Treatment and reuse of wastewater generated by fracking and oil extraction

• 1. What is fracking
• 2. Environmental risks derived from extraction using fracking technology
• 3. Composition of wastewater generated during fracking
• 4. Wastewater treatment resulting from fracking
• 5. DAF flotation treatment of fracking wastewater
• 6. Reuse of wastewater generated during fracking.
• 7. Summary

What is fracking?

Fracking , also known as “hydraulic fracturing,” is a method used to extract hydrocarbons from sedimentary soils .

Rocks retain methane in their pores due to their low permeability, allowing the formation of pockets of gas and hydrocarbons. To extract them, hundreds of wells are drilled, which can cover very large areas.

During fracking , a mixture of water, chemicals, and sand is injected into shale rock formations, with the goal of releasing the oil and gas trapped within the rock. Upon returning to the surface, this mixture carries away not only the hydrocarbons, but also the water originally present in the formation and a significant portion of the chemicals used in the process.

The wastewater generated in this process is typically stored in tanks or pits before being treated and disposed of, or reused for future fracking operations.

2. Environmental risks derived from extraction using fracking technology

Fracking involves several environmental risks:

• Drilling risks. During drilling to construct the wells, there are risks of explosions, gas and hydrogen sulfide leaks, and even rupture of the pipelines. If this were to happen, the contaminants that would be contributed to the ground would be highly toxic. Among these materials we can find heavy metals and even radioactive elements.
• Aquifer contamination. Approximately 200,000 m3 of water are used in a borehole, and chemicals are then injected, which can represent up to 2% of the water injected (4,000 tons). These significant pollutants must be treated before the water is returned to the environment.
• Air pollution. Some of the chemicals added to water are volatile and enter the atmosphere. During hydrocarbon extraction, there is a risk of emitting methane and nitrous gases into the atmosphere.
• Risk of seismic movements. Studies have shown that fracking increases the risk of earthquakes, especially if carried out near geological faults.                                          
• Environmental and landscape impact. The space required for drilling is very large (approx. 3 ^km2) and the wells operate for an average of 5 to 7 years.

3. Composition of wastewater generated during fracking.

A 2016 EPA report identified more than 1,600 chemicals in fracking wastewater, nearly 200 of which are considered carcinogenic or toxic to humans. The same report warned that fracking fluid could leak into these underground wells, which store millions of gallons of wastewater.

The composition of the wastewater generated during gas and oil extraction through fracking can vary depending on the geology of the area, the chemicals used in the process, and the quality of the water used. The most common contaminants are :

• High levels of salts and minerals such as calcium, magnesium, and sodium. Therefore, produced water may have high levels of total dissolved solids (TDS).
• Hydrocarbons such as benzene, toluene, ethylbenzene, and xylene (BTEX), which are toxic and carcinogenic, can seep into groundwater or surface water, contaminating drinking water sources.
• High levels of heavy metals such as arsenic, cadmium, chromium, lead, and mercury. These metals are toxic and can have serious consequences for human health, including neurological and kidney damage and cancer.
• They may contain naturally occurring radioactive materials such as radium, uranium and thorium, which are released from shale formations during the fracking process.

As mentioned above, fracking uses various chemicals such as surfactants, biocides, corrosion inhibitors and friction reducers, which may also remain present in wastewater. Some of these chemicals are toxic and affect health if ingested or inhaled.

Each stage of the fracking process contributes different contaminants to the formation of the final waste effluent.

Types of reagents	Application	Examples of reagents
Surfactants / wetting agents	Reduction of the surface tension of liquids, viscosity increases	Isopropanol
salt	Generates a brine carrier fluid	Potassium chloride
Gelato (gelling agent)	Improved proppant transport	Guar gum, Hydroxymethyl cellulose
Scale inhibitor	Prevention of poorly soluble precipitate deposition, antifreeze	Ethylene glycol
pH regulators	Maintains the effectiveness of other components	Sodium or Potassium Carbonate
Chain Braker (Breaker)	Reducing the viscosity of the gel-containing fluids to deposit the proppant	Ammonium Persulfate
Reticulant	Maintains fluid viscosity with temperature increases	Boron salts
Iron Ion Control	Preventing iron oxide precipitation	Citric Acid
Corrosion inhibitor	Prevents corrosion of pipelines	N, n Dimethylformamide
Biocide/Bactericide	Prevention of bacterial growth, prevention of bilayer, avoidance of hydrogen sulfide formation by sulfate-reducing bacteria	Glutaraldehyde
Acids	Cleaning of drilling parts and cement; resolution of acid-soluble minerals	Hydrochloric Acid or Muriatic Acid
Friction reducer (additives)	Reduced friction within the fluids allows the fracturing fluid to be pumped at faster rates and lower pressures	Polyacrylamide, Mineral Oil
Anti-Oxidant	Removes oxygen for corrosion protection	Ammonium Bisulfate
Supporting agents	Holds fractures open to allow gas to exit	Silica, Quartz Sand

In addition, high-temperature stabilizers are used to prevent premature decomposition of the gel; foams that facilitate the transport of proppants; and solvents that improve the solubility of additives and reduce corrosion of the system. Clay stabilizers are also used to minimize swelling and displacement.

4. Treatment of wastewater resulting from fracking

Fracking wastewater is difficult to manage. Its treatment involves multiple stages using different technologies to remove contaminants and bring the water within discharge limits.

One process that has proven highly effective for treating fracking water is the combination of electrocoagulation, chemical oxidation, and UV oxidation. This process breaks down the compounds into forms that can be subsequently removed by physical, chemical, and biological processes.

These are the different stages of the typical processes for the treatment of these discharges:

1. Chemical neutralization and coagulation.
2. Free oil separator / Precipitator
3. Electrocoagulation
4. Secondary coagulation/flocculation
5. Dissolved air flotation
6. Biological treatment and clarification/flotation
7. Advanced UV oxidation
8. Multiple filtration processes
9. Ultrafiltration

The combination of technologies and the design of the treatment plant vary depending on factors such as the composition of the wastewater and the regulatory requirements of the area.

Below is a standard process for treating fracking wastewater:

• Screening of wastewater to remove debris and large solids that could damage auxiliary equipment. During this stage, chemical treatment can also be performed to adjust the pH or remove specific contaminants.
• Dissolved air flotation can also be used in this pretreatment phase, or as a primary treatment. The purpose of DAF systems is to remove suspended solids, oils, and grease.
• There are other processes for the physical separation of solids and liquids, such as decanting, centrifugation or filtration.
• The selection of the most suitable advanced treatment depends on the objectives set by the customer and on the regulations in force in the territory where the oil and/or gas extraction is carried out. If the water is to be reused or if raw materials and by-products present in the wastewater are to be recovered, technologies such as vacuum evaporation, crystallization, reverse osmosis, membrane filtration, activated carbon adsorption or ion exchange must be used.
• Additional processes such as disinfection are used to eliminate any remaining microorganisms in the water before it is discharged or reused. This process involves the use of chemicals or other methods, such as UV rays or ozone.

5. Dissolved air flotation (DAF) treatment of wastewater from fracking.

DAF systems are used to separate suspended solids, oils, greases and lubricants, as well as some metals and suspended hydrocarbons .

Dissolved air flotation (DAF) is a process that involves introducing microbubbles of air into wastewater, which adhere to suspended solids and cause them to float to the surface for removal.

DAF technology is combined with a physicochemical physicochemical process that consists of adding a coagulant and flocculant to the wastewater to form larger particles that can be more easily separated from the water. to form larger particles that can be more easily separated from the water.

However, dissolved air flotation (DAF) is not sufficient to remove all contaminants present in fracking wastewater , so other technologies are necessary to achieve the legally required thresholds.

The selection of post-treatment processes will depend on the specific contaminants present in the wastewater and the regulatory requirements for the discharge or reuse of treated water.

The most common options are biological treatment followed by filtration technologies, such as reverse osmosis, or other advanced technologies, including concentration and evaporation processes.

6. Reuse of wastewater generated during fracking.

Reusing wastewater generated by fracking provides important benefits , such as:

• Reduction of water consumption.
• Reduction in the costs of sending wastewater to a waste management company.
• Lower environmental impact of fracking operations.

It is important to ensure that treated water meets regulatory requirements for reuse and does not pose any risk to human health or the environment.

Block diagram of fracking effluent treatment:

Wastewater generated by fracking can be reused in different areas:

• Reuse treated water as a base fluid in a subsequent fracking operation. Recycled water is typically treated with sedimentation, filtration, and disinfection to remove remaining contaminants.
• Irrigation of crops and vegetation by applying water directly to the soil or using it for sprinkler irrigation. However, it is important to ensure that irrigation water meets quality standards and does not contain contaminants that could harm crops or the soil.
• Treated water can also be used for industrial purposes, such as cooling water for power plants or as a source of process water for manufacturing operations.
• In some cases, fracking wastewater can be reused to recharge underground aquifers. To do this, treated water is injected into the ground to replenish depleted streams. However, this use requires careful monitoring to ensure that the treated water does not contain contaminants that could harm the aquifer or nearby groundwater sources.

7. Conclusion

The continued dependence on fossil fuels to meet global energy demand leads to the exploitation of natural deposits, which only allow the extraction of these hydrocarbons through processes such as fracking .

Fracking is a process with a significant environmental impact, both in terms of water consumption and the use of complex and aggressive reagents that are injected into the rocks.

SIGMADAF provides technologies for the treatment and recovery of wastewater generated during fracking, with the aim of mitigating the damage caused by these extraction systems to the environment.

Bibliographic references and consultations

• 2021RodriguezJemnifer.pdf (usta.edu.co) Adapted from Arnedo, A and Yunes, K, (2015, p.8).
• Fracking in the dark: Biological fallout of shale-gas production still largely unknown (Frontiers in Ecology and the Environment) | New research findings from Princeton University.