MICROBIAL DETERIORATION OF MATERIALS - BI OFILM AND BIOFOULING - COUNTERMEASURES AGAINST BIOFOULING IN WATER-SYSTEMS

Countermeasures against biofouling include three steps: i) detection, ii) sanitization and iii) prevention of biofouling. The detection has to refer to surfaces. Cell counts in water samples do not reflect site or extent of biofilms. Biocides display only limited value in terms o f removal of biofouling layers. First, biofilm organisms are protected against biocides and tolerate 10-1000 fold higher concentrations. Sec ond, water sytems usually cannot be kept sterile. Thus, dead biofilms provide nutrients and suitable surfaces for further growth of cells im ported with the raw water. Cleaning of a system is an integral part of sanitization and even more important than disinfection. It has to bas e on a designed strategy. Efficiency control is mandatory, which has t o occur on representative surfaces. The prevention of biofouling is fr equently achieved by continuously dosage of biocides. This is, however , only possible with suitable raw waters and many failures are reporte d. Chlorine is still the biocide most frequently used. Reasons of effe ctivity and environmental protection give rise to other strategies. '' Good housekeeping'' is recommended as countermeasure. It consists of f requent cleaning, efficiency control, biofilm monitoring, limitation o f nutrients, maintenance of high shear forces and a cleaning-friendly design.