PRACTICAL ASPECTS OF BIOFOULING CONTROL IN INDUSTRIAL WATER-SYSTEMS

Both water consumption and discharge in industrial water systems are currently minimised. The circulation of such water results in concentration of dissolved and suspended substances, promoting the growth of waterborne microbes, biofouling and subsequent macrofouling of the system and concomitant microbially induced corrosion. A number of reviews have been published on the mechanisms of microbially induced corrosion and the organisms involved. The subject of biofilm formation has also been well covered in the literature. A lack of information on the community structure and physiology is, however, apparent. Many advances have, nevertheless, been made in biofouling control. Probably the most important is the shift in emphasis from planktonic bacterial monitoring to sessile bacterial monitoring. This led to the introduction of a variety of different sessile monitoring techniques. Much experience has since been obtained on the use and limitations of these techniques and, to date, one of the main problem areas remaining is the monitoring of biofouling. Research has also indicated the problem of microbial resistance to nonoxidising biocides. This has suggested that some of these compounds may be mutagens. From an environmental point of view, it has become very important to verify this. This has also indicated the need to develop biocides which do not induce resistance in micro-organisms, and to investigate whether oxidising biocides are also capable of inducing resistance in micro-organisms, Recent studies have indicated that biofilm ecosystems respond to stress (i.e. biocides) in ways similar to macro-ecosystems. Generally, there is a decline in species diversity and a selection of more tolerant isolates. These developments have placed the spotlight on alternative technologies, like biodispersants, which have shown potential as biofouling control agents, and which should be investigated further. Physical control measures are currently still limited to pigging, although a number of other technologies show promise. Although fluid dynamics and their effect on biofouling control programmes have been well reported in the literature, it remains an aspect which is neglected by industry in terms of practical applications.