The field test site is Xing 2 Oilfield of Yanchang Oil Production Company in Mengxinzhuang, Jianhua Temple Township, Ansai County, Yan 'an City, Shaanxi Province. The well site is free of water and electricity, with idle workshops, belonging to Xingzichuan oil production area of Yanchang Petroleum Company, 30km away from Ansai County (Figure 6-9).
Figure 6-9 Location map of Xingzichuan Xinger Oilfield in Ansai ☆ The location of Xinger Well.
During the test, water is necessary. On the one hand, water should be continuously added to the test soil layer to achieve the minimum water content required for the test. On the other hand, when testing samples, it is necessary to dilute samples with water and scrub utensils. At the same time, the number of soil samples to be tested in the test is huge. If it is brought back to the indoor test, it is not only time-consuming and laborious, but also needs to be transported, which increases the error probability of the test. This test has been carried out for 52 days, and the test site needs long-term strict management.
Well Xing 2 can meet the above conditions, and the test process is easy to manage, saving time and effort. In addition, the oil production wells in this well site are being exploited, which is convenient for the collection of test crude oil.
Second, the experimental design
1. Optimization of preparation of flora preparation
Firstly, the indoor cultured flora is expanded step by step, the inoculation amount is 10%, and the oil-degrading bacteria are enriched in a combined culture medium:
K2HPO4( 1.0g), KH2PO4( 1.0g), mgso 4·7H2O(0.5g), NH4NO3( 1.0g), soluble starch (10.0g), FeCl3(0.02g 12 1℃ for 30 minutes.
A sufficient amount of bacterial liquid preparation to be amplified is cultured in proportion, and each amplification culture takes 5-8 days. Finally, before going out to the field, store the cultivated bacterial liquid preparation in a large plastic bucket of 25L, and prepare three buckets according to the need and possible quantity, accounting for 75L. Before leaving the field, examine the bacterial liquid in the vat with a microscope to see if the growth and quantity of the flora are rich.
2. Experimental equipment
Chemical reagents: MgSO4 7H2O, NH4NO3, CaCl2, FeCl3, KH2PO4, K2HPO4, KCl, hydrochloric acid, potassium sodium tartrate, petroleum ether and chloroform are all analytically pure.
Experimental oil is crude oil produced at 2400 meters below the test site.
Glassware for experiment, etc. : 150mL, 250mL triangular bottle with stopper, 125mL, 1000mL reagent bottle with narrow mouth, 50mL, 25mL colorimetric tube, one set each, rubber stopper, 25L plastic bucket, etc.
Main instruments: QZD- 1 electromagnetic oscillator, KQ2 18 ultrasonic cleaning machine, biological constant temperature incubator, high-speed centrifuge, high-pressure steam sterilizer, aseptic laboratory, biochemical incubator, shaking table incubator, Leica biomicroscope, 752N ultraviolet-visible grating spectrophotometer, pHB-3 meter-3, DDB-.
3. Detection method
The contents of petroleum hydrocarbon and NO-3 were determined by ultrasonic-ultraviolet spectrophotometry provided by Germany, the content of NH+4 was determined by Nessler's reagent colorimetry, the pH value was directly determined by pHB-3 pH meter, and the TDS was calculated by the conductivity measured by DDB-303A conductivity meter.
4. Layout of experimental field and testing of basic physical parameters.
Before the test, the test area was leveled and the surface humus layer was removed, and then it was divided into eight test areas: test area 1, test area 2, test area 3, test area 4, test area 5, test area 6, control area and blank area. The size of each plot is 120cm× 120cm, and each plot is 20cm apart. The experimental design depth is 0 ~ 15cm, and finally reaches 50cm. The plots are arranged from west to east, as shown in Figure 6- 10 of the experimental area.
Take the basic data of each experimental area: first, remove the artificial fill on the surface of the experimental area to expose the in-situ soil. The lithology of the original soil is loess, containing a small amount of gravel or ginger stone of 2 ~ 10 mm, and the wet bulk density of the soil is1.821g/cm3; The natural water content is 9.18%; The pH value is 8.4; The nitrate content is 55.3 mg/kg; The content of ammonium is 8.85 mg/kg; The content of soil background oil is 1.3 ~ 4.6 mg/kg.
Calculation of soil layer weight in the test area:120cm×15cm×1.82g/cm3 = 393120g = 393.12kg.
5. Test steps
Due to the failure to find a suitable oil pollution site in the experimental stage, the experimental method of artificially adding pollution sources was chosen as the experimental study. Usage of crude oil: After dewatering the crude oil produced by local well Xing-2, weigh 800g, dilute it with 500ml analytical pure petroleum ether, and spray it evenly to the test area, and add basically the same amount of oil to each test area. However, the oil content in each region is not necessarily the same, but it is similar, subject to the test data in each region.
The test soil layer of crude oil in each test area is sprayed evenly, and the added oil is evenly mixed into the test layer after repeated turning. Then add the experimental additive materials prepared in each experimental area one by one. 1 The additive in the experimental area is crushed fresh thatch. Experimental area 2 is chicken manure and chicken manure (50% each). Test area 3 consists of chaff and chaff. Test area 4 is wheat bran. In addition to adding crude oil, the No.5 experimental area was inoculated with bacterial liquid preparation and nutrient solution. Experimental area 6 is the same as experimental area 5, except that it is covered with agricultural plastic film for heat preservation, moisture preservation and rain protection like 1 ~ 4. Only crude oil is added in the control area, and nothing else is added. There is no material in the blank area, only blank monitoring. After the additive is added to the test area, the test soil layer is continuously turned to make the soil layer mix evenly.
Fig. 6- 10 Schematic diagram of experimental area of Xingzi Sichuan Xinger Oilfield in Ansai, Shaanxi Province
Inoculate the cultured bacterial liquid preparation according to the inoculation amount of 3% of the test soil layer weight in each test area, and mix well. A nutrient solution is prepared, and the main components of the nutrient solution are MgSO4 7H2O, NH4NO3, CaCl2, FeCl3, KH2PO4 and K2HPO4. The proportion of preparation is based on the proportion of culture medium components.
Add 30L of the prepared nutrient solution to the prepared test area. The test water is local shallow groundwater, with pH value of 8.2 and TDS content of 420.5 mg/L. Add about 5L of groundwater to keep the water content of soil layer in the test area above 20% (water content calculation: bacterial liquid is about 3% 12kg, nutrient solution is 30L, groundwater is 5L, original soil water content is 9. 18%, water content is 9. The purpose of covering the experimental area with plastic film is to keep warm, moisturize and prevent rain. Sampling at regular intervals, the sampling method is to take five soil samples with the same depth at different points in each district according to plum blossom shape, and after fully mixing, sample and detect them by four-point method. After sampling, the test layer in the test area was ploughed to make it ventilated and oxygenated, and a certain amount of water was added to ensure that the water content of the test soil was about 20%. The control area was added with the same amount of oil as the experimental area, and the others were not added, which was regarded as natural degradation. No substance is added to the blank area as a monitoring sample. At the same time, samples from all districts were tested, and the tested components were oil content, pH value, soil soluble salt, water content, NH+4, NO-3 and so on. At the same time, monitor the temperature of the surface and test the soil. After the end of the test period, the lower part of the test layer in each district was sampled by layers.
Third, the test process and results of the test area
(1) 1
On the basis of the preparation of the above test area, according to the proportion of soil weight 1.4% in the test area, chopped fresh thatch with the length of 1 ~ 3 cm is added as an additive. Then, the soil in the experimental area was plowed evenly, and the nutrient elements such as nitrogen, phosphorus, calcium, magnesium, sulfur and iron were adjusted according to the proportion of culture medium components, and the water content of the experimental soil layer was controlled at about 20% with local groundwater. The purpose of covering the experimental area with plastic film is to keep warm, moisturize and prevent rain. Sampling shall be carried out at regular intervals. The sampling method is to take five soil samples with the same depth (15cm) at different points in the plum blossom shape in this area, and sample and test them by four-point method after thorough mixing. See table 6- 16 ~ 6- 19 and figure 6- 1 1.
Table 6- 16 Test results of soil oil content change with time in test area 1, control area and blank area
Table 6- 17 1 Test results of soil pH, water content (W) and contents of TDS, NH+4 and NO-3 with time.
Table 6- Changes of oil content, pH value, water content (W), TDS, NH+4 and NO-3 content with depth in subsoil in 1 area after test. Test results of TDS content, NH+ content and NO content of oil content.
Table 6- 19 2 test results of soil oil content changing with time
Note: The oil removal rate is calculated with the average oil content of 0 ~ 7d as the initial concentration (23 18.5mg/kg); Omit the representative difference of the data on the third day.
Fig. 6- 1 1 Variation of oil removal rate with time in experimental soil.
1. Removal rate of oil in micro-ecological remediation soil
From Table 6- 16 and Figure 6- 1 1, it can be seen that through field experiments, microecological technology is effective for the remediation of soil oil pollution. The optimized bacterial liquid added in the experimental area from 0 to 7 days did not play a role, that is to say, when the indoor optimized bacterial liquid was applied in the field, it went through an adaptation period or lag period, and the adaptation period in this experimental area was about 7 days. Then the proliferative phase is also logarithmic. Figure 6- 1 1 shows that the removal rate is above 40% on the first1day after the adaptation period, and reaches 80.32% on the 32nd day. However, the oil content in the soil in the control area has little change (except for two abnormally low values, which are basically within 10%), indicating that the oil degradation in the soil is slow under natural conditions. The blank area reflects the oil content in the soil, and no substance is added. However, in the later stage of the test, it may be because the experimental area and the control area are adjacent to the blank area, and the rainfall and manual sampling activities have polluted the area, resulting in an increase in the content.
2. Analyze soil pH, water content (W), TDS, NH+4 and NO-3.
The pH value of the environment has a certain influence on the life activities of microorganisms, which can cause the changes of cell membrane charges and enzyme activities in microorganisms, thus affecting the normal absorption of nutrients by microorganisms. Abnormal pH value changes the effectiveness of nutrients and the toxicity of harmful substances in the environment. The existence of each microorganism has a certain pH range and optimum pH value. The optimum pH of most bacteria is 6.5 ~ 7.5, and that of actinomycetes is 7.5 ~ 8.0. Fungi can grow and develop in a wide pH range, such as pH below 3 or above 9, and the optimum pH is 5 ~ 6. From the monitoring of pH value in Table 6- 17, it can be seen that due to the addition of a certain amount of phosphate buffer, the pH value of 1 experimental area is kept between 7.6 and 8.4, mostly around 8, and the most suitable environment for oil-degrading bacteria is alkaline. The pH value of blank area and control area is between 8. 1 ~ 8.9, which is slightly higher than that of experimental area. However, in this pH range, it has little effect on this experiment. The phosphate added in 1 zone is mainly to increase nutrient elements for the growth of microorganisms.
Water plays an important role (medium and oxygen source) in the process of microbial degradation of petroleum pollutants. Therefore, in order to ensure that there is enough water for the growth and reproduction of microorganisms in the experimental area, the water content is generally kept at about 20%. After each sampling, add about 4% water. The data in Table 6- 17 shows that the soil water content in the test layer remains stable, which provides a basic guarantee for the test effect. The blank area has a naturally changing water content, and the control area can play a certain role in water conservation because of artificial ploughing after sampling. The water content is slightly higher than the blank area, and it does not significantly promote the degradation of soil oil.
Nutrient elements are the constituent elements of microbial cells and biological enzymes in microorganisms. The main elements of microbial cells are carbon, hydrogen, oxygen, nitrogen and phosphorus. , in which c and h come from organic substances such as oil pollutants; Oxygen comes from water, air and other regulated oxygen sources; However, nitrogen, phosphorus and trace elements such as S, K, Ca, Mg and Fe need to be supplemented and regulated as nutrients. Therefore, we use nitrogen, phosphorus, sulfur, potassium, calcium, magnesium, iron and other elements to supplement and adjust the soil in the experimental area, and use local fresh grass (chopped) as an additive to supplement other biological elements and nutrients. Table 6- 17 shows the changes of soluble salt, NH+4 and NO-3 contents with the experimental process, from which it can be seen that various nutrient elements were supplemented in the experimental area on August 2 1 day. With the progress of the experiment, oil and various elements are utilized, degraded and transformed by microbial activities, and the content in the soil gradually decreases.
3. Influence of test process on subsoil
From the test results (Table 6- 18), it can be seen that the oil content in the test area 1 subsoil has not increased significantly. Compared with the control and blank area, it is still lower, indicating that the oil in the experimental soil has not diffused downward or degraded, and a small amount of soluble salt nutrients such as nitrogen and phosphorus enter the lower soil with water. This result has a particularly important guiding significance for the requirements and adding methods of water and soluble nutrients in the future restoration work.
(ii) Test results of the second test area
On the basis of the above test preparation, chicken manure and chicken manure were used as additives and evenly mixed according to the proportion of 4.3% of the soil weight in test 2. Other conditions are the same as 1 area. See table 6- 19 and figure 6- 12 for the test results.
Fig. 6- 12 2 Variation of oil removal rate with time in micro-ecological remediation soil.
1. Removal rate of oil in micro-ecological remediation soil
Through the above-mentioned field experiment, the optimized bacterial liquid added 0 ~ 7 days before the experiment in Zone 2 is the same as that in Zone 1, which means that there needs to be an adaptation period of about 7 days. Then it entered the proliferation period. Table 6- 19 shows that the removal rate reached more than 80% on the first 1 1 day of the experiment, that is, in the late adaptation period. Due to different locations, the sample collection makes the sample test result slightly higher. However, the removal rate of 16d was over 68% and 84.3% at 32d.
2. Analyze the pH value, water content (W), TDS, NH+4 and NO-3 content of the soil.
Due to the addition of a certain amount of phosphate buffer, the pH value in the experimental area is kept at 7.3 ~ 8. 1, and the most suitable environment for oil-degrading bacteria is alkaline, which basically ensures the normal growth of microorganisms. The pH value of the blank area and the control area is between 8. 1 ~ 8.9, which is higher than that of the experimental area, but this pH value range has little effect on the experiment.
The soil water content in the experimental layer remains stable, generally around 20%. After each sampling, about 4% water was added, and the adjusted water content promoted the degradation of bacteria, which basically ensured the experimental effect. The blank area has naturally changing water content, and the control area can play a certain role in water conservation because of artificial ploughing every time sampling, and the water content is slightly higher than that of the blank area.
Table 6-20 shows the changes of TDS, NH+4 and NO-3 contents in different regions with the test process, reflecting the utilization, degradation and transformation of petroleum and various elements with microbial activity in the test process.
Table 6-20 2 Test results of soil pH, water content (W), TDS, NH+4 and NO-3 contents changing with time.
3. Influence of test process on subsoil
Table 6-2 1 shows the contents of oil, pH value, water (W), TDS, NH+4 and NO-3 in Area 2, the control area and the lower part of the blank area after the test. From the test results, it can be seen that the oil content of the lower soil in the experimental layer of Area 2 has not increased significantly, which is similar to that in the control and blank area. It shows that the oil in the experimental soil has not diffused downward or been degraded, and it is also different from the control area and blank area in terms of pH value, water content (W), TDS, NH+4 and NO-3 content, which means that some soluble salt nutrients such as nitrogen and phosphorus enter the lower soil with water, but it does not affect the experimental results.
Table 6-2 1 Test results of oil content, pH value, water content (W), TDS, NH+4 and NO-3 contents in subsoil of each district varying with depth.
(3) the third experimental area
On the basis of the preparation in the experimental area, 50% corn husk and 50% millet husk were evenly mixed as additives according to the proportion of 65438+ 0.4% of the soil weight in the experimental layer. Other conditions are the same as 1 area. See table 6-22 and figure 6- 13 for the test results.
Table 6-22 Experimental results of soil oil content changing with time in the third experimental area
Note: The oil removal rate is calculated with the oil content of 0d as the initial concentration (1886.0mg/kg).
Fig. 6- 13 3 Variation of oil removal rate with time in micro-ecological remediation soil in area 3
1. Removal rate of oil in micro-ecological remediation soil
Through the field remediation test, the effectiveness of geological microecology technology in the in-situ remediation of soil oil pollution was recognized and understood. On the third day of the initial experiment in Zone 3, the optimized bacteria solution played a role, that is to say, the bacteria in the indoor optimized in-situ soil had a short adaptation period, which was 1 ~ 2 days in Zone 3, and then entered the proliferation period. On the third day of the experiment, after the adaptation period, the removal rate reached more than 62%, but on the seventh day, the data was abnormal. The removal rate of 1 1d is more than 76%, that of 2 1d is 80.62%, that of 32 days is 77.29%, and the average removal rate after 1 1d is 77.22%. The results showed that the bacteria entered a stable period after 1 1 days, and the degradation rate of oil in soil was slow and relatively stable.
2. Analyze soil pH, water content (W), TDS, NH+4 and NO-3.
Table 6-23 Test results of soil pH, water content (W), TDS, NH+4 and NO-3 contents in Area 3 with time.
3. Influence of test process on subsoil
Table 6-24 shows the oil content, pH value, water content (W), TDS, NH+4 and NO-3 at different depths in the lower part of each test area after the test is completed. It can be seen from the test results that the oil content in the lower soil of the test layer in the test area has increased slightly. Compared with the control and blank area, the increase is not very large, indicating that the oil in the soil of the experimental layer has partially diffused downward.
Table 6-24 Test results of soil oil content, pH value, water content (W), TDS, NH+4, NO-3 content varying with depth in Area 3 and the lower layer after the test.
(4) the fourth experimental area
On the basis of the preparation of the above experimental area, wheat bran was evenly mixed as an additive according to the proportion of 2.5% of the soil weight in the experimental area. Other conditions are the same as 1 zone, and the test results are shown in Table 6-25.
1. Removal rate of oil in micro-ecological remediation soil
From Table 6-25 and Figure 6- 14, it can be seen that the optimized bacterial liquid added in the experimental area did not play a role in the initial 0-7 days of the experiment, and the removal rate reached more than 70% on the first 1 1 day after the adaptation period, and the maximum removal rate reached 88.1/kl on the 26th day of the experiment. The reason is that the oil content in the soil is uneven, and the stability of the data is affected by the uniformity of bacteria, nutrients and additives. But overall, the effect is remarkable, and the average removal rate can reach 78. 15%.
Table 6-25 Test Results of Soil Oil Content with Time in Area 4
Note: The oil removal rate is calculated by taking the average oil content in the test areas of 3d and 7d as the initial concentration; 0d data may be ignored due to unequal sampling.
Fig. 6- 14 4 Variation of oil removal rate with time in micro-ecological remediation soil.
2. Analyze soil pH, water content (W), TDS, NH+4 and NO-3.
The pH value in the experimental area was kept between 6.6 and 9.0, and most of them were above 8, which caused the pH value to drop to 6.6, which was caused by a large amount of acid production in the early stage of bacterial fermentation just after adding additives. Then the growth of bacteria produces alkali, making the environment alkaline.
The soil water content in the experimental layer is basically stable, generally above 20%. Ammonia nitrogen was also adjusted in the experiment (Table 6-26).
Table 6-26 Test results of soil pH, water content, TDS, NH+4, NO-3 content changing with time in Area 4.
3. Influence of test process on subsoil
As can be seen from Table 6-27, the oil content in the lower layer of the experimental zone has little increase, only slightly higher than that in the control and blank zone, indicating that the oil in the soil of the experimental zone has not diffused downward or has been degraded. From the pH value, water content (W), TDS, NH+4 and NO-3 contents, it can also be seen that it is different from the control area and blank area, that is to say, a small part of soluble salt nutrients such as nitrogen and phosphorus enter the lower soil with water.
Table 6-27 Test results of oil content, pH value, water content (W), TDS, NH+4 and NO-3 in the subsoil of Area 4 after the test.
(5) the fifth experimental area
On the basis of preparation in the experimental area, the expanded culture bacteria solution was inoculated into the experimental area evenly according to 3% of the weight of the experimental layer in the experimental area 5, and then nutrient solutions such as nitrogen, phosphorus, calcium, magnesium, sulfur and iron were added evenly according to the proportion of the components of the culture medium, and the water content of the experimental soil layer was controlled at about 20% with local groundwater. Sampling at certain time intervals, the test results are shown in Table 6-28 and Figure 6- 15.
Table 6-28 Test Results of Soil Oil Content with Time in Area 5
Note: The oil removal rate is calculated by taking the average oil content in the test area of 0d and 7d as the initial concentration; 3d data may be omitted due to unequal sampling.
1. Removal rate of oil in micro-ecological remediation soil
The optimized bacteria solution added at the initial stage of the experiment in Zone 5 did not play a role, and an adaptation period was needed, about 7 days, and then it entered the proliferation period. On the first 1 1 day after the adaptation period, the removal rate reached more than 84.6%, and the maximum removal rate reached 88.99% on the 26th day of the experiment, but the data was somewhat unstable from the removal rate, ranging from 64.84% to 88.99%. No additives and plastic films were added in the experimental area, but the removal effect was still good, and the average removal rate could reach 82.438 0%, which indicated that the treatment measures were also feasible.
Fig. 6- 15 5 Variation of oil removal rate with time in micro-ecological remediation soil.
2. Analyze soil pH, water content (W), TDS, NH+4 and NO-3.
The pH value in zone 5 is kept between 7.7 and 8.5, mostly above 8, which causes the pH value to drop to 7.7. The reason is that phosphate is only added to play a buffering role and make the soil pH value tend to be neutral. Subsequently, the growth of bacteria produces alkali, and the role of the environment makes the environment alkaline. The contents of water and ammonia nitrogen are adjusted and stabilized (Table 6-29).
Table 6-29 Test results of soil pH value, water content, TDS, NH+4 and NO-3 contents in Area 5 with time.
3. Influence of test process on subsoil
As can be seen from Table 6-30, the oil content in the lower soil of the experimental layer in Area 5 has increased, but it is less, which is higher than that of the control and blank area, indicating that the oil in the soil of the experimental layer has spread downward. It can also be seen from the pH value, water content (W), TDS, NH+4 and NO-3 contents, which is different from the control area and blank area, that is to say, a small part of soluble salt nutrients such as nitrogen and phosphorus also enter the lower soil with the water, because the plastic film is not covered during the whole experiment, and the pollutants and nutrients in precipitation migrate downward in the middle several times.
(vi) Test results of the sixth experimental field
On the basis of the preparation of the experimental area, the cultured bacterial liquid is evenly inoculated into the experimental area 6 according to 3% of the soil weight of the experimental layer in the experimental area 6, and then nutrient solutions such as nitrogen, phosphorus, calcium, magnesium, sulfur and iron are evenly added according to the proportion of the culture medium components, and the water content of the experimental soil layer is controlled at about 20% with local groundwater. Cover the test area with plastic film, keep warm, moisturize and rain-proof, and take samples at regular intervals. See table 6-3 1 and figure 6- 16 for the test results of samples.
Table 6-30 Test results of oil content, pH value, water content (W), TDS, NH+4, NO-3 content in the subsoil of Area 5 after the test.
1. Removal rate of oil in micro-ecological remediation soil
The adaptation period of zone 6 is also about 7 days, and the optimized bacterial solution added from 0 to 7 days at the beginning of the experiment did not play a role. Then enter the proliferative phase. On 1 1 day, that is, on the 5th day after the adaptation period, the removal rate was above 90%, and reached 8 1.88% on the 32nd day, with an average removal rate of 87.2 1%.
Table 6-3 1 6 Test Results of Soil Oil Content Changing with Time
Note: The oil removal rate is calculated by taking the average oil content in the test area of 0d and 7d as the initial concentration; 3d data may be omitted due to unequal sampling.
Fig. 6- 16 6 Variation of oil removal rate with time in micro-ecological remediation soil.
2. Analyze soil pH, water content (W), TDS, NH+4 and NO-3.
From the monitoring of pH value in Table 6-32, it can be seen that the pH value in Area 6 is kept between 7.6 and 8.4, and most of them are above 8, which leads to the pH value dropping to 7.6, and it is the buffering effect after phosphate is added that makes the soil pH value tend to be neutral. Subsequently, the growth of bacteria produces alkali, and the role of the environment makes the environment alkaline.
Table 6-32 6 Test results of soil pH, water content, TDS, NH+4 and NO-3 contents changing with time.
3. Influence of test process on subsoil
From the test results (Table 6-33), it can be seen that the oil content in the lower soil of the experimental layer in Area 6 has increased, but it is less than that in Area 5, because the experimental area is covered with plastic film, which reduces the influence of precipitation, and there is no additive. Compared with the control and blank area, it is higher, indicating that the oil in the soil of the experimental layer has a certain downward diffusion.
Table 6-33 Test results of oil content, pH value, water content (W), TDS, NH+4 and NO-3 content in the subsoil of Area 6 after in-depth test.
(7) Test results of control area and blank area.
On the basis of the preparation in the experimental area, only crude oil was added in the control area, and no other experimental materials were added, and then plowed for many times to make it evenly mixed. No other test materials are added to the blank area, and it will not be turned over. At the same time, the two areas and other test areas were sampled at certain time intervals, and the sampling method was the same as that of the test area: five soil samples with the same depth (15cm) were taken at different points of plum blossom shape, and then they were fully mixed and sampled by four-point method. The detected components include petroleum content, pH value, water content (W), TDS, NH+4, NO-3 content, etc. After the end of the test period, the lower part of the test layer in each district was sampled by layers. See Table 6-34 ~ 6-36 for the sampling results.
Table 6-34 Test results of soil oil content in control area, time unit: mg kg- 1
Table 6-35 Test results of soil pH, water content (W), TDS, NH+4 and NO-3 contents with time in control area and blank area.
Table 6-36 Test results of oil content, pH value, water content (W), TDS, NH+4, NO-3 content changing with depth in the control and blank soil after the test.
Through the field in-situ test, it was found that the oil content of the soil in the control area did not change much during the test, except for two abnormally low values (basically around 10% and the maximum 13.3%). It shows that the degradation of oil in soil is slow in a short time under natural conditions, and the test data of 16d and 2 1d may be caused by the uneven content in soil, which also reflects the heterogeneity and complexity of soil material composition. The blank area reflects the oil content in the soil, and no substance is added. However, in the later stage of the experiment, because the experimental area and the control area are adjacent to the blank area, the area is polluted by rainfall and manual sampling, and the content has increased. The change of other components basically changes with the change of precipitation under natural conditions.
Four. Experimental discussion and conclusion
1. Oil removal rate in soil
It can be seen from Table 6-37 that the optimized bacterial liquid added in most experimental areas did not play a role in the initial stage of the experiment, that is to say, when the indoor optimized bacterial liquid is applied in the field, it needs an adaptation period or lag period of bacteria, and the adaptation period of most experimental areas in this experiment is basically about 7 days. Then the proliferative phase is also logarithmic. Table 6-37 shows that on the first 1 1 day of the experiment, the removal rate after the adaptation period exceeds 40%. Only the experiment in area 3 is slightly different, and the adaptation period of bacteria in this area is short, which is 3 ~ 4 days. From the whole test process and test results, the test effect is remarkable, but some data are low or high because of the sampling location and soil heterogeneity. However, the removal rate reached more than 68% at 16d. Of course, due to different test conditions, the results of each test area are also different. Overall, the maximum removal rate of each experimental area is above 80%. However, the oil content in the soil in the control area has little change, except for two abnormally low values, which are basically around 10%, indicating that the oil degradation in the soil is slow in a short time under natural conditions. The test data of 16 and 2 1d may indicate that the content in soil is uneven, which also reflects the heterogeneity and complexity of soil material composition. The blank area reflects the oil content in the soil, and no substance is added. However, in the later stage of the experiment, because the experimental area and the control area are adjacent to the blank area, the area is polluted by rainfall and manual sampling, and the content has increased.
Table 6-37 Degradation rate of oil over time in in-situ micro-ecological remediation soil of Xing 2 oil production well site in Xingzichuan Oilfield:%
2. Controlling factors of micro-ecological restoration technology
Micro-ecological restoration technology is an in-situ restoration technology that fully optimizes the use of in-situ microbial flora, supplemented by physical and chemical methods and combined with geological environment, and changes the macro-environment with micro-effects. The key to the application of this technology is the combination, interdependence, interaction and regulation of microorganisms and geological environment. The regulatory factors mainly include the improvement of temperature, water, oxygen, nutrient elements and geological environment, which are used to promote the transformation of elements, degrade toxic and harmful substances and control and repair environmental pollution in situ.
(1) soil temperature control
Temperature is one of the important factors affecting the growth and survival of microorganisms, and the activity intensity and biochemical function of microorganisms are related to this. The optimized microbial flora in the experimental area is mostly mesophilic microorganisms (13 ~ 45℃), and the optimum growth temperature is 25 ~ 38℃. By monitoring the maximum and minimum temperatures of the surface in the experimental stage, it is shown that the blank area is the natural maximum and minimum temperature of the surface. From late August to early September, the highest surface temperature in this area is mostly above 25℃, but the lowest temperature is less than 20℃, and the temperature difference between day and night is large. How to control the temperature is the key to the test results. Therefore, we use agricultural plastic film to keep warm in the experimental area, and then cover it with grass curtain at night after the temperature drops obviously in September. From the control effect, the soil temperature in the experimental area increased obviously at 15cm, which was 5 ~ 8℃ higher than that in the blank area, especially before the first ten days of September. However, with the decrease of temperature, the removal rate of oil in soil is also decreasing. Through this experiment and temperature monitoring, we can also draw the conclusion that the best temperature period for developing micro-ecological restoration technology in this area should be from late June to early September every year. Through adjustment, the soil temperature is kept above 25℃, and the vitality and fecundity of microorganisms and bacteria are ensured.
(2) Regulation of oxygen in soil
The supply of oxygen has become one of the important regulatory factors in the process of microbial degradation of organic matter. This experiment regulates the supply of soil oxygen from four aspects. First, fully plough the test soil layer, and plough it after each sampling to make it fully mix with the atmosphere. The second is to ensure that the test soil has a certain water content, so that the water content is kept at about 20%, and the oxygen provided by the water is obtained. In addition, some experimental areas use additives, such as fresh grass, chicken manure, chaff, wheat bran and so on. These additives are not only cheap and easy to obtain, but also can supplement nutrients for the soil, improve the soil in the experimental layer, increase bulkiness and permeability, and make oxygen in the air easily enter. The added oxygen-containing nutrients, such as K2HPO4, KH2PO4, MgSO4 7H2O, NH4NO3 and NO-3, not only increase nitrogen, phosphorus and magnesium, but also are one of the sources of oxygen. The above control measures provide sufficient oxygen source for microbial degradation of oil in soil, and ensure the oxygen needed for microbial bacteria to degrade oil in soil.
3. In-situ repair test conclusion
The following main conclusions can be drawn from the whole test process and method:
1) Through the experimental study on the in-situ micro-ecological remediation method of oil-contaminated soil in Xingzichuan loess area of northern Shaanxi, the in-situ microbial flora is optimized and combined with the micro-ecological technology of physical and chemical methods to regulate the soil temperature, moisture, oxygen, nutrient elements and geological environment factors in the experimental area, and the degradation and remediation experiment of oil in soil is carried out. The experimental results show that the average oil content of soil exceeds 2000mg/kg. After 1 1 ~ 32d in-situ micro-ecological remediation technology, the removal rate of oil content in soil can reach more than 40% ~ 80%, which verifies the effectiveness, scientificity and ecology of geological micro-ecological remediation technology in the remediation of soil oil pollution in Xingzichuan loess area, and explores the feasibility of popularization and application.
2) It is concluded that the best temperature season for applying micro-ecological restoration technology in this area should be from late June to early September every year, and the soil temperature can be kept above 25℃ through regulation and control to ensure the temperature demand of microbial bacteria vitality and fecundity.
3) It is verified that the adjustment of nutrient elements and the improvement of soil environment in this experiment are moderate and the method is feasible.
The experimental process verified the effectiveness and feasibility of in-situ micro-ecological remediation technology in in-situ soil oil pollution remediation test, which has the advantages of simple treatment method, low cost, good remediation effect, little environmental impact, no secondary pollution and in-situ treatment. Although it is an experimental study, it needs to be improved for large-scale field repair, but it can be achieved through continuous efforts. It can not only effectively restore soil, vadose zone and control oil pollution of groundwater in situ, but also increase soil fertility and improve soil environment without negative effects. It is of great significance to the remediation of contaminated soil and the increase of crop production, and it is also one of the effective methods to fundamentally repair and control large-scale oil pollution in soil, which has a certain promotion and application role.