Low Effluent pH | Activated Sludge Process | Wastewater Treatment Plant

 Low Effluent pH 

Low influent pH or low alkalinity water with nitrification are the most common causes. Both can result in regulatory noncompliance.

If the influent pH is low (acidic), the condition is likely to pass through the plant and be detected in the effluent. The immediate solution is to add chemicals to raise the pH. For pH adjustment, lime, soda ash, or sodium bicarbonate are commonly used. The ultimate solution, however, is to eliminate the low pH source from the collection system by requiring pretreatment. A pH adjustment may be required in an industrial system.

Low effluent pH is often induced by nitrification in conjunction with low natural alkalinity in the wastewater if the influent pH is appropriate. If ammonia removal is required, nitrification must be maintained. Using on/off aeration or creating an anoxic zone can often provide enough alkalinity to elevate the pH to a satisfactory level. If neither of these options is available, pH adjustment may be necessary.

When the influent pH is near 7.0 and nitrification is not required, the MCRT or DO can often be reduced sufficiently to inhibit nitrification. Because there is no nitrification, there is no reduction in alkalinity during the aeration process, and the pH remains stable. However, in systems that naturally nitrify, such as extended aeration, a solution may be required if MCRT and DO control are ineffective.