In contrast, trends in nitrite concentration were opposite to ammonia, with much lower nitrite concentrations in the F system (0.007 ± 0.015 mg.L− 1 and 0.009 ± 0.012 mg·L− 1 respectively for the treatments FC and FL) as compared to the R system (0.046 ± 0.024 mg·L− 1 and 0.032 ± 0.018 mg·L− 1 respectively for the treatments RC and RL) (Fig. 3b).