By separating the sediment in the unprocessed wastewater in the primary clarifier, the amounts of the pollutants in the wastewater are reduced. These substances form deposits in the unprocessed wastewater and can be determined by allowing 1 l of the wastewater sample to stand in an Imhoff funnel for two hours. The quantity of solids that settle in the Imhoff funnel over this time provides a basis for calculating the primary sludge deposit at the wastewater treatment plant, as the primary clarifiers at the mechanical treatment stage are designed for a settling time of approx. two hours.
In addition to the volumetric determination of the substances that form sludge deposits over this period, the dry residue after evaporation or the mass concentration can be determined gravimetrically after treatment in the drying oven.
Furthermore, by annealing the residue after evaporation in the manner employed in wastewater technology, the deposits are differentiated into minerals, as ash content, as well as organic substances, calculated as annealing losses.
Wastewater generated in the industrial production of beer and food
Well-mixed wastewater is poured into an Imhoff funnel, and the volume of sludge is recorded using the volumetric scale on the graduated cylinder after a settling time of two hours.
After decanting the supernatant, the deposits are quantitatively transferred to a platinum dish in which, after drying at 105 °C, the dry residue after evaporation is determined by weight.
After annealing in a muffle furnace at 550 °C for 30 min, the ash content is determined gravimetrically.
The annealing losses are calculated from the difference in weight between the dry residue after evaporation and the ash content.