Sulphur Oxidizing Bacteria: The Cause of Fast Corrosion Processes

How to prevent problems from SOB’s

Sulpher oxidizing bacteria are a type of microorganism that can cause severe corrosion damage to various types of materials. In this post, we will explain what these bacteria are, and how they trigger fast corrosion processes. If you are concerned about the possibility of your business being impacted by Sulpher oxidizing bacteria, make sure to read this post!

Sulpher oxidizing bacteria are a type of microorganism that thrive in environments with high levels of sulphur. These bacteria are able to convert sulphur into sulphuric acid, which is a very corrosive substance. When sulphuric acid comes into contact with metal surfaces, it can cause them to corrode very quickly.

There are a few different ways in which Sulpher oxidizing bacteria can cause problems for industrial assets. Firstly, they can cause severe damage to metal surfaces, leading to the need for expensive repairs or replacements. Secondly, they can clog pipes and other water-based systems, causing them to malfunction. Finally, Sulpher oxidizing bacteria can produce unpleasant odours, which can be very off-putting for workers or the direct environement of the assets.

If you think that your business may be at risk of sulpher oxidizing bacteria, there are a few things you can do to protect yourself. Firstly, you should make sure that all metal surfaces are clean and free of sulphur. Secondly, you should install Sulphur filters in your water-based systems to prevent the bacteria from causing damage. Finally, you should keep an eye out for any signs of corrosion or clogging, and act quickly to fix any problems.

For some systems, sulpher is just instrinsically present. Read further to learn more about this group of organisms.

What are SOB’s Sulpher oxidizing bacteria?

First of all, the metabolic end product of SRB’s is (hydrogen)sulphide, this a toxic and even harms the SRB that produces it. But this is the starting point for Sulpher oxidizing bacteria. Opposite to sulpher reducing bacteria, SOBs usually live in environments where oxygen is present. An important subdivision here, however, is that these can also be systems that are predominantly oxygen-free, but contain small bits of oxygen

SOB’s can be catagorized into two different groups:

  • phototrophic, and
  • chemolithotroph

Phototropic SOB’s

Phototrophic SOB’s are using a similar energy conversion process like plants, they both use light as energy source for their metabolism. The basic mechanism is that during their metabolism sulphide is oxidized and carbon dioxide is fixed. The underlying process is also known as the reversed kerbs cycle. While in the usual kerbs cycle, carbohydrates are used for energy conversion (it is then a starting point), within the reversed kerbs cycle it is the end stage of the metabolic process.

Figure 1: reversed kerbs cycle (source: Wikipedia)

The SOBs are phototropic, meaning they require light for their metabolism and can’t live in environments without any. This also means that other forms of EMIC like nanowires or outer membrane cytochromes won’t be expressed by them either since these types of metabolic processes do not produce energy through photosynthesis but instead rely on food sources such as glucose solutions found within cells which produces hydrogen gas when cleaved apart during cellular respiration – one way your body gets rid off toxins! It’s been shown though there may still exist some type-II

Chemolithotrophic SOB’s

Chemolithotrophic SOB’s, also known a colorless bacteria that cannot be effectively grouped. Despite this fact three subcategories exist:

  • obligate chemolithotrophs (OCL),
  • facultative chemolithotrophs (FCL) and
  • chemolithoheterotrophs (CLH)

SOB’s that can be catagorized under obligate chemolithicorganisms (OCL)

Obligate Chemolithotrophs (OCL) fixate carbon dioxide by using the Calvin–Benson–Bassham (CBB) cycle . It’s is known from scientific studies that the metabolism of such a bacteria could extract the sulphur compounds out of crude oil for its metabolism. And secandary that SOB’s can use nitrate as an electron acceptor and sulphate as its end product.

It is then not a suprise that these SOB’s are are commonly found together with SRB’s living in cocultures in a symbiosis manner by continuously cycling sulphur

The discovery of a new enzyme capable to convert metal ions into hydrogen has opened up an entirely different way for how these bacteria work. This phototropic SOB is not limited in its ability when it comes down converting sulphur-based compounds, but can also use other organic molecules as electron donors such like sugars and lipids. The production rates are generally low due mainly because most microbes require very precise conditions which aren’t always met inside living cells. There’s still much debate going on about what exactly causes corrosion damage within environments – some believe it could even come from something else altogether!

SOB’s that can be catagorized under Facultative chemolithicorganisms (FCL)

FCL can use organic substrates, but they also have the ability to function with just OCL. Though, depending on the species, they employed different metabolisms. Some will be examined closer in relation to corrosion mechanisms. The final group is CLH and though they are not as common , very little is known about them compared to other two groups. Arcobacter peruensis is a new species discovered in recent years via this mechanism. They named the microbe Arcobacter peruensis after discovering that it thrived best in a medium that combined sulphide and organic matter. Although, it could also grow without sulphide, albeit very slowly, thus suggesting it isn’t completely in line with the metabolism grouped under chemolithoheterotrophs (CLH).

The study also found that when sulphide was absent from the environment, Arcobacter peruensis metabolism changed and it began to consume alternative fuels such as glucose, acetate, pyruvate, malate and glutamate for energy.

SOB’s that can be catagorized under chemolithoheterotrophs (CLH)

Chemotrophs are micro-organisms that obtain their energy from oxidizing reduced compounds. The substrates chemotrophs use can either be organic or inorganic. Also, depending on the carbon source, chemotrophs can be split into two more categories: chemoautotrophs and chemoheterotrops.

Chemoheterotrophs, on the other hand, use lower organic compounds as a source of energy and carbon. Heterotrophs are usually known as chemoheterotrophs despite the fact that the term only refers to the carbon source since, strictly speaking, chemoautotrophs consume inorganic forms of energy and rely on reduced organic chemicals as their carbon source. Chemoolithoheterotrophs are a type of chemotropHybrids between autotrophic organisms and heterotrophic ones.

Sulpher Oxidizing micro-organisms and their mechanism to corrode metals

There are quite a number of mechanisms. Scientists have multiple theories about how SOB’s contribute to corrosion processes, the metabolic production of sulfuric acid and their special relationship with SRB. However, a recent discovery revealed that some phototropic SOB are capable to excrete a hydrogenase that directly oxidizes metals .

This enzyme absorbs electrons, which are then utilized to make hydrogen. Phototropic SOB do not just use sulphide as an electron donor; most of them can also consume hydrogen. Because these extracellular enzymes are often extremely complex, they can remain active for months. The phototropic SOBs, because they need light for their metabolism, are rarely found in the gas/oil sector. Although outer membrane cytochromes do not express EMIC, nanowires or outer membrane cytochromes can transport electrons to a cathode.

There is no indication that it promotes corrosion in any way. The majority of the research on corrosion by SOB has been devoted to their interactions with concrete. This is due to the fact that sulfuric acid is very effective in corroding concrete. The actual process is quite complicated, but it is thought to be a two-step process. Hydrogen ions (H+), which are present in large amounts, dissolve calcium hydroxide (Ca(OH)2) to create calcium ions and water. Subsequently, the calcium ions react with the sulphate to form mainly gypsum (CaSO4·2H2O) and ettringite (3CaO·Al2O·3CaSO4·32H2O).  Both products lack structural integrity and, more significantly, contain a greater amount. This leads to an increase in internal pressure, which diminishes the concrete matrix’s structural integrity even further. Corrosion of concrete is a significant concern in sewage systems. SOB thrive in these environments, but which species do so is largely determined by the pH value.

SOB’s and degradation of concrete sewer systems

The most research in the corrosion by SOB has gone into their interactions with concrete. This is due to sulfuric acid being incredibly effective at corroding concrete, and it’s believed that there are two steps involved: first hydroxides from calcium carbonate react with hydrogen ions on site; then these combine together through a chemical reaction resulting mostly out of gypsum. It can be difficult for scientists studying this process because they do not know exactly how or why certain things happen.

The pH of on the surface a fresh part of concrete is generally around 12-13. This means that some calcium hydroxide, which acts as a strong base and dissolves in water during its creation will slowly decrease due to buffer working of environment carbon dioxide (CO2). As this occurs there are two types species ASOBs or NSOBs who thrive within these environments with one group being more acidophilic while another has higher levels metal ions like iron causing them be less degraded over time under high concentrations – thus having greater potential for corrosion than others nearby!

To elaborate in more detail about these mechanisms. SOB in sewers are classified as acidophilic sulphur-oxidising bacteria (ASOB) and neutrophilic sulphur-oxidising bacteria (NSOB). The pH of fresh concrete is usually around 12-13. This is because some calcium hydroxide, which is a strong base, dissolves in water 114. After the initial peak, the pH will slowly decrease due to buffer working of atmospheric dissolved carbon dioxide (CO2).

Ones the surface pH reaches 9 NSOB will start colonizing the surface of the sewers. These do not attach directly to concrete but to the condensate layer that has formed just above it. In this layer, this hydrogen sulphide accumulates which further decreases the pH. The hydrogen sulphide is produced by SRB living in sewers. The hydrogen sulphide is converted to sulfuric acid which lowers the pH even further. One study placed 60 concrete coupons in an active sewer for one year. They observed that the surface pH started at 12 but after 100 days it had reached 1,6. This rapid change in pH also has great influence in which bacteria can grow. The NSOB will be succeeded by the ASOB as they thrive in an acid environment.

They can stimulate the development of SRB in two ways: by removing dissolved oxygen and secondly, by cycling sulphide. Oxygen is one of the most damaging elements to SRB because it significantly inhibits reproduction. However, they may endure oxygen exposure and even utilize it as an electron acceptor for their metabolism. Oxygen, on the other hand, is hazardous to SOBs but fortunate SOBs do use oxygen for oxidation since their electron acceptor. This is beneficial for the SOB since they rely on SRB for their sulfide supply.

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