A/O Operations of Aerobic Digesters
asked 1 January 2017 asked by Chuck (480 points)
Many facilities use air on / air off cycles to control pH in aerobic digesters. A good rule of thumb is to have the air on for 50% to 70% of the total time. If the solids settle, mixers should be used to keep the solids in suspension so they will remain in contact with the nitrate in the water. If no mixers are available, cycle the air to keep the solids in suspension. Cycling between aerobic and anoxic conditions can help keep the alkalinity and pH from dropping too low. For every 1 mg/L of nitrate-nitrogen denitrified, you gain 3.57 mg/L of alkalinity as CaCO3. Nitrification consumes 7.14 mg/L of alkalinity for every 1 mg/L of ammonia converted to nitrate.