JPS588593A - Anaerobic digesting treatment of waste liquid containing sulfate ion - Google Patents

Abstract

PURPOSE:To perform an anaerobic digesting treatment efficiently, by a method wherein an organic waste liquid containing sulfate ions is treated by an electrolyzer, and then it is introduced into an anaerogic digesting treatment device to convert sulfur contained in the liquid into a soluble difficult iron-sulfur compound. CONSTITUTION:The liquid to be treated is introduced into an electrolyzing treatment tank 2 provided with an iron electrode 3 and a carbon electrode 4 through an introducing pipe 12, and an electric current is passed through the liquid to dissolve iron ions in an amount of 1-2 times of the equivalent required for the reaction with the sulfate ions generated by the anaerobic digsting treatment. The liquid with the iron ions dissolved therein is introduced into an anaerobic digesting treatment tank 1 in which anaerobic bacteria are cultivated, and is decomposed into gaseous methane and gaseous carbon dioxide by the anaerobic digesting treatment. On the other hand, the sulfate ions are converted into sulfide ions by the function of sulfuric acid reducing bacteria. The sulfide ions react with the iron ions dissolved in the liquid, and iron sulfide is precipitated in the tank.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for anaerobic digestion of organic wastewater containing sulfate ions.

The anaerobic digestion treatment method is used to treat organic wastewater with relatively high concentration, and is generally performed under anaerobic conditions at a reaction temperature of 30 to 40%.
There are two methods: a method of processing at around 0°C (medium temperature fermentation method) and a method of processing under anaerobic conditions at a reaction temperature of around 55 to 60°C (high temperature fermentation method).In the anaerobic digestion method, organic matter in the liquid to be treated is is first decomposed into volatile fatty acids such as acetic acid and propionic acid (liquefaction reaction), and then the volatile fatty acids produced are decomposed into flammable methane gas, making it an excellent energy recovery method.

However, if sulfate ions are contained in the liquid to be treated during this anaerobic digestion treatment, the sulfate ions in the liquid to be treated are reduced by the action of sulfate-reducing bacteria living in the digestion tank, and converted into sulfur ions. Dissolved in digestive juices. These sulfur ions are discharged into the generated gas as corrosive hydrogen sulfide, but if the liquid to be treated contains a relatively large amount of sulfate ions, the sulfur ions are discharged from the system as hydrogen sulfide. However, concentrations that still inhibit anaerobic digestion (Me1'
oom/%) of sulfur ions, which prevents good anaerobic treatment.

Conventionally, pretreatment methods for anaerobic digestion treatment have been attempted, in which sulfate ions are precipitated and separated as calcium sulfate by adding, for example, carunium to such liquids to be treated. could not be removed sufficiently, and good treatment effects could not be obtained. Another method was considered to suppress the action of sulfate-reducing bacteria by injecting chlorine gas into the digester, but there were concerns about the impact on other anaerobic bacteria living at the same time, and the injection of chlorine gas. There are various problems such as setting the amount, and it has not been put into practical use yet.

An object of the present invention is to provide an anaerobic digestion treatment for organic waste liquid, which eliminates the drawbacks of the prior art, removes sulfuric acid or sulfur ions that inhibit anaerobic treatment, and allows efficient anaerobic digestion treatment. The purpose is to provide a method.

The present invention focuses on the fact that when the sulfur present in the anaerobic digestion tank exists in the form of insoluble iron sulfide, it does not inhibit anaerobic digestion treatment. - As a means of converting the liquid into sulfur compounds, an electrolytic treatment device configured with iron as an anode plate and an insoluble electrode plate, such as a carbon plate as a cathode, is attached to an anaerobic digestion treatment tank, and the liquid to be treated is electrolytically treated. After leaching iron ions into the treated liquid through a treatment device, anaerobic digestion is performed to remove the sulfur in the digestion tank as insoluble iron sulfide. .

That is, the anaerobic digestion method according to the present invention uses an electrolytic treatment apparatus having an iron electrode as an anode, and uses 1 to 2 sulfur ions necessary for reaction with sulfur ions generated in the anaerobic digestion treatment in the liquid to be treated.
It is characterized by dissolving twice the equivalent amount of iron ions by adjusting the voltage during electrolytic treatment, and then performing anaerobic digestion treatment.

Next, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a system diagram of an apparatus for carrying out anaerobic digestion according to the present invention. The liquid to be treated is first introduced into the electrolytic treatment tank 2 equipped with an iron electrode plate 3 (anode) and a carbon electrode plate 4 (cathode) through the liquid to be treated introduction pipe 12, and iron ions are eluted into the liquid to be treated by applying electricity. be done. At this time, 1 to 2
The voltage is adjusted by the DC transformer 13 so that double equivalent amount of Chichi ions are dissolved. Further, the liquid to be treated is circulated and stirred inside the electrolytic treatment tank 2 via the liquid to be treated circulation pump 5 and the circulation piping 6. The liquid to be treated in which iron ions have been dissolved by the above-described process is introduced into the anaerobic digestion tank 1 via the liquid to be treated pump 7 and the communication pipe 8 . Anaerobic bacteria, such as liquefaction bacteria, gasification bacteria, and sulfate-reducing bacteria, live in the digestion tank l, and there are a stirring gas pipe 9 as a stirring means in the tank, a steam introduction pipe 10 as a heating means, Also, a generated gas pipe 14 and a desorbed liquid pipe 11 are provided.

In such a configuration, the liquid to be treated introduced into the digestion tank 1 is decomposed by anaerobic digestion and becomes methane gas and carbon dioxide gas, while sulfate ions are affected by sulfate-reducing bacteria and become sulfur ions.

These sulfur ions react with iron ions dissolved in the liquid to be treated, and iron sulfide is precipitated in the tank.

Next, FIG. 2 shows the results of continuous treatment for about 30 days of organic waste liquid having the properties shown in Table 1 using the method of the present invention and the precipitation separation method using calcium. In the figure,
5 shows the results for the method of the present invention, 16 shows the results for the calcium precipitation method, and 17 shows the results for no treatment. As is clear from Table 1, in the case of no treatment a7>, after the start of the experiment, Gas generation almost stops after about 1 to 6 days, and even in the case of the calcium precipitation method, the gas generation gradually decreases to about 20ONt/~-゛vS after 30 days, but the present invention In the case of α, the generated fjx amount is 500
-VS was extremely high at ~60 ONt/, and no increase in sulfur ions in the digester was observed. It is also clear that hydrogen sulfide in the generated gas is maintained at a lower concentration than the other two methods, and it has been found that the method of the present invention suppresses the generation of hydrogen sulfide gas.

As described above, according to the present invention, sulfur ions that inhibit anaerobic digestion treatment can be removed and efficient anaerobic treatment can be performed.

[Brief explanation of the drawing]

FIG. 1 is an apparatus system diagram showing an example of the method for anaerobic digestion of sulfate ion-containing waste liquid according to the present invention, and FIG. 2 is a diagram showing the results of the example of the method of the present invention. 1... Anaerobic digestion tank, 2... Electrolysis treatment tank, 3
... Iron plate, 4... Carbon plate, 12...
・Introduction pipe for liquid to be treated.

Claims (1)

[Claims] fi+ Organic waste liquid containing sulfate ions is passed through an iron electrode (
Water is passed through an electrolyzer having an anode (anode) and an insoluble electrode (negative) to dissolve iron ions in excess of the equivalent amount required for reaction with sulfate ions in the liquid to be treated, followed by anaerobic treatment. 1. A method for anaerobic digestion of sulfate ion-containing waste liquid, which comprises introducing the sulfur ion-containing waste liquid into an anaerobic digestion apparatus and converting the sulfur form in the treated liquid into a hardly soluble iron-sulfur compound.