Purification of water with high permanent hardness and salinity

Summary

Chemical softening methods have been widely used in the practice of water treatment, primarily in the energetics and industry for softening, decarbonization and decoloration of water. In combination with reverse osmosis, they provide for preparing water of the required qualitative composition. In drinking water supply softening methods are used quite rarely due to a number of circumstances, such as the need to use various chemicals that are not typical for public water supply; generation of a large volume of sludge subject to subsequent processing, and, what is most important, resulting in highly alkaline water with pH of more than 10 unacceptable for drinking water. However, in case only but water sources with such a complex composition are available, then chemical methods have to be used. In Mediana-Filter Research and Production Company, JSC studies were carried out to obtain high-quality water from an underground source of uncharacteristic salt composition, with a high content of sulfates and low alkalinity, provided that the purification technology should generate minimum liquid waste. After testing several technology options in pilot plants, a scheme was proposed that met the requirements of the customer. It should be noted that underground water of the southern regions of the country has a partially similar salt composition, so the results of pilot tests can also be applied to obtain drinking water from similar sources.

Key words

reagent treatment , flow chart of treatment , reverse osmosis , desalination , hardness , pilot plant , sulphates , water , dynamic softening system , liming , sodium liming , soda softening , sludge blanket , dynamic softening system water conditioning

Chemical softening of the Don River water in a dynamic softening system – a unit with fluidized inert bed

Summary

Underground water sources with high levels of hardness salts are often used for drinking water supply. To provide for the potable water quality, water softening is required. The known softening methods result in significant amounts of liquid and solid waste, i. e. mineralized wastewater or sludge not subject to utilization. Chemical softening of drinking water in clarifiers is rarely used because of the difficulties in preparing chemicals, maintaining the required constant water temperature, and the complexity of the installations and their maintenance. Since the 1990s, the chemical softening technology in intensified reactors with contact media – such as vortex and fluidized bed reactors – has been developed and found widespread application in drinking water supply. These units are widely used in Europe and the USA being much easier to maintain than clarifiers. The capacity of these units reaches thousands of cubic meters per hour. Their main advantage is the elimination of liquid discharge and generation of solid waste that can be easily disposed of, with a virtually 100% clean water yield. In Russia, RPC Mediana-Filter JSC is actively developing this technology using DSS® (the proprietary dynamic softening system).

Key words

potable water , reagent treatment , suspended layer , pilot plant , water softening , contact media , fluidized bed , intensified reactor , liming , soda softening , river water purification , soda liming , DSS® dynamic softening system