Technical Requirements and Prohibitions for Reverse Osmosis Inlet Chemical Dosing
April 16, 2026
When it comes to chemical dosing for reverse osmosis (RO) systems, there are numerous field cases where improper dosing sequences have led to membrane damage. Below is a detailed guide on the correct procedures and critical precautions:
1. Oxidizing Agents
Common Example: Sodium hypochlorite (NaClO).
Dosing Point: Typically added after the raw water pump and before the multimedia filter.
Purpose: To kill bacteria and algae, preventing microbial growth in the pretreatment stage.
Critical Prohibition: Oxidizing agents must never enter the RO membrane. Polyamide membranes are highly sensitive to residual chlorine, which causes irreversible oxidation, leading to a sharp decline in salt rejection.
Mitigation: After adding sodium hypochlorite, a reducing agent (e.g., sodium bisulfite) must be added to neutralize residual chlorine. The reducing agent should be dosed after the oxidizing agent and before the security filter, with sufficient pipe length or a static mixer to ensure a reaction time of at least 20-30 seconds.
2. Flocculants
Usage: Generally avoided unless necessary (e.g., high turbidity in raw water).
Dosing Point: If required, added before the sand filter.
Critical Issue: Compatibility with scale inhibitors—Cationic flocculants (e.g., polyacrylamide or polyaluminum chloride) can react with anionic scale inhibitors, forming sticky precipitates that clog the security filter and foul the membrane surface, which is harder to clean than scaling.
