Sewage discharge could be a major source of polycyclic aromatic hydrocarbons （PAHs） in the coastal waters. Stonecutters Island and Shatin Sewage Treatment Works （SCISTW and STSTW） in Hong Kong, ...adopted chemically enhanced primary treatment and biological treatment, respectively. This study aimed at （1） determining the removal efficiencies of PAHs, （2） comparing the capabilities in removing PAHs, and （3） characterizing the profile of each individual PAHs, in the two sewage treatment plants （STPs）. Quantification of 16 PAHs was conducted by a Gas Chromatography. The concentrations of total PAHs decreased gradually along the treatment processes （from 301 ± 255 and 307 ± 217 ns/L to 14.9 ± 12.1 and 63.3 ± 54.1 ng/L in STSTW and SCISTW, respectively）. It was noted that STSTW was more capable in removing total PAHs than SCISTW with average total removal effidency 94.4% ± 4.12% us. 79.2% ± 7.48% （p 〈 0.05）. The removal of PAHs was probably due to sorption in particular matter, confirmed by the higher distribution coefficient of individual and total PAHs in solid samples （dewatered sludge contained 92.5% and 74.7% of total PAHs in SCISTW and STSTW, respectively） than liquid samples （final efffluent-total contained 7.53% and 25.3% of total PAHs in STSTW and SCISTW, respectively）. Despite the impressive capability of STSTW and SCISTW in removing PAHs, there was still a considerable amount of total PAHs （1.85 and 39.3 ks/year, respectively for the two STPs） being discharged into Hone Kon coastal waters, which would be an environmental concern.
This study aimed at investigating the removal efficiencies of perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS) and bisphenol A (BPA) of two major sewage treatment works in Hong Kong: ...Stonecutters Island STW (SCISTW) which adopts chemically enhanced primary treatment (CEPT) process and Sha Tin STW (STSTW) which employs biological treatment. Liquid portion (LP) and particulate matter (PM) of liquid sewage samples and sludge samples were collected and followed by liquid chromatograph system. It was found that BPA (44.6 ± 35.1%) generally achieved higher TRE than the two other chemicals (PFOS (−18.8 ± 34.8%) and PFOA (−104 ± 86.8%)) in STSTW (p < 0.05). Most of the PFOA, PFOS and BPA was discharged through final effluent (PFOA: 95.6 ± 1.00% and 94.5 ± 3.13%; PFOS: 77.7 ± 1.48% and 72.6 ± 6.07%; BPA: 99.2 ± 0.950% and 92.8 ± 7.25%, respectively) rather than stored in the sludge/cake (PFOA: 4.45 ± 1.00% and 5.47 ± 3.13%, PFOS: 22.3 ± 1.48% and 27.4 ± 6.07%, BPA: 0.844 ± 0.950% and 7.20 ± 7.25%, respectively). After the sewage purification process, the two STW released considerable amounts of PFOA, PFOS and BPA in the final effluent (PFOA: 0.638 ± 0.227 kg/year; PFOS: 0.409 ± 0.126 kg/year; BPA: 10.4 ± 3.83 kg/year in STSTW; PFOA: 3.08 ± 1.415 kg/year; PFOS: 2.13 ± 0.452 kg/year; BPA: 714 ± 768 kg/year in SCISTW) and in the sludge (PFOA: 0.0360 ± 0.0250 kg/year; PFOS: 0.149 ± 0.00100 kg/year; BPA: 1.09 ± 1.47 kg/year in STSTW; PFOA: 0.139 ± 0.0670 kg/year; PFOS: 0.606 ± 0.0780 kg/year; BPA: 3.05 ± 3.95 kg/year in SCISTW). This study may help to provide crucial information for further development of municipal sewage system in treating synthetic emerging chemicals.
•Wastewater treatment processes (WTP) were not effective in removing PFOA/PFOS.•Majority of PFOA, PFOS and BPA presented in the effluent rather than in the sludge.•Substantial amount of PFOA/S and BPA discharged into the Victoria Harbor, Hong Kong.
This study was to investigate removal efficiencies and profiles of 14 polybrominated diphenyl ether (PBDE) congeners by two different types of sewage treatment work (STW) in Hong Kong: Stonecutters ...Island STW (SCISTW) which uses chemically enhanced primary treatment (CEPT) process and Sha Tin STW (STSTW) which adopts biological treatment. The results indicated that both SCISTW and STSTW had a high total removal efficiency for BDE-47, BDE-99 BDE-209 and total PBDEs (SCISTW: 71.6±15.8, 84.7±12.3, 96.0±2.62 and 87.4±8.02%, respectively; STSTW: 74.8±9.5, 90.7±9.14, 96.2±2.41 and 89.3±2.62%, respectively) and PBDEs were chiefly removed by sorption. However, the profile of PBDEs demonstrated that the relative proportions of BDE-28 and BDE-47 in total PBDEs markedly increased, while that of BDE-209 decreased in the effluent samples of the two sewage treatment works, especially in STSTW. The percentage of BDE-209 in total PBDEs in effluent (49.3%) of SCISTW was 21.2% lower than that in influent (70.5%), and the percentage of BDE-209 in total PBDEs in effluent (13.8%) of STSTW was 34.1% reduced from influent (47.9%). Despite overall removal, the percentage of BDE-47 in total PBDEs in effluent (17.6%) of SCISTW was 6.85% higher than that in influent (10.7%), and the percentage of BDE-47 in total PBDEs in effluent (33.5%) of STSTW was 18.1% increased from influent (16.8%). The increase in proportion of BDE-47 in the effluent might raise environmental and public health concerns. Our study is a first attempt in reporting the PBDE congener profiles in different phases of sewage treatment.
•Wastewater treatment processes (WTP) were very effective in removing PBDEs.•BDE-209 was degraded to BDE-28 and BDE-47 in wastewater treatment processes.•BDE-28 and BDE-47 were the dominant congeners detected in effluent of WTP.
Many enzymes are subject to allosteric control, often with inhibitors and activators binding to the same effector site. Phosphofructokinase in Escherichia coli is such an enzyme, being inhibited by ...phosphoenolpyruvate (PEP) and activated by ADP and GDP. How do individual interactions with effectors affect the balance between activation and inhibition, especially when both ligands share aspects of the same binding site? We find that mutation of a single residue in the effector site, Glu---Ala 187, leads to PEP being an activator rather than an inhibitor. With low concentrations of the substrate fructose-6-phosphate, the mutant enzyme is more than one hundred times more active than wild-type enzyme at millimolar concentrations of PEP. The classical Monod-Wyman-Changeux two-state model is too simple to account for the properties of the mutant enzyme.
A systematic study by site-directed mutagenesis has been conducted on the effector site of phosphofructokinase from Escherichia coli to delineate the role of side chains in binding the allosteric ...activator, GDP, and inhibitor, PEP, and to search for key residues in the allosteric transtion. Target residues were identified from the crystal structure of the enzyme-nucleoside diphosphate complex. It is found that both activator and inhibitor bind to the same set of amino acid side chains. Deletion of positively charged groups (Arg21, Arg25, Arg54, Arg154, and Lys213 mutated to alanine) weakens binding of both effectors by 2-3 kcal/mol, consistent with the disruption of charged hydrogen bonds. Residue Glu187, which is known from the crystal structure to bind the coordinated Mg2+ ion of GDP, is found to have a unique behavior on mutation and appears to be crucial in triggering the allosteric transition. All other residues mutated simply weaken binding of both PEP and GDP in a parallel manner. However, mutation of Glu---Ala187 reverses the roles of GDP and PEP, causing GDP to become an allosteric inhibitor and PEP an activator. Mutation of Glu---Gln187 has only a small effect on the binding of PEP, and both PEP and GDP are inhibitors. Studies are described in which mutations in different subunits of a tetrameric complex complement each other. The effector site is composed of residues from two subunits. In particular, Arg21 and Lys213 in each site are from different subunits. Mutations of either one of these residues abolishes activation by GDP of the homotetramer.
A new vector for the expression of phosphofructokinase (pfk-1) was constructed with pEMBL, which allows reliable, inducible, high-expression, and facile mutagenesis of the gene. Two mutants in the ...effector site of the enzyme were produced by site-specific mutagenesis of residue Tyr-55 to assess the role of its side chain in binding an allosteric inhibitor, phosphoenolpyruvate (PEP), and an activator, guanosine 5'-diphosphate (GDP): Tyr-55---Phe-55 and Try-55---Gly-55. The dissociation constant of PEP from the T state is unaffected by the mutations. Mutation of Tyr-55---Phe-55 only slightly increases the dissociation constant of GDP from the R state, indicating a minimal involvement of the hydroxyl group in binding. A 5.5-fold increase in the dissociation constant of GDP on the mutation of Tyr-55---Gly-55 suggests a small hydrophobic interaction of the aromatic ring of the tyrosine residue with guanine of GDP.
