "Testing Methods for Industrial Wastewater." Since a lower COD of the treated water is preferable, it was evaluated using a four-point scale (◎: ≦9.9 mg / L, ○: 10-19.9 mg / L, △: 20-49.9 mg / L, ×: ≧50 mg / L). The results are shown in Table 2.

[0091] [Table 2]

[0092] As shown in Table 2, when the additive rate of condensed polyglyceryl ricinoleate (surfactant) was in the range of 0.1 to 20% (w / w), the COD of the treated water was ≦20 mg and there was not much surfactant leakage, but as the additive rate increased, peeling from the carrier became severe and the COD of the treated water tended to worsen. From these results, it became clear that the additive rate of the agent is preferably 0.1 to 20% (w / w), and more preferably 0.1 to 10% (w / w).

[0093] 3) Evaluation test of the biofilm formation promotion effect of surfactants using simulated wastewater The purpose of adding a surfactant is to form a conditioning film, i.e., to adhere organic matter to the carrier in the early stages of biofilm formation. Therefore, we considered that even a low surfactant addition rate would promote biofilm formation compared to no surfactant addition. Therefore, we evaluated the biofilm formation promotion effect of a low surfactant addition rate.

[0094] One liter of simulated wastewater (0.4 g / L glucose, 0.4 g / L peptone, 0.03 g / L potassium dihydrogen phosphate, 42 g / L seed sludge, pH 7.0-7.5, made up to 1 liter with tap water) was poured into a 2-liter glass measuring cylinder. The MLSS of the seed sludge was 12,000 mg / L, so the MLSS of the simulated wastewater was approximately 500 mg / L. MLSS stands for Mixed Liquor Suspended Solids and refers to the suspended solids in the sludge mixed liquor in the aeration tank during activated sludge treatment. It is expressed in mg / L.

[0095] The carrier was added to the simulated wastewater at a loading rate of 30% (unit: w / w, volume 300 ml, weight approximately 42 g). The surfactant was added at 0 (no addition), 0.1, 1, or 10% (w / w). To suppress rapid foaming, three drops of an antifoaming agent (Awazeron (registered trademark) P-520, manufactured by Suing Co., Ltd.) diluted 10 times with pure water were added to each test area, and the mixture was constantly aerated at room temperature using an air stone.

[0096] Seven days after the start of aeration, the carriers were removed, and the attached biofilm was removed in pure water using a brush. The SS of the suspension after removal was calculated to measure the amount of biofilm attached per carrier (mg / carrier).

[0097] SS is a general term for insoluble substances suspended in water with particle diameters of 2 mm or less, and is expressed as a weight concentration (mg / L). In this example, SS was measured using the glass fiber filter paper method. In this method, a sample is suction-filtered through a glass fiber filter paper with a pore size of 1 μm, and the residue is dried at 105 to 110°C for 2 hours, after which the weight of the residue is measured.

[0098] Although it is assumed that some surfactant remains in the biofilm, the white mass characteristic of surfactants was not observed, and most of the deposits showed the brown to black color characteristic of biofilms, so all of the deposits were considered to be biofilm. Test plots that showed a significant amount of biofilm adhesion compared to the untreated control were considered to have an effect of promoting biofilm formation, and the amount of biofilm adhesion per carrier was evaluated using a two-point scale (×: <10 mg / carrier, ○: ≦10 mg / carrier). The results are shown in Table 3.

[0099] [Table 3]

[0100] As shown in Table 3, significant biofilm adhesion was observed at addition rates of 0.1% (w / w) or higher compared to 0% (w / w). Figure 2 shows a micrograph of the carrier surface in the test area with a 0% (w / w) addition rate, 7 days after the start of aeration, and Figure 3 shows a micrograph of the carrier surface in the test area with a 1% (w / w) addition rate, 7 days after the start of aeration. Observations were made at 20x magnification using a microscope equipped with a vibration-resistant, high-magnification observation system VH-S5 and a low-magnification zoom lens VH-Z05 (Keyence Corporation).

[0101] A significant amount of biofilm formation can be seen on the surface of the carrier in the test area with an addition rate of 1% (w / w) in Figure 3 compared to the surface of the carrier in the test area with an addition rate of 0% (w / w) in Figure 2. Although not shown, the same tendency was observed in the carriers in the test areas with addition rates of 0.1 and 10% (w / w).

[0102] Therefore, it was determined that the surfactant of the present invention has a significant effect of promoting biofilm formation even at low addition rates, and considering the effect on treated water COD in the confirmation test of the effect of surfactant addition on treated water COD above (2), it was revealed that the surfactant addition rate is preferably 0.1 to 20% (w / w), and more preferably 0.1 to 10% (w / w). [Explanation of symbols]

[0103] 10 Wastewater treatment equipment 12 Adjustment tank (drainage tank) 14 Reactor 20 Means of addition

Claims

1. A method for promoting biofilm formation on a carrier in wastewater treatment, which biologically treats wastewater, is characterized by adding a surfactant with a low HLB (Hydrophile Lipophile Balance) value to a fixed-bed or fluidized-bed reaction tank or an upstream position of the fixed-bed or fluidized-bed reaction tank having a carrier whose surface is hydrophobic at least.

2. The method for promoting biofilm formation on a carrier according to claim 1, wherein the surfactant has a low HLB value of 1 or more and 6 or less.

3. The method for promoting biofilm formation on a carrier according to claim 1, characterized in that the surfactant addition rate is 0.1 to 20% (w / w) relative to the weight of the carrier.

4. 2. The method for promoting biofilm formation on a carrier according to claim 1, wherein at least the surface portion of the hydrophobic carrier is made of plastic.

5. A biofilm formation promoter for a carrier, which is added to a fixed-bed or fluidized-bed reactor having a carrier whose surface is hydrophobic or at least its surface portion is hydrophobic, or to a position upstream of the reactor, in a wastewater treatment site for biologically treating wastewater, and which is characterized by being a surfactant with a low HLB (Hydrophile Lipophile Balance) value.

6. A wastewater treatment device that biologically treats wastewater, a drainage tank into which the drainage water is introduced; a fixed bed or fluidized bed reactor having a carrier whose surface is hydrophobic and which serves as a site for the biological treatment; adding means for adding a surfactant having a low HLB value at a rate of 0.1 to 20% (w / w) based on the weight of the carrier to the fixed-bed or fluidized-bed reactor or to a position upstream of the reactor; A wastewater treatment device comprising:

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