Overview
Maintaining microbial control in USP water systems is critical, especially within storage tanks, distribution loops, and RO systems where biofilm and contamination can persist.
This field trial evaluated the effectiveness of Ultra-Pure chlorine dioxide generated directly in the system to fully decontaminate a USP water purification and distribution loop, including RO membranes and storage infrastructure.
System Description
The system consisted of:
- Two 125-gallon storage tanks holding RO/DI water
- A full recirculating distribution loop
- Reverse osmosis (RO) system with thin-film composite membranes
- UV treatment and DI components
At the start of the process:
- Tanks were full
- DI tanks were removed
- UV systems were shut off
- The loop was fully recirculating
Objectives of Testing
- Eliminate microbial contamination throughout the distribution loop
- Achieve full system penetration, including valves and dead legs
- Validate effectiveness through microbial testing (TPC)
- Decontaminate both feed and permeate sides of RO membranes
Methodology
Distribution Loop Treatment
Chlorine dioxide was generated directly in the storage tanks using:
- Two 12G units in one tank
- One 12G + one 5G in the second tank
Total ClO₂ generated: 41 grams
System conditions:
- Continuous recirculation during generation
- No incoming make-up water
- Even distribution across tanks and loop
Measured concentrations:
- ~26–28.7 ppm within first few hours
- 40.7 ppm after ~16 hours of recirculation
All valves were opened and flushed until concentrations matched the loop.
RO System Decontamination
A separate chlorine dioxide solution was prepared:
- 12G generated in ~5 gallons of water
- Measured concentration: 608 ppm
Injection setup:
- Dosatron pump at 8.5% injection rate
- Target concentration: ~50 ppm
Key observation:
- Chlorine dioxide passed through RO membranes and reached both sides of the system
Measured results:
- Feed/reject: 54.8 ppm
- Permeate: 53.0 ppm
System was then:
- Statically soaked for 60 minutes
- Fully flushed with clean water to <1 ppm
Results
Microbial testing (TPC) showed:
- Before treatment: TNTC (Too Numerous To Count) across multiple points
- After treatment: NG (No Growth) throughout the system
No residual impact:
- Chlorine dioxide reduced to <1 ppm after flushing
- No conductivity increase in RO product water
- System returned to normal operation immediately
Key Takeaways
- Full system penetration achieved, including valves and RO membranes
- Identical concentrations on both sides of RO membranes confirm true gas-phase diffusion in water
- Complete microbial elimination from heavily contaminated system
- No residual chemistry or operational disruption after flushing
Conclusion
This study demonstrates that Ultra-Pure chlorine dioxide can fully decontaminate complex USP water systems, including storage tanks, distribution loops, and RO membranes, in a single integrated process.
Unlike traditional chemistries, chlorine dioxide remains effective across the entire system, including permeate-side surfaces that are typically difficult to reach.
The result is complete microbial control, minimal downtime, and a clean return to operation without residual impact on water quality.
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