Thursday, August 18, 2011

Biofouling–A life of its own.

Is your system ready to take on a new life? Many technology solutions require clean water for their process. In the semiconductor industry, ultra-high purity water is a must with extreme deionization of water. Residential water heaters even have problems with scaling, and many of the high-efficiency tankless systems cannot be installed in areas with hard water.

Scaling issues with calcium and magnesium are commonly on the mind of a system developer maybe because it is something we experience everyday. On the other hand, biofouling is not always considered until it is too late. Much like scaling, once biofouling starts it may be impossible to treat, control or recover from the growth.

In system testing, it is common to set specifications for the end user and test for the environment that is readily available. Water quality around the world is not equal.

Crazy_Red_BugA Tale of Two Microbes

A problem was experienced when multiple systems tested in the Boston Massachusetts area over several years had no indication of problems with water except for hardness, which was treated with standard filtration and ion exchange materials. A major market was a well developed European country. The problem started with system overheating that required a tweak to the cooling pump curves every few months to keep the system operational. When a shutdown occurred and the system

sit dormant for a few weeks to get an engineer on site to evaluate, he found that the cooling flow was a mere trickle. A high pressure reverse flush was in order.

During the back-flush a large amount of rust-colored  material flowed from the high-surface area heat exchangers. Piping in the system was 316 stainless and the only other materials in water contact were none metallic. Over a few hours of flushing the material turned bright red it was realized it was not rust in the system, but something else. A sample was taken and sent back to the states for lab testing. At the same time, a request to send a sample of the Boston facility water to the lab for testing was done.

The water from the facility in Boston was found to contain a bacterium known as Ralstonia Paucula and a few other low species counts. Ralstonia Paucula is a microbe that is rather common in the water supply and has low pathogenicity, so it is not considered a problem in the water supply.

The sample from Europe reached the same testing laboratory for analysis with statements that if the sample was not less than 24 hours old it would be useless. An attempt must be made however. Results came in, and the major microbe count pointed to a species of the same genus, Ralstonia.

Ralstonia Picketti, the microbe found in the European system, is the evil brother of Ralstonia Paucula that can destroy a process system. It is an oligotroph (ability to live in environments that offer extremely low levels of nutrients like 316 stainless steel) and creates a biofilm called an extracellular polymeric substance (EPS). In other words, it forms a polymer matrix around the microbe as protection that also attaches it to the metallic structure of a heat exchanger or other surfaces.

The Cure may be Worse than the Disease

There are several biofouling microbes. Some microbes can be treated with biocide disinfectants, but if your system is not tolerant to extreme pH or is susceptible to certain chemicals the only options are to continue neutral flush treatments or replace the system and employ preventative measures.

The best option is prevention. Understand the environment and the potential effects it may have on a system. Ensure that you understand how critical system parameters may be affected by the environment and then compensate for all market environments. You may be faced with a situation to either employ over compensation for some markets or system modifications for extreme markets. It is just one more aspect to consider in system design tradeoffs.

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