Supplementary Material for Interpreting the Effect of Increasing COD Loading Rates On

Supplementary Material for “Interpreting the effect of increasing COD loading rates on the performance of a pre-anoxic MBBR system: implications on the attached and suspended biomass dynamics and nitrification-denitrification activity”

P.S. Lima, M. Dezotti, J. P. Bassin*

Federal University of Rio de Janeiro - COPPE - Chemical Engineering Program, Rio de Janeiro, Brazil

* Corresponding author. Mailing address: Chemical Engineering Program/COPPE, Federal University of Rio de Janeiro, P.O. Box 68502, 21941-972, Rio de Janeiro, Brazil. Tel. +55 21 25628347, Fax +55 21 25628300, Email address:

Figure S1

Fig. S1: COD profiles during the course of operation of the two-stage MBBR system. Influent COD (▲), effluent of MBBR1 (▲) and effluent of MBBR2 (∆). The experimental conditions are displayed above the graph. The dashed lines separate a particular experimental run from the next.

Figure S2

Fig. S2: Fraction of the total COD removed in the anoxic (MBBR1) and aerobic (MBBR2) reactor over the course of the five experimental conditions (runs are indicated in the top of the graph, together with their corresponding COD/N ratios obtained experimentally). Average fraction of the incoming COD removed in MBBR1 was 89, 66, 39, 29 e 43% for runs 1, 2, 3, 4 and 5, respectively. In MBBR2, the corresponding fractions of COD removal were 8, 30, 56, 68 e 54%, respectively.

Figure S3

Fig. S3: Ammonium concentrations in the influent (▲), effluent of MBBR1 (▲) and effluent of MBBR2 (∆). The numbers displayed above the data points correspond to the different runs during which the COD loading rate was increased. The dashed lines separate one experimental condition from the next. As no nitrification takes place anoxically, the ammonium concentrations in the effluent of the anoxic tank (MBBR1) appear lower than in the influent due to dilution of the feeding medium with the internal recycle stream from the aerobic nitrifying tank.

Figure S4

Fig. S4: Average fractions of ammonium, nitrite and nitrate in the effluent of the MBBR system over runs 1 – 5. The highest accumulation of nitrite was observed in the last two experimental conditions, as indicated by dashed circles in the graph.

Figure S5

Fig. S5: Percentage of nitrite and nitrate in relation to the total amount of oxidized nitrogen in runs 1 – 3. [DO] corresponds to dissolved oxygen concentration.

Figure S6

(a) /
(b)

Fig. S6: Actual (a) and maximum (b) speficic denitrification rates observed at the pseudo-steady state conditions of the experimental runs. As the maximum rates were much higher than the ones observed under normal operating condidions, they were displayed in separate graphs. The specific denitrification potential (y-axis) is expressed in mgNO3-N/(gVS.h), where VS corresponds to both volatile attached (VAS) and suspended (VSS) solids. The exception is for a particular experiment conducted in the last run (indicated by 5*), in which only the VSS was kept inside the reactor to evaluate the denitrifying activity of the suspended biomass.

Figure S7

Run 1 /
Run 2

Run 3 /
Run 4

Run 5 /
Run 5* (*with suspended biomass)

Fig. S7: Concentration profiles of nitrate and nitrate in the denitrification activity tests. The experimental runs to which the experiment belong are displayed below each graph. In run 5, in particular, an experiment was conducted only with the suspended biomass, as indicated above.

Figure S8

Fig. S8: Suspended solids (expressed as VSS) load in the influent and effluent of MBBR1 and effluent of MBBR2 (treated effluent). The VSS (i.e., particulate COD) entering the anoxic reactor arises only from the internal recycle (400% of the influent flow rate), as the synthetic medium used to feed the MBBR system comprises only soluble COD. The effluent of MBBR2 correspondes to the outflow of the system.

Figure S9

Fig. S9: Gelatinous material observed at 30% media filling ratio (run 5) under anoxic conditions (MBBR1).

Figure S10

Fig. S10: COD removal obtained in the anoxic and aerobic stages of the MBBR system at different influent COD/N ratios. The displayed COD/N ratios represent the average values of both COD and N in the influent for each experiment run.