removing Mn and NH4 + -N. Additionally, the change in the color of
the quartz sand from white to gray was an indication of a ‘‘mature’’
biofilter (see supplementary material, Fig. S1). In order to keep the
water flow constant, upflow filtration was used. The value of the
empty bed contact time (EBCT, i.e., the time needed for the water
to fill the empty column) was twenty minutes. The backwashing
procedure was carried out once a week to wash out metallic oxides
and excess organisms.