Abstract
Isothiazolone biocides have been used for microbial control in a variety of industrial water treatment applications. The most widely used product is a mixed isothiazolone biocide (methylchloro-methylisothiazolone; MCMI). MCMI has broad spectrum efficacy versus bacteria, algae, and fungi. The other isothiazolone biocide is a new micro-emulsion technology based on 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI). DCOI is primarily an algicide for cooling water treatment and a fungicide for papermill applications. MCMI and DCOI inhibit certain dehydrogenase enzymes which disrupt metabolic activity and stop cell growth within minutes. The rate and extent of killing may be enhanced by addition of surfactants. MCMI controls microbial fouling on surfaces and prevents loss of heat transfer efficiency. MCMI efficacy versus problem-causing bacteria, including SRB's and Legionella, has been demonstrated in controlled lab studies. Lab and field studies with DCOI showed excellent fouling control against algae in cooling towers. Isothiazolones are stable in process waters containing ammonia, high hardness, and oxidizing biocides. They are compatible with additive packages, materials of construction, ion exchange media, and ultrafiltration membranes. They are degraded by reducing agents and high pH (>9). MCMI and DCOI rapidly biodegrade in aquatic environments to non-toxic byproducts which do not affect waste treatment systems.
