The efficacy of biocides and other chemical additives in cooling water systems in the control of amoebae.
OBJECTIVE
In vitro experiments were undertaken to evaluate biocide formulations commonly used in cooling water systems against protozoa previously isolated from cooling towers. The investigations evaluated the efficacy of these formulations against amoebic cysts and trophozoites.


RESULTS
Laboratory challenges against protozoa isolated from cooling towers using chlorine, bromine and isothiazolinone biocides showed that all were effective after 4 h. The presence of molybdate and organic phosphates resulted in longer kill times for bromine and isothiazolinones. All treatments resulted in no detectable viable protozoa after 4 h of exposure.


CONCLUSIONS
The chemical disinfection of planktonic protozoa in cooling water systems is strongly influenced by the residence time of the formulation and less so by its active constituent. Bromine and isothiazolinone formulations may require higher dosage of concentrations than currently practiced if used in conjunction with molybdate- and phosphate-based scale/corrosion inhibitors.


CONCLUSIONS
Cooling water systems are complex microbial ecosystems in which predator-prey relationships play a key role in the dissemination of Legionella. This study demonstrated that at recommended dosing concentrations, biocides had species-specific effects on environmental isolates of amoebae that may act as reservoirs for Legionella multiplication in cooling water systems.
Critchley
M
M
CSIRO Materials Science and Engineering, Clayton, VIC 3168, Australia.
Bentham
R
R
D000389:Air Conditioning; D000656:Amoeba / Q000187:drug effects* / Q000254:growth & development; D000818:Animals; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development; D001966:Bromine / Q000494:pharmacology; D002713:Chlorine / Q000494:pharmacology; D004202:Disinfectants / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D013696:Temperature; D013844:Thiazoles / Q000494:pharmacology; D053058:Trophozoites / Q000187:drug effects; D014867:Water; D014871:Water Microbiology
D004202:Disinfectants; D013844:Thiazoles; C512915:isothiazolidinone; D014867:Water; D002713:Chlorine; D001966:Bromine