| Nonylphenol polyethoxylates (NPEOs) are used in large amounts in industrial and institutional applications as nonionic surfactants, encompassing more than 80% of the world market. Studies have found that some biodegradation intermediates of NPEOs such as nonylphenol (NP) are weakly estrogenic. Therefore, the biodegradation behaviors of NPEOs have raised public concern. The biodegradation behaviors of NPEOs under aerobic and different reducing conditions and effects of temperature, organic substrate, initial concentration, and typical intermediate were investigated which was financially supported by the National Foundation of Science of China (Grant No. 50478019). High-performance liquid chromatography (HPLC) analysis, gas chromatography-mass spectrometry (GC-MS) analysis, and liquid chromatography-mass spectrometry (LC-MS) analysis were performed to monitor the biodegradation behaviors of NPEOs under aerobic and different reducing conditions. Biochemistry and molecular biology analysis methods were also used to elucidate the mechanism for NPEO biodegradation by isolated bacteria. The results were shown as follows: (1) NPEOs were readily degraded under both aerobic and anaerobic conditions. The removal efficiency of the aerobic treatment was much higher than that of the anaerobic treatment. The maximum biodegradation rates in aerobic and anaerobic bioprocesses were 35.15μM·d-1 and 28.37 M·d-1, respectively. NPEOs were biodegraded through an oxygen-independent nonoxidative pathway, through which NPEOs were degraded via sequential removal of ethoxyl units to the nonyphenol (NP), under both aerobic and anaerobic conditions. Oxygen played an important role in the biodegradation pathway of short-chain NPEOs. Nonylphenol polyethoxycarboxylates (NPECs) were formed under aerobic conditions. Typical estrogenic intermediates of NPEOs accumulated under both aerobic and anaerobic conditions. Although the accumulation of these estrogenic intermediates was alleviated under aerobic conditions, significant accumulation of short-chain NPECs, which were more harmful than their parent compounds, occurred.(2) The results showed that NPEOs were readily degraded in the denitrifying activated sludge process. NPEO maximum biodegradation rate in nitrate-reducing treatment was 34.00μM·d-1, which was much higher than that of anaerobic treatment and a little lower than that of aerobic treatment. The addition of tungstate resulted in immediate inhibition of NPEOs biodegradation, suggesting that nitrate reduction was necessary for NPEOs biodegradation. NPEOs were biodegraded through a non-oxidative pathway, through which NPEOs were degraded via sequential removal of ethoxyl units (as acetaldehyde) to NP. The accumulation of NP, nonylphenol monoethoxylate (NP1EO), and nonylphenol diethoxylate (NP2EO) coincided with the rapid removal of total NPEOs. Concentrations of NP, NP1EO, and NP2EO reached their tops on day 14 when about 85 percent of the total NPEOs were removed. The subsequent decrease in the concentrations of NP, NP1EO and NP2EO suggested that these persistent intermediates could also be biodegraded in denitrifying activated sludge process. Concentrations of the estrogenic intermediates and calculated estrogen equivalent in denitrifying treatment were much lower than those in anaerobic treatment during NPEO biodegradation. Since NPEO contaminants could be rapidly biodegraded under denitrifying conditions without forming NPECs, it seemed that denitrifying bioprocess may have advantage in NPEO removal. To our knowledge, it is the first report on the biodegradation of NPEOs in denitrifying activated sludge process.(3) The study demonstrated that NPEOs could also be rapidly biodegraded under both Fe(III)-reducing and sulfate-reducing conditions. The maximum biodegradation rate was 34.95μM·d-1 under Fe(III)-reducing conditions. The maximum biodegradation rate was 34.85μM·d-1 under sulfate-reducing conditions. NPEOs were degraded via sequential removal of ethoxyl units under both Fe(III)-reducing and sulfate-reducing conditions. No NPECs were formed in this process. NP, NP1EO, and NP2EO slightly accumulated in the anaerobic biodegradation process. The accumulation of these estrogenic metabolites led to a significant increase in the estrogenic activity during the biodegradation period. The calculated estrogenic activity reached its top on day 14 when the total concentration of these estrogenic metabolites was maximal under Fe(III)-reducing conditions. The highest estrogenic activity appeared on day 21 when the total concentration of these metabolites reached its top (18.03μM) under sulfate-reducing conditions. Concentrations of estrogenic intermediates in sulfate-reducing and Fe(III)-reducing treatments were also lower than those of normal anaerobic treatment, suggesting that the anaerobic biodegradation of these contaminants was enhanced under sulfate-reducing and Fe(III)-reducing conditions. This is the first report of the primary biodegradation behavior of NPEOs under Fe(III)-reducing and sulfate-reducing conditions.(4) Temperature had great influence on the biodegradation of NPEOs. The decrease in temperature caused a sharp decrease in the removal efficiency of NPEOs. The temperature coefficient (Ф) for the biodegradation of NPEOs in the denitrifying activated sludge process was 0.011℃-1. The decrease in temperature caused a sharp decrease in the removal efficiency of NPEOs. The temperature coefficient (Ф) for typical anaerobic biodegradation of NPEOs was 0.01℃-1. Compared to the biodegradation of NPEOs under sulfate reducing-conditions whoseФwas 0.008℃-1, the NPEO biodegradation in denitrifying or normal anaerobic activated sludge process was more sensitive to temperature.(5) Organic substance and biodegradation intermediates such as NP had inhibition effect on anaerobic and anoxic biodegradation of NPEOs. The biodegradation of NPEOs was severely inhibited in the presence of organic substance. Different organic substances had different inhibition ability on the biodegradation of NPEOs. Anaerobic and anoxic biodegradation of NPEOs was not inhibited even at very high initial concentrations of NPEOs. The maximum biodegradation rate increased 1.24μM·d-1, 1.3μM·d-1, and 2.51μM·d-1 for each ten micromoles increase in initial concentration under typical anaerobic, sulfate-reducing, and nitrate-reducing conditions, respectively. NP, the typical intermediate of NPEOs, could inhibit anaerobic and anoxic biodegradation of NPEOs only at high concentration.(6) Two strains capable of NPEO removal were isolated. NPEOs were readily degraded by strain Serratia sp. LY and Bacillus sp. LJ-1 without forming more harmful NPECs. More than 80 percent of the total NPEOs were removed within seven days. NPEO biodegradation rate constants for strain LY and strain LJ-1 were 0.325 d-1 and 0.599 d-1, respectively. To our knowledge, this is the first report of NPEO biodegradation by Serratia and Bacillus strains. Heterotrophic nitrogen removal simultaneously occurred during NPEO biodegradation by strain LY. Moreover, NPEOs could be degraded by strain LY in the presence of different nitrogen contaminants. NPEOs were biodegraded through a nonoxidative pathway, through which NPEOs were degraded via sequential removal of ethoxyl units to NP. NP could also be removed by strain LY and LJ-1. The biodegradation rate constants for NP were 0.435 d-1 and 0.852 d-1, respectively. Enzyme activity analysis showed that NP phenyl was biodegraded through the ortho cleave pathway.
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