Abstract:
Nonylphenol polyethoxylates (NPnEOs) are non-ionic surfactants found ubiquitously in the environment due to
the uncontrolled discharging after industrial and domestic usage. Nonylphenol (NP), an endocrine disrupting chemical,
is the major product from the environmental degradation of NPnEOs. Environmental contaminated NP has relatively
low toxicity to mammals but high toxicity to aquatic organisms. The goal of this study was to investigate the NP degradation
ability of microorganism in the activated sludge from wastewater treatment plants and sediment from natural streams
around Bangkok area. Different conditions were set up for the biodegradation studies especially anaerobic condition.
In NP analysis, dichloromethane:methanol at 9: 1 was use as an extractant. NP and its products were analyzed by gas
chromatography-mass spectrometry (GC-MS). In the test of NP in fresh stream sediment, the results showed all sediment
samples were contaminated by NP at the ppm level. The NP degradation test by indigenous microorganisms from these
sampling sites showed that NP could be degraded under anaerobic conditions, but occurred relatively slowly. On the
other hand, the results of NP degradation in the activated sludge under three conditions including anaerobic, aerobic
and aerobic with periodical shaking conditions indicated that the half-life of NP under anaerobic condition was 4 weeks
while in aerobic with periodical shaking condition was 2 weeks. It suggested that NP degradation was more efficient under
aerobic condition rather than anaerobic condition. In comparison of the NP concentration in activated sludge and stream
sediment during the incubation period, it indicated that the NP disappearance in the sludge was more rapidly than the sediment.
However, the increase of NP in some canal sediments during the incubation which leading to slow NP reduction might be from
the continuously degradation of original NPnEOs accumulated in the sediments. During the NP degradation, both oxidative
and reductive intermediates were found. The reductive products were always happened in anaerobic sets, and the oxidative
products were mostly found in aerobic sets.