Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 30 3-4 2001 12 15 91 94 MK Sharifi-Yazdi1 C Azimi1 MB Khalili 2015 10 03 Activated sludge or extended aeration treatment involves a continous system where aerobic biological growths are mixed with waste water and then separated in a gravity clarifier. Therefore, waste treatment system such as the activated sludge system depend on the activities of communities of living organism. In this study, an attempt was made on the indentification of the bacterial population involved in the laboratory activated sludge unit. The results showed that gram-negative bacilli with a yellow pigment was considered as a major group of the population. https://ijph.tums.ac.ir/index.php/ijph/article/view/1648 https://ijph.tums.ac.ir/index.php/ijph/article/download/1648/1629