In-line carbon dioxide pH neutralisation

Project summary

High-pH water treatment in dewatering previously relied on substantial tank volume, dilution, manual set-up and a large operational footprint. A new prototype in-line CO₂ pH neutralisation system designed by Minerex Environmental to replace a previous traditional tank-based treatment system continuously treats water and could reduce set-up time and costs.

The background

High-pH water treatment is currently undertaken using multiple 2500 L treatment tanks, 110 V pumps, recirculation pipework and bubble diffuser systems. While effective, this approach requires a large operational footprint to hold the substantial tank volume, in addition to complicated manual set-up.

Minerex Environmental identified an opportunity to achieve compliant pH treatment through a more efficient and practical solution that could be deployed on constrained sites and respond more effectively to variable operating conditions. The resulting innovation was developed as a prototype in-line CO₂ neutralisation system that treats water continuously as it flows to discharge, removing the need for bulk holding tanks.

The prototype is already in use on-site and a second prototype has been built, which is undergoing more rigorous testing.

The challenges

The primary challenge was finding a way to achieve compliant pH treatment performance without relying on tanks, pumps and large infrastructure used in the conventional treatment process. The existing system benefited from several passive treatment mechanisms, including dilution within stored water volumes, gradual CO₂ introduction, recirculation and large buffer capacities that stabilised treatment.

Additional challenges were maintaining stable pH control without a large buffer volume and achieving effective gas transfer and mixing in a flowing stream.

The solutions

The development team analysed the strengths and limitations of the existing tank-based treatment process, redesigned gas transfer and mixing through a purpose-built diffusion chamber, and implemented proportional–integral–derivative (PID)-based control systems to provide dynamic dosing in response to changing flow and pH conditions.

The diffusion chamber and downstream pipework was designed to maximise contact between flowing water and injected CO₂, creating sufficient mixing time to reduce pH without a tank to retain water in.

The PID control strategy allowed dosing rates to respond proportionally to changing process conditions, providing a more intelligent and stable treatment response than conventional on/off dosing.

Practical site requirements were also incorporated into the design through footprint reduction, simplified mobilisation and automatic CO₂ cylinder changeover. This integrated approach ensured the solution was technically effective while remaining practical for field deployment.

The impact

The prototype is already in use on-site and a second prototype has been built, which is undergoing more rigorous testing. Results from both show that the system can maintain the operational efficiency of a tank-based set-up, while significantly reducing equipment requirements.

The project allows pH control to be managed with a portable, controllable and scalable treatment solution, enabling faster mobilisation, simpler installation and deployment on sites where conventional systems would be difficult or impractical. The solution was progressively tested and refined under live operating conditions at flows of up to 16 L/s and will be used to develop a more standardised and scalable approach to high-pH water treatment across multiple projects and site types.

One of the biggest practical benefits is the dramatic reduction in size and complexity. Traditional tank-based systems can be cumbersome to transport, position and install, particularly on urban or constrained sites, so the smaller footprint opens up many possibilities for these sites.