Abstract: A method of suspending bio-solids in an activated sludge during wastewater treatment in an activated sludge system is provided. In one example embodiment, the method may include treating the activated sludge under anaerobic conditions and flowing the activated sludge through an open channel into a separation vessel. The bio-solids are suspended in the activated sludge by either intermittent agitation comprising an agitation interval and a rest interval or by upright flow of an influent and/or activated sludge. Diffusion of gas, mechanical devices, flow of an influent, and flow of the activated sludge can be utilized to agitate the bio-solids.