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  • Writer's pictureDavid Bennett

Understanding Sulfate-Oxidizing Bacteria (SOB):

Sulfate-oxidizing bacteria are a group of microorganisms that thrive in environments with high sulfate concentrations. They can be found in soil, groundwater, and other natural water sources. Unlike sulfate-reducing bacteria, which produce sulfide, SOB oxidize sulfide into sulfate as part of their metabolic process. While sulfate itself is not harmful, the activities of SOB can lead to various issues when they colonize wells.

Impact on Wells:

1. Corrosion: Sulfate-oxidizing bacteria indirectly contribute to corrosion by producing sulfuric acid as a metabolic byproduct. Sulfuric acid can lower the pH of the water, creating an acidic environment that accelerates the corrosion of metal components in the well infrastructure, such as pipes, pumps, and casings. Corrosion weakens the well structure, increases the risk of leaks, and may require costly repairs or replacements.

2. Scaling: SOB can promote the formation of mineral scales, particularly calcium sulfate (gypsum) and calcium carbonate (calcite), in wells. These scales can accumulate on the well surfaces, screens, and pumps, reducing the diameter of the well and obstructing water flow. Scaling diminishes the well's performance, leading to decreased water yield and increased energy consumption for pumping.

3. Decreased Well Performance: The combined effects of corrosion and scaling caused by SOB can significantly impact the overall performance of wells. Corroded or scaled components restrict water flow, leading to decreased well yield and reduced efficiency. This can result in insufficient water supply for various applications and necessitate costly measures to restore the well's functionality.

4. Water Quality Issues: SOB activity can compromise the quality of well water. The presence of sulfuric acid can lower the pH of the water, making it more corrosive and potentially harmful. Additionally, the accumulation of mineral scales may harbor other bacteria, affecting the microbial quality of the water and potentially causing health concerns.

Mitigation Strategies:

1. Well Maintenance and Monitoring: Regular well inspection and maintenance are crucial to detect early signs of SOB colonization. Monitoring parameters such as pH, sulfate levels, and corrosion indicators can help identify potential issues and initiate appropriate mitigation measures.

2. pH Control: Adjusting the pH of the well water to a neutral or slightly alkaline range can help inhibit the growth of SOB. This can be achieved through the addition of alkaline substances, such as lime or soda ash, to counteract the acidity caused by sulfuric acid production.

3. Chemical Treatment: Application of chemical inhibitors, such as biocides and scale inhibitors, can help control the growth of SOB and prevent scaling in wells. Biocides can target and kill bacteria, while scale inhibitors can disrupt scale formation and reduce the potential for mineral deposition. This is often done with a BoreSaver ionic shock treatment.

4. Physical Cleaning and Rehabilitation: Mechanical cleaning methods, such as brushing, jetting, or acid treatments, can help remove mineral scales and biofilms from well components. These techniques can restore well performance, improve water flow, and mitigate the negative impacts of SOB colonization.

5. Well Design Considerations: Implementing appropriate well design features, such as corrosion-resistant materials, protective coatings, and effective well seals, can help minimize the entry of SOB into wells. Proper construction practices can reduce the potential for bacterial colonization and mitigate associated issues.


Sulfate-oxidizing bacteria can pose significant challenges to the integrity and performance of wells. Corrosion, scaling, decreased well performance, and compromised water quality are among the potential consequences of SOB colonization. It is crucial for well owners and operators to be aware of these issues and implement proactive measures to mitigate the effects of SOB. Regular monitoring, pH control, chemical treatments, physical cleaning, and proper well design are key strategies to control SOB and ensure the longevity and reliability of wells, providing safe and high-quality water resources for various purposes.

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