A layer boundary acts like a channel for all particles more than 10-20 nm in estimate: dust, green growth, microbes, infections, germs and natural atoms.
Thickening is usually the first step in sludge treatment because it is impractical to handle thin sludge, a slurry of solids suspended in water. Thickening is usually accomplished in a tank called a gravity thickener. A thickener can reduce the total volume of sludge to less than half the original volume.
The Biological Treatment fully Utilizes the micro organisms for treatment of the wastewater. Depending upon the type of microbes used, the biological treatment is classified as : Aerobic Treatment Using aerobic Organisms. Anaerobic treatment uses the aerobic microbes. The example of anaerobic treatment unit is sludge digester