Formaldehyde biodegradation and its inhibitory effect on nitrification

The simultaneous removal of formaldehyde and ammonium in aerobic cultures and the inhibitory effect of formaldehyde on ammonium oxidation were investigated. The influence of a co-substrate, methanol, on formaldehyde biodegradation and on the nitrification process was also evaluated. Formaldehyde was completely removed at all concentrations tested (30–3890 mg dm−3) in assays with that compound as the single carbon source and in the presence of methanol as co-substrate. An initial formaldehyde biodegradation rate of 4.6 g CH2O g−1 VSS d−1 was obtained for 2000 mg CH2O dm−3 as single carbon source compared with a rate of 7.3 g CH2O g−1 VSS d−1 when methanol was added. Formaldehyde was inhibitory to the nitrification process at initial concentrations higher than 350 mg dm−3. Increasing the initial formaldehyde concentration or adding a co-substrate such as methanol resulted in a longer lag phase before ammonium oxidation and caused a decrease in the degree of nitrification. Nitrification was completely inhibited at initial formaldehyde concentrations higher than 1500 mg dm−3.