Hardness and alkalinity of water quality: the "gatekeepers" in reclaimed water reuse systems

In the process of reclaimed water treatment and reuse, water hardness and alkalinity are two crucial indicators that act as "gatekeepers" and directly affect the operational efficiency, equipment safety, and economy of the system.

The Influence and Control of Hardness

The hardness of water mainly refers to the content of calcium and magnesium ions. Excessive hardness can lead to serious scaling problems. In reclaimed water reuse systems, especially in reverse osmosis (RO) membrane filtration, heat exchangers, and pipelines, scale such as calcium carbonate can rapidly deposit, leading to membrane pore blockage, energy consumption surge, water production decrease, and even equipment damage. Therefore, for high-quality reuse (such as boiler feedwater and process water), it is necessary to soften the reclaimed water. Common methods include lime softening, ion exchange, or adding scale inhibitors to control the hardness within the allowable range of the membrane element or system.

The role and regulation of alkalinity

Alkalinity represents the ability of water to neutralize acids, mainly composed of bicarbonate, carbonate, and hydroxide. It plays a dual role in the reuse of reclaimed water:

Buffer pH value: Suitable alkalinity can effectively stabilize the pH value of the system, prevent a sharp drop in pH caused by the addition of coagulants or nitrification reactions, and create a stable environment for microorganisms in biological treatment units (such as MBR).

Correlation with hardness: Alkalinity and hardness jointly determine the tendency of water to scale. The Langmuir Index (LSI) and other parameters are used to predict the risk of calcium carbonate scaling by comparing pH, hardness, alkalinity, and other parameters. During the processing, scaling can be controlled by adjusting the alkalinity.

Collaborative Management and Application

In practical applications, hardness and alkalinity need to be managed collaboratively. For example, by aeration or adding acid, alkalinity can be reduced, promoting the premature precipitation of calcium carbonate (i.e. inducing crystallization), thereby simultaneously reducing hardness and alkalinity. This collaborative control is crucial for protecting subsequent precision processing units, ensuring stable quality of recycled water, and extending system lifespan.

Jensprima PACON series online total hardness and total alkalinity analyzer adopts the commonly used titration colorimetric method in the laboratory, with stable measurement values and good repeatability. Currently, more than 5000 units have been installed and used in the domestic industry. If you also have the same application scenarios and needs, you can contact us through regular channels!