JP2017056373A - Purification method by microorganism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a purification method by microorganisms which purifies by microorganisms an underground area contaminated with cyanogen compounds, shortens a purification period, and reduces construction cost.SOLUTION: In a purification method by microorganisms, a step is performed of adding nutrients to a contaminated underground area contaminated with cyanogen compounds and controlling the oxidation-reduction potential (ORP) of contaminated underground water to -250 mV or more and 100 mV or less, and propagating inhabitant cyanogen compound-decomposing microorganisms in situ to purify the contaminated underground area.SELECTED DRAWING: None

Description

  The present invention relates to a method for purifying an underground region such as groundwater or ground contaminated with a toxic substance of cyanide using microorganisms that live in situ.

  Cyanide compounds have high reactivity and are used in large quantities in chemical manufacturing plants such as pharmaceuticals, agricultural chemicals, plastic manufacturing, electroplating, metal processing plants or gas manufacturing plants, or are generated as by-products. Inevitable leakage from these factories into the ground. The law stipulates that cyanide is not detected in groundwater because it is highly toxic. That is, it is desirable that the cyanide discharged into the environment is quickly decomposed and removed by microorganisms or the like.

  Since cyanide is highly water-soluble, once it is released into the groundwater, the contamination spreads over a wide area in a short time due to its flow. In such a case, in-situ countermeasures are appropriate from the viewpoint of cost and environment. That is, a method using a bioremediation technique is effective as a method for purifying cyanide compounds.

  On the other hand, JP-A-2005-21759 measures ORP (oxidation reduction potential / silver / silver chloride electrode standard) in water contained in contaminated soil after adding fresh water containing nitrate ions to the contaminated soil, A method for purifying contaminated soil that controls the amount of fresh water added so as to maintain the measured ORP at -100 mV or higher and +300 mV or lower is disclosed.

JP-A-2005-21759

  However, the method for purifying contaminated soil disclosed in JP-A-2005-21759 is purification of contaminated soil containing oil, aromatic hydrocarbons, and halogen-containing hydrocarbons, and is not intended for cyanide compounds.

  Accordingly, it is an object of the present invention to provide an improved biostimulation technique for purifying underground areas contaminated with cyanide with microorganisms.

  Under such circumstances, the present inventors have conducted intensive studies, and as a result, found that cyanide-decomposing microorganisms are likely to grow under conditions where the oxidation-reduction potential (ORP) is −250 mV or more and 100 mV or less. It came to be completed.

  That is, the present invention solves the above-mentioned problems, and a nutrient source is input to a contaminated underground area contaminated with cyanide, and the oxidation-reduction potential (ORP) of the contaminated groundwater is set to −250 mV or more and 100 mV or less. The present invention provides a microorganism purification method characterized by performing a step of purifying a contaminated underground region by growing indigenous cyanide-degrading microorganisms in situ.

  Moreover, this invention provides the purification method by the said microorganisms characterized by making dissolved oxygen concentration (DO) of this contaminated groundwater into 0-1.0 mg / l.

  Moreover, this invention provides the purification method by the said microorganisms characterized by supplying oxygen water to this contaminated underground area | region.

  In addition, the present invention provides the purification method using microorganisms, wherein the ORP is −200 mV or more and 100 mV or less.

  The present invention also provides a method for pumping ground water from a pumping well installed in a contaminated area, performing an on-ground culturing of microorganisms with an ORP of −250 mV or more and 100 mV or less, and subjecting the grown culture to the contaminated area. The present invention provides a method for purifying with microorganisms, which is characterized by being injected into the groundwater.

  The present invention also provides the purification method using microorganisms, wherein the culture solution is injected into an injection well installed in a contaminated area.

  In addition, the present invention provides the purification method using microorganisms, wherein the culture solution is added and injected while stirring the ground using a ground stirring and mixing device.

  According to the present invention, decomposition of cyanide in groundwater proceeds. For this reason, a purification period is shortened and construction cost can be reduced.

  In the present invention, examples of the cyan compound include inorganic cyan compounds and organic cyan compounds. These cyan compounds include nitrile compounds, metal cyano complexes and the like. Examples of nitrile compounds include acetonitrile, dinitriles and trinitriles. Examples of metal cyano complexes include iron cyano complexes, copper cyano complexes, silver cyano complexes, and nickel cyano complexes. These exemplified cyan compounds include one kind or two or more kinds.

  In the present invention, the contaminated underground area includes contaminated ground water and contaminated underground ground. The underground ground is a sand ground, a silt ground, a clay ground, or a silt ground or clay ground containing sand. Examples of the silt ground or clay ground containing sand include an alternating layer ground of a sand layer and a silt / clay layer. Examples of the alternate layer ground include a ground including a two-layer structure of a sand layer and a silt / clay layer, and particularly a ground including a three-layer structure of a sand layer, a silt / clay layer and a sand layer.

  In the microorganism purification method of the present invention, first, a nutrient source is introduced into a contaminated underground region, and the oxidation-reduction potential (ORP) (silver / silver chloride standard) of the contaminated groundwater is within a specific range, and inhabiting cyanide compounds A process (I process) for purifying the contaminated underground area by growing the decomposed microorganisms in situ is performed. The nutrient source may be a known one, and examples thereof include nutrient salts such as oxygen, air, nitrogen source and phosphorus source, and sugars such as glucose, fructose and sucrose. By adding these, harmful substance-decomposing microorganisms present in the contaminated underground region (contaminated site) can be propagated and activated. The addition of the nutrient source may be performed a plurality of times at appropriate intervals. In step I, a pH adjuster may be added in addition to the nutrient source.

  In step I, groundwater is collected from pumping wells (observation wells) distributed in the contaminated area, the redox potential of the groundwater collected for each pumping well is measured, and the purification level is measured if necessary. The pumping wells are preferably installed evenly distributed in the contaminated area near the injection well or slightly downstream thereof. The oxidation-reduction potential of groundwater can be measured with a known oxidation-reduction potentiometer. In addition, the purification level can be measured by a known method, and a method of judging from the concentration of microorganisms or the concentration of harmful substances in groundwater is preferable.

  In step I, the redox potential of groundwater is −250 mV or more and 100 mV or less, preferably −200 mV or more and 100 mV or less, and particularly −200 mV or more and 80 mV or less. If the oxidation-reduction potential of the contaminated groundwater is within this range, the growth of cyanide-decomposing microorganisms proceeds. Such a redox potential can be controlled by introducing oxygen water into groundwater. Generally, the oxidation-reduction potential of groundwater is -400 mV to -300 mV, and the oxidation-reduction potential can be increased by adding oxygen water thereto. In the present invention, in order to set the oxidation-reduction potential of the contaminated groundwater to −250 mV or more and 100 mV or less, oxygen water is injected into the target region of the contaminated groundwater, and the oxidation-reduction potential is measured in the observation well. The injection of oxygen water should be stopped when the value reaches the value of. The oxygen water injection rate is preferably in the range of 0.5 to 3.0 liters / minute. Moreover, in order to continue the oxidation-reduction potential of groundwater to be -250 mV or more and 100 mV or less, reinjection of oxygen water may be started, for example, every week or every month.

  As the oxygen water, known oxygen water may be used. That is, the water placed in the air contains about 9.3 milligrams of oxygen per liter at 20 ° C in an equilibrium state, but oxygen water contains 2 to 4 times as much oxygen. is there. In Step I, the dissolved oxygen concentration (DO) of the contaminated groundwater is preferably 0 to 1.0 mg / l. If the contaminated groundwater DO is within the above range, the growth of cyanide-decomposing microorganisms proceeds.

  In the process I of the present invention, as a method of feeding nutrient sources and oxygen water into the contaminated underground area, the method of feeding nutrient sources and oxygen water from the injection wells dispersed and installed in the contaminated area and the contaminated area A method in which a nutrient source and oxygen water is added while stirring the ground using a ground stirring and mixing device can be mentioned.

For example, the injection wells distributed in the contaminated area are preferably divided into blocks with respect to the contaminated area and installed equally for each block. That is, the injection well is preferably divided into several blocks so that the area in plan view is substantially the same with respect to the entire contaminated region, and the injection wells are preferably installed uniformly in the block. In addition, the installation pitch of the injection wells in one block is 8 to 12 m, preferably about 10 m. One block is a triangular or polygonal or circular which is formed by connecting the injection wells, and an area in plan view, is generally 50 to 300 m ^2, particularly of about 70~150m ^2. That is, at least the injection well is installed at the corner of each polygon or the center of the circle forming the block, or the ground is stirred and mixed.

  In the method of using the ground agitation and mixing device for the contaminated area and adding the nutrient source and oxygen water while stirring the ground, as the ground agitation and mixing device, a known device in the ground improvement field can be used, For example, a hollow rotary shaft that is rotated by a rotary shaft driving means, one or more stirring blades provided radially below the rotary shaft, and a ground supply means disposed at a hollow portion of the rotary shaft. And a nutrient source supply pipe connected at the other end to a discharge port near the stirring blade. In addition, the ground stirring and mixing device is installed and used at the same position as the injection well. In addition, when using a ground stirring mixing apparatus, it is not necessary to install an injection well. The ground agitation and mixing device is effective in the alternate ground of sand layer and silt / clay layer including clay layer in contaminated ground. That is, in the alternating layer ground, harmful substances are likely to be accumulated in the clay layer, but by mixing the parts containing the harmful substances in the depth direction, the aquifer can be formed to promote purification. The step I is performed for a predetermined period in which harmful substances in the contaminated underground area are decomposed and purified by microorganisms.

  In addition, in step I, oxygen water is added, and even if the oxidation-reduction potential is within the above range, the underground environment changes with time, so it is preferable to periodically add oxygen water. And, when the redox potential of groundwater collected for each pumping well is -250 mV or less, a method such as increasing the number of times oxygen water is added is taken, and when it exceeds 100 mV, the oxygen water is stopped for a while. Should be taken. For example, if the oxygen water is supplied for a purification period of several months, the oxygen water may be supplied for a specific period of about 4 days to 1 week during the purification period. Times. That is, it is preferable that the redox potential of groundwater is in the above range over a long purification period, but there may be a period in which the redox potential of groundwater is outside the above range.

  In the present invention, during the process I, groundwater is pumped from a pumping well installed in a contaminated area, and the ORP of the groundwater is -250 mV or more and 100 mV or less, preferably -200 mV or more and 100 mV or less, particularly preferably -200 mV on the ground. As described above, it is preferable to carry out a step of incubating and culturing microorganisms at 80 mV or less and injecting the culture solution thus grown into groundwater in the contaminated area. By performing this growth culture process, the growth of cyanide-degrading microorganisms further proceeds. Moreover, it is good to make DO into 0-1.0 mg / l also in the growth culture process similarly to the I process.

  Examples of the method for growing and culturing microorganisms in the groundwater pumped up include a method performed in a culture plant equipped with a reaction tank. FIG. 1 shows an example of a method for growing and culturing microorganisms in the groundwater pumped up in a culture plant 20. The culture plant 10 includes a reaction tank 12, one end connected to a pumping pump 13, and the other end connected to the reaction tank 12, a groundwater supply pipe 16, a nutrient source storage tank 11, and a nutrient source supply that supplies the nutrient source to the reaction tank 12. Pipe 17, oxygen water storage tank 21, oxygen water supply pipe 23 for supplying oxygen water to reaction tank 12, discharge pipe 18 for supplying ground water containing microorganisms grown and cultured to injection well 1, nutrient supply pump 14, oxygen It is composed of a water supply pump 22 and a discharge pump 15. In addition, when using a ground agitation mixing apparatus instead of an injection well for the growth culture solution, the discharge pipe 18 is connected to a nutrient source supply pipe of the ground agitation mixing apparatus described in the step I.

  Groundwater in the contaminated area is supplied from the pumping well 2 to the reaction tank 12 through the pump 13 and the groundwater supply pipe 16. On the other hand, the nutrient source stored in the nutrient source storage tank 11 is supplied to the reaction tank 12 from the nutrient source supply pump 14 and the nutrient source supply pipe 17. The oxygen water stored in the oxygen water storage tank 21 is supplied to the reaction tank 12 from the oxygen water supply pump 22 and the oxygen water supply pipe 17. In the reaction vessel 12, the oxidation-reduction potential and DO are within the above ranges, and a pH adjuster is added to adjust the pH to 9.0. And culturing for a predetermined period. The determination of the ORP value and the growth culture of the microorganism is determined or determined by sampling from the reaction tank 12 at an appropriate time.

  In the growth culture step, after the microorganisms are grown to a predetermined concentration, a step of injecting groundwater containing the grown microorganisms into the contaminated underground region is performed. The decomposing microorganisms in the growth culture are a group of microorganisms suitable for decomposing cyanide compounds, and are effective for the purification of cyanide compounds. Examples of a method for injecting groundwater containing microorganisms grown and cultured into a contaminated underground region include a method of injecting from an injection well and a method of adding and introducing the ground while stirring the ground using a ground stirring and mixing device.

  In the process I or the combined process of the process I and the growth culture process, the contaminated underground region is subjected to decomposition and purification of cyanide compounds by the microorganisms grown and cultured. In addition, the culture solution containing the microorganisms grown and cultured during the step I may be added in a plurality of times at an appropriate time. In the decomposition and purification after the growth and culture step, the microorganisms that have been grown and cultured are microorganisms that have the ability to decompose harmful substances that live in situ, and can be expected to decompose and purify cyanide compounds.

  EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention.

Example 1
As shown in FIG. 2, three injection wells (IW-1 to IW-3) are provided in the underground region X in which groundwater is contaminated with cyanide having a cyan concentration of 4 to 6 mg / l. A pumping well was provided 22m downstream (OW-1 to OW-4). Purification of the contaminated area X surrounded by the sheet pile 20 started from August 18 and ended on October 15. During this period, as shown in Table 1, oxygen water was injected into wells (IW-1 to IW- for 4 days every day from August 18 to 4 days from October 9 to October 15). Injected from 3). The injection amount of oxygen water was 700 liters per well, and was continuously injected for about 8 hours per day. Nutrient sources were added at appropriate times during the purification period. The amount of oxygen water added was previously determined in a laboratory test. Moreover, the oxidation-reduction potential (mV) of the groundwater pumped from the pumping wells (OW-1 to OW-4) and the cyanide concentration (mg / l) in the groundwater were measured by a conventional method. The results are shown in Tables 1 and 2, respectively. The cyan concentration in the groundwater was measured on the date shown in Table 2. Moreover, although dissolved oxygen (DO) was measured on the said month, DO in the groundwater pumped up from OW-1 to OW-4 was the range of 0-1.0 mg / l. Note that the symbol “-” is “not measured”.

(Comparative Example 1)
In FIG. 2, except that a barrier well is provided at a position indicated by reference signs PW1 to PW3 and oxygen water is not supplied from the barrier well, the same method as in Example 1 is used, Cyanide concentration (mg / l) in groundwater was measured. That is, the comparative example 1 measured the ORP etc. of the groundwater pumped up from the barrier well which is not the object of purification. The results are shown in Tables 1 and 2.

  From the results of Table 1 and Table 2, in the well where the redox potential of the pumped-up groundwater is −250 mV or more and 100 mV or less and the DO is 0 to 1.0 mg / l, the groundwater cyanide concentration is 4 to 6 mg / l. Decreased to 0.8-1.8 mg / l. This is the progress of the growth of cyanide-decomposing microorganisms under the above ORP conditions. On the other hand, in the well where the redox potential of the pumped-up groundwater was −325 mV or less, no decrease in the cyanide concentration of the groundwater was observed.

(Reference example)
<In-house test (accumulation culture)>
Cyanogen-degrading microorganisms are obtained under the conditions A, B, and C shown below by pumping groundwater from four pumping wells installed in a contaminated area contaminated with cyanide and mixing the groundwater as test water. The activity of was evaluated. Evaluation was made on the 7th, 14th, 21st and 28th days, and the cyan density and ORP were measured, respectively. The results are shown in Table 3. The properties of groundwater are shown in Table 4. The groundwater pumped up from the four pumping wells was being purified in situ, and the cyanide concentration of the mixed groundwater was 1.0 mg / l. And in the 28-day test results of this laboratory test, the A condition where the ORP is −250 mV or more and 100 mV or less is a cyanolytic microorganism compared to the B condition where the ORP exceeds 100 mV or the C condition where the ORP is less than −250 mV. Activity was high and the cyan density could be reduced by 40%.

(Condition A)
The Erlenmeyer flask was sealed by adding 300 ml of pumped ground water, 0.5% of a nutrient, and 0.7% of a pH adjuster. Next, the Erlenmeyer flask was shaken at 100 rpm to stir the mixed solution. The surface of the mixed solution was slightly shaken. In addition, the nutrient was added in the same amount every week and cured at 25 ° C. The weekly ORP of this mixture was −250 mV or more and 100 mV or less.

(Condition B)
The Erlenmeyer flask was sealed by adding 150 ml of pumped ground water, 0.5% of a nutrient, and 0.7% of a pH adjuster. Next, the Erlenmeyer flask was shaken at 100 rpm to stir the mixed solution. The surface of the mixed solution was greatly shaken. In addition, the nutrient was added in the same amount every week and cured at 25 ° C. The weekly ORP of this mixture exceeded 100 mV.

(C condition)
In an Erlenmeyer flask, 500 ml of pumped ground water, 0.5% of a nutrient, and 0.7% of a pH adjuster were added and sealed, and left standing. In addition, the nutrient was added in the same amount every week and cured at 25 ° C. The weekly ORP of this mixture was -400 mV to -300 mV.

  According to the present invention, the growth of microorganisms capable of decomposing cyanide in situ proceeds, and the cyanide in groundwater is decomposed by microorganisms. For this reason, the purification period of the whole contaminated area is shortened, and construction costs can be reduced.

It is a figure which shows the proliferation culture plant in the purification method of this invention. It is a figure which shows the contamination area | region where the Example and the comparative example were performed in the purification method of this invention.

DESCRIPTION OF SYMBOLS 1 Injection well 2 Pumping well 10 Culture plant 11 Nutrient source storage tank 12 Reaction tank 18 Discharge piping 20 Sheet pile 21 Oxygen water storage tank OW-1-4 Pumping well IW-1-3 Injection well PW-1-3 Barrier well X Contamination region

Claims (7)

  Nutrient sources are introduced into the contaminated underground area contaminated with cyanide, and the oxidation-reduction potential (ORP) of the contaminated groundwater is set to -250 mV to 100 mV, and the indigenous cyanide-degrading microorganisms are propagated in situ and contaminated. A purification method using microorganisms, comprising performing a step of purifying an underground region.   The method for purifying microorganisms according to claim 1, wherein the dissolved oxygen concentration (DO) of the contaminated groundwater is 0 to 1.0 mg / l.   The method for purifying with microorganisms according to claim 1 or 2, wherein oxygen water is poured into the contaminated underground region.   The ORP is -200 mV or more and 100 mV or less, and the purification method using microorganisms according to any one of claims 1 to 3.   Pumping groundwater from a pumping well installed in the contaminated area, and growing the microorganism on the ground with the ORP of the groundwater set to -250 mV or more and 100 mV or less, and injecting the grown and cultured medium into the groundwater in the contaminated area The purification method by microorganisms of any one of Claims 1-4 characterized by these.   6. The method according to claim 5, wherein the culture solution is injected into an injection well installed in a contaminated area. The method for purifying with microorganisms according to claim 5, wherein the culture solution is added and injected while stirring the ground using a ground stirring and mixing device.

Images