Microbial carrier and water treatment method

Abstract

To provide a microbial carrier that stabilizes and improves denitrification efficiency, and a water treatment method using the same.SOLUTION: A microbial carrier of the present invention carries microorganisms having denitrification ability; the microbial carrier of the present invention includes an iron-containing carrier containing a biodegradable resin and iron; a molar ratio X of phosphorus to iron in the iron-containing carrier (phosphorus / iron) is 0<X≤0.5 when the iron-containing carrier contains phosphorus; when the iron-containing carrier does not contain phosphorus, then X=0; and the iron content of the iron-containing carrier is 1.0×10-4 mass% or more and less than 2.0 mass% based on the mass of the iron-containing carrier.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a microbial carrier and a water treatment method. This application claims priority based on Japanese Patent Application No. 2022-059131, filed with the Japan Patent Office on March 31, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] A two-stage reaction using microorganisms is known as a method for treating water containing ammonia nitrogen. This method consists of a nitrification reaction, in which ammonia is converted to nitrate using microorganisms capable of nitrification (hereinafter sometimes referred to as "nitrifying bacteria"), and a denitrification reaction, in which nitrate is decomposed into nitrogen using microorganisms capable of denitrification (hereinafter sometimes referred to as "denitrifying bacteria"). The resulting nitrogen is released into the air, making this an environmentally friendly nitrogen removal method.

[0003] Since most denitrifying bacteria used in denitrification reactions are heterotrophic bacteria, a carbon source is required for the denitrification reaction. Methanol is a typical carbon source, but it is toxic and poses safety concerns during operation. Furthermore, to achieve stable denitrification, an amount of methanol corresponding to the concentration of nitrate nitrogen must be supplied to the water being treated, but controlling the supply amount is not easy. Furthermore, when denitrifying water for aquatic organisms, for example, residual unconsumed methanol can harm the aquatic organisms.

[0004] As a method for solving such problems, Patent Document 1 proposes a biological denitrification method in which a biodegradable resin is added to the water to be treated instead of methanol. Biodegradable resins have the advantage of being able to sustain denitrification activity without requiring precise control of the amount added, due to their slow release of carbon sources. However, the denitrification efficiency, such as the denitrification rate and amount of denitrification, has not yet reached a sufficient level. In recent years, from the perspective of environmental protection, nitrate nitrogen emission standards have become stricter, and there is a demand for the development of denitrification treatment methods with even higher denitrification efficiency.

[0005] One possible way to improve denitrification efficiency is to promote the growth and activation of denitrifying bacteria. It is known that denitrifying bacteria can be activated by nutrients such as phosphates, mineral activators, etc. Patent Document 2 proposes a microbial carrier that combines mineral activators, etc. However, the details of the elemental species, concentrations, etc. that are appropriate for improving denitrification efficiency are still unknown. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-175848 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-008923 Summary of the Invention [Problem to be solved by the invention]

[0007] In biological denitrification treatment using a microbial carrier containing a biodegradable resin (hereinafter sometimes simply referred to as "carrier"), denitrifying bacteria settle on the surface of the carrier and form a biofilm. The carbon source necessary for denitrification is mainly supplied by the biodegradable resin that makes up the carrier, but in addition to the carbon source, nutrients such as phosphate and activators such as minerals must also be supplemented. In particular, iron is an essential component for efficient denitrification, as it allows denitrifying bacteria to settle efficiently on the carrier and form a biofilm.

[0008] Therefore, in the denitrification reaction, it is important that denitrifying bacteria can effectively take up iron. One possible method for supplementing iron components is to add iron or iron compounds to the water being treated in advance, but at a near-neutral pH where denitrifying bacteria can remain active, iron is quickly oxidized by oxygen and exists as trivalent iron. Trivalent iron mainly precipitates as poorly soluble iron hydroxide. This means that the iron concentration in the water being treated is likely to decrease, making it difficult for denitrifying bacteria to effectively take up iron.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a microbial carrier that stabilizes and improves denitrification efficiency, and a water treatment method using the same. [Means for solving the problem]

[0010] To solve the above problems, the inventors conducted extensive research and found that, since the only iron that denitrifying bacteria can take up is iron present near the surface of the carrier, an iron-containing carrier made of a biodegradable resin containing iron is effective for efficiently supplying iron to denitrifying bacteria. Furthermore, they found more suitable types of iron compounds and conditions for combining them with phosphorus compounds to improve denitrification.

[0011] The present invention has the following configuration. [1] A microbial carrier carrying microorganisms having denitrification ability, The iron-containing carrier contains a biodegradable resin and iron, The molar ratio X of phosphorus to iron (phosphorus / iron) in the iron-containing support is When the iron-containing support contains phosphorus, 0 <X≦0.5であり、 When the iron-containing support does not contain phosphorus, X=0; The iron content of the iron-containing carrier is 1.0 × 10 -4 % by mass or more and less than 2.0% by mass. [2] The composition further includes a phosphorus-containing carrier containing a biodegradable resin and phosphorus, The molar ratio Y of iron to phosphorus (iron / phosphorus) in the phosphorus-containing carrier is When the phosphorus-containing support contains iron, 0 <Y≦0.1であり、 The microbial carrier according to [1], wherein Y=0 when the phosphorus-containing carrier does not contain iron. [3] A microbial carrier according to [1] or [2], wherein the iron-containing carrier contains trivalent iron. [4] The microbial carrier according to any one of [1] to [3], wherein the biodegradable resin is a biodegradable polyester. [5] The microbial carrier described in [4], wherein the biodegradable polyester contains two or more types of structural units derived from dicarboxylic acids. [6] The microbial carrier according to any one of [1] to [5], which further supports microorganisms capable of decomposing the biodegradable resin. [7] A water treatment method using a microbial carrier carrying microorganisms having denitrification ability, The microbial carrier includes an iron-containing carrier containing a biodegradable resin and iron, The molar ratio X of phosphorus to iron (phosphorus / iron) in the iron-containing support is When the iron-containing support contains phosphorus, 0 <X≦0.5であり、 When the iron-containing support does not contain phosphorus, X=0; The iron content of the iron-containing carrier is 1.0 × 10 -4 % by mass or more and less than 2.0% by mass. [8] The microbial carrier further comprises a phosphorus-containing carrier containing a biodegradable resin and phosphorus; The molar ratio Y of iron to phosphorus (iron / phosphorus) in the phosphorus-containing carrier is When the phosphorus-containing support contains iron, 0 <Y≦0.1であり、 The water treatment method according to [7], wherein Y=0 when the phosphorus-containing carrier does not contain iron. [Effects of the Invention]

[0012] According to the microbial carrier and water treatment method of the present invention, denitrification efficiency is stabilized and improved. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a denitrification treatment system. DETAILED DESCRIPTION OF THE INVENTION

[0014] Below, several embodiments of the present invention will be described in detail. However, the following descriptions are representative examples of embodiments, and the present invention is not limited to these contents, and can be implemented in various modifications within the scope of its gist.

[0015] The meanings of the terms are as follows: Denitrifying bacteria refer to microorganisms that have the ability to denitrify. The decomposing bacteria refer to microorganisms that have the ability to decompose biodegradable resins. The term "microorganisms" refers to microorganisms including denitrifying bacteria and decomposing bacteria. Denitrifying bacteria and decomposing bacteria may be the same type of microorganism. In other words, there may be microorganisms that fall under both denitrifying bacteria and decomposing bacteria. The low molecular weight organic matter refers to organic matter that has been decomposed into low molecular weights by microorganisms when the biodegradable resin is decomposed. Carrier A refers to an iron-containing carrier that contains a biodegradable resin and iron. Carrier A may further contain phosphorus. Carrier B refers to a phosphorus-containing carrier that contains a biodegradable resin and phosphorus. Carrier B may further contain iron. A microbial carrier means a carrier comprising one or more carriers A. The microbial carrier may further comprise one or more carriers B. Total organic carbon (TOC) refers to the concentration of organic matter present in water. TOC is measured using a combustion-type TOC analyzer, such as the Nitto Seiko Analytech TOC-300V. Total iron refers to the soluble and insoluble iron contained in water, and is measured by ICP atomic emission spectrometry as specified in JIS K0102 57.4. Total phosphorus refers to soluble and insoluble phosphorus contained in water and is measured by the molybdenum blue absorptiometry method described in JIS K0102 46.3.1-3. The symbol "to" indicating a range of values means that the values before and after it are included as the lower and upper limits. The ranges disclosed in this specification can be combined in any way to create new ranges.

[0016] <Microbial carrier> A microorganism carrier according to one embodiment will now be described in detail. The microbial carrier is a microbial carrier that supports microorganisms having denitrification ability. A microbial carrier contains at least one carrier A. A microbial carrier may contain two or more carriers A. A microbial carrier may further contain, in addition to carrier A, one or more carriers B. When a microbial carrier contains two or more types of carriers, it is an aggregate of those carriers. The microbial carrier is preferably a microbial carrier that supports microorganisms capable of decomposing biodegradable resins.

[0017] The iron is derived from an iron compound, and is preferably contained in the carrier A in the form of an iron compound. Furthermore, an iron compound that is insoluble in water in the neutral range of pH 6 to 8 is preferred, and examples of the iron compound include iron oxide (III), iron oxide (II, III), and iron hydroxide (III), which contain trivalent iron.

[0018] If carrier A contains these iron compounds, the pH near the surface of carrier A in the treated water is maintained in a pH range suitable for the activity of microorganisms that have settled on the carrier surface. Therefore, the denitrification promotion effect is efficiently achieved after iron is replenished from carrier A. Furthermore, when microorganisms decompose the biodegradable resin and perform denitrification, the trivalent iron in carrier A is reduced to divalent iron by the action of the microorganisms and taken up by the microorganisms, or is taken up by the microorganisms in the form of trivalent iron.

[0019] Therefore, iron is not dissociated from carrier A except by being taken up by the microorganisms, and excess iron is not released into the treated water and remains there, so the iron necessary for denitrification by the microorganisms can be efficiently replenished.

[0020] Generally, the iron that microorganisms can take up is mainly divalent iron. However, divalent iron makes the treated water acidic when it is eluted. In acidic conditions, divalent iron is oxidized to trivalent iron, so microorganisms cannot efficiently take up the iron. In the case of trivalent iron, the treated water is neutral, and the trivalent iron is reduced to divalent iron by the action of microorganisms, allowing the microorganisms to efficiently take up the iron.

[0021] The iron content C(Fe) of carrier A is 1.0×10 -4 % by mass or more and less than 2.0% by mass is preferable, and 2.0 × 10 -4 % by mass or more and 1.8% by mass or less is more preferable, and 5.0 × 10 -4 % by mass or more and 1.5% by mass or less is more preferable, and 1.5 × 10 -3 Mass% or more 8.0×10 -1 % by mass or less is particularly preferred. The decomposing bacteria decompose the biodegradable resin on the surface of carrier A into low molecular weight organic matter and consume it, while also consuming the dissolved oxygen near the surface, thereby creating an environment near the surface of carrier A that is close to anoxic. Thereafter, the denitrifying bacteria take up and utilize the iron in carrier A to perform denitrification. If the iron content of carrier A is within the above range, the decomposing bacteria will efficiently produce and consume low molecular weight organic matter, and a good anoxic environment will be formed, resulting in rapid and stable denitrification. If the iron content of carrier A is 1.0 x 10 -4 If the iron content of carrier A is 2.0% by mass or more, carrier A will replenish iron sufficiently, improving denitrification efficiency. If the iron content of carrier A is less than 2.0% by mass, low-molecular-weight organic matter is consumed by the decomposing bacteria while an anoxic environment is formed, stabilizing denitrification and improving denitrification efficiency. If the iron content is 2.0% by mass or more, it is thought that the biofilm will aggregate when iron ions are eluted from carrier A during the process of forming a biofilm on the surface of carrier A, resulting in a decrease in denitrification performance.

[0022] Furthermore, phosphorus is also an important nutrient source for denitrifying bacteria to settle on carrier A and efficiently consume low-molecular-weight organic matter. The phosphorus content of the microbial carrier is effective in efficiently replenishing phosphorus to the denitrifying bacteria.

[0023] When carrier A contains phosphorus, the molar ratio of phosphorus to iron (phosphorus / iron) X contained in carrier A is more than 0 and 0.5 or less (0 < X ≤ 0.5), preferably 0.1 or less, and more preferably 0.05 or less. If the molar ratio X of phosphorus / iron in carrier A is within the above range, iron and phosphorus are efficiently supplied to microorganisms, so that the denitrification efficiency is improved.

[0024] When the molar ratio X of phosphorus / iron in carrier A becomes a predetermined value or more, iron becomes a compound that is difficult for organisms to take up, such as iron(III) phosphate. Carrier A is a carrier that contains more iron than phosphorus, and supplies iron to microorganisms. In an anaerobic environment where the activity of denitrifying bacteria becomes active, it is presumed that a part of trivalent iron is reduced to divalent iron by microorganisms, and a part of iron(III) phosphate is also taken up by microorganisms.

[0025] When carrier A does not contain phosphorus, the molar ratio of phosphorus to iron (phosphorus / iron) X is 0 (X = 0).

[0026] Moreover, by using in combination carrier B containing a biodegradable resin and phosphorus with respect to carrier A, an improvement in denitrification efficiency by the supply of iron and phosphorus can be expected. When combining carrier A and carrier B, the mixing ratio is preferably carrier A / carrier B of 10 / 90 or more in terms of mass ratio. Within this range, since iron and phosphorus are efficiently supplied to microorganisms, the colonization of microorganisms on carrier A and carrier B becomes good, and the denitrification efficiency is improved.

[0027] The phosphorus content rate of carrier B is not particularly limited, but is preferably 0.002 to 0.5% by mass, and more preferably 0.005 to 0.1% by mass with respect to the weight of carrier B. If the phosphorus content rate is within the above range, phosphorus is efficiently supplied to microorganisms. Therefore, the colonization of microorganisms on the microorganism carrier becomes good, and the denitrification efficiency is improved.

[0028] When carrier B contains iron, the molar ratio (iron / phosphorus) Y of iron to phosphorus contained in carrier B is more than 0 and 0.1 or less (0 < Y ≤ 0.1), and preferably 0.05 or less. When the molar ratio Y of iron / phosphorus in carrier B is within the above range, iron and phosphorus are efficiently replenished to microorganisms, so the denitrification efficiency is improved.

[0029] When carrier B does not contain iron, the molar ratio (iron / phosphorus) Y of iron to phosphorus is 0 (Y = 0).

[0030] Carrier B is a carrier containing more phosphorus than iron. Carrier B replenishes phosphorus to microorganisms in any of aerobic, anaerobic, and anoxic environments. However, in an aerobic environment, trivalent iron is not reduced, and iron(III) phosphate remains in a state that is difficult to be taken up by organisms. Therefore, in an anaerobic or anoxic environment where carrier A can easily replenish iron, iron(III) phosphate is relatively easily taken up by microorganisms. In contrast, carrier B can replenish phosphorus in any of aerobic, anaerobic, and anoxic environments, but in an aerobic environment, iron(III) phosphate is difficult to be taken up by microorganisms. For this reason, it is considered that the upper limit of the molar ratio X of phosphorus to iron in carrier A is larger than the upper limit of the molar ratio Y of iron to phosphorus in carrier B.

[0031] There are no particular restrictions on the phosphorus contained in carrier A and carrier B. Examples include calcium compounds and magnesium compounds such as calcium phosphate and magnesium phosphate.

[0032] The iron content C(Fe) (mass%) and phosphorus content C(P) (mass%) of carrier A and carrier B are measured by the following methods (I) to (VII). (I) Weigh 10 g of carrier A or carrier B and 30 ml of a 2 mol / l aqueous sodium hydroxide solution into a pressure-resistant tube with a volume of 50 to 100 ml, and tightly cover the lid. (II) After heating at 105 °C for 12 hours, cool it with tap water or the like to around 20 °C. (III) After cooling, take out the entire amount of the aqueous solution α present in the pressure-resistant tube and transfer it to a 200 ml glass beaker. (IV) The pH of the aqueous solution α is adjusted to 7.0 using 2 mol / l hydrochloric acid. (V) The pH-adjusted aqueous solution α is transferred to a 100 ml measuring flask, and purified water is added to adjust the volume of the aqueous solution α to 100 ml. (VI) The TOC α (mg / l), total iron α (mg / l), and total phosphorus α (mg / l) of the aqueous solution α are measured by the above-mentioned measurement methods. (VII) The iron content C(Fe) can be calculated using the following formula 1. The phosphorus content C(P) can be calculated using the following formula 2.

[0033] C(Fe) (mass%) = total iron α (mg / l) ÷ TOC α (mg / l) × 100 … Formula 1 C(P) (mass %) = total phosphorus α (mg / l) ÷ TOCα (mg / l) × 100…Equation 2

[0034] The iron contained in carrier A is preferably an iron compound that is insoluble in water with a pH of 6 to 8. If carrier A contains an iron compound that is soluble in water in the neutral range of pH 6 to 8, when carrier A is immersed in water, the soluble iron compound quickly elutes from carrier A into the water, and the pH near the surface of carrier A drops to less than 5. This significantly reduces the colonization of microorganisms on carrier A and the activity of the microorganisms.

[0035] The shapes of Carrier A and Carrier B are not particularly limited and may be any shape, such as columnar, spherical, cylindrical, chip-like, etc. Considering ease of packing into a denitrification tank, it is preferable that Carrier A and Carrier B have a columnar, spherical, cylindrical, etc. shape.

[0036] The microbial carrier of the present invention contains a biodegradable resin. Low-molecular-weight organic components produced by hydrolysis of this biodegradable resin are used as a carbon source necessary for denitrification.

[0037] The biodegradable resin is preferably a biodegradable polyester, such as a PLA (polylactic acid)-based resin, a PBS (polybutylene succinate)-based resin, a PCL (poly caprolactone)-based resin, a PHB (poly hydroxybutyrate)-based resin such as PHBH (poly-3-hydroxybutyrate-co-3-hydroxyhexanoate) or PHBV (poly-3-hydroxybutyrate-co-3-hydroxyvalerate), a PHA (polyhydroxy alkanoate)-based resin, a P3HA (poly-3-hydroxyrate)-based resin, a PBAT (polybutylene adipate / terephthalate), or a poly(terephthalate / succinate). Among biodegradable polyesters, those having structural units derived from dicarboxylic acids are preferred, and those having structural units derived from dicarboxylic acids and diols are more preferred. If the biodegradable resin is a biodegradable polyester, the iron contained in carrier A can be more efficiently taken up by denitrifying bacteria, thereby stabilizing the growth and activity of the denitrifying bacteria and improving denitrification efficiency.

[0038] Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, adipic acid, glutaric acid, suberic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid, and phthalic acid. The biodegradable resin preferably has two or more types of structural units derived from dicarboxylic acids. When a biodegradable resin having two or more types of structural units derived from dicarboxylic acids is used, the denitrification rate tends to be faster and the denitrification performance tends to be higher than when a biodegradable resin having one type of structural unit derived from dicarboxylic acids is used.

[0039] Among the dicarboxylic acids mentioned above, preferred biodegradable resins are those having constituent units derived from succinic acid. Polybutylene succinate (PBS)-based biodegradable resins, primarily containing butylene succinate units, are preferred. Suitable PBS-based biodegradable resins include, for example, polybutylene succinate, poly(butylene succinate / adipate) (PBSA), poly(butylene succinate / carbonate), poly(butylene adipate / terephthalate) (PBAT), and poly(ethylene terephthalate / succinate). Among these, PBSA is particularly preferred due to its high biodegradability and the ability to sustainably supply the carbon source necessary for denitrification. Furthermore, PBSA decomposes more readily than other biodegradable resins, such as PHB-based resins, resulting in favorable production of low-molecular-weight organic components. The PBSA-derived low-molecular-weight organic compounds are also produced, consuming dissolved oxygen at the same time, creating a nearly oxygen-free environment near the biodegradable resin, which is effective for denitrifying bacteria to carry out denitrification reactions. Furthermore, the PBSA-derived low-molecular-weight organic compounds are favorable as substrates or hydrogen donors for the growth and proliferation of denitrifying bacteria.

[0040] The biodegradable resin may be a mixture of a biodegradable polyester having structural units derived from a carboxylic acid and a resin such as polylactic acid, PHA, polyvinyl alcohol, cellulose, etc. By mixing a biodegradable resin having structural units derived from a dicarboxylic acid with these resins having different biodegradability, the biodegradable resin can be used as a carbon source for a long period of time.

[0041] The microbial carrier of the present invention may further contain other resins besides the biodegradable resin, as long as the effects of the present invention are not impaired. Examples of other resins include polyvinyl alcohol, polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyacetic acid, polyvinyl chloride, and polystyrene.

[0042] There are no particular limitations on the method for incorporating iron into carrier A. For example, a method may be used in which iron and / or an iron compound is mixed in advance with a biodegradable resin at a high concentration to prepare a dispersed master batch, and then the master batch and the biodegradable resin are fed into a single-screw or twin-screw kneading extruder or the like to melt and incorporate iron.

[0043] There are no particular limitations on the method for incorporating phosphorus and / or a phosphorus compound into carrier B. For example, a method may be used in which phosphorus and a phosphorus compound are mixed in advance with a biodegradable resin at a high concentration to prepare a dispersed master batch, and then the master batch and the biodegradable resin are fed into a single-screw or twin-screw kneading extruder or the like to be melted and incorporated therein.

[0044] The denitrifying bacteria to be supported on the microbial carrier of the present invention are not particularly limited and can be appropriately selected from known bacteria having denitrifying ability, but heterotrophic denitrifying bacteria are preferred.

[0045] Furthermore, the microbial carrier of the present invention preferably carries microorganisms (hereinafter sometimes simply referred to as "decomposing bacteria") capable of decomposing biodegradable resins. The decomposing bacteria attach to the microbial carrier and decompose the biodegradable resin contained in the microbial carrier. This allows a larger amount of carbon source to be supplied to the denitrifying bacteria than when the decomposing bacteria are not carried on the microbial carrier, promoting the growth or activity of the denitrifying bacteria. As a result, the denitrification rate and amount are improved. The decomposing bacteria are not particularly limited, but any known bacteria capable of decomposing biodegradable resins can be used as appropriate.

[0046] The water to be treated that is the target of purification treatment using a microbial carrier is not particularly limited as long as it contains nitrite nitrogen and / or nitrate nitrogen. The water to be treated may be water used to raise the above-mentioned aquatic organisms, or may be wastewater such as livestock wastewater, food wastewater, sewage, or septic tank wastewater. The water to be treated may be freshwater or seawater. "Seawater" means water containing salt at a concentration of 3.2% by mass or more. "Brackish water" means water containing salt at a concentration of 0.05% by mass or more and less than 3.2% by mass. On the other hand, "freshwater" may be water that does not contain any salt, or water that contains salt at a concentration lower than the salinity of brackish water.

[0047] The nitrate nitrogen concentration of the water to be treated is not particularly limited, but is preferably 10 mg-N / L or more, more preferably 20 mg-N / L or more, even more preferably 50 mg-N / L or more, particularly preferably 100 mg-N / L or more, and is preferably 5000 mg-N / L or less, more preferably 2000 mg-N / L or less. If the nitrate nitrogen concentration of the water to be treated is within the above range, denitrification will proceed efficiently.

[0048] The iron concentration of the water to be treated is not particularly limited, but is preferably 0 mg-Fe / L or more, more preferably 0.01 mg-Fe / L or more, even more preferably 0.1 mg-Fe / L or more, particularly preferably 0.5 mg-Fe / L or more, and preferably 1 mg-Fe / L or less. If the iron concentration of the water to be treated is within the above range, denitrification will proceed efficiently.

[0049] The phosphorus concentration of the water to be treated is not particularly limited, but is preferably 0.01 mg-P / L or more, more preferably 0.1 mg-P / L or more, even more preferably 1.0 mg-P / L or more, particularly preferably 5.0 mg-P / L or more, and preferably 20 mg-P / L or less, more preferably 10 mg-P / L or less. If the phosphorus concentration of the water to be treated is within the above range, denitrification will proceed efficiently.

[0050] <Water treatment method> A water treatment method according to one embodiment will now be described in detail. The water treatment method relates to a denitrification treatment method using the microbial carrier of the above-mentioned embodiment. In the water treatment method, a microbial carrier containing one or more carriers A is used as a microbial carrier that supports microorganisms capable of denitrification. More specifically, the water treatment method includes a denitrification treatment step in which the water to be treated is supplied to a denitrification tank filled with microbial carriers carrying denitrifying bacteria, and denitrification is carried out by converting the nitrite nitrogen and / or nitrate nitrogen in the water to nitrogen through a denitrification reaction.

[0051] (Denitrification process) In the water treatment method, the method for supplying the water to be treated to the denitrification tank filled with the microbial carrier is not particularly limited. For example, the water to be treated can be supplied to the denitrification tank using a circulation type, overflow type, intermittent type, or batch type denitrification treatment system. Of these, it is preferable to use a circulation type denitrification treatment system.

[0052] Figure 1 is a schematic diagram showing an example of a denitrification treatment system. The denitrification treatment system shown in Figure 1 includes a water storage tank 101, a pump 102, a supply tube 103, a denitrification column 105 filled with microbial carriers 104, and a return tube 106. In this circulation-type denitrification treatment system, the water to be treated placed in the water storage tank 101 is supplied to the denitrification column 105 through the supply tube 103 by the pump 102, comes into contact with the microbial carriers 104, and then is returned to the water storage tank 101 through the return tube 106, thereby circulating.

[0053] In the denitrification treatment step, the temperature of the water to be treated may be within the temperature range that the natural environment can maintain, and is 0°C or higher, preferably 10°C or higher, more preferably 20°C or higher, and 40°C or lower, preferably 35°C or lower, and even more preferably 30°C or lower. The water to be treated contains nitrate nitrogen and may also contain ammonia nitrogen and nitrite nitrogen. The water to be treated may also contain organic components derived from sources other than biodegradable resins. A suitable example of the water to be treated is breeding water used for cultivating aquatic organisms. The water treatment method is suitable for supporting microorganisms and stably promoting the activity of denitrifying bacteria in the denitrification treatment of breeding water containing nitrate nitrogen after nitrification treatment.

[0054] The circulating denitrification treatment system may have various other elements not shown in Fig. 1. Examples of such elements include a transfer means, such as a siphon, for transferring the water to be treated so that it can be supplied to the denitrification tank, a heater and / or a cooler for adjusting the temperature of the water to a temperature suitable for the denitrification reaction, and a nitrification carrier carrying nitrifying bacteria for converting ammonia nitrogen into nitrate when the water to be treated contains ammonia nitrogen.

[0055] The water treatment method may be incorporated into a water treatment method using a two-step reaction: a nitrification reaction that converts ammonia into nitrate, and a denitrification reaction that decomposes nitrate into nitrogen. Examples of such water treatment methods include a method for purifying water used to raise aquatic organisms such as salmon, trout, sweetfish, char, eels, crabs, and shrimp. In this case, the water used to raise aquatic organisms contains ammonia nitrogen. Therefore, the water is supplied to a nitrification tank equipped with a nitrification carrier carrying nitrifying bacteria to convert the ammonia nitrogen into nitrite nitrogen and / or nitrate nitrogen. The water (water to be treated that can be used in the water treatment method) that has passed through the nitrification tank and now contains nitrite nitrogen and / or nitrate nitrogen is then subjected to a denitrification treatment step.

[0056] The nitrification tank and the denitrification tank may be provided as separate tanks or may be the same tank. When the nitrification tank and the denitrification tank are the same tank, a nitrification carrier carrying nitrifying bacteria and a microbial carrier carrying denitrifying bacteria may be placed in one tank, and the nitrification carrier and the microbial carrier may be separated by a fibrous separator, filter paper, etc. The nitrification tank, nitrifying bacteria, nitrification carrier, fibrous separator, filter paper, etc. may be appropriately selected from known items and used.

[0057] As described above, according to the microbial carrier and water treatment method of the present invention, the activity of the microorganisms that have settled on the microbial carrier promotes good hydrolysis of the biodegradable resin that constitutes the microbial carrier, and a good biofilm is formed on the microbial carrier, thereby stabilizing and improving denitrification efficiency.

[0058] Furthermore, according to the microbial carrier and water treatment method of the present invention, iron is efficiently replenished to microorganisms, including denitrifying bacteria, that have settled on the iron-containing carrier during denitrification treatment, thereby suppressing iron deficiency and improving denitrification.

[0059] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. [Example]

[0060] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the embodiments shown in the following examples.

[0061] <Examples 1 to 24 and Comparative Examples 1 to 6> (Preparation of microbial carriers) Carriers A1 to A14, carrier a1, carrier a2, carriers B1 to B4, and carrier c were prepared by the methods described below.

[0062] "Preparation of Carrier A1" 200 g of pelletized poly(butylene succinate / adipate) (PBSA; manufactured by PTT MCC Biochem; minor axis approximately 3 mm, major axis approximately 6 mm) (hereinafter referred to as PBSA) was placed in a heat-resistant PTFE universal container (120 mm diameter, manufactured by Fluorochemical Co., Ltd.) (hereinafter referred to as PTFE dish). Powdered red iron(III) oxide (manufactured by Hayashi Pure Chemical Industries, Ltd.) and powdered tricalcium phosphate (manufactured by Kanto Chemical Co., Ltd.) were added in the amounts (g) listed in the "Amount of iron compound added (g) per 200 g of PBSA" and "Amount of phosphorus compound added (g) per 200 g of PBSA" columns in Table 1 below. The entire amount of added iron(III) oxide and tricalcium phosphate was mixed with the PBSA by stirring using a PTFE rod (diameter 12 mm, length 300 mm) (hereinafter referred to as PTFE rod). The PBSA was then heated together with the PTFE dish in a thermostatic bath at 125°C for 30 minutes to melt the PBSA. The molten PBSA was then kneaded with iron oxide using a PTFE rod. The PBSA was then heated together with the PTFE dish again at 125°C for 30 minutes to melt the PBSA. The entire molten PBSA was then transferred onto a heat-resistant PTFE plate (50 mm x 50 mm) and crushed with a PTFE rod to form a plate with a thickness of 3 mm and dimensions of approximately 3000 mm x 300 mm. The PBSA was then cut into chips measuring 10 mm x 10 mm x 3 mm with scissors to prepare carrier A1.

[0063] "Preparation of Carriers A3 to A5, Carrier a1, and Carriers B2 to B4" Carriers A3 to A5, carrier a1, and carriers B2 to B4 were prepared in the same manner as carrier A1, except that the amounts of iron oxide (III) and tricalcium phosphate added were the amounts listed in the "Amount of iron compound added (g) per 200 g of PBSA" column for each carrier in Table 1.

[0064] "Preparation of Carrier A2" Carrier A2 was prepared in the same manner as Carrier A1, except that iron oxide (II, III) was added instead of iron oxide (III).

[0065] "Preparation of Carrier A6" Support A6 was prepared in the same manner as Support A1, except that iron(II) sulfate heptahydrate was added instead of iron(III) oxide.

[0066] "Preparation of Carriers A7, A9 to A13, and Carrier a2" Carriers A7, A9 to A13, and a2 were prepared in the same manner as for carrier A1, except that tricalcium phosphate was not added.

[0067] "Preparation of Carrier A8" Carrier A8 was prepared in the same manner as Carrier A1, except that iron oxide (II, III) was added instead of iron oxide (III) and tricalcium phosphate was not added.

[0068] "Preparation of Carrier A14" Carrier A14 was prepared in the same manner as Carrier A1, except that iron(II) sulfate heptahydrate was added instead of iron(III) oxide and tricalcium phosphate was not added.

[0069] "Preparation of Carrier B1" Carrier B1 was prepared in the same manner as Carrier A1, except that iron (III) oxide was not added.

[0070] "Preparation of carrier c" Carrier c was prepared in the same manner as Carrier A1, except that iron (III) oxide and tricalcium phosphate were not added.

[0071] [Table 1]

[0072] (Adjustment of acclimatized sludge) Suspended water was collected from the denitrification tank of the aquaculture water purification treatment facility and concentrated by centrifuging at 3000 rpm for 5 minutes to produce activated sludge with a MLSS of 3600 mg / L.

[0073] (Denitrification test) A simulated wastewater solution was prepared by dissolving sodium nitrate (NaNO3), dipotassium hydrogen phosphate (K2HPO4), magnesium sulfate heptahydrate (MgSO4·7H2O), disodium ethylenediaminetetraacetic acid (EDTA), and calcium chloride dihydrate (CaCl2·H2O) in pure water so that the concentrations of nitrate nitrogen, phosphorus, magnesium ion, sodium ion, and calcium ion were 100 mg-N / L, 5 mg-P / L, 8.8 mg-Mg / L, 1.03 mg-Na / L, and 0.57 mg-Ca / L, respectively.

[0074] Next, a denitrification test was carried out using the circulating denitrification treatment system shown in Figure 1. First, 200 g of the microbial carriers of Examples 1 to 24 and Comparative Examples 1 to 6, which were prepared by combining them in the mixing ratios shown in the "Microbial Carrier" column in Table 2 below, were placed into a denitrification column 105 having an inner diameter of 3.5 mm, a length of 450 mm, and an effective volume of 300 mL.

[0075] Next, 2000 mL of the water to be treated was mixed with 20 mL of seed sludge in a water storage tank 101 having a capacity of 2.2 L, and the water was fed by a pump 102 at a flow rate of 10 mL / min to circulate the water to be treated.

[0076] As shown in Figure 1, in the denitrification test, the water to be treated in the water storage tank 101 was supplied through a supply tube 103 into the denitrification column 105 from a supply inlet at the bottom of the denitrification column, and then discharged from a return outlet at the top of the denitrification column and returned to the water storage tank 101 through a return tube 106, thereby circulating the denitrification treatment system.

[0077] The nitrate nitrogen concentration C (mg / L) of the water to be treated in the water storage tank 101 on the 10th day from the start of the test was measured using a compact nitrate ion meter (HORIBA, Ltd.: "LAQUAtwin NO3-11"). Table 2 below shows the nitrate nitrogen concentration after the denitrification test.

[0078] [Table 2]

[0079] As shown in Tables 1 and 2, when the molar ratio X of phosphorus to iron (phosphorus / iron) contained in carrier A was 0.5 or less (Examples 1 to 24), the nitrate nitrogen level in the treated water after the denitrification test was lower than that in Comparative Examples 1 and 3, where the ratio was greater than 0.5. High denitrification efficiency was confirmed. It was confirmed that the examples in which the iron content of the iron-containing carrier was less than 2.0 mass% relative to the mass of the iron-containing carrier had lower nitrate nitrogen values in the treated water after the denitrification test and exhibited higher denitrification efficiency than comparative example 6 in which the iron content of the iron-containing carrier was 2.0 mass% relative to the mass of the iron-containing carrier. Furthermore, in Examples 1 to 21 in which the iron compound contained trivalent iron, higher denitrification efficiency was confirmed. Furthermore, when the molar ratio X of phosphorus to iron contained in the carrier A (phosphorus / iron) was 0.05 or less (Examples 1 to 16), a particularly high denitrification efficiency was confirmed.

[0080] In Comparative Examples 2, 4, and 5, a microbial carrier was used that did not contain carrier A. In these cases, it is thought that the iron necessary for denitrification was not replenished to the microorganisms, which caused denitrification to stagnate and prevented a decrease in nitrate nitrogen in the treated water.

[0081] From the above, it was confirmed that high denitrification efficiency can be achieved by using a microbial carrier including an iron-containing carrier that contains a biodegradable resin and iron and has a molar ratio of phosphorus to iron (phosphorus / iron) X of 0.5 or less. [Industrial Applicability]

[0082] According to the microbial carrier and water treatment method of the present invention, denitrification efficiency is stabilized and improved. [Explanation of symbols]

[0083] 101...Water tank 102...Pump 103...Supply tube 104...Microbial carrier 105...Denitrification column 106...Return tube

Claims

1. An iron-containing carrier contained in a microbial carrier carrying heterotrophic denitrifying bacteria having denitrification ability, The iron-containing carrier has a mixture of a biodegradable polyester and trivalent iron, The molar ratio X of phosphorus to iron (phosphorus / iron) in the iron-containing support is When the iron-containing support contains phosphorus, 0<X≦0.5; When the iron-containing support does not contain phosphorus, X=0; The iron content of the iron-containing carrier is 1.0 × 10 －４ % by mass or more and less than 2.0% by mass of iron-containing support.

2. The iron-containing carrier according to claim 1 , wherein the biodegradable polyester contains two or more types of structural units derived from dicarboxylic acids.

3. An iron-containing carrier described in claim 1 or 2, which supports microorganisms capable of decomposing the biodegradable polyester.

4. A water treatment method using an iron-containing carrier contained in a microbial carrier carrying heterotrophic denitrifying bacteria having denitrification ability, The iron-containing carrier has a mixture of a biodegradable polyester and trivalent iron, The molar ratio X of phosphorus to iron (phosphorus / iron) in the iron-containing support is When the iron-containing support contains phosphorus, 0<X≦0.5; When the iron-containing support does not contain phosphorus, X=0; The iron content of the iron-containing carrier is 1.0 × 10 －４ % by mass or more and less than 2.0% by mass.

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