Biofilm on sensor

Biofilm growing on a BioSense sensor

The BioSense biofilm sensors are available with different controllers to give you the same great performance with different communication, display, and control options. With the BioSense range of biofilm analyzers, you get everything that you need – and nothing that you don’t.

The BioSense sensor was developed to provide on-line and real-time indication of biofilm activity in cooling towers, hospital water systems, pools, and spas, in fact anywhere biofilm cover grows. The probe is designed and operated so that microorganisms in the environment will settle on probe surfaces before they settle on vessel walls or piping. This gives an early warning of potentially dangerous biological activity in the process. By closely tracking biofilm activity on the probe, the BioSense can take remedial action such as increasing the dosing of a biocide or dispersant. The BioSense biofilm controller can also be used to assess the effectiveness of a treatment, or to schedule maintenance activities. By monitoring biofilm activity on surfaces, costly over-treatment can be avoided and chemical treatments can be optimized.

The controller applies a potential between the probe electrodes that encourages microorganisms to settle or adhere or grow on the surface of the probe before they would settle on the surfaces of a pipe or a vessel. The biological activity of the biofilm creates a signal. A BioSense controller collects and monitors that signal continually. An increasing trend in the signal indicates the onset of biofilm activity on the probe.

The controller can then take remedial action automatically by, for example, increasing or decreasing the biocide levels. The CRONOS BioSense is a simple controller capable of automatically changing, dosing regimes etc. With the more sophisticated CRIUS® and CRATOS controllers providing, data logging, remote access and control via GSM.

Cooling towers systems, cooling and heating systems in e.g. hospitals, airports, government buildings, hotels and very large office blocks can be a source of the Legionella or Pseudomonas bacterium. The bacteria often grow in biofilms that adhere to the walls of a pipe or other vessel. The BioSense sensor allows you to monitor for the development of this biofilm buildup and dose the appropriate chemical to reduce and disperse the biofilm prior to building up a dangerous level of Legionella.

Measuring the residual biocide in a body of water only tells half the story. It tells you that there is little or no biological activity in the bulk water. This doesn’t necessarily mean that biofilm isn’t building up on the walls of pipes and vessels with the possibility of the development of harmful bacterial colonies. The BioSense allows you to monitor the build up of that biofilm and in turn take the appropriate action AUTOMATICALLY to return the system to a clean condition. This could be as simple as triggering an alarm for a manual intervention or as complex as increasing biocide levels or shock dosing, all controlled by the BioSense controllers. The BioSense gives you:

  • Control of system surface biological activity
  • Treatment effectiveness monitoring
  • Biocide program optimization
  • Indication of a “clean” state

Remote Access Control

The Process Instruments CRIUS & CRATOS controllers can provide as an option, remote access via LAN or GPRS modem. This capability is unique in that it

  • provides two way communications allowing not just the downloading of data but the uploading of new settings, set-points, PID controls, etc.
  • provides peer to peer communication so the controller talks directly to the internet, there is no web site in the middle to have to log on to.
  • email alarms and daily emails can be sent to up to 5 email addresses. The daily email has the previous 24 hours data attached, so you need never download data again, it just arrives in your in-box.

Pi provides a live demonstration of this capability. Click here to view it.


What is Biofilm?
A biofilm is a matrix on natural or man made surfaces that is made up of a group of microorganisms. These microorganisms are often embedded in a matrix of self produced extracellular polymeric substances (EPS) or slime.

The cells growing in a biofilm are different from the cells of the same species in the water which are often planktonic or free floating.

Why do biofilm form?
The cells of a species that makes up a biofilm undergo a phenotypic shift in which large suites
of genes are differentially regulated. Put simply the behaviour of the cells change when they are in a biofilm versus when they are planktonic. Forming a biofilm can give the cells an advantage over their planktonic existence in that they can alter the environment; for example, the pH, the chemical make up of the water, and they can be protected from biocides by the ‘slime’.

Biofilm formation can be triggered by many things but they often form when they are in a ‘lean’ environment i.e. an environment where they are under attack or where nutrients and other resources are low.

What can BioSense tell me?
The BioSense measures the electricity generated by biofilm growing on its surface. It also provides a preferential site for biofilm growth. In effect the BioSense provides a landing site for adherent cells, and an electrically stimulating environment to give any biofilm the best chance of survival. If a biofilm can grow in a water system then it will grow on the BioSense. BioSense tells you when the conditions in your water system are changing in a way that can support Biofilm growth. This may be from a system with no biofilm growth to some biofilm growth (eg. a hospital water system) or may be a cooling tower going from some biofilm growth to more biofilm growth.

What can’t the BioSense tell me?

  • There is no correlation between planktonic counts and the outputs from a BioSense.
  • There is no correlation between biofilm thickness and the BioSense. The BioSense measures the biological electrical activity of the Biofilm not the thickness.
  • The BioSense can’t differentiate species.

Can I test the BioSense in the lab?
Generally people don’t have a lot of success in the lab, which is extremely predictable. A biofilm tends to form in ‘lean’ conditions when a biofilm gives it a survival advantage. In a lab, biofilms tend not to be the same as in the field in that they are monocultural, they are induced and generally they are fed. Lab biofilms are normally non representative of a field biofilm and so the BioSense doesn’t give the biofilm an advantage and so the results are often poor as opposed to the results from field tests.

If I am worried about Legionella and Legionnaires’ disease how can the BioSense help me?
Legionnaires’ disease is caused by the incubation of Legionella bacteria which have often grown in biofilm where they are protected from disinfectants. The BioSense can tell you if you have biofilm growing in your water system and is a great tool in the fight against Legionnaires’.


Focus Ons are a series of short articles distributed by email providing technical information regarding instrumentation, process measurement in potable, waste, process and pool waters. If you would like to join the mailing list, please contact us.

1. Did you know that Biofilm in any water system is a source of bacterial infection (legionella), a cause of corrosion and a cause of heat loss?

You probably did!

2. But did you know that there is now a low cost way of online monitoring for the growth of biofilm?

You probably didn’t!


1. Biofilms (slime) can grow in any water system, but are more likely to grow in those systems that are humid, aerated, circulating and with a source of nutrients. When a biofilm grows it can create a very localized environment that may have very different conditions from the ‘bulk’ recirculating water. It is the ability of biofilms to form micro-environments that means that they are often associated with corrosion and scale formation. Biofilms are made up of free floating microorganisms that weakly adhere (fix) themselves to a surface. If they aren’t immediately separated from the surface, they can bind more strongly to the surface, allowing further species to attach and colonize (grow) into a biofilm. This biofilm layer that develops is commonly referred to as ‘slime’ (Fig. 1).

Wy do we need to monitor for biofilm?

What’s the problem?

Most water systems are very safe with no worrying levels of biofilm, so the actions taken by operators successfully mitigate the risk of developing biofilm, or control it to acceptable levels, so what’s the problem?

The problem is that whilst the vast majority of water systems are safe and well managed, we know that every year people die as a direct result of biofilms growing in managed water systems. Some monitoring regimes measure excess oxidant residual, and assume from a positive residual oxidant that the system is sterile. Biofilms, by producing a micro-environment can effectively protect bacteria from biocides in the water.

Currently there are no reliable, affordable and online real time monitors, that can check the efficacy of the chemical treatment used in preventing a biofilm build up, or to check that conditions haven’t changed since the chemical treatment regime was introduced, such as:

  • A change of environmental temperature
  • A change in water usage
  • An air leak has introduced undesired materials e.g. oxygen and nutrients

What is current and state of the art?

There are various options currently available to measure the build up of biofilm. Probably the most successful is a device with a series of plastic plates. Every day/week/month a plate can be removed and checked for biofilm. Alternatively there are commercially available devices that measure the rate of heat loss from an online sensor, whilst effective false positives can be produced from a reduction in heat loss caused by a build up of sediment or scale.

What’s the solution?

The solution to the current issues associated with biofilm growth and chemical overdosing is to continually monitor with an easy to use, affordable biofilm monitor. This monitor should be:

  • Affordable
  • Simple
  • Continuous
  • Reliable

The BioSense from Pi meets all these criteria (Fig. 3).