Copper zinc water filtration is a high-purity
brasswater filtration process that relies on the
redox potential of dissolved oxygen in water in the presence of a
zincanode and
coppercathode. It uses dissolved
impurities within water as constituent substrate, which are reduced to more physiologically inert compounds.[1]
Due to inherent limitations in
bactericidal and
antiprotozoal activity and poor filtration of organic chemicals (in particular
organophosphate pesticides), copper zinc water filters are not commonly used in the household setting unless combined with
carbon based
systems. They also have application in the industrial setting to extend the life of carbon based filtration systems for
waste water effluent.
Chemistry
In the filtration process, zinc acts as an
anode and copper as a
cathode in an
electrolytic cell. Ionic contaminants are removed by electron exchange (a
redox reaction), in which they are converted to a more physiologically inert form.[2] This redox reaction generates an
electric potential of about 300mV, which may be responsible for the partial
antimicrobial effect, along with
hydroxyl radicals that form during the process.[2][3]
Specifications
The process can remove
chlorine,
hydrogen sulfide,
heavy metals,
iron, and can reduce certain
inorganic contaminants.[3][2][4] The filter also inhibits the growth of
algae,
fungi, and
bacteria to an extent.[2][5] Copper zinc filtration has been used in municipal processing,[6] and the treatment of medical and dental waste water,[1][2][7] as well as for industrial effluents.[6][8] They can be a component of whole home water filtration systems at point of entry[3][9][10] or inline with shower heads or sink heads at point of use, as they remove many forms of dissolved chlorine and are effective at higher temperatures.[11][12][13]
One of the earlier described commercial methods for copper zinc water filtration is via kinetic degradation fluxion media (KDF), a product whose main filtration line consists of brass granules with varying proportions of
zinc and
copperalloy.[14][15] It was developed in 1984 and patented by Don Heskett in 1987.[16][17] An alternative KDF media is a matrix of fine metal similar to
steel wool.[3]
Filtration and usage
Amongst copper zinc water filtration methods, KDF is certified to the
NSF International Standard 61 for water treatment plant applications,[18] and the 2010 NSF standard for drinking water treatment units.[19] A 2005 report by the
US Department of Health and Human Services found that, under normal operating conditions, a treatment of contaminated groundwater in the
Cedar Brook area consisting of KDF and activated carbon filtration removed
volatile organic compounds and mercury to levels compliant with the state drinking water standards, though they also noted the water used may already need to be "exceptionally clean" prior to filtration.[20]
Limitations
Copper zinc water filtration does not remove organic chemicals, such as pesticides and disinfection byproducts, nor is it effective against the
parasitic cysts of
giardia or
cryptosporidium.[7][21] and must be periodically backwashed with hot water to clean them. This reduces their efficiency, and the pollutants dislodged by washing can lead to water contamination.[1][7][22] The United States
Environmental Protection Agency found that copper zinc water filtration can remove mercury from contaminated water, but only at low concentrations, and recommends that for highly contaminated water other processes be used.[23]
Due to their bactericidal action, copper zinc water filtration devices are considered by the EPA to be "pesticidal". However,
Stanford physician
Paul Auerbach recommends against their usage as a sole means of germicidal water treatment, and he does not include them amongst his recommended protozoal disinfection methods at either point of entry or point of use.[3] A 1995 United States
Environmental Protection Agency report found that such systems were employed at approximately 20 US-based
cooling towers in 1993. The report documented variable results, with some systems discontinued because they were ineffective at controlling bacterial growth, though in other instances they were preferred because of comparatively safe waste production and simpler maintenance.[24]
There is also concern about environmental damage due to the release of zinc in areas with high concentrations of metals or certain pollutants, in particular copper[25] and chlorine.[26] Publications of the
American Water Works Association do not recommend the use of copper zinc water filtration systems to treat chlorinated water that outflows to streams.[26]
Studies have also shown that regulation standards for the systems can vary widely or be nonexistent depending on the industry and region of their usage.[27]
^M.J.O’Donnell; M.Boyle; J.Swan; R.J.Russell; D.C.Coleman (2009), "A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: A 2-year longitudinal study", Journal of Dentistry, 37 (10): 748–762,
doi:
10.1016/j.jdent.2009.06.001,
PMID19573971
^
abM Wethern; W Katzaras (1995), "Reverse osmosis treatment of municipal sewage effluent for industrial use", Desalination, 102 (1–3): 293–299,
doi:
10.1016/0011-9164(95)00066-B
^Arianna Catenacci (2014),
Heavy metal removal from water: characterization and applicability of unconventional media(PDF), Politecnico di Milano, Department of Civil and Environmental Engineering, p. 18: "A typical application of the KDF media in the treatment of industrial effluents pertains the removal of lead in the circuit board manufacturer industry: lead is removed for 94.4% thus enabling the recycle of water in a closed-loop rinse-down system. When filtered through KDF media, soluble lead cations are reduced to insoluble lead atoms, which are electroplated onto the surface of the media"
^In Business, Volumes 13-14.
JG Press. 1991. p. 16. In 1987, Haskett had patented a new fluid treatment technology that utilizes a copper-zinc alloy called KDF (Kinetic Degradation Fluxation) to remove chlorine, heavy metals and other inorganic contaminants...
^M.J.O’Donnell; M.Boyle; J.Swan; R.J.Russell; D.C.Coleman (2009), "A centralised, automated dental hospital water quality and biofilm management system using neutral Ecasol maintains dental unit waterline output at better than potable quality: A 2-year longitudinal study", Journal of Dentistry, 37 (10): 748–762,
doi:
10.1016/j.jdent.2009.06.001,
PMID19573971: "The KDF-85 filter medium and the granular activated charcoal medium are certified to NSF International Standard 61 for water treatment plant applications." with a reference "NSF International Standard NSF/ANSI 61-2008. Drinking Water System Components – Health Effects."
^National Risk Management Research Laboratory (1997),
Aqueous mercury treatment, Environmental Protection Agency, Office of Research and Development, p. 5-1