Optimization of an A(2)/O process for tetracycline removal via response surface methodology coupled with a Box-Behnken design.

Response surface methodology (RSM) was used to optimize the operating conditions of an anaerobic-anoxic-oxic (A(2)/O) process by maximizing the removal efficiency of tetracycline (TC). Solid retention time (SRT), hydraulic retention time (HRT) and initial TC concentration (CTC, in) were selected as independent variables for incorporation in the Box-Behnken design. The results showed SRT and CTC, in were more significant parameters than HRT for the removal efficiency of TC. TC could be completely removed under the optimal conditions of an SRT of 15.5 days, an HRT of 9.9 h and a CTC, in of 283.3 µg L(-1). TC removal efficiencies of 99% and 96% were attained for synthetic and real wastewater, respectively, under the optimal conditions. This indicated the constructed model was validated and reliable for optimizing the A(2)/O process for TC removal.

Toxicity reduction of municipal wastewater by anaerobic-anoxic-oxic process.

OBJECTIVE: This study was conducted to optimize the operational parameters of anaerobic-anoxic-oxic (A²/O) processes to reduce the toxicity of municipal wastewater and evaluate its ability to reduce toxicity. METHODS: A luminescent bacterium toxicity bioassay was employed to assess the toxicity of influent and effluent of each reactor in the A²/O system. RESULTS: The optimum operational parameters for toxicity reduction were as follows: anaerobic hydraulic retention time (HRT) = 2.8 h, anoxic HRT = 2.8 h, aerobic HRT = 6.9 h, sludge retention time (SRT) = 15 days and internal recycle ratio (IRR) = 100%. An important toxicity reduction (%) was observed in the optimized A²/O process, even when the toluene concentration of the influent was 120.7 mg·L⁻¹. CONCLUSIONS: The toxicity of municipal wastewater was reduced significantly during the A²/O process. A²/O process can be used for toxicity reduction of municipal wastewater under toxic-shock loading.

[Adsorption of Sb(â ¤) in Water by Natural Pyrite: Performance and Mechanism].

The adsorption performance of three iron ores (pyrite, hematite, and magnetite) on Sb(Ⅴ) was compared and pyrite was shown to exhibit the highest adsorption performance. The effects of particle size, concentration, and pH on the adsorption performance were investigated with pyrite as the absorbent. The rejection of Sb(Ⅴ) was the highest (>80%) when pyrite (particle size <0.074 mm) was used as the absorbent with a concentration of 1 g ·L-1 and pH=7. The ion competition experiment indicated that PO43- can inhibit the adsorption of Sb(Ⅴ), while SO42- and CO32- have no significant effects on the adsorption of Sb(Ⅴ) because PO43- can compete with Sb(Ⅴ) for active adsorption sites on the surface of pyrite. The results also showed that the quasi-second-order kinetic model and Langmuir model can better simulate the adsorption process, which shows a single-layer adsorption behavior and chemisorption plays a main role in the rejection of Sb(Ⅴ). FTIR analysis suggested that the removal of Sb(Ⅴ) by pyrite was a coordinated ion exchange reaction. EDS and XPS results further confirmed that Sb(Ⅴ) was adsorbed on the surface of pyrite and was not reduced to Sb(Ⅲ), which is more toxic.

Correlation among extracellular polymeric substances, tetracycline resistant bacteria and tetracycline resistance genes under trace tetracycline.

Antibiotic resistance occurrences and proliferation in activated sludge have attracted more and more attention nowadays. However, the role which extracellular polymeric substance (EPS) plays on the antibiotic resistance is not clear. The changes and correlation among EPS, tetracycline (TC) resistant bacteria (TRB) and TC resistance genes (TRGs) of sequencing batch reactors (SBRs) were investigated. Performance of SBR without TC was compared with two other SBRs to which different amounts of TC were added. Total average EPS contents were found to increase significantly from 66 mg g−1 VSS to 181 mg g−1 VSS as the TC concentrations increased from 0 to 100 µg L−1. As the EPS content increased, TRB in sludge of the three SBRs increased significantly from 105 to 106 colony forming unit mL−1 after being exposed to TC. In addition, the concentrations of three groups of TRGs (copies mL−1) were determined by real-time fluorescence quantitative polymerase chain reaction and followed the order: efflux pump genes > ribosome protected genes > degradation enzyme genes. The numbers of TRGs in the idle stage were larger than those in the aeration sludge. Correlation coefficients (R2) between EPS and TRB in sludge were 0.823 (p < 0.01) while the correlation between EPS and total TRGs was poor (R2 = 0.463, p > 0.05). But it showed the same tendency that EPS and TRGs in sludge increased with the increasing of TC.

[Effects of HRT on fate of typical polycyclic musk by A2O process].

Fate of galaxolide (HHCB) and tonalide (AHTN) during the A2O process was investigated under different hydraulic retention time (HRT). Solid phase extraction (SPE) and gas chromatography mass spectrometry (GC/MS) were applied to determine the concentrations of the targets in the aqueous phase and sewage sludge. The results showed that HRT has an influence on the proportions of biodegradation and the discharge of excess sludge for HHCB by the A2O process, and it also affected the discharge of excess sludge for AHTN. With the extension of HRT, removal rates and removal contribution rates of HHCB and AHTN decreased in the anaerobic tank, while increased in the anoxic tank and aerobic tank. The final removal rates of the targets in the four operating conditions (6 h, 8 h, 10 h and 12 h) were 73.93%, 73.05%, 75.14%, 76% and 48.76%, 44.27%, 57.17%, 62.9%, respectively. The removal efficiency was good for HHCB, but the removal efficiency of AHTN was poor by the A2O process. Meanwhile, with the extension of HRT, the removal efficiency showed no significant effect on HHCB, but it promoted the removal efficiency of AHTN.

Effect of trace tetracycline concentrations on the structure of a microbial community and the development of tetracycline resistance genes in sequencing batch reactors.

The objective of this study was to investigate effects of different concentrations of tetracycline (TC) on the microbial community and development of tetracycline resistance genes (TRGs) of sequencing batch reactors (SBRs). Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis of 16S rRNA and real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) were used to detect the structural changes of the microbial community and the variations of eight TC resistance genes tet(A), tet(B), tet(C), tet(E), tet(M), tet(O), tet(S) and tet(X), respectively. The results indicated that, trace TC could substantially change the structure of the microbial community. Bacteria which could not adapt to environment with TC were gradually replaced by those adapting to tetracycline. Shannon's diversity index (H) and Simpson's index (D) reached maximum values when the concentration of TC was 1 µg L(-1). The resistance genes in the activated sludge proliferated under the pressure of trace TC.

[Relationship between typical organic matters in domestic wastewater and water characteristic parameters in activated sludge models].

The contribution of typical organic matters such as proteins, sugars, lipids and linear alkylbenzene sulfonate (LAS) to COD of the domestic wastewater was investigated. Nitrate utilization rate was used to determine wastewater characteristic parameters. Relationship between these typical organic matters and wastewater characteristic parameters (Ss, Xs, SI, XI) in activated sludge models were investigated. The results showed that YH of activated sludge under denitrifying conditions was 0.683. Proteins, sugars, lipids and LAS accounted for 24%-35%, 17%-35%, 5.78%-10.56% and 3.77%-7.23% of the total COD, respectively. It indicated that these four pollutants were the main COD source in the domestic wastewater. SS and XI were in the ranges of 22%-29% and 29%-38% of the total COD, respectively. Concentrations of the four typical target organic matters (proteins, sugars, lipids and LAS) correlated well with the wastewater characteristic parameters (Ss, Xs, SI, XI) of activated sludge models (ASMs) with the correlative coefficients above 0.9.

[Transformation of linear alkylbenzene sulphonate in the anaerobic-anoxic-oxic wastewater treatment process].

The removal characteristics of linear alkylbenzene sulphonate (LAS) was studied in anaerobic/anoxic/oxic (AAO) municipal wastewater treatment processes. A removal (biological degradation and sorption) model was formulated, and kinetic parameters were evaluated with batch experiments under anaerobic, anoxic, oxic conditions. The resulting model calculations were then compared with sampling campaigns performed on AAO process. The results show that the removal efficiency of LAS in the AAO activated sludge processes is more than 99%. Effluent concentrations vary between 0 and 20 microg L(-1). The concentration of LAS adsorbed by sludge in anaerobic tank, anoxic tank, aerobic tank is 490 - 710 microg g(-1), 280 - 390 microg g(-1) and 69 - 109 microg g(-1) respectively. From the result of biodegradation kinetic tests, it can be concluded that LAS is well biodegraded under anaerobic/anoxic/oxic conditions, and the removal rate of LAS in anaerobic and anoxic conditions accounts for respectively 67% and 71% of that in oxic condition. The model can well forecast the effluent quality of anaerobic/ anoxic/oxic tank of the AAO process, and the relative error is less than 8%.