36), were used with a fixed filter bed height of 0.
After the filtration step, backwash trials were performed in each filter individually and the procedure consisted in applying a flow rate from the fourth filter of the module (FR) in the opposite direction of the filtration process, in order to generate a filter bed expansion of 25%, according to the guidelines of Brouckaert (2004), which corresponded to the height of 0.
Backwash was evaluated based on the collection of sand samples at different depths inside the filter bed (four sampling points in the filter bed profile).
1 and, based on its sum, the total mass of solids present in the filter bed ([MS.
Fi]--mass of solids present in the filter bed after filtration trial (degree of soiling) in each fraction of volume of the filtering layer i (g); and
2 was used to determine the mass of solids removed in each backwash trial in the filter bed individual layers ([MS.
DRi]--mass of solids present in the filter bed after backwash trials, in each fraction of volume of the filtering layer i (g);
L] - cleaning efficiency for the entire filter bed (%).
There was a difference in the contamination between the evaluated filter bed layers for the use of finer sand granulometry (G1), especially at the highest filtration rate (TF75), resulting in greater amount of solids adhered to the superficial layers (Figure 2).
At the same time, it can be claimed that filter bed contamination is not uniform between the layers.
The reduction in the mass of solids adhered to the filter bed along the three filtration cycles of the experiment shows a probable decrease in the removal capacity of the filter bed (Figure 3).