pH Control in Water Treatment - with CO₂

Using CO₂ to Lower pH Levels More Accurately without Compromising Process Safety

The operators of water and wastewater treatment plants are challenged to maintain and in some cases tighten control over pH levels. Environmental regulations and tariffs usually stipulate that wastewater may only be discharged to a municipal pipeline or outlet channel if the pH value is within a narrow range, just above neutral. Many operators rely on strong mineral acids for pH regulation. However, acids have a number of disadvantages, including handling and safety hazards as well as the risk of overdosing. An overcorrection of mineral acids can cause a sudden and dramatic fall in the pH value, often leading to fines, regulatory intervention or damage to downstream assets.

Overcoming the Downsides of Stronger Mineral Acids for pH Control in Water Treatment

The use of carbon dioxide (CO₂) gas for pH control of wastewater is a more accurate, effective and even method. When dissolved in water, carbon dioxide forms carbonic acid, an effective neutralization agent that reduces the pH value to the appropriate level so the water can be released to downstream biological wastewater treatment processes, municipal receiving works or outlet channels. A fundamental advantage of carbonic acid is the almost flat gradient of its neutralization curve. Under atmospheric pressure, the minimum pH level achieved with CO₂ is around 6.5-7.0. The naturally self-buffering effect of CO₂ avoids the danger of over-acidification, allowing the desired pH value to be easily and precisely adjusted even if the raw water parameters are variable. Precise pH control can also increase the efficiency of many coagulation and precipitation reactions used in water treatment by controlling and buffering pH around the point where many coagulants are at their most effective.

Our SOLVOCARB^® portfolio is an environmentally friendly alternative to mineral acids. It uses CO₂ gas in order to neutralize alkaline waters. CO₂ is an effective, safe and cost-effective means of pH control that forms no harmful by-products and does not require specialist handling, storage or safety systems.

How Does Carbon Dioxide Compare with Mineral Acids for pH Control?

Compared with mineral acids, CO₂ for pH regulation and adjustments has many advantages:

• Elimination of handling and safety risks associated with highly corrosive mineral acids
• Highly effective, precise control of pH values
• Avoidance of excessive acidification of wastewater thanks to self-buffering pH control with CO₂
• Lower maintenance costs due to elimination of corrosion damage to plant fabric or pipework
• Maintenance of water alkalinity and prevention of the accumulation of unwanted anions such as chlorides or sulfates
• CAPEX and OPEX savings thanks to ease of deployment, safety benefits and reduced maintenance

Neutralizing and Remineralizing Desalinated Water with CO₂

CO₂ gas is also an effective tool in the treatment of desalinated water, which cannot be used directly as it is slightly acidic, lacks minerals and requires buffering. Consequently, desalinated water is prone to corrosion and has adverse effects on human health and the environment. In order to meet drinking water standards, water produced by desalination needs to be remineralized before it can be sent to the consumer. Our SOLVOCARB product line is a reliable and safe way of meeting neutralization and remineralization needs across a broad application spectrum from wastewater through process water to drinking water.

Protecting Local Ecosystems by Neutralizing pH with Carbon Dioxide

Carbon dioxide can also play a valuable role in helping to restore local ecosystems. Controlling pH is a key challenge in resolving legacy pollution from coal-fired power stations and other industrial plants. The fly ash that deposits in dams and lagoons pushes the water pH up. This alkaline water overflows into adjacent waterways during snow melt or heavy rainfall. Disused mines present a similar problem. Accumulated water absorbs minerals from the seams, which causes pH values to rise.

Our SOLVOCARB solutions are used to inject CO₂ into these water bodies, bringing elevated pH values under control, restoring water quality and preventing damage to surrounding ecosystems. SOLVOCARB is also idea for in-situ pH neutralization in lakes or lagoons that have suffered from industrial pollution.

Supporting all Steps in Your Water Neutralization and Remineralization Project Lifecycle

Our SOLVOCARB family was designed specifically to support pH control by directly injecting CO₂ in gaseous form or, for an even faster reaction, as an aqueous carbonic acid mixture into water. Our SOLVOCARB portfolio spans a number of solution models for different pH regulation tasks, including remineralization, re-carbonation, pH control of raw blended waters, alkaline wastewater and process water, and calcite solubility control. It is suited to inline or bypass operations. SOLVOCARB CO₂ neutralization equipment can also be applied to drinking water.

Regardless of your individual application, you can rely on our water treatment experts to support you at every stage of your water treatment project, from the process design and build phase, through installation and commission to pilot trials. Our extensive SOLVOCARB portfolio includes gas metering and gas dissolution equipment.

All SOLVOCARB carbonation systems are designed to bring you the following benefits:

• Efficient use of CO₂
• Easy to install and use
• Fully automatic PLC for pH, flow and other process signals
• Accurate control of CO₂ dosing and pH control
• Automated design for minimal operator input and maintenance
• Adaptable to suit individual flow and pH requirements
• Suitable for integration into existing processes
• Complete process train and turnkey packages

Our SOLVOCARB systems come with a carbon dioxide supply scheme as standard. Depending on your volume requirements, this may be based on bulk deliveries or gaseous cylinder delivery systems.

Click on the links below for more information on our SOLVOX family members.

Accurate Water and Wastewater Analysis with High-purity Gases and Precision-engineered Equipment

To meet your water analysis needs, we supply high-purity gases, accurate gas mixtures, precision-engineered gas supply systems and high-quality supporting services for results you can rely on. The ongoing expansion of our portfolio ensures that our mixtures support the latest species and analytical techniques. All of our gases and mixtures come with certificates of analysis to ensure you comply with applicable quality assurance and traceability requirements. Regardless of your analytical requirements, you can always rely on us for customized solutions that meet your individual analysis and calibration challenges. In many regions, we also offer complete analysis and technical support services to determine how much CO₂ is required to adequately treat your water to your target pH level.