pH is the measure of the acidity or alkalinity of a solution and ranges from 0-14.
pH is the measure of the acidity or alkalinity of a solution and ranges from 0-14. In solution, hydrogen ions occur as cations as both H+ and H3O+. In pure water at 25°C, the concentration of H+ equals the concentration of hydroxide ions (OH-) because water naturally dissociate into these two ionic species. This corresponds to a pH level of 7.0 and is defined as "neutral". Solutions in which the concentration of H+ are higher than that of OH- have pH values lower than 7.0 and are known as acids. Solutions in which the concentration of OH- exceeds H+ have a pH value greater than 7.0 and are known as bases.
The range of pH values that occur in the wastewater controls equilibrium of chemical and organic species in the sewer system. This can e.g. influence emission of the volatile ammonia (NH3) from the liquid phase which might cause odour problems.
Ammonia is in equilibrium with the non-volatile ammonium ion (NH4+) in the liquid phase. At pH values below 9.25 the volatile ammonia will be the predominating species of the two. The increase in concentration of ammonia in the liquid phase will influence the equilibrium between the liquid and air phases and ammonia will evaporate from the wastewater until the equilibrium is restored.
pH does also influence the biological processes taking place as the microorganisms in the wastewater and biofilms have certain pH optimum. At the pH optimum the metabolic functions of the microorganism work at optimal rate, this is usually in the range around pH 7.