Study of chloride concentration effect on the generation of active chlorine in direct electrolysis

Summary

Electrochemical sodium hypochlorite has been most often used in water treatment at the water and wastewater treatment facilities. Natural water containing chlorides can be used as raw material for its production. The results of studies of electrolysis of low mineralized water with 25, 50 and 100 mg/dm³ chloride concentration are presented. The simulated solution was prepared by «Ekstra» table salt dilution in distilled water. The tests were carried out within 10–500 A/m² current density range. The concentration of active chlorine is increasing alongside with the electrolysis time. It is stated that at the preset values of anodic current density active chlorine of different concentrations can be obtained, e. g. up to 220 mg/dm³ at 100 A/m² current density and 100 mg/dm³ chloride concentration. The process is notable for the amount of generated active chlorine exceeding the stoichiometric chloride concentration in water in process up to 1.7–1.9 times; this can be caused by the formation of other oxidants, e. g. hydrogen peroxide. At the current density less than 500 A/m² the output of active chlorine decreases. According to the experimental results a nomogram for determining the active chlorine current yield depending on the chlorine concentration in the solution and current density is proposed.

Key words

sodium hypochlorite , chlorides , underground and surface water , direct water electrolysis , oxidants , current density

The study of direct electrolysis of water in the Vietnam Sea
in the production of sodium hypochlorite

Summary

Electrochemical sodium hypochlorite is used at water supply facilities all around the world. The use of natural waters containing chlorides as a raw material is very promising since it greatly simplifies the process flow scheme for producing sodium hypochlorite. Direct electrolysis technology can be retrofitted into the existing water treatment schemes without significant changes. The use of natural water containing chlorides eliminates the purchase of salt which reduces the cost of the finished product. The results of studies of direct electrolysis of water in the Vietnam Sea are presented. During the experiments the effect of seawater flow rate and current density on the concentration of active chlorine in the resulting sodium hypochlorite, the change in the current chlorine yield and the specific energy consumption per 1 kg of generated active chlorine were determined. The main process parameters are determined that provide for producing sodium hypochlorite by direct electrolysis of sea water using an iridium-ruthenium oxide titanium anode as electrodes. It was shown that the current chlorine yield reaches maximum values (85–90%) at an active chlorine concentration in the product of 2 ± 0.2 g/dm3 which motivate the technological and economic feasibility of obtaining sodium hypochlorite from sea (ocean) water.

Key words

sodium hypochlorite , chlorides , sea water , direct water electrolysis , current density

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Comparative evaluation of the economic effectiveness of using chlorine-containing media in water disinfection technologies

Summary

An engineering and economic comparison of three methods of water disinfection using: gaseous chlorine, high concentrated sodium hypochlorite and low concentrated sodium hypochlorite is presented. A comparative analysis was carried out using the example of an operating chlorination plant located on the territory of the wastewater treatment facilities in the city of Leninsk-Kuznetsky, Kemerovo Region. The economic analysis has shown that the use of low concentrated sodium hypochlorite compared to high concentrated sodium hypochlorite is beneficial, as the payback period is reduced. This confirms the expediency of using this technology since it provides for implementing a socially oriented tariff policy for consumers to a greater extent. Besides, while choosing a chemical, its advantages should be sought in the safety of delivery and storage, technological effectiveness in use, the amount of by-products in the preparation of the product at the place of use, as well as the delivery price of a chlorine-containing chemical or the cost of apparatus that produce it directly at the premises of the water treatment facilities from purchased raw materials.

Key words

gaseous chlorine , low-concentrated sodium hypochlorite , direct water electrolysis , high concentrated sodium hypochlorite , comparative analysis