The sand
filters were built with cylindrical boxes with internal
diameter of 1.00 m. The bed was composed of three stratified layers
from the reactor’s bottom up (Fig. 3). The
first one was 0.20 m deep
and consisted of gravel with effective size (D10) of 16.12 mm and UC
(Uniformity Coefficient) of 45.80
0.40%. The second layer
consisted of gravel with D10 amounting to 7.51 mm and UC of
1.66, with a depth of 0.05 m. This material supported the sand in
such a way to prevent that particles
flowed out of the apparatus
(Tonetti et al., 2010).