By: Kate
Email:kate@aquasust.com
Date: 7th February 2025
Sodium chlorate and sodium hypochlorite are both oxidants, but sodium chlorate does not produce hypochlorous acid when dissolved in water, nor does it oxidize COD at room temperature, and has no effect on removing COD at all.
01 Sterilization & membrane washing
Sodium hypochlorite can sterilize and disinfect for two reasons. First, the new ecological oxygen, with its strong oxidizing property, denatures the proteins on the surface of bacteria and viruses, thereby killing pathogenic microorganisms. It is an external boxing method.
Secondly, the surface of the cell membrane is negatively charged, while hypochlorous acid is a neutral small molecule that can penetrate the cell membrane and enter the cell, reacting with DNA and mitochondria to directly kill bacteria, which is an internal skill.
If there happens to be some ammonia nitrogen in the water, it will react with sodium hypochlorite to form chloramine compounds, which are slightly weaker in oxidizing property than hypochlorous acid, but can be stable in water and continue to sterilize.
Membrane washing refers to backwashing the MBR membrane with drugs. People who use MBR technology know that microorganisms will attach to the membrane after it has been used for a long time, and if it is full, it will seriously affect the membrane flux.
The essence of membrane washing is still sterilization, and sodium hypochlorite will naturally fall off the MBR membrane.
02 Removal of COD
Sodium hypochlorite can be used as a COD remover. This is not a heresy. It is due to the strong oxidizing property of new ecological oxygen. It can oxidize part of COD, but it is not very friendly to sludge, so try to use it as little as possible.
The chloride ions decomposed by sodium hypochlorite in water will also interfere with the determination of COD, but the interference of sodium chlorate is different. The interference of sodium hypochlorite is to make COD falsely high.
03 Decolorization & bleaching
Still rely on the strong oxidizing property of new ecological oxygen. Sodium hypochlorite is often used as a decolorizer or bleaching agent in printing and dyeing wastewater. The general difference between the two is: the reaction with metal ions to form a precipitate is called decolorization; the oxidation of organic dyes is called bleaching.
04 Removal of ammonia nitrogen
As mentioned earlier, sodium hypochlorite will produce chloramine compounds with ammonia nitrogen. Now let's formally introduce the three chloramine brothers.
NH3+HOCL →H2O+NH2CL Monochloramine NH2CL+HOCL →H2O+NHCL2 Dichloramine NHCL2+HOCL →H2O+NCL3 Trichloramine
These three reactions are reversible reactions. The three brothers can change back at any time. As for whether they change or not, it all depends on the pH. If you want to stabilize the denitrification, you have to make the pH weakly alkaline, continuously consume H+, promote CLO- ionization, and ensure that the reaction will not reverse.
05 Cyanide Destruction in Electroplating Wastewater
Cyanide plays a complexing role in the electroplating process, which can make the coating fine and smooth. Therefore, besides heavy metals, this is the most abundant substance in electroplating wastewater. There is a special process called cyanide destruction when treating electroplating wastewater.
Sodium hypochlorite destruction of cyanide is called chlorine oxidation method. Cyanide is first oxidized into cyanate, and then oxidized into harmless nitrogen and carbonate. The process is relatively complicated.