Various Indicators of Water Quality - ph Value, Suspended Matter

pH Value of Water

The pH value of water is the negative logarithm of the hydrogen ion concentration in water, expressed as: pH = -lg[H+].

The pH value is sometimes also called the hydrogen ion index. The concentration of hydrogen ions in water indicates whether the aqueous solution is alkaline, neutral, or acidic. Since the numerical value of hydrogen ion concentration is often very small and inconvenient to use, the pH value is used as an indicator of the acidity or alkalinity of an aqueous solution. Furthermore, the negative logarithm of the hydrogen ion concentration precisely reflects the magnitude and degree of change in acidity or alkalinity, making it very convenient to use. Therefore, we can conclude that:

(1) Neutral aqueous solution, pH = -lg[H+] = -lg10-7 = 7;

(2) Acidic aqueous solution, pH < 7, the smaller the pH value, the stronger the acidity;

(3) Alkaline aqueous solution, pH > 7, the larger the pH value, the stronger the acidity;

If we further classify water quality according to pH value (acidity, alkalinity), we can conclude that:

(1) Strongly acidic aqueous solution, pH < 5.0;

(2) Strongly acidic aqueous solution, pH = 5.0-6.4;

(3) Neutral aqueous solution, pH = 6.5-8.0;

(4) Weakly alkaline aqueous solution, pH = 8.1-10.1;

(5) Strongly alkaline aqueous solution, pH > 10.0;

Suspended matter in water

Suspended matter in water consists of particles with a diameter of approximately 10⁻⁴ mm or larger, which are visible to the naked eye. These particles are mainly composed of silt, clay, protozoa, algae, bacteria, viruses, and high-molecular-weight organic matter. They are often suspended in water flow, causing turbidity. These particles are very unstable and can be removed through sedimentation and filtration. When water is left to stand, heavier particles (mainly inorganic substances such as sand and clay) will sink. Lighter particles (mainly organic compounds such as plant and animal remains) will float on the surface and can be removed by separation methods such as filtration. Suspended solids are the main source of turbidity, color, and odor. Their concentration in water is also unstable, often varying with the season and region.