Deaerator Tower: A perfect breeding ground for Microbes?

24 Nov 2025

How microbes affect the efficiency of a DA Tower and can cause its downfall.

In oil production, the natural pressure within a reservoir declines over time, affecting the efficiency to extract crude oil.  A common practice to overcome this is to use secondary recovery methods, such as water injection, to maintain reservoir pressure.  However, the water must be treated before subsurface injection to remove impurities that could damage the topside systems or the reservoir itself. A critical component of a water injection system is the deaerator (DA) tower, which removes dissolved gases, primarily oxygen (O₂) from the injection water.

While oxygen is a primary driver of corrosion, it also significantly influences the growth of certain microorganisms, dependent on its availability. In DA towers, the removal of dissolved oxygen creates an anoxic environment that promotes the proliferation of anaerobic bacteria such as sulphate-reducing bacteria (SRBs) and iron-reducing bacteria (IRB). These microbes can cause serious issues, including reservoir souring, biofilm formation, and corrosion, all of which can jeopardize oil recovery operations. Therefore, understanding the behaviour and impact of these microorganisms is essential for optimizing production processes and ensuring the long-term integrity of the system.

Function of DA Towers

A DA tower is a large vertical vessel designed to remove dissolved gases, particularly oxygen, from injection water. This is crucial because carbon steel, commonly used in high-pressure water injection pipelines, is highly susceptible to oxygen-induced corrosion. The tower typically contains internal packing material that enhances contact between the downward-flowing water and an upward-flowing stripping gas (usually natural gas or steam), allowing oxygen to be stripped from the water. An alternative, though less common, method is vacuum degassing, where the internal pressure is reduced below atmospheric levels, lowering the solubility of oxygen and allowing it to be released as a gas. Furthermore, in order to remove any residual oxygen downstream of the DA, an oxygen scavenger, usually ammonium bisulphite or sodium bisulphite is added.  The treated (deaerated) water is then collected, either at the bottom of the tower or in residence tanks downstream of the DA tower, ready for injection into the reservoir.  

Microbes in DA Towers

Interestingly, the very design features that make a DA tower efficient at removing dissolved gases, such as maximizing liquid-to-gas contact surface area, can also inadvertently create an ideal environment for anaerobic bacterial growth. Many DA configurations provide favourable conditions for sulphate-reducing bacteria (SRB), especially where sulphate-rich seawater is used, and effectively function as unintentional fermentors. These bacteria thrive in oxygen-depleted environments, and the combination of degassing, and the addition of oxygen scavengers (such as ammonium or sodium bisulphite) ensures that conditions within the tower are highly anaerobic.

Moreover, some oxygen scavengers themselves can act as alternative terminal electron acceptors in microbial respiration which may be metabolically advantageous. For example, some SRBs are capable of reducing bisulphite, which bypasses the energy-intensive activation of sulphate (SO₄²⁻) to adenosine phosphosulphate (APS)—a key step in the microbial sulphate reduction pathway. This makes the environment not only suitable but energetically favourable for SRB metabolism and proliferation.

Environmental conditions within the DA further support rapid microbial growth. Usually, water is heated to approximately 30°C to enhance oxygen removal which can accelerate bacterial metabolism. Where gas stripping is used and seawater is degassed using produced hydrocarbon gases, the release of CO₂ and other acidic gases causes a decrease in pH that can further stimulate bacterial growth. Additionally, the use of produced gas may unintentionally enrich the water with trace hydrocarbons or other nutrient compounds, enhancing the nutrient profile and promoting microbial colonization.

In summary, while DA towers are critical for oxygen removal in water injection systems, their design and operating conditions can inadvertently encourage and support the growth of problematic anaerobic microbes, particularly SRBs. As such, proactive microbial control measures are necessary to maintain system integrity and prevent issues such as:

• Biofilm formation within the DA tower: Microorganisms can colonize the packing material reducing oxygen removal efficiency and risking blockages (see images).
• Downstream effects: Microbes leaving the deaerator DA can contribute to reservoir souring and microbially influenced corrosion (MIC).

In short, if not properly maintained, the DA tower can become breeding grounds for microorganisms that can cause multiple problems.

How to Keep Your DA Tower Microbe-free

Preventing microbial growth in your DA tower starts before the water even gets there. Upstream filtration (to remove solids which microbes can utilise) and pre-treatment (such as chlorination of source water) helps reduce the number of microbes entering the system. It is also beneficial to apply a fast-acting oxidising biocide throughout the process to prevent bacteria colonisation.  Once the water enters the DA the addition of an organic biocide (such as THPS) can provide added protection. The choice of chlorination mechanisms and type of biocide depends on the system, e.g. pipe material, fluid make-up, system setup, and environmental conditions and will need to be chosen accordingly.

Ready to Take a Closer Look at Your DA Tower?

If it’s been a while since your last system survey, or if microbial issues are already creeping in, it might be time to audit your water injection setup. A few proactive steps today can prevent costly problems tomorrow, from reservoir souring to equipment failure. Need help evaluating your system or setting up a microbial control program? Get in touch with our team, we’re here to help you keep your operations running clean, safe, and efficient.

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