Aumentos Disminuciones Traspasos conversión 31.12.01

Electro-chemical disinfection refers to the use of an electro-chemical cell to trigger disinfection. Research has been done about the implementation of a variety of electro-chemical cells with different electrodes and their efficiency as disinfecting technology (Gusmão, Moraes et al. 2010). Many of the electrodes that have been tested are not practical and/or financially sustainable solutions for water disinfection. The identified technologies that are currently used for disinfection have been divided into two main categories, namely electrolytic cells, which cause the formation of an oxidising agent, and electrolytic cells, that release metallic ions. With oxidation and reduction taking place at the anode and cathode of any electro-chemical cell, it is difficult to distinguish what the actual disinfection mechanism is and what redox reactions take place. The disinfection mechanisms have been classified into oxidation through the formation of ozone, free chlorine or other oxidisers, and the biocidal effect of metallic ions.

The electrolytic cell causes two half reactions that take place at the two electrodes, oxidation (loss of electrons) takes place at the anode and reduction (gain of electrons) take place at the cathode. Depending on the voltage, water composition and electrode composition, different half reactions take place. The most common electro-chemical cells that are available on the market make use of oxide- coated electrodes and are also known as Dimensionally Stable Anodes (DSA). The idea is to have an electrolytic system that does not use the electrodes, but that the released electrons trigger a cycle of half reactions using the oxide coatings. The complexity of the reactions differs, but often concludes with the formation of the oxide layer on the anodes completing the cycle (Gusmão, Moraes et al. 2010). The formation of radicals and positively or negatively charged ions often deactivate bacteria and disinfect the water amid the cycle of reactions that are occurring (Pavlović, Pavlović et al. 2014). A simple electrolytic setup usually disinfects water through the formation of free chlorine, ozone, peroxide, or oxygen. If there is any dissolved sodium chloride (NaCl) or other source for chlorine ions (Cl-_{) in the water, then chlorine will be oxidised at the anode which will lead to the formation of free}

chlorine as the chlorine reacts with the water molecule (H2O) (Singer, Reckhow 1999, Kraft 2008). The

free chlorine acts as the biocide. The use of electrolysed oxidising water (EOW) or “activated water” is modern technology that results in the formation of strong oxidisers at the anode and hydroxyl ions at the cathode that are both biocidal (Badruzzaman, Khan 2002, Meireles, Giaouris et al. 2016). According to research done by Kraft on electro-chemical disinfection technologies, systems that made

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use of platinum (Pt) and titanium electrodes proved to have the longest life spans (Kraft 2008). Kraft specifically investigated the technology of G.E.R.U.S. namely the ‘Hypocell B4’ and ‘AQUADES-EL’, developed by AquaRotter. Research by Kerwick, Reddy et al. (2005), however, showed that electro- chemical cells do not necessarily need the formation of chlorination species for disinfection (Kerwick, Reddy et al. 2005, Zinkevich, Beech et al. 2000).

Electro-chemical systems can also be used to produce other oxidisers. On-site formation of oxidisers through an electrolytic cell decrease transportation cost and hazards of storing chemicals (Kiuru, Sievänen et al. 2011, Martínez‐Huitle, Brillas 2008). The pure electrolytic cell produces oxygen which functions as a biocide for anaerobic bacteria (Kraft 2008). Ozone can be formed at special anodes and be used as disinfectant. These special anodes make use of a diamond anode/ solid polymer electrolyte (SPE)/ cathode sandwich system such as Nafion (Kraft 2008). Graphite cathodes have proved the most efficient to produce hydrogen peroxide (H2O2) with higher amounts of dissolved oxygen in the water

(Kraft 2008). Porous cathodes have also been developed to increase the oxygen present and support peroxide formation. Some researchers are supporting a concept of electro-sorption and direct electron transfer from the cathode to micro-organisms, as the disinfecting mechanism (Gusmão, Moraes et al. 2010, Jeong, Kim et al. 2007). Studies on the formation of OH radicals support theories that electrolytic cells could be triggering the formation of OH radicals which then act as biocide (Feng, Suzuki et al. 2004, Vega-Mercado, Martin-Belloso et al. 1997, Ohshima, Sato et al. 1997, Diao, Li et al. 2004).

When electro-chemical cells are designed correctly, the electric current causes the break-up of the electrode. An ioniser is such a special type of electro-chemical cell with a metal cathode that releases metal ions. Silver and copper-silver ionisation have grown in popularity over the last decade, commonly used in cooling towers, swimming pools, and small house-hold installations (Pavlović, Pavlović et al. 2014, Kusnetsov, Iivanainen et al. 2001, Cachafeiro, Naveira et al. 2007). The mode of disinfection is believed to be the same as using metal salts or pure metals, but the metal ions are activated and released by an electric current. The metals used for disinfection differ, but combinations used include silver, silver-copper, copper-zinc, and silver-copper-zinc. NASA was one of the technology leaders to use silver-copper ionisation for water disinfection on its spaceships and now similar technology is implemented by numerous water bottling companies. The use of electro-chemical technology leads to the reduction in water usage due to bleeding-off and financial gains due to less disinfecting chemicals used (Becker, Cohen et al. 2009).

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