Biodegradation and effect of formaldehyde and phenol on the denitrification process

Formaldehyde and phenol biodegradation during the denitrification process was studied at lab-scale, first in anoxic batch assays and then in a continuous anoxic reactor. The biodegradation of formaldehyde (260 mg l−1) as single carbon source and at phenol concentrations ranging from 30 to 580 mg l−1 was investigated in batch assays, obtaining an initial biodegradation rate around 0.5 g CH2O g VSS−1 d−1. With regard to phenol, its complete biodegradation was only observed at initial concentrations of 30 and 180 mg l−1. The denitrification process was inhibited at phenol concentrations higher than 360 mg l−1. Studies were also done using a continuous anoxic upflow sludge blanket reactor in which formaldehyde removal efficiencies above 99.5% were obtained at all the applied formaldehyde loading rates, between 0.89 and 0.14 g COD (CH2O) l−1 d−1. The phenol loading rate was increased from 0.03 to 1.3 g COD (C6H6O) l−1 d−1. Phenol removal efficiencies above 90.6% were obtained at phenol concentrations in the influent between 27 and 755 mg l−1. However, when the phenol concentration was increased to 1010 mg l−1, its removal efficiency decreased. Denitrification percentages around 98.4% were obtained with phenol concentrations in the influent up to 755 mg l−1. After increasing phenol concentration to 1010 mg l−1, the denitrification percentage decreased because of the inhibition caused by phenol.