nonbicarbonate

Nonbicarbonate refers to the portion of a solution’s alkalinity that is not contributed by bicarbonate ions. Alkalinity is the water’s capacity to neutralize acids and is largely driven by conjugate bases such as bicarbonate (HCO3−), carbonate (CO3 2−), hydroxide (OH−), and other weak bases. Nonbicarbonate alkalinity, therefore, represents the part of alkalinity that arises from bases other than bicarbonate.

In practice, total alkalinity is measured by acidifying a sample until a designated endpoint is reached, and bicarbonate-based alkalinity is separated from the nonbicarbonate portion by comparing contributions of different base species. Nonbicarbonate alkalinity is typically calculated as total alkalinity minus the bicarbonate alkalinity, yielding the buffering capacity provided by bases such as hydroxide and other non-bicarbonate species.

The composition of nonbicarbonate alkalinity varies with water chemistry. It can include hydroxide and other base species such as borate, silicate, and certain phosphate forms, depending on the water source and treatment history. In many natural waters, nonbicarbonate alkalinity is small relative to bicarbonate alkalinity, especially where carbonate weathering dominates. However, in systems influenced by industrial inputs, groundwater with specific mineralogy, or certain treatment processes, nonbicarbonate alkalinity can be more substantial and influence pH buffering, corrosion control, and chemical dosing strategies.

Related concepts include total alkalinity, bicarbonate alkalinity, carbonate alkalinity, and overall water chemistry.