JP3346242B2 - Biological purification method for oil contaminated soil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for biologically remediating oil-contaminated soil.

[0002]

2. Description of the Related Art Conventionally, as a method for removing contaminants from soil contaminated with a hydrocarbon compound or the like, a physical treatment method (incineration, etc.), a chemical treatment method (washing with a surfactant or the like), a biological treatment method, or the like. Treatment methods (microbial degradation of contaminants) have been implemented. Above all, biological treatment methods have attracted much attention in recent years because of their advantages of low cost and low energy. In bioremediation of oil-contaminated soil, a method of adding nutrients (nitrogen and phosphorus compounds) to contaminated soil to increase the ability of indigenous microorganisms to decompose organic substances is often used for purification.

[0003] Japanese Patent Publication No. Hei 9-501841 discloses a method for recovering oil-contaminated soil by aerobic microorganisms so that C / N / P becomes about 100/20/1 based on the carbon content in the soil. A method for adding lipophilic N / P-type nutrients and the like is described. In this method, when the amount of carbon is large, the amount of added nitrogen / phosphorous increases proportionally, but since nitrogen / phosphorus itself causes groundwater pollution, it is used at a concentration as low as possible. It is necessary. However, no minimum requirements have been considered so far.

[0004] Japanese Patent Publication No. 7-507208 describes a method of adding a phosphate ester and an N source to contaminated soil. Japanese Patent Publication No. Hei 6-500495 describes that phosphate has a pH buffering ability in soil. Also,
JP-A-59-66882 describes the addition of N and P nutrients for culturing microorganisms. However, although inorganic salts added to activate indigenous decomposing bacteria have various compositions depending on the experimenter, it has not been studied which composition is most effective.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a method for purifying contaminated soil by adding inorganic nutrients to oil-contaminated soil to activate microorganisms in the soil. It is intended to provide the type and amount of the source.

[0006]

As a result of various studies to solve the above problems, the present inventors have set the soil pH to 6 to 8 and set the N / P ratio (nitrogen / phosphorus ratio) to 0.3. To 8.5, and the amount of nitrogen is 100 to 500 ppm based on the weight of the soil.
It has been found that by adding an inorganic nitrogen source and an inorganic phosphorus source so that the oil content of the soil is decomposed effectively, the present invention has been completed. Accordingly, the present invention is a method for biologically remediating oil-contaminated soil, wherein the N / P ratio is 0.3 to 8.5 when the pH of the soil is 6 to 8, and the amount of N relative to the weight of the soil is To a soil, wherein an inorganic nitrogen source and / or a phosphorus source are added to the soil so as to be 100 to 500 ppm.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be applied to various soils contaminated with oil, for example, sandy soil, fine-grained soil and the like. As a method of the experiment, for example, a stirring (tiling) culture method (Landfarm) in which soil to which an inorganic additive is added is cultivated is used.
static culture method (Pi) in which an inorganic additive is added and the mixture is allowed to stand as it is, and if necessary, a device for performing aeration or the like is added.
lng), a semi-liquid (slurry) culture method in which soil is suspended in water for culture (Slurry), and a liquid culture method in which soil is suspended in a large amount of water for culture (Liquid cul)
The method is selected in consideration of the properties of the soil, the amount of soil to be treated, the degree of contamination, and the like.

The N / P ratio (weight ratio as an element) is preferably from 0.3 to 8.5, more preferably from 1.5 to 1.9. For example, the N / P ratio is optimally about 1.7. If this ratio is too low (ie, the phosphorus content is relatively low), the ability to purify the oil will decrease, and if this ratio is too high (ie, the phosphorus content is relatively high), the potential for soil contamination by phosphorus will be high. There is. Next, the amount of nitrogen is preferably about 100 to 500 ppm, particularly about 250 ppm, based on the weight of the soil. Although no harm will occur even if the amount is more than this, the purification effect does not increase depending on the amount, which is not economically preferable.

The nitrogen source may be any one which can be assimilated by microorganisms in the soil, and is preferably ammonium nitrogen such as ammonium chloride or ammonium sulfate or nitrate nitrogen such as sodium nitrate or potassium nitrate. For example, ammonium chloride is preferred. The inorganic phosphate compound may be any compound that can be assimilated by microorganisms in the soil, and examples thereof include phosphate, superphosphate, metaphosphate, and polyphosphate. Having.

Specific examples include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium metaphosphate, potassium pyrophosphate, potassium tripolyphosphate, and the like. Of these, potassium dihydrogen phosphate and dihydrogen phosphate Potassium is preferred from an economic point of view. In the method of the present invention, the pH of the soil needs to be in the range of 6 to 8 in order to produce the effect of adding the inorganic nitrogen source or the phosphorus source, and when the soil is acidic, It is necessary to neutralize, and as the basic agent, for example, calcium carbon is preferable. The amount of calcium carbonate added depends on the acidity of the soil, but is, for example, about 1%. When the soil is basic, it can be neutralized by adding, for example, ferrous sulfate or calcium sulfate.

[0011]

As a result of examining the effect on soils having different oil contents, if the same amount of the nutrient mixture of the present invention is added,
High purification efficiency can be obtained regardless of the amount of carbon (3000 to 35000 ppm). According to conventional knowledge, 30000
Although 3000 to 6000 ppm of nitrogen is required for ppm of carbon, the present invention can purify with 500 to 100 ppm of nitrogen. Therefore, in the method of the present invention, the risk of secondary contamination due to the large addition of the nitrogen source is small.

[0012]

Next, the present invention will be described more specifically with reference to examples. Example 1 Soil contaminated with lubricating oil was removed with a 6 mm mesh sieve to remove gravels and the like, and then fractionated using a 2 mm mesh sieve, and the passing fraction was used as a test soil. In this experiment, a soil containing 5,000 ppm oil and a highly contaminated soil containing 50,000 ppm oil were used. The test system was a slurry system in which 5 g of soil and 5 ml of culture solution were added to a 100 ml Teflon bottle at 2 rpm.
And vortexed. The culture was performed in a constant temperature room controlled at 20 ° C. As the composition of the culture solution, Z shown in Table 1 below was used.
S, NP-S and YM-A, and water as a control.

[0013]

[Table 1]

Oil content analysis Oil content in soil is analyzed by crushing sufficiently dried soil
-Extraction was carried out with hexane, and the method was performed by measuring the weight of the evaporation residue of the extract. The error b in the figure
ar represents the standard error (n is 3 for each). The results are shown in FIG. Water purification did not proceed at all in both low and high concentration soils. However, ZS showed the highest purification rates for both low and high concentration contaminated soils. In NPS medium,
It showed a purification effect on low concentration soil for up to 2 weeks,
After 4 weeks, the purification activity was slight, and hardly any purification activity was observed in highly contaminated soil. The modified YM medium also showed the same purification rate as NPS. In FIG. 1, those with a “High” symbol are oil components 5000
The results for the highly contaminated soil at 0 ppm are shown.

Example 2 Effect of Inorganic Salt and Inorganic Fertilizer A stainless steel round pot (10 cm in diameter × 6 cm in height, with a lid) was used as an incubator, and was contaminated with lubricating oil.
Approximately 11 test soils excluding gravel etc. through a 5mm mesh sieve
0 g (wet soil weight) was added. This incubator is placed in an incubator (IC600 manufactured by Yamato, Lo-Temp Champ).
ber IH16) and cultured by standing still. The moisture content of the test soil was adjusted to 20%. The adjustment was performed by adjusting the water content, measuring the weight about twice a week, and replenishing the same amount of distilled water as the weight reduced by drying. Once a week
Each time, the soil was agitated by being evenly mixed by scooping up from the bottom of the cup. The addition of the additive was performed by adding the additive to the container and then stirring the mixture with the soil by stirring with spatelve.

Samples were taken at the start of culturing, two weeks, four weeks, and eight weeks. Approximately 6 g of wet soil (dry soil weight of about 5% (4.5 to
5.53). The initial oil content of the experimental soil was about 5000 ppm. Only the salt contained in the following medium was added to the test soil. By changing the amount of salt added, the weight ratio of nitrogen to soil is 50,100,25.
It was set to 0 or 500 ppm.

(1) ZS medium (see Table 1 above) (2) ZS (N, P); K ₂ HPO ₄ , KH in the above ZS medium
₂ PO ₄ and NH ₄ shall only consist _{Cl (3) ZS (NO 3} -N); Figure 2 shows the results obtained by changing the KNO ₃ equimolar amount of NH ₄ Cl in the ZS medium. As shown in FIG. 2, the amount of nitrogen is preferably about 250 ppm based on the soil, and the medium is Z
S (N, P) medium was the best.

Example 3 A method using a ZS (N, P) medium
Sampling of the rum experimental soil and the soil contaminated with the adjusted lubricating oil were sieved with a 6 mm mesh to remove pebbles and the like. The sieved soil and the unsieved soil obtained by removing large gravel without sieving were subjected to the experiment. The moisture content of the test soil was adjusted to 20%. The water content was adjusted once or twice a week by the gravimetric method of confirming the weight at the time of adjusting the water content and supplying water of reduced water content. After completion of the cultivation, 5 cm each of the upper, middle and lower layers of the soil column was collected and the oil content was measured.

On the test soil, as in Example 2, 250
ZS (N, P) containing a ppm equivalent of nitrogen source was added and a 5 cm diameter column was lightly packed with 800 g of soil. At this time,
The soil depth was 35 cm. Culture at 30 ° C without stirring for 4 hours.
Went for a week. The initial oil concentration in the experimental soil was about 4000
5,000 ppm. Results The purification effect in the column experiment is shown in FIG. Oil is removed up to 60% at the top of the column, and the bottom (deep)
In this case, the oil was removed up to 70%.

Example 4 A soil prepared in the same manner as in Example 1 was tested. The soil is
Clay, moisture content about 10-15%, initial oil concentration about 5
000 ppm. 5 g of soil in a 300 ml Erlenmeyer flask with screw cap made of glass
light) and 50 ml of NPS medium at 20.degree.
The culture was reciprocated for 2 weeks at a rate of 2 min / min. However, sludge adhered to the vessel wall during the culturing, so that the sludge was dropped manually by stirring once a day.

In the first experiment, the nitrogen component of the NPS medium was adjusted to 1
Samples that were made 0 times (X10N) and those without the nitrogen component (-N) were tested. As a result, even when the amount of the nitrogen component was increased by 10 times, only the same effect as that of the NPS medium was observed, but when the amount was removed, it was significantly inhibited. Therefore, it was considered that the nitrogen component was essential for purification, and the amount contained in the NPS medium was almost the optimal value.

Next, in the second experiment, the sample containing only the nitrogen component (N) and the sample containing the nitrogen component in the NPS medium converted to the number of moles of N (NH ₄ ) were all replaced with only ammonia (ammonium sulfate). ) And (NO ₃ ), all of which were replaced with nitrate (potassium nitrate) (FIG. 4). As a result, no effect was observed only with the nitrogen component, and a cooperative contribution of the NPS medium other than the nitrogen component was confirmed. When compared with the result of Example 2, it is understood that a phosphorus component is necessary in addition to the nitrogen component. Neither nitrate nor ammonia showed an effect exceeding that of the NPS medium, but ammonia was slightly more effective than nitrate.

Example 5 In a test soil prepared in the same manner as in Example 2, ammonium chloride was used as a nitrogen source at 250 ppm in terms of nitrogen, and potassium dihydrogen phosphate + dipotassium hydrogen phosphate (ZS) was used as a phosphorus source.
(N, P)) or potassium metaphosphate, potassium pyrophosphate, or potassium tripolyphosphate was added so as to be 150 ppm in terms of phosphorus. This soil was cultured in a 30 ° C. incubator for 8 weeks. During the culture, the water content was adjusted to 10% once a week, and stirring was performed. The initial oil concentration in the soil was about 7500 ppm. Two weeks later, when the oil content in the soil was measured, it was found to be about 50% purified using any phosphorus supply condition. FIG. 5 shows the results.

Example 6 Application to highly contaminated soil A lubricating oil was added to a test soil prepared in the same manner as in Example 3,
This was agitated so as to be uniform in the soil. Thus, the oil concentration was 10,000 ppm, 20,000 ppm and 35,000.
ppm soil was prepared. 250pp ZS (N, P) on soil
m (K ₂ HPO ₄ : KH ₂ PO ₄ : NH ₄ Cl = 18: 12: 40 and 250 ppm of N is added to the soil weight) in the same manner as in Example 2 and an incubator at 30 ° C. The cultivation was carried out at a rate of 2 times / week, and the stirring was performed once / week.

From each test plot, three samples of soil were collected and dried, and the amount of residual oil in the soil was determined by extraction with n-hexane. The results are shown in FIGS. ZS (N,
In the case where P) was added, as can be seen from each figure, even if the contamination concentration was increased to 3.5%, the purification rate did not decrease. In addition, purification did not reach a plateau due to the high concentration of contamination. The fact that the purification rate did not decrease to the contaminant concentration of 3.5% indicated that the same amount of nutrient as in the case of the contaminant concentration of 0.5% was sufficient.

Example 7 A purification experiment was carried out in the same manner as in Example 2 using seven types of soils having various physical properties contaminated with lubricating oil. The properties of the tested soil are shown in Table 2 below.

[0027]

[Table 2]

FIGS. 8 and 9 show the time-dependent changes in the residual oil ratio when ZS is added to the above-mentioned seven different soils in addition to the conventionally used soil. At this time, the initial oil concentration other than G was about 3500 to 4000 ppm, and the concentration of G was about 10000 ppm. In A and B, the experiment was stopped by the fourth week because there was no effect of adding ZS. C, F
In the above, the addition of ZS shows very good results,
At eight weeks, the residual oil rate had dropped to 20%. G soil could be purified to 5000 ppm or less by the fourth week after ZS addition.

Further, in order to investigate the effect of pH on the purification rate of oil-contaminated soil, ZS was added to A and B,
Further, the difference in the purification rate between the case where CaCO ₃ was added in an amount of 1% and the case where CaCO ₃ was not added in order to adjust the pH was examined. The pH at this time is shown in Table 3, and the change over time in the purification rate is shown in FIG. It was found that the addition of CaCO ₃ promotes purification of both A and B. On the other hand, it was reproduced that purification did not proceed at all when CaCO ₃ was not added.

[0030]

[Table 3]

Example 8 Inorganic fertilizer ZS (N, P) was added to soil contaminated with heavy oil C at a concentration of 250 ppm in terms of nitrogen, and cultured in an incubator at 30 ° C. for 8 weeks. During the culture, the water content was adjusted to 10% once a week, and stirring was performed. The initial oil concentration was 15000 ppm. Two weeks later, when the oil content in the soil was measured, the oil content in the soil was reduced by about 40%. Even if the target substance is C heavy oil, ZS (N,
It was confirmed that the addition of P) promoted purification. The results are shown in FIG.

[Brief description of the drawings]

FIG. 1 is a graph showing the time course of the degradation of oil in oil contaminated soil in various media.

FIG. 2 is a graph showing the time course of the degradation of oil in oil contaminated soil in various inorganic salt media.

FIG. 3 shows the residual ratio of oil when oil-contaminated soil was packed in a column and inorganic nitrogen and phosphorus were added.
It is a graph divided into middle and bottom.

FIG. 4 is a graph showing that addition of inorganic nitrogen is required for purification of oil-contaminated soil, and that ammonia-based nitrogen is preferred over nitrate-based nitrogen.

FIG. 5 is a graph showing that various inorganic phosphates exert equivalent effects for remediation of oil-contaminated soil.

FIG. 6 shows that the concentration of contaminated oil in soil is 5000 ppm.
5 is a graph showing the change over time in the residual oil ratio and residual oil concentration at 10000 ppm and 10000 ppm.

FIG. 7 shows that the concentration of contaminated oil in soil is 20,000 pp.
5 is a graph showing the change over time in the residual oil ratio and residual oil concentration when m and 35000 ppm.

FIG. 8 is a graph showing the change over time in the concentration of contaminated oil in various soils.

FIG. 9 is a graph showing the change over time in the concentration of contaminated oil in various soils.

FIG. 10 is a graph showing the effect of pH adjustment on purification of oil-contaminated soil.

FIG. 11 is a graph showing the effect of adding a nitrogen source and a phosphorus source on purification of soil contaminated with heavy fuel oil C.

Continuation of the front page (72) Inventor Koichi Numata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-10-202240 (JP, A) JP 4-9916 (JP, B2) Special Table Hei 9-501841 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B09C 1/10

Claims (3)

(57) [Claims] 1. A method for biologically purifying oil-contaminated soil, comprising:
When the soil pH is 6 to 8, the N / P ratio is 1.5 to 1.9 ,
A method comprising adding an inorganic N source and / or a P source to soil such that the amount of N relative to the weight of the soil is 100 to 500 ppm. A wherein inorganic ammonia nitrogen compounds to provide N or nitrate nitrogen compound, The method of claim 1. 3. The inorganic substance providing P is a phosphate, a superphosphate, a metaphosphate or a polyphosphate.
Or the method of 2 .