AWWA WQTC69244

Advances in chemical feed equipment provide options for cost-effective alkalinity addition that were previously unavailable. In the past, carbon dioxide systems required deep basins and a significant amount of reaction time to achieve stable water. Solution carbon dioxide feed systems allow for instantaneous dissolution of "liquid" carbon dioxide and provide a means for depressing the pH in an inexpensive and safe method which when used in combination with lime addition can allow utilities to "dial-in" both the optimal pH for coagulation as well as provide a significant increase in presoftened, coagulated, and finished water alkalinity. Carbon dioxide addition in combination with lime prior to coagulation allows additional buffering capacity in the coagulation process to minimize basin corrosion while providing an optimal enhanced coagulation pH. Lime or caustic addition prior to media filtration or after membrane filtration allows the shift in the carbonate species and stabilizes the water quality. Improved technology, which provides faster reacting lime slurry allows for addition of lime after filtration, without significantly impacting the turbidity of the finished water (depending on the water quality). Includes tables.