358 
Theodore Sedgwick Johnson 
Sewage enters the sedimentation chamber from the channel over 
a weir, which is of wood or steel, and can be adjusted in length 
to produce satisfactory velocities in the tank. Scum-boards are 
provided* at points of inflow and outflow, which may be dis- 
pensed with if the sewage is screened previously to its admittance 
in the tank. 
Concrete for the tank shall be in the proportion of 1 : 2 : 4, 
with either gravel or broken stone of graded sizes. Reinforce- 
ment steel is of best quality and must satisfy the specifications 
of the American Society of Civil Engineers, as found in their 
last report. Two lines of perforated pipe are placed in the bottom 
of the digestion chamber, to aid in stirring up the sludge and 
facilitating its discharge through the discharge pipe. 
Circular tank — description. The circular tank is 19 feet in 
internal diameter, and has a depth below the water line of 22 
feet 6 inches. The bottom is conical shaped, the concrete be- 
ing 15 inches thick and reinforced by radiating bars with circu- 
lar rods at 18 inch intervals. The dividing walls between the 
upper and lower compartments is of reinforced concrete, sup- 
ported by 4 inch brackets to the main wall of the tank at regular 
intervals. The upper part of conical partition terminates in a 
circular vent, which supports the distributing channel. Inflow- 
ing sewage is conducted by a cast iron pipe to this circular trough 
or channel, from which it flows through openings of adjustable 
size into the sedimentation chamber, down under a baffle and 
out to the outer wall of the tank, portions of which are constructed 
as weirs and allow the discharge of the clarified sewage into a 
circular trough on the outside wall, from which it is led to the 
drainage or filter beds. 
Sludge is removed by a 12 inch cast iron pipe lying along the 
bottom and up one side to an elevation far enough below the 
water level to furnish proper hydrostatic head. 
Baffling is secured by means of a circular baffle, constructed 
of steel and hung from beams across the top of the tank. These 
beams are standard I beams encased in a concrete coating to 
prevent corrosion and add homogeneity to the appearance. 
Reinforcement is placed in the outside of the walls and on the 
conical bottom, and concrete and reinforcement are subject to 
the same specifications as in the rectangular tank. 
