Increasing the pH of wastewater to high levels with different gases-Co-2 stripping

The potential of increasing the pH of wastewater to high levels by CO2 stripping through air, N-2, O-2 and a gas mixture (95% N-2 + 5% CO2) has been examined in this work. Wastewater collected after the biological treatment from a large-scale plant was monitored for pH in a continuous, computer controlled laboratory setup. The use of air as the gaseous medium for CO2 stripping increased the pH to a maximum value of approximately 8.53. Using pure N-2 instead of air increased the pH of wastewater to a final value of 10.3 after 24 h at a flow rate of 1.5 L min(-1). An experimental system dismantling air from its CO2 content by precipitation as CaCO3 in a super-saturated lime solution ( in a closed circulation operation), increased the pH of wastewater to a final value of 9.4 after 24 h at a flow rate of 0.7 L min(-1). Applying the same closed circulation operation to an artificial carbonate solution instead of wastewater resulted in final pH values of 9.8 after 24 h using a flow rate of 0.7 L min(-1). The results suggest that a closed circulation operation with CO2-freed air has the potential to increase the pH of wastewater to high levels. The process may be applied for phosphorus precipitation from domestic wastewater not requiring chemicals for a pH increase.