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RO Antiscalant Selection: Water Analysis and Membrane Protection

Antiscalant selection based on water analysis to prevent silica, carbonate and sulfate precipitation on the final stage membrane surface in reverse osmosis systems.

In reverse osmosis (RO) systems, 70-82% of the water is separated as pure water (permeate), while the remaining dissolved ions are concentrated 3 to 6 times in the concentrated (reject) phase. This condensation causes saturation limits to be exceeded, especially on the final stage membrane surface.

Therefore, RO antiscalant should not be chosen by heart. Calcium, magnesium, barium, strontium, sulfate, bicarbonate alkalinity, reactive silica (SiO₂), iron, pH, water temperature and conductivity data in raw water analysis; It is evaluated together with the target recovery rate and membrane sequence of the system. Fixed dosage should not be applied without seeing the water analysis.

Older generation products such as standard sodium hexametaphosphate (SHMP) may hydrolyze in the solution tank, creating calcium phosphate precipitation, and are inadequate in high silica well waters. Elif Çevre Kimya's product line includes calcium carbonate, calcium sulfate, barium/strontium sulfate and phosphonate, polycarboxylate and dendrimeric polymer-based RO antiscalant options for high silica loads.

In addition, the interaction of aluminum or iron cations that may escape from pretreatment with the antiscalant and the chemical compatibility criteria of the membrane manufacturer (polyamide TFC membrane) must be taken into account.

Even if the most appropriate antiscalant is selected, air release from the dosing pump, continued operation of the pump when the RO system stops, or over-dosing may cause organic/polymeric contamination on the membrane surface. The pump should be electrically interlocked with the feed line, daily chemical consumption should be verified with the feed water meter, and normalized differential pressure/flow trends should be recorded.

Do not choose antiscalant with the mentality of “one product for every water”

In reverse osmosis (RO) systems, 70-82% of the water is separated as pure water (permeate), while the remaining dissolved ions are concentrated 3 to 6 times in the concentrated (reject) phase. This condensation causes saturation limits to be exceeded, especially on the final stage membrane surface. Therefore, RO antiscalant should not be chosen by heart. Calcium, magnesium, barium, strontium, sulfate, bicarbonate alkalinity, reactive silica (SiO₂), iron, pH, water temperature and conductivity data in raw water analysis; It is evaluated together with the target recovery rate and membrane sequence of the system. Fixed dosage should not be applied without seeing the water analysis.

Correct Chemistry Against Silica, Carbonate and Sulfate Precipitation

Older generation products such as standard sodium hexametaphosphate (SHMP) may hydrolyze in the solution tank, creating calcium phosphate precipitation, and are inadequate in high silica well waters. Elif Çevre Kimya's product line includes calcium carbonate, calcium sulfate, barium/strontium sulfate and phosphonate, polycarboxylate and dendrimeric polymer-based RO antiscalant options for high silica loads. In addition, the interaction of aluminum or iron cations that may escape from pretreatment with the antiscalant and the chemical compatibility criteria of the membrane manufacturer (polyamide TFC membrane) must be taken into account.

Dosing Automation and Concentrate Line Tracking

Even if the most appropriate antiscalant is selected, air release from the dosing pump, continued operation of the pump when the RO system stops, or over-dosing may cause organic/polymeric contamination on the membrane surface. The pump should be electrically interlocked with the feed line, daily chemical consumption should be verified with the feed water meter, and normalized differential pressure/flow trends should be recorded.

Field Control and Monitoring List

Chemical dosage and system capacity decisions should be determined by analysis and facility conditions; There is no guarantee of fixed dosage or performance.

  • Control of calcium, sulfate, alkalinity, silica (SiO₂), iron and pH values ​​in current raw water analysis
  • Calculation of saturation limits in the concentrate stream at the targeted RO recovery rate (% recovery)
  • Verification of antiscalant compatibility with coagulant (PAC/Aluminium/Iron) residue used in pretreatment
  • Automatic start/stop (interlock) connection of antiscalant dosing pump with RO feeding pump
  • Weekly recording of final stage pressure difference and concentrate/product conductivity trends

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