Winterport's Wastewater Treatment Process

The Spiragester is a two-story combination sedimentation and sludge digestion unit contained in one tank. The sewage enters the tank at the periphery of the tank at the sewage surface, passing around the race located between the wall of the tank and the deep skirt suspended from the tank wall. As the sewage flows around the race of the tank, scum and grease are removed as they rise to the surface in the race and are carried out of the race by the surface velocity moving the scum and grease around to the slotted scum pipe for discharge into the scum box. The grosser solids will settle out of the sewage during its passage through the race and drop into the digestion compartment below. As the sewage is flowing around the race it is also traveling downward to the bottom of the skirt. The liquid and lighter solids pass underneath the skirt into the main clarifier section, which provides and average detention period of 2-hour sedimentation. Here the lighter solids settle out due to the reduction of velocity in the settling compartment, and slide down the surface of the cone into the digestion compartment, passing thru the clearance provided between the bottom of the skirt and the lower portion of the cone. The rotation of the liquid in the clarifier assist in moving the solids down the cone slope into the digester.

The settled liquid is then skimmed by the adjustable weirs of the effluent trough as the liquid passes over the eight-sided weir trough into the effluent pipe. These weirs should always all be maintained level. This can be determined by observation and adjusting so that all V-notches are discharging equally. The long peripheral length of the skirt which acts as a submerged weir, and the substantial length of effluent weir provided by the eight weirs on the effluent trough, provide low inlet and outlet velocities.

The cone in the center of the tank covers most of the digestion compartment, and therefore most of the material, and therefore most of the floating material rising in the digester will pass into the cone, with a smaller amount of solids and gas rising into the race of the clarifier between the skirt and tank wall. Those solids rising in the race will be carried around and into the scum pipe, along with the scum, by the rotation in the race.

 

The scum and sludge recirculation pump, which operates on a time clock control, discharges all the scum and solids which rise in the race and are passed into the scum and sludge recirculation box, back into the top of the cone. The discharge from the scum and sludge recirculation pump into the cone is terminated a considerable distance above the sewage surface in order to provide a spraying action to break up scum which may accumulate in the stack of the cone. The discharge action of the pump will beat down the material which rises in the stack, releasing accumulated gas, and permitting this material to settle in the digestion compartment. With the arrangement of the cone, and the discharge of recirculated scum and sludge into the top of the stack, the Spiragester provides the only type of combination sedimentation and sludge digestion tank in which the scum can be completely broken up by direct recirculation to one point of the digestion section. This is true because the Spiragester concentrates all scum and floating material in a single small area.

The bottom of the cone extends underneath the skirt and beyond it into the race several inches, thus providing an overlap which separates the sedimentation compartment from the sludge digestion compartment. This overlap forces all rising material from the digestion compartment to rise either in the race or into the stack of the cone, thus preventing rising material from interfering with sedimentation taking place in the center settling compartment.