Formaldehyde degradation in an anaerobic packed-bed bioreactor

The development of appropriate technologies for the treatment of formaldehyde discharged into the environment is important to minimize its impact. Aerobic systems have been employed, although alternative anaerobic treatments have also been widely studied, mainly due to their low energy consumption and sludge production. However, toxic substances can lead to disturbances in anaerobic reactors. Some research has already been developed on formaldehyde anaerobic biological treatment, but no consensus has yet been reached about its behavior nor has the most efficient system been identified. Aiming at finding supporting evidence for this issue, therefore, this study investigated the degradation and toxicity of formaldehyde in a Horizontal-Flow Anaerobic Immobilized Sludge Reactor. Formaldehyde concentrations of 26.2–1158.6 mg HCHO/L were applied in the reactor, resulting in formaldehyde and chemical oxygen demand removal efficiencies of 99.7% and 92%, respectively. Volatile fatty acids with up to five carbons, found during the degradation of formaldehyde, are believed to indicate that the degradation followed routes unlike those suggested in the literature, which reports the formation of intermediates such as methanol and formic acid. The Monod kinetic model adhered to the experimental data well, with apparent kinetic parameters estimated as rmaxapp=2.79×10−3 mg HCHO/mg SSV h and Ksapp=242.8 mg HCHO/L.