pH Adjustment

pH Adjustment

pH is a measure of the how acidic or basic water is, with a range from 0 to 14. More exactly, it is the measurement (negative logarithm) of hydrogen ion concentration H+. The scale ranges from 0 (most acidic) to 14 (most basic). The term pH refers to "pondus hydrogenii" or power of hydrogen.

pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH+, in a solution.

Wastewater Discharge Requirements

Neutralization of wastewater that is highly acidic or highly basic is required for discharge to municipal sewer systems, rivers, and streams. The allowable pH range is generally 6 to 9 standard units, but can vary depending on the source of discharge. Reasons to control pH include:

• Protecting human health and the environment.
• Protecting wastewater infrastructure from corrosion.
• Protecting biological treatment processes.
• Supporting coagulation, flocculation, and metals precipitation.

Sources

Many industries have multiple sources of wastewater that, if discharged untreated, will violate pH requirements. Acids and bases are used throughout plant production and cleaning operations.

Treatment

Low-pH wastewater is generally neutralized using sodium hydroxide, lime, magnesium hydroxide, or calcium hydroxide. High-pH wastewater is generally neutralized with sulfuric acid, hydrochloric acid, or carbon dioxide. The most common chemicals are sulfuric acid and sodium hydroxide.

Neutralization can be accomplished by batch treatment or continuous-flow processes. Most continuous systems consist of one or two neutralization tanks, depending on flow rate and pH swings. A pH sensor measures the water and activates a metering pump to dose acid or caustic as needed.