In an industrial Reverse Osmosis (RO) system, mineral scaling is the main reason membranes get choked, flow rate drops, and electricity bills go up.
When clean water (permeate) is separated by the membranes, the remaining wastewater (reject) becomes highly concentrated with minerals like calcium, silica, and sulfates. If these minerals exceed their limits, they form a hard white crust on the membrane surface.
To prevent this scaling, antiscalant chemicals are continuously injected into the raw water feed line.
Under-dosing: Causes fast membrane choking and frequent chemical cleaning (CIP).
Over-dosing: Wastes expensive chemical money and can cause biological slime inside membranes.
Here is a simple, step-by-step guide to calculating the exact antiscalant dosing for your system.
Key Information You Need First
Before doing any calculation, note down these 4 basic details about your plant:
Feed Water Flow Rate: Total raw water entering the RO plant in Liters per Hour ($\text{LPH}$) or Cubic Meters per Hour ($\text{m}^3/\text{hr}$).
Recommended Chemical Dose: Chemical dose required in $\text{ppm}$ (parts per million or $\text{mg/L}$). Your chemical supplier suggests this based on your water test report (usually 2 ppm to 5 ppm).
Chemical Tank Size: Total volume of your chemical dosing tank (e.g., $100\text{ Liters}$).
Pure Chemical Added to Tank: Liters of pure liquid antiscalant mixed in the dosing tank.
Golden Rules for Plant Operators
Always Mix in RO Water: Never mix antiscalant chemical using raw borewell water. Always use clean RO water in the chemical tank, otherwise white powder will settle at the bottom of the tank.
Inject Before Cartridge Filter: Install the dosing point before the 5-micron security cartridge filter so the chemical mixes properly before entering high-pressure pumps and Industrial RO Membranes.
Check Pressure Drop Daily: If pressure gauge difference between feed and reject increases by 15%, check your dosing pump immediately.
Adjust for Hard Water: If your raw water hardness is very high, consider installing an upstream Water Softener Plant alongside antiscalant dosing to protect your complete Industrial RO Plant.