L. Hably szerk.: Studia Botanica Hungarica 21. 1989 (Budapest, 1989)
Ács, Éva; Lakatos, Gyula: Preliminary algological study on biofouling in industrial water systems
It is characteristic in general that the algal flora consists of particular species occurring in a mosaic-like pattern which is visible to the naked eye on the basis of different colours of the biofouling. The fouling is mainly composed of filamentous blue algae with the exception of samples collected at TIFO. Although the species number of diatoms was higher, their estimated biomass was only a small part of the biomass of filamentous Cyanophyta algae. Diatoms occurring in the biofouling belonged to the Pennales but some Centrales species were also found, e.g. Melosira variáns, observed in unexpectedly high numbers at the sampling sites TVK 5 and MGM 3. Among the Pennales, the species Nitzschia palea can be mentioned as a constant species, which was especially abundant in the samples collected from TIFO, MGM 2. and TVK 3. The Gomphonema parvulum in samples MGM and a Gyrosigma species in samples TVK 1-5 were also of high degree. The green algae belonging to the Chlorococcales were characteristic of the samples taken from TIFO and a lot of Scenedesmus species were present in the samples collected at TVK 3. In the sample LKM 1, a species of Lyngbya was very frequent among the blue algae, while in other samples they were absent. Beside the typical phytotectonic species (e.g. Achnanthes sp., Gomphonema sp., etc.), euplanctonic species also occurred many times (Crucigenia sp., Scenedesmus sp., etc.) which might have suspended into the biofouling from the supplemental water. The distribution of taxa by phylum in different samples is illustrated on Fig. 2. Based on the results of algological investigations, cluster analysis was applied using the Jaccard's similarity index (Fig. 3). The LKM and MGM were found to be the most similar sampling sites, while the other two sites (TVK and TIFO), which use the same supplemental water differed considerably from each other, in respect of their algal-fouling. This provides evidence on the observation that the population of the surface depends only partly on the supplemental water, while it can be attributed more significantly to the spreading of spores by air. Because of the very low level of similarity, there is a need for analysing the composition of biofouling in the different cooling water systems which may provide a good basis for successful protection. POSSIBILITIES OF BIOFOULING ELIMINATION The raw water supplemented to the Works is treated first mechanically and later with alum. Subsequently, it moves on through the cooling systems in two ways: - flows through the cooling system and returns to the river, - after cooling off in a recycling system, the water returns again to the cooling system. In the former flow-through system, however, only some kinds of substrate treatment can be considered because the water returns to the river immediately and this puts a limit on the application of chemicals due to their toxic effect on the living environment. In the latter, recirculating cooling water systems biocide and biostatic compounds can be applied as well. Considering the possibilities of protection it is advisable to pay attention to the ratio of living and dead fraction of biofouling. The mud in the dead fraction provides, partly, an appropriate nutrient reservoir and a good adhesive surface for the algae. The circulating water constantly transports the nutrients which are needed for living algae, and this is an open cooling system thus natural light is abundant, available, while temperature have is also favourable for the algae. The possible of the solutions biofouling formation for the prevention on the heat exchange surfaces are as follows:
