Sylvie Willis
Bioremediation is a process that leverages biological activity to destroy harmful pollutants. One of the most effective ways to treat diesel-contaminated soil is through the use of a biopile system, which involves assembling contaminated soils into piles and stimulating the biodegrading activity of microbial populations by optimising conditions such as moisture content, pH, air circulation, temperature, and nutrients. This process can be used to treat a wide range of petrochemical contaminants in soils, including diesel fuel. The construction of a biopile can vary in complexity depending on the specific requirements and scale of the project, ranging from simple temporary systems to complex permanent designs.
| Characteristics | Values |
|---|---|
| Definition | Biopiling is an ex situ bioremediation technology that leverages biological processes to convert contaminants to low-toxicity byproducts. |
| Use case | Biopiling has been used successfully to treat diesel fuel-contaminated soil. |
| Effectiveness | Jabbar et al. (2017) reported a removal efficiency of 75% from the sample treated using a biopile system for bioremediation. |
| Size | Biopiles are typically designed to be between 3 and 10 ft high. The length and width of the pile are unlimited but are often determined by the equipment used and space availability. |
| Foundation | Biopiles are constructed with an impermeable base to prevent contaminated groundwater and/or leached contaminants from being released back into the environment. |
| Liquid barriers | Can be as simple as plastic sheets or as sophisticated as a permanent concrete pad, depending on the mass of soil to be treated. |
| Moisture content | Water should be added periodically to maintain a moisture content between 40% and 85% of field capacity to support biodegradation. |
| Nutrients | Nitrogen, phosphorus, and oxygen are required for biodegradation reactions. |
| Temperature | Optimum biopile temperatures range from 10°C to 38°C for a permanent concrete facility. |
| Microbial population | The indigenous microbial population is typically sufficient for bioremediation, but bioaugmentation products may be used to enhance the process. |
| Phytoremediation | Planting rye grass in diesel-contaminated soil increased the rate of TPH degradation by 25%. |
| Construction | A biopile can use a simple, low-cost design for a temporary system or a complex, permanent design for long-term operation. |
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What You'll Learn
Preparing the construction site
Clear and Grade the Area
Clear any debris, vegetation, or obstacles from the chosen construction site. Grade the area to create a level surface, ensuring it is free of any uneven patches or holes. Determine the size of the biopile based on the equipment available and the space constraints. A substantial area is typically required for biopile construction, but it is generally less space-intensive than alternative technologies such as composting or land farming.
Create a Sloped Foundation
Design the foundation with a slight slope to facilitate effective drainage and rainwater collection. This sloped foundation will ensure that any rainwater or excess liquids can easily flow away from the biopile, preventing pooling and potential contamination of the surrounding area.
Construct a Berm
Build a protective earthen berm around the perimeter of the pile. This berm should be approximately two feet high. It serves as a barrier to prevent the run-on of surface waters and the runoff of leachate, protecting the biopile from potential contamination. If the berm is constructed from soil, cover it with a durable polyethylene liner to safeguard against erosion.
Prepare the Liner
Lay a double-layered polyethylene liner on top of a 2-3 inch layer of sand and the berms. Ensure the liner is robust and puncture-resistant to withstand soil-moving equipment without tearing. The liner should be impermeable to leachate, preventing any contaminated liquids from seeping into the soil beneath the biopile.
Pile the Soil
Now, you can start to pile the contaminated soil onto the liner. Create a flat-top pile with a height of 4-5 feet. Add the soil in layers or lifts of 1 to 2 feet at a time. With each lift, install air distribution piping and incorporate lime, fertilizer, and water to stimulate microbial activity and biodegradation. The addition of fertilizer and lime enhances the growth conditions for the microorganisms, promoting their ability to break down the contaminants.
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Designing the biopile
When constructing a biopile for diesel fuel remediation, several factors and design specifications must be considered. Biopiling is an ex situ bioremediation technology that leverages biological processes to convert contaminants into low-toxicity byproducts. It involves assembling contaminated soils into piles and stimulating the biodegrading activity of microbial populations by optimising growth conditions.
Firstly, it is important to determine the space required for construction and installation. The biopile's dimensions typically range from 3 to 10 feet in height, while the length and width are generally unlimited. However, the overall size is often dictated by the equipment used for construction and the available space. A substantial area may be necessary, but it is usually less than that required for alternative ex situ technologies such as composting or land farming.
The foundation of the biopile should be carefully prepared to prevent the release of contaminated groundwater or leached contaminants back into the environment. An impermeable base is essential, and this can range from a simple plastic sheet to a more sophisticated permanent concrete pad, depending on the amount of soil to be treated. The foundation should be sloped to facilitate the drainage and collection of rainwater. A two-foot earthen berm can be built around the pile to prevent the runoff of surface waters and leachate. If constructed of soil, this berm should be covered with a durable polyethylene liner to protect against erosion.
The biopile is then constructed by piling the soil onto the prepared base. The soil should be placed in lifts of 1 to 2 feet, with each lift incorporating air distribution piping, lime, fertiliser, and water. The fertiliser should be mixed thoroughly with the soil and lime. The biopile's height should be between 4 and 5 feet. It is important to maintain a moisture content between 40 and 85 percent of field capacity to provide a suitable environment for biodegradation. Water can be added using spray or drip irrigation systems.
To stimulate biodegradation, air circulation is essential and can be achieved through natural microorganisms or mechanical means such as slotted pipes. Additionally, the growth conditions for microbial populations can be optimised by controlling parameters such as temperature, moisture content, pH, carbon-to-nitrogen proportion, and oxygen content. The addition of nutrients and bacterial inoculum, such as sawdust, can further enhance the bioremediation process.
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Creating optimum conditions for biodegradation
Bioremediation is one of the most effective and promising ways to treat diesel-contaminated soil. It involves leveraging biological processes to convert contaminants into low-toxicity byproducts. To create optimum conditions for biodegradation, several factors must be considered:
Temperature
The ideal temperature range for a permanent concrete biopile facility is between 10°C and 38°C. Maintaining this temperature range helps optimize the activity of the microorganisms involved in the biodegradation process.
Microbial Population
The indigenous microbial population is typically sufficient for bioremediation, and it is unnecessary to add microbes to the system. However, commercial bioaugmentation products are available to enhance the process. Additionally, planting certain plants, such as rye grass (*Lolium multiflorum*), can stimulate microbial activity and increase the rate of TPH degradation.
Nutrients
Nutrient requirements for biodegradation reactions include nitrogen, phosphorus, and oxygen. The addition of nutrients, such as fertilizer, lime, and bacterial inoculum, promotes the growth of microorganisms. In one study, mixing the contaminated soil with 1.5% sawdust and supplying the necessary nutrients and water resulted in enhanced microorganism growth.
Moisture Content
Maintaining a moisture content between 40% and 85% of field capacity is crucial for providing a suitable environment for biodegradation. Water can be added to the top of the biopile using sprays or drip irrigation systems.
Oxygen
Adequate oxygen supply is essential for the biodegradation process. Oxygen can be introduced through tilling or by using a system of slotted pipes to ensure even distribution throughout the biopile.
Design and Construction
The design and construction of the biopile also play a role in creating optimum conditions for biodegradation. The biopile should be constructed on an impermeable base or pad to prevent contaminated groundwater or leached contaminants from being released back into the environment. The foundation should be sloped to facilitate drainage and rainwater collection. A cover can be used to manage exposure to precipitation, and probes can be installed to monitor temperature, moisture content, and contaminant concentrations.
By carefully considering and controlling these factors, optimum conditions for biodegradation in a biopile system can be achieved, leading to the effective remediation of diesel-contaminated soil.
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Adding nutrients and bacteria
The addition of nutrients and bacteria is a critical aspect of constructing a biopile for diesel fuel remediation. The process involves creating optimal conditions for the growth and activity of microorganisms that break down diesel contaminants. Here are the key considerations for adding nutrients and bacteria:
Nutrient Requirements
To effectively stimulate microbial activity, specific nutrients are necessary. These include nitrogen, phosphorus, and oxygen. The amounts of these nutrients required for the biodegradation process can be calculated based on the type and amount of contaminants in the soil. For example, the average composition of gasoline and fuel oil contaminants can be used to determine the necessary nutrient levels.
Sources of Nutrients
Nutrients can be added to the biopile in various ways. One method is through the use of fertilizers, which are mixed with the soil as the biopile is constructed. Additionally, water can serve as a carrier for nutrients. By injecting air into the ground, it is possible to supply nutrients and oxygen to the bacteria, optimising their growth and decomposition capabilities.
Bacterial Strains
Certain bacterial strains have been shown to be particularly effective in diesel fuel remediation. For instance, the strain C7S3A exhibits high diesel degradation capabilities, with a 96% success rate. A consortium containing six bacterial strains also demonstrated high diesel degradation of 97%.
Phytoremediation
Phytoremediation is a technique that involves using plants and their associated microbiomes to enhance the remediation process. For example, planting rye grass (*Lolium multiflorum*) in diesel-contaminated soil has been shown to increase the rate of diesel degradation by 25%. When combined with specific bacteria, phytoremediation can further boost remediation rates, as seen with the Ecopiling process, which resulted in degradation rates 67-84% higher than control soils.
Supplementation
The use of supplements, such as carbon substrates and red bran, in biopiles has been shown to effectively activate microbial activities and accelerate the biodegradation process. In a pilot-scale study, a biopile system with mixed supplements achieved a TPH removal efficiency of 79%.
By carefully considering the nutrient requirements, utilising appropriate sources of nutrients, selecting effective bacterial strains, incorporating phytoremediation, and exploring supplementation options, the addition of nutrients and bacteria to a biopile for diesel fuel remediation can be optimised.
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Monitoring and maintenance
Regular Testing and Adjustments
- Regularly test the moisture content, pH, air circulation, temperature, and carbon-to-nitrogen ratio. These parameters can be adjusted to optimise the biodegradation process. For example, water can be added through sprays or drip irrigation systems to maintain optimal moisture levels.
- Ensure adequate oxygen supply by tilling at least once a week or using a system of slotted pipes for even oxygen distribution.
- Monitor and maintain the temperature within the optimal range of 10°C to 38°C for permanent concrete facilities.
- Test nutrient levels, including nitrogen, phosphorus, and oxygen, and adjust as necessary to support microbial activity.
Microbial Population Management
- The indigenous microbial population is typically sufficient for bioremediation, but commercial bioaugmentation products can be used if needed.
- Enhance microbial activity by planting specific plants, such as rye grass (Lolium multiflorum), which has been shown to increase the rate of diesel degradation.
- In some cases, the addition of bacterial inoculum, such as diesel-degrading bacteria, may be beneficial.
Structural Maintenance
- Inspect the biopile structure regularly for any signs of damage or erosion, especially the liner and drainage systems.
- Ensure that the drainage system is functioning properly to manage precipitation and prevent the runoff of contaminated water.
- Regularly inspect and maintain any optional equipment, such as the moisture addition system, leachate collection system, and off-gas treatment systems.
Performance Monitoring
- Monitor the progress of remediation by testing contaminant levels at regular intervals.
- Compare the results with the defined end-point clean-up targets, which can be determined through human risk assessments and ecotoxicological hazard assessments.
- Make adjustments to the biopile design or parameters if remediation progress is slower than expected. This may include adding clean soil to dilute high concentrations of contaminants.
It is important to note that the specific monitoring and maintenance requirements may vary depending on the scale and specifics of the biopile construction. Flexibility and adaptability are crucial to ensure the optimal conditions for diesel fuel remediation.
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Frequently asked questions
A biopile is an ex situ treatment technology that leverages biological processes to convert contaminants to low-toxicity byproducts. Biopiling involves assembling contaminated soils into piles and stimulating the biodegrading activity of microbial populations by creating near-optimum growth conditions.
Biopiles are used to treat contaminated soil and water. They are particularly effective for diesel fuel remediation.
Biopiles typically have a height between 3 and 10 feet. The length and width are usually determined by the equipment used and the space available. Biopiles are constructed with an impermeable base to prevent contaminated groundwater and/or leached contaminants from being released back into the environment.
Capital equipment includes a blower, liquid knockout equipment, any necessary vapor treatment equipment, and plumbing for the aeration system.
First, procure and prepare the necessary space. Then, perform treatability testing to determine the ability to achieve remedial goals and the associated timeframe. Clear and grade an area for construction, ensuring it has a slight slope to allow for drainage and rainwater collection. Construct a curb or berm to prevent water runoff. Lay an impermeable liner, then pile the soil on top, installing piping and adding fertilizer, lime, and water as you go.
