JPH09220593A - Treatment of ammonia nitrogen-containing organic waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance methane fermentation efficiency within a short stagnation time in a small-sized treatment tank by treating a liquid to be treated in the presence of phosphate ions and magnesium ions in a state of specific pH or more to form magnesium ammonium phosphate and separating this phosphate to perform methane fermentation. SOLUTION: A liquid to be treated being an ammonia nitrogen-containing org. waste liquid is treated in the presence of phosphate ions and magnesium ions to form magnesium ammonium phosphate which is, in turn, separated to perform methane fermentation. As this waste liquid, there is excretion. In this case, as a source of phosphate ions, phosphoric acid or sodium phosphate can be used. As a source of magnesium ions, magnesium chloride or magnesium sulfate is used. As the magnesium source, seawater may be used. pH is pref. adjusted to 8-11 if necessary by adding a pH controller, for example, sodium hydroxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for treating an organic effluent containing ammoniacal nitrogen by methane fermentation.

[0002]

BACKGROUND ART When anaerobic treatment of organic nitrogen-containing effluent such as human waste and surplus sludge of activated sludge is carried out, organic acid fermentation first occurs due to the action of acid-producing bacteria, and low molecular weight solid organic matter is dissolved. , Produces organic acids. After that, methane fermentation occurs due to the action of methanogens, and organic acids are decomposed into methane and carbon dioxide. In the one-phase anaerobic digestion method, organic acid fermentation and methane fermentation occur in parallel, but in the two-phase anaerobic treatment, organic acid fermentation and methane fermentation are performed in separate tanks.

By the way, organic nitrogen compounds contained in human waste, sludge and the like are decomposed into ammoniacal nitrogen by lowering the molecular weight in the stage of acid fermentation. This ammoniacal nitrogen is toxic to methanogenic bacteria, and when a high concentration of ammoniacal nitrogen is present, the methanogenic bacteria are inhibited and the rate of methane fermentation is reduced. The toxicity of ammonia nitrogen in methane fermentation depends on pH, and the higher the pH, the stronger the toxicity. However, near pH 7, NH ₄ -N shows toxicity at 1000 mg / l or more, and at 2000 mg / l, the rate of methane fermentation is about 1
It becomes about 1/4 at / 2 and 3000 mg / l.

[0004]

In the conventional anaerobic treatment method, the toxicity of ammoniacal nitrogen is not taken into consideration, and it is diluted with a liquid containing no ammoniacal nitrogen or treated with a large volume. Processing is performed with a long residence time using a tank. For example, if there is no inhibition, a residence time of about 10 days is sufficient, but a residence time of about 30 days is required, so the apparatus becomes large and the treatment efficiency is poor.

[0005] Further, in high load anaerobic treatment such as UASB and fixed bed, the activity is reduced by ammonia nitrogen, and when the liquid to be treated contains phosphorus, calcium phosphate, magnesium ammonium phosphate, etc. There is a problem that the high-load anaerobic treatment cannot be applied to the treatment of the ammoniacal nitrogen-containing waste liquid because the scale is likely to be deposited in the pipes and the methane fermentation tank to cause clogging.

In order to solve the above problems, an object of the present invention is to eliminate or reduce the inhibition of ammonia nitrogen on methane fermentation, and thereby efficiently perform methane fermentation with a short residence time using a small treatment tank. It is to propose a method of treating an organic waste liquid containing ammoniacal nitrogen, which is capable of applying high-load anaerobic treatment as well.

[0007]

The present invention relates to a method for treating an ammoniacal nitrogen-containing organic waste liquid by methane fermentation, wherein the liquid to be treated is treated with phosphorus at pH 8 or higher in the presence of phosphate ions and magnesium ions. A method for treating an organic effluent containing ammoniacal nitrogen, which comprises producing and separating magnesium ammonium salt and performing methane fermentation.

The waste liquid to be treated in the present invention is an organic waste liquid containing ammonia nitrogen. Here, the ammoniacal nitrogen is contained in the state of ammonium ion (ammonia), and may be generated by decomposition of the organic nitrogen compound or originally contained in the state of ammoniacal nitrogen.

Examples of such drainage liquid include night soil, liquefied surplus sludge of activated sludge, and fertilizer production wastewater. Liquids that originally contain ammoniacal nitrogen, such as human waste, can be directly used as the liquid to be treated, but if they contain organic nitrogen compounds, solids, or other polymeric substances, those that have been liquefied should be treated. It is preferably a liquid.

Liquefaction of night soil, sludge and the like can be carried out by the above-mentioned acid fermentation or wet oxidation. Acid fermentation manure, sludge, etc. are maintained in an anaerobic state in an acid fermentation tank,
Acid-producing bacteria are grown to decompose organic nitrogen compounds, solids, and polymeric substances, and liquefy. Wet oxidation is, for example, 10 to
It is decomposed by heat treatment under pressure of 70 Kg / cm ² at 150 to 250 ° C. in the presence of oxygen.

The above ammoniacal nitrogen-containing organic waste liquid is separated by generating magnesium ammonium phosphate (hereinafter referred to as MAP) at a pH of 8 or more in the presence of phosphate ions and magnesium ions as a liquid to be treated. To do. MAP is generated in the liquid to be treated by the following equation.

[Chemical formula 1] Mg (OH) ₂ + NH ₄ OH + H ₃ PO ₄ + 4H ₂ O → MgNH ₄ PO ₄ · 7H ₂ O ・ ・ ・ (1)

The reaction of the formula (1) is an equimolar reaction, and the phosphate ion and the magnesium ion need not be added when they are contained in the liquid to be treated, but they are added when they are insufficient. Since human waste, excess sludge and the like usually contain phosphorus compounds, the liquefaction thereof does not need to be newly added because it contains phosphate ions, but magnesium ions are not usually added, so they are added externally.

As the phosphate ion, phosphoric acid, sodium phosphate, potassium phosphate or the like can be added.
Magnesium chloride, magnesium sulfate, magnesium hydroxide or the like can be added as magnesium ions. 1000-1500 magnesium in seawater
Since it is contained in mg / l, seawater may be added as a magnesium source. The addition amount of these varies depending on the concentration of ammonium ions and is usually equimolar, but in some cases it may be added in excess.

Since the reaction of the formula (1) proceeds at a pH of 8 or higher, preferably pH 8 to 11, a pH adjusting agent is added if necessary to adjust the pH. Examples of pH adjusters include sodium hydroxide, calcium hydroxide, magnesium hydroxide and the like. Magnesium hydroxide is preferable because it can be used as both a magnesium source and a pH adjuster.

By adding the required amount of phosphate ion, magnesium ion and pH adjusting agent to the liquid to be treated, MA
P (usually heptahydrate) is generated and precipitated as insoluble crystals, which are separated from the reaction solution. The MAP can be separated by a method such as crystallization and aggregation separation. Crystallization was carried out by passing the reaction solution through the packed bed of seed crystals and MAP on the seed crystal surface.
Can be precipitated and granulated, and can be collected as MAP particles and used as a fertilizer or the like. The aggregated precipitate is reacted in a reaction tank to precipitate MAP, and separated by solid-liquid separation means such as precipitation and membrane separation.

The liquid from which MAP has been separated decomposes organic substances by carrying out methane fermentation. Methane fermentation is performed by anaerobic treatment in the presence of sludge containing methanogens. In this step, it is preferable that only the methane fermentation by the methanogen is performed on the liquid to be treated after the solubilization of the solid organic matter, the high molecular weight compound, etc. and the organic acid fermentation, but the solid organic matter, the high molecular weight compound, etc. remain. Regarding the treatment liquid, sludge containing acid-producing bacteria and methanogenic bacteria can be used to perform acid fermentation and methane fermentation in parallel.

As the methane fermentation method, any method such as a floating type, a UASB (upflow type sludge blanket type), a fixed bed type and a fluidized bed type can be used. The floating type is a method in which biological sludge in a floating state and a liquid to be treated are mixed and treated anaerobically, and a relatively long residence time is required. Although it is carried out only by methane fermentation, it is also possible to carry out acid fermentation and methane fermentation in parallel.

UASB is a method in which sludge blanket is formed by anaerobic treatment by using sludge in which methanogens are granulated with high density and passing through in an upward flow. The fixed bed system is a method of performing anaerobic treatment using sludge in which methanogens are attached to the surface of a fixed bed type carrier at high density. The fluidized bed method is a method in which biological sludge containing methane bacteria at a high density is supported on a granular carrier to form a fluidized bed for anaerobic treatment. These are high-load anaerobic treatments, both of which are methods of passing a liquid at a high load and a high flow rate for a relatively short time. It is preferred that the treatment is performed as follows.

When mesophilic bacteria having a high activity at around 35 ° C. are used for methane fermentation, anaerobic treatment can be carried out at a temperature of 30 to 40 ° C. and a residence time of 6 hours to 25 days.
It is preferable to use a thermophilic bacterium having a high activity at around 55 ° C., in which case a temperature of 45-60 ° C. for 3 hours-20
Anaerobic treatment can be performed with a residence time of one day. In these cases, it is necessary to lengthen the residence time when acid fermentation and methane fermentation are performed in parallel, but the retention time can be shortened when only methane fermentation is performed on the liquid matter that has undergone acid fermentation.

Methane fermentation is carried out after the production and separation of MAP. In some cases, the reaction liquid treated in the methane fermentation step is returned to the MAP production step to separate MAP and circulate in the methane fermentation step to produce methane. It is also possible to reduce the concentration of ammoniacal nitrogen in the fermentation process.
However, in high-load anaerobic treatments such as UASB and fixed bed, by performing only methane fermentation on the liquefied product after acid fermentation and MAP separation, it is possible to increase the density of methanogenic bacteria in biological sludge, and thus high load. In addition to high-speed processing, MAP precipitation and scale formation can be prevented.

By carrying out the methane fermentation as described above, the organic acid in the liquid to be treated is decomposed into methane and carbon dioxide gas. When the liquid to be treated contains solid organic substances, polymer compounds and the like, organic acids are produced here by organic acid fermentation and then decomposed into methane and carbon dioxide gas. In this case, by removing ammoniacal nitrogen as MAP in advance, the activity of methanogens becomes high, and treatment with a short residence time becomes possible, and at the same time, calcium phosphate, MAP
It is possible to prevent scale formation due to precipitation of the like.

In the case of high-load anaerobic treatment, the presence of ammoniacal nitrogen makes it impossible to perform high-speed treatment due to a decrease in activity and also causes clogging and reduction in effective volume due to precipitation of MAP and scaling of calcium phosphate. Separation eliminates such problems, streamlines processing, and facilitates operation management. Therefore, it is possible to apply high load anaerobic treatment.

[0023]

Embodiments of the present invention will be described below. Comparative Example 1 The synthetic urine shown in Table 1 was introduced into a methane fermenter having a capacity of 3 liters, mixed with floating biological sludge, and stirred at a temperature of 35 ° C. under anaerobic conditions for treatment. When the residence time was 30 days, the TOC removal rate was 94% on average, but when the retention time was 20 days, the TOC removal rate was 91% on average. When the residence time was shortened to 10 days, the TOC removal rate decreased to 50% or less.

[0024]

[Table 1]

Example 1 The pH of the synthesized urine in Table 1 was adjusted to 9.0, magnesium chloride was added at 600 mg / l, the mixture was slowly stirred for 60 minutes, and the resulting precipitate was filtered. The phosphorus in the filtrate was 11 mg / l.
Met. Ammonia (as N) is 2,610 mg /
l. When this filtrate was subjected to methane fermentation in the same manner as in Comparative Example 1, the TOC removal rate was 9 on average at the retention time of 30 days.
5%. When the residence time was 20 days, TOC
The removal rate was 93% on average, and 80 to 86% could be maintained in 10 days.

Example 2 To the synthetic wastewater shown in Table 1, magnesium chloride was added in an amount of 1.2% by weight and monopotassium phosphate was added in an amount of 1.5% by weight.
The H was adjusted to 9 and slowly stirred for 60 minutes. As a result, the ammonia in the filtrate was 976 mg / l (as N). When this filtrate was subjected to methane fermentation in the same manner as in Comparative Example 1, a TOC removal rate of 90 to 92% was obtained at a residence time of 10 days.

[0027]

According to the present invention, ammoniacal nitrogen is added to M
By separating as AP and performing methane fermentation, it is possible to remove or reduce the inhibition by ammoniacal nitrogen and perform methane fermentation with high efficiency, which enables efficient ammoniacal reaction with a short treatment time using a small processing apparatus. Since the nitrogen-containing organic waste liquid can be treated and the precipitation of MAP and the formation of scale can be prevented, it is possible to obtain effects such as high-load anaerobic treatment.

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[Procedure amendment]

[Submission date] February 16, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

The present invention SUMMARY OF], in a method of treating a methane fermentation ammonium nitrogen-containing organic effluent, in pH8 or more states in the presence of a liquid to be treated phosphate ions and magnesium ions, A method for treating an organic effluent containing ammoniacal nitrogen, which comprises producing and separating magnesium ammonium phosphate and performing methane fermentation.

Claims (1)

[Claims] 1. A method for treating an ammoniacal nitrogen-containing organic effluent by methane fermentation, which comprises producing magnesium ammonium phosphate in the presence of phosphate ions and magnesium ions at a pH of 8 or more. A method for treating an organic effluent containing ammoniacal nitrogen, which comprises separating and performing methane fermentation.