JPH08323387A - Anaerobic treatment - Google Patents

Abstract

PURPOSE: To provide the treatment with which organic waste water can be treated at a low cost without generating hydrogen sulfide and the maintenance of treating facilities can easily be performed by adding iron ions to the organic waste water in an amount expressed in terms of the number of moles equal to or more than that of sulfur compounds in the waste water and subjecting the waste water contg. iron ions to anaerobic treatment. CONSTITUTION: In this treatment, iron ions are added to organic waste water in an amount expressed in terms of the number of moles equal to or more than that of sulfur compounds in the waste water and the resulting organic waste water contg. iron ions is subjected to anaerobic treatment, wherein the anaerobic treatment is an operation for decomposing organic matter in organic waste water through acid formation reaction and methane formation reaction by utilizing the action of anaerobic microorganisms while maintaining the waste water contg. organic substances to be treated in an anaerobic state. Examples of waste water to which this anaerobic treatment can be applied are sewage, human waste, industrial waste water, etc., each of which contains a small amount of sulfur compounds such as sulfate and sulfite ions. At the time of performing this anaerobic treatment, organic matter in waste water is decomposed through acid formation reaction and methane formation reaction effected by the action of anaerobic bacteria and on the other hand, sulfate ions, etc., are reduced to hydrogen sulfide by the action of sulfate reducing bacteria.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for anaerobic biological treatment of organic wastewater containing a small amount of sulfur compounds such as sulfuric acid and sulfite ions. In particular, the present invention relates to a biological treatment method capable of easily reducing hydrogen sulfide in biogas generated during anaerobic treatment.

[0002]

BACKGROUND ART Anaerobic biological treatment is performed as a method for treating organic wastewater such as sewage, night soil, industrial wastewater and the like. In this anaerobic treatment, wastewater containing organic matter is brought into contact with anaerobic bacteria (sludge) to decompose carbon dioxide gas and methane gas,
Biogas is generated. In addition to methane and carbon dioxide, biogas contains hydrogen sulfide due to sulfur compounds in wastewater. Such biogas is usually used effectively as fuel for boilers and incinerators for the purpose of recovering energy, but in order to prevent corrosion of incinerators, etc.,
Removal of hydrogen sulfide (desulfurization) in biogas is essential to prevent air pollution. Conventionally, as a desulfurization method of biogas, there are a dry method in which a gas is brought into contact with iron oxide to fix hydrogen sulfide, and a wet method in which a gas is brought into contact with an alkali absorbing liquid.

[0003]

However, in the conventional desulfurization method, an apparatus for desulfurization needs to be provided separately from the anaerobic treatment apparatus, and in the dry method waste is generated, and replacement of the filler is difficult. However, the wet method has a problem of high cost. The present invention solves these problems, and provides an anaerobic treatment method that does not generate hydrogen sulfide and is low cost and easy to maintain.

[0004]

DISCLOSURE OF THE INVENTION The present invention is characterized in that organic wastewater is characterized in that an anaerobic treatment is carried out by adding to the organic wastewater iron ions in an equimolar amount or more to the sulfur compound contained in the wastewater. Anaerobic treatment method. In the present invention, the anaerobic treatment is an operation in which wastewater containing an organic substance which is an object to be treated is kept in an anaerobic state, and the action of an anaerobic microorganism is used to decompose an organic substance through an acid-forming reaction and a methanogenic reaction. Yes, anaerobic digestion that puts in and digests the whole organic substance and anaerobic treatment of soluble organic substances by removing solids
High load anaerobic treatments such as ASB (upflow sludge blanket method), fluidized bed method and fixed bed method are generally used. The anaerobic treatment may be a one-phase system in which the acid production reaction and the methane production reaction are carried out in one anaerobic reaction tank, or a two-phase system in which both reactions are carried out in separate reaction tanks.

The organic waste water to be subjected to the anaerobic treatment is, for example, waste water such as sewage, night soil, industrial waste water, etc., and waste water containing a small amount of sulfur compounds such as sulfate ion and sulfite ion. Preferably, the amount of sulfur compound is 40 as S
It is preferably mg / l or less. When anaerobically treating such wastewater, iron ions are added to the wastewater. As the iron ion, any iron compound that dissociates the iron ion in water may be used, and for example, iron salts such as ferrous chloride, ferric chloride, ferrous nitrate, and ferric nitrate can be used. The iron salt is preferably added to the raw water flowing into the anaerobic reaction tank, preferably the inlet of the methane fermentation tank. The amount of iron salt added is preferably equimolar or more, preferably 1.2 to 2 times the amount of sulfur such as sulfuric acid or sulfurous acid in the waste water. For example, sulfuric acid and sulfurous acid as S in the wastewater that is the target of high-load anaerobic treatment such as the UASB method is 10%.
If about 20 mg / L is included, it is necessary to add F
The e concentration is 17 to 35 mg / L or more. The wastewater to which the iron salt has been added is anaerobically treated as usual.

When anaerobic treatment is carried out, the organic matter is decomposed due to the reaction of acid production and methane production due to the action of anaerobic bacteria.
Reduced to hydrogen sulfide by sulfate-reducing bacteria. ^{SO4 2- + CH3COO- → CO2 + S2} - + H2O + HCO3 - generated hydrogen sulfide is rapidly reacts with the added iron ions produce iron sulfide. Fe2 + + S2- → FeS The produced iron sulfide adheres to the sludge and is not retained in the system, and hydrogen sulfide does not migrate to the biogas. The sludge to which iron sulfide is attached is discharged from the reaction tank as excess sludge at any time. In this way, the content of hydrogen sulfide in the biogas generated during the anaerobic treatment is remarkably reduced, and problems such as corrosion can be alleviated even if the biogas is effectively used.

In the present invention, the larger the ratio (Fe / S) between the added iron ions and the S concentration derived from the waste water, the lower the concentration of hydrogen sulfide remaining in the water in the reaction tank,
It is relatively easy to set the hydrogen sulfide concentration in the processing gas to about 20 to 30 ppm or less. However, in order to further reduce the hydrogen sulfide in the treated gas to obtain a high-purity gas, the treated gas is washed with water or water in which an alkali is dissolved, and the washing liquid is used as the raw water in the methane generation reaction tank. By circulating the hydrogen sulfide in the gas phase, it is possible to efficiently capture the hydrogen sulfide flowing out to the gas phase. In this case, if an alkaline agent is used for the cleaning liquid, the equipment and chemical cost will be slightly higher, but if an attempt is made to obtain a high-purity gas by the conventional technique, the amount of the alkaline agent will be remarkably large, so that the present invention is far more advantageous. It is economical. The amount of iron salt added is usually
Based on the upper limits of sulfuric acid and sulfite concentrations in raw water, equimolar or more is added, but the hydrogen sulfide concentration in the generated gas is detected with a hydrogen sulfide sensor, etc., and the flow rate of the iron salt supply pump is added according to the detected amount. Can also be changed to obtain stable removal performance.

The present invention has a relatively low sulfide ion concentration such as beer wastewater and potato processing wastewater to which a high load anaerobic treatment system such as UASB is applied (40 mg / L as S).
In the following cases), it is effective and economical, and can be burned without adversely affecting a combustion device such as a boiler without a desulfurization device as a gas treatment. Further, when a large amount of sulfur compounds is contained in the waste water, the proportion of iron sulfide in the sludge gradually increases, and the amount of bacteria retained in the reaction tank decreases, which may lead to insufficient progress of biological treatment.

[0009]

[Example] Capacity 9 L (diameter 10 cm, height about 100 c
The effect of the iron salt concentration on the generated hydrogen sulfide concentration was investigated using an experimental apparatus consisting of the UASB methane generation tank of m) and the acid generation tank of 2.5 L in capacity. The substrate is glucose + ethanol (mixed as CODcr 3: 1), N (nitrogen) and P (phosphorus) as CODcr: N: P 1000:
Ammonium chloride and monopotassium phosphate were added to 10: 2, and further diluted with tap water so that CODcr was about 4000 mg / L. The experimental apparatus was installed in a thermostatic chamber at 30 degrees Celsius, and 25% NaOH was added so that the pH in the acid production tank would be 6.2. Approximately 3 granule sludge from the actual equipment that processes beer wastewater in the tank
L (VSS: 45000 mg / L) was collected and filled,
Operation The CODcr load was continuously operated at about 8 kg / m ³ / d. About 3 to 5 m in synthetic wastewater diluted with tap water
It contains g / L (as S) of sulfate ions, and the equimolar amount of Fe ³⁺ is 5.2 to 8.7 mg / L. In the experiment, Run-1 (Comparative Example) was not added, and Run was not added.
-2 (Comparative Example) was added with ferric chloride so that Fe was 3 mg / L and Run-3 (Example) was 10 mg / L, and the hydrogen sulfide concentration in the generated gas was examined. The results were as follows. As is clear from the above results, it is found that the presence of equimolar or more iron ions relative to sulfuric acid suppresses the transfer of hydrogen sulfide into the gas.

[0010]

EFFECTS OF THE INVENTION According to the present invention, equipment for desulfurization is not required, and therefore maintenance is facilitated only by adding chemicals, and desulfurization cost can be remarkably reduced. In addition, since conventional desulfurization processes biogas after biological reaction,
Hydrogen sulfide generated by a biological reaction may cause activity inhibition to living organisms, but in the present invention, the generated hydrogen sulfide reacts with iron ions and is rendered harmless, so there is no such fear. Furthermore, when applied to the UASB method, the F
The eS precipitates and the sludge settling property, which is a drawback of UASB, is improved.

Claims (1)

[Claims] 1. A method for anaerobic treatment of organic wastewater, which comprises adding to the organic wastewater at least an equimolar amount of iron ions with a sulfur compound contained in the wastewater to perform anaerobic treatment.