Title: Calcium carbonate as an effective new alternative for pH and alkalinity control in the activated sludge process
The main objective of this presentation is to educate the audience on the chemistry, capabilities and demonstrated advantages of using calcium carbonate for pH and alkalinity control in activated sludge systems.
Chandler Mancuso will be the exclusive presenter for this presentation. The bio is provided in the ‘Presenter Bio’ section.
The activated sludge process is a well-established wastewater treatment process used to treat municipal wastewater as well as industrial wastewater with high organic and nutrient content. The nitrification reactions involved in the activated sludge process, along with the addition of acidic coagulants such as ferric chloride and aluminum sulfate, induce acidification and alkalinity consumption in the wastewater. If wastewater pH and alkalinity are driven too low, negative effects such as a reduction in nitrification rate, complications with solids management, and heightened corrosion rates of treatment system components can result. If the wastewater has a low background of alkalinity, high organic loading, or high coagulant demand, chemical additives are often necessary to maintain proper pH and alkalinity levels in the system. The most common additives for this purpose are sodium hydroxide, magnesium hydroxide, and lime. However, calcium carbonate can serve as a safe and effective new alternative to these materials for activated sludge systems.
Many aspects of carbonate chemistry are highly compatible with activated sludge system design. The carbonate equilibria dynamics provide copious buffering capacity in the form of bicarbonate alkalinity in the ideal pH range for activated sludge systems, which is generally understood to be 7.0 – 7.5. Therefore, calcium carbonate’s unique buffer capacity helps to maintain pH stability in the wastewater system and nearly eliminates the harmful pH spikes that can occur with high basicity chemistries. Furthermore, carbon dioxide input from the microorganisms enhances calcium carbonate solubility, and the aeration in the treatment process exports excess carbon dioxide to maximize pH adjustment capacity. If any material is left undissolved, some will return to the system through the return activated sludge and perform as an alkalinity reserve for additional pH and alkalinity stability.
Lab studies and full-scale implementations have provided data on the comparative performance between calcium carbonate and other traditional alkalis. Lab studies have verified the stoichiometrically equivalent dosage requirements of calcium carbonate against sodium hydroxide and magnesium hydroxide, and reaction kinetics and dissolution dynamics were found to be acceptable for activated sludge systems. Full-scale applications have uncovered enhanced stability of key system performance indicators with calcium carbonate in comparison to sodium hydroxide and magnesium hydroxide. Additional advantages observed in full-scale applications are improved storage and feed reliability as well as enhanced sludge management.
Chandler’s educational background includes a Bachelor’s degree in Environmental Science and a Master’s Degree in Chemistry, both from Oakland University in Rochester, MI. He earned his Certified Water Technologist and LEED Green Associate designations in 2018, and in 2020 Chandler was selected for Water and Waste Digest’s 2020 Young Professionals Award. He now works for Omya and has over 5 years of research and application experience in wastewater treatment, specializing in chemical treatment applications.