This treatment was the same as treatment 2, except that refilling
time was reduced from 4 h to 10–15 min, i.e. total drain and
refill cycle 20–25 min. Each week during treatment 3, water samples
were taken for analysis from the inlet at the start of the week
and outlet of all biofilters on day 7 (i.e. water that passed through
the biofilter four times).