Oxygen concn. regulated in activated sludge treatment - by full aeration rate at two-thirds of desired concn.

摘要

A method of maintaining optimum oxygen concn. to suit varying biological oxygen demand in activated sludge tanks in sewage treatment is as follows. The specific oxygen content at the outlet from the activated tank is determined and, when approx. 2/3rds. of the intended content is reached, the aerating appts. is operated to its full output; as the theoretical or set-point is approached, the output is reduced to a minimum level which maintains the set-point; if the value then drops from the set- point, then on each occasion the supply of air through the aeration device is adjusted to rectify this. Pref. the instantaneous result of the oxygen content measurement is used as a control variable for adjusting the output of the aeration appts. the latter being attained by varying the speed of the aerator drive. This may be done by speed control of a direct current machine, but a frequency converter with an asynchronous motor, by a pneumatically or hydraulically driven machine, or by an internal combustion engine, or by a variator drive of any type.