Method and system for the biological purification of treated water

Abstract

To provide a method and a system for biological purification of treated water containing heavy metal ions and sulfate ions that can easily control stable and continuous treatment of treated water.SOLUTION: A biological purification method for treated water containing heavy metal ions and sulfate ions includes: making treated water pass through a biological purifier containing grain hulls bearing sulfate-reducing bacteria stored in a treatment vessel in which anaerobic conditions are maintained and reducing sulfate ions by the sulfate-reducing bacteria to produce hydrogen sulfide ions, and making the hydrogen sulfide ions react with the heavy metal ions to precipitate sulfide and thereby obtaining treated water from which heavy metal ions have been removed; and feeding liquid organic matter as a nutrient source to activate the sulfate-reducing bacteria into the treatment vessel. The amount of liquid organic matter supplied is adjusted to control the degree of reduction of sulfate ions in the treated water. A system corresponding thereto is also disclosed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a biological purification method and a biological purification system for removing heavy metal ions and sulfate ions from treated water containing heavy metal ions and sulfate ions. In particular, the present invention relates to a continuous and controlled biological purification method and a biological purification system using a biological purification agent containing grain husks carrying sulfate-reducing bacteria, which can be effectively utilized for so-called passive treatment of mine wastewater. [Background technology]

[0002] Mining-derived wastewater, such as that from metal mines, and various types of wastewater, such as industrial wastewater, generally contain various heavy metal ions such as Fe, Zn, Cu, Pb, Cd, and As, as well as sulfate ions (SO4). 2- These heavy metal ions may also be present. Many of these heavy metal ions have harmful effects on the human body and the environment. Therefore, when discharging water containing these heavy metal ions, treatment is required to meet the wastewater standards set by each country.

[0003] Examples of methods for treating such wastewater and removing heavy metal ions contained in it include neutralizing the water by adding alkaline agents such as slaked lime or calcium carbonate, thereby precipitating the heavy metal ions as hydroxides or carbon dioxide, or adding sulfiding agents such as hydrogen sulfide to the water, thereby precipitating the heavy metal ions as sulfides. However, methods such as adding an alkaline agent may require a neutralization process in which the treated water is neutralized while being stirred with an electric motor, and a solid-liquid separation process in which the precipitate produced by the neutralization process is separated. This raises concerns about electricity consumption and costs associated with solid-liquid separation work. Furthermore, methods that add a sulfurizing agent actively generate hydrogen sulfide, a toxic gas, which poses a significant safety management burden.

[0004] Active treatment, which directly treats water by administering chemicals that react with heavy metal ions, requires chemicals, electricity, and maintenance personnel at all times, and demands frequent maintenance, resulting in high costs. Therefore, in order to reduce treatment costs and energy consumption, research is being conducted on passive treatment technologies that utilize natural purification processes, such as precipitating and removing heavy metals with microorganisms or filtering and absorbing heavy metals with plants, to treat water.

[0005] As an example of such passive treatment technology, Patent Document 1 discloses a biological purification method using unused biomass resources that can remove heavy metal ions from treated water containing heavy metal ions and sulfate ions over a long period of time, while also suppressing organic contamination of the treated water. More specifically, Patent Document 1 describes a method for the biological purification of water to be treated, in which a biological purification agent containing grain husks carrying sulfate-reducing bacteria is pre-sealed with water to be treated and allowed to stand, thereby cultivating the sulfate-reducing bacteria attached to the grain husks under anaerobic conditions, and then the water to be treated is continuously passed through the biological purification agent under anaerobic conditions, thereby using the sulfate-reducing bacteria to precipitate and release sulfides of heavy metal ions and remove heavy metal ions from the water to be treated.

[0006] Furthermore, Patent Document 2 discloses a biological purification method that improves upon the technology of Patent Document 1, enabling the removal of heavy metal ions from treated water over a long period of time, even in a wide temperature range including low temperatures of 15°C or below. More specifically, the biological purification method of treated water described in Patent Document 2 is characterized by using an organic matter-containing material selected from sake lees, okara (soy pulp), rice bran, tea leaves, lotus, timothy grass, and clover as a nutrient source for sulfate-reducing bacteria supported on grain husks. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent No. 5773541 [Patent Document 2] Japanese Patent No. 5761884 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] However, in the biological purification method of treated water using rice bran or the like, which is considered to be the best in the above-mentioned conventional technology, as a nutrient source for sulfate-reducing bacteria, in order to perform the purification treatment by sulfate-reducing bacteria for as long a period as possible, it is necessary to batch a large amount of rice bran or the like into the treatment tank at the start of the treatment or in multiple batches thereafter. By thus batch-administering a large amount of rice bran or the like into the treatment tank, biofilms frequently occur due to the excessive decomposition of rice bran or the like by sulfate-reducing bacteria. When a large amount of biofilm occurs, operational problems such as deterioration of water permeability in the treatment tank, clogging of the treated water discharge system, and rise in the water level of the treated water may occur, making it difficult to continue the stable purification treatment of the treated water over a long period. In addition, the drainage standards for treated water discharged into the environment are stipulated by laws and regulations. For example, the drainage standard for COD (chemical oxygen demand: the amount of oxygen consumed when oxidizing organic substances in water with an oxidant, which is a typical index for measuring organic pollution in lakes and seas) has an allowable limit of 160 mg / L (daily average 120 mg / L). However, when using rice bran or the like as a nutrient source for sulfate-reducing bacteria in the biological purification method of treated water, especially when batch-administering a large amount of rice bran or the like into the treatment tank as described above, the initial COD immediately after the input of the nutrient source into the treatment tank may exceed the drainage standard and increase, and it may take time to meet the drainage standard, so it may be necessary to perform treatments such as separately pooling and diluting.

[0009] Therefore, the object of the present invention is to provide a biological purification method and purification system for water containing heavy metal ions and sulfate ions, in which the formation of biofilms is effectively suppressed, the initial rise in COD immediately after administration of a nutrient source for sulfate-reducing bacteria into the treatment system is small, and control for stable and continuous treatment of the water to be treated is easy. [Means for solving the problem]

[0010] As a result of diligent research, the inventors unexpectedly discovered that by using liquid organic matter as a nutrient source to activate sulfate-reducing bacteria, and supplying this liquid organic matter to the treatment container together with the water to be treated, biological purification of the water to be treated containing heavy metal ions and sulfate ions can be performed. By adjusting the amount of liquid organic matter supplied and controlling the degree of reduction of sulfate ions in the water to be treated (in other words, by setting the concentration of liquid organic matter to be approximately constant according to the concentration of heavy metal ions in the water to be treated, so that the amount of hydrogen sulfide ions in the treated water after reaction with heavy metal ions is continuously adjusted to a surplus within a predetermined target range), it is possible to perform biological purification suitable for the above purpose, and thus the inventors completed the present invention. In this specification, "controlling the degree of reduction of sulfate ions in the treated water" means that sulfate-reducing bacteria interact with liquid organic matter, which serves as a nutrient source, and sulfate ions (SO4) in the treated water. 2- ) incorporates and reduces sulfate ions, and hydrogen sulfide ions (HS) - This refers to the progress of the reaction that produces hydrogen sulfide ions (HS) produced by the reaction. - This can be evaluated by measuring the concentration of hydrogen sulfide ions remaining in the treated water after the compound has combined with heavy metal ions in the treated water.

[0011] One aspect of the present invention for achieving the above objective is as follows: A biological purification method for water to be treated that contains heavy metal ions and sulfate ions, The method involves passing the water to be treated through a biological purification agent containing grain husks carrying sulfate-reducing bacteria, which is housed in a treatment container where anaerobic conditions are maintained. The sulfate-reducing bacteria reduce the sulfate ions to generate hydrogen sulfide ions, and the hydrogen sulfide ions react with the heavy metal ions to precipitate sulfides, thereby obtaining treated water from which the heavy metal ions have been removed. A liquid organic substance is supplied into the processing container as a nutrient source to activate the sulfate-reducing bacteria. Includes, The amount of liquid organic matter supplied is adjusted to control the degree of reduction of sulfate ions in the water to be treated. Biological purification methods.

[0012] Furthermore, another aspect of the present invention for achieving the above objective is as follows. A biological purification system for water to be treated that contains heavy metal ions and sulfate ions, A treatment container containing a biological purification agent containing grain husks carrying sulfate-reducing bacteria, and in which anaerobic conditions are maintained, A supply system for supplying both the water to be treated and liquid organic matter as a nutrient source for activating the sulfate-reducing bacteria into the treatment container, The system includes a discharge system for discharging treated water from the treatment container, which is formed by reducing sulfate ions with sulfate-reducing bacteria to produce hydrogen sulfide ions, reacting the hydrogen sulfide ions with the heavy metal ions to precipitate sulfides, thereby removing the heavy metal ions from the treated water. The means includes adjusting the supply amount of the liquid organic matter and controlling the degree of reduction of the sulfate ions in the water to be treated, Biological purification system. [Effects of the Invention]

[0013] According to the biological purification method and system for treated water of the present invention, by using liquid organic matter, typically one or more of methanol, ethanol, and propanol, as a nutrient source to activate sulfate-reducing bacteria, and by adjusting the supply amount of liquid organic matter to control the degree of reduction of sulfate ions in the treated water (i.e., by setting the concentration of liquid organic matter to be approximately constant according to the concentration of heavy metal ions so that the amount of hydrogen sulfide ions contained in the treated water is adjusted to a surplus within a predetermined target range), the formation of biofilm caused by excessive decomposition of the nutrient source can be effectively suppressed, the initial rise in COD immediately after administering the nutrient source into the treatment system can be reduced, and furthermore, excellent advantages such as easy control for stable and continuous treatment of the treated water can be obtained. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic diagram of a biological purification treatment apparatus according to the first embodiment of the present invention. [Figure 2] Figure 2 shows a simplified process flow of a preferred example of a biological purification treatment method according to a second embodiment of the present invention. [Figure 3] Figure 3 is a graph showing the change in zinc ion concentration in the treated water over time (days) from the start of treatment, when the supply of ethanol, which is a nutrient source for sulfate-reducing bacteria, is set to a predetermined constant concentration in Example 1 described later. [Figure 4] Figure 4 is a graph showing the change in hydrogen sulfide ion (HS-) concentration in the treated water over time (days) from the start of treatment, when the ethanol supply was set to a predetermined constant concentration in Example 1, described later. [Figure 5] Figure 5 is a graph showing the change in total organic carbon (TOC) of treated water over time (days) from the start of treatment, when the supply of ethanol is set to a predetermined constant concentration, as described in Example 1 below. [Figure 6]Figure 6 is a graph showing the change in the difference in total organic carbon (TOC) before and after treatment, in relation to the change in the difference in sulfate ion (SO4 2-) concentration before and after treatment, when the supply of ethanol is set to a predetermined constant concentration in Example 1 described later. [Figure 7] Figure 7 is a graph showing the change in total organic carbon (TOC) of the treated water over time (days) from the start of treatment, when rice bran, which is a nutrient source for sulfate-reducing bacteria, was supplied in large batches in three separate batches in Comparative Example 1, described later. [Figure 8] Figure 8 is a graph showing the change in the concentration of each ion after mixing treatment with respect to the mixing ratio (volume of treated water:volume of water to be treated) when treated water containing a large excess amount of hydrogen sulfide ions is simply mixed with newly supplied water to be treated in Example 2 described later. [Modes for carrying out the invention]

[0015] The following describes embodiments for carrying out the present invention (first and second embodiments). The present invention is not limited to the following embodiments. The biological purification system for treated water containing heavy metal ions and sulfate ions according to the present invention is a system that includes components for realizing the biological purification method for treated water according to the present invention, and the two have substantially common technical matters; therefore, the following description will mainly be from the perspective of the biological purification method.

[0016] A biological purification method for water to be treated containing heavy metal ions and sulfate ions according to the first embodiment includes passing the water to be treated through a biological purification agent containing grain husks carrying sulfate-reducing bacteria housed in a treatment container where anaerobic conditions are maintained, reducing the sulfate ions with the sulfate-reducing bacteria to generate hydrogen sulfide ions, reacting the hydrogen sulfide ions with the heavy metal ions to precipitate sulfides, thereby obtaining treated water from which the heavy metal ions have been removed, and supplying liquid organic matter as a nutrient source to activate the sulfate-reducing bacteria into the treatment container together with the water to be treated. In this specification, "water to be treated" means water before purification treatment with a biological purifying agent, i.e., treatment to remove heavy metal ions, and "water after treatment" means water after said purification treatment. The water to be treated is not particularly limited as long as it contains heavy metal ions and sulfate ions, and can include, for example, wastewater from mines such as mine wastewater from metal mines, and industrial wastewater. For example, mine wastewater from metal mines in Japan generally contains heavy metal ions such as Fe, Zn, Cu, Pb, Cd, and As, and further contains sulfate ions (SO4 2- It also contains approximately 50-3000 mg / L of [unspecified substance]. The pH of the treated water is not particularly limited, but is usually around 2.5-8.0.

[0017] The "heavy metals" to be treated in this specification are not particularly limited, as long as they can be precipitated as sulfides by the reaction formula (B) below. Examples of heavy metals include Fe, Zn, Cu, Pb, Cd, As, etc., as mentioned above. In Japan, the wastewater standards for heavy metal ions are stipulated by the Water Pollution Control Act (Act No. 45 of June 2, 2017) and the Ministerial Ordinance Establishing Wastewater Standards (Ministry of the Environment Ordinance No. 15 of November 18, 2019). These standard values ​​are, for example, Cd ions: 0.03 mg / L, Pb ions: 0.1 mg / L, Zn ions: 2 mg / L, Cu ions: 3 mg / L, and As ions: 0.1 mg / L. As a non-limiting example, it is understood that if the water to be treated has upper limits of approximately Cd ions: 0.06 mg / L, Pb ions: 0.14 mg / L, Zn ions: 18 mg / L, Cu ions: 4.5 mg / L, and Fe ions: 10 mg / L, the biological purification treatment of this embodiment can purify the treated water to contain heavy metal ions below the standard values.

[0018] In this specification, the concentration of sulfate ions contained in the treated water is not particularly limited, but may be, for example, 1 mg / L or more, 5 mg / L or more, 10 mg / L or more, 20 mg / L or more, 30 mg / L or more, 40 mg / L or more, or 50 mg / L or more.

[0019] In this specification, the "sulfate-reducing bacteria" are anaerobic bacteria that mainly act in the neutral range (pH 5 to 8), and any bacteria that act using liquid organic matter as a nutrient source (energy source) and reduce sulfate may be used. Any known sulfate-reducing bacteria may be used, and there is no particular limitation. For example, Desulfovibrio vulgaris, Desulfosporosinus sp., etc. may be mentioned.

[0020] Since sulfate-reducing bacteria usually exist in the water to be treated such as mine wastewater and industrial wastewater, it is not necessary to add sulfate-reducing bacteria from outside the system. Alternatively, sulfate-reducing bacteria may be further added from outside the system.

[0021] Sulfate-reducing bacteria act to reduce sulfate ions in the water to be treated and generate hydrogen sulfide ions. The hydrogen sulfide ions react with the heavy metal ions in the water to be treated, and sulfides of the heavy metal ions precipitate. As a result, the heavy metal ions in the water to be treated precipitate and settle as sulfides, thereby removing the heavy metal ions. That is, in this embodiment, the sulfate-reducing bacteria take in liquid organic matter and sulfate ions (SO4 2- ), reduce the sulfate ions as shown in the following reaction formula (A), and have the action of discharging hydrogen sulfide ions (HS - ). 2CH2O + SO4 2- → 2HCO3 - + HS - + H + ···(A) (However, CH2O represents liquid organic matter as a nutrient source.)

[0022] When the reduction reaction (the reaction in the right direction) of the above reaction formula (A) proceeds, hydrogen sulfide ions (HS - ) are generated, and the generated hydrogen sulfide ions (HS - ) combine with the heavy metal ions in the water to be treated, and as shown in the following reaction formula (B), the heavy metal ions can be precipitated as sulfides and detoxified. Me 2+ + HS - → MeS↓ + H + ····(B) (However, Me 2+ This indicates a heavy metal ion (a divalent ion is shown as an example).

[0023] Prior to the purification treatment, the sulfate-reducing bacteria may be pre-acclimatized (or cultured / activated) by placing grain husks carrying sulfate-reducing bacteria together with the water to be treated under anaerobic conditions, for example, at a water temperature of about 15-30°C. Alternatively, such pre-acclimatization of sulfate-reducing bacteria may be omitted.

[0024] In the biological purification treatment of the water to be treated according to this embodiment, liquid organic matter as a nutrient source to activate sulfate-reducing bacteria is preferably continuously supplied to the treatment container together with the water to be treated. By preferably continuously supplying liquid organic matter as a nutrient source for sulfate-reducing bacteria into the treatment container, and simultaneously preferably continuously supplying the water to be treated into the treatment container, the problems that occur in the conventional technology described above when rice bran or the like is added in large batches, such as the formation of biofilm and the significant increase in initial COD immediately after the addition of the nutrient source, are suppressed, and stable treatment of the water to be treated becomes possible over the long term.

[0025] In this specification, "liquid organic matter" is not particularly limited, as long as it functions as a nutrient source for sulfate-reducing bacteria to perform the above-mentioned actions and can maintain a liquid state under atmospheric pressure at normal temperatures in the environment in which the biological purification treatment is actually carried out (preferably at least around room temperature, typically between -10°C and 40°C). The liquid organic matter may preferably contain at least one alcohol. The alcohol is not particularly limited, but may be, for example, a linear, branched, or cyclic alcohol with 8 or fewer carbon atoms. The alcohol may contain one or more of methanol, ethanol, and propanol, and preferably contains ethanol. In this embodiment, the nutrient source for sulfate-reducing bacteria may not include any of the following: rice bran, rice hulls, hay, wood chips, livestock manure, sake lees, okara (soy pulp), tea leaves, lotus, timothy, or clover molten or dispersed media. Alternatively, the nutrient source for sulfate-reducing bacteria may not include any solid organic matter.

[0026] The method for supplying the water to be treated and the liquid organic matter, which is a nutrient source for sulfate-reducing bacteria, is not particularly limited, as long as it can be set and adjusted so that they can be supplied to the treatment vessel (reaction tank) at a desired constant flow rate. The water to be treated and the liquid organic matter can be supplied to the treatment vessel separately through transfer channels such as separate pipes. If the transfer channels such as pipes for supplying the water to be treated and the liquid organic matter are located at a higher position than their inlets in the treatment vessel, an electric pump, for example, may be used to provide supply energy (lift). In natural-use passive treatment systems, it is desirable to configure the system so that the water and liquid organic matter to be treated, from the supply to the treatment and discharge systems, can move by gravity, minimizing the use of electricity from the perspective of labor saving and cost reduction. Therefore, in actual application fields, it is preferable to set the height of the transfer paths such as piping and the inlet of the treatment container so that electric pumps are not used. Furthermore, if electric pumps are used, it is possible to create a natural-use passive treatment system by supplying power using solar cells or the like.

[0027] The treatment vessel (reaction tank) that can be used in the biological purification treatment of the water to be treated in this embodiment is not particularly limited in shape, material, capacity, etc., as long as it is possible to carry out the treatment and the biological treatment (reactions of reaction formulas (A) and (B) above) can proceed while the water to be treated and liquid organic matter move downwards within the treatment vessel according to gravity. The treatment vessel may consist of a main body, a top lid, and a bottom. The top lid of the treatment vessel may be configured to be openable and resealable. The bottom of the treatment vessel may include a sealing plug. The material of the treatment vessel when it consists of a main body, a top lid, and a bottom is not particularly limited, but for example, it may be mainly made of resin, and some parts may include metal, ceramics, rock, clay, etc. The shape of the main body of the treatment vessel when it consists of a main body, a top lid, and a bottom is not particularly limited, but it may be elongated or flattened, approximately rectangular, approximately cube, approximately spherical, approximately cylindrical (approximately cylindrical), or a combination thereof. Furthermore, the processing container can also be an artificial pond, artificial wetland, large tank, etc. The volume of the processing container used outside the laboratory is not limited, but for example, 1 m³ 3 ~1 × 10 5 m 3 , 10m 3 ~5×10 4 m 3 or 20m 3 ~1 × 10 4 m 3 It can be to a certain extent.

[0028] The treatment container is provided with inlets for the water to be treated and the liquid organic matter, respectively, and an outlet for the treated water. If the treatment container consists of a main body, a top lid, and a bottom, the inlets for the water to be treated and the liquid organic matter may be located on or near the lid, and the outlet from the treatment container may be located on or near the bottom. If the treatment container is an artificial pond, artificial wetland, large tank, etc., in order to maintain an anaerobic environment, the inlets for the water to be treated and the liquid organic matter can be connected to the bottom of the treatment container, and the contents can be allowed to flow underground within the container. Furthermore, if the water to be treated is groundwater, the treatment container can be a permeable reaction wall buried underground, and the groundwater flow can be used for the supply system of the water to be treated, the discharge system of the treated water, and the energy for supply and discharge.

[0029] The treatment container may typically include a layer of grain husks carrying sulfate-reducing bacteria, which are a purification agent for water to be treated containing heavy metal ions. Furthermore, it is preferable to provide a layer of crushed stone, typically, within the treatment container to support the grain husks at the bottom, as well as to prevent the outflow of solid matter from the container and to prevent clogging of the drainage system. In order to stably hold the grain husks in place, it is preferable that the grain husks in the grain husk layer carrying sulfate-reducing bacteria are mixed with, for example, mineral stones such as limestone, or with mineral stones such as limestone and soil. The mixing ratio of grain husks to limestone is not particularly limited, but may be, for example, a mass ratio of about 1:2 to 1:10.

[0030] In the biological purification treatment of water to be treated according to this embodiment, liquid organic matter as a nutrient source for activating sulfate-reducing bacteria and water to be treated are preferably continuously supplied to the treatment container from each inlet of the treatment container, and the water to be treated and liquid organic matter are mixed and move downward through the grain layer by gravity, and in the process the reactions of reaction formulas (A) and (B) above occur (i.e., sulfate-reducing bacteria use the liquid organic matter as a nutrient source to reduce sulfate ions and hydrogen sulfide ions (HS) - ) is generated, and then the generated hydrogen sulfide ions (HS) are produced. - A reaction in which ) combines with heavy metal ions in the treated water and precipitates as sulfides gradually proceeds, and the treated water is discharged from the outlet (typically at the bottom) of the treatment container.

[0031] In the biological purification method for water to be treated according to this embodiment, the amount of liquid organic matter supplied is adjusted to control the degree of reduction of sulfate ions in the water to be treated. More specifically, the concentration of liquid organic matter relative to the total amount of water to be treated and liquid organic matter in the treatment container can be set to be substantially constant, according to the concentration of heavy metal ions contained in the water to be treated, so that after a predetermined period has elapsed since the start of treatment by supplying water to be treated and liquid organic matter, there is a surplus amount of hydrogen sulfide ions contained in the treated water after reaction treatment with heavy metal ions and it is adjusted to be within a predetermined target range. By using liquid organic matter instead of solid organic matter as a nutrient source for sulfate-reducing bacteria, and by adjusting the supply amount of liquid organic matter to control the degree of reduction of sulfate ions in the treated water, more specifically, by adjusting and setting the supply concentration of liquid organic matter to be approximately constant according to the concentration of heavy metal ions in the treated water, so that the excess amount of hydrogen sulfide ions after reaction treatment with heavy metal ions remains within a predetermined target range greater than zero, not only can the formation of biofilm caused by excessive decomposition of nutrient sources be effectively suppressed, but the initial rise in COD immediately after the nutrient source is introduced into the treatment system can also be reduced. Consequently, it becomes easier to control the treatment of the treated water stably and continuously over a long period of time. Therefore, this biological purification method can be suitably utilized in a natural-use passive treatment system.

[0032] In this context, "start of treatment by supplying water to be treated and liquid organic matter" refers to the point in time when the supply of both water to be treated and liquid organic matter to the treatment container begins. Here, the "predetermined period" in which a surplus amount of hydrogen sulfide ions in the treated water continues to react with heavy metal ions after treatment and is adjusted to a predetermined target range is preferably as short as possible, and may be within 90 days, preferably within 80 days, 70 days, 60 days, 50 days, or 40 days, and even more preferably within 30 days. Furthermore, the longer the "continuous" period after the predetermined period (i.e., the period of stable operation), the more desirable it is to be 10 days or more, 20 days or more, 30 days or more, 40 days or more, 50 days or more, or 60 days or more, and more preferably 70 days or more, 80 days or more, 90 days or more, 100 days or more, 110 days or more, or 120 days or more.

[0033] Here, "depending on the concentration of heavy metal ions in the water to be treated" means that the water to be treated is treated such that the concentration of heavy metal ions in the treated water obtained by subjecting the water to be treated, which contains a certain concentration of heavy metal ions, to the purification method according to this embodiment is at least below the upper limit of the legal wastewater standards (Cd ions: 0.03 mg / L, Pb ions: 0.1 mg / L, Zn ions: 2 mg / L, Cu ions: 3 mg / L, As ions: 0.1 mg / L). Although the wastewater standards for Fe ions are not defined by the aforementioned regulations, if Fe ions are to be considered for removal, it is preferable to treat the water to be treated so that the concentration is at least 1 mg / L or less.

[0034] In the biological purification method of the water to be treated according to this embodiment, hydrogen sulfide ions (HS) are released according to the above reaction formula (B). - The reaction between the hydrogen sulfide ions and heavy metal ions in the treated water proceeds, resulting in the precipitation and detoxification of sulfides containing heavy metal ions. Therefore, the existence of a "surplus amount of hydrogen sulfide ions in the treated water after the reaction with heavy metal ions" means that the reaction process is proceeding successfully. Accordingly, the preferred range of time required from the start of treatment by supplying the treated water and liquid organic matter (preferably by continuous supply) until the concentration of heavy metal ions in the treated water reaches below the predetermined upper limit mentioned above is preferably as short as possible, similar to the "predetermined period" mentioned above, and may usually be within 90 days, preferably within 80 days, 70 days, 60 days, 50 days, or 40 days, and even more preferably within 30 days.

[0035] As described above, the liquid organic matter that serves as a nutrient source for sulfate-reducing bacteria may preferably contain at least one alcohol, which is a linear, branched, or cyclic alcohol with 8 or fewer carbon atoms. The alcohol may contain one or more of methanol, ethanol, and propanol, and preferably ethanol. More preferably, the liquid organic matter may consist solely of ethanol. In one embodiment, the liquid organic matter may contain 90% to less than 100% by mass of ethanol and other alcohols (e.g., methanol or propanol) in amounts greater than 0% and 10% or less by mass. In another embodiment, the liquid organic matter may contain 95% to less than 100% by mass of ethanol and other alcohols (e.g., methanol or propanol) in amounts greater than 0% and 5% or less by mass. When a liquid organic matter consisting substantially solely of ethanol is used as a nutrient source for sulfate-reducing bacteria, all of the desirable advantages of suppressing biofilm formation, suppressing the rise in initial COD, and controlling the stable and continuous treatment of the treated water over a long period of time can be achieved most easily.

[0036] According to the biological purification method for treated water of this embodiment, by setting the concentration of liquid organic matter, which is a nutrient source for sulfate-reducing bacteria, to approximately constant and preferably supplying it continuously to the treatment container, the initial rise in COD of the treated water (and the accompanying initial rise in TOC: total organic carbon) can be effectively suppressed. In this method, the TOC (total organic carbon) of the treated water immediately after the start of treatment by supplying the treated water and liquid organic matter may usually be less than 150 mg / L or 100 mg / L or less, and preferably 80 mg / L or less.

[0037] The concentration of liquid organic matter relative to the total amount of water and liquid organic matter in the treatment container is set to be approximately constant, depending on the concentration of heavy metal ions in the water. A higher concentration of liquid organic matter is preferable because it shortens the predetermined time and reduces the time required for the heavy metal ion concentration to reach below a predetermined upper limit. On the other hand, it is also preferable to set the concentration of liquid organic matter below a predetermined upper limit from the viewpoint of preventing increased costs and waste of carbon resources due to excessive use of liquid organic matter, as well as suppressing biofilm formation and the rise in initial COD. The concentration is not limited, but is usually between 1 mg / L and 200 mg / L, and is preferably between 3 mg / L and 100 mg / L, 3 mg / L and 80 mg / L, 5 mg / L and 60 mg / L, 5 mg / L and 40 mg / L, 7 mg / L and 30 mg / L, or 7 mg / L and 20 mg / L. It is preferable to continuously maintain the concentration of liquid organic matter relative to the total amount of water to be treated and liquid organic matter in the treatment container at a substantially constant concentration initially set, from the predetermined period through a continuous period after the predetermined period has elapsed. In another embodiment, the concentration of liquid organic matter can also be maintained at a substantially constant concentration that has been changed from the point in time when the predetermined period has elapsed or at some point after the predetermined period has elapsed.

[0038] The target range for the excess amount of hydrogen sulfide ions in the treated water after reaction with heavy metal ions is not particularly limited, but its lower limit can usually be set to greater than 0 mg / L, preferably 0.1 mg / L or more, 0.2 mg / L or more, 0.3 mg / L or more, 0.4 mg / L or more, 0.5 mg / L or more, 0.6 mg / L or more, 0.7 mg / L or more, 0.8 mg / L or more, 0.9 mg / L or more, or 1 mg / L or more. Its upper limit can usually be 80 mg / L or less, preferably 70 mg / L or less, 60 mg / L or less, 50 mg / L or less, 40 mg / L or less, 30 mg / L or less, 25 mg / L or less, 20 mg / L or less, 15 mg / L or less, 10 mg / L or less, or 5 mg / L or less.

[0039] As described above, the shorter the predetermined period from the start of treatment by supplying the water to be treated and liquid organic matter until the excess amount of hydrogen sulfide ions after reaction with heavy metal ions falls within a predetermined target range greater than zero, the better. Furthermore, the longer the period of stable operation during which the excess amount of hydrogen sulfide ions remains within the predetermined target range greater than zero, the better. In the biological purification method for water to be treated according to this embodiment, the predetermined period can be shortened and the period of stable operation can be lengthened by continuously adjusting and setting the supply concentration of liquid organic matter to a substantially constant level according to the concentration of heavy metal ions in the water to be treated so that the excess amount of hydrogen sulfide ions remains within a predetermined target range from the start of treatment by supplying the water to be treated and liquid organic matter until a predetermined period has elapsed. In other words, in the biological purification method for treated water according to this embodiment, when the supply concentration of liquid organic matter, which is a nutrient source for sulfate-reducing bacteria, is adjusted and set to be approximately constant according to the concentration of heavy metal ions in the treated water, it is preferable to select a specific type of liquid organic matter and determine its supply concentration so that the excess amount of hydrogen sulfide ions remains within a predetermined target range for as long as possible, after as short a period of time has elapsed since the start of treatment by supplying the treated water and liquid organic matter.

[0040] The reason for setting the concentration of liquid organic matter relative to the total amount of water and liquid organic matter in the treatment container to be approximately constant, "according to the concentration of heavy metal ions contained in the water to be treated," is that, for example, in embodiments where the water to be treated is mine-derived wastewater such as mine wastewater from a metal mine, or industrial wastewater, the amount of water to be treated may fluctuate to some extent over time. Therefore, it may not be easy in practice to maintain a perfectly constant concentration of liquid organic matter relative to the total amount of water and liquid organic matter in the treatment container. The range of "approximately constant" concentration is not intended to be particularly limited, but it may include cases where the concentration fluctuates within a range of approximately ±20% from the initial set concentration, or within a range of approximately ±10% from the initial set concentration. Nevertheless, if there is virtually no fluctuation in the amount of water to be treated over time, or if a means is provided to keep the amount of water to be treated constant over time, it is more preferable to "set the concentration of liquid organic matter relative to the total amount of water and liquid organic matter in the treatment container to be constant, "according to the concentration of heavy metal ions contained in the water to be treated."

[0041] Furthermore, in embodiments where the water to be treated is mine-derived wastewater such as mine wastewater from a metal mine, or industrial wastewater, the concentration of heavy metal ions contained therein, in addition to the amount of water to be treated, may also fluctuate to some extent over time. In this case, due to the fluctuations in the concentration of heavy metal ions, it may not be easy in practice to adjust the excess amount of hydrogen sulfide ions in the treated water after reaction with heavy metal ions to a predetermined target range over a long period of time by "setting the concentration of liquid organic matter relative to the total amount of water to be treated and liquid organic matter in the treatment container to be approximately constant, according to the concentration of heavy metal ions contained in the water to be treated." Therefore, in the biological purification method for water to be treated according to this embodiment, it is also preferable to appropriately review and reset the concentration of liquid organic matter at predetermined intervals (for example, every 10, 20, 30, 40, 50, 60, or 120 days) in response to the changes over time in the amount of water to be treated and the concentration of heavy metal ions contained therein.

[0042] Figure 1 shows a non-exclusive example of an apparatus for implementing the biological purification method / purification system for treated water according to this embodiment. In Figure 1, the reference numerals are as follows: 1 is the treatment vessel (reaction tank), 2 is the upper lid of the treatment vessel, 3 is the bottom sealing plug of the treatment vessel, 4 is the grain layer located above the crushed stone layer inside the treatment vessel, 5 is the crushed stone layer located below the grain layer inside the treatment vessel and supporting the grain layer, 6 is the transfer pipe for transferring the water to be treated to the treatment vessel, 7 is the water to be treated introduction pump installed when there is a height difference between the water to be treated transfer system and the treatment vessel, 8 is the transfer pipe for transferring liquid organic matter to the treatment vessel, 9 is the liquid organic matter introduction pump installed when there is a height difference between the liquid organic matter transfer system and the treatment vessel, 10 is the discharge pipe for discharging the treated water from the reaction vessel, and 100 refers to the entire biological purification treatment system.

[0043] In Figure 1, the treatment container 1 comprises a vertically elongated main body made of transparent resin and formed in a roughly cylindrical shape, an upper lid 2 disposed on the top (top) of the main body so as to be removable or openable, and a bottom sealing plug 3 disposed on the bottom (bottom) of the main body so as to be removable or openable. The shape of the treatment container 1 is shown as a roughly cylindrical container, but it may be a vertically elongated or flattened roughly rectangular parallelepiped, roughly cubic, roughly spherical, etc. In addition, the material of the treatment container 1 may include translucent or opaque resin, metal, ceramics, rock, clay, etc., in whole or in part of the container, in addition to transparent resin. In a natural passive treatment system, the treatment container 1 can be replaced with an artificial pond, artificial wetland, large tank, etc.

[0044] Furthermore, in Figure 1, a crushed stone layer 5 is formed inside the processing container 1 at the bottom so as to cover the area above the discharge port, and a grain layer 4 is arranged above it, supported by the crushed stone layer. The crushed stone layer 5 has the function of preventing the outflow of solid matter from inside the container, thereby preventing clogging of the drainage system. The crushed stone of the crushed stone layer 5 is not particularly limited as long as it performs such a function, and any commercially available crushed stone may be used. The grain layer 4 is composed of grain husks that carry sulfate-reducing bacteria inside the processing container. The grain husks in the grain layer are mixed with mineral stones such as limestone, or with mineral stones such as limestone and soil in an appropriate mixing ratio. By mixing the grain husks with mineral stones such as limestone in the grain layer in this way, the grain husks can be stably held in place.

[0045] In the biological purification apparatus illustrated in Figure 1, the water to be treated A passes through the water to be treated transfer pipe 6, utilizing the lift provided by the water to be treated introduction pump 7, and the liquid organic matter B (typically alcohols such as ethanol) passes through the liquid organic matter transfer pipe 8, utilizing the lift provided by the liquid organic matter introduction pump 9, and both are continuously introduced into the treatment container 1 via the upper lid 2, forming a mixed liquid C of water to be treated and liquid organic matter. The mixed liquid C of water to be treated and liquid organic matter moves downward through the grain layer 4 of the treatment container 1 according to gravity, and its biological treatment (reactions of reaction equations (A) and (B) above) gradually proceeds. After the mixed liquid C undergoes biological treatment in the grain layer 4 and reaches the bottom of the treatment container 1 via the crushed stone layer 5, the treated liquid D is discharged from the discharge pipe 10 through the discharge port of the bottom sealing plug 3. Here, from the start of treatment by supplying water A and liquid organic matter B for treatment, after a predetermined period has elapsed, the concentration of liquid organic matter B relative to the total amount of water A and liquid organic matter B in the treatment container 1 is set to be approximately constant, according to the concentration of heavy metal ions contained in water A for treatment, so that there is a surplus amount of hydrogen sulfide ions contained in treated water C after the reaction treatment with heavy metal ions and that it is adjusted to a predetermined target range.

[0046] In a particularly preferred embodiment (the second embodiment), the biological purification method for water to be treated involves adjusting the supply amount of liquid organic matter to control the degree of reduction of sulfate ions in the water to be treated, thereby obtaining treated water containing a surplus amount of hydrogen sulfide ions greater than a predetermined value. Subsequently, this treated water is mixed with newly supplied water to be treated containing heavy metal ions and sulfate ions, thereby precipitating sulfides containing heavy metal ions contained in the water to be treated. More specifically, the biological purification method for water to be treated in this embodiment involves, from the start of treatment by supplying water to be treated and liquid organic matter (preferably continuously), continuously adjusting the concentration of liquid organic matter relative to the total amount of water to be treated and liquid organic matter in the treatment container so that the excess amount of hydrogen sulfide ions after the reaction treatment with heavy metal ions in the treated water is intentionally adjusted to be greater than a predetermined value, thereby obtaining treated water containing an excess amount of hydrogen sulfide ions greater than the predetermined value, and then, preferably without separately supplying a biological purification agent and liquid organic matter, mixing this treated water with newly supplied water to be treated containing heavy metal ions and sulfate ions, thereby precipitating the sulfides containing heavy metal ions contained in the treated water.

[0047] The water to be treated, heavy metal ions, liquid organic matter, sulfate-reducing bacteria, treatment container, and biological treatment mechanism in this embodiment may be the same as those described in the first embodiment above. Furthermore, the "newly supplied water to be treated containing heavy metal ions and sulfate ions" in this embodiment may be the same as the water to be treated above, except that it is newly supplied.

[0048] In this embodiment, the "predetermined value," which is the lower limit of the excess amount of hydrogen sulfide ions in the treated water after the reaction treatment with heavy metal ions, can be appropriately set according to the amount of newly supplied water to be treated, its ion content, and the mixing ratio of the treated water and the newly supplied water to be treated. This "predetermined value" is not particularly limited, but is usually 1 mg / L, preferably 2 mg / L, 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, or 80 mg / L. Furthermore, in this embodiment, the "continuous" period after the predetermined period has elapsed is not particularly limited as long as treated water containing a sufficient amount of hydrogen sulfide ions necessary for subsequent mixing treatment with newly supplied treated water is obtained, but may be, for example, 1 day or more, 2 days or more, 3 days or more, 5 days or more, 10 days or more, 20 days or more, 30 days or more, 40 days or more, 50 days or more, 60 days or more, 70 days or more, 80 days or more, or 90 days or more.

[0049] In this embodiment, the mixing ratio of treated water to newly supplied treated water containing heavy metal ions and sulfate ions can be appropriately set depending on the ionic composition of the treated water and the excess amount of hydrogen sulfide ions in the treated water, and is not particularly limited. The mixing ratio of treated water to newly supplied treated water may be, for example, 10:1 to 1:50 (volume ratio), and more typically 5:1 to 1:40, 5:1 to 1:30, 5:1 to 1:20, 5:1 to 1:10, 3:1 to 1:40, 3:1 to 1:30, 3:1 to 1:20, 3:1 to 1:10, 1:1 to 1:40, 1:1 to 1:30, 1:1 to 1:20, or 1:1 to 1:10.

[0050] The mixing vessel for this mixing is not particularly limited, as long as it has a volume capable of accommodating the treated water and the newly supplied water to be treated. The mixing vessel may be made of the same material as exemplified as the material of the treatment vessel (reaction tank) in the above embodiment. The mixing vessel may also be an artificial pond, artificial wetland, large tank, etc. If the transfer path, such as piping, for supplying the treated water and the newly supplied water to be treated to the mixing vessel is located at a higher position than the inlet of the mixing vessel, an electric pump may be used, for example, to provide supply energy (lift).

[0051] To facilitate understanding, a simplified process flow of a preferred example of the biological purification treatment method according to this embodiment is shown in Figure 2. In Figure 2, a surplus amount of hydrogen sulfide ions (HS) greater than a predetermined value was obtained from a biological purification treatment apparatus 100 similar to the one shown in Figure 1. - The treated water containing ) and the newly supplied treated water containing heavy metal ions and sulfate ions are simply mixed. At this time, neither the biological purification agent (exemplified as grain layer 5 in Figure 1) nor the liquid organic matter (exemplified as liquid organic matter B in Figure 1) is supplied separately to the mixing system.

[0052] As described above, in the biological purification method of the water to be treated according to the first embodiment, hydrogen sulfide ions (HS) are produced according to the above reaction formula (B). - The hydrogen sulfide reacts with heavy metal ions, causing sulfides containing heavy metal ions to precipitate and become harmless. Therefore, the presence of a surplus of hydrogen sulfide ions in the treated water after the reaction with heavy metal ions indicates that the reaction has proceeded successfully. Conversely, this means that there are always hydrogen sulfide ions present that are not utilized in the reaction. According to this preferred second embodiment (which belongs to a sub-concept of the first embodiment described above), the fact that there are always hydrogen sulfide ions that are not utilized in the reaction process is taken advantage of, and a surplus amount of hydrogen sulfide ions (HS) greater than a predetermined value is intentionally created. -By obtaining treated water containing ) such a large surplus of hydrogen sulfide ions, this treated water can be effectively utilized for the treatment of newly supplied water to be treated.

[0053] Sulfate-reducing bacteria generally exhibit activity fluctuations with temperature. When biological treatment is performed at room temperature or ambient temperature, their activity tends to be higher in the summer months (resulting in a larger excess of hydrogen sulfide ions) and lower in the winter months (resulting in a smaller excess of hydrogen sulfide ions). Releasing treated water containing a large excess of hydrogen sulfide ions into the environment as waste means discarding a valuable substance capable of treating heavy metal ions. According to this preferred embodiment, treated water containing a large excess of hydrogen sulfide ions can be effectively utilized for treating newly supplied water to be treated. This suppresses the wasteful discharge of hydrogen sulfide ions, a valuable substance capable of treating heavy metal ions, thereby increasing the utilization efficiency of hydrogen sulfide ions and enabling stable and efficient treatment throughout the year, including the hot summer months. Furthermore, this method offers the significant advantage of allowing for a smaller-scale treatment facility. For example, by reducing the capacity of the treatment container by several tens of percent (e.g., 30%, 40%, 50%, 60%, or 70%), while performing biological treatment on some of the water to be treated, along with the simultaneous supply of liquid organic matter as a nutrient source, the remaining water can be simply mixed with the treated water. This significantly reduces both treatment and equipment costs. [Examples]

[0054] The effects of the present invention will be described in more detail below based on the examples. However, the present invention is not limited to these examples.

[0055] <Preparing the processing container> For this experiment, a container was prepared that included a cylindrical body made of transparent polyvinyl chloride, with a diameter of approximately 10 cm and a height of approximately 150 cm (manufactured by Miyata Kogyosho Co., Ltd.). This container has an upper lid on the top side and a lower sealing plug on the bottom side. The upper lid has inlets for the water to be treated and liquid organic matter, and the container is configured to connect to transfer pipes and pumps corresponding to each inlet. The lower sealing plug has a discharge port, and by attaching and connecting a discharge pipe (discharge tube) to the discharge port, the treated water can be discharged from the discharge tube. As the solution (water to be treated) used in this experiment, we used raw treatment water (iron removed by another process), which is acidic (pH 3.0) mine wastewater containing Cd ions: 0.05 mg / L, Zn ions: 17 mg / L, Cu ions: 4.3 mg / L, and Fe ions: 8.0 mg / L. First, before forming the layer containing the biological purification agent, approximately 400g of crushed stone was filled into the bottom of the cylindrical container to prevent the contents from leaking out, creating a crushed stone layer approximately 5cm high. The crushed stone used was a commercially available product (manufactured by Nichiei Pharmaceutical Co., Ltd.) with a particle size of 5-13mm. In addition to the discharge port at the bottom of the container, this processing vessel is also equipped with an outlet for sampling and analysis on the side of the main body (approximately in the middle position) corresponding to the grain layer containing the biological purification agent.

[0056] <Formation of grain layers containing biological purification agents> A mixture of 870g of rice hulls and 3500g of limestone (4370g / mixing weight ratio approximately 1:4) was pre-mixed and placed on top of the crushed stone layer to form a 100cm high rice hull layer. The rice hulls were procured from farmers, and the limestone was a commercially available product with a particle size of 13-20mm (manufactured by Nichiei Pharmaceutical Co., Ltd.).

[0057] Example 1 <Continuous supply of treated water and liquid organic matter> Three treatment containers with the above configuration were arranged in parallel. The flow rate of the water to be treated was set to approximately 2.7 mL / min, and ethanol was used as the liquid organic matter. The concentrations of ethanol in the mixture of water to be treated and ethanol were set to 24 mg / L, 36 mg / L, and 48 mg / L for each of the three treatment containers. The water level in the treatment container body of the water to be treated mixed with ethanol was adjusted to be approximately 10 cm above the top of the grain layer, and the hydraulic residence time (HRT) was adjusted to be approximately 25 hours. Three treatment containers were used to supply ethanol at concentrations of 24 mg / L, 36 mg / L, and 48 mg / L. Each of these was continuously supplied from the inlet of the treatment container using a pump. The supplied water and ethanol formed a mixture, which underwent biological treatment as it moved downward through the grain layer. After passing through the crushed stone layer and reaching the bottom of the treatment container, the treated liquid was discharged through the outlet of the bottom seal via a discharge pipe.

[0058] <Measurement of zinc ion concentration in treated water> For each of the cases where the constant concentration of ethanol in the mixture of water to be treated and ethanol was set to 24 mg / L, 36 mg / L, and 48 mg / L, the zinc ions (Zn) in the unfiltered treated water were measured. 2+ The zinc ion concentration (mg / L) was measured periodically using ICP-AES. Figure 3 shows graphs illustrating the change in zinc ion concentration in the treated water over time (days) from the start of treatment for ethanol concentrations of 24 mg / L, 36 mg / L, and 48 mg / L. Figure 3 also shows the change in zinc ion concentration of the treated water (labeled "raw water" in the graph) overlaid for comparison. Figure 3 shows that when the ethanol concentration is 48 mg / L, zinc ions can be almost completely removed after 30 days from the start of treatment, and even when the ethanol concentration is 24 mg / L, stable removal of zinc ions can be achieved after 60 days from the start of treatment. The time required to achieve stable removal of zinc ions decreased as the ethanol concentration increased. Although not shown in the graph in Figure 3, when we collected intermediate treated water from an outlet on the side of the treatment container and similarly observed the change in zinc ion concentration, we found that it tended to be slightly higher overall than the zinc ion concentration of the treated water (however, the effect of the amount of alcohol concentration was the same). This is understood to indicate that the biological treatment (reactions in reaction equations (A) and (B) above) actually progressed gradually as the mixture of water to be treated / ethanol moved downward through the grain layer of the treatment container due to gravity.

[0059] <Measurement of hydrogen sulfide ion concentration in treated water> For each case where the constant concentration of ethanol in the mixture of water to be treated and ethanol is set to 24 mg / L, 36 mg / L, and 48 mg / L, the hydrogen sulfide ions (HS) in the unfiltered treated water were measured. - The sulfide ion concentration (mg / L) was measured periodically using the methylene blue absorption spectrometry method (JIS K0102 2016 39.1). Figure 4 shows graphs illustrating the change in hydrogen sulfide ion concentration in the treated water over time (days) from the start of treatment for ethanol concentrations of 24 mg / L, 36 mg / L, and 48 mg / L. In this specification, "controlling the degree of sulfate ion reduction" refers to the relationship between sulfate-reducing bacteria and sulfate ions (SO4) in the treated water, which serve as nutrients for the sulfate-reducing bacteria. 2- ) incorporates and reduces sulfate ions, and hydrogen sulfide ions (HS) - Since this refers to the degree of progress of the reaction that produces ), the degree of reduction of sulfate ions can be evaluated by measuring the concentration of hydrogen sulfide ions remaining in the treated water after combination with heavy metal ions in this way.

[0060] Figure 4 shows that when the ethanol concentration was 48 mg / L, excess hydrogen sulfide ions began to continuously form in the treated water around 30 days after the start of treatment, and then gradually increased to about 25 mg / L. After 60 days, the excess hydrogen sulfide ions remained generally stable, although there were some fluctuations. Similarly, when the ethanol concentration was 24 mg / L, excess hydrogen sulfide ions began to form around 60 days after the start of treatment, and thereafter remained generally stable at less than 5 mg / L. As the ethanol concentration increased, the time until excess hydrogen sulfide ions began to form shortened, and the amount of excess ions increased. Therefore, considering this relationship between ethanol concentration and the excess amount of hydrogen sulfide ions in the treatment of the water to be treated, for example, if the target range for the excess amount of hydrogen sulfide ions after the reaction of heavy metal ions in the treated water is set to 20 mg / L or less, adjusting the ethanol concentration to a constant value greater than 48 mg / L would likely result in an excess amount of hydrogen sulfide ions exceeding the target range. Therefore, it is preferable to adjust the ethanol concentration to a constant value of approximately 48 mg / L or less. Another example in the treatment of the water to be treated is if the target range for the excess amount of hydrogen sulfide ions after the reaction of heavy metal ions in the treated water is set to 10 mg / L or less. Adjusting the ethanol concentration to a constant value greater than 24 mg / L would likely result in an excess amount of hydrogen sulfide ions exceeding the target range. Therefore, it is preferable to adjust the ethanol concentration to a constant value of approximately 24 mg / L or less.

[0061] <Measurement of total organic carbon (TOC) in treated water> For each of the following cases, where the ethanol concentration in the mixture of water to be treated and ethanol was set to 24 mg / L, 36 mg / L, and 48 mg / L, the total organic carbon (hereinafter referred to as "TOC") of the unfiltered treated water was periodically measured using the NPOC method with a TOC analyzer (Shimadzu Corporation "TOC-L"). Figure 5 shows graphs illustrating the change in TOC of the treated water over time (days) since the start of treatment for each of the ethanol concentrations of 24 mg / L, 36 mg / L, and 48 mg / L. As shown in Figure 5, favorably, even at a high ethanol concentration of 48 mg / L, the TOC of the treated water immediately after the start of treatment was less than 100 mg / L, and although there was a temporary increase thereafter, the overall trend was a gradual decrease. After 30 days from the start of treatment, it never exceeded 20 mg / L, and after 60 days, it never exceeded 15 mg / L. When the ethanol concentration was low at 24 mg / L, the TOC of the treated water immediately after the start of treatment was less than 50 mg / L, and although there was a temporary increase thereafter, the overall trend was a gradual decrease. After 30 days from the start of treatment, it never exceeded 15 mg / L, and after 60 days, it never exceeded 10 mg / L. The lower the ethanol concentration, the lower the TOC of the treated water immediately after the start of treatment, and the lower the TOC thereafter remained.

[0062] <Evaluation of the relationship between the difference in sulfate ions before and after treatment and the difference in TOC> For each case where the constant concentration of ethanol in the mixture of water to be treated and ethanol is set to 24 mg / L, 36 mg / L, and 48 mg / L, the sulfate ions (SO4) in the water to be treated at the inlet of the treatment container are measured. 2- ) concentration and sulfate ions (SO4) in the water after treatment 2- ) Difference from concentration (Δ In-Out SO4 2- The TOC (Δ) of the water to be treated and the TOC of the water after treatment at the inlet of the treatment container are measured periodically by ion chromatography, and the difference (Δ) between the TOC of the water to be treated and the TOC of the water after treatment is measured. In-Out TOC (Total Oxygen Content) [mg / L] was periodically measured using the NPOC method with a TOC analyzer (Shimadzu Corporation "TOC-L"). For ethanol concentrations of 24 mg / L, 36 mg / L, and 48 mg / L, sulfate ions (SO4) were measured before and after treatment. 2- ) difference (Δ In-Out SO4 2- The difference in TOC before and after processing (Δ) for the change in [mg / L] In-Out Figure 6 shows a graph illustrating the trend of TOC (total Oxygen Content [mg / L]). From Figure 6, in all cases of ethanol concentration, sulfate ions (SO4) before and after treatment. 2-) Difference in concentration (Δ In-Out SO4 2- As the [mg / L] increases, the difference in TOC before and after processing (Δ In-Out A clear correlation was found (with some fluctuation) that TOC [mg / L] also increased. Furthermore, in all cases of ethanol concentration, the sulfate ions (SO4) before and after treatment were also found to increase. 2- ) Difference in concentration (Δ In-Out SO4 2- Even when the [mg / L] was zero, meaning no sulfate reduction was occurring at all, approximately 5 mg / L of organic matter was consumed in terms of TOC.

[0063] <Observation of the presence or absence of biofilm formation in the treatment container> The presence or absence of biofilm formation in the treatment container was monitored for each of the following conditions: the ethanol concentration in the mixture of treated water and ethanol was set to 24 mg / L, 36 mg / L, and 48 mg / L. Although some biofilm formation was observed at all ethanol concentrations, it did not worsen water permeability, and no rise in water level was observed for at least 200 days.

[0064] Comparative Example 1 In Example 1, one treatment container and the acidic mine wastewater described above were prepared as the raw water to be treated. In addition, 4 tons of rice bran, which had been previously soaked in the raw water to be treated, were prepared as a nutrient source for sulfate-reducing bacteria. The rice bran was added to the treatment container in three batches of approximately equal amounts, and then the soaking liquid of the rice bran was also added to the reaction vessel. The water to be treated was supplied continuously at the flow rate described above for Example 1. Figure 7 shows a graph illustrating the change in TOC of the treated water over time (days) from the start of treatment, including the continuous supply of water to be treated and the initial batch addition of rice bran.

[0065] As shown in Figure 7, the TOC of the treated water immediately after the start of treatment was very high at 750 mg / L. The BOD of the treated water was also high at 1500 mg / L and the COD was high at 690 mg / L (160 mg / L; significantly exceeding the COD emission standard of 120 mg / L per day). In this example, it took more than 50 days for the TOC of the treated water to stabilize below 50 mg / L. After more than 100 days from the start of treatment, a biofilm gradually formed, and the water permeability slowly decreased.

[0066] Example 2 The water to be treated (pH 3.7, Cd ions: 0.04 mg / L, Pb ions: 0.8 mg / L, Zn ions: 6.2 mg / L, Cu ions: 8.0 mg / L, Fe ions: 0.1 mg / L) and the treated water (pH 7.0, hydrogen sulfide ions: 10 mg / L) obtained by adding a certain concentration of ethanol were used. 400 ml of treated water with an excess hydrogen sulfide ion content of approximately 10 mg / L was mixed in a container with 100 ml of newly supplied water to be treated, in a mixing ratio of 4:1. At this time, the mixture was simply left to stand without introducing ethanol, which is a biological purification agent and nutrient source, into the container. After standing for about 1 minute, the concentrations of each ion (mg / L) were measured by ICP-AES. Furthermore, the mixing ratio of treated water to newly supplied water to be treated was changed to 375ml:125ml (3:1), 330ml:165ml (2:1), 250ml:250ml (1:1), 165ml:330ml (1:2), 125ml:375ml (1:3), 100ml:400ml (1:4), 80ml:400ml (1:5), 70ml:420ml (1:6), and 60ml:420ml (1:7). After mixing and letting the mixture stand as described above, the ion concentrations (mg / L) were measured by ICP-AES. Figure 8 shows the newly supplied treated water and the ion concentrations (mg / L) after mixing and standing at each of the above mixing ratios.

[0067] As shown in Figure 8, it was found that heavy metal ions such as zinc ions were completely removed by simple mixing treatment when the mixing ratio of the newly supplied treated water to the treated water was reduced from 4:1 to 1:3 (i.e., up to three times the amount of newly supplied treated water). When the mixing ratio of the newly supplied treated water to the treated water was set to 1:4 (i.e., four times the amount of newly supplied treated water), zinc ions were detected at approximately 3 mg / L, but no other heavy metal ions were detected. When the mixing ratio of the newly supplied treated water to the treated water was increased to 1:5 or higher, the amount of zinc ions detected increased further. In this experiment, we used treated water with a relatively small excess of hydrogen sulfide ions, approximately 10 mg / L. However, it is naturally expected that by further increasing the excess amount of hydrogen sulfide ions, it will be possible to remove heavy metal ions from a larger volume of newly supplied treated water through this simple mixing process. The various aspects and embodiments that may be included in the present invention can be summarized as follows. [1] A biological purification method for water to be treated that contains heavy metal ions and sulfate ions, The method involves passing the water to be treated through a biological purification agent containing grain husks carrying sulfate-reducing bacteria, which is housed in a treatment container where anaerobic conditions are maintained. The sulfate-reducing bacteria reduce the sulfate ions to generate hydrogen sulfide ions, and the hydrogen sulfide ions react with the heavy metal ions to precipitate sulfides, thereby obtaining treated water from which the heavy metal ions have been removed. A liquid organic substance is supplied into the processing container as a nutrient source to activate the sulfate-reducing bacteria. Includes, The amount of liquid organic matter supplied is adjusted to control the degree of reduction of sulfate ions in the water to be treated. Biological purification methods. [2] The method according to item 1, wherein the liquid organic matter contains at least one alcohol. [3] The method according to item 2, wherein the at least one alcohol comprises one or more of methanol, ethanol, and propanol. [4] The method according to any one of items 1 to 3 above, wherein the TOC (total organic carbon) of the treated water immediately after the start of treatment by supplying the water to be treated and the liquid organic matter is less than 100 mg / L. [5] By adjusting the supply amount of the liquid organic matter and controlling the degree of reduction of the sulfate ions in the water to be treated, it is possible to obtain treated water containing a surplus amount of hydrogen sulfide ions greater than a predetermined value, and The method according to any one of items 1 to 4 above, comprising mixing the treated water with newly supplied treated water containing heavy metal ions and sulfate ions to precipitate sulfides containing the heavy metal ions contained in the treated water. [6] A biological purification system for water to be treated that contains heavy metal ions and sulfate ions, A treatment container containing a biological purification agent containing grain husks carrying sulfate-reducing bacteria, and in which anaerobic conditions are maintained, A supply system for supplying both the water to be treated and liquid organic matter as a nutrient source for activating the sulfate-reducing bacteria into the treatment container, The system includes a discharge system for discharging treated water from the treatment container, which is formed by reducing sulfate ions with sulfate-reducing bacteria to produce hydrogen sulfide ions, reacting the hydrogen sulfide ions with the heavy metal ions to precipitate sulfides, thereby removing the heavy metal ions from the treated water. The means includes adjusting the supply amount of the liquid organic matter and controlling the degree of reduction of the sulfate ions in the water to be treated, Biological purification system. [7] The system according to item 6, wherein the liquid organic matter contains at least one alcohol. [8] The system according to item 7, wherein the at least one alcohol comprises one or more of methanol, ethanol, and propanol. [9] A means for obtaining treated water containing a surplus amount of hydrogen sulfide ions greater than a predetermined value by adjusting the supply amount of the liquid organic matter and controlling the degree of reduction of the sulfate ions in the water to be treated, and The system according to any one of items 6 to 8 above, comprising means for precipitating sulfides containing heavy metal ions contained in the treated water by mixing the treated water with newly supplied treated water containing heavy metal ions and sulfate ions. [Explanation of Symbols]

[0068] 1: Processing vessel (reaction vessel) 2: Upper lid part 3: Bottom sealing plug 4: Grain layer 5: Crushed stone layer 6: Pipe for transferring treated water 7: Pump for introducing water to be treated 8: Liquid organic matter transfer pipe 9: Pump for introducing liquid organic matter 10: Discharge pipe for treated water 100: Biological purification treatment equipment A: Water to be treated B: Liquid organic matter C: Water to be treated / Mixture of liquid organic matter D: Treated water

Claims

1. A biological purification method for water to be treated that contains heavy metal ions and sulfate ions, The method involves passing the water to be treated through a biological purification agent containing grain husks carrying sulfate-reducing bacteria, which is housed in a treatment container where anaerobic conditions are maintained. The sulfate-reducing bacteria reduce the sulfate ions to generate hydrogen sulfide ions, and the hydrogen sulfide ions react with the heavy metal ions to precipitate sulfides, thereby obtaining treated water from which the heavy metal ions have been removed. A liquid organic substance is supplied into the processing container as a nutrient source to activate the sulfate-reducing bacteria. Includes, From the start of treatment by supplying the water to be treated and the liquid organic matter, after a predetermined period has elapsed, the degree of reduction of sulfate ions in the water to be treated is controlled by setting the concentration of the liquid organic matter relative to the total amount of the water to be treated and the liquid organic matter in the treatment container to be approximately constant, according to the concentration of the heavy metal ions in the water to be treated, so that there is a surplus amount of hydrogen sulfide ions in the treated water after the reaction treatment with the heavy metal ions and it is adjusted to be within a predetermined target range. Biological purification methods.

2. The method according to claim 1, wherein the liquid organic matter comprises at least one alcohol.

3. The method according to claim 2, wherein the at least one alcohol comprises one or more of methanol, ethanol, and propanol.

4. The method according to any one of claims 1 to 3, wherein the TOC (total organic carbon) of the treated water immediately after the start of treatment by supplying the water to be treated and the liquid organic matter is less than 100 mg / L.

5. By adjusting the supply amount of the liquid organic matter and controlling the degree of reduction of the sulfate ions in the water to be treated, it is possible to obtain treated water containing a surplus amount of hydrogen sulfide ions greater than a predetermined value, and The method according to any one of claims 1 to 4, comprising mixing the treated water with newly supplied treated water containing heavy metal ions and sulfate ions to precipitate sulfides containing the heavy metal ions contained in the treated water.

6. A biological purification system for water to be treated that contains heavy metal ions and sulfate ions, A treatment container containing a biological purification agent containing grain husks carrying sulfate-reducing bacteria, and in which anaerobic conditions are maintained, A supply system for supplying both the water to be treated and liquid organic matter as a nutrient source for activating the sulfate-reducing bacteria into the treatment container, The system includes a discharge system for discharging treated water from the treatment container, which is formed by reducing sulfate ions with sulfate-reducing bacteria to produce hydrogen sulfide ions, reacting the hydrogen sulfide ions with the heavy metal ions to precipitate sulfides, thereby removing the heavy metal ions from the treated water. The method includes means for controlling the degree of reduction of sulfate ions in the water to be treated by setting the concentration of the liquid organic matter relative to the total amount of the water to be treated and the liquid organic matter in the treatment container to be substantially constant, in accordance with the concentration of the heavy metal ions in the water to be treated, so that, after a predetermined period has elapsed since the start of treatment by supplying the water to be treated and the liquid organic matter, there is a surplus amount of hydrogen sulfide ions in the treated water after reaction with the heavy metal ions and it is adjusted to a predetermined target range, Biological purification system.

7. The system according to claim 6, wherein the liquid organic matter comprises at least one alcohol.

8. The system according to claim 7, wherein the at least one alcohol comprises one or more of methanol, ethanol, and propanol.

9. A means for obtaining treated water containing a surplus amount of hydrogen sulfide ions greater than a predetermined value by adjusting the supply amount of the liquid organic matter and controlling the degree of reduction of the sulfate ions in the water to be treated, and The system according to any one of claims 6 to 8, comprising means for precipitating sulfides containing heavy metal ions in the treated water by mixing the treated water with newly supplied treated water containing heavy metal ions and sulfate ions.

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