How long must a pH of 12 be maintained when lime is used for stabilizing solids?

When using lime for stabilizing solids in wastewater treatment, maintaining a pH of 12 is crucial for effective pathogen reduction and ensuring proper stabilization of organic materials. A pH of 12 must be sustained for at least 2 hours to ensure that the chemicals have sufficient time to act. This duration allows for the necessary chemical reactions to occur, which include the inactivation of pathogens and the breakdown of organic compounds, making the solids safer for disposal or further treatment.

Maintaining the pH for a shorter duration, such as 30 minutes, would not provide enough time to achieve the desired stabilization and pathogen management. Similarly, longer durations (1 day or 12 hours) exceed what is necessary for effective treatment and may lead to unnecessary resource expenditure and operational inefficiencies. Therefore, the requirement to sustain the elevated pH specifically for 2 hours is a well-established guideline in wastewater management practices.