Alkaline chemicals, such as sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)₂), are frequently used to adjust the pH levels of wastewater. Many biological processes in STP require a specific pH range for optimal activity. For example, certain bacteria used in activated sludge processes thrive at a pH of around 6.5 to 8.5. By adding alkaline substances, the pH can be increased, creating a favorable environment for microbial action that breaks down organic matter.