Industrial wastewater contains in its composition undissolved parts of various sizes and different types of composition and form of aggregation. Solid impurities with larger dimensions are separated on grates, sieves and belt filters, while suspensions with various degrees of dispersion are removed in flotators.
Larger solid impurities must be removed from raw wastewater, regardless of the adopted treatment technology, due to the safety of equipment operation, while the desirability of removing suspensions depends on the further applied methods of biological wastewater treatment.