Biological treatment of wastewater

An arrangement comprising:

• a basin having a wastewater inlet at one end and an outlet for treated wastewater at another end;
• an aeration region for aerating wastewater received in the basin;
• a clarification region for clarifying aerated wastewater;
• a wall separating the aeration region and the clarification region and providing a passage to permit aerated wastewater to pass from the aeration region into the clarification region;
• a sludge removal arrangement in the clarification region to remove sludge which has settled from wastewater during clarification;
• at least one turbulence generating arrangement in the clarification region for periodically stirring up sludge which has settled in the clarification region;
• and
• a movable wall separating the aeration region and the clarification region permitting the relative volumes of the aeration region in the clarification region to be changed;
• wherein the movable wall comprises a flexible curtain supported from the surface of the liquid in the basin and having a weighted bottom edge.

An arrangement for biological treatment of waste water comprising:

• a basin having a wastewater inlet at one end and an outlet for treated wastewater at another end;
• an aeration region for aerating wastewater received in the basin;
• a clarification region for clarifying aerated wastewater;
• a wall separating the aeration region and the clarification region and providing a passage to permit aerated wastewater to pass from the aeration region into the clarification region;
• a sludge removal arrangement in the clarification region to remove sludge which has settled from wastewater during clarification;
• at least one turbulence generating arrangement in the clarification region for periodically stirring up sludge which has settled in the clarification region;
• and
• a movable wall separating the aeration region and the clarification region permitting the relative volumes of the aeration region and the clarification region to be changed;
• wherein the movable wall comprises a flexible curtain supported from the surface of the liquid in the basin and having a bottom edge anchored to a basin wall.

An arrangement for biological treatment of waste water comprising:

• a basin having a wastewater inlet at one end and an outlet for treated wastewater at another end;
• an aeration region for aerating wastewater received in the basin;
• a clarification region for clarifying aerated wastewater;
• a wall separating the aeration region and the clarification region and providing a passage to permit aerated wastewater to pass from the aeration region into the clarification region;
• a sludge removal arrangement in the clarification region to remove sludge which has settled from wastewater during clarification;
• at least one turbulence generating arrangement in the clarification region for periodically stirring up sludge which has settled in the clarification region;
• a weir in the clarification region to remove clarified effluent therefrom;
• and
• an effluent control arrangement to prevent effluent from being withdrawn from the clarification region when the turbulence generating arrangement in the clarification region is stirring up sludge in that region.

A method for biological treatment of wastewater comprising the steps of:

• introducing wastewater into a basin;
• aerating the wastewater with air diffusers in an aeration region of the basin;
• passing the aerated wastewater to a clarification region of the basin;
• clarifying the wastewater in the clarification region;
• removing sludge from the clarification region through a sludge removal arrangement having a fixed sludge removal duct;
• and
• periodically activating an array of air diffusers at locations remote from the fixed sludge removal duct in the clarification region to stir up sludge which has settled in that region but has not been removed by the sludge removal duct to facilitate removal of sludge through the fixed sludge removal duct.