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