Technology: CDOX 

Application: Recarbonation 

Location: Midwest 

Goals: Precise & Automated pH Control | Implement Process Water As Carrier Stream | Reduce Operational Cost



The replacement of an existing diffused carbon dioxide (CO2) system at a 120 MGD municipal water treatment plant in the Midwest was needed so that pH control in a recarbonation process could be improved. The treatment facility desired a more efficient dissolution system that would provide tighter control over process pH levels and ultimately save money on operation and maintenance expenses associated with carbon dioxide usage.

BlueInGreen’s CDOX® technology was sought out for its highly efficient process for automatic pH control. BlueInGreen’s proprietary process makes it possible to deliver large quantities of gas in very small quantities of water, as much as ten times less water than the leading competitor’s system. 

BlueInGreen provides a fully- integrated, skid-mounted system. Since all components necessary for system operation are provided with CDOX®, installation is as simple as connecting carrier water lines, gas and vent lines, power, and Ethernet for automatic control, as seen in Figure 1. 

Figure 1.

Figure 1.



Figure 2 shows the recarb basin pH trend with competing CO2 dissolution technology in comparison to BlueInGreen’s CDOX®. The data clearly shows that the CDOX® is very effective at controlling pH within a tight range and automatically making adjustments for changes in water quality. A comparison of the CO2 delivery rates for the two systems on this day shows that for the same influent pH, the CDOX® used 35% less CO2 to achieve the desired recarb basin pH. During the entire course of the study, the CDOX® on average used 40% less CO2 than the diffusers. 

Figure 2.

Figure 2.

Figure 3.

Figure 3.


The 40% reduction in CO2 usage corresponds to an annual operation cost savings of $49,000 under current conditions. In the near future, when the plant starts targeting a lower pH in the recarbonation basins, the savings are estimated to be $124,000 annually.

Notably, the existing diffused CO2 system requires a large concrete basin to provide the depth necessary for gas transfer. In contrast, the CDOX® technology can be applied either in-basin, using a much smaller structure, or in-pipe, which ultimately results in a lower total cost of installation.

In this application, the only available pH feedback signal was located about 20-min downstream from the CDOX® injection
point. Without this long delay, the pH control range would be even tighter than what is illustrated here.

Figure 3 clearly illustrates the effectiveness of BlueInGreen’s unique control algorithms. The CDOX® responded well to both an increase in operator selected pH set point, as well as an increase in plant production.

BlueInGreen’s CDOX® technology demonstrated effective pH control with fast response to influent water quality as well as plant production rate changes. The process is highly efficient, having excellent mass transfer capabilities and near 100% utilization of vaporized gas. Combined with a fully-integrated control scheme that is unmatched in the industry, the CDOX® excels at carbon dioxide delivery.