NOVELTY - Wastewater and activated sludge mixture are aerated. Dissolved oxygen concentration (C1) in mixture of balance point of oxygen supply speed and oxygen consumption coefficient is measured after decomposition. Aeration is stopped, concentration (C1) is reduced, and mass transfer coefficient (K) is calculated. Specific liquid is added to mixture, decomposition rate of liquid is measured, and nitrification activity of sludge is evaluated.    USE - For evaluating nitrification activity during wastewater treatment, such as activated sludge treatment and biological nitrification-denitrification method.    ADVANTAGE - The nitrification activity of sludge and nitrification inhibition property of natural water are measured quantitatively and precisely within a short period of time.    DETAILED DESCRIPTION - Aeration of wastewater sampled from aerator, and a liquid mixture containing activated sludge is carried out. The biological oxygen demand (BOD) component decomposition in liquid mixture is carried out. The dissolved oxygen concentration (C1) in liquid mixture of balance point of oxygen supply speed and oxygen consumption coefficient is measured, by change curve (I). The aeration is stopped, and dissolved oxygen concentration is reduced. The dissolved oxygen concentration change curve (II) is measured during restart of aeration. The mass transfer coefficient (K) is calculated in oxygen supply unit based on curve (II) and concentration (C1). A liquid (L) containing salt, such as ammonium sulfate and ammonium chloride capable of dissolving in water and producing ammonium ion and urea, nitrile amide, hydroxylamine and formamide is added to liquid mixture. The decomposition rate of liquid is measured based on dissolved oxygen concentration change, mass transfer coefficient (K) and concentration (C1). The nitrification activity of activated sludge in liquid mixture is then evaluated.    An INDEPENDENT CLAIM is included for operation evaluation equipment. The equipment has unit for aerating wastewater and activated sludge liquid mixture, unit for measuring dissolved oxygen concentration change curve, unit for calculating mass transfer coefficient, unit for carrying out evaluation acquisition of nitrification activity of activated sludge, unit (A) for adding raw water, and unit (B) for evaluating inhibition extent of nitrification activity. Raw water is added after decomposition completion of liquid (L), when the nitrification activity is larger than predetermined set value. Biological oxygen demand component of raw water is added to liquid (L) after completing decomposition, and decomposition rate of liquid (L) is calculated based on dissolved oxygen concentration change, concentration (C1) and coefficient (K) in unit (A). The unit (B) evaluates inhibition extent of nitrification activity with respect to activated sludge by comparing the decomposition rate of liquid before and after addition of raw water.    DESCRIPTION OF DRAWING(S) - The figure shows the pattern illustrating the measurement of dissolved oxygen change. (Drawing includes non-English language text).