Environmental Technology最新文献

The inevitable UV aging of microplastics (MPs) is one of the key factors affecting their interaction with antibiotics. In this study, polyethylene (PE) and polystyrene (PS) MPs were aged with UV irradiation. The adsorption isotherms and kinetics of ciprofloxacin (CIP) to virgin and aged MPs were investigated through various models, and the effects of pH on the adsorption amount were explored. Characterization revealed that the surfaces of aged MPs became rougher, and the hydrophilicity increased. These aged MPs were still in the early stage of aging on the basis of their carbonyl index (CI) (<0.2) and O/C (<0.04) values. The adsorption isotherms indicated that the adsorption mechanism of aged PE was different from that of virgin PE. Compared with virgin PE, the adsorption amount of aged PE increased by 87.80-95.45%, and the adsorption rate decreased by 65.52-80.74%. However, aging did not significantly affect the equilibrium adsorption amount or adsorption rate of aged PS. The external diffusion rate (K_ext) (about 2.29-0.36 h^-1) was almost 30 times greater than the internal diffusion rate (K_int) in the film-pore mass transfer (FPMT) model, indicating that CIP adsorption rate was dominated by external diffusion. A hydrated functional zone is thought to form around aged MPs, thus changing the adsorption mechanism and adsorption amount of aged PE. Therefore, more attention should be given to alterations in the hydrated functional zone in the early stage of MPs aging.

Although anaerobic ammonia oxidation (anammox) is considered a promising process due to its high efficiency and low energy in nitrogen removal, nitrite inadequacy was one of the bottlenecks for the application of anammox. However, endogenous partial denitrification (EPD) has been emerging as a stable pathway to provide nitrite for anammox. Furthermore, denitrifying glycogen-accumulating organisms (DGAOs) are believed to be associated with EPD. In this study, firstly, GAOs were gradually enriched in a sequencing batch reactor (SBR) with the dual strategy of influent phosphorus limitation and withdrawal after the anaerobic stage. DGAOs were successfully induced by adding sodium nitrate solution at the end of the anaerobic stage, resulting in NO₃^--N concentration increasing from 15 to 30 mg/L. During a typical SBR cycle, DGAOs contributed up to 96% of the conversion of intracellular carbon sources and up to around 95% of nitrate reduction during the anoxic stage. The maximum nitrate-to-nitrite transformation ratio (NTR) of the system reached 80%. Microbial community analysis demonstrated that the Ca. Compatibactors were the dominant functional bacteria for EPD, with a relative abundance of 31.12%. However, the relative abundance of phosphorous-accumulating organisms (PAOs) was only 1.02%. This study reveals the important role of DGAOs in the EPD process, which can provide a stable nitrite for anammox.

A new type of particle material modified zeolite molecular sieve (CTS/ZMS) is developed for the simultaneous removal of NH₄⁺-N and NO₃^--N in groundwater. To ascertain the optimal performance of CTS/ZMS, a custom central composite design (CCD) was utilised to assess the operational parameters (dosage and contact time) of CTS/ZMS composites. Batch experiments were carried out to determine the removal efficiency and adsorption capacity across varying pH values (3-12) and temperatures (5 °C to 30 °C). The results of response surface three-dimensional analysis showed the removal efficiencies of nitrate and ammonium ions are the highest at a dosage of 5.5 g/L of CTS/ZMS adsorbents and adsorption time of 6.25 h and are respectively observed to be 40%, and 80.2%. Adsorption thermodynamic analysis (ΔG⁰<0, ΔH⁰>0, ΔS⁰>0) revealed ammonia and nitrate adsorption on CTS/ZMS composites are spontaneous and feasible at high temperatures. SEM, EDS, BET, FTIR and XPS were employed for analyzing the adsorption mechanism of CTS/ZMS for NH₄⁺-N and NO₃^--N and included mostly ion exchange, electrostatic interaction, and hydrogen bonding. Different regeneration methods including water regeneration, thermal regeneration, and chemical regeneration for CTS/ZMS composites were analyzed to evaluate the removal efficiency of NH₄⁺-N and NO₃^--N. The saturated CTS/ZMS composites regenerated by first 1 mol/L NaCl solution, followed by 1 mol/L Na₂CO₃ solution demonstrated the highest ammonia and nitrate removal efficiency. The experimental data indicated pseudo-second-order kinetic model and the Freundlich model explained well the ammonia and nitrate adsorption process of regenerated CTS/ZMS composites. According to the Langmuir model, the regenerated CTS/ZMS can adsorb a maximum of 0.92 mg/g of ammonia and 1.98 mg/g of nitrate. The results demonstrate that CTS/ZMS composites serve as a potentially efficient adsorbent for removing ammonia and ions from groundwater. This study offers technical guidelines and support for the future production and application of CTS/ZMS.

Secondary iron minerals play significant roles in the immobilization of As under acidic conditions, such as acid mine drainage. However, previous research works have not clarified the effect of pH on As(III) removal through coprecipitation with secondary minerals. Therefore, in this study, we aimed to investigate the discrepancy in As(III) coprecipitation with biogenic synthesized schwertmannite (Sch) and jarosite (Jar) at different pH values. For this, concentrations of Fe²⁺, TFe, $S{O}_4^{2-}$, and As(III) in shake flasks were monitored during an overall incubation period of 83 h at initial pH of 1.5, 2.0, and 2.5. In addition, the physicochemical properties of collected minerals after incubation were identified using scanning electron microscopy, X-ray diffraction, pore size distribution, and Brunauer - Emmett - Teller surface area analyses. Our results showed that almost no mineral synthesis and no As(III) removal were detected in coprecipitated schwertmannite (Co-Sch) system and coprecipitated jarosite (Co-Jar) system at an initial pH of 1.5. The TFe precipitation efficiencies and As(III) removal efficiencies increased considerably and morphologies of Co-Sch and Co-Jar improved significantly when the initial pH value increased from 2.0-2.5. The maximum TFe precipitation efficiency and As(III) removal efficiency reached 30.8% and 89.6%, respectively, for the Co-Sch system, and were 47.5% and 37.4%, respectively, for the Co-Jar system. The overall results show that pH significantly affects the formation of Co-Sch and Co-Jar and the behaviour of As(III) coprecipitation.

Humins (HMs), the insoluble faction of humic substances (HSs), play a pivotal role in the bioremediation of pollutants by acting as electron shuttles that modulate the interactions between microorganisms and pollutants. This crucial function is intricately linked to their structural composition and electron transfer capabilities. However, the dynamics of the electron transfer capacity (ETC) of HM extracted during the composting process and its determinants have yet to be fully elucidated. This study undertakes a comprehensive analysis of the ETC of HM derived from composting, employing electrochemical techniques alongside spectroscopic methods and elemental analysis to explore the influencing factors, including the electron accepting capacity (EAC), electron donating capacity (EDC), and electron reversible rate (ERR). Our findings reveal substantial variations in the EAC and EDC of HM throughout the composting process, with EAC values ranging from 133.03-220.98 μmol e^- gC^-1 and EDC values from 111.17-229.33 μmol e^- gC^-1. Notably, the composting process enhances the ERR and EDC of HM while diminishing their EAC. This shift is accompanied by an augmented presence of aromatic structures, polar functional groups, quinones, and nitrogen - and sulfur-containing moieties, thereby boosting the HM's EDC. Conversely, the reduction in EAC is associated with a decline in lignin carbon content and the abundance of oxygen-containing moieties, as well as the diminishment of visible fulvic-like and protein-like substances within HM. Importantly, humic-like substances and nitrogen-containing moieties within HM demonstrated the capacity for repeated electron transfer, underscoring their significance in the context of environmental remediation.

The present work focused on the isolation of a bacterial strain multi-resistant to heavy metals with a high potential for reducing hexavalent chromium (Cr(VI)) and studied its Cr(VI) removal performance in immobilized state and the mechanisms involved. Bacterial isolate was identified as Bacillus safensis CCMM B629 (B. safensis), is able to completely reduce 50, 100 and 200 mg/L of Cr(VI) after 24, 48 and 120 h, respectively under optimized conditions of pH 7 and 30°C. The coexistence of nitrates, cadmium and mercury inhibits reduction, while copper and iron significantly improve removal efficiencies. Additionally, the presence of electron donors such as glycerol, glucose and citrate significantly increases bioreduction rate. Cells immobilized in alginate beads successfully reduced Cr(VI) compared to free cells, showing the performance of biobeads in Cr(VI) reduction. Membrane fraction exhibited highest rate of Cr(VI) reduction (65%) compared to other cellular components, indicating that Cr(VI) reduction occurred primarily in cell membrane. Further characterization of Cr(VI) removal by B. safensis cells using scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis showed its ability to reduce and adsorb Cr(VI), confirming that hexavalent chromium was taken up successfully on bacterial cell surfaces. Based on Fourier transform infrared spectroscopy analysis (FTIR), hydroxyl, carboxyl, amide, and phosphoryl functional groups participated in combination with Cr(III). In conclusion, B. safensis is a bacterium with great potential for Cr(VI) removal, and it is a promising and competitive strain for use in bioremediation of Cr(VI) contaminated industrial effluents.