How To Treat Shale Gas Wastewater

The treatment of shale gas fracturing flowback fluid wastewater is a complex and critical process aimed at reducing environmental pollution, protecting water resources and realizing the resource utilization of wastewater.

In the process of shale gas fracturing flowback fluid treatment, MVR evaporation technology introduces wastewater into the evaporator and uses heat energy to evaporate the water in the wastewater, thereby reducing the amount of wastewater. At the same time, due to the crystallization of salt in the wastewater during the evaporation process, the useful components in the wastewater can be separated and recovered, thereby realizing the resource utilization of wastewater. Weishengda’s environmentally friendly and efficient high-salt mother liquor drying technology can not only efficiently treat wastewater, but also reduce the cost of wastewater treatment.

Characteristics of fracturing flowback fluid wastewater
Shale gas fracturing flowback fluid wastewater has the following main characteristics:

• High salinity: Due to the minerals dissolved or carried out in the formation, the salt content in the wastewater is high.
• High organic matter content: Contains fracturing fluid additives (such as guar gum, organic boron cross-linking agent, gel breaker, etc.) and natural organic matter in the formation.
• High suspended matter content: The amount of suspended matter is high at the initial discharge, but it gradually decreases as the backflow proceeds.
• Heavy metals and radioactive substances: In rare cases, it may contain heavy metals and naturally occurring radioactive substances.

Treatment process flow
The process flow of shale gas fracturing backflow fluid wastewater treatment usually includes the following steps:

1. Pretreatment
Purpose: Remove large suspended matter, some organic matter and heavy metals in the wastewater.

Method: Use cyclone, flotation, flocculation precipitation, agent softening and filtration and other technologies. For example, pretreat wastewater by electroflocculation, composite alkali method to soften water quality, breakpoint method to remove ammonia nitrogen and other methods.

2. Desalination treatment
Purpose: Reduce the salt content in wastewater to meet subsequent treatment or discharge standards.

Method: Use deep treatment processes such as four-effect evaporation desalination. These methods can effectively remove salt and heavy metal ions in wastewater, reduce its conductivity and total dissolved solids content.

3. Deep treatment
Purpose: Further remove organic matter, heavy metals and other pollutants in wastewater.

Method: Use activated carbon adsorption, membrane separation and other technologies. These technologies have the advantages of high efficiency, stability, and easy automatic control, which can significantly improve the wastewater treatment effect.

4. Resource utilization
Purpose: To realize the resource utilization of wastewater, reduce treatment costs and reduce environmental pollution.

Method: The water in the wastewater is evaporated by vacuum evaporation experiment, and the condensed water obtained can meet the discharge requirements; the crystallized salt after evaporation and crystallization meets the secondary requirements of industrial salt and can be used in chemical production and other fields.

5. Final treatment and discharge
Purpose: To ensure that the treated wastewater meets the discharge standards and is safely discharged or reused.

Method: The treated wastewater is tested to ensure that all its indicators meet the first-level standards of the comprehensive sewage discharge standard. In some areas or specific cases, more stringent purification treatment may be required to meet more stringent discharge standards or reuse requirements.

Technical challenges and solutions
In the treatment of shale gas fracturing flowback wastewater, the main technical challenges faced include complex wastewater composition, difficulty in treatment and high treatment costs. In response to these challenges, the following solutions can be adopted:

Develop efficient treatment technologies: such as developing new desalination technologies, optimizing deep treatment processes, etc., to improve treatment efficiency and reduce treatment costs.

Realize wastewater resource utilization: Through resource utilization technology, wastewater is converted into valuable resources, such as industrial salt, to reduce treatment costs and achieve economic benefits.

Fracturing flowback fluid external discharge treatment technology
The standard external discharge treatment technology must include the removal of SS, oil, COD, ammonia nitrogen, hardness and TDS, and the difficulty and focus is to separate high TDS from water to meet the external discharge standards.

According to the external discharge standards, external discharge treatment includes flotation, catalytic oxidation, softening precipitation, ultrafiltration, concentration, evaporation crystallization and deep treatment. This process can not only meet the external discharge standards, but also extract NaCl in the flowback fluid as a product. The separated NaCl can be used as a chemical raw material and livestock salt, achieving the purpose of valuable material resource utilization. The deep treatment device in the standard discharge process is mainly added for non-compliance caused by different membrane concentration processes or different evaporation conditions, but different deep treatment devices need to be set according to different water qualities. If an electrodialysis device is used, a fresh water COD removal device needs to be added; if evaporation crystals evaporate under alkaline conditions, ammonia nitrogen enters the condensed water, and an ammonia nitrogen removal device needs to be added. Since the standard for the discharge of fracturing return fluid is high, the treatment process is more complicated and the process is longer, it is advisable to collect the return fluid and build a sewage plant for centralized treatment.