WestWater (a Centurion company) replaced sodium hypochlorite with a ChloriDOS iOX Chlorine Dioxide system to tackle THM compliance risks. The upgrade reduced by-products, improved iron and manganese removal, and delivered safer, higher-quality water for the community. 

Scope of Work

A water utility client was using sodium hypochlorite as the oxidising agent for iron and manganese removal. However, this process was causing an increase in Trihalomethanes (THMs) to beyond acceptable levels, creating compliance risks and treatment inefficiencies. 

The client’s existing process relied on 10% sodium hypochlorite combined with a coagulant prior to filtration. This approach led to: 

• High THM formation, with average levels of 122µg/L and spikes up to 250µg/L, exceeding tolerable limits 
• Longer contact times required for sodium hypochlorite to effectively oxidise manganese and iron 
• The need for a safer, more efficient oxidation process to reduce by-products and improve overall water quality 

Execution

WestWater implemented the ChloriDOS iOX Chlorine Dioxide generation system as an alternative oxidant. Chlorine dioxide was chosen for its stronger and faster oxidation capacity (2.5x that of chlorine) and lower THM formation. 

The system operates by: 

• Using 9% hydrochloric acid (HCl) and 7.5% sodium chlorite (NaClO₂) in a controlled chemical process to generate chlorine dioxide solution 
• Volumetrically metering and mixing reagents under vacuum from dedicated chemical storage containers 
• Producing a homogeneous solution that is diluted with cold water before being safely stored under atmospheric pressure for dosing. 

Outcome & Value Delivered 

• THMs reduced to less than 5µg/L, a major improvement on the previous system 
• Iron reduced from an average of 0.009mg/L pre-dose to 0.002mg/L post-dose 
• Manganese reduced from 0.325mg/L pre-dose to 0.005mg/L post-dose 
• Reduced demand for secondary disinfection chlorine, further lowering THM formation in the network 



By implementing the ChloriDOS Chlorine Dioxide system, WestWater delivered a safer, more efficient oxidation process that significantly reduced THMs and improved iron and manganese removal. This project demonstrates how advanced oxidation technology can improve compliance, reduce by-products, and deliver high-quality water for communities.