The concept of unit operations, over time, and subsequent concepts in chemical technology have evolved into a unified field of separation processes. Sustainability in this field and its significance for the chemical and process industry will be commented, because the need for fresh sources of drinking water is becoming urgent worldwide. The biosorption of metal ions via residual biomass will be specifically examined in this review paper, as a separation technique. It has been recognized that the increased application of ion exchange and also membrane processes for producing potable water necessitates the use of advanced technologies as well as combinations of these. Therefore, a new hybrid cell of microfiltration combined with flotation will be also described in the present and applied effectively downstream for the same purpose (i.e., metals removal). Flotation is a separation process originated from minerals processing.