pH Control Systems
Two Typical CO₂ pH control systems are described below in detail.

CO₂ is introduced into the high pH water by means of a CO₂ injection manifold, which is typically installed at the bottom of a basin or tank.  Small CO₂ bubbles are released by the injection manifold into the high pH water. A pH probe is installed in an optimal location inside the basin or tank, thus measuring pH in the water after absorption and C0₂ reaction. A pH control panel is used to modulate gas flow automatically and achieve high efficiency and reliability with little supervision from plant personnel.  The CO₂ pH control technology can be customized to suit your control needs. 

CO₂ is introduced into the high pH water by means of a diffuser, which is typically installed in an existing pressurized pipe.  Small CO₂ bubbles are released by the diffusers into the high pH water.  A pH probe is installed downstream of the CO₂ injection point, thus measuring pH in the water after absorption and C0₂ reaction.   A pH control panel is used to modulate gas flow automatically and achieve high efficiency and reliability with little supervision from plant personnel.  The CO₂ pH control technology can be customized to suit your control needs.

Benefits of CO₂ pH Control
Safe-to-use:  carbon dioxide in the absence of water is inert and non-corrosive.  It does not require mechanical transfer or handling equipment.  It becomes active only when dissolved in water.  CO₂ leaks dissipate safely into the atmosphere, leaving no residue to be neutralized.  Furthermore, carbon dioxide does on corrode metal equipment.  No special alloy or plastic distribution piping is required for the CO₂ system. 

Accuracy of Regulation:  CO₂ is better than strong acids for controlling pH because it forms a mild but highly reactive acid which minimizes risks of over acidification and rapidly responds to any variations of the incoming pH or water flow rate.  Over or under treatment with mineral acids will often result in a pH, which rapidly deviates from the compliance range. 

Low Maintenance System:  Systems are generally engineered to be pressure driven.  With a minimum number of moving parts, this system offers continuous trouble free operation.  Moreover, trained technicians can be rapidly dispatched to service the bulk CO₂ tank in the unlikely event of a problem.

Flexibility:  With a turndown ratio in control of the CO₂ injection rate exceeding 10:1, the pH control system will efficiently and rapidly respond to any fluctuation of flow rate or incoming pH.

Safe for the Environment:  There is no secondary pollution introduced into the treated water by salts such as chlorides (from HCL) or Sulfates from (H2SO4).  The introduction of CO₂ will contribute to the chemical equilibrium of water by forming neutral carbonates and bicarbonates.

The Chemistry
Carbon dioxide is a gas, which once dissolved into water produces a weak acid called carbonic acid.  Carbonic acid reacts immediately with alkalis such as caustic soda, sodium carbonate and dissolved lime, turning them into neutral carbonates and bicarbonate salts.

C0₂ + H₂0 à H₂CO₃
H₂CO₃ + 2NaOH à Na₂CO₃ + 2H₂O
H₂CO₃ + Na₂CO₃ à 2NaHCO₃

Carbonic acid is mild acids present in water as ions H⁺ and HCO3^-, which are highly reactive.  They will immediately react with ions responsible for alkalinity of water.

Safety of C0₂
For many years now, sulfuric acid has been used control alkalinity in.  It’s a product that works, but it also has many potential problems.  Sulfuric acid can be difficult to apply and control.  It is potentially dangerous to store and handle.  Special safety clothing must be worn by personnel and emergency wash down showers need to be installed and readily available. 

Mineral Acids being extremely corrosive acid requires special equipment and piping construction.  These acid systems require many hours of maintenance resulting in costly repairs and replacement.  Carbon dioxide systems require very little upkeep, are safe, easy to operate, efficient and environmentally friendly.

If pH control is crucial to your process or water quality, C02 can be a practical alternative.