A method for utilizing goethite to enhance endogenous microbial degradation of petroleum hydrocarbons in soil

Abstract

This invention discloses a method for enhancing the degradation of petroleum hydrocarbons in soil by endogenous microorganisms using goethite. Goethite is used as a biostimulant to activate the activity of endogenous functional bacteria in the soil in degrading petroleum hydrocarbons. The dominant phyla of these endogenous functional bacteria are Proteobacteria, Actinobacteria, and Firmicutes, with a relative abundance of 50%–80%. Under conditions of soil pH 6.0–9.0 and soil moisture content 20%–50%, the degradation rate of total petroleum hydrocarbons in the soil is ≥ 60%, and the degradation rate of components such as colloids and asphaltene is ≥ 45%.

Description

Technical Field

[0001] This invention relates to the field of petroleum hydrocarbon contaminated soil remediation technology, specifically to a method for utilizing goethite to enhance the degradation of petroleum hydrocarbons by endogenous microorganisms in contaminated soil. Background Technology

[0002] Petroleum hydrocarbon contamination of soil not only damages the soil ecosystem, but also poses a threat to the health of plants, animals, and even humans through the food chain and groundwater. Microbial remediation technology has become one of the core technologies for remediating petroleum hydrocarbon-contaminated soil due to its environmental friendliness and low cost. Traditional microbial remediation methods aim to degrade petroleum hydrocarbons by adding exogenous microorganisms to the soil. However, due to multiple limitations such as the soil environment, the characteristics of the microorganisms themselves, and the physicochemical properties of petroleum hydrocarbons, practical applications face technical bottlenecks: 1) High proportion of recalcitrant components. Short-chain alkanes in petroleum hydrocarbons are easily degraded, while long-chain alkanes, polycyclic aromatic hydrocarbons, colloids, and asphaltenes have stable structures and are difficult to degrade by microorganisms alone; 2) Toxicity inhibition. High concentrations of petroleum hydrocarbons or their degradation intermediates (such as phenols and ketones) are toxic to microorganisms, damaging cell membrane permeability, inhibiting respiration, leading to decreased bacterial activity or even death.

[0003] Biostimulation is a remediation technology that "enhances the soil's own purification potential." Without introducing exogenous bacteria, it activates the metabolic activity and proliferation capacity of endogenous petroleum hydrocarbon-degrading bacteria in the soil by optimizing the soil microenvironment and supplementing key limiting factors. The most common method to achieve biostimulation is the addition of nutrients to meet the proliferation and metabolic needs of degrading bacteria. Common inorganic nutrients include urea (providing nitrogen), potassium dihydrogen phosphate (providing phosphorus), and ammonium nitrate (nitrogen source); organic nutrients include well-rotted organic fertilizer, straw compost, and fish protein. To improve water-oil interface contact and enhance the bioavailability of petroleum hydrocarbons, biosurfactants such as rhamnolipids, sophorolipids, and saponins, and chemical surfactants such as sodium dodecylbenzenesulfonate and polyoxyethylene ethers are commonly reported methods for biostimulating the degradation of petroleum hydrocarbons in contaminated soils. Although biostimulation has become one of the mainstream technologies for the remediation of petroleum hydrocarbon-contaminated soils due to its advantages such as low cost and ecological safety, the reported application methods are still subject to multiple limitations such as soil characteristics, pollution features, and technology adaptability. They have prominent problems such as low removal rate of total petroleum hydrocarbons, long degradation time, and limited removal of difficult-to-degrade components such as colloids and asphaltenes. Summary of the Invention

[0004] This invention provides a method for enhancing the degradation of petroleum hydrocarbons in soil by endogenous microorganisms using goethite. It addresses the problems of existing microbial remediation technologies, such as limited removal of recalcitrant components, the tendency of high concentrations of petroleum hydrocarbons and their intermediate products to inhibit microbial activity, and the low efficiency of traditional biostimulation technologies. By enhancing the degradation activity of endogenous microorganisms in soil for petroleum hydrocarbons using goethite, the degradation rate of total petroleum hydrocarbons in soil is improved.

[0005] This invention is achieved through the following technical solution:

[0006] A method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms involves using goethite as a biostimulant. Goethite is added to contaminated soil, mixed thoroughly, and the soil pH is controlled between 6.0 and 9.0. The soil is then placed under natural ventilation conditions, maintaining a soil moisture content of 20%–50%. The soil is stirred every 5–10 days for 5–15 minutes each time, with a remediation time of 25–50 days. The preferred remediation time is 30–40 days.

[0007] Furthermore, the goethite is goethite with a purity of not less than 95%, or it is a combination of pure goethite and naturally occurring iron minerals containing goethite. The general chemical formula for goethite is α-FeOOH.

[0008] Furthermore, the mass ratio of the pure goethite to naturally occurring iron minerals containing goethite is 1:(0.5~5).

[0009] Furthermore, the naturally occurring iron mineral containing goethite is at least one of shale or limonite.

[0010] Furthermore, the goethite in the swamp iron ore comprises 60% to 80% by mass, and the goethite in the limonite comprises 40% to 60% by mass; the purity of the pure goethite is ≥ 95%.

[0011] Furthermore, the dosage of the biostimulant is 0.5% to 10% of the dry weight of the contaminated soil.

[0012] Furthermore, during the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 50% to 80% of the total microbial community in the soil.

[0013] Furthermore, the concentration of petroleum hydrocarbons in the contaminated soil is 0.5% to 5% (w / w).

[0014] After remediation, samples were collected, and the petroleum hydrocarbon content in the soil was measured using a gravimetric method to calculate the degradation rate of petroleum hydrocarbons. Simultaneously, the concentrations of colloids and asphaltenes in the soil were determined using a four-component analysis method for petroleum hydrocarbons, and their degradation rates were calculated. Further, after remediation, the total petroleum hydrocarbon degradation rate in the soil should be ≥ 60%, with the degradation rates of colloids and asphaltenes ≥ 45%. Preferably, after remediation, the total petroleum hydrocarbon degradation rate in the soil should be ≥ 65%, or even greater than 70%, with the degradation rates of colloids and asphaltenes ≥ 55%, or even greater than 60%.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] This invention provides a method for enhancing the degradation of petroleum hydrocarbons in soil by endogenous microorganisms using a goethite-containing biostimulant. By activating the degradation activity of endogenous functional bacteria in the soil against petroleum hydrocarbons through goethite, the degradation rate of total petroleum hydrocarbons in the soil is increased. Compared with other iron-containing mineral (such as ferrihydrite) biostimulants, under the same conditions (iron mineral dosage, petroleum hydrocarbon concentration, moisture content, pH, remediation time, etc.), the degradation rate of petroleum hydrocarbons in the soil is higher, as shown in Table 1.

[0017] Table 1. Comparison of the effects of different biostimulants on enhancing the degradation of petroleum hydrocarbons by endogenous microorganisms in soil.

[0018] Detailed Implementation

[0019] The present invention will be described in detail below through specific embodiments. The uses and purposes of these exemplary embodiments are only for illustrating the present invention and are not intended to limit the actual scope of protection of the present invention in any way, nor are they intended to limit the scope of protection of the present invention to these embodiments.

[0020] Example 1

[0021] This embodiment utilizes goethite to enhance the degradation of petroleum hydrocarbons in soil by endogenous microorganisms. Pure goethite with a purity of 99.5% was used alone as a biostimulant. Specifically, the biostimulant was added at 0.5% of the dry weight of the contaminated soil to contaminated soil with a petroleum hydrocarbon concentration of 2.0% (w / w), and thoroughly mixed while maintaining the soil pH at 8.0. The soil was then placed in a naturally ventilated environment, maintaining a soil moisture content of 30% during the remediation process to create a suitable soil microenvironment for endogenous microbial growth and the effectiveness of goethite. The soil was stirred every 7 days for 10 minutes each time to maintain soil aeration and ensure microbial activity. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric analysis, and the degradation rate was calculated to be 60.2%. Simultaneously, the concentrations of colloids and asphaltene in the soil were determined using a four-component petroleum hydrocarbon analysis method, and the degradation rates were calculated to be 48.3% for colloids and 49.1% for asphaltene. During the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 55% of the total microbial community in the soil.

[0022] Example 2

[0023] In this embodiment, the biostimulant was a 1:1 mass mixture of pure goethite and pyrite, with the goethite purity being 99.5% and the pyrite comprising 75% of the goethite mass. The specific method was as follows: 5.0% of the above biostimulant was added to contaminated soil with a petroleum hydrocarbon concentration of 2.0% (w / w), and thoroughly mixed while controlling the soil pH to 7.0. The soil was then placed in a naturally ventilated environment, maintaining a soil moisture content of 30% during the remediation process to create a suitable soil microenvironment for endogenous microbial growth and the effectiveness of goethite. The soil was stirred every 7 days for 10 minutes each time to maintain soil aeration and ensure microbial activity. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured using a gravimetric method, and the petroleum hydrocarbon degradation rate was calculated to be 71.5%. Simultaneously, the concentrations of colloids and asphaltene in the soil were determined using a four-component petroleum hydrocarbon analysis method, and the colloid degradation rate was calculated to be 60.1% and the asphaltene degradation rate to be 60.8%. During the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 75% of the total microbial community in the soil.

[0024] Example 3

[0025] In this embodiment, the biostimulant was a 1:1 mass mixture of pure goethite and limonite, with the goethite purity being 99.5% and the limonite comprising 56% of the goethite mass. The specific method was as follows: the biostimulant was added at 5.0% of the dry weight of the contaminated soil to contaminated soil with a petroleum hydrocarbon concentration of 2.0% (w / w), and thoroughly mixed while maintaining the soil pH at 7.0. The soil was then placed in a naturally ventilated environment, maintaining a soil moisture content of 30% during the remediation process to create a suitable soil microenvironment for endogenous microbial growth and the effectiveness of goethite. The soil was stirred every 7 days for 10 minutes each time to maintain soil aeration and ensure microbial activity. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured using a gravimetric method, and the petroleum hydrocarbon degradation rate was calculated to be 70.2%. Simultaneously, the concentrations of colloids and asphaltene in the soil were determined using a four-component petroleum hydrocarbon analysis method, and the colloid degradation rate was calculated to be 58.5%, and the asphaltene degradation rate was 59.0%. During the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 72% of the total microbial community in the soil.

[0026] Example 4

[0027] This embodiment utilizes goethite-enhanced endogenous microbial degradation of petroleum hydrocarbons in soil. The raw materials and process are the same as in Embodiment 1, except that the biostimulant dosage is 5.0% of the dry weight of the contaminated soil. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric analysis, and the degradation rate was calculated to be 72.6%. Simultaneously, the concentrations of colloids and asphaltenes in the soil were determined using a four-component petroleum hydrocarbon analysis method, with a colloid degradation rate of 61.8% and an asphaltene degradation rate of 62.5%. During the remediation process, the dominant phyla of the indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with these three phyla accounting for 80% of the total microbial community in the soil.

[0028] Example 5

[0029] In this embodiment, the biostimulant was a mixture of pure goethite, shale iron, and limonite in a mass ratio of 1:2:2, wherein the purity of the goethite was 99.5%, the mass percentage of goethite in the shale iron was 75%, and the mass percentage of goethite in the limonite was 56%. Specifically, the biostimulant was added at 5.0% of the dry weight of the contaminated soil to contaminated soil with a petroleum hydrocarbon concentration of 5.0% (w / w), and thoroughly mixed while maintaining the soil pH at 7.0. The soil was then placed in a naturally ventilated environment, maintaining a soil moisture content of 20% during the remediation process to create a suitable soil microenvironment for the growth of endogenous microorganisms and the effectiveness of goethite. The soil was stirred every 7 days for 10 minutes each time to maintain soil aeration and ensure microbial activity. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric method, and the petroleum hydrocarbon degradation rate was calculated to be 68.5%. Meanwhile, the concentrations of colloids and asphaltenes in the soil were determined using a four-component analysis method for petroleum hydrocarbons. The degradation rate of colloids was calculated to be 56.7%, and the degradation rate of asphaltenes was 58.5%. During the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 68% of the total microbial community in the soil.

[0030] Example 6

[0031] In this embodiment, the biostimulant was a mixture of pure goethite and pyrite at a mass ratio of 2:1. Specifically, the biostimulant was added at 5.0% of the dry weight of the contaminated soil to contaminated soil with a petroleum hydrocarbon concentration of 1.0% (w / w), and thoroughly mixed while maintaining the soil pH at 6.0. The soil was then placed in a naturally ventilated environment, maintaining a soil moisture content of 40% during the remediation process to create a suitable soil microenvironment for endogenous microbial growth and the effectiveness of goethite. The soil was stirred every 7 days for 10 minutes each time to maintain soil aeration and ensure microbial activity. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured using a gravimetric method, and the petroleum hydrocarbon degradation rate was calculated to be 73.0%. Simultaneously, the concentrations of colloids and asphaltenes in the soil were determined using a four-component petroleum hydrocarbon analysis method, and the colloid degradation rate was calculated to be 61.0%, and the asphaltenes degradation rate was 61.5%. During the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 77% of the total microbial community in the soil.

[0032] Example 7

[0033] This embodiment utilizes goethite-enhanced endogenous microbial degradation of petroleum hydrocarbons in soil. The raw materials and process are the same as in Example 1, except that the biostimulant dosage is 10.0% of the dry weight of the contaminated soil. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric analysis, and the degradation rate was calculated to be 74.3%. Simultaneously, the concentrations of colloids and asphaltenes in the soil were determined using a four-component petroleum hydrocarbon analysis method, with a colloid degradation rate of 62.8% and an asphaltenes degradation rate of 63.4%. During the remediation process, the dominant phyla of the indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with these three phyla accounting for 80% of the total microbial community in the soil.

[0034] The degradation conditions and effects of the above embodiments on petroleum hydrocarbons in soil are shown in Table 2.

[0035] Table 2. The degradation conditions and effects of petroleum hydrocarbons in soil according to the embodiments listed in this invention.

[0036]

[0037] Comparative Example 1

[0038] The steps in this comparative example are the same as in Example 1, except that the biostimulant used in this comparative example is hematite, which is added at 5.0% of the dry weight of the contaminated soil. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric method, and the degradation rate of petroleum hydrocarbons was calculated to be 38.6%. At the same time, the concentrations of colloids and asphaltenes in the soil were determined by the four-component analysis method of petroleum hydrocarbons, and the degradation rate of colloids was calculated to be 22.3% and that of asphaltenes to be 20.1%.

[0039] Comparative Example 2

[0040] The steps in this comparative example are the same as in Example 1, except that the biostimulant used in this comparative example is magnetite, which is added at 5.0% of the dry weight of the contaminated soil. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric method, and the degradation rate of petroleum hydrocarbons was calculated to be 41.3%. At the same time, the concentrations of colloids and asphaltenes in the soil were determined by the four-component analysis method of petroleum hydrocarbons, and the degradation rate of colloids was calculated to be 25.7% and that of asphaltenes to be 23.5%.

[0041] Comparative Example 3

[0042] The steps in this comparative example are the same as in Example 1, except that the biostimulant used in this comparative example is ferrihydrite, which is added at 5.0% of the dry weight of the contaminated soil. The ferrihydrite is prepared from KOH and Fe(NO3)3·9H2O through solution preparation, dropwise addition and stirring, centrifugation, washing, and freeze-drying. After 35 days of remediation, the petroleum hydrocarbon content in the soil was measured by gravimetric method, and the degradation rate of petroleum hydrocarbons was calculated to be 48.3%. Simultaneously, the concentrations of colloids and asphaltenes in the soil were determined using a four-component analysis method for petroleum hydrocarbons, and the degradation rates of colloids and asphaltenes were calculated to be 35.2% and 34.7%, respectively.

[0043] The degradation conditions and effects of the above comparative examples on soil petroleum hydrocarbons are shown in Table 3.

[0044] Table 3. Comparative examples listed in this invention: conditions and effects of petroleum hydrocarbon degradation in soil.

[0045]

[0046] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms, characterized in that, Goethite was used as a biostimulant. It was added to the contaminated soil and mixed evenly while the soil pH was controlled between 6.0 and 9.

0. The soil was then placed under natural ventilation conditions. During the remediation process, the soil moisture content was maintained at 20% to 50%. The soil was stirred once every 5 to 10 days for 5 to 15 minutes each time, and the remediation time was 25 to 50 days. The goethite is goethite with a purity of not less than 95%, or it is a combination of pure goethite and naturally occurring iron minerals containing goethite.

2. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to claim 1, characterized in that, The mass ratio of pure goethite to naturally occurring iron minerals containing goethite is 1:(0.5~5).

3. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to claim 1, characterized in that, The naturally occurring iron mineral containing goethite is at least one of shale or limonite.

4. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to claim 3, characterized in that, The swamp iron ore contains 60% to 80% goethite by mass, and the goethite contains 40% to 60% goethite by mass.

5. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to claim 1, characterized in that, The biostimulant is added at a rate of 0.5% to 10% of the dry weight of the contaminated soil.

6. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to claim 1, characterized in that, During the remediation process, the dominant phyla of indigenous degrading bacteria were Proteobacteria, Actinobacteria, and Firmicutes, with the relative abundance of these three phyla accounting for 50% to 80% of the total microbial community in the soil.

7. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to claim 1, characterized in that, The mass concentration of petroleum hydrocarbons in the contaminated soil is 0.5% to 5%.

8. The method for enhancing the degradation of petroleum hydrocarbons in soil using goethite-enhanced endogenous microorganisms according to any one of claims 1-7, characterized in that, After remediation, the degradation rate of total petroleum hydrocarbons in the soil is ≥ 60%, of which the degradation rate of colloids and asphaltene is ≥ 45%.

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