Section Env-Wq 711.07 - Secondary Settling Tanks: Design Criteria for Return Sludge(a) Return sludge rate capabilities shall be designed to be the greater of 100 percent of maximum month design flow or 150 percent of annual average day design flow.(b) At least one return sludge pumping unit shall be provided for each settling tank. The maximum required return sludge capacity shall be available with the largest pumping unit out of service. Pumps may be placed on suction headers, but the arrangement and valving shall be such that any one settling tank can be isolated with a single pump.(c) A positive suction head shall be provided for all return sludge pumps.(d) Return sludge pumps shall have at least 3-inch suction and discharge openings.(e) Rate of sludge return shall be varied by means of variable speed motors, drives, or timers.(f) Return sludge suction and discharge piping shall be at least 4 inches in diameter and designed to maintain a velocity of not less than 2 feet per second when operating at average sludge return rates.(g) Suitable devices shall be provided for sampling and measuring return sludge flow rates. Measuring devices shall totalize and record, as well as indicate flows.(h) Capability shall be provided to return and waste sludge concurrently.(i) Provisions shall be made for the draining and flushing of discharge lines.N.H. Code Admin. R. Env-Wq 711.07
Adopted byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.