Section Env-Wq 711.06 - Secondary Settling Tanks: Design Criteria for Sludge and Scum Removal(a) Sludge collection and withdrawal facilities shall be designed to accommodate the withdrawal of sludge solids.(b) Circular units shall be designed to allow alternate sludge wasting and tank drainage from the center of the units.(c) Rapid sludge removal systems in circular settling tanks shall be designed so that return rates can be directly varied by changes in return sludge pumping rates. Sludge collection tubes on rapid sludge removal systems shall have a submerged discharge to the center well.(d) Chain and flight sludge collectors in rectangular settling tanks shall be designed with a minimum horizontal velocity of 2 to 3 feet per minute with flights at least 10 feet on center.(e) Effective baffling to prevent velocity and density currents within the tank and scum removal equipment shall be provided in each secondary settling tank. Scum removal equipment shall facilitate the positive movement of scum to the scum hoppers.(f) Scum hoppers shall have provisions to facilitate the flushing of scum from the hopper.(g) Scum piping shall be sized for proper movement of viscous foams.N.H. Admin. Code § Env-Wq 711.06
Adopted byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.