1. (a) Solids Retention Time Control.

   1. (1) A facility design must include the necessary equipment for a facility operator to control the solids retention time (SRT) in the aeration tanks by wasting a measured volume of surplus activated sludge from either a mixed liquor tank, a sludge re-aeration tank, or the return sludge.
   2. (2) The report and the operating manual must provide the formulas for determining the SRT.
   3. (3) The SRT required for nitrification applies to the aerobic portion of the facility.

2. (b) Aeration System Control. Aeration control must include the total air supplied and the distribution of air to the aeration tanks.

   1. (1) In order to conserve energy, a facility design may include the ability to adjust the airflow in proportion to the oxygen demand of the facility.
   2. (2) If this adjustable type of airflow control is installed, the aeration equipment must be field adjustable over the entire range of oxygen demands and must maintain solids in suspension.

Source Note:The provisions of this §217.159 adopted to be effective August 28, 2008, 33 TexReg 6843.