Fig. 4.
Heterotrophic activity test conducted by spiking different carbon sources to assess the potential heterotrophic activity in R1. (a) Time profiles of ammonium (NH4+), nitrite (NO2−), nitrate (NO3−), and soluble organic carbon (CODsol; corrected by considering the contribution of the NO2− concentration to COD with the theoretical factor of 1.143 mgCODsol/mgNO2-N). (b) Cumulative curves of the observed consumption of CODsol (black crosses) and the amount of COD equivalents required for denitrification only (D, black diamonds), denitrification and growth on NO2− and NO3− (D + G, white diamonds) and for anoxic storage (AS, gray diamonds) with the consumed NO3− and NO2−. The stoichiometry of these reactions is described in Table S2 in the Supporting Information.