Impact of increased phenol loading rate on the phenol removal of an anaerobic membrane bioreactor operated at high sodium concentration

Certain industrial wastewaters have posed a big challenge to biological water treatment systems because of their high toxic organic compounds concentration (e.g. phenol) and high salinity. The maximum biomass specific phenol bioconversion rate (PhCR) of a mesophilic (35 °C) anaerobic membrane bioreactor (AnMBR) under high sodium concentration [18.6 g Na+/L] condition was studied by an increase in the biomass specific phenol loading rate (PhLR) through hydraulic retention time (HRT) decrease. The maximum PhCR achieved in our research was 73 mg Ph-COD/gVSS-COD.d, with acetate as co-substrate [2g AC-COD/L]. This result was lower than that reported by the previous study of Bioxtreme (193 mg Ph-COD/gVSS-COD.d) at lower sodium concentration [8.0 g Na+/L]. On the other hand, a simplified ADM1 model was used to model the conversion of acetate to methane in batch experiments, among which, the inhibition of substrate (acetate or phenol) on microbial growth rate was described by Haldane equation. The kinetic parameters for acetate degradation were Ks,AC=300 mg COD/L, KI,AC=821mg COD/L, km,AC I =0.246 mg COD/mg COD.h without phenol addition and Ks,AC=300 mg COD/L, KI,AC=806 mg COD/L, km,AC I=0.236 mg COD/mgCOD.h with the addition of 714 mg Ph-COD/L (300 mg Ph/L) at sodium concentration of 18.6 g Na+/L, while it was Ks,AC=6.7 10-9 mg COD/L, KI,AC=5670 mg COD/L, km,AC I=0.043 mg COD/mgCOD.h at lower sodium concentration [8.0 g Na+/L] without phenol addition. The kinetic parameters estimated for the batch experiments were applied in a mathematical model describing a dynamic experiment carried out in the AnMBR1 and validated with different HRTs. In the model, the conversion from phenol to acetate was considered and the kinetic parameters estimated for phenol degradation were Ks,Ph=20 mg COD/L, KI,Ph=300 mg COD/L, km,Ph I=0.008 mg COD/mgCOD.h. It was proved that the simplified ADM1 model could well predict the phenol and acetate concentrations in the reactor at different PhLRs. This research has provided an experimental and modeling approach for the maximum PhCR determination and could contribute to the understanding of the inhibition effect of sodium and phenol on PhCR in the treatment process of saline phenolic wastewater.