Role and levels of real-time monitoring for successful anti-fouling strategies--an overview.

Biofouling is a biofilm problem and any anti-fouling strategy will be greatly improved if the site and extent of biofilm growth can be monitored. A suitable monitoring system will provide early warning capacity and allow for specific optimization of countermeasures. As water samples do not give reliable information about biofilms, surface sampling is mandatory. Conventional biofilm monitoring techniques rely on removal of material from representative sites or on analysis of test surfaces which have been exposed. This procedure is time consuming and, depending on the parameters to be measured, requires skilled laboratory personnel. There is a strong demand for direct, on-line, in situ, continuous, non-destructive real-time information about biofilms in a system. Such demands can only be fulfilled by physical or physico-chemical methods, a number of which have already been successfully applied for biofilm monitoring. It is important, however, to be aware of the actual parameter they refer to in order to interpret the data properly. Three levels of information can be identified: (i) systems which detect increase and decrease of material accumulating on a surface but cannot differentiate between biomass and other components of a deposit, (ii) systems which provide biological information and distinguish between biotic and abiotic material, and (iii) systems which provide detailed chemical information. Examples for all three levels are presented and discussed.