Roots blowers for soil remediation and FAQ about on this subject that explains where roots blowers may be evaluated in soil and groundwater remediation. It distinguishes vacuum extraction from positive-pressure air injection and summarizes the process data, protection and operating conditions needed for equipment selection.
Remediation Applications and SVE Duty
What is soil remediation? Soil remediation includes the engineering methods used to remove, contain, transform or reduce contaminants in soil and groundwater.
The appropriate treatment depends on contaminant properties, soil permeability, contamination depth, groundwater conditions, site use, and nearby buildings. Performance also depends on required cleanup objectives and environmental and safety requirements. These blowers are relevant to remediation methods that use controlled air injection or vacuum extraction.
Which soil-remediation processes can use roots blowers? Potential applications include soil vapor extraction, air sparging, bioventing, biosparging, combined air sparging and SVE, and the vapor side of multi-phase extraction after effective gas-liquid separation. The required blower configuration differs between positive-pressure and vacuum applications.
How is a roots blower used in soil vapor extraction? In an SVE system, the roots blower creates vacuum in the extraction manifold and draws contaminated soil gas from the unsaturated zone through extraction wells.
Before entering the blower, gas passes through branch piping, the main vacuum manifold, a moisture separator and a particle filter. Install vapor treatment downstream, and separate liquid and damaging particles upstream to protect the blower.
What contaminants can soil vapor extraction remove? SVE is generally most effective for contaminants that can transfer into the vapor phase.
Potentially suitable compounds include gasoline-related hydrocarbons; benzene, toluene, ethylbenzene and xylenes; selected chlorinated solvents; volatile organic compounds; and certain lighter fuel components. Suitability depends on volatility, soil adsorption, temperature, moisture and contaminant age.
Can SVE remove heavy metals? SVE does not normally remove heavy metals because they are not volatile under ordinary soil-remediation conditions.
Heavy-metal contamination generally requires another treatment method, such as excavation, stabilization, washing, chemical treatment or another site-specific process. A site containing both volatile organics and metals may require a combined remediation strategy.
Is maximum vacuum always better for SVE? No. Excessive vacuum does not always produce a proportional increase in useful soil airflow.
It can cause greater groundwater entry, increased condensate, surface-air short-circuiting, high blower temperature, increased energy consumption, and excessive treatment airflow. The appropriate vacuum is the level required to produce controlled airflow through the contaminated zone.
What is the difference between vacuum and airflow? Vacuum is the pressure difference that causes gas to move. Airflow is the volume of gas actually extracted.
High vacuum with low airflow can indicate low-permeability soil, wet soil, blocked well screen, closed valve, water-filled piping, and dirty filter. High airflow with low vacuum can indicate permeable soil, but it can also indicate atmospheric leakage or surface short-circuiting.
How is blower capacity determined for SVE? Base blower capacity on airflow from simultaneously active wells, required wellhead vacuum, manifold losses, separator and filter resistance, treatment-system resistance, site altitude, gas temperature and the required operating range. Pilot-test results provide the strongest preliminary basis.
Can the blower be selected according to the number of wells? No. Two sites with the same number of wells can require completely different blower capacities.
Well airflow depends on soil permeability, well depth, screen length, soil moisture, groundwater elevation, and pipe length. Performance also depends on valve setting and surface sealing. The design should use measured or reliably estimated airflow and vacuum for each operating zone.
What airflow reference should be used? State whether airflow is actual volume at the blower inlet, standard flow, normal flow or free-air flow. Report measured wellhead flow separately. Because an SVE blower inlet operates below atmospheric pressure, actual inlet volume can differ from equivalent standard volume; provide the pressure and temperature reference.
Can a standard positive-pressure roots blower be used for vacuum? Not automatically.
A blower model may be available in both configurations, but vacuum service requires verification of inlet and discharge pressures, pressure ratio, rotor clearances, shaft sealing and cooling. Selection must also account for lubrication, motor power and discharge temperature, and it should use approved vacuum-performance data.
Does a roots blower inject oil into the soil gas? A roots blower normally does not inject lubricant into the gas chamber. Bearings and timing gears still require lubricant, but seals separate these compartments from the transported gas. Maintain the complete system to prevent seal deterioration or lubricant migration. “Oil-free gas transport” does not mean that the blower package contains no oil.
Can a roots blower handle water? A standard roots blower should not handle groundwater, condensate slugs or free-phase liquid directly.
Liquid entry can cause rotor contact, mechanical overload, corrosion, bearing or seal damage, lubricant contamination, and serious blower failure. An SVE installation should include a correctly sized gas-liquid separator, demister and automatic high-level shutdown.
Can a roots blower be used for multi-phase extraction? It can be used conditionally on the separated vapor side.
In an MPE system, the extracted stream may contain soil gas, groundwater and free product. These phases must be separated before the vapor reaches a roots blower. A standard roots blower should not act as the direct pump for an untreated gas-liquid mixture.
If the MPE process requires direct liquid handling or very deep vacuum, another vacuum technology may be more appropriate.
Air Sparging and Biological Treatment
How does air sparging use a roots blower? In air sparging, a positive-pressure roots blower injects clean air below the groundwater table.
The blower must overcome groundwater hydrostatic resistance, formation-entry pressure, injection-well losses, pipeline and valve losses, and non-return valve resistance. Air sparging is often combined with SVE to capture volatile contaminants released into the unsaturated soil zone.
How is air-sparging pressure calculated? The required pressure is based on the complete system, including groundwater depth and the additional resistance required for air to enter and move through the soil. Groundwater depth alone is insufficient.
Pilot testing should determine formation-entry pressure, airflow at different pressures, radius and direction of influence, groundwater response, interaction with SVE, and maximum safe injection pressure.
What happens if air-sparging pressure is too high? Excessive pressure can cause uncontrolled subsurface airflow, groundwater displacement, vapor migration, formation fracturing, high blower temperature, and relief-valve operation. Possible consequences include excessive energy consumption. Pressure should be increased gradually and remain below the approved site and equipment limits.
What is the difference between air sparging and biosparging? Air sparging primarily emphasizes transferring volatile contaminants from groundwater into the gas phase, although biodegradation may also occur. Biosparging primarily supplies oxygen to support aerobic biodegradation in saturated soil and groundwater. The same equipment may support both mechanisms, but the airflow and monitoring strategy can differ.
What is bioventing? Bioventing supplies controlled air to the unsaturated soil zone to support microorganisms that degrade suitable organic contaminants. Unlike aggressive SVE, bioventing does not necessarily aim to maximize vapor extraction.
It may use low-rate air injection, low-rate vacuum extraction, combined injection and extraction, and pulsed operation. Oxygen, carbon dioxide, moisture and contaminant concentration should be monitored.
Does more airflow improve biological remediation? Not always. Once sufficient oxygen reaches the treatment zone, another factor may limit biological activity.
Possible limitations include nutrient deficiency, unsuitable pH, low temperature, excessive contaminant toxicity, insufficient or excessive moisture, and poor contaminant biodegradability. Increasing blower airflow cannot correct every biological limitation.
Why is pilot testing important? Pilot testing reveals how the actual site responds to applied vacuum or pressure.
A pilot test can measure airflow at several vacuum levels or injection pressures, formation-entry resistance, subsurface pressure response, well interaction and moisture carryover. Interpret the results alongside contaminant concentration and likely treatment coverage. Soil classification alone cannot provide all the information needed for blower selection.
What is the radius of influence? The radius of influence describes the area around an extraction or injection well where a measurable pressure response occurs. It is not necessarily circular and does not represent a sharp treatment boundary.
Its shape depends on soil layering, horizontal and vertical permeability, moisture, fractures, surface cover, and nearby wells. A measurable pressure response does not automatically demonstrate effective contaminant removal.
Why do different wells have different airflows? Each well has a different combination of soil permeability, screen depth, screen length, moisture, groundwater position, and branch resistance. Relevant design inputs include valve setting and contaminant condition. Air follows the easiest path. Individual well airflow and pressure should therefore be measured and balanced.
Should every well receive the same airflow? No. Equal airflow is not necessarily the correct objective.
A well serving a large or highly contaminated zone may require more capacity. Another well may operate mainly for containment or oxygen delivery.
Balancing should consider contaminant concentration, mass-removal rate, soil response, vapor capture, treatment priority and moisture carryover. Equal valve positions do not necessarily produce equal airflow, so adjust branches from measurements.
Wellfield Performance and Operating Control
Why does SVE airflow decrease after rainfall? Rainwater fills soil pores and reduces the air-filled space available for gas movement.
Rainfall can also raise the groundwater table, submerge well screens, increase condensate, create liquid blockage, and change surface-air entry. Airflow may recover as the soil dries, but groundwater and pipeline conditions should be checked.
Why does blower vacuum increase while airflow decreases? This combination usually indicates increasing system resistance.
Wet soil, blocked well screens, a dirty inlet filter, a water-filled manifold, closed branches or loaded treatment media can restrict airflow. Check the demister for blockage or liquid carryover, and identify the cause before increasing blower speed.
Why does the system show high airflow but remove little contaminant? Possible causes include atmospheric leakage, surface short-circuiting, airflow through clean soil, depletion near extraction wells, contamination in low-permeability layers, and low contaminant volatility. Possible consequences include remaining free-phase liquid. Airflow should be evaluated with contaminant concentration and mass-removal rate.
What is contaminant rebound? Rebound is an increase in contaminant concentration after extraction stops.
Contaminants can move back into soil gas through desorption from soil particles, diffusion from low-permeability layers, evaporation from residual liquid, and groundwater movement. Rebound testing helps determine whether contamination remains after the initial easily removable vapor has been extracted.
Can an SVE system operate intermittently? Yes, if site conditions and containment requirements allow it. Pulsed operation may improve efficiency when contaminant release is controlled by slow diffusion. The system can operate, stop for a defined period and restart after concentration rebounds. Continuous extraction may still be necessary near buildings or other sensitive receptors where vacuum provides vapor containment.
Why use a variable-frequency drive? A variable-frequency drive adjusts blower speed to match changing system demand.
It can support different numbers of active wells, constant manifold pressure, pulsed operation, seasonal changes, reduced treatment demand, and lower energy consumption. The blower must remain within its approved minimum and maximum speeds.
Can blower capacity be controlled by closing valves? Branch valves are necessary for wellfield balancing, but heavy throttling of every branch is inefficient.
Closing several branches while a positive-displacement blower remains at full speed can increase SVE vacuum, sparging pressure, motor power, discharge temperature, and relief-valve operation. Total capacity should preferably be controlled through blower speed, staged operation or another engineered method.
Equipment Protection and Vapor Treatment
What is the purpose of a vacuum-relief valve? A vacuum-relief valve protects an SVE blower by admitting controlled air if inlet vacuum becomes excessive. Excessive vacuum may result from closed wells, blocked filters or liquid-filled piping. The valve is a protective device. It should not remain continuously open as the normal capacity-control method.
What is the purpose of a pressure-relief valve? A pressure-relief valve protects an air-sparging blower if discharge pressure exceeds the approved limit. High pressure can result from blocked wells, closed valves or rising groundwater resistance. Continuous relief operation indicates a system or capacity-control problem.
Why is blower discharge temperature important? Discharge temperature from a roots blower increases with pressure ratio, speed and inlet temperature.
Excessive temperature can affect blower clearances, bearings and seals, lubricant life, flexible connectors, plastic piping and vapor-treatment equipment. The design should reflect the area’s hazardous-area classification. Monitor discharge temperature continuously in demanding or unattended installations.
Where should the moisture separator be installed? The main moisture separator should normally be installed upstream of the SVE blower. It should remove bulk liquid and include sufficient volume for normal condensate and credible water surges.
Protection may include demister, level indication, high-level alarm, independent high-high-level shutdown, automatic liquid transfer, and inspection and cleaning access.
Why does condensate collect in SVE pipelines? Humid soil gas condenses when it cools. Liquid also collects because of groundwater entry and rainfall infiltration. Pipelines should slope toward controlled drainage points. Unplanned low points can form liquid seals and block airflow.
What happens if the inlet filter becomes blocked? A blocked SVE inlet filter can cause higher blower vacuum, lower well airflow, higher discharge temperature, and increased energy consumption. A blocked air-sparging inlet filter can reduce available airflow and pressure. Filter differential pressure should be monitored.
How are extracted vapors treated? Possible treatment technologies include activated-carbon adsorption, thermal oxidation, catalytic oxidation, condensation, biological treatment, and chemical scrubbing, as well as combined treatment stages. Selection depends on contaminant type, concentration, gas flow, moisture and required treatment performance.
Does vapor-treatment equipment affect blower selection? Yes. Treatment-system pressure loss affects blower selection.
Design calculations should include pressure loss across carbon vessels, oxidation equipment, scrubbers, biofilters, condensers, flame arresters, final filters and the exhaust stack. Evaluate the system under both clean and maximum acceptable loaded conditions.
Can contaminated vapor be discharged without treatment? Extracted vapor should not be assumed suitable for direct atmospheric discharge. The required treatment and monitoring depend on contaminant composition, concentration, airflow and applicable site requirements. The purpose of SVE is not to transfer contamination from soil into uncontrolled air emissions.
Can SVE vapor be flammable? Yes. Petroleum hydrocarbons and solvents can form flammable mixtures with air.
Vapor concentration may be highest during initial startup, after rebound, when a new well opens, when air sparging begins, and when groundwater level changes. The gas, equipment location and treatment system require a site-specific safety assessment.
Is a suitably rated motor enough for a hazardous area? No. The complete package must be assessed.
The complete-package assessment should include the motor, instruments, switches, variable-frequency-drive location, valves and actuators, gas detectors, surface temperature, static grounding, ventilation, blower sealing and hazardous-area suitability. Motor rating alone does not establish package suitability.
Monitoring and Maintenance
What should be monitored during operation? A typical monitoring program tracks total and individual-well airflow, wellhead vacuum or injection pressure, blower inlet and discharge pressure, discharge temperature, motor current and speed. It may also include separator level, filter differential pressure, vapor concentration, contaminant mass-removal rate, groundwater level and treatment efficiency. Interpret these environmental measurements together with mechanical data.
How often should the blower be maintained? Maintenance intervals depend on operating hours, dust, moisture, gas composition, temperature and vibration. Follow the manufacturer’s instructions. Routine work may include oil inspection, belt or coupling checks, filter maintenance, vibration monitoring, seal inspection and protection-device testing. Contaminated equipment requires additional precautions before it is opened.
Blower Selection
What information is needed to select a roots blower? The technical enquiry should state the remediation process, required actual airflow, inlet and discharge pressures, minimum and maximum duty points, gas temperature, site altitude, gas composition, moisture and particle conditions, active-well count, treatment-system resistance, control method, electrical supply, hazardous-area requirements and expected operating hours. The supplier can then select the roots blower model, speed, motor power and package protection using verified performance data.
What is the most important principle in blower selection? The blower should be selected for the complete remediation system rather than one isolated value. Wells, soil resistance, groundwater, piping, separators, filters and vapor treatment all influence the final operating point.
A correctly selected roots blower provides the required airflow and pressure difference. Effective remediation still depends on directing that airflow through the contaminated zone and verifying the result through monitoring.
Glossary
Biosparging: Controlled air or oxygen injection in the saturated zone primarily to enhance aerobic biodegradation.
Bioventing: Controlled delivery or extraction of air in unsaturated soil primarily to support aerobic biodegradation.
Gas-Liquid Separator: A vessel that removes entrained or collected liquid from a gas stream before downstream equipment.
Multi-Phase Extraction: Simultaneous or coordinated recovery of soil gas, groundwater and potentially separate-phase product under vacuum.
Radius Of Influence: The observed distance over which a test well produces a measurable pressure or vacuum response.
Soil Vapor Extraction: A remediation process that applies vacuum to remove volatile contaminants as soil gas from the unsaturated zone.
Vapor Treatment: An aboveground process that captures, destroys or recovers contaminants from extracted soil gas before approved discharge.