Decrease of inhibitory effect of 2-chlorophenol on nitrification in sequencing batch reactors

Abstract

The metabolic and kinetic behaviour of a nitrification process in the presence of 2-chlorophenol (2-CP) was evaluated in two sequencing batch reactors (SBR1, SBR2) inoculated with nitrifying sludge previously exposed to phenolic compounds. The SBR1 was inoculated with sludge previously exposed to 2-CP, while the SBR2 was inoculated with sludge previously exposed to p-cresol. An inhibitory effect of 20 mg 2-CP-C/L on both nitrification processes was observed, as specific rates decreased according to a control assay in the absence of 2-CP. However, the inhibitory effect decreased throughout the cycles. At the end of cycle 6, a stable nitrifying process was observed with the sludge previously exposed to 2-CP (SBR1), as an ammonium consumption efficiency and a nitrate production yield close to 99.6 ± 0.3% and 0.99 ± 0.02 were respectively achieved. Despite a complete ammonium consumption being achieved with the sludge previously exposed to p-cresol (SBR2), partial nitrification was observed as nitrate production yield accounted for 0.28 ± 0.08 and nitrite was accumulated within the culture. Nevertheless, both nitrifying sludges had the ability to completely consume 2-CP. The use of SBR systems with nitrifying sludge previously exposed to 2-CP resulted in a better nitrification performance, thus it may be a good alternative for achieving a stable nitrifying respiratory process where complete and simultaneous ammonium and 2-CP consumption can be acquired.

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

“…Mineral medium . The SBR cultures were fed with a mineral medium mixture composed of nitrogen (A) and carbon (B) sources, as reported by Martínez‐Jardines et al 12 . Medium A consisted of (g/L): NH 4 Cl 0.385, (NH 4 ) 2 SO 4 0.47, KH 2 PO 4 0.56, MgSO 4 0.4, and NaCl 0.4.…”

“…and from SBR2, previously exposed to p ‐cresol and 2‐CP) were used as inoculum. A detailed description of the inocula can be found elsewhere 12 . Nitrifying activity of inocula during five sequential batch cultures was confirmed with 91.3 ± 5.7 mg NH 4 + ‐N/L and 19.4 ± 1.1 mg 2‐CP‐C/L, as average values of 99.92 ± 0.06% for ammonium consumption efficiency and 0.98 ± 0.01 mg NO 3 − N/mg NH 4 + ‐N consumed for nitrate production yield with no nitrite accumulation were determined.…”

“…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 .…”

“…Authors indicated that despite the inhibitory effects exerted by 2‐CP on the respiratory process, it was possible to recover a part of the nitrifying activity of the sludge. Recently, it has been reported that by employing nitrifying consortia previously exposed to recalcitrant compounds and sequencing batch reactors (SBR), the sludge had the ability to simultaneously eliminate ammonium and 20 mg of 2‐CP‐C/L in 30 days of culture 12 . Under these conditions, inhibition of the nitrification process was presented, as a significant decrease in the specific rates of ammonium consumption and nitrate production was determined.…”

“…It has been proposed that the metabolic improvement and reduction of the inhibitory effect of 2‐CP on the nitrification process observed in SBR systems can be associated with the constant exposure of the nitrifying sludge to phenolic compounds; 12 nevertheless, changes in the microbial community might occur. Regarding this, it has been observed that environmental changes, such as type and concentration of nutrients, modify the metabolism of the microbial population and determine the type of populations present in a consortium 17 .…”