Efficacy of Biocides in a Model Plumbing System

Treatment of Non-Potable Water Systems and Cooling Towers

Biocide	Concentration (ppm)	Control Rating for Legionella	Comments	References
Oxidizing
Chlorine	0.5-1.0	Highly effective	Highly corrosive	Cooling Technology Institute, 2000
Ozone	0.1 - 0.5	Highly effective	Difficulty maintaining residuals	-
Chlorine dioxide	0.5 - 1.0	Highly effective	Difficulty maintaining residuals	Gao, 2001
Bromine	0.5 - 1.5	Moderately effective	More effective than chlorine at higher pH	Thomas, 1999
Stabilized bromine chloride	4 - 10 ppm as Br2	Effective	More effective than chlorine at higher pH	McCall, 1999 and Nalepa, 2001
Non-oxidizing
DBNPA	1.9 - 4.0 dry   8 - 10 liquid	Highly effective   Moderately eff.	98% active powder my be more effective than liquid	Gao, 2001 and Thomas, 1999
Gluteraldehyde	50 - 100	Effective	-	Thomas, 1999
Carbamates	4 - 12	Ineffective	-	McCall, 1999
Polymeric quaternary amine	8 - 12 Ineffective	-	-	McCall, 1999

 

Disinfection Methods for Legionella in Potable Water Systems

Parameters	Copper/Silver Ionization	Continuous Chlorination	Heat and Flush	Chlorine Dioxide
Concentration Applied	Cu = 0.2 - 0.8 ppm Ag = 0.02 - 0.08 ppm	2 - 4 ppm  as free chlorine	160 F for  30 min	0.5 - 1 ppm  as ClO2
On-site efficacy documented in peer-reviewed literature	Yes	Yes	Yes	Yes
Residual protection throughout the distribution system	Yes	Yes	No	Yes
Time to recolonization after system shut-down	6 -12 weeks	1 -2 weeks	Varies1	No information available
Temperature	Residuals unaffected by high temperature	Residuals decrease as temperature increases	NA2	Residuals decrease as temperature increases
pH	Elevated pH (>8.5) may affect efficacy	Elevated pH (>8.0) affects efficacy	No effect	No effect
Disinfection by-product	None known	Trihalomethane (THMs)	None	Chlorate and Chlorite
Taste and odors	None	Yes	No	Minimal at high concentrations
Pipe corrosion	Non observed	Highly corrosive	Old pipe may be affected	Corrosive
Maintenance issues	Scale control Routine electrode cleaning Routine ion monitoring with AA or ICP3	Chlorine storage Concentration control and monitoring. Corrosion control with silicate	Scalding possible Labor intensive	Concentration control and monitoring using DPD method

                                                                  1. The delay of recolonization is variable.  Elevated hot water temperature can delay recolonization

                                                                  2.  Not applicable.

                                                                  3.  Atomic absorption (AA)/Inductively coupled plasma mass spectroscopy (ICP)