Microscopic view of Bacillus biofilm on a water filtration membrane.

Battling Biofilms: How to Protect Your Water Systems from Bacterial Invaders

Kai Mendoza in Science & Nature September 2025 • 4 min read.

"Learn how chlorine-resistant Bacillus species impact membrane biofouling and what you can do to maintain clean and efficient water systems."

Biofouling is a widespread problem across numerous industries, from water treatment and desalination plants to marine and medical environments. It occurs when microorganisms, such as bacteria, algae, and fungi, attach to surfaces and form complex communities known as biofilms. These biofilms can cause a range of issues, including reduced efficiency, increased energy consumption, equipment damage, and even health risks.

One of the major concerns in water treatment is membrane biofouling, where biofilms develop on the surfaces of filtration membranes, hindering their performance. This can lead to decreased water flow, increased pressure, and the need for more frequent cleaning or replacement of membranes. Traditional methods of controlling biofouling often involve the use of chlorine and other disinfectants. However, some bacteria have developed resistance to these chemicals, making it even more difficult to manage biofilm formation.

Recent research has shed light on the role of chlorine-resistant bacteria, particularly Bacillus species, in membrane biofouling. These bacteria can survive and thrive in chlorinated environments, contributing to the development of persistent biofilms that are difficult to eradicate. Understanding the mechanisms by which these bacteria resist chlorine and form biofilms is crucial for developing effective strategies to combat biofouling and ensure the efficient and safe operation of water systems.

Understanding Chlorine Resistance in Bacillus Species

Microscopic view of Bacillus biofilm on a water filtration membrane.

Bacillus species are commonly found in various environments, including soil, water, and air. Their ability to form spores allows them to survive harsh conditions, such as high temperatures, desiccation, and exposure to disinfectants. Some Bacillus species have developed specific mechanisms to resist the effects of chlorine, including:

Here are some of the protective mechanisms:

Enzyme Production: Certain Bacillus strains produce enzymes that can neutralize or degrade chlorine, reducing its effectiveness.
Cell Wall Modifications: Changes in the cell wall structure can make it more difficult for chlorine to penetrate and damage the bacterial cells.
Biofilm Formation: Biofilms provide a protective barrier that shields bacteria from the harmful effects of chlorine. The extracellular matrix of the biofilm can bind to chlorine, preventing it from reaching the bacteria within.

A recent study published in "Biofouling" investigated the impact of feedwater chlorination on membrane biofouling caused by chlorine-resistant Bacillus species. The researchers found that even low levels of chlorine can promote the attachment and biofilm formation of certain Bacillus strains, leading to increased membrane fouling. This highlights the need for a more nuanced approach to biofouling control that considers the specific characteristics of the microbial community present in the water system.

Strategies for Combating Biofouling

While chlorine remains a widely used disinfectant, it is clear that relying solely on chlorination is not always sufficient to control biofouling, particularly in systems where chlorine-resistant bacteria are present. A multi-faceted approach is needed, incorporating a combination of physical, chemical, and biological methods. Some potential strategies include:

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Everything You Need To Know

What is biofouling and why is it a problem?

Biofouling is the undesirable accumulation of microorganisms on surfaces. This is significant because it leads to many problems, including reduced efficiency of industrial processes, increased energy consumption, equipment damage, and potential health risks. In water treatment, membrane biofouling, specifically, decreases water flow, increases pressure, and necessitates more frequent membrane cleaning or replacement. Biofouling is relevant to many industries, ranging from water treatment plants to marine and medical environments.

How do Bacillus species resist chlorine?

Chlorine resistance in Bacillus species arises from several protective mechanisms. These include the production of enzymes that neutralize chlorine, modifications to the cell wall that prevent chlorine penetration, and the formation of biofilms that shield bacteria from chlorine's harmful effects. Spore formation also allows them to survive harsh conditions, such as high temperatures, desiccation, and exposure to disinfectants. The biofilm's extracellular matrix binds to chlorine, stopping it from reaching the bacteria within.

What is membrane biofouling and how is it usually controlled?

Membrane biofouling refers to the development of biofilms on the surfaces of filtration membranes. This is a problem because it hinders the performance of the membranes, leading to decreased water flow and increased pressure. Controlling membrane biofouling typically relies on chlorine and other disinfectants. Traditional chlorination isn't always effective because some bacteria, like Bacillus species, are chlorine-resistant and can still develop persistent biofilms.

Why isn't chlorine always effective against biofouling?

Chlorine, while widely used, may not always be sufficient for controlling biofouling, particularly where chlorine-resistant bacteria are present. This is because some bacteria, like Bacillus species, have developed mechanisms to survive and thrive even in chlorinated environments. A multi-faceted approach, incorporating physical, chemical, and biological methods, is needed to combat biofouling effectively. Relying solely on chlorine can lead to persistent biofilms and continued operational issues.

What mechanisms do Bacillus species use to resist chlorine?

Bacillus species can resist chlorine through several mechanisms. They produce enzymes to neutralize chlorine, modify their cell walls to prevent chlorine penetration, and form biofilms that act as protective barriers. The ability to form spores also makes them very resilient. Understanding these mechanisms is crucial for developing effective strategies to combat biofouling, particularly in water systems where these bacteria are present.