The authors regret that there were some errors in the text and Figure 5 of their original paper and apologise for any inconvenience caused. The corrected text is given below.

Clogging sensitivity

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Figure 5 should be shown as

The initial headloss has been normalized with the volume of beads and K5-media and with the water rising velocity. It varies from 1 to 3.6 cm H2O/m/m.h−1 for the K5-media equipped biofilter (Figure 5(a)). For the reference biofilter, excluding two results under 1 cm H2O/m/m.h−1, the initial headloss ranged from 2.3 to 6.1 cm H2O/m/m.h−1 and is always above those of the K5-media equipped biofilter. Figure 5(b) shows the same results under boxplot form. This form, introduced by Tukey (1977) consists of a box extending from the first quartile (Q1) to the third quartile (Q3); a...