Methanogenic biodegradation of aromatic amines

Batch methanogenic toxicity and biodegradability of 2-, 3- and 4-aminobenzoic acids (ABA) as well as 4- and 5-aminosalicylic acids (ASA) have been studied in the presence of two mesophilic (Shell and cattle) and one thermophilic sludges. The aminoaromatics tested practically did not inhibit methanogenesis up to concentrations of 3-7 g/l; moreover, some of them (2-ABA, 4-ABA and 5-ASA) even exert a stimulating effect on aceticlastic activity of the sludges. Concerning biodegradability, 8-ASA was completely mineralised by all the sludges tested; however, 4-ASA was not degraded at all by any of the sludges. Both mesophilic sludges were able to perform a complete mineralization of 2-ABA but this was not a case for the thermophilic sludge. 3-ABA was not biodegraded only in the presence of the Shell sludge. On the contrary, 4-ABA was quantitatively mineralised only by the Shell sludge. All the adapted sludges were able to mineralise the corresponding aminoaromatics in N-deprived media. Cross-acclimatisation trials showed that 2-ABA-, 5-ASA- and salicylic acid adapted sludges were unable to degrade any other aminoaromatics tested that manifest about a different nature of key bacteria responsible for primary decomposition of these substrates. The main possibility of continuous mineralization of 2-ABA as a unique source of carbon and nitrogen has been demonstrated using mesophilic UASB reactor inoculated by adapted sludge. Keywords Aminobenzoic acids; aminosalicylic acids; biodegradability; toxicity; UASB reactor.