JP2005288371A - Wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment method which enables the inexpensive desulfurization of organic wastewater with a simple structure in the wastewater treatment method for anaerobically treating the organic wastewater containing sulfur and nitrogen. <P>SOLUTION: When treated water in an anaerobic reaction tank 1 is introduced into a denitrification tank 2 to be circulated between the denitrification tank 2 and a nitrification tank 3, and denitrification is performed, a biogas containing hydrogen sulfide generated in the anaerobic reaction tank 1 is introduced into the denitrification tank 2 from a line L10. In the denitrification tank 2, hydrogen sulfide reacts with nitrate-nitrogen in the treated water in the anaerobic reaction tank 1 by the action of sulfur oxide bacteria to progress denitrification. This reaction reduces the concentration of hydrogen sulfide in the treated water in the anaerobic reaction tank, however, the hydrogen sulfide from the introduced biogas is dissolved to further progress the reaction, thereby simultaneously progressing desulfurization of biogas and denitrification of treated water. Further, an organic gas in a biogas becomes the source of nutrient for denitrifying bacteria in the denitrification tank 2, and as a result, the denitrification efficiency is enhanced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wastewater treatment method for biologically treating organic wastewater, and more particularly to a treatment method for treating organic wastewater containing sulfur and nitrogen by anaerobic biological treatment.

  As a method of treating organic wastewater such as food factories, domestic wastewater, and agricultural settlement wastewater, a method of biological treatment using anaerobic microorganisms is known (for example, see Patent Document 1). In this anaerobic biological treatment, the organic matter is decomposed into biogas containing methane gas. This biogas is effectively recycled as fuel for boilers and the like.

By the way, when sulfur content is contained in waste water, hydrogen sulfide (H ₂ S) may be generated by a sulfuric acid reduction reaction in anaerobic treatment. This H ₂ S is discharged from the treatment system together with the biogas, but H ₂ S becomes a source of malodor and has the property of corroding piping, gas tanks, etc., and therefore needs to be removed by providing a separate desulfurization system.
JP 11-57674 A

Food production wastewater, such as beer production wastewater, contains sulfur as well as nitrogen. The sulfur content in the wastewater becomes H ₂ S by the reduction reaction by the anaerobic biological treatment, and the concentration thereof can be a high concentration exceeding several thousand ppm as the H ₂ S concentration in the biogas. As described above, when the H ₂ S concentration is increased, the conventional dry and wet desulfurization apparatuses are disadvantageous in that the apparatus is increased in size and the required amount of chemicals is increased to increase the running cost. As a result, the cost associated with biogas resource increase also increases.

  Then, this invention makes it a subject to provide the waste water treatment method which can perform a desulfurization process by simple structure at low cost in the waste water treatment method which carries out the anaerobic biological treatment of the organic waste water containing sulfur and nitrogen.

  In order to solve the above problems, a wastewater treatment method according to the present invention is a wastewater treatment method for biologically treating organic wastewater containing sulfur and nitrogen, and after treating the organic wastewater by anaerobic biological treatment, anaerobic The biodenitrification treatment is carried out while introducing the biogas generated by the sex biological treatment, whereby the denitrification treatment of the liquid to be treated and the desulfurization treatment of the biogas are carried out simultaneously.

In biological denitrification, biodenitrification was performed while introducing biogas, so that nitrate nitrogen (NO ₃ -N) present in the liquid to be treated and biogas dissolved into the treatment liquid. H ₂ S is decomposed by the following reaction due to the recent action of sulfur oxidation.

5H ₂ S + 6NO ₃ ⁻ + 2H ₂ O → 3N ₂ + 5SO ₄ ²⁻ + 14H ⁺
Thereby, denitrification and desulfurization processing can be performed at once. In addition, a part of organic gas such as methane gas in biogas is also used as an organic source in the denitrification treatment.

  Thus, after performing the biological denitrification treatment, the treatment can be stably performed by performing the nitrification treatment.

According to the present invention, the denitrification treatment of the liquid to be treated and the desulfurization treatment of the biogas are simultaneously performed by performing the biological denitrification treatment while introducing the biogas containing H ₂ S obtained by the anaerobic biological treatment. be able to. Therefore, it is possible to reduce the H _{2 S} concentration in biogas, it can be reduced costs associated with the desulfurization process, even if necessary further desulfurization. Furthermore, even in the case of a liquid to be treated having a low organic substance concentration, the denitrification reaction can be advanced using H ₂ S and organic gas in biogas, so that the treatment efficiency of the denitrification treatment is improved.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a wastewater treatment facility 100 for implementing a wastewater treatment method according to the present invention. The wastewater treatment facility 100 is for treating wastewater discharged from a food factory, for example.

  The wastewater treatment facility 100 includes an anaerobic reaction tank 1, a denitrification tank 2, a nitrification tank 3, a desulfurization facility 4, and a reuse facility 5.

  The anaerobic reaction tank 1 is for decomposing organic components into methane gas, carbon dioxide gas, etc. by anaerobic microorganisms. Various types of anaerobic treatment tanks such as EGSB type and UASB type upflow type anaerobic treatment tanks are used. Can be used.

  The denitrification tank 2 holds denitrifying bacteria that reduce and remove nitrate or nitrite in the treatment solution to nitrogen gas in an anaerobic state, and the nitrification tank 3 contains ammonia nitrogen in an aerobic state. Nitrifying bacteria that oxidize to nitrate or nitrite are held in the tank. Although not shown, the nitrification tank 3 is provided with an aeration device for aeration of air or oxygen.

  The desulfurization equipment 4 includes a dry or wet desulfurization device that removes sulfur components (hydrogen sulfide, sulfurous acid gas, etc.) in the gas. The reuse facility 5 includes a boiler and the like in addition to the gas holder.

  The anaerobic reaction tank 1 is connected with a line L1 for introducing the water to be treated, and the denitrification tank 2 is connected with a line L2 for conveying the treatment liquid and a line L10 for conveying the generated gas (biogas). Yes.

  The denitrification tank 2 and the nitrification tank 3 are connected to each other through lines L3 and L4 for circulating the processing liquid, and the denitrification tank 2 and the desulfurization facility 4 are connected to each other through a line L11 that conveys the generated gas. The desulfurization facility 4 is further connected to the reuse facility 5 through the gas transport line L12. The nitrification tank 3 is further connected with a line L5 for discharging treated water.

  Next, the operation of this embodiment, that is, the waste water treatment method according to the present invention will be specifically described.

  A relatively low concentration organic waste water containing both nitrogen and sulfur is introduced into the anaerobic reaction tank 1 from the line L1. In the anaerobic reaction tank 1, organic components are decomposed into methane gas, carbon dioxide gas, etc. by anaerobic microorganisms in the tank. At this time, the sulfur content is decomposed into solid sulfur content or hydrogen sulfide by the following sulfuric acid reduction reaction. A part of the reacted hydrogen sulfide is dissolved in the treatment liquid by gas-liquid equilibrium.

SO ₄ ²⁻ + 4H ₂ → S ²⁻ + 4H ₂ O
4H ₂ + 2O ₂ → 4H ₂ O
SO ₄ ²⁻ + 3H ₂ → S ⁰ + 2H ₂ O + 2OH ⁻
The treatment liquid in which most of the organic components are decomposed in this way is sent directly to the denitrification tank 2 through the line L2. Further, biogas composed of hydrogen sulfide, methane gas, and carbon dioxide gas generated in the anaerobic reaction tank 1 is also introduced into the denitrification tank 2 through the line L10.

  In the denitrification tank 2, in an anaerobic state, nitrate nitrogen (nitrate ions and nitrite ions) is reduced to nitrogen gas by denitrifying bacteria according to the following reaction.

2NO ₂ ⁻ + 6H ⁺ → N ₂ + 2H ₂ O + 2OH ⁻
2NO ₃ ⁻ + 10H ⁺ → N ₂ + 4H ₂ O + 2OH ⁻
In this reaction, a BOD component more than 3 times that of nitrate nitrogen is required. However, since the organic content in the treatment liquid is decomposed and removed by the treatment in the anaerobic reaction tank 1, the BOD component in the treatment liquid introduced into the denitrification tank 2 remains at a low level. In the present invention, denitrification reaction by sulfur-oxidizing bacteria occurs using hydrogen sulfide dissolved in the treatment liquid. In addition, since hydrogen sulfide is continuously supplied by introducing biogas, the reaction can be suitably advanced even in a state where the BOD concentration in the processing liquid is low. For this reason, it is not necessary to add a separate nutrient source, and the processing cost can be reduced.

  That is, the hydrogen sulfide dissolved in the treated water and the hydrogen sulfide dissolved from the introduced biogas and the nitrate nitrogen undergo the following reaction by the sulfur-oxidizing bacteria to reduce the nitrate nitrogen and sulfide Hydrogen oxidation occurs.

5H ₂ S + 6NO ₃ ⁻ + 2H ₂ O → 3N ₂ + 5SO ₄ ²⁻ + 14H
Thereby, the desulfurization process from biogas and the denitrification process of a process liquid can be performed simultaneously. Among the components in biogas, hydrogen sulfide is more soluble than methane gas and may be consumed by the above reaction, and is easily dissolved in the processing solution. However, the methane gas required for resource recycling is in the processing solution. Since the solubility in is originally low, most of it passes through the denitrification tank 2 except for a part consumed as a nutrient source for denitrifying bacteria.

The treatment liquid treated in the denitrification tank 2 is conveyed to the nitrification tank 3 through a line L3. In the nitrification tank 3, ammoniacal nitrogen (NH ₄ ⁺ ) in the treatment liquid is oxidized into nitrate nitrogen by the nitrifying bacteria in an aerobic state by the following reaction.

2NH ₄ ⁺ + 3O ₂ → 2NO ₂ ⁻ + 2H ₂ O + 4H ⁺
2NO ₂ ⁻ + O ₂ → 2NO ₃ ⁻
The treatment liquid thus treated is returned to the denitrification tank 2 through the line L4 and is circulated between the denitrification tank 2 and the nitrification tank 3, thereby finally removing both nitrate nitrogen and ammonia nitrogen in the liquid to be treated. Decompose and remove to nitrogen gas. If the nitrogen is sufficiently removed by repeating the circulation, it is discharged from the line L5 to the sewer or sent to another subsequent processing facility.

  On the other hand, the biogas desulfurized in the denitrification tank 2 is sent to the desulfurization facility 4 through the line L11. Since desulfurization in the denitrification tank 2 does not completely remove hydrogen sulfide, when a gas containing almost no hydrogen sulfide is required, desulfurization may be further performed by a known dry or wet desulfurization method. In addition, when it may contain the low concentration hydrogen sulfide at the time of resource utilization, it can be set as the format which does not require the desulfurization equipment 4. FIG. Since the biosulfur gas introduced into the desulfurization facility 4 has a reduced hydrogen sulfide concentration compared to when it was discharged from the anaerobic reaction tank 1, the biogas introduced in the desulfurization facility 4 compared to the case where this biogas is directly introduced. The equipment can be downsized, and even when chemicals are used, the amount of use can be reduced. For this reason, there is an advantage that the running cost required for the desulfurization process can be reduced.

  The biogas desulfurized in the desulfurization facility 4 is sent to the reuse facility 5 and is separately used as boiler fuel or the like.

  In order to confirm the effectiveness of the wastewater treatment method according to the present invention, the inventor conducted an example of introducing biogas generated in the anaerobic reaction tank 1 in the denitrification process, and a denitrification process without introducing biogas. Since the comparison experiment which compares with the comparative example to perform was done, the result is described below.

In the comparative experiments, synthetic wastewater simulating the same food production wastewater was used. The synthetic wastewater used in the experiment had a BOD of 2000 mg / l, COD _Cr of 3000 mg / l, a total nitrogen concentration of 80 mg / l, and a total sulfur concentration of 20 mg / l. As a result of anaerobic biological treatment of this in the anaerobic reaction tank 1 under the condition of COD _Cr load 20 kg-COD _Cr / m ³ · d, the treated water after passing through the anaerobic reaction tank 1 has a BOD of 130 mg / l and total nitrogen concentration Was 60 mg / l, and the total sulfur concentration was 10 mg / l. The hydrogen sulfide concentration in the biogas was 5000 ppm.

In this example, while introducing this biogas into the denitrification tank 2, the treatment liquid is circulated between the denitrification tank 2 and the nitrification tank 3, so that the nitrogen load of the denitrification tank is 0.7 kg-N / m ³ · d, and nitrification. Denitrification / desulfurization treatment was performed under conditions of a tank nitrogen load of 0.2 kg-N / m ³ · d and a nitrification circulating fluid flow rate of 5Q (Q is the flow rate of water to be treated). On the other hand, in the comparative example, denitrification was performed without introducing biogas. The conditions other than the biogas supply were the same for the examples and comparative examples.

  As a result, in the examples, in the final treated water, the BOD was less than the measurement limit of 10 mg / l, the total nitrogen concentration was 10 mg / l, and the total sulfur concentration was 10 mg / l. Moreover, the hydrogen sulfide concentration in the biogas after passing through the denitrification tank 2 was 500 ppm.

  On the other hand, in the comparative example, in the final treated water, the BOD and the total sulfur concentration were the same as in the example, but the total nitrogen concentration was 20 mg / l, and the denitrification efficiency reached the example. There wasn't. Further, the comparative example differs from the examples in that biogas desulfurization needs to be performed separately.

  As a result of the comparative experiment, it was confirmed that the biogas itself was denitrified by introducing biogas and the treatment solution was improved in denitrification efficiency. Moreover, the influence of the increase in the total sulfur concentration in denitrification treated water accompanying desulfurization from biogas was not seen. This is thought to be because hydrogen sulfide dissolved in the anaerobic treated water was consumed in the denitrification reaction by the sulfur-oxidizing bacteria, and this consumption was replenished by introducing biogas. Thereby, the effectiveness of the present invention could be confirmed.

  In the above description, the case where the denitrification tank and the nitrification tank are provided separately has been described as an example, but the present invention is not limited to such equipment. For example, a structure in which the denitrification tank and the nitrification tank are separated by a partition wall that can overflow, a membrane, etc., a facility that performs denitrification and nitrification alternately by changing aeration conditions in the same tank, and oxidation The present invention can be suitably applied to facilities such as a ditch where the treated water is flowed and the region satisfying the aerobic condition and the region satisfying the anaerobic condition coexist in the flow path.

It is a schematic block diagram of the waste water treatment facility 100 which enforces the waste water treatment method which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Anaerobic reaction tank, 2 ... Denitrification tank, 3 ... Nitrification tank, 4 ... Desulfurization equipment, 5 ... Reuse equipment, 100 ... Waste water treatment facility, L1-L5 ... Treatment liquid conveyance line, L10-L12 ... Gas conveyance line.

Claims (2)

A wastewater treatment method for biologically treating organic wastewater containing sulfur and nitrogen,
After treating the organic wastewater by anaerobic biological treatment,
A wastewater treatment method, wherein a denitrification treatment of a liquid to be treated and a desulfurization treatment of a biogas are simultaneously performed by performing a biological denitrification treatment while introducing a biogas generated by the anaerobic biological treatment.   A wastewater treatment method comprising performing a nitrification treatment after the biological denitrification treatment.

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