N.H. Code Admin. R. Env-Wq 713.05

Current through Register No. 25, June 20, 2024

Section Env-Wq 713.05 - Activated Sludge: Aeration Tank Design

(a) The aeration tank size for any particular adaptation of the activated sludge process shall be determined by:

(1) Pilot studies; or

(2) Rational calculations based primarily on solids retention time (SRT) and MLSS levels while also considering other factors, including but not limited to capacity, wastewater characterization relevant to the proposed process, diurnal load variations, degree of treatment required, pH, temperature, alkalinity, and dissolved oxygen.

(b) The engineer shall furnish aeration tank sizing calculations to the department with the engineering design documents.

(c) Aeration tank volume requirements for nitrification shall be based on maximum monthly loading.

(d) The dimensions of each independent mixed liquor aeration tank or return sludge re-aeration tank shall be such as to maintain effective mixing and use of air, provided that liquid depths shall be not less than 12 feet nor more than 25 feet.

(e) Inlets and outlets for each aeration tank unit shall be equipped with valves, gates, stop plates, weirs, or other devices to permit flow control to any unit and to maintain a constant liquid level while preventing short-circuiting through the tank.

(f) Channels and pipes carrying liquids with solids in suspension shall be designed to maintain self-cleansing velocities or shall be agitated to keep such solids in suspension at all rates of flow within the design limits.

(g) Piping shall allow flexible operation sequence of tanks and returned sludge inlets.

(h) Aeration tank freeboard shall be:

(1) Not less than 3 feet if a mechanical surface aerator is used; and

(2) Not less than 18 inches in all other aeration tanks.

(i) Froth and foam control or removal shall be provided at the aeration tanks.

(j) Thorough mixing of the mixed liquor to prevent deposition of solids at any point in the tanks shall be provided.

(k) Aeration tanks shall have probes to monitor dissolved oxygen in place, to control power consumption and match oxygen demand with oxygen supply.

(l) Diffusers shall be spaced to satisfy oxygenation requirements through the length of the channel or tank, and to facilitate spacing adjustments without major revisions to the existing air header piping.

N.H. Code Admin. R. Env-Wq 713.05

(See Revision Note at chapter heading for Env-Wq 700) #8590, eff 3-25-06

Amended byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.