SECTION 252:656-19-3. Aerobic sludge digestion

(a)   General. Aerobic digestion can be used to stabilize primary sludge, secondary sludge or a combination of the two. Multiple units are required at treatment facilities with a capacity of 1,000 PE or more. Treatment plants, designed for less than 1,000 PE, may use a single unit if adequate provisions are made for sludge handling and redundency.

(b)   Mixing and air requirements. Provide sufficient air to keep the solids in suspension and maintain dissolved oxygen between 1 and 2 mg/l. A minimum mixing and air requirement of 30 ft/min/1,000 ft tank volume shall be maintained with the largest blower out of service.

(c)   Tank capacity. Determine total tank(s) capacity by rational calculations based on such factors as volume of sludge added, sludge characteristics, time of aeration, sludge temperature and ultimate disposal methods. Submit all calculations and design assumptions for review.

(d)   Volatile solids loading. Volatile suspended solids loading must not exceed 100 lb/1,000 ft tank volume per day.

(e)   Time and temperature. Install a temperature probe and recording device to continuously record digester temperature.

(f)   Supernatant separation. Provide for separation and withdrawal of supernatant and for collection and removal of scum and grease.

(1)   Supernatant withdrawal. Design for supernatant withdrawal at least 6 inches below the liquid surface level after a minimum one-hour settling period. Return supernatant to the head of the plant.

(2)   Sampling facilities. Provide a sampling line (at least 1.5 inches in diameter) with a quick-closing valve no more than 1 foot from the tank bottom.

(3)   Maintenance provisions. Slope the tank bottoms toward the sludge withdrawal pipe. Minimum slope to be at least 1 foot vertical to 4 feet horizontal.

[Source: Added at 17 Ok Reg 1140, eff 6-1-00; Amended at 23 Ok Reg 937, eff 6-15-06; Added at 28 Ok Reg 1282, eff 7-1-11]