Abstract: The alkalinity and hardness characteristics of secondary drainage from municipal sewage plant were introduced. The influence of noncarbonate alkalinity on the lime required dosage, the sulfuric acid required dosage, and the rudimental alkalinity and the hardness of the output water in lime softening treatment system was analyzed. It is pointed out that in the lime softening treatment process of secondary drainage from municipal sewage plant, the influence of noncarbonate alkalinity can not be neglected.

Key words: municipal sewage plant, secondary drainage, non-carbonate alkalinity, lime softening treatment