Abstract: An aerated grit tank is provided having a longitudinally extending control wall dividing the tank into parallel lift and settling chambers. An air discharge apparatus is provided at the bottom of the lift chamber to induce an upward flow of sewage causing a generally helical flow of sewage around the control wall. The control wall is supported in the tank by mechanisms selectively operable to vertically position the wall with a bottom longitudinally extending edge in predetermined spaced relationship to a bottom floor of the tank whereby the velocity of the cross currents may be effectively controlled. One form of the structure has a single control wall unit while a second form of the invention has two wall forming panels with an uppermost panel supported in fixed relationship to the tank and a lowermost panel supported for vertical displacement.

Abstract: A hammer is provided for pulverizing and comminutating apparatus of the hammer mill-type with this hammer including both tearing and shearing edges for enhanced effectiveness in obtaining size reduction of both friable and non-friable materials. This pulverizer hammer includes a relatively narrow tearing edge which is disposed in spaced parallel relationship to the pivot bearing of the hammer. A side edge surface of the hammer associated with that tearing edge is formed in arcuately curved, receding relationship thereto for directing and urging particles of waste material radially outward toward the tearing edge where they will be subjected to further pulverizing action. A shearing edge is also formed along one corner of the side edge surface of the hammer and extends radially in receding relationship to the tearing edge. The arculately curved and contoured surface is also configured to extend in receding relationship with respect to the shearing edge.