overliming

Overliming is the practice of adding lime to a system in excess of the amount needed to reach a targeted pH or alkalinity. Lime, typically calcium hydroxide (Ca(OH)2) or quicklime (CaO), is used to raise pH and total alkalinity by neutralizing acidity and shifting carbonate equilibria. Overliming can occur in water and wastewater treatment, soil management, and environmental remediation when dosing is not carefully controlled or when process conditions change unexpectedly.

In water and wastewater contexts, liming is often employed to precipitate certain contaminants as hydroxides or carbonates and to stabilize the effluent. If the lime dose is too large, the pH can rise above the desired level, sometimes beyond pH 9 or 10. This can cause practical problems such as scaling and deposition of calcium carbonate in pipes and equipment, increased sludge production, and the potential dissolution or mobilization of some constituents through changes in solubility and complexation.

In soils, liming is used to raise soil pH and reduce acidity. Overliming can lead to excessive pH increases, which may reduce the availability of micronutrients such as zinc, iron, manganese, and boron, and can promote phosphorus fixation, reducing plant uptake. It can also alter soil microbial activity and cation exchange dynamics.

Management strategies emphasize monitoring pH, alkalinity, and relevant solute concentrations, and employing controlled dosing, staged liming, or rebalancing with acids or alternative amendments to avoid overshooting target conditions.