Biodegradability of N-substituted aromatics and alkylphenols under methanogenic conditions using granular sludge

Abstract

The biodegradability of seventeen N-substituted aromatic and six alkylphenol compounds were evaluated under methanogenic conditions. Biodegradation was assessed in batch assays inoculated with unacclimated and predigested anaerobic granular sludge at 30°C under agitated conditions over a 150 day period. The compounds were supplied at sub-toxic concentrations in the assays in order to prevent inhibition to the methanogens. The biodegradability test was performed by the measurement of the methane composition in the headspace of the serum flasks. The methanogenic consortia completely mineralized 2-, 3-aminobenzoate, 2-aminophenol and 4-cresol; whereas, 4-aminobenzoate was only partially degraded. The other N-substituted compounds and the alkylphenols tested were not biodegradable under the experimental conditions employed. An additional biodegradability assay was conducted with sludge from an upward-flow anaerobic sludge bed reactor adapted to the degradation of 2-nitrophenol. This sludge mineralized 2-aminophenol without any lag phase while the unadapted sludge required 110 days of acclimation. The three aminobenzoate isomers were fully mineralized by the adapted sludge after similar lag periods observed in the unadapted sludge. The 2-nitrophenol adapted sludge cross-acclimatized to the mineralization of 5-aminosalicylate and 4-aminophenol. This constitutes the first report demonstrating the anaerobic mineralization of 5-aminosalicylate, which indicates that at least some azo dye cleavage products can be degraded in methanogenic consortia.