The pH value indicates the acidity and alkalinity of sewage. It is the logarithmic value of the reciprocal of the hydrogen ion concentration in water. Its range is 0-14. If the pH value is equal to 7, the water is neutral. If it is less than 7, it is acidic. The smaller the value, the stronger the acidity. If it is greater than 7, it is alkaline. The larger it is, the more alkaline it is.