Method for decolorization in explosive wastewater via hypochlorite and reuse of the emitted chlorine gas

Abstract

Chlorine-based oxidants are commonly used for decolorization and disinfection as they have the advantage of low prices and longer retention times compared to high oxidation forces. In particular, color wastewater is difficult to decompose naturally due to its small amount of visible and mostly stable molecular structure, and most of it is toxic, so it should be discharged after decolorization. In the case of defense wastewater, the growth rate has continued to rise since 2015, and the high proportion of explosive manufacturers is increasing the need to develop effective and economical wastewater treatment technologies. However, chlorine oxidant used in the bleaching process has a fatal problem. Large amounts of exposure can cause corrosion of building exterior walls, ecosystem destruction, and damage to human respiratory organs. If exposed to 30 ppm for more than an hour, the substance is toxic enough to cause death. One of the problems with the deadly chlorine oxidant is the odor problem. Chlorine exists in various forms according to pH, hypochlorite in basicity, hypochlorous acid in neutral, and chlorine gas in acid, which is a malodor substance that is exposed to the atmosphere and has a small threshold value of 0.31 ppm. Besides, chlorine oxidant is combined with ammonia in wastewater and present in the form of combined chloramine, where the combined residual chlorine also exists in various forms depending on pH. It exists in the form of monochloramine in basicity, dichloramine in neutral, and trichloramine in acid, which is another odorous substance because it is released into the atmosphere without melting in water due to its low solubility, and the WHO restricts emissions to less than 0.5 ppb. Because of this odor problem, to solve this problem, there are wastewater treatment methods to reduce chlorine-based oxidant, which is the original cause of the odor, and air treatment methods to remove chlorine gas that is discharged without reacting with bleached substances.

Chapter 1 was intended to reduce the amount of hypochlorite used for decolorization to reduce the amount of chlorine gas generated during wastewater treatment. By adding radical, which is more oxidative than hypochlorite, it was expected that the same efficiency of bleaching would be treated with less amount than conventional hypochlorite Similar to the Fenton reaction, which reacts hydrogen peroxide and iron to form radical, the Fenton-like reaction was applied to the decolorization treatment by reacting hypochlorite and iron. In order to reduce the amount of trichloramine, which is another odor substance, we tried to remove ammonia quickly by applying a Fenton-like reaction, just like decolorization treatment.

Chapter 2 attempted to effectively remove the impeller-based scrubber to remove chlorine gas that was released unreacted to dye during the process of decolorization. The conventional chlorine gas treatment uses a basic solution in a wet scrubber. However, there are problems with gas backflow, mist discharge, and additional wastewater treatment, which are pointed out as disadvantages of conventional wet scrubbers. By introducing a new type scrubber, the installation of an impeller that helps flow fluid and inner wall to remove mist prevented backflow and mist discharge problems. It also reduced the additional wastewater treatment burden by returning a minimal amount of absorbent. Using chlorine gas removal as a reduction of chlorine, we compared the efficiency of chlorine gas removal by using a basic solution as well as a sulfite solution to find a solution that works well. The advantage of using a basic solution is that chlorine gas can be used again as a decolorant because it reacts with ions of hydroxide and converts to hypochlorite, and to prove this, the actual wastewater was decolorized with an absorption solution used to remove 100 ppm of high concentration chlorine gas for 350 minutes.

In conclusion, the effective desorption process of defense wastewater using hypochlorite, a chlorine oxidant, was developed, and in the case of discharged chlorine gas, the circulation system of chlorine, which is removed with the impeller-based scrubber and reused to decolorization chlorine collected with hypochlorite, was studied.