Study of the current waveform effect on the formation of cathode deposits during direct electrolysis
Part 2. Electrolysis of sea water

Summary

Sodium chloride is a raw material for the production of sodium hypochlorite; however, the cost of its purchase and delivery is up to 25–30% of the total cost of the disinfectant produced. An alternative raw material for the production of sodium hypochlorite can be chlorides present in natural mineral water, e. g., underground, sea and oceanic water. Mineral water will be the raw material for obtaining sodium hypochlorite solution of a sufficiently high concentration that can then be added to the treated water. The experience of operating CHLOREFS units manufactured by EKOFES SPE LLC showed that the main problem related to the electrolyzer operation reliability is associated with the formation of deposits of hardness salts – calcium carbonate on the surface of the cathodic electrode, and magnesium hydroxide on the surface of the electrolyzer cathodes. This results in a negative electrolysis regime, an increase in voltage, overheating and warping of the electrode system, destruction of the oxide coating of the anodes, etc. The results of studies of direct electrolysis by direct and reverse current of salt water of the South Vietnam Sea are presented. During the tests the effect of reverse current in comparison with direct current on the reduction of the formation of insoluble substances on the cathodes of the electrolyzer was estimated, and besides, the electrolysis process parameters were determined. The current chlorine yield for seawater was above 100% in the reverse mode with a current density of 100 A/m².

Key words

disinfection , water treatment , sea water , sodium hypochlorite , direct electrolysis with constant and reverse current

DOI 10.35776/VST.2021.10.02
UDC 628.166:541.135

Pchel'nikov I. V., Nguen Tkhi Tuan Z’ep, FESENKO L. N.

Study of the current waveform effect on the formation of cathode deposits during direct electrolysis.
Part 1. Electrolysis of fresh water

Summary

During the electrochemical processing of chloride-containing natural water in a membraneless electrolyzer, salts of hypochlorous acid are formed that are exhibiting oxidizing properties. This process is widely used for the production of sodium hypochlorite disinfectants. The raw material for the production of sodium hypochlorite can be not only artificially prepared saline solutions, but also natural mineral water containing chlorides. The electrolysis of such solutions results in the formation of insoluble calcium and magnesium salts at the cathode of the electrolyzer thus inhibiting mass transfer in the interelectrode space and the occurrence of emergency situations. The first part of the article presents the results of studies of direct electrolysis of fresh water with constant and reverse current in Dong Hoi city, Republic of Vietnam. In the conducted tests the effect of reverse current in comparison with direct current on the reduction of the formation of insoluble substances at the cathodes of the electrolyzer was determined. The experiments have shown the advantage of reverse current over direct current. So, during the electrolysis with reverse current for a period of up to 6 hours, the amount of deposits on the electrodes did not increase, however, with direct current the deposits accumulated from the very beginning of the electrolysis process. This is due to the fact that the precipitate formed during the cathodic half cycle is dissolved during the anodic half cycle by acid, a product of water oxidation. The current output of chlorine for tap water was no more than 23% with a current density of 100 A/m².

Key words

disinfection , water treatment , sodium hypochlorite , direct electrolysis with constant and reverse current , fresh water

bbk 000000

UDC 628.166.094.3

Zenitov N. A.

DKT-425 vehicle for pipeline disinfection

Summary

Maintaining water facilities in proper condition requires mandatory sanitary measures, i. e. disinfection. Lately many water companies in Russian cities have been increasingly using sodium hypochlorite as a disinfecting agent. Using it makes the technology of water disinfection easier and provides for maintaining the residual active chlorine in water. Disinfection is carried out by filling a water network section with water with addition of sodium hypochlorite in dosages rated for a time period required for killing hazardous microorganisms – bacteria, viruses etc. To provide for precise sodium hypochlorite dosing and supplying to the water network section under disinfection, for distributing the disinfecting agent uniformly along the entire length of the section, and for convenient transporting and dispensing sodium hypochlorite in accordance with the safety rules DKT-425 vehicle based on Hyundai HD-65 automobile was suggested. It includes: a dosing unit with a membrane pump; a plastic tank for sodium hypochlorite; a tank for equipment washing with a self-priming pump, a hose and a nozzle; a filling hose and a feeding hose on hand-driven drums; a generating set; an air heating unit; and a plenum system. The technology of pipeline disinfection with the use of the dosing equipment of the vehicle is presented. The calculating formulae for determining the required amount of sodium hypochlorite, the time required for uniform filling the disinfected section with account of the carriage water flow are given. The examples of calculating the disinfection process parameters are set.

Key words

water pipeline disinfection , sodium hypochlorite , dosing equipment , vehicle for disinfection

UDC 628.166.094.3:661.418
DOI 10.35776/VST.2023.09.06

Gao Yuan, NEFEDOVA E. D., KINEBAS A. K., Lobanov Fedor

Disinfection of water with low-concentration sodium hypochlorite

Summary

An advanced safe technology for the production of low-concentration sodium hypochlorite from salt brine is considered. The main stages of the technological process are described in detail. Particular attention is paid to the issues of industrial safety and reliable operation of electrolyzers – units for the preparation of sodium hypochlorite at the Southern and Northern water treatment facilities of SUE «Vodokanal of St. Petersburg». The use of low-concentration solutions of sodium hypochlorite provides for improving the safety of water purification processes. Salt is the raw material for the production of sodium hypochlorite. Since the chemical is used directly at the place of production, there is no need for transportation. The combination of disinfection of treated water with low-concentration sodium hypochlorite (first stage) with ultraviolet irradiation (second stage) before supplying it to the city water supply network guarantees full compliance of water quality in terms of microbiological indicators with current standards and its high epidemiological safety.

Key words

disinfection , water treatment , sodium hypochlorite , epidemiologic safety

FaLang translation system by Faboba