<p>A sewerage treatment tank for providing both anaerobic and aerobic treatment of sewerage the tank being integrally moulded from concrete and having an inner and an outer cylindrical wall coaxially aligned and a bottom extending below both walls and having a place of the anaerobic treatment which is around the walls between the inner and outer walls and where the length of the chamber provididng a passageway for anaerobic treatment defined by cross walls is at least seven times longer than the width of the chamber throughout that passage length, and there are means to provide aerobic treatment within the chamber.</p>
