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

Desalination of sea water: trends, experience and development prospects in the Russian Federation

Summary

Fresh water is a limited and unevenly distributed resource. Despite significant fresh water resources, some regions of the Russian Federation experience a shortage of it, which affects the dynamics of the economic development and living standards. This fact requires a revision of the classical approach to the environmental management, in particular, to the extraction of fresh water from sea and brackish waters. The most common desalination technologies are thermal (distillation) and pressure membrane (reverse osmosis and nanofiltration) processes. Over the past quarter century, reverse osmosis has become the predominant water desalination technology, accounting for more than 70% of all production capacity in the world. Nevertheless, reverse osmosis has a number of significant limitations, the consideration of which while designing desalination plants is a prerequisite for the subsequent efficient and reliable operation of the facilities. Strict requirements for the quality of source water supplied to reverse osmosis membranes necessitate the use of complex and often multi-stage seawater pretreatment systems. The choice of technical solutions for pre-treatment and «architecture» of reverse osmosis plants is the subject of a comprehensive technical and economic analysis with account of local aspects, including the region of construction, its natural and climatic conditions and available infrastructure. The shortage of water resources and the climatic and oceanological conditions of the coastal regions of the Russian Federation atypical for the global desalination industry make the solution to this optimization problem relevant and appropriate.

Key words

reverse osmosis , desalination , membranes , desalination , sea water , fresh water , distillation , pretreatment