CONTINUOUS DETOXIFICATION, TRANSFORMATION, AND DEGRADATION OF NITROPHENOLS IN UPFLOW ANAEROBIC SLUDGE BLANKET (UASB) REACTORS

The anaerobic transformation and degradation of nitrophenols by granul ar sludge was investigated in upflow anaerobic sludge blanket (UASB) r eactors continuously fed with a volatile fatty acid (VFA) mixture as t he primary substrate. During the start-up, subtoxic concentrations of 2-nitrophenol (2-NP), LF-nitrophenol (4-NP), and 2, 4-dinitrophenol (2 , LF-DNP) were utilized. 4-NP and 2, LF-DNP were readily converted to the corresponding aromatic amine; whereas 2-NP was converted to nonaro matic products via intermediate formation of 2-aminophenol (2-AP). The se conversions led to a dramatic detoxification of the mononitrophenol s because the reactors treated the nitrophenolics at the concentration s which were over 25 times higher than those that caused severe inhibi tion. VFA removal efficiencies greater than 99% were achieved in both reactors at loading rates greater than 11.4 g COD per liter of reactor volume per day even at volumetric loading of mononitrophenols up to 9 10 mg/L . d. The sludges obtained from each of the reactors at the end of the continuous experiments were assayed for their specific nitroph enol reducing activity in the pres ence of different primary substrate s. Reduction rates of 45 and 26 mg/g volatile suspended solids per day were observed for 2-NP and 4-NP, respectively, when utilizing the VFA mixture as primary substrate. Hydrogen, an interspecies-reduced compo und, and substrates that provide interspecies-reducing equivalents-suc h as butyrate, propionate, and ethanol stimulated nitrophenol reductio n, whereas acetate and methanol did not. Anaerobic batch biodegradabil ity tests with the 2-NP-adapted sludge revealed that its corresponding aromatic amine, 2-AP, was degraded to methane at a specific rate of 1 4.5 mg/g VSS . d. Acetate was observed to be the major intermediate du ring 2-AP degradation in the presence of a specific methanogenic inhib itor 2-bromoethanesulfonate. The results of this study indicate that U ASB reactors can be applied to rapidly detoxify and, under certain cir cumstances, degrade nitroaromatic compounds. (C) 1996 John Wiley & Son s, Inc.