JP2001340896A - Organic waste treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic waste treatment method not requiring conventional complicated injection control of a chemical agent, simply and efficiently preventing the generation of an offensive smell from a sludge treatment equipment, or the like, and utilizing a deodorant capable of being utilized as a compost raw material comprising a dehydrated cake. SOLUTION: In the organic waste treatment method, a metal salt and a chelating agent or a metal chelate compound are added to organic waste. The metal chelate compound is a chelate compound with at least one kind of metal ions selected from iron ions, zinc ions and silver ions and the metal salt and the chelating agent or the metal chelate compound are preferably adjusted so that the chelating agent becomes 0.2-2 mol with respect to one mol of a metal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of sludge generated in the treatment of wastewater such as sewage, human waste, and industrial wastewater, and the treatment of organic waste such as anaerobic treatment of other organic waste and fermentation. More specifically, in a sludge treatment facility or the like, a treatment method capable of efficiently suppressing odors therefrom, a treatment method for detoxifying an inhibitory component in an anaerobic treatment of a fermentation solution, and a sulfide generated in a fermentation treatment. The present invention relates to a method for treating organic waste represented by a method for reducing the concentration of hydrogen.

[0002]

2. Description of the Related Art Organic waste such as sludge and fermentation waste liquid has been treated by various treatment methods. Sludge generated by wastewater treatment such as sewage, human waste, and industrial wastewater is easily rotted, and emits sulfur-based odors such as hydrogen sulfide and methyl mercaptan.
A large amount of nitrogen-based odor such as ammonium is generated, and serious problems such as deterioration of the working environment in the sludge treatment facility and corrosion of the equipment occur. Further, when the dewatered cake after the sludge is subjected to the dewatering treatment is carried out of the site, there is a problem that the odor is generated at the receiving destination at the time of carrying out, during transportation, and at the receiving destination. In the anaerobic treatment of the fermentation liquor, in the case of methane fermentation, sulfides such as hydrogen sulfide are generated, and this sulfide is an inhibitory component of methane fermentation and hinders the progress of methane fermentation. It is required to be removed. Furthermore, hydrogen sulfide in biogas generated from biomass in a fermentation process is required to reduce the concentration of hydrogen sulfide in order to prevent corrosion of the boiler when used as fuel for a boiler or the like.

Conventionally, deodorants have been used or deodorizing methods have been used to remove odors generated from sludge or sludge dewatered cakes in these sludge treatment facilities. Regarding the odor method, it has been proposed to use the following various substances and employ various means. Among them, a method of deodorizing by adding an aqueous solution containing a metal salt such as ferric chloride or zinc chloride to sludge is widely and generally employed. Brominated or chlorinated chemicals having strong oxidizing power, such as bromate and hypochlorite, are effective against various odor components. Bactericidal deodorants such as organic halogen compounds such as chlorinated isocyanuric acid and thiocyanate compounds are widely used as household deodorants. In addition, in the anaerobic treatment of the fermentation liquor, the addition of some drug to the fermentation liquor changes the composition of the fermentation liquor, which changes the fermentation conditions. is there.

[0004]

However, the deodorant mainly composed of heavy metals such as copper added to sludge is
Although the removal effect of hydrogen sulfide is high, the dewatered cake generated from the sludge to which these are added contains metals derived from the deodorant. There is a limit. In addition, halogen-based oxidizing agents such as bromate and hypochlorite lack immediate effect, change the properties of sludge depending on the location of addition, reduce the dehydration performance, or because the chemical itself is a dangerous chemical However, there is a problem that care is required for handling. Furthermore, the germicidal deodorant has a disadvantage that if it is used in excess, the dehydrated cake cannot be reused for composting because of its bactericidal properties because of the immediate effect of deodorization. Need precise control. In the anaerobic treatment of fermentation liquor, etc., when taking measures to add some chemicals to the fermentation liquor, the composition of the fermentation liquor will be changed. Is necessary.

SUMMARY OF THE INVENTION An object of the present invention is to simply and efficiently prevent the generation of odors in sludge treatment facilities and fermentation treatment equipment, and do not require complicated injection control as in the above-mentioned chemicals. An object of the present invention is to provide a method for treating organic waste, which can be deodorized by using a deodorant that can be used as a compost material for cake. Further, an object of the present invention is to prevent the anaerobic treatment by sulfide in the anaerobic treatment by adding a drug that does not deteriorate the fermentation state when taking a means of adding any agent to the fermentation liquid in anaerobic treatment and the like. An object of the present invention is to provide a method for treating organic waste, which can reduce the concentration of hydrogen sulfide in biogas.

[0006]

In order to solve the above problems, the present invention provides a method for treating an organic substance having the following constitution. (1) A method for treating organic waste, comprising adding a metal salt and a chelating agent or a metal chelate compound to the organic waste when treating the organic waste. (2) The method for treating organic waste according to (1), wherein the metal chelate compound is a chelate compound with at least one metal ion of iron ion, zinc ion and silver ion. (3) The metal salt and the chelating agent or the metal chelating compound are used in an amount of 0.2 to 0.2 moles per mole of the metal.
The method for treating organic waste according to (1), wherein the amount is adjusted to 2 mol. (4) A hydrogen sulphide agent used when treating organic waste, the metal sulphide agent using a metal salt and a chelating agent or a metal chelate compound.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The organic wastes that are the subject of the present invention include sewage, night soil, industrial wastewater and the like, sludge generated from sewage, night soil, industrial wastewater treatment, dewatered cake obtained by dewatering sludge, various organic industrial wastes, and fermentation. Fermentation liquor in anaerobic treatment of liquid, fermentation undiluted liquid in fermentation process are mentioned, sludge generated in particular with industrial wastewater treatment, and various organic industrial wastes such as dewatered cake obtained by dewatering sludge are preferable targets. .
The object to be treated in the present invention is not particularly limited, but it is generally sludge that generation and decay of odor is a concern,
It is desirable to apply mainly to organic sludge. Further, the sludge to which the treatment method of the present invention is applied is subjected to a dehydration treatment, and the resulting dewatered cake can be deodorized as a result. The odor component targeted by the present invention is an odor generated by the decay of an object to be treated, such as hydrogen sulfide, methyl mercaptan, methyl sulfide, methyl disulfide, ammonia, tritylamine, and aldehydes.

In one embodiment of the present invention, a chelating agent is added to and mixed with an organic waste such as sludge, and then a water-soluble metal salt is added and mixed, or a water-soluble metal salt and a chelating agent are mixed. This is a method in which a sludge is deodorized by the added metal ions by adding and mixing a metal chelate compound prepared and mixed in advance with sludge. A method of mixing and preparing a water-soluble metal salt and a chelating agent in advance is as follows.
What melt | dissolved 1 mol of chelating agents per mol may be used as a metal chelate compound. Also, a water-soluble metal chelate compound, for example, an analytical reagent Z used for quantitative analysis
n-EDTA or the like can be applied. In the present invention, a metal chelate mixed and prepared in an equimolar amount is referred to as a metal chelate compound, and when used as a deodorant, this metal chelate compound, and those containing an excess chelating agent described later, Called chelating agents.

[0009] Metal salts are all in the sludge dissociated into metal ions, the metal ions, HS hydrogen sulphide sludge is dissociated in water ^- and react with S ^2- sulfide ion, sparingly water Metal sulfide, fixed to sludge and deodorized. Generally, the pH of sludge is in the range of 5 to 7. When a metal salt is added to sludge, metal ions generated in the sludge become H
S ^- and S ^2- and reacts, remaining excess metal ions becomes hardly soluble metal hydroxides. Once a hardly soluble metal hydroxide is formed, even if sludge is decayed and new hydrogen sulfide is generated, the hardly soluble metal hydroxide can be reduced to HS ^- or S ² due to the hydrogen sulfide. ^- I can not react with, deodorant becomes difficult.

Further, when a metal is added to sludge, if the concentration of HS ^- or S ^2- in the sludge is high, there is a high possibility that the sludge will react with metal ions first. When the alkali content of the sludge is high, all or most of the added metal ions react with the alkali content first to form a metal hydroxide. in this way,
HS of added metal ions is due to the effective hydrogen sulfide ^-
And S not used in ^2, not only the drug is wasted, it is necessary to the addition of a large amount of the drug in order to obtain a deodorant effect.

[0011] By increasing the amount of chemicals added to the sludge, sludge and
The metal content of the dewatered cake is increased, resulting in sludge and dewatering.
When water cakes are used effectively,
An obstacle to using it. As in the present invention, a metal salt and
Add a chelating agent or use a metal chelate compound
Exists in sludge in the form of ions of metal chelates
And present in sludge so that it does not become metal hydroxide
HS^-And S^2-And newly generated HS^-And S ^2-And quickly anti
In response, the added chemical is used for deodorization without waste
In addition, a single drug addition can maintain the deodorant effect for a long time,
Savings.

In the second aspect of the present invention, iron, zinc, silver, or a combination of these metals is used as a metal when a metal salt and a chelating agent are added, or when a metal chelate compound is used. It is. metal,
That is, as the metal ions, the above-mentioned three types exhibit particularly favorable effects. In the case where the sludge is used in a combo-storage case, the sludge may be contained in the combo-storage bath, and the only metals allowed to be used are iron and zinc. Therefore, iron and zinc are preferable as the metals in the present invention. Iron can be used in both ferrous and ferric salts. Anions that bind to metal salts are chloride ions, sulfate ions,
There are nitrate ions and the like. In particular, nitrate ions have a high deodorizing effect because they prevent anaerobicization of sludge by releasing oxygen in the sludge. The agent of the present invention and a nitrate can be used in combination. However, nitrate cannot be used in the anaerobic treatment because absolute anaerobic needs to be maintained.

A chelating agent is an agent that coordinates with a metal ion and has a binding force that does not generate a metal hydroxide even if the pH of the aqueous solution changes from 3 to 10.
Specific examples include EDTA salts, citric acid, triethanolamine, nitrilotriacetic acid (NTA), thiocyanic acid and the like. The chelating agent may be conventionally referred to as a sequestering agent, which also corresponds to the chelating agent of the present invention.
EDT, a common drug with strong coordination bond with metal
Salt A is suitable as the chelating agent of the present invention. ED
TA salt refers to ethylenediaminetetraacetic acid or a metal salt thereof. Generally, the EDTA salt is EDTA2Na in which disodium is bound to ethylenediaminetetraacetic acid having high solubility in water. In addition, as an effective use of waste, since the waste cleaning solution used for metal cleaning contains iron and a chelating agent, it can be used as the metal chelating agent of the present invention.

According to a third aspect of the present invention, a metal salt and a chelating agent or a metal chelating compound adjusted to be 0.2 to 2 mol per 1 mol of a metal, This is a deodorizing method in which a mixture obtained by adding only a chelating agent or a metal salt to the sludge is added to sludge as a metal chelating agent. If the sludge contains a metal that is more easily coordinated than the added metal, the metal of the added metal chelate compound is replaced with the original metal, and metal ions effective for deodorization become metal hydroxides, and The effectiveness of the chelating agent is reduced. In order to prevent this, an excess of a chelating agent corresponding to the added metal is added, so that the added metal or the metal of the metal chelating agent is effectively deodorized.

Usually, the metal and the chelating agent react in equimolar amounts. The metal ion concentration present in the sludge is at most 100
Since the amount is not more than mg / liter, 1.1 mole of the chelating agent is sufficient for 1 mole of the added metal. Since the addition of excess chelating agent is not economical, the upper limit is preferably 2 mol. Excess chelating agent does not affect the deodorizing effect or dehydration performance. Rather, when a polymer flocculant is added during dehydration, metal ions in the sludge that affect the deterioration of the polymer flocculant, such as iron and calcium, are immobilized with a chelating agent and the water content of the dewatered cake is reduced. An excess of chelating agent is advantageous as it reduces the On the other hand, since the chelating agent is more expensive than the metal salt, it is necessary to consider the molar ratio of the chelating agent to the metal according to the properties of the sludge. Therefore, if the deodorizing effect is somewhat sacrificed, or if a short-term deodorizing effect is expected, the molar ratio of the metal chelating agent to the metal is 1: 1. Can be 2. If you want to keep the deodorant effect,
The metal to chelating agent is at least 1: 0.2.

The chemical addition site of the present invention is a sludge storage tank for storing sludge, a sludge receiving tank for temporarily receiving sludge, a transfer pipe connecting the sludge tank, and a dehydrator for dewatering sludge. In the vicinity of the dehydrator, there are a storage tank for sludge supplied to the dehydrator, a mixing tank to which a polymer flocculant is added, and a pipe connecting them. Preferably, it is desirable to add the sludge to the sludge in the sludge storage tank where the reaction time is sufficient. In the case of methane fermentation in anaerobic treatment of a fermentation liquor, it is preferable to add it before the treatment step. The same applies to the fermentation process

[0017]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A deodorizing test was performed on sewage sludge having the properties shown in Table 1. Note that TS is evaporation residue, SS is suspended matter, VSS
Is the loss on ignition of suspended solids. To 500 ml of the above-mentioned sludge, EDTA2Na was added and mixed in different amounts as shown in Table 2, and then, ferric chloride was added and mixed, and a volume of 20 ml was added.
Put in a 00 ml odor measurement container,
After purging 500 ml with nitrogen and sealing, 3
It was stored in a thermostat at 0 ° C. At predetermined time intervals, the concentration of hydrogen sulfide in the gas phase was measured with a Kitagawa detector tube. Table 2 shows the test results. The results of the blank test with no added chemical and the ferric chloride alone are also shown. The deodorizing effect of hydrogen sulfide was high from the beginning of the test, and the deodorizing effect was maintained.

[0019]

[Table 1]

[0020]

[Table 2]

Example 2 20 g of ferric chloride and 40 g of EDTA2Na were mixed with 0.8 g of pure water.
Dissolve in water and add 20% aqueous sodium hydroxide
H was adjusted to about 6, and this was made up to 1 liter with pure water to be used as an iron chelating agent. The concentration of the iron chelating agent comprising the aqueous solution of the iron chelating agent was 6% (w / v). An aqueous solution of an iron chelating agent was added to the sludge of Example 1, and a test was conducted in the same manner as in Example 1. The results are shown in Table 3. The generation of hydrogen sulfide was effectively suppressed from the beginning of the test, and the deodorizing effect was maintained by increasing the addition rate of the iron chelating agent.

[0022]

[Table 3]

Example 3 EDTA2Na was added to 500 ml of the sludge of Example 1.
Was added and mixed with 0.2 to 1.2 moles per mole of iron, and then ferric chloride 200 mg / liter or 500 m2 was added.
g / L was added and tested as in Example 1. Table 4 shows the test results. Increasing the molar ratio of the chelating agent to iron in the iron chelating agent increases the deodorizing effect.

[0024]

[Table 4]

Example 4 A soybean broth waste liquid containing 15 g / L of COD _{Cr and} 8 g / L of protein was placed in an anaerobic treatment apparatus having a fermenter capacity of 2 L per line in a anaerobic treatment apparatus having a COD _Cr sludge load of 3 kg / kg.
On the day, water was continuously passed at a fermenter temperature of 35 ° C. When the COD _Cr removal rate reached 80%, the COD _Cr sludge load was increased 1.5 times. Approximately three months later, three series of anaerobic treatment equipment COD
_Cr sludge load is 10 kg / kg-day, and CO
The D _Cr removal rate was 84%, and the amount of generated biogas was 4.9 liter / liter. The composition of biogas is 78% methane, 22% carbon dioxide, and 1000 ppm hydrogen sulfide.
Met.

200 g of ferric chloride and 400 g of EDTA4Na are dissolved in 0.8 liter of pure water, adjusted to about pH 6 with 20% sodium hydroxide, and made up to 1 liter with pure water to obtain an iron chelate. Agent. The concentration of the iron chelating agent in the aqueous solution of the iron chelating agent was 70 g / liter. The addition of the iron chelating agent aqueous solution was continuously started at 0 to 70 mg / liter with respect to 1 liter of soybean broth waste liquid. Table 5 shows the results after about one month. A reduction in the COD _Cr removal rate of the treated water could be prevented, and the concentration of hydrogen sulfide in the biogas could be kept low.

[0027]

[Table 5]

Example 5 The three-series anaerobic treatment apparatus of Example 4 was continuously operated,
After the COD _Cr sludge load was set at 15 kg / kg / day, the iron chelating agent of Example 3 was continuously added at 0 to 80 mg / L to 1 L of soybean broth waste liquid. Table 6 shows the treatment results when the COD _Cr sludge load was 15 kg / kg · day and the iron chelating agent was added, and about one month had passed. COD _Cr sludge load is 15k compared to Example 4.
Even if the amount was increased to g / kg / day, by using the iron chelating agent, it was possible to prevent a decrease in the COD _Cr removal rate of the treated water and to keep the concentration of hydrogen sulfide in the biogas low.

[0029]

[Table 6]

[0030]

As described in detail above, the present invention has the following excellent effects. (1) Deodorization of organic waste such as sludge can be performed with a small amount of chemicals. (2) Organic waste such as sludge after the addition of a deodorant can be dewatered and reused in compost, which can contribute to effective use of resources and reduction of waste. (3) Since there is no handling of dangerous drugs, safety and workability are improved. (4) The deodorizing effect of organic waste such as sludge is maintained for a long time. (5) Since the inhibition of sulfide ions in the anaerobic treatment is suppressed, the activity of the anaerobic sludge is increased, and the anaerobic treatment capacity is improved. (6) The concentration of hydrogen sulfide in biogas generated by anaerobic treatment can be reduced, and the amount of desulfurizing agent used can be reduced.

Claims (4)

[Claims] 1. A method for treating organic waste, comprising adding a metal salt and a chelating agent or a metal chelate compound to the organic waste when treating the organic waste. 2. The metal chelate compound is an iron ion,
2. The method for treating organic waste according to claim 1, wherein the compound is a chelate compound of at least one metal ion of zinc ion and silver ion. 3. The method according to claim 1, wherein the metal salt and the chelating agent or the metal chelating compound are adjusted so that the chelating agent is 0.2 to 2 mol per 1 mol of the metal. Organic waste treatment method. 4. A hydrogen sulphide agent used for treating organic waste, which comprises a metal salt and a chelating agent or a metal chelate compound.