Effects of temperature on biological degradation of phenols, benzoates and phthalates under methanogenic conditions

The effect of temperature on the efficiency of degradation of the aromatic compounds benzoic acid, 2,3,5-trichlorobenzoic acid, phthalic acid, methyl- and ethylphthalate, resorcinol, phenol, pentachlorophenol, 4-nitrophenol, 4-ethylphenol and o-, m- and p-cresol by a mesophilic or a thermophilic anaerobic community was examined. Anaerobic batch systems were incubated at different temperatures and inoculated with microbial communities from either of two biogas reactors fed with the same substrate, but run at 37 °C or 55∘C. Benzoic acid, phthalic acid, methylphthalate, phenol, m- and p-cresol were mineralised by the mesophilic cultures incubated at 37∘C. Apart from benzoic acid, no aromatic compounds were mineralised by the thermophilic community incubated at 55∘C, suggesting that channelling reactions to the central intermediate benzoyl-CoA were inoperative in this microbial community. The restricted degradation of phenols observed at 55∘C was confirmed by chemical analyses of the anaerobic digestion residue, which contained a higher level of phenols (322μgg-1 total solids) in the system that was run at 55∘C than that run at 37∘C (65μgg-1). However, a decrease from 55∘C to 48∘C triggered the degradation of phenol by the thermophilic batch system, most likely due to an activation of enzymes involved in the phenol degradation.