Present Status of Electrolytic Technologies in the Field of Functional Water Treatment

Abstract

A new electrolytic system has been proposed according to social requests, such as energy saving and environmental acceptability. Functional water is defined as "the water produced by artificial methods and its scientific basis has been clarified about the process and the function in solution with reproducibility and the water which is going to be clarified" (Functional Water Foundation, http://www.fwf.or.jp/). Among various kinds of functional water, electrolyzed water and ozonized water are very common due to their clear functionalities, as classified in Figure 1. The former water includes hypochlorite or hypochlorous acid produced by the electrolysis of hydrochloric acid or chlorides solution (called Denkaisui here), accompanying with alkaline and hydrogen generation. Several kinds of electrolyzer have been commercialized to produce the water with proper concentration of hypochlorite or hypochlorous acid and pH with simpler and safer way compared to the dilution of high concentrated NaClO solution. The safety of Denkaisui has been certified by several toxicity and irritation tests. Main topics in the history of Denkaisui in Japan are as follows; 1. Ministry of Health certified as a food additive in 2002. 2. JIS (Japanese Industrial Standards) for its home-use was established in 2005. 3. Ministry of Education recommended its use at school lunch processing in 2009. 4. Ministry of Agriculture certified as an agricultural chemicals in 2015. Pt and or IrO2coated Ti electrodes are preferably selected due to the reason of high chlorine current efficiency and less corrosion to protect human health. Ozonized water has been placed on food additive lists in Japan and has gained approval from the Food and Drug Administrations of US. A superior sterilization power was certified by bactericidal tests, and therapy effect of the water is beneficial for human and pet animals with symptoms. The safety has been clarified for human body except inhalation. Silent discharge-type ozone gas generator is conventionally used for the ozonized water production, however, it is not simple because an ozone gas-liquid contactor should be added, resulting in a time loss. Electrolytic method is superior to produce ozonized water of from 0.1 mg L-1 to 10 mg L-1, because the ozone source is water that enables a rapid response. Pt and BDD (Boron Doped Diamond) electrodes are preferably selected due to the reason of high ozone current efficiency, though PbO2has still been used in semiconductor industry due to its robustness with high concentration. These functional waters are prepared by in-situ and on site equipment, but it is recommendable to use under flow condition, because the produced chemicals with relatively small concentration are easily consumed in the presence of large organic dosage. The produced oxidant concentration is strongly depended on the source water quality and is preferable to monitor. The application based on the functional water has been spreading in agriculture, food processing, medical and hygiene uses in hospital and house, dental and pet animal fields, and so on. In addition to the above oxidative waters, hydrogen (dissolved water) is becoming popular to take in body since medical effects have recently been reported. Electrolytic method for the hydrogen production is a best way to keep a safety with low cost when applying in hospital or house. Several apparatus based on electrolytic processes will be introduced in the presentation. Figure 1