| Summary: | The enantiospecific fate of three common pharmaceuticals was monitored in a laboratory�scale membrane bioreactor (MBR). The MBR was operated with a hydraulic retention time
of 24 h and a mixed liquor suspended solids concentration of 8.6e10 g/L. Standard solu�tions of ibuprofen, ketoprofen and naproxen were dosed into the synthetic feed of the MBR.
Influent and permeate samples were then collected for enantiospecific analysis. The
individual (R)- and (S )-enantiomers of the three pharmaceuticals were derivatised using
a chiral derivatizing agent to form pairs of diastereomers, which could then be separated
and analysed by gas chromatographyetandem mass spectrometry (GCeMS/MS). Accurate
quantitation of individual enantiomers was undertaken by an isotope dilution process. By
comparing the total concentration (as the sum of the two enantiomers) in the MBR influent
and permeate, ibuprofen, ketoprofen and naproxen concentrations were observed to have
been reduced as much as 99%, 43% and 68%, respectively. Furthermore, evidence of
enantioselective biodegradation was observed for all three pharmaceuticals. (S )-Ibuprofen
was shown to be preferentially degraded compared to (R)-ibuprofen with an average
decrease in enantiomeric fraction (EF ) from 0.52 to 0.39. In contrast, (R)-ketoprofen was
preferentially degraded compared to (S )-ketoprofen with a relatively minor increase in EF
from 0.52 to 0.63. The use of a relatively pure enantiomeric solution of (S )-naproxen
resulted in a significant change in EF from 0.99 to 0.65. However, this experiment consis�tently revealed significantly increased concentrations of (R)-naproxen during MBR treat�ment. It is hypothesised that the source of this (R)-naproxen was the enantiomeric
inversion of (S )-naproxen. Such enantiomeric inversion of chiral pharmaceuticals during
wastewater treatment processes has not previously been reported.
|
|---|