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UDC 628.165:66.081.63

Removing calcium carbonate from reverse osmosis concentrate
by crystallization with seeding agent

Summary

The technology of removing calcium carbonate from reverse osmosis concentrate in the process of crystallization with seeding agent is described. Seed crystals are suspended in recycling concentrate flow. Owing to calcium carbonate depositing on the seeding agent the total salt content of concentrate decreases and high filtrate flow rate is provided that facilitates concentrate disposal. To implement the technology membrane apparatus with «open channel» are used that are resistant to the impact of membrane transfer of slightly water-soluble salts and suspended matter. Seed crystal growing is provided by dosing into concentrated caustic soda solution. Grown seed crystals were partially removed by sedimentation after hydraulic membrane wash. With the help of experimental diagrams it is possible to determine calcium carbonate crystallization rate depending on the influent water composition, the number of the seeded crystals, and filtrate yield. Process flow diagram of a continuously operating reverse osmosis plant is suggested. The methods of the process design are described: selecting the amount of recycling seed crystals, determining caustic soda consumption and tank size for calcium carbonate sludge precipitation. The estimations showed that to provide for calcium carbonate crystallization du­ring continuous operation of the reverse osmosis plant caustic soda solution in amount of less than 5% of its stoichiometric amount required for the precipitation of the same amount of calcium carbonate from the influent water shall be regularly dosed into the recycling concentrate flow.

Key words

concentrate , water stabilization , concentrate utilization , reverse osmosis unit , calcium carbonate crystallization , seed crystals

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UDC 628.165

Pervov A. G., Andrianov A. P., Efremov R. V., Spitsov D. V.

Utilization of reverse osmosis concentrate with removing from it calcium and magnesium ions

Summary

The possible use of pre-developed technology of removing calcium carbonate with seeding agent to reduce the consumption of concentrate from large-scale units operating at the heat power facilities was studied. Concentrate of the operating reverse osmosis units contains inhibitors that inhibit the rate of seed crystal growth and impede the process of its utilization. The correlations between the calcium carbonate growth rate in the concentrate containing inhibiting substances and the dosage of the introduced seed, pH value and permeate yield were studied. For the implementation of the technology membrane apparatus with open channels are used that are resistant to the impact of membrane transfer of low-soluble salt deposits and suspended substances on the process. The developed by the authors technology of the concentrate utilization from reverse osmosis units installed at the heat power facilities for boiler feed water preparation is described. With the help of the developed technology softened water with lowered alkalinity and salt content can be produced. Herewith no chemicals are needed, and the unit does not consume water for its own needs. The technology provides for the complete utilization of reverse osmosis concentrate by improving its quality (in terms of hardness, alkalinity and total dissolved so­lids) to the requirements that allow using it for engineering purposes (for adding into a heat supply system or a circulation water supply system). Herewith any saline discharges into the environment are eliminated.

Key words

concentrate , inhibitor , reverse osmosis unit , concentrate utilization , calcium carbonate crystallization , seed crystals