N.H. Code Admin. R. Env-Wq 716.06

Current through Register No. 25, June 20, 2024

Section Env-Wq 716.06 - Anaerobic Sludge Digestion: Tanks

(a) Multiple tanks piped to operate both in series and in parallel shall be provided for the anaerobic sludge digestion process unless alternate methods of sludge stabilization and emergency storage are provided.

(b) Tank capacity shall be determined based on:

(1) Volume of sludge added;

(2) Percent solids and character;

(3) Temperature to be maintained in the digesters;

(4) Mixing to be obtained;

(5) Degree of volatile solids reduction required. For high rate digestion, the volatile solids loading shall not exceed 0.16 pounds per cubic foot per day; and

(6) Allowance for grit accumulation.

(c) If the digesters will serve as supernatant separation tanks, the tank sidewater depth shall:

(1) Be a minimum of 20 feet; and

(2) Allow for the formation of supernatant liquor.

(d) Digester tanks shall be covered.

(e) Sludge mixing systems shall be capable of:

(1) Mixing sludge to a uniform consistency; and

(2) Controlling foam.

(f) Digestion tanks shall incorporate the following features to facilitate emptying, cleaning, and maintenance:

(1) The tank bottom shall slope to drain toward the withdrawal pipe at a slope of not less than 3 inches per foot unless mechanical sludge collection is employed and then slope of not less than one inch per foot;

(2) At least 2 access manholes having 36-inch diameters and one gas dome shall be provided in the top of the tank with stairway access to the manholes;

(3) At least one additional access manhole shall be provided and shall be large enough to permit the mechanical removal of grit and sand;

(4) Non-sparking tools, rubber-soled shoes, safety harness, gas detectors for flammable and toxic gases, and gas masks of the hose or oxygen helmet type shall be specified for use in the tanks; and

(5) Alarms shall be installed to warn of:

a.Any drop of the liquid level below minimum operating elevation; or

b.Low pressure in the space above the liquid level.

(g) Digestion tanks shall incorporate the following inlet and draw-off features:

(1) Multiple sludge inlets and draw-offs ports and, where used, multiple recirculation suction and discharge points, to facilitate flexible operation and effective mixing of the digester contents shall be provided unless adequate mechanical mixing facilities are provided within the digester;

(2) One inlet shall discharge above the liquid level and be located at approximately the center of the tank to assist in scum breakup;

(3) The inlet discharge shall be isolated from the gas draw-off point of the cover; and

(4) Raw sludge inlet discharge points shall be located so as to minimize short-circuiting.

N.H. Code Admin. R. Env-Wq 716.06

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