**4. Deposition of particulate matter in wastewater**

Industrial and sanitary wastewaters are not completely cleaned of suspended materials despite passing through multiple filters (littering). Many of these small particles will settle on the floor of the treatment plant, depending on their weight if they have the opportunity. The second important process in the physical treatment of industrial and sanitary wastewaters is to allocate time for settling suspended materials in special pools. By doing so, largely fine and particulate matter is transferred to the bottom of the pool and gradually converted into sludge, which will be periodically drained (**Figure 6**) [7].
