By: Bernard Banga, Freelance Writer, French Technology Press Office
Legionnaires' disease is considered so catastrophic
that, in France, it must be reported to the medical authorities immediately. This
practice has been in place since 1987. During the last decade, public health
monitoring systems for this disease have been strengthened. Today, this hazard
that arises from buildings has become an emerging public health problem in
industrialized countries. The resulting respiratory infections are behind the
recurrent epidemics emanating from hot water systems in buildings and
air-conditioning cooling towers.
New Health Hazards from Buildings
Sensitive populations, mainly the elderly or people with immune
deficiencies, are at risk from this respiratory disease, particularly in public
buildings such as healthcare establishments (hospitals and clinics), hotels,
campsites, swimming pools and gymnasiums. "Infection arises from
inhalation by these receptive people of a large dose of micro-droplets carrying
pathogenic bacteria," explain experts from France's Public Health
Council, the authors of a recent report on the management of Legionella
hazards.
The cause of this new bacteriological hazard is bacilli that
have a particular affinity for hot water in the range from 77°F to
104°F. These bacilli tend to multiply within biofilms in pipework.
Contamination of the lungs occurs only with the inhalation of an aerosol that
can come from showers, lengthy baths, and outlets for air cooling towers. Two
processes exist for eradicating Legionella from contaminated water systems:
thermal shock and chemical disinfection (chlorination).
Cyclical, Continuous Pasteurization of Hot Water
As the optimal temperature conditions for the growth of
Legionella are between 86°F and 113°F, raising the temperature of the
water to 158°F for one minute in the water system will destroy the
Legionella. The French company PM Industrie, located in southwestern France's
Gironde region, is developing an exclusive process patented in August 2000 by
the firm Jean-Jacques Boiffier--the Pastor Master.
"Our process acts on three levels. It provides cyclic
and continuous pasteurization of domestic hot water, it maintains the
temperature of the distribution network and it ensures constant circulation
including inside the fixtures," explains Jean-Jacques Boiffier, the
inventor.
One thermal substation constructed in 316 L stainless steel
ensures bacteriological sterilization by the controlled passage of domestic hot
water through a semi-instantaneous exchanger. PM Industrie offers two ranges of
compact monobloc substations: the PM 130 SI with a power of 185 kW and a peak
flow rate of 300 cubic feet per hour, and the PM 250 SI with a power of 300 kW
and a peak flow rate of 459 cubic feet per hour. The Back Flow Master
three-channel adapter makes it possible to quickly modify (installed as a
by-pass on the header) the fittings of standard two-channel showers to
three-channel fittings with an integral loop. "This ensures bacterial
disinfection of the hot water tank from where the water is constantly
circulated," Boiffier says. To date, 10 French hospitals have adopted
this innovative process.
Disinfection Using a Chlorine Dioxide Generator
The second method of treating water systems uses shock
chlorination (57 to 76 mg/gallon of chlorine added during a 24-hour time
period). However, this type of decontamination strongly corrodes pipework,
damages joints and gives the water a strong smell of chlorine. It also requires
draining the installations. To solve this problem, Thétis Environnement
has developed an emerging technology in collaboration with the EDF Research
Center and with the support of ANVAR.1 "We designed a generator of
chlorine dioxide using electrolysis, which avoids the storage of dangerous
reagents, corrosion of the installations and increased maintenance," says
Charles Dubost, founder of Thétis Environnement.
Available since the start of 2001, the monobloc system (4.9
ft. high, 6.6 ft. wide and 3.3 ft. deep) includes sodium chlorite tanks, a
holding tank for chlorine dioxide, an electrically powered electrolyzer and one
or more dosing pumps to inject precisely the required quantity of chlorine
dioxide into the water system. This SECUROX generator produces 5 to 100 grams
per hour of chlorine dioxide. Thanks to its self-monitoring system that
maintains continuity of treatment and, in particular, continuous monitoring of
effectiveness, it always is operational. With this system, the production of 35
cubic feet of water costs about three cents. The SECUROX has been adopted by
several French hospitals for combating Legionella, and is being used by
drinking water producers and agro-food companies.
Combination of Biocides to Treat Cooling Towers
The principle of air-cooling towers is to extract the heat
of condensation from air-conditioning units. The water in the condensation
system flows from the top to the bottom of the tower. This water, condensed into fine droplets to increase surface
area, is sprayed head-on into a jet of air. It is precisely this process
that causes the entrapment of
droplets in an aerosol, which forms a plume that can be colonized by
Legionella.
The water treatment company Protec now offers an alternative
treatment to highly corrosive chlorine. "We make use of the complementary
and alternative activity of two organic nonoxidizing biocides that attack both
the Legionella organisms and their nutritive environment, biofilm,"
says Marc Georgelin, Protec's managing director. The isothiazolone-based
Bio Top 35 has the chemical effect of cellular lysis on Legionella, while Bio
Top 20 based on tetra hydroxyl phosphonium salt inhibits the enzymes necessary
for the growth of bacteria. Using them alternately prevents the bacteria from
developing tolerance. Two dosing pumps automatically inject these products
without the need to shut down the air-conditioning system. Results announced by
Protec show a reduction of at least 103 Colony Forming Units per liter.
About The Author: Bernard Banga is a freelance writer in Paris. For more information, contact the French Technology Press Office in Chicago at 312-222-1235; [email protected].
