When there are filamentous bacteria too much in the system, it means efficiency of bio-sludge is decreasing. The presence of this bacterium is because of low dissolved oxygen, low ratio F/M (food/mass), low nutrient or high sulfur concentration. Therefore, we use microscope for detecting filamentous bacteria in bio-sludge, then we will find out solution to prevent from their development.Some good bacteria types for aerobic pool are: flagella bacteria (consume soluble organic nutrient), ciliates bacteria and flagellum bacteria, nematode bacteria (consume suspended solids), protozoa (this bacteria is common in bio-sludge)…