4-nitrophenol biodegradation in a sequencing batch reactor: kinetic study and effect of filling time

Biodegradation kinetics of 4-nitrophenol (4NP) was investigated in a lab-scale sequencing batch reactor fed with the compound as the sole carbon source. The experimental results showed that complete 4NP removal can be easily achieved with acclimatized biomass, even if an inhibition kinetics is observed; furthermore, an improvement in the removal kinetics is obtained if the substrate concentration peak, reached in the reactor at the end of the filling time, is maintained to quite a low value. Both long feed phase and high biomass concentration are effective in reducing the substrate concentration peak and then improving the process efficiency. Kinetic test data are well correlated by the Haldane equation, with a saturation constant Ks and an inhibition constant KI, of 17.6 and 30.7 (mg l−1 4NP), respectively, whereas the maximum removal rate was in the range of 3.3–8.4 (mg 4NP mg VSS−1 d−1) depending on the substrate concentration peak reached in the reaction phase.