Liming Process:

The liming process is a common method used in wastewater treatment plants to remove excess lime from the system. Lime, or calcium hydroxide (Ca(OH)2), is commonly added to the wastewater treatment process to neutralize acidity and precipitate impurities. However, excess lime can cause problems such as high pH levels and scaling in the system. To address this issue, the liming process is employed to convert the excess lime into bicarbonate, which is more soluble and less likely to cause operational issues.

Re-carbonation:

The re-carbonation process is a crucial step in the liming process. It involves the addition of carbon dioxide (CO2) to the system, which reacts with the excess lime to form calcium carbonate (CaCO3) and water (H2O). This reaction can be represented by the following equation:

Ca(OH)2 + CO2 -> CaCO3 + H2O

By introducing carbon dioxide, the excess lime is converted into calcium carbonate, a compound that is more soluble and less likely to cause operational issues.

Advantages of Re-carbonation:

- Improved Solubility: The conversion of excess lime into calcium carbonate increases its solubility in water. This ensures that the compound remains in solution and does not precipitate, reducing the risk of scaling in the system.

- pH Regulation: The re-carbonation process helps regulate the pH levels in the system. Excess lime can cause high pH levels, which can be detrimental to the treatment process. By converting the excess lime into calcium carbonate, the pH levels can be controlled within the desired range.

- Operational Efficiency: The conversion of excess lime into calcium carbonate improves the efficiency of the wastewater treatment process. It prevents the accumulation of lime deposits and scaling, which can reduce the effectiveness of equipment and increase maintenance requirements.

- Cost Savings: By effectively utilizing excess lime through re-carbonation, the need for additional lime dosing is minimized. This can result in cost savings for the wastewater treatment plant.

In conclusion, the re-carbonation process is an important step in the liming process. It converts excess lime into more soluble calcium carbonate, improving solubility, pH regulation, operational efficiency, and cost savings in wastewater treatment plants.