JPH0763712B2 - Biological denitrification method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitrogen oxides contained in liquids such as tap water, sewage, human waste, irrigation water, sea water and waste water, or nitrogen oxides produced during the treatment of these liquids. TECHNICAL FIELD The present invention relates to a method and an apparatus for the reduction treatment.

[0002]

2. Description of the Related Art Conventionally, nitrogen oxides in a liquid are denitrified by using microorganisms (denitrifying bacteria) immobilized on the surface of an organism-attached medium or entrapped and immobilized by a resin or the like. A treatment technology is known, and this method has an advantage that the apparatus becomes compact as compared with the activated sludge denitrification method.

[0003]

By the way, in order to carry out economical and rational treatment in a method of denitrifying nitrogen oxides in a liquid by utilizing denitrifying bacteria adhered to or entrapped in a medium. It is necessary to inject an appropriate amount of reducing agent in response to fluctuations in inflowing nitrogen oxides. For this reason, a method has been proposed in which the amount of a reducing agent remaining in the denitrification treatment liquid, for example, commonly used methanol is detected using gas chromatography and the injection amount of methanol is appropriately controlled. However, gas chromatography is expensive, the analysis mechanism is complicated, and the analysis becomes difficult even if a small amount of SS (floating solid matter) is present in the liquid. In the present invention, when the reducing agent injection amount becomes excessive, the S
The biological denitrification method was made based on the finding that the S concentration is increased, and can solve the above-mentioned problems, appropriately control the injection amount of the reducing agent, and obtain an economically high-quality treatment liquid. And an apparatus thereof.

[0004]

According to the present invention, a reducing agent is injected into a liquid containing nitrogen oxides to carry out reductive denitrification by utilizing a denitrifying bacterium in which nitrogen oxides in the liquid are adhered to or entrapped in a medium. In the method, a biological denitrification method is characterized in that the SS concentration in the outflowing denitrification treatment liquid is detected by an absorptiometric method, and the reducing agent injection amount is controlled based on the detected value. An absorptiometric SS measuring device is connected to the denitrification treatment liquid outflow path of the denitrification tank that is equipped with agent injection equipment and uses the denitrifying bacteria attached to or entrapped in the medium to reduce and denitrify nitrogen oxides in the liquid. The biological denitrification device is characterized in that the SS measuring device is connected to the reducing agent injecting facility through an arithmetic and control circuit for controlling the reducing agent injecting amount according to the detected value.

[0005]

The liquid which is the subject of the present invention is a liquid containing nitrogen oxides, or a liquid obtained by previously oxidizing NH ₃ -N in the liquid to nitrogen oxides such as nitric acid by a nitrification step under aerobic conditions. The denitrifying bacteria immobilized by injecting a reducing agent such as methanol, ethanol or propyl alcohol into these liquids and adhering them to the surface of the biofouling medium such as activated carbon, sand or honeycomb tube under anaerobic conditions, Alternatively, it is introduced into a denitrification process using denitrifying bacteria that are entrapped and immobilized with polyvinyl resin or the like, and nitrogen oxides in the liquid are reduced to nitrogen gas to be denitrified. The denitrification treatment liquid that has been subjected to the reductive denitrification contains S in the liquid by an absorptiometry SS measuring device such as a turbidimeter or a fluorometer.
S is detected, the detection signal from the SS measuring device is input to the arithmetic control circuit, and the calculated SS concentration is compared and calculated, and then the injection amount of the reducing agent is controlled. In this case, the set SS concentration is
It is the SS concentration when the reducing agent is injected just enough.
In this way, a high-quality denitrification treatment liquid with reduced turbidity, reducing agent and BOD concentration can be obtained. There is a correlation between the reducing agent injection amount and the SS concentration in the liquid, and the SS concentration increases when the reducing agent injection amount becomes excessive. When the reducing agent injection amount becomes excessive, the SS concentration rises because nitrogen oxide, which is an oxygen source of the denitrifying bacteria, is not sufficiently distributed in the denitrification process,
This is because the entire denitrification process became an absolute anaerobic state (a state in which neither dissolved oxygen nor bound oxygen was present), so that the denitrifying bacteria were inactivated and separated from the immobilized product. In particular, when sulfate ions are present, the sulfate ions are reduced by the sulfate-reducing bacteria to generate colloidal sulfur particles, so that when the nitrogen oxides disappear, the SS concentration increases remarkably. Therefore, the present invention is particularly effective for a nitric oxide-containing liquid containing sulfuric acid, for example, an oxidizing liquid of human waste or wastewater containing seawater.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus of the present invention will be described with reference to FIG. 1. Reference numeral 1 is a denitrifying bacterium adhered to or immobilized on the surface of a bioadhesive medium such as anthracite, or is covered with polyvinyl resin or the like. A nitrification solution in which NH ₃ —N in the solution is oxidized to nitric acid or the like under aerobic conditions in a denitrification tank filled with immobilized denitrifying bacteria and in a nitrification tank 2 filled with a honeycomb tube or the like,
Alternatively, another nitrogen oxide-containing liquid inflow pipe 3 is connected, and a reducing agent injection facility 5 for injecting a reducing agent 4 such as methanol into the inflow liquid from the nitrogen oxide-containing liquid inflow pipe 3 is provided. The nitrogen oxide-containing liquid that has flowed into the denitrification tank 1 together with the reducing agent 4 undergoes denitrification of nitrogen oxides into nitrogen gas under anaerobic conditions, and the denitrification treatment liquid flows out from the denitrification treatment liquid outflow pipe 6. However, the denitrification treatment solution outflow pipe 6 is connected with an absorptiometry SS measuring device for measuring the SS concentration of the denitrification treatment solution flowing out, for example, a turbidimeter 7 by the absorptiometry method. There is. Further, the turbidity meter 7 is connected to the arithmetic control circuit 8, and the detected value of the turbidity detected by the turbidity meter 7 is input to the arithmetic control circuit 8 and, after being compared and calculated with the set turbidity, The arithmetic control circuit 8 and the reducing agent injection equipment 5 are connected so as to control the reducing agent injection amount by the reducing agent injection equipment 5.

Next, 3 to 4 mm with denitrifying bacteria adhered and immobilized
The volume of φ anthracite is 25 l (180 mmφ × 10
(00 mm) is filled in a cylindrical tank to form a denitrification tank, and an example of an experiment in the case where the NO ₃ —N concentration of the inflowing nitrification water is changed and the denitrification treatment is performed in a downward flow is shown. The experimental conditions are as shown in Table 1, and the reagent NaN was used as fresh water and seawater as nitrifying water.
Artificial nitrification water prepared with O ₃ was used. As a comparative example of the present invention, as is conventionally done, methanol was continuously injected in an amount sufficient to completely denitrify even when the nitrification water NO ₃ —N was high.

[0008]

[Table 1] FIG. 2 and FIG. 3 show the fluctuation patterns of NO ₃ —N concentration of nitrification water flowing into the denitrification tank, residual methanol of denitrification treated water, and turbidity of experiments 1-1 and 2-1 when continuous injection of methanol was performed. Shown in. From these figures, it can be seen that the fluctuation of NO ₃ -N causes methanol to remain and the turbidity increases.
In 1), it turns out that it is especially remarkable. The results of these comparative examples (Experiments 1-1 and 2-1) are as shown in Table 2, and the same NO ₃ -N concentration time variation as in the comparative example was given.
The method of the present invention in which the methanol injection amount was controlled by detecting the turbidity of denitrification-treated water with an automatic turbidity measuring instrument by the absorptiometric method
-2 and 2-2) are also shown in Table 2.

[0009]

[Table 2] The amount of methanol injected in the method of the present invention is controlled by continuously passing denitrification treated water through a 50 mm cell of an automatic turbidity measuring instrument,
The absorption value was continuously detected at a wavelength of 600 nm and automatically controlled. Specifically, in Experiment 1-2, the absorption value was 0.010.
The amount of methanol injected was reduced to 50% of the set value when the value increased to 1, and the amount of methanol injected was adjusted to the set amount (100%) when the absorption value decreased to 0.009. Experiment 2
-2, when the absorption value increased to 0.060, the amount of methanol injected decreased to 25% of the set value, and the absorption value was 0.0
The set value (100%) was injected when the temperature dropped to 50. The turbidity is the absorption value multiplied by 82. When the nitrification water originally has turbidity, it is advisable to set the turbidity for automatic control of the amount of injected methanol in consideration of the turbidity. Therefore, the turbidity, the injection amount of methanol, and NO ₃
The relationship of the -N removal rate may be experimentally grasped in advance and finely adjusted at the implementation stage.

[0010]

As described above, according to the present invention, the following extremely beneficial effects are exhibited. Since the injection amount of the reducing agent for denitrification can be controlled by a simple means such as an absorptiometric method, automatic injection of the reducing agent can be performed easily and stably. The turbidity of the denitrification treatment liquid and the concentration of the reducing agent BOD can be reduced, and a high-quality treatment liquid can be obtained. The amount of reducing agent injected can be reduced, and economical denitrification can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration of a device of the present invention.

FIG. 2 is a diagram showing fluctuation patterns of NO ₃ —N concentration in nitrifying water, residual methanol in denitrification-treated water, and turbidity in Experiment 1-1, which is a comparative example to the present invention.

FIG. 3 is a diagram showing fluctuation patterns of NO ₃ —N concentration in nitrifying water, residual methanol in denitrification-treated water, and turbidity in Experiment 2-1 which is a comparative example to the present invention.

[Explanation of symbols]

 1 Denitrification tank 2 Nitrification tank 3 Nitrogen oxide-containing liquid inflow pipe 4 Reductant 5 Reductant injection facility 6 Denitrification treatment liquid outflow pipe 7 Turbidimeter 8 Operation control circuit

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location C02F 3/10 Z G01N 33/18 A 7055-2J // G01N 21/59 Z

Claims (2)

[Claims] 1. A method for reductive denitrification using a denitrifying bacterium in which a reducing agent is injected into a nitrogen oxide-containing liquid and nitrogen oxide in the liquid is adhered to or entrapped in a medium, and denitrifying outflows. A biological denitrification method characterized by detecting the SS concentration in a liquid by an absorptiometric method and controlling the injection amount of the reducing agent based on the detected value. 2. An absorptiometric method provided in a denitrification treatment solution outflow path of a denitrification tank for reducing and denitrifying nitrogen oxides in the solution by using denitrifying bacteria attached to or entrapped in a medium, which is equipped with a reducing agent injection facility. A biological denitrification device, comprising an SS measuring device connected to the reducing measuring agent injection device, and the SS measuring device is connected to the reducing agent injection equipment via an arithmetic and control circuit for controlling the reducing agent injection amount according to the detected value.