Simultaneous oxidation of ammonium and cresol isomers in a sequencing batch reactor: physiological and kinetic study

Abstract

The aim of this study was to evaluate the physiological and kinetic capacities of a nitrifying consortium to simultaneously oxidize ammonium (138 mg N/L day), m-cresol, o-cresol, and p-cresol (180 mg C/L day in mixture) in a sequencing batch reactor (SBR). A 1-L SBR was firstly operated without cresol addition (phase I) for stabilizing the nitrification respiratory process with ammonium consumption efficiencies close to 100 % and obtaining nitrate as the main end product. When cresols were added (phase II m-cresol (10, 20, and 30 mg C/L); phase III m-cresol (30 mg C/L) and o-cresol (10, 20, and 30 mg C/L); phase IV a mixture of three isomers (30 mg C/L each one)), inhibitory effects were evidenced by decreased values of the specific rates of nitrification compared with values from phase I. However, the inhibition diminished throughout the operation cycles, and the overall nitrifying physiological activity of the sludge was not altered in terms of efficiency and nitrate yield. The different cresols were totally consumed, being o-cresol the most recalcitrant. The use of SBR allowed a metabolic adaptation of the consortium to oxidize the cresols as the specific rates of consumption increased throughout the cycles, showing that this type of reactor can be a good alternative for treating industrial effluents in a unique reactor.

Population dynamics of nitrifying sludge supplemented with 2‐chlorophenol in SBR reactors

“…12 These results evidenced that the addition of higher 2-CP concentrations provoked different effects on the ammonium and nitrite-oxidizing processes, the former being the most affected, whereas the nitrite oxidation into nitrate remained complete and stable. These results are in accordance with those reported in batch assays amended with 5 mg 2-CP-C/L 16 and nitrifying SBR reactors added with mixtures of o-cresol, m-cresol, and p-cresol, 10 where the nitrite oxidation process was not affected by the presence of phenolic compounds. Negative effects on the ammonium-oxidizing process by adding aromatic compounds have also been reported in nitrifying consortia 16 and axenic cultures of Nitrosomonas europaea.…”

“…In summary, the previous history of both sludges played a critical role in achieving the capacity for biodegrading up to 60 mg 2‐CP‐C/L simultaneously to the total consumption and oxidation of ammonium into nitrate. This capacity might be attributed to the sludge tolerance developed to phenolic compounds along both the previous exposure to p ‐cresol and/or 2‐CP and during the nitrifying sludge exposition to increasing 2‐CP concentrations, as well as to the metabolic adaptation acquired as cycles elapsed in the SBR systems, which have been proved to be a good alternative for removing inhibitory or toxic aromatic compounds 10,11,36 . The negative effects on the ammonium and nitrite oxidation processes exerted by the high concentration of 2‐CP, might be related to affectations in transport systems, 16 lower activity of nitrifying enzymes, 5 changes in membrane structure, 37 changes in the amount of nitrifying bacteria, 38 and/or to the microbial community composition acquired along the operation cycles evolved.…”

“…Regarding mixotrophy, the participation of a series of enzymes to degrade p ‐cresol and the further assimilation of the degradation products into the three carboxylic acid (TCA) cycle have been proposed to occur in Nitrosomonas eutropha C91 8 . Likewise, the capacity of nitrifying consortia to biodegrade different compounds (such as phenol, 9 m ‐cresol, o ‐cresol, p ‐cresol) 10 and mixtures of these compounds 11 has been reported. Nevertheless, the inhibitory effects of phenolic compounds on nitrification processes are also well documented 10,12 .…”

“…Likewise, the capacity of nitrifying consortia to biodegrade different compounds (such as phenol, 9 m ‐cresol, o ‐cresol, p ‐cresol) 10 and mixtures of these compounds 11 has been reported. Nevertheless, the inhibitory effects of phenolic compounds on nitrification processes are also well documented 10,12 . Such is the case of 2‐chlorophenol (2‐CP), a chlorophenolic contaminant frequently detected in sediments and aquifers due to its extensive use in the wood industry as a preservative or pesticide 13 .…”

“…Nevertheless, the inhibitory effects of phenolic compounds on nitrification processes are also well documented. 10,12 Such is the case of 2-chlorophenol (2-CP), a chlorophenolic contaminant frequently detected in sediments and aquifers due to its extensive use in the wood industry as a preservative or pesticide. 13 The incomplete degradation of pentachlorophenol (PCP), a widespread environmental contaminant in soils, surface water, and groundwater, also contributes to 2-CP accumulation.…”