Use of the reverse osmosis method for the preparation of concentrated sodium chloride solutions for the production of sodium hypochlorite

Summary

The use of membrane reverse osmosis and nanofiltration plants for the production of drinking water is described. It is noted that using hypochlorite obtained by the electrolysis of concentrated solutions of table salt is an effective method of disinfection in drinking water supply systems. A new area of application of reverse osmosis systems is considered, i. e., the preparation, in addition to clean water, of concentrated solutions of sodium chloride used for the production of sodium hypochlorite to reduce the operating costs of a drinking water treatment plant eliminating the purchase of the chemical, i. e., table salt. A process flow scheme of the proposed technology is presented, that involves cascade processing of the source water using nanofiltration membranes of low selectivity to provide for separating the concentrate into the solutions of monovalent and divalent ions. The experimental procedure is described and experimental dependencies are presented to determine the efficiency of the concentrate separation. Based on the results of the experiments, an economic calculation of the costs of designing an additional system for producing concentrated solutions was performed proving the economic efficiency of the proposed process compared to the use of table salt.

Key words

disinfection , sodium hypochlorite , reverse osmosis , reverse osmosis unit , nanofiltration , concentrate utilization , water treatment , electrolysis method

The experience of operating new water treatment facilities
at the South Water Treatment Plant in Saint-Petersburg

Summary

The information on specific features of the process flow schemes of drinking water preparation at the municipal water treatment plants in Saint-Petersburg is presented. The process of drinking water treatment at the new water treatment facilities (K-6 Block) of the South Water Treatment Plant is described where the cutting-edge technologies of water treatment are used. The technologies ensure the standard drinking water quality as regards all the indicators prescribed by Sanitary Rules and Regulations 2.1.4.1074-01 at any possible changes in the Neva River water quality, in particular in case of unfavorable and accidental events in water sources (in case of accidental discharges, storms at the Ladoga etc.). An automated water quality control system with the use of flow-type analyzers fed with water samples taken continuously at different points of the treatment process has been introduced at the plant. This provides for the on-line information on the operation efficiency of separate units for operating control. The analysis of the operational data for K-6 Block that includes lamella clarifiers, double-layer filters with sand media and activated carbon is presented. Herewith wash water and sludge treatment and utilization are provided. The results of the comprehensive water quality analysis for 51 parameters at the outlet of K-6 Block at the South Water Treatment Plant are given.

Key words

best available techniques , water supply plant , lamella settler , water treatment , double-layer filter

Comparative analysis of the physicomechanical properties
of natural materials used as filter media

Summary

The results of the study of physicomechanical properties of filtering materials – crushed expanded clay with a bulk density of 525 and 555 kg/m³ and Diamix AQUA with a bulk density of 670 kg/m³ are presented. Easy upheaving clays of a certain chemical and mineral composition serve as raw materials for expanded clay production, for Diamix AQUA production raw material based on natural diatomite that includes exoskeletons of diatoms is used. Oxide concentration in Diamix AQUA is: SiO₂ more than 83%, Al₂O₃ less than 6% and Fe₂O₃ less than 3.5%. Diamix AQUA filtering material has a National Registration Certificate. The research results showed that the new filtering material based on Diamix AQUA can be used as media for newly constructed filtration facilities. To regenerate the filter media, an increased backwashing rate is needed, which requires checking the throughput of the filter drainage and distribution system to pass through the increased water flow rate.

Ключевые слова

water treatment , filtering material , bulk density , apparent specific gravity , physical integrity , backwash rate