APPARATUS FOR CONTROLLING POST-INJECTION OF CHLORINE

PURPOSE:To perform the post-injection of chlorine on a proper level, by correcting the difference between the concn. of free chlorine and that of free chlorine at a water supply point to a chlorine post-injection objective value with due regard to time delay. CONSTITUTION:A circuit 11 outputting a correction signal 24 due to the difference between the concn. of free chlorine at a chlorine post-injection point and that of free chlorine at a water supply point inputs a raw water ammoniacal nitrogen concn. signal 7, a chlorine pre-injection ratio signal 8 and pH 9 of flocculated water and selects the pattern corresponding to the raw water ammoniacal nitrogen concn. signal 7, the chlorine pre-injection ratio signal 8 and the pH 9 of flocculated water from the pattern preliminarily stored in a memory to output the difference between the concn. of free chlorine at the chlorine post-injection point and that of free chlorine at the water supply point as a correction signal 24. The correction signal 24 is stored in a delay circuit 12 and treated water passes a filter basin to obtain a filtrate and the time delay generated during the flowing down of the filtrate to the chlorine post-injection point is corrected to be outputted as a delay correction signal 25.