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Health and sanitation
Copper – silver ionisation
Commercially available CSI systems typically consist of flow cells that contain metal bars or anodes( containing copper and silver metals) surrounding a central chamber through which piped water flows. A direct electric current is passed between these anodes, releasing the copper and silver ions into the water stream. The amount of ions released depends on the composition of the anode and is controlled by the electrical current applied to the bars and the water flow rate.
By the Environmental Protection Agency, document EPA 810-R-16-001
The use of silver ionisation for water disinfection was developed by the National Aeronautics and Space Administration( NASA) for Apollo spacecraft drinking water and wastewater systems( Albright et al., 1967). The combined use of copper and silver ions for water treatment initially focused on the disinfection of swimming pools( Yahya et al., 1989) as an alternative to using high levels of chlorine. Liu et al.( 1994) first reported on the effective use of CSI treatment for controlling legionella in hospital water systems, specifically for L. pneumophila. CSI systems are currently used in buildings with complex water systems to control the growth and occurrence of legionella bacteria. Lin et al.( 2011b) documented CSI applications controlling legionella in hospitals worldwide.
Characterisation of effectiveness against legionella Case studies constitute the majority of the published reports on the efficacy of CSI in controlling legionella in premise plumbing systems( Demirjian et al., 2015; Dziewulski et al., 2015; Chen et al., 2008; Mòdol et al., 2007; Blanc et al., 2005; Stout and Yu, 2003; Kusnetsov et al., 2001; Rohr et al., 1999; Liu et al., 1998; States et al., 1998; Liu et al., 1994). The studies generally describe situations where legionella bacteria were found in a premise plumbing system and CSI was initiated in an attempt at legionella control. Many of the reviewed laboratory studies indicate that copper and silver ions can inactivate legionella and reduce the incidence of legionellosis. However, as with other technologies, other studies showed that legionella can be protected from copper and silver ions when it is associated with biofilms or amoebae. The potential for legionella to develop resistance to copper and silver ions has also been suggested by several studies.
• Dziewulski et al.( 2015) demonstrated the efficacy of CSI for inactivating both L. pneumophila and L. anisa under alkaline water conditions( pH 8.7 – 9.9) in two health care facilities. No cases of legionellosis occurred during the study period. CSI treatment reduced the number of CFU and the percentage of samples found to be culture-positive. After CSI treatment was established, culture positivity was reduced from 70 % to < 30 %. The study suggests that silver ions played a major role in controlling legionellae, generally in the range of 0.01 – 0.08mg / L.
• Demirjian et al.( 2015) characterised an outbreak at a Pennsylvania hospital between 2011 and 2012, and evaluated contributing factors in a large hospital using CSI to prevent legionella growth. Of 25 locations where samples were collected for legionella culture, 23 were positive for legionella, while the mean copper and silver ion concentrations were measured at or above the manufacturer’ s recommended levels for legionella control( 0.30ppm and 0.02ppm, respectively). They observed that legionella remained viable in vitro in the presence of copper and silver ion concentrations within the manufacturer’ s recommended levels, while chlorine residual levels were low or not present during the investigation. They hypothesized that organic material could have increased during construction work in the hospital. The authors concluded that this could have led to consumption of the chlorine residual, leaving CSI as the only method for legionella control.
• Chen et al.( 2008) studied the implementation of copper – silver ionisation in both hot and cold water at the point of entry to a hospital in Taiwan. CSI was applied to cold water because the subtropical climate in Taiwan resulted in cold water with temperatures up to 30 degrees C( 86 degrees F). During the first three months of implementation, copper / silver concentrations in the hospital wards were 0.094 / 0.020, 0.114 / 0.014, and 0.110 / 0.007mg / L at months 1, 2, and 3, respectively. The percentage of positive L. pneumophila samples declined from 30 to 20 %. During months 4 – 7, the hospital increased the copper / silver levels to 0.143 / 0.008, 0.157 / 0.011, 0.180 / 0.017 and 0.212 / 0.014mg / L, respectively. The percentage of positive samples declined to 5 % and, in months 7 – 11, to zero. In the ICUs, however, the hospital was able to reduce but not completely control legionella during the study. Copper and silver levels in the ICUs were thought to be diluted by connection with a reverse osmosis system installed in the unit.
May 2017 Volume 23 I Number 3 www. plumbingafrica. co. za