TOXICITY AND BIODEGRADATION OF FORMALDEHYDE IN ANAEROBIC METHANOGENICCULTURE

Formaldehyde is present in several industrial wastewaters including pe trochemical wastes. in this study, the toxicity and degradability of f ormaldehyde in anaerobic systems were investigated. Formaldehyde showe d severe toxicity to an acetate enrichment methanogenic culture. As to w as 10 mg/L (0.33 mM) of formaldehyde in the reactor completely inhib ited acetate utilization. Formaldehyde however, was, degraded while ac etate utilization was inhibited. Degradation of formaldehyde (initial concentration less than or equal to 30 mg/L) followed Monod model with a rate constant, k, of 0.35-0.46 d(-1). At higher initial concentrati ons (greater than or equal to 60 mg/L), formaldehyde degradation was i nhibited and partial degradation was possible. The initial formaldehyd e to biomass ratio, S-0/X-0, was useful to predict the degradation pot ential of high formaldehyde concentrations in batch systems. When S-0/ X-0 less than or equal to 0.1, formaldehyde was completely degraded wi th initial concentration of up to 95 mg/L; when S-0/X-0 greater than o r equal to 0.29, formaldehyde at higher than 60 mg/L was only partiall y degraded. The inhibition of formaldehyde degradation in batch system s could be avoided by repeated additions of low concentrations of form aldehyde (up to 30 mg/L). Chemostats (14-day retention time) showed de gradation of 74 mg/L-d (1110 mg/L) of influent formaldehyde with a rem oval capacity of 164 mg/g VSS-day. A spike of 30 mg/L (final concentra tion in the chemostat) formaldehyde to the chemostat caused only a sma ll increase in effluent acetate concentration for 3 days. But a spike of 60 mg/L (final concentration in the chemostat) formaldehyde to the chemostat resulted in a dramatic increase in acetate concentration in the effluent. The results also showed that the acetate enrichment cult ure was not acclimated to formaldehyde even after 226 days. (C) 1997 J ohn Wiley & Sons, Inc.