JP7527657B2 - Water treatment method, method and system for producing denitrification agent or nitrification promoter - Google Patents

Description

The present invention relates to a water treatment method that performs biological nitrification/denitrification treatment by adding an organic carbon source, a method for producing a denitrification agent or a nitrification promoter, and a production system for a denitrification agent or a nitrification promoter.

In recent years, in order to prevent global warming, there has been progress in the development of alternative fuels to conventional fossil fuels that reduce carbon dioxide emissions and lead to resource recycling. One such fuel that has attracted attention is biodiesel fuel, which is made from vegetable oils and waste cooking oils. The mainstream method of synthesizing biodiesel fuel is to use animal and vegetable fats and monohydric alcohols as raw materials and synthesize the fuel through an ester exchange reaction using an alkaline substance such as potassium hydroxide as a catalyst (for example, Non-Patent Document 1). In this synthesis reaction, a by-product containing glycerin (also referred to as "waste glycerin" in this specification) is also produced.

In addition, when producing free fatty acids from fats and oils industrially, methods for producing them include high-temperature, high-pressure decomposition and enzymatic decomposition, all of which involve hydrolyzing fats and oils derived from animals and plants to liberate fatty acids. This type of hydrolysis also produces by-products containing glycerin.

Glycerin-containing waste contains a large amount of impurities such as catalysts and unreacted fats and oils. Therefore, although glycerin itself can be used as a raw material for pharmaceuticals, cosmetics, etc., the above-mentioned glycerin-containing waste must be purified at great cost in order to be used as a raw material for pharmaceuticals, cosmetics, etc., which is not practical. For this reason, glycerin-containing waste has often been disposed of as industrial waste.

On the other hand, when fats and oils such as edible oils deteriorate, hydrolysis occurs, the carbon chains are broken and further oxidized, resulting in oils with a high acid value (high acid value oils). Also, in the deacidification process during the refining of vegetable oils and fats, soapstock is separated from fats and oils (crude oil). These high acid value oils and soapstocks are waste products that contain fatty acid glycerin esters.

Journal of the Japan Society of Marine Engineering, 2012, Vol. 47, No. 1, pp. 45-50

Attempts have been made to effectively utilize glycerin-containing waste and fatty acid glycerin ester-containing waste in order to reduce the environmental burden. However, none of the methods proposed so far have been sufficient, and with the recent attention being given to biodiesel fuel, the establishment of a method for utilizing glycerin-containing waste and fatty acid glycerin ester-containing waste has become an even more urgent issue.

The present invention has been made in consideration of the above problems, and aims to provide new applications that can effectively utilize glycerin-containing waste and fatty acid glycerin ester-containing waste, and a method for treating glycerin-containing waste and fatty acid glycerin ester-containing waste that is suitable for use in such applications.

As a result of intensive research by the present inventors to solve the above problems, they have discovered that by adding an inorganic acid to a raw material containing at least one of glycerin and fatty acid glycerin esters, and then neutralizing the glycerin liquid and separating fats and oils and salts, it is possible to produce a glycerin-containing liquid that can be suitably used as an organic carbon source in biological nitrification denitrification treatment, and also to effectively recycle glycerin-containing waste and fatty acid glycerin ester-containing waste, thereby completing the present invention.
Specifically, the present invention is as follows.

[1] A water treatment method in which an organic carbon source is added to perform biological nitrification/denitrification treatment,
a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating a first oil component and a first glycerin liquid;
a neutralization step of neutralizing the first glycerin liquid with an alkaline substance;
a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
A glycerin-containing liquid is produced by
The resulting glycerin-containing liquid is added as an organic carbon source for the biological nitrification/denitrification treatment, and/or the denitrification treatment step is included.
Water treatment methods.
[2] The water treatment method according to [1], further comprising, after the second separation step, an alcohol separation step of separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated.
[3] A method for producing a denitrifying agent or a nitrification promoter used as an organic carbon source in a biological nitrification/denitrification treatment, comprising the steps of:
a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating a first oil component and a first glycerin liquid;
a neutralization step of neutralizing the first glycerin liquid with an alkaline substance;
a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
A glycerin-containing liquid is produced by
The method for producing said glycerin-containing liquid is characterized in that the obtained glycerin-containing liquid is added to said denitrification agent or said nitrification promoter as an organic carbon source for said biological nitrification/denitrification treatment.
[4] The method for producing a denitrification agent or a nitrification promoter according to [3], wherein the raw material in the first separation step includes at least one of waste glycerin produced as a by-product in the production process of biodiesel fuel and glycerin produced as a by-product in the production process of free fatty acids.
[5] The method for producing a denitrifying agent or a nitrification promoter according to [3] or [4], wherein the raw material in the first separation step contains a high acid value oil having an acid value of 10 mgKOH/g or more.
[6] The method for producing a denitrifying agent or a nitrification promoter according to any one of [3] to [5], wherein the inorganic acid in the first separation step is concentrated sulfuric acid.
[7] The method for producing a denitrifying agent or a nitrification promoter according to any one of [3] to [6], wherein in the first separation step, a mixed liquid of the raw material and the inorganic acid has a pH of 3 or less.
[8] The method for producing a denitrification agent or a nitrification promoter according to any one of [3] to [7], wherein in the neutralization step, the glycerin solution is neutralized so that the pH of the solution is 4.0 to 7.5.
[9] The method for producing a denitrification agent or a nitrification promoter according to any one of [3] to [8], wherein the alkaline substance comprises waste glycerin and/or soapstock.
[10] The method for producing a denitrifying agent or a nitrification promoter according to any one of [3] to [9], further comprising, after the second separation step, an alcohol separation step of separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated.
[11] The method for producing a denitrifying agent or a nitrification promoter according to [10], further comprising, after the alcohol separation step, a dilution step of diluting the glycerin liquid from which the monohydric alcohol has been separated.
[12] The method for producing a denitrifying agent or a nitrification promoter according to [11], wherein in the dilution step, the glycerin solution is diluted so that the TOC index and/or the COD index become equivalent to those of a predetermined concentration of methanol used as an organic carbon source in a biological nitrification/denitrification treatment using heterotrophic microorganisms.
[13] The method for producing a denitrifying agent or a nitrification promoter according to any one of [10] to [12], further comprising an oil removal step of separating and removing a third oil component after the alcohol separation step.
[14] The method for producing a denitrifying agent or a nitrification promoter according to any one of [10] to [13], further comprising, after the alcohol separation step, an oil separation suppression step of suppressing separation of oil by adding a surfactant.
[15] A second esterification step of producing a fatty acid alkyl ester by at least one method other than an alkali catalyst method selected from the group consisting of an acid catalyst method, an acid-alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method, and a solid catalyst method,
In the second esterification step, the first oil fraction separated in the first separation step and/or the second oil fraction separated in the second separation step and the monohydric alcohol separated in the alcohol separation step are used as raw materials.
A method for producing a denitrification agent or a nitrification promoter according to any one of [10] to [14].
[16] A system for producing a denitrifying agent or a nitrification promoter used as an organic carbon source in a biological nitrification/denitrification treatment, comprising:
a first separation device for mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating the raw material into a first oil component and a first glycerin liquid;
a neutralization device for neutralizing the first glycerin liquid with an alkaline substance;
a second separation device for separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
A system for producing a denitrifying agent or a nitrification promoter, comprising:
[17] The system for producing a denitrifying agent or a nitrification promoter according to [16], further comprising an alcohol separation device disposed downstream of the second separation device, for separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated.

By using the denitrification agent or nitrification promoter produced by the water treatment method and the production method or production system of the present invention, by processing a raw material containing at least one of glycerin and fatty acid glycerin esters, it becomes possible to suitably use the raw material as an organic carbon source in biological nitrification denitrification treatment, and glycerin-containing waste and fatty acid glycerin ester-containing waste can be effectively recycled.

FIG. 1 is a diagram showing a flow of a method for producing a denitrifying agent or a nitrification promoter according to one embodiment of the present invention. FIG. 2 is a diagram showing the flow of a second esterification step in a preferred embodiment of the present invention. FIG. 1 is a diagram showing the flow of a denitrification treatment step and a nitrification treatment step in a water treatment method according to one embodiment of the present invention. FIG. 1 is a diagram illustrating a system for producing a denitrifying agent or a nitrification promoter according to one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
[Method of producing denitrification agent/nitrification promoter]
A method for producing a denitrifying agent or a nitrification promoter according to one embodiment of the present invention includes a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating a first oil component and a first glycerin liquid; a neutralization step of neutralizing the first glycerin liquid with an alkaline substance; and a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid to produce a glycerin-containing liquid, and incorporating the obtained glycerin-containing liquid into a denitrifying agent or nitrification promoter (hereinafter sometimes abbreviated as "denitrifying agent/nitrification promoter") as an organic carbon source for biological nitrification denitrification treatment.

Figure 1 is a diagram showing the flow of a particularly preferred embodiment of the method for producing a denitrifying agent/nitrification promoter according to this embodiment. In Figure 1, in addition to the first separation step, neutralization step, and second separation step, optional steps of an alcohol separation step, a dilution step, an oil removal step, and an oil separation inhibition step are illustrated as being performed after the second separation step.

The denitrification agent/nitrification promoter of this embodiment contains the obtained glycerin-containing liquid as an organic carbon source for biological nitrification/denitrification treatment, which allows for effective use of glycerin-containing waste and fatty acid glycerin ester-containing waste, and has excellent denitrification and nitrification promotion effects. In addition, since refined glycerin is biodegradable, there is little risk of it being a burden on the environment.

As described later, waste containing glycerin contains components other than glycerin. Therefore, if these are used as denitrifying agents/nitrification promoters as they are, they may have a negative effect on biological nitrification denitrification treatment using microorganisms. However, according to this embodiment, the contents of oil, inorganic salts, etc. are reduced by the first separation step, neutralization step, and second separation step, so that they can be suitably used as an organic carbon source (i.e., denitrifying agent/nitrification promoter) for biological nitrification denitrification treatment using microorganisms. In addition, since various oils and fats are used as raw materials for biodiesel fuel, free fatty acids, etc., there is a problem that the quality of glycerin-containing waste is not constant. However, according to this embodiment, it is possible to provide denitrifying agents and nitrification promoters with stable quality.
Furthermore, in this embodiment, by carrying out the first separation step, the neutralization step, and the second separation step, it is possible to increase the yield of glycerin and to increase the efficiency of separation of the oil component, and furthermore, various raw materials (e.g., waste containing fatty acid glycerin esters) other than glycerin-containing waste can be treated by this method.

(1) Raw Materials The raw materials used in this embodiment are not particularly limited as long as they contain at least one of glycerin and fatty acid glycerin esters.
Examples of raw materials containing glycerin include waste materials containing glycerin. Raw materials containing fatty acid glycerin esters can also be suitably used because they produce glycerin through an acid-catalyzed transesterification reaction or the like in the first separation step described below.
The glycerin-containing waste and the fatty acid glycerin ester-containing composition will be described in some detail below.

(1-1) Glycerin-Containing Waste Examples of glycerin-containing waste that can be used in the present embodiment include waste glycerin produced as a by-product in the process of producing biodiesel fuel, glycerin waste liquid produced as a by-product in the process of producing free fatty acids, sweet water, and wastewater from washing fatty acid alkyl esters.

Here, the glycerin waste liquid by-produced in the production process of free fatty acids refers to waste by-produced when free fatty acids are produced by hydrolyzing animal and vegetable fats and oils. Methods for producing free fatty acids by hydrolysis include high-temperature, high-pressure decomposition and enzymatic decomposition. The glycerin waste liquid by-produced in such a production process contains, in addition to glycerin, unreacted fats and oils, partially hydrolyzed fats and oils, etc.
Sweet water is a by-product produced when fats and oils are saponified (alkaline hydrolysis) to produce fatty acid salts (for example, in the process of producing soap), and contains glycerin, water, alkali, etc.
The wastewater from washing fatty acid alkyl esters is wastewater generated when reactants are washed in the process of producing fatty acid alkyl esters, including biodiesel fuel, and contains, in addition to water, glycerin, which is a by-product in the production reaction of fatty acid alkyl esters, as well as unreacted free fatty acids and their salts, monohydric alcohols, etc.

Next, we will explain in some detail about waste glycerin, which is a by-product in the production process of biodiesel fuel.
Fatty acid alkyl esters that can be used as biodiesel fuels can be obtained by adding a monohydric alcohol such as methanol and an alkali catalyst such as potassium hydroxide to a raw material oil such as vegetable oil, and carrying out an ester exchange reaction.

Examples of raw oils and fats for biodiesel fuel include vegetable oils such as rapeseed oil, palm oil, olive oil, sunflower oil, soybean oil, rice oil, and hemp oil; animal fats such as fish oil, lard, and beef and pork fats; and waste cooking oils such as tempura oil.
As the monohydric alcohol, methanol, ethanol, 1-propanol, ethylhexanol, etc. can be used, with methanol and ethanol being preferred, and methanol being particularly preferred.
As the alkaline catalyst, potassium hydroxide, sodium hydroxide, calcium oxide, etc. can be used, but potassium hydroxide is preferred from the viewpoints of the precipitability and ease of reuse of the inorganic salt separated and recovered in this embodiment.

In the above transesterification reaction, the fatty acid glycerin esters contained in the raw oil react with monohydric alcohol to produce fatty acid alkyl esters and glycerin. The resulting reaction liquid is separated into a fatty acid alkyl ester phase and a waste glycerin phase, and in the production of biodiesel fuel, the resulting fatty acid alkyl ester phase is recovered and washed to produce biodiesel fuel.

On the other hand, the waste glycerin phase contains not only glycerin at a high concentration, but also unreacted monohydric alcohol, unreacted fats and oils, fatty acids and their salts, an alkali catalyst, and impurities derived from the raw fats and oils, etc. The waste glycerin may be liquid waste glycerin or solid waste glycerin, but from the viewpoints of workability, handling, etc., liquid waste glycerin is preferable.
The contents of glycerin, monohydric alcohol, fats and oils, and fatty acids and their salts in the waste glycerin are not particularly limited, but usually, based on the entire waste glycerin, the glycerin content is 25% by mass to 65% by mass, the monohydric alcohol content is 2% by mass to 20% by mass, and the total of fats and oils, fatty acids and their salts is 30% by mass to 50% by mass. From the viewpoint of enabling the production method for the denitrification agent/nitrification promoter according to this embodiment to be carried out more stably, the glycerin content may be 30% by mass to 65% by mass, the monohydric alcohol content is 3% by mass to 15% by mass, and the total of fats and oils, fatty acids and their salts is 25% by mass to 55% by mass, based on the entire waste glycerin.

Since waste glycerin contains a large amount of an alkaline catalyst, the pH is often 9 or higher, and in this embodiment, the pH may be 9 to 13.
In the first separation step, from the viewpoint of facilitating the progress of an acid-catalyzed esterification reaction between the unreacted fats and oils contained in the waste glycerin and the monohydric alcohol, the water content in the waste glycerin is preferably 5% by mass or less, and particularly preferably 3% by mass or less. The water content in the waste glycerin can be appropriately adjusted by heating, reducing pressure, using a drying agent or the like, permeating the waste glycerin through purified glycerin, or the like.

Here, glycerin can be used as a raw material for pharmaceuticals, cosmetics, etc., but in order to use the glycerin contained in the waste glycerin for such purposes, it is necessary to purify it to a high purity, which requires a great deal of cost and energy. Therefore, the value of waste glycerin as glycerin is quite low, and it has been difficult to process in the past.
However, when used as a denitrification agent/nitrification promoter, even glycerin purified by a relatively simple method exhibits sufficient denitrification and nitrification promotion effects, so inexpensive waste glycerin is particularly suitable as a raw material for the denitrification agent/nitrification promoter of this embodiment. Furthermore, according to this embodiment, the environmental load can be reduced from the viewpoint of effectively utilizing waste glycerin, which is an industrial waste.

In this embodiment, from the viewpoint of ease of use in the first separation process described below, it is preferable to use at least one of the waste glycerin produced as a by-product in the biodiesel fuel production process and the glycerin waste liquid produced as a by-product in the free fatty acid production process among the glycerin-containing waste materials described above, and it is particularly preferable to use the waste glycerin produced as a by-product in the biodiesel fuel production process.

(1-2) Composition containing fatty acid glycerin ester In this embodiment, a composition containing a fatty acid glycerin ester can also be used as a raw material. In this embodiment, the first separation step, neutralization step, and second separation step are performed using an inorganic acid, and the yield of glycerin can be increased by an acid-catalyzed esterification reaction in the first separation step using a composition containing a fatty acid glycerin ester. Examples of compositions containing fatty acid glycerin ester include fats and oils mainly composed of fatty acid glycerin esters of waste edible oil, animal and vegetable oils, and high acid value oils (grease trap oil, sewage oil, gutter oil, wastewater treatment regenerated oil, mayonnaise, dressing, etc.); compositions mainly composed of fatty acid salts such as oil cake and soap; and the like.
In this specification, "mainly as a component" means that the component having the largest content in the composition (however, when the component having the largest content is water, the component having the second largest content), and the content is preferably 40% by mass or more, and more preferably 50% by mass or more.

Here, the high acid value oil refers to fats and oils with an acid value of 10 mgKOH/g or more, and includes fatty acid glycerol esters, which are the main components of fats and oils, as well as free fatty acids. The acid value may be 20 mgKOH/g or more, or even 50 mgKOH/g or more. The upper limit of the acid value is usually 200 mgKOH/g or less.
Sodash is a by-product separated from fats and oils (crude oil) in the deacidification process in the refining of vegetable fats and oils, and contains fatty acid salts, fatty acid glycerin esters, alkali, water, etc.

(2) First Separation Step The first separation step is a step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid, and subjecting the mixture to phase separation into a first oil component and a first glycerin liquid.
The oil fraction separated in this step includes fatty acid alkyl esters, fatty acid glycerol esters, and free fatty acids.

When using a raw material containing glycerin, especially waste glycerin, in this process, the salts of fatty acids contained in the waste glycerin are converted to free fatty acids by inorganic acids. Furthermore, fatty acids and their salts are esterified with unreacted monohydric alcohol contained in the waste glycerin using inorganic acids as an acid catalyst to produce fatty acid alkyl esters.

In addition, when the fatty acid glycerin ester-containing composition is used as a raw material, fatty acid alkyl ester and glycerin are produced by transesterification with monohydric alcohol. In this case, the monohydric alcohol can be added separately, for example, the monohydric alcohol recovered in the alcohol separation step described below can be used. In addition, the unreacted monohydric alcohol contained in the waste glycerin can be utilized by treating the fatty acid glycerin ester-containing composition and the waste glycerin at the same time.
When the first separation step is carried out in the presence of a monohydric alcohol, this step can also be referred to as an acid-catalyzed esterification step. In addition, the first separation step may be referred to as a "first esterification step" in comparison with the second esterification reaction described later.

Even if the raw material does not contain a monohydric alcohol, the fatty acid glycerin ester produces glycerin in the presence of an acid in the first separation step. In addition, if the raw material contains a fatty acid salt, the fatty acid salt is converted to a free fatty acid by the acid, which makes it easier to separate from the glycerin.
Therefore, even if the raw material does not contain a monohydric alcohol, this embodiment can be suitably applied.

In this embodiment, since the first separation step is performed in the presence of an inorganic acid, various raw materials can be simultaneously treated. In addition, by performing the first separation step, waste materials containing glycerin and fatty acid glycerin esters, such as waste glycerin, waste edible oil, and high acid value oil, can be effectively utilized, which contributes to reducing the environmental load.
In particular, high acid value oils have a high acid value of 10 mgKOH/g or more, and therefore are difficult to use as a raw material for the above-mentioned alkali-catalyzed transesterification reaction, but in the first separation step, which can be called an acid-catalyzed esterification reaction, high acid value oils can also be used suitably as a raw material.

When waste glycerin or a fatty acid glycerin ester-containing composition is used as a raw material, the fatty acid alkyl ester and free fatty acid generated in the first separation step are transferred to an oil phase consisting of the first oil, and can be separated from the first glycerin liquid. When the oil phase is recovered, the obtained first oil (fatty acid alkyl ester, free fatty acid, etc.) can be subjected to a further esterification reaction (the second esterification step described later) and can ultimately be used as a raw material for biodiesel fuel, etc. In addition, the obtained oil can be used as a compost material in addition to the production of fatty acid alkyl esters.
On the other hand, the first glycerin liquid is acidified by adding an inorganic acid. The first glycerin liquid contains an inorganic salt generated from the inorganic acid and the alkali contained in the waste glycerin. Note that a part of the inorganic salt may be precipitated, that is, the first glycerin liquid may contain an acidic glycerin phase and precipitated inorganic salt.

The raw material that can be used in the first separation step preferably has a moisture content of 10% by mass or less, and more preferably 5% by mass or less. By using a raw material with a low moisture content (e.g., waste glycerin with a low moisture content, etc.), it is easy to reduce the moisture content of the reaction liquid described below. The moisture content of the raw material can be appropriately adjusted by heating, reducing pressure, using a drying agent, etc., or passing the raw material through purified glycerin.

Inorganic acids used in the first separation step include concentrated sulfuric acid, phosphoric acid, concentrated nitric acid, hydrogen chloride, etc., but concentrated sulfuric acid and phosphoric acid, which have a low water content, are preferred, and concentrated sulfuric acid is particularly preferred.

In the first separation step, the pH of the mixture (reaction liquid) of the raw material and the inorganic acid is preferably adjusted to 3 or less, and particularly preferably to 1 or less. The pH of the reaction liquid can be adjusted by the amount of the inorganic acid added.
The water content of the reaction liquid is preferably 10% by mass or less, and particularly preferably 0.5% by mass or less. The water content of the reaction liquid can be appropriately adjusted by adjusting the water content and input amount of each raw material, using a desiccant in the reaction liquid, etc.
By setting the pH and water content of the reaction liquid within the above ranges, the efficiency of the acid-catalyzed esterification reaction can be increased, and the first oil component and the first glycerin liquid (containing an acidic glycerin phase and inorganic salts) can be effectively separated.

The temperature of the reaction solution in the first separation step can be 30 to 64° C., and can further be 50 to 60° C. The reaction time can be 0.5 to 12 hours, and can further be 4 to 12 hours. It is preferable to stir the reaction solution during this period.
After the reaction (or stirring) is completed, the mixture is allowed to stand for 0.2 to 12 hours, whereby a first oil fraction containing fatty acid alkyl esters, unreacted fats and oils, etc., is separated from a first glycerin liquid containing an acidic glycerin phase and inorganic salts. The first oil fraction can be used to produce fatty acid alkyl esters by subjecting it to a further esterification reaction (the second esterification step described below). Meanwhile, the first glycerin liquid is subjected to the subsequent neutralization step.

(3) Neutralization Step The neutralization step is a step of neutralizing the first glycerin liquid obtained in the first separation step with an alkaline substance.
As such an alkaline substance, hydroxides such as potassium hydroxide, sodium hydroxide, etc. can be used. In the present embodiment, since the second separation step is performed after the neutralization step, various substances can be used as the alkaline substance.

For example, a substance containing glycerin can be used as the alkaline substance. Examples of such glycerin-containing alkaline substances include the above waste glycerin and other by-products of alkali-catalyzed transesterification of fats and oils. These substances can not only neutralize acidic glycerin but also increase the yield of glycerin, so that the use of glycerin-containing alkaline substances is preferable from this viewpoint as well. Such glycerin-containing alkaline substances may contain fatty acid salts or fatty acid glycerin esters.
The glycerin-containing alkaline substance preferably has a glycerin content of 25% by mass or more, particularly preferably 50% by mass or more. The upper limit is not particularly limited, but may be, for example, 99% by mass or less, or 90% by mass or less.
The glycerin-containing alkaline substance preferably has a pH of 9 or more, and more preferably 9 to 13.

Furthermore, the alkaline substance may be a composition containing a fatty acid salt as a main component. Examples of alkaline substances containing a fatty acid salt as a main component include cake of oil and alkaline soap.

In the neutralization step, it is preferable to neutralize the glycerin solution so that its pH is 4.0 to 7.5, preferably 4.5 to 7.0, and particularly 5.0 to 6.5. Neutralizing the glycerin solution so that its pH is within this range makes it easier to separate the oil and precipitate inorganic salts in the subsequent second separation step. The pH of the glycerin solution can be adjusted as appropriate by controlling the amount of alkaline substance added.

The glycerin solution obtained in the neutralization step preferably has a water content of 10% by mass or less, and particularly preferably 3% by mass or less. In the neutralization step, there is no problem of reaction inhibition due to water, but from the viewpoint of sufficiently precipitating inorganic salts in the subsequent second separation step to increase separation efficiency, it is preferable to specify the upper limit of the water content as described above. The lower limit of the water content is not particularly limited, but may be, for example, 0.5% by mass or more.

In the neutralization step, it is preferable to add the alkaline substance while stirring the acidic glycerin liquid so that the liquid property changes from acidic to near neutral. As described above, a substance containing a fatty acid salt may be used as the alkaline substance used for neutralization, and by using the above-mentioned addition order, the fatty acid salt is converted to free fatty acid by the acid. The free fatty acid moves to the oil phase separated from the glycerin liquid, and is difficult to re-dissolve in the glycerin liquid even if the pH of the glycerin liquid increases. This makes it even easier to separate in the subsequent second separation step. In addition to the above-mentioned substances mainly composed of fatty acid salts, fatty acid salts are also included in by-products of alkali-catalyzed ester exchange reactions and alkali hydrolysis of fats and oils.

The first glycerin liquid obtained in the first separation step is neutralized by the alkaline substance. The neutralized glycerin liquid is then subjected to the second separation step.

(4) Second Separation Step The second separation step is a step of separating the second oil component and the precipitated inorganic salt from the neutralized glycerin liquid obtained in the neutralization step. The glycerin liquid obtained by separating the second oil component and the precipitated inorganic salt in this step is sometimes referred to as the second glycerin liquid.

The second oil component to be separated here includes not only fats and oils and fatty acids that were not separated in the first separation step and remained in the first glycerin liquid, but also fats and oils and free fatty acids derived from the alkaline substance added in the neutralization step.
The inorganic salt separated in the second separation step is a salt of an inorganic acid (concentrated sulfuric acid, etc.) and an alkali (potassium, sodium, etc.) added in the first separation step, and is preferably potassium sulfate. The alkali is contained in the raw material (waste glycerin, etc.) input in the first separation step or the alkaline substance added in the neutralization step, and the inorganic salt is precipitated in the first separation step or the neutralization step.

On the other hand, the second glycerin liquid contains, in addition to glycerin, monohydric alcohol derived from waste glycerin, and may also contain water, etc. Since oils and inorganic salts have low solubility in the second glycerin liquid, they are separated from the second glycerin liquid.

In the second separation step, the neutralized raw material is left to stand for about 3 to 12 hours, and then the upper liquid (oil) and the lower liquid (second glycerin liquid) are separately collected to obtain the second glycerin liquid as the lower liquid, but it is preferable to increase the separation speed by centrifugation or the like. In such centrifugation, a three-phase separation type centrifuge capable of separating light liquid (i.e., oil), heavy liquid (i.e., second glycerin liquid) and solids (i.e., inorganic salts) can be suitably used. In addition, since a large amount of inorganic salts precipitate in this embodiment, it is also preferable to separate a certain amount of inorganic salts in advance using a centrifuge capable of solid-liquid separation such as a decanter type, and then further separate the liquid phase portion using a three-phase separation type centrifuge.

The second oil fraction obtained in the second separation step can be used to produce fatty acid alkyl esters, for example, by combining with the first oil fraction separated in the first separation step and subjecting it to a further esterification reaction (the second esterification step described below).
Furthermore, the inorganic salts can be used as raw materials for inorganic fertilizers, for example, after undergoing a washing process or the like.
On the other hand, the second glycerin solution obtained as described above can be used as it is as a denitrifying agent/nitrification promoter (an organic carbon source for biological nitrification/denitrification treatment).
However, there are problems with workability and the need to handle the product as a hazardous material. In order to avoid these problems, it is preferable to subject the product to a further alcohol separation step or the like.

(5) Alcohol Separation Step The alcohol separation step is a step of separating monohydric alcohol from the second glycerin liquid obtained in the second separation step.

The second glycerin liquid may contain monohydric alcohol derived from waste glycerin and remaining in the first separation step (acid-catalyzed esterification reaction). Such monohydric alcohol may remain in the denitrification agent/nitrification promoter since it does not interfere with the effect of the biological nitrification denitrification treatment as an organic carbon source, but depending on the concentration of the monohydric alcohol, it may be necessary to treat the glycerin liquid as a hazardous material. That is, since the second glycerin liquid is a trihydric alcohol, it falls under the third petroleum of the fourth class of hazardous materials (flammable liquids). And, since the second glycerin liquid contains monohydric alcohol (e.g., methanol, etc.) that did not contribute to the transesterification reaction, it becomes a designated flammable material when the volume is 2000 L or more.

Here, methanol is widely used as a conventional denitrifying agent. According to the Fire Service Act, products that contain no components other than alcohol and water and have an alcohol content of 60% or more are classified as Class 4 hazardous materials (flammable liquids) alcohols, and the structure of storage facilities and the like is subject to regulations to ensure safety, but methanol used as a denitrifying agent has an alcohol content adjusted to about 50% so that it can be treated as a non-hazardous material, and storage facilities are constructed without being restricted by the regulations.
When the second glycerin liquid is used as it is as a substitute for methanol, an existing storage facility for methanol can be used as it is if the storage facility has a capacity of less than 2000 L, but if the capacity is 2000 L or more, it becomes subject to regulation as a designated flammable material, and an existing storage facility for methanol cannot be used as it is. In contrast, the glycerin liquid after the monohydric alcohol is separated in the alcohol separation process is determined to be a non-hazardous material because it has no flash point, even if it is a Class 4 flammable liquid as specified in the Fire Service Act, and an existing storage facility for methanol can be used as it is even if the capacity is 2000 L or more.

In the alcohol separation step, a reduced pressure distillation method, a gas-liquid contact method, a membrane separation method, or the like can be used.
The reduced pressure distillation method is a method in which a glycerin solution is heated (for example, to about 60° C.) to evaporate the monohydric alcohol, etc., and then the pressure is reduced to separate the monohydric alcohol, etc. The separated monohydric alcohol, etc. can be recovered by cooling.
The gas-liquid contact method is a method in which a glycerin liquid is brought into contact with a gas phase in the form of fine droplets, and a monohydric alcohol having a low boiling point is transferred to the gas phase and separated. Specifically, a spray drying method or the like can be suitably adopted.
Membrane separation is a method that uses a membrane that preferentially allows the monohydric alcohol to permeate.

The second glycerin solution may further contain water. Such water does not impede the effect of the glycerin solution as a denitrifying agent/nitrification promoter and may remain in the glycerin solution, but in a vacuum distillation method or a gas-liquid contact method, for example, the water can be removed because it is transferred to the gas phase together with the monohydric alcohol.
Further, before or after the alcohol separation step for separating the monohydric alcohol, a further purification treatment may be carried out using an ion exchange method or activated clay, diatomaceous earth, carbon, zeolite, or the like.

The glycerin liquid obtained in this process preferably has a glycerin purity of 85% by mass or more, more preferably 90% by mass or more, particularly preferably 97% by mass or more, and particularly preferably 99% by mass or more. In this embodiment, by going through the above-mentioned separation process and alcohol separation process, it is possible to obtain a glycerin liquid of high purity such as in the above numerical range, despite the fact that glycerin-containing waste is the raw material, using a relatively simple method. The purity of glycerin is a value measured by gas chromatography.

On the other hand, the separated monohydric alcohol can be reused as it is or, if necessary, purified by redistillation or the like as a raw material for alkali-catalyzed ester exchange reactions or acid-catalyzed esterification reactions. It may also be used as a washing liquid for inorganic salts, etc., separated in the second separation step.

(6) Oil Removal Process, Oil Separation Suppression Process The second glycerin liquid (and further the glycerin liquid from which the monohydric alcohol has been separated) may contain a small amount of oil such as free fatty acid. These oils are well dissolved in the glycerin liquid and do not impair the denitrification effect and the nitrification promotion effect. However, when the glycerin liquid is diluted, these oils may not dissolve in water and may undergo phase separation as oil. In addition, when the hydrophilic phase of neutralized sweet water or fatty acid alkyl ester washing wastewater is used in the dilution process, the oil derived from these may also undergo phase separation after dilution. The phase-separated oil may have an unfavorable effect on the storage system and liquid delivery system of the denitrification agent/nitrification promoter.
To avoid such effects, oil may be removed before or after the dilution step (oil removal step), or a surfactant may be added to suppress phase separation (oil separation suppression step).

(6-1) Oil Removal Step The specific method in the oil removal step is not particularly limited, and in addition to separating the oil by static separation, centrifugation, membrane separation, filter removal, etc., the oil or water may be adsorbed and removed by an adsorbent such as activated clay, diatomaceous earth, activated carbon, silica gel, zeolite, molecular sieve, etc., or these may be combined appropriately. A particularly preferred embodiment is a method in which most of the remaining oil is separated and removed by static separation or centrifugation, and then the remaining oil as well as impurities such as pigments and remaining inorganic salts are removed by membrane separation, filter removal, adsorbent, etc.

In addition, in order to promote the separation of oil, it is one of the particularly preferred embodiments to add a specific surfactant. Specifically, a surfactant having an HLB value of 14 or less, more preferably 13 or less, is added. The lower limit of the HLB value is not particularly limited, but may be, for example, 8 or more, or 10 or more. The HLB value in this specification is a calculated Griffin HLB value.
The surfactant for promoting oil separation is not particularly limited as long as it has the above HLB value, but it is preferably a biodegradable surfactant, and more preferably a nonionic surfactant. More specifically, it is preferably a polyoxyethylene alkyl ether.

The amount of surfactant added is not particularly limited as long as the oil separation promoting effect is exhibited. For example, the oil separation promoting effect is suitably exhibited when the surfactant is added in an amount of 0.05 mass % or more, preferably 0.1 mass % or more, and more preferably 0.15 mass % or more relative to the denitrification agent/nitrification promoter.
On the other hand, the upper limit of the amount of the surfactant added is not particularly limited, but it can be added so as to be 10% by mass or less, further 5% by mass or less, and further 1% by mass or less, relative to the denitrifying agent/nitrification promoter.

The surfactant may be added at any timing. For example, in the dilution step described above, the surfactant may be added to purified glycerin simultaneously with the water or aqueous solution used for dilution, or the surfactant may be added to the purified glycerin for dilution. Furthermore, the surfactant may be added to the diluted denitrification agent/nitrification promoter.
Furthermore, as shown in FIG. 4, the above-mentioned surfactant may be added to purified glycerin before dilution to separate and remove oil, and the purified glycerin from which the oil has been separated may be subjected to a further process such as a dilution process.

The addition of such a surfactant promotes separation of the oil, so that the oil can be separated by a simple method such as static separation, centrifugation, etc. In the case of static separation, the static separation time may be, for example, 2 hours or more, 24 hours or more, 3 days or more, or 7 days or more.
The oil separates into the upper layer of the glycerin liquid, so the oil can be removed by recovering the lower layer, which is the glycerin liquid.

The removed oil may be recovered and reused. For example, it may be combined with the first and second oil fractions separated in the first and second separation steps and subjected to a further acid-catalyzed esterification reaction to produce fatty acid alkyl esters.

(6-2) Oil-separation suppression step The oil-separation suppression step is a step of suppressing separation of oil by adding a specific surfactant. This step may be performed directly on the purified glycerin obtained by the above-mentioned refining method, but is preferably performed on the glycerin that has been subjected to the above-mentioned oil removal step. By performing the oil-separation suppression step after the oil removal step, a considerable amount of oil has been removed in advance, so that further separation of oil is effectively suppressed.

The surfactant added in this step preferably has an HLB value of 15 or more, particularly preferably 17 or more.
The type of surfactant is not particularly limited as long as it has the above HLB value, but it is preferably a biodegradable surfactant, and more preferably a nonionic surfactant. More specifically, it is particularly preferably a polyoxyethylene alkyl ether.

The amount of the surfactant added is not particularly limited as long as the oil separation suppression effect is exerted, but for example, when it is added to the denitrifying agent/nitrification promoter so as to be 0.05% by mass or more, preferably 0.1% by mass or more, the oil separation suppression effect is suitably exerted. Moreover, it may be added at a higher concentration as necessary. Specifically, it may be added to the denitrifying agent/nitrification promoter so as to be 1% by mass or more, or even 2% by mass or more.
On the other hand, the upper limit of the amount of the surfactant added is not particularly limited, but can be, for example, 10% by mass or less, further 5% by mass or less, and further 1% by mass or less relative to the denitrifying agent/nitrification promoter.

(7) Dilution step The glycerin solution obtained in this embodiment can be used as a denitrifying agent/nitrification promoter as it is, but since it contains glycerin at a high concentration, it has a high viscosity, which may cause problems in workability, and it must be handled as a hazardous material. In order to avoid these problems, in this embodiment, it is preferable to further carry out a dilution step.
The dilution step is a step of diluting the glycerin liquid. By diluting the highly viscous glycerin liquid, workability can be improved and handling of the glycerin liquid as a hazardous material becomes unnecessary.
In Fig. 1, the dilution step is illustrated after the oil removal step and the oil separation inhibition step, but the order of steps in this embodiment is not limited to this. For example, the refined glycerin may be diluted in the dilution step, and then subjected to the oil removal step or the oil separation inhibition step.

For dilution, water such as tap water can be used as appropriate. In addition, an aqueous solution containing glycerin, such as neutralized sweet water or a hydrophilic phase of washing wastewater of fatty acid alkyl ester, may be used as long as it does not impair the denitrification effect or nitrification promotion effect according to this embodiment.
Here, the neutralized sweet water is the neutralized sweet water (a by-product produced when fats and oils are saponified to produce fatty acid salts) and contains glycerin, water, and small amounts of inorganic salts.
The hydrophilic phase of the fatty acid alkyl ester washing wastewater is obtained by removing free fatty acids and their salts from the above-mentioned fatty acid alkyl ester washing wastewater, and contains water, glycerin, monohydric alcohol, etc.
In addition, since these aqueous solutions containing glycerin may contain fatty acids, fatty acid alkyl esters, etc., when these are used for dilution, it is preferable to carry out this step before the oil removal step or oil separation inhibition step described below.
Neutralized sweet water and the hydrophilic phase of fatty acid alkyl ester washing wastewater are aqueous solutions that contain components other than glycerin. However, by adjusting the amount used, there is no hindrance to the denitrification and nitrification promotion effects, and these can be effectively utilized despite being industrial waste, thereby reducing the environmental burden.
The dilution ratio is not particularly limited as long as the denitrification effect or nitrification promotion effect is exhibited. For example, when diluting with water, the ratio of glycerin solution:water may be 1:0.5 to 1:4, or may be 1:2 to 1:4.

When the glycerin-containing liquid is used as a denitrifying agent, it is preferable to dilute the glycerin liquid from which the monohydric alcohol has been separated in the dilution step so that the TOC index and/or the COD index are equivalent to those of methanol of a predetermined concentration used as an organic carbon source in a biological nitrification/denitrification treatment using heterotrophic microorganisms. This makes it possible to effectively use the glycerin liquid as a denitrifying agent that exhibits the same denitrifying performance as methanol of a predetermined concentration that has been conventionally used as an organic carbon source.
Here, TOC (total organic carbon) is an index that expresses the total amount of organic matter in water as "the amount of carbon contained in the organic matter". COD (chemical oxygen demand) is an index that expresses the amount of organic matter in water as "the amount of oxygen consumed when decomposed by an oxidizing agent", and there are several types depending on the type of oxidizing agent used and the reaction conditions. In this embodiment, "COD _Cr ", which uses potassium dichromate as the oxidizing agent, can be suitably used as the COD index. This is because "COD _Mn ", which uses potassium permanganate as the oxidizing agent, has a low capture rate with respect to the actual amount of organic matter.

The glycerin-containing liquid obtained as described above is suitable as an organic carbon source for biological nitrification/denitrification treatment, and can be used as a denitrification agent/nitrification promoter.
The denitrifying agent/nitrification promoter may contain additives within the range that does not impair the effect of the present embodiment. Examples of such additives include pH adjusters, bactericides, chelating agents, colorants, and fragrances.

The denitrifying agent/nitrification promoter produced by the above method has excellent denitrification and nitrification promotion effects as an organic carbon source for biological nitrification/denitrification treatment. According to this embodiment, by treating glycerin-containing waste, it can be suitably used as an organic carbon source in biological nitrification/denitrification treatment, and glycerin-containing waste can be effectively recycled.

In addition, each element in the above embodiment can be appropriately modified in design, etc. For example, the manufacturing method of the denitrifying agent/nitrification promoter according to the above embodiment may further include a second esterification step described below.

(8) Second esterification step In the first and second separation steps described above, the first and second oil fractions are respectively recovered from the separated oil phase. In addition, in the alcohol separation step described above, the separated monohydric alcohol is recovered. These may be recycled and supplied as raw materials in the production of fatty acid alkyl esters by an alkali catalyst method, but since their purity is not necessarily high, it may be difficult to efficiently produce fatty acid alkyl esters if they are used as raw materials as they are. In addition, the first and/or second oil fractions contain oils and fats with high acid values such as free fatty acids, and the first oil fraction in particular is an acidic oil fraction because it was separated in the first separation step (first esterification step), which can be said to be an esterification reaction using an acid catalyst. Therefore, it is even more difficult to use the first and second oil fractions as raw materials for the production of fatty acid alkyl esters by an alkali catalyst.

However, if a method other than the alkaline catalyst method is used, it is possible to produce fatty acid alkyl esters even from oils and fats with high acid values. Therefore, in this embodiment, it is preferable to have a second esterification step in which fatty acid alkyl esters are produced by a method other than the alkaline catalyst method.

In the second esterification step, it is preferable to use the first oil fraction separated in the first separation step and/or the second oil fraction separated in the second separation step as a raw material.
In addition, when a monohydric alcohol is recovered in the alcohol separation step, it is also preferable to use the recovered monohydric alcohol as the raw material.
As the other raw materials, the same raw materials (high acid value oil, etc.) as those in the above-mentioned acid reaction step (first esterification step) can be used.

By using these as raw materials, it becomes possible to recycle industrial waste more efficiently in the production of the above-mentioned denitrification agent/nitrification promoter. These raw materials can also be used suitably as long as the method is other than the alkaline catalyst method.

Methods that can be used in the second esterification step are methods other than the alkali catalyst method, and more specifically, examples include the acid catalyst method, acid-alkali catalyst method, biocatalyst method, ion exchange resin method, supercritical method, subcritical method, and solid catalyst method. These methods can carry out an ester exchange reaction with a monohydric alcohol such as methanol even if the waste edible oil or oils and fats have a high acid value, or even if the oils and fats contain unreacted free fatty acids.

In the second esterification step, glycerin is by-produced together with the oil containing the fatty acid alkyl ester. The oil obtained in the second esterification step and the glycerin liquid can be phase-separated by standing, centrifugation, etc. The fatty acid alkyl esters can be recovered from the separated oil and used as biodiesel fuel, etc. Meanwhile, the by-produced glycerin can be supplied to the neutralization step together with the first glycerin liquid obtained in the first separation step (first esterification step), for example. In this manner, the glycerin by-produced in the second esterification step can also be made into part of the glycerin liquid through the neutralization step, second separation step, etc., and can be recycled more efficiently.

As the second esterification step, it is particularly preferable to employ an acid catalyst method among the methods other than the above-mentioned alkali catalyst method.
As shown in Fig. 2, when an acid catalyst method is adopted for the second esterification step, the first oil and/or the second oil are used as the raw material. As the other raw material, the monohydric alcohol recovered in the alcohol separation step can be used, and further, the same raw material (high acid value oil, etc.) as that in the first separation step (first esterification step) can be used.
The reaction liquid obtained in the second esterification step is separated into an oil fraction containing fatty acid alkyl esters and a glycerin liquid containing by-produced glycerin, an acid catalyst and its salts, etc. The obtained oil fraction and glycerin liquid are both acidic, and the acidic glycerin liquid can be supplied to the neutralization step or the like.

On the other hand, it is preferable to neutralize and dehydrate the oil containing fatty acid alkyl esters. Here, a preferred example of a method for neutralization and dehydration is a method using waste glycerin produced as a by-product in the production process of biodiesel fuel. Specifically, waste glycerin produced as a by-product in the production process of biodiesel fuel is dealcoholized and stored in a tank, etc., and the oil to be neutralized is introduced from the bottom of the tank to contact the waste glycerin. As a result, the acidic oil is neutralized by the alkali of the waste glycerin, and the water and monohydric alcohol contained in the oil are absorbed into the waste glycerin liquid. The oil introduced from the bottom overflows from the top due to the difference in specific gravity, so it can be easily recovered. By this method, neutralization, dehydration, and dealcoholization can be performed simultaneously, and high-quality oil can be easily obtained. The waste glycerin liquid that has absorbed the water and monohydric alcohol can be supplied to the neutralization process described above, and can be made into a part of the glycerin-containing liquid through a second separation process, etc.

In the second esterification step, preferred examples of methods other than the acid catalyst method include a biocatalyst method, a supercritical method, and a subcritical method.
The biocatalytic method is a method that promotes transesterification using lipases or phospholipases that have catalytic activity for ester conversion reactions. The biocatalytic method has the characteristics that, although the reaction conditions are mild, it can promote transesterification even in oils and fats with high acid values, and produces few by-products.
The supercritical and subcritical methods are methods in which the raw materials are converted into a supercritical or subcritical state by adjusting the temperature and pressure, thereby changing the phase state of the substance from a gas-liquid two-phase to a liquid-liquid two-phase, and then to a single phase by lowering the dielectric constant, thereby converting a reaction system that originally required the use of a catalyst into a catalyst-free system and promoting hydrolysis.

By carrying out this second esterification process, it becomes possible to recycle industrial waste even more efficiently.

[Water treatment method]
The denitrifying agent/nitrification promoter produced by the above method can be used as an organic carbon source in biological nitrification/denitrification treatment in wastewater treatment carried out in sewage treatment plants and the like.
The denitrification treatment step and the nitrification treatment step using the above-mentioned denitrification agent/nitrification promoter will be described below.
As shown in Fig. 3, in sewage treatment plants, biological nitrification denitrification methods using heterotrophic microorganisms, such as circulating denitrification, are used to treat nitrogen-containing organic wastewater. The nitrification denitrification method is a method in which ammonia nitrogen in the water to be treated is oxidized to nitrite nitrogen by ammonia oxidizing bacteria, and the nitrite nitrogen is further oxidized to nitrate nitrogen by nitrite oxidizing bacteria, and the ammonia nitrogen in the water to be treated is decomposed to nitrogen gas through a nitrification treatment process in which the nitrite nitrogen and nitrate nitrogen are decomposed to nitrogen gas by heterotrophic denitrifying bacteria. The nitrification liquid from the nitrification treatment process is circulated and supplied to the denitrification treatment process.

As a substitute for methanol in this denitrification process, the glycerin-containing liquid extracted through the first and second steps of the above-mentioned glycerin-containing waste treatment is added as an organic carbon source to the biological nitrification/denitrification process using heterotrophic microorganisms. In this case, the glycerin-containing liquid used acts mainly as a denitrification agent.

On the other hand, in the nitrification treatment step, the above-mentioned glycerin-containing liquid can be added as an organic carbon source for biological nitrification/denitrification treatment using heterotrophic microorganisms. In this case, the glycerin-containing liquid used mainly acts as a nitrification promoter.
The nitrification promoter according to the present embodiment is particularly suitable for use in treating water with a high ratio of ammonia nitrogen (NH ₄ -N) to BOD (biochemical oxygen demand). Such water can be said to have a shortage of BOD relative to ammonia nitrogen, and the nitrification reaction by nitrifying bacteria (ammonia oxidizing bacteria, nitrite oxidizing bacteria) may not proceed sufficiently, but by adding the nitrification promoter according to the present embodiment, the organic carbon source is supplemented, achieving a good balance between NH ₄ -N and BOD, making it easier for the nitrification reaction by nitrifying bacteria to proceed satisfactorily.
Examples of such water to be treated include water having a ratio of NH ₄ -N (mg/L):BOD (mg/L) of 50:100 or more, or even 100:100 or more. By adding the nitrification promoter according to the present embodiment to such water to adjust the ratio of NH ₄ -N (mg/L):BOD (mg/L) to, for example, 30:100 or less, or even 20:100 or less, the nitrification reaction can be more suitably promoted.

The glycerin-containing liquid may be added to either the denitrification process or the nitrification process, or to both processes. These can be adjusted appropriately depending on the degree of the denitrification reaction and the nitrification reaction.

The glycerin-containing liquid is decomposed in a short period of time as an organic carbon source for biological nitrification/denitrification treatment using heterotrophic microorganisms, so organic pollutants are less likely to remain.

In this way, instead of adding large amounts of methanol or the like as an organic carbon source in the denitrification treatment step of the biological nitrification denitrification method, by effectively utilizing glycerin-containing waste materials such as waste glycerin produced as a by-product in the fatty acid methyl ester manufacturing process, and fatty acid glycerin ester-containing waste materials such as high acid value oils and oil cakes, it is possible to reduce the chemical costs for methanol and suppress greenhouse gas emissions by not using methanol derived from fossil fuels.

[Denitrification agent/nitrification promoter manufacturing system]
A system for producing a denitrifying agent/nitrification promoter according to one embodiment of the present invention, which can realize the method for producing a denitrifying agent/nitrification promoter according to the above-mentioned embodiment, will be described below.

As shown in Fig. 4, the denitrification agent/nitrification promoter production system 1 is configured to include a first separation device 11, a neutralization device 12, and a second separation device 13. The denitrification agent/nitrification promoter production system 1 illustrated in Fig. 4 further includes an alcohol separation device 14, a storage tank 15, and a second esterification device 21.

The raw material, a composition containing glycerin or a fatty acid glycerin ester, is introduced into a first separation device 11 together with an inorganic acid, where an acid-catalyzed transesterification reaction or the like is carried out. After a certain period of time has passed, the reaction liquid undergoes phase separation into an acidic glycerin phase (first glycerin liquid) and an oil phase (first oil component).
The first glycerin liquid contains glycerin, inorganic salts, monohydric alcohol, etc., and is supplied to a neutralization device 12, in which an alkaline substance is added to neutralize the first glycerin liquid.

The neutralized glycerin liquid obtained by neutralization in the neutralization device 12 is supplied to a second separation device 13, where it is separated into a second glycerin liquid, an oil component (second oil component), and inorganic salts. As the second separation device 13, a three-phase separation type centrifuge or the like can be suitably used, and a centrifuge capable of solid-liquid separation, such as a decanter type, may be provided in the preceding stage.
The inorganic salt separated by the second separator 13 can be used as fertilizer or the like.

The second glycerin liquid separated in the second separation device 13 contains remaining monohydric alcohol, which is separated in the alcohol separation device 14. The diluted glycerin-containing liquid (denitrification agent/nitrification promoter) is sent to and stored in a storage tank 15.
The alcohol separation device 14 and the denitrification agent/nitrification promoter storage tank 15 do not need to be installed on the same site. For example, the denitrification agent/nitrification promoter, which is a glycerin liquid from which monohydric alcohol has been separated in the alcohol separation device 14, may be transported to the storage tank 15 located at a distance by a vehicle-mounted tank or the like.

Furthermore, in a preferred embodiment of the present invention, the denitrification agent/nitrification promoter production system 1 further includes a second esterification apparatus 21. The second esterification apparatus 21 is configured as an esterification reaction tank for producing fatty acid alkyl esters by a method other than the alkali catalyst method. The second esterification apparatus 21 is supplied with the oil separated in the first separation apparatus 11 (first oil) and/or the oil separated in the second separation apparatus 13 (second oil), and is further supplied with the monohydric alcohol separated in the alcohol separation apparatus 14.
In the second esterification device 21, a method other than the alkali catalyst method, more specifically, an acid catalyst method, an acid-alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method, or a solid catalyst method is carried out. An esterification reaction (including an ester exchange reaction) is carried out by any of these methods, and an oil component containing fatty acid alkyl esters is separated from a glycerin liquid. The by-produced glycerin liquid is supplied to the above-mentioned neutralization device 12, for example, and can be recycled as a raw material for a denitrification agent/nitrification promoter after neutralization and separation.
In addition, the oil containing fatty acid alkyl esters is acidic when the esterification reaction is carried out by an acid catalyst method in the second esterification device 21. Such acidic oil may be injected from the bottom of a tank (not shown) storing waste glycerin and allowed to overflow to the top of the glycerin phase, thereby simultaneously carrying out neutralization, dehydration, and dealcoholization.

The above-described embodiments are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples.

(Preparation of waste glycerin)
Biodiesel fuel was produced by transesterification of waste edible oil with methanol using an alkaline catalyst method with potassium hydroxide as a catalyst. The by-products produced during this process, including glycerin, were collected as waste glycerin.

Zeolite was added to this waste glycerin in an amount of 20 g per kg of waste glycerin to remove moisture. The waste glycerin to which zeolite had been added was passed through a 250 mesh filter to remove the zeolite and solid impurities.
The composition and physical properties of the waste glycerin thus obtained as a raw material (hereinafter referred to as "raw material waste glycerin") are shown in Table 1.

(First separation step)
500 kg of raw waste glycerin and 300 kg of high acid value oil (150 mgKOH/g) were put into a 1000 L reaction tank with heating and cooling functions, and heated to 55° C. while stirring (120 rpm). In this state, 32 L of concentrated sulfuric acid was added to the reaction vessel over 15 minutes. When adding concentrated sulfuric acid, care was taken to ensure that the temperature of the mixture in the reaction vessel did not exceed 65° C. The pH of the reaction liquid after the entire amount of concentrated sulfuric acid was added was 1. After the addition of concentrated sulfuric acid was completed, stirring was continued for 240 minutes. Then, the mixture was left to stand for 10 hours, separated into an oil phase (first oil) and an acidic glycerin phase (first glycerin liquid), and the first glycerin liquid (acidic glycerin phase, containing precipitated potassium sulfate) was collected. By repeating the above operations, 5000 kg of the first glycerin liquid was obtained.

(Neutralization process)
Into a reaction tank having a capacity of 15,000 L, 5,000 kg of the first glycerin liquid and 5,000 kg of waste glycerin were charged with stirring. The pH was 5.0. Stirring was continued for another 4 hours, and then the mixture was allowed to stand for 24 hours.

(Second Separation Step)
The neutralized glycerin was treated at 5,500 rpm for 180 minutes in a decanter centrifuge (product name: Z18H-V, manufactured by Tanabe Wiltec Co., Ltd.), and the precipitated potassium sulfate was separated and collected. The liquid phase was further treated at 8,000 rpm for 180 minutes in a three-phase separation centrifuge (manufactured by Alfa Laval Co., Ltd.), and the second oil, second glycerin liquid, and potassium sulfate were each separated and collected.

(Alcohol removal process, dilution process)
The glycerin-containing liquid obtained by the three-phase separation was distilled to remove methanol and water, thereby obtaining purified glycerin having a purity of 99% by mass (measured by gas chromatography).
The resulting purified glycerin was diluted with water and allowed to stand for one week, the separated oil phase was removed, and the resulting diluted glycerin phase was passed through a 5 micron bag filter and a column packed with activated clay to remove the oil (and impurities) to obtain a denitrifying agent/nitrifying agent A. In addition, 0.1 mass % of a surfactant (product name: Softanol, manufactured by Nippon Shokubai Co., Ltd.) was added to the denitrifying agent/nitrifying agent A to obtain a denitrifying agent/nitrifying agent B.

(Denitrification test)
The denitrifying effects of the thus obtained denitrifying agents A and B were tested as follows.

Activated sludge after biological treatment in the existing facility was collected and divided into 2L portions in beakers and left to stand at 30°C for 24 hours while stirring with a stirrer, to nitrify all remaining ammonia and other substances to nitrate. After this pretreatment, the nitrate nitrogen (NO ₃ -N) was 10.2 mg/L, and no nitrite nitrogen (NO ₂ -N) was detected. Next, 5 mL of 10% potassium nitrate was added to 2 L of activated sludge after pretreatment, and the initial NO ₃ -N, including the NO ₃ -N remaining after pretreatment, was set to 44.5 mg/L.

Ten minutes after adding potassium nitrate, 2 mL each of denitrifiers A and B were added, and the denitrification test was started. As a control, a test area was set up where 2 mL of water was added, and as a comparative example, a test area was set up where 2 mL of 50% methanol was added. The settings of each test area, the specific gravity of the carbon source, and the TOC amount are shown in Table 2. The TOC amount was measured using a portable spectrophotometer (DR900, manufactured by HACH) and measuring reagents provided by the manufacturer.

In the denitrification test, samples were taken 0, 3, 6, 9, 12 and 24 hours after the start of the test, and immediately centrifuged (3500 rpm x 15 min) and filtered using filter paper (No. 5C). The filtrate was measured for nitrate nitrogen (NO ₃ -N) and nitrite nitrogen (NO ₂ -N) using anion ion chromatography, and NO _x -N was calculated as the sum of these two species.

In test plots 2 and 3, _NOX -N had decreased to 16-17mg/L 3 hours after the start of the test, and had almost completely disappeared after 6 hours. In contrast, in test plot 4, which is a comparative example, about 30mg/L of _NOX -N remained after 6 hours, and had almost completely disappeared after 24 hours. In test plot 1, which is the control, about 40mg/L of _{NOX -} N remained after 6 hours, and about 32mg/L even after 24 hours.
From these results, it was confirmed that the denitrifying agents A and B of the present invention have excellent denitrifying effects. However, no effect on the denitrifying effect was observed due to the addition of Softanol (Denitrifying Agent B).

(Nitrification treatment test)
The nitrification promoter B thus obtained was tested for its nitrification promoting effect as follows.

In the nitrification treatment test, activated sludge after biological treatment in the existing facility and permeate after membrane separation were used. The analysis results of the activated sludge and membrane permeate were as follows.

Test areas 1 and 2 were set up with a total of 10 L, consisting of 2.5 L of the above activated sludge, 2.5 L of the above permeate, and 5 L of tap water. A blank area was set up with a total of 4 L, consisting of 1 L of the above activated sludge and 3 L of the above permeate. All of these were adjusted to have a suspended solids (SS) of 2,300 mg/L.

Each of the above test plots was placed in a container and aeration was performed in a thermostatic chamber at 27° C., and then the nitrification test was started.
In the test area 1 (Example), nitrification promoter B (BOD: 400,000 mg/L) was added as a carbon source at a rate of 7.5 mL/day. The BOD/SS load in the test area 1 was 0.13 kg/kg/day.
On the other hand, 7.5 mL/day of 50% methanol was added to test group 2 (comparison example), and no carbon source was added to the blank.
For the test plots in which the pH fell below 6 after 7, 13, and 18 days, 0.3 M NaOH was added to adjust the pH. In addition, the dissolved oxygen concentration was measured appropriately during the test to confirm that there was no shortage of dissolved oxygen.

In the nitrification test, 40 mL samples were taken 4, 8, 14, and 19 days after the start of the test, and immediately centrifuged (3500 rpm x 5 min) and filtered using filter paper (No. 5C). The NH ₄ -N (mg/L) of the obtained filtrate was measured using a simple analyzer manufactured by HACH.

In the blank, _NH4 -N gradually increased from about 1200 mg/L at the start of the test. This is thought to be because the BOD of the activated sludge used in this test was so small that the nitrification reaction did not proceed, and because no carbon source (BOD source) was added during the acclimation period, self-decomposition proceeded and ammonia increased.
In test area 1 (nitrification promoter B), NH ₄ -N did not change significantly from 600 mg/L at the start of the test until 4 and 8 days later (500-700 mg/L), but after 14 days it had dropped significantly to below the detection limit, and the same was true after 19 days. This result indicates that the BOD deficiency in this activated sludge was compensated for by adding nitrification promoter B, promoting the nitrification reaction by nitrifying bacteria and reducing NH ₄ -N. Furthermore, since the presence of anaerobic zones where sludge was retained was visually confirmed in the containers containing each test area, it is believed that denitrification reactions also progressed along with nitrification reactions.
On the other hand, in test area 2 (50% methanol), no significant change was observed in NH ₄ -N concentration (500-700 mg/L) even after 4, 8, 14 and 19 days from 600 mg/L at the start of the test. In other words, it was recognized that the use of methanol as a carbon source had little effect on promoting nitrification.
From these results, it was confirmed that the nitrification promoter of the present invention has an excellent nitrification promoting effect.

According to the present invention, it is possible to produce a denitrifying agent/nitrification promoter that has excellent denitrification and nitrification promotion effects as an organic carbon source for biological nitrification/denitrification treatment, and to provide a treatment method that can suitably use glycerin-containing waste as an organic carbon source in biological nitrification/denitrification treatment, thereby enabling glycerin-containing waste to be effectively recycled. Furthermore, it is possible to utilize waste glycerin and high acid value oils, which have traditionally been considered to have low utility value, and this has great industrial utility value.

1: Denitrification agent/nitrification promoter manufacturing system 11: First separation device 12: Neutralization device 13: Second separation device 14: Alcohol separation device 15: Storage tank 21: Second esterification device

Claims (20)

A water treatment method for carrying out biological nitrification/denitrification treatment by adding an organic carbon source, comprising the steps of:
a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating a first oil component and a first glycerin liquid;
a neutralization step of neutralizing the first glycerin liquid with an alkaline substance;
a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
an alcohol separation step of separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated;
A glycerin-containing liquid is produced by
The glycerin-containing liquid thus obtained is added as an organic carbon source for the biological nitrification/denitrification treatment, and a denitrification treatment step and/or a nitrification treatment step are provided.
a second esterification step of producing a fatty acid alkyl ester by at least one method selected from the group consisting of an acid catalyst method, an acid-alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method, and a solid catalyst method, which is a method other than an alkali catalyst method;
In the second esterification step, the first oil fraction separated in the first separation step and/or the second oil fraction separated in the second separation step and the monohydric alcohol separated in the alcohol separation step are used as raw materials.
Water treatment methods. A water treatment method for carrying out biological nitrification/denitrification treatment by adding an organic carbon source, comprising the steps of:
a first separation step of reacting a raw material containing a fatty acid glycerin ester with an inorganic acid in the presence of a monohydric alcohol and separating a first oil component and a first glycerin liquid;
a neutralization step of neutralizing the first glycerin liquid with an alkaline substance;
a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
A glycerin-containing liquid is produced by
The glycerin-containing liquid thus obtained is added as an organic carbon source for the biological nitrification/denitrification treatment, and/or the nitrification treatment step is provided.
The reaction in the first separation step has a reaction solution having a pH of 3 or less and a reaction time of 4 hours or more.
Water treatment methods. The water treatment method according to claim 2 , further comprising, after the second separation step, an alcohol separation step of separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated. A method for producing a denitrifying agent or a nitrification promoter used as an organic carbon source in a biological nitrification and denitrification treatment, comprising the steps of:
a first separation step of mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating a first oil component and a first glycerin liquid;
a neutralization step of neutralizing the first glycerin liquid with an alkaline substance;
a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
an alcohol separation step of separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated;
A glycerin-containing liquid is produced by
The obtained glycerin-containing liquid is added to the denitrification agent or the nitrification promoter as an organic carbon source for the biological nitrification/denitrification treatment ,
a second esterification step of producing a fatty acid alkyl ester by at least one method selected from the group consisting of an acid catalyst method, an acid-alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method, and a solid catalyst method, which is a method other than an alkali catalyst method;
In the second esterification step, the first oil fraction separated in the first separation step and/or the second oil fraction separated in the second separation step and the monohydric alcohol separated in the alcohol separation step are used as raw materials.
A manufacturing method comprising: 5. The method for producing a denitrification agent or a nitrification promoter according to claim 4 , wherein the raw material in the first separation step includes at least one of waste glycerin produced as a by-product in a process for producing a biodiesel fuel and glycerin produced as a by-product in a process for producing a free fatty acid. A method for producing a denitrifying agent or a nitrification promoter used as an organic carbon source in a biological nitrification and denitrification treatment, comprising the steps of:
a first separation step of reacting a raw material containing a fatty acid glycerin ester with an inorganic acid in the presence of a monohydric alcohol and separating a first oil component and a first glycerin liquid;
a neutralization step of neutralizing the first glycerin liquid with an alkaline substance;
a second separation step of separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
A glycerin-containing liquid is produced by
The obtained glycerin-containing liquid is added to the denitrification agent or the nitrification promoter as an organic carbon source for the biological nitrification/denitrification treatment;
The reaction in the first separation step is carried out with a reaction solution having a pH of 3 or less and a reaction time of 4 hours or more.
A manufacturing method comprising: 7. The method for producing a denitrifying agent or a nitrification promoter according to claim 6, wherein the raw material in the first separation step contains waste glycerin produced as a by-product in the process of producing a biodiesel fuel. The method for producing a denitrifying agent or a nitrification promoter according to claim 6 or 7 , further comprising, after the second separation step, an alcohol separation step of separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated. a second esterification step of producing a fatty acid alkyl ester by at least one method selected from the group consisting of an acid catalyst method, an acid-alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method, and a solid catalyst method, which is a method other than an alkali catalyst method;
In the second esterification step, the first oil fraction separated in the first separation step and/or the second oil fraction separated in the second separation step and the monohydric alcohol separated in the alcohol separation step are used as raw materials.
A method for producing a denitrifying agent or a nitrification promoter according to claim 4, 5 or 8 . 10. The method for producing a denitrifying agent or a nitrification promoter according to claim 4, further comprising, after the alcohol separation step, a dilution step of diluting the glycerin liquid from which the monohydric alcohol has been separated. 11. The method for producing a denitrifying agent or a nitrification promoter according to claim 10, wherein in the dilution step, the glycerin solution is diluted so that the TOC index and/or the COD index become equivalent to a predetermined concentration of methanol used as an organic carbon source in a biological nitrification/denitrification treatment using heterotrophic microorganisms. The method for producing a denitrifying agent or a nitrification promoter according to any one of claims 4, 5, and 8 to 11 , further comprising an oil removal step of separating and removing a third oil component after the alcohol separation step. The method for producing a denitrifying agent or a nitrification promoter according to any one of claims 4, 5 and 8 to 12 , further comprising an oil separation suppression step of suppressing separation of oil by adding a surfactant after the alcohol separation step. The method for producing a denitrifying agent or a nitrification promoter according to any one of claims 4 to 13 , wherein the raw material in the first separation step contains a high acid value oil having an acid value of 10 mgKOH/g or more. The method for producing a denitrifying agent or a nitrification promoter according to any one of claims 4 to 14 , wherein the inorganic acid in the first separation step is concentrated sulfuric acid. The method for producing a denitrification agent or a nitrification promoter according to any one of claims 4 to 15 , wherein in the neutralization step, the glycerin solution is neutralized so that the pH of the glycerin solution is 4.0 to 7.5. The method for producing a denitrification agent or a nitrification promoter according to any one of claims 4 to 16 , wherein the alkaline substance comprises waste glycerin and/or soapstock. A system for producing a denitrifying agent or a nitrification promoter used as an organic carbon source in a biological nitrification/denitrification process, comprising:
a first separation device for mixing a raw material containing at least one of glycerin and a fatty acid glycerin ester with an inorganic acid and separating the raw material into a first oil component and a first glycerin liquid;
a neutralization device for neutralizing the first glycerin liquid with an alkaline substance;
a second separation device for separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
an alcohol separation device that separates a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated;
In addition to providing
a second esterification apparatus for producing a fatty acid alkyl ester by at least one method other than an alkali catalyst method selected from the group consisting of an acid catalyst method, an acid-alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method, and a solid catalyst method;
The second esterification unit is supplied with the first oil fraction separated in the first separation unit and/or the second oil fraction separated in the second separation unit, and the monohydric alcohol separated in the alcohol separation unit.
A system for producing a denitrifying agent or a nitrification promoter, comprising: A system for producing a denitrifying agent or a nitrification promoter used as an organic carbon source in a biological nitrification/denitrification process, comprising:
a first separation device that reacts a raw material containing a fatty acid glycerin ester with an inorganic acid in the presence of a monohydric alcohol and separates a first oil component and a first glycerin liquid;
a neutralization device for neutralizing the first glycerin liquid with an alkaline substance;
a second separation device for separating a second oil component and precipitated inorganic salts from the neutralized glycerin liquid;
Equipped with
The reaction in the first separation device has a reaction liquid having a pH of 3 or less and a reaction time of 4 hours or more.
A system for producing a denitrifying agent or a nitrification promoter, comprising: The system for producing a denitrification agent or a nitrification promoter according to claim 19 , further comprising an alcohol separation device disposed downstream of the second separation device, for separating a monohydric alcohol from the glycerin liquid from which the second oil component and the inorganic salt have been separated.

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