A Short Methodology Review: for the evaluation of biocides against biofilms in recirculating water systems

Biofilm formation in recirculating water systems such as cooling towers lead to many undesired conditions in terms of public health concern, operational damage and economic loss. Accumulation of pathogenic bacteria (i.e. Legionella pneumophila), increased resistance to antimicrobial compounds, a significant energy loss by increasing heat transfer resistance, equipment damage through microbiologically influenced corrosion (MIC) and premature replacement of equipment constitute some of the important adverse effects of biofilm. To eliminate or reduce the biofouling problem various mechanical and chemical methods are used. The most common approach is chemical treatment primarily using biocides, since mechanical methods have disadvantages due to application difficulties, economical losses because of the system closure during applications and above all the risk of transmission of pathogens. Manufacturers recommend a variety of biocides and concentrations for decontamination recirculating water systems, however, these recommendations are not suited for every system and target microorganisms. To establish a successful biocide program in full scale systems, it is necessary to evaluate the antibacterial activity of correct biocide and/or combinations against both planktonic and sessile bacteria in terms of dosage and contact times in laboratory conditions with taking into consideration of important issues. Thus, the minimum amount of biocide which is necessary for biofouling control will be used and that will not affect either the environment or the performance of the plant itself adversely. In this review, important considerations for accurate evaluation of antibacterial activity will be highlighted.