Formaldehyde biodegradation and its effect on the denitrification process

Abstract

Simultaneous formaldehyde biodegradation and denitrification in batch assays and in a continuous lab-scale reactor were studied. In batch assays, initial biodegradation rates between 0.7 and 3.3 g CH2O g VSS-1 d-1 were obtained at formaldehyde concentrations between 300 and 2150 mg l-1. The denitrification process was affected by the presence of formaldehyde. The nitrite accumulation increased with the initial formaldehyde concentration. In the continuous reactor, removal efficiencies above 98.5% were obtained at formaldehyde loading rates between 0.37 and 2.96 kg COD m-3 d-1 (625 - 5000 mg CH2O l-1). Formaldehyde removal led to the appearance of methanol and formic acid in the medium. Denitrification process was almost complete (around 99.7%) at nitrogen loading rates up to 0.44kg N-NO3- m-3 d-1. Nitrite occasionally appeared in the effluent at concentrations less than 2.9 mg l-1. The composition of the biogas indicated that denitrification and methanogenesis occurred simultaneously in the same unit.