The tap water or "water" with calcium salt added in it is obtained by cathodic electrolysis to obtain alkaline ionized water. At present, the alkaline ionized water machine, such a manufacturing device, is mainly sold in the market as a circulating (continuous) type, which is easy to use. A variety of materials are also used in this water machine. Therefore, focusing on the substances dissolved from the water machine and the possible trihalomethane harmful substances produced by the water machine, the physical properties of the water machine were investigated for its safety.
Most of the commercial circulating alkaline ionized water dispensers are constructed as shown in Figure 1. Because the water is electrolyzed to produce alkaline water, a reduction reaction takes place at the cathode to produce hydrogen. When the water becomes alkaline, the water at the anode is oxidized to produce oxygen and generate acidic water. In order to prevent alkaline water and acidic water from mixing and becoming neutral water, a diaphragm is set in the middle. At this time, if there are chloride ions in the raw water, it will be oxidized at the acid water side and become chlorine. In order to maintain and clean the machine, most of the flow type electrolytic water machines will change the power supply access mode from time to time to reverse the electrode, so that the electrode originally used as the cathode will be changed into the anode, and the anode will be changed into the cathode for short-term electrolytic work. Therefore, we also investigated and analyzed the influence of this reverse electrode.
Materials for electrolytic water machine
We choose Pt Ti electrode and some ferrite electrodes as test objects. The experimental model device shown in Fig. 1 was made with this kind of electrode, and the alkaline ionized water was analyzed. Platinum titanium electrode has not found the problem of heavy metal precipitation. When using ferrite electrode to produce alkaline ionized water, there is no problem of heavy metal precipitation. However, a small amount of heavy metal precipitation was observed when the reverse electrode was cleaned. After the reverse electrode is completed, the heavy metals can be washed away as long as the water is used for flushing, which is no problem in normal water preparation. But for the sake of safety, we hope to use platinum titanium electrode instead.
In addition to the electrode test, we also tested the hose, gasket materials, shell materials and other major components immersed in alkaline ionized water, and found no problematic substances separated.
By products in alkaline ionic water
When the raw water used by the alkaline ionized water machine contains chloride, it is feared that it will be oxidized to chlorine at the anode, and then react with trace organic substances in the water to generate organic chloride compounds. Especially under basic conditions, it is possible to generate trihalomethanes through haloform reaction.
In general, the haloform reaction cannot be continued for the electrolytic water machine, but if the acidic water containing chlorine flows through the diaphragm to the alkaline water side, sometimes the conditions for haloform reaction are met, producing substances such as trihalomethane. We made a little effort on the test device in Figure 1 to make the water flow from the acidic water side to the alkaline water side. The inspection results show that the trihalomethanes have increased and exceeded the specified harmful concentration standard. During electrolysis, depending on the characteristics of the diaphragm used, electroosmosis may sometimes occur, causing acidic water to flow to the alkaline water side. However, several alkaline ion water dispensers were actually tested, and no products with large electroosmosis were found. In addition, efforts were made to make the water flow from the alkaline water side to the acidic water side through the inflow of water to the electrolysis part and the outflow of electrolytic water, so that the conditions for haloform reaction were not met, so trihalomethanes were not detected.
In order to ensure product safety, it has been reported to the Industry Association for revision of product safety standards.
2. Characteristics of alkaline ionized water
Although several new theories on the characteristics of alkaline ionized water that are completely different from those of electrochemistry have been put forward, the test results show that they do not go beyond the theoretical scope of traditional electrochemistry. That is, hydrogen is generated on the cathode side by electrolysis, and the water near the cathode becomes alkaline.
PH of alkaline ionized water
After the water is electrolyzed, as shown below, hydrogen is generated to generate OH -, which becomes alkaline near the cathode. In order to maintain electrical neutrality, while cations such as Ca+move towards the cathode, OH - moves towards the acidic water side. In addition, the H+on the acid water side also moves in the opposite direction. The pH of alkaline ionized water is determined by the balance reached by the movement of these substances. The higher the electrolysis current is, the faster the OH - generation speed is. As long as the liquid flow rate is slowed down, the pH will rise.
Hydrogen concentration in alkaline ionic water
Water is electrolyzed at the cathode to produce hydrogen, which is initially very small bubbles. As shown in Fig. 2, they polymerize with other small bubbles in solution and become large bubbles. On the cathode side, hydrogen atoms become hydrogen molecules, and the hydrogen molecules dissolved in the solution become tiny bubbles together. In order to become such a bubble, additional energy is required. Near the electrode, hydrogen is dissolved in water at a concentration with higher equilibrium solubility. For example, when the diameter of hydrogen is 100 nm, the air pressure of its bubble is 30 atmospheres, and the solubility of hydrogen around it is also 30 atmospheres to maintain balance. It has been reported that the supersaturation of hydrogen even exceeds 100. It can be inferred that the solubility of hydrogen in alkaline ion water is very high. The solubility of hydrogen reduces the "redox potential" of alkaline ionized water, showing reducibility. Therefore, the solubility of hydrogen in alkaline ion water affects its own characteristics.
It is not easy to measure the solubility of hydrogen, and even if it is supersaturated, it will gradually decline. We use several saline water to make alkaline ionized water, and then place it at 2 ℃. The change of its hydrogen concentration is shown in Figure 3. It dropped sharply on the second day, but it can still be preserved in high concentration for a long time.