Development of technology and society is increasing the need for wastewater treatment. Although the treatment plant it is necessary in order to preserve water resources, but it is a very expensive procedure, and therefore its use is very small. The activated sludge is follicular construction consisting of bacteria, protozoa, metazoa, and suspended particles of organic matter. The biological treatment of water have the greatest role of bacteria and protozoa then metazoa. The role of these organisms is reflected in the water purification process, which in its biomass incorporated organic matter from wastewater and produce a product gas and not degradable rest. It was found that the amoebae predominate at system startup, while the presence of flagellates to amoebae is a sign of toxic overload the system. The presence of free-floating ciliates is a good indicator of the operating system. Attached ciliates are good bio-indicators of toxicity in crossing the free-swimming forms when exposed to such conditions. Brachionus are a sign of a stable activated sludge and found them during favorable conditions. Each of these types of talks on different kind of loading system for wastewater treatment. Given that the biological activity of microorganisms depends on a number of parameters (temperature, pH, concentration of dissolved oxygen, the type and concentration of dissolved substances in the water) are excellent indicators of the quality of sludge, because of their abundance and diversity of talking about the quality and capacity of activated sludge wastewater treatment.