Biofilms and biofilmreactor



Figure: Schematic structure of a biofilm

Microorganisms are found almost everywhere, only ultra-clean rooms should be clear of them. They are widely spread because they are specialists in adaptation, thus they exist in the deep sea and volcanic craters as well as in arctic regions or in the intestines of humans and animals. The biofilm provides protection and habitat for them. Microorganisms live in the biofilm in a special arrangement, like people in a big city. There are many different types of microorganisms in a biofilm, because a fundamental principle of nature, that is, biodiversity equals quality of life, holds true herein as well. There is much evidence that biofilm systems like that existed on earth already 3.5 billion years ago.

Over time, microorganisms settle on all water-accessible surfaces in the pond and will develop biofilms. This development requires a lot of time because the necessary conditions for the creation of a robust biofilm are usually not fulfilled. The more unfavorable the conditions for the biofilm formation are, the less effective is the biofilm development in terms of quality and quantity. This is comparable to the building of a house which can only be as good as the materials and the services which have been used.

The formation of a biofilm, e.g. if the pond is being refilled, often causes problems until an active biofilm has finally developed on the biological entity. This can take months or even a year, which is not surprising from a microbiological point of view. The content of koi excretions, which can be utilized for the microbiology, differs to a high degree by the different feed compositions (carbohydrates, fats, proteins).


Photo: Biofilm, stained under the microscope

It may seem simple; however, it is essential for the formation of a biofilm. Thus the formation of a flimsily-built biofilm, also caused by other factors, may take place. That means that not every biofilm is a really active “solid” biofilm. Research results provide a great deal of evidence for that. A potent biofilm in the biofilm reactor is, in particular, characterized in that it also will resist drug treatments. In conventional biological systems, such as a chamber filter, the biology in the water cycle is usually bypassed after a drug administration to protect the biology in the chamber against the effects of the drugs. There is, however, a feature of biofilmreactor, which appears to be resistant against the drugs, and the fish can also be fed after the drug administration. This has already been practiced in many applications and complies with the nature of a robust biofilm. Another advantage is that no excessive biofilm is created in the biofilmreactor. There is only as much biofilm in the reactor as the water values will allow. This renders the time-consuming cleanings, especially known for chamber filters, redundant.


The biofilm reactor has been developed to improve the slow and poor development of a biofilm as well as the poor cleaning performance of the purification process of the pond water in terms of quality and quantity.

Under certain conditions, a robust biofilm is developed in the biofilm reactor on appropriate surfaces. In the biofilm reactor microorganisms will accumulate which are also present in the pond. Since in each pond the type and number of microorganisms varies (up to 80 several microbial species can be assumed), the development of the biofilmreactor is built up with original inoculating water from the biofilm reactor of the pond which is to be equipped.


Photo: biofilm stained; under a confocal laser scanning electron microscope,(Max Planck Inst., Dortmund)

After the setup, which usually takes 4 to 7 days, the biofilm reactor is implemented in the water cycle of the pond and will achieve an efficiency of approximately 75% right from the start. It will have reached its full potential, depending on the temperature, after 3 to 4 weeks.

Its efficiency usually involves a closed nitrogen cycle, meaning there are active microorganisms in the filter which perform the nitrification and denitrification. To monitor theses activities, an appropriate analysis for the pond water has to be set up over a certain period of time.