China has experienced an unparalleled urbanization process in recent decades, which has dramatically changed the water environment. Quantification of the water environment carrying capacity (WECC) is crucial given its importance to sustainable development. Existing studies have typically focused on the overall WECC system and lacked analysis of its internal features. In this study, the concepts, calculations, and classifications of the WECC were further developed. Using Nanjing, China, as a case study, we developed a hierarchical evaluation indicator system including three system layers (social, environmental and economic subsystems). We applied the entropy weight and fuzzy comprehensive evaluation method to evaluate the temporal variation tendency of WECC, and explored the deep-seated problems stemming from urbanization. The results indicated that WECC in Nanjing was 0.3045–0.5302 during 2006–2017, thus approaching a moderate grade with a relatively slow growth rate. Social, environmental, and economic subsystems increased by 29.3%, 83.1%, and 97.2%, respectively. Overall, Nanjing had a solid foundation regarding its economic subsystem, but its social and environmental subsystems were under pressure. Factors such as slow population growth as well as reduced energy and water use intensity improved WECC, whereas factors such as increased population density and excessive water consumption blocked WECC. Practical suggestions were proposed to resolve the primary problems of the WECC under urbanization. This holistic approach is urgently needed to achieve water environmental sustainability, both for Nanjing and for other emerging cities.

A pilot-scale experiment is carried out for treating mixed wastewater containing pharmaceutical wastewater (PW) and domestic wastewater (DW), by a process that is a combination of hydrolysis acidification-ozone-modified anaerobic–anoxic–aerobic-ozone (A²/O) (pre-ozone) or hydrolysis acidification-modified A²/O-ozone (post-ozone). The effects of different mixing ratios of PW and DW and pre-ozone treatment or post-ozone treatment on the removal of nitrogen and phosphorus and chemical oxygen demand (COD) are compared and studied. The optimal ratio of PW in mixing wastewater is 30%, which has the optimal COD removal efficiency and minimum biotoxicity to biological treatment. The pre-ozone treatment shows more advantages in removing nitrogen and phosphate but the post-ozone treatment shows more advantages in COD removal. Analysis of dissolved organic matter (DOM) demonstrates that post-ozone treatment has a more significant effect on the removal of fulvic acid and humic acid than the effect from the pre-ozone treatment, so the COD removal is better. Overall DOM degradation efficiency by post-ozone treatment is 55%, which is much higher than the pre-ozone treatment efficiency of 38%. Microbial community analysis reveals that the genus Thauera and the genus Parasegetibacter take great responsibility for the degradation of phenolics in this process. All the results show that the post-ozone treatment is more efficient for the mixed wastewater treatment in refractory organics removal.

The conventional precursor preparation of metal–organic frameworks (MOFs) for nitrogen-doping carbon materials is divided into the preparation of MOFs and the mixing of the nitrogen source, which is a complex and time-consuming step. In this study, Fe-BTC gel/nitrogen source-derived carbon materials were synthesized using one or more of the following raw ingredients: Fe(NO₃)₃·9H₂O, FeCl₃·6H₂O, Fe₂(SO₄)₃, trimesic acid, melamine and dicyandiamide. The influence of different raw ingredients on the preparation and performance of catalysts was investigated. Fe(NO₃₎₃·9H₂O can react with trimesic acid to form a gel with ethanol as solvent, and the gel helped the homogeneous dispersion of the added melamine and did not precipitate. Fe-C-N(M), synthesized from the three materials mentioned, was identified as the optimal catalyst; the removal rate of 5 mg/L sulfadimethoxine (SMZ) reached 100% at 15 min when the Fe-C-N(M) dosage was 50 mg/L, PMS concentration was 0.5 mM, and the pH was 5.78 (initial pH of the solution). The removal of SMZ was not significantly inhibited by the pH (3–9) and 0–10 mM inorganic anions (Cl⁻, NO₃⁻, HCO₃⁻ and H₂PO₄²⁻). Through quenching tests, electron paramagnetic resonance and probe experiments, ¹O₂ and a small amount of free radicals (•OH and SO₄^•−) bound on the catalyst surface are discovered to be the primary active ingredients that activate PMS to degrade SMZ.

A novel coagulation combined with UV/O₃ process was employed to remove the effluent organic matter (EfOM) from a biotreated pharmaceutical wastewater for harmlessness. The removal behavior of EfOM by UV/O₃ process was characterized by synchronous fluorescence spectroscopy (SFS) integrating two-dimensional correlation (2D-COS) and principal component analysis (PCA) technology. The highest dissolved organic carbon (DOC) and ratio of UV₂₅₄ and DOC (SUVA) removal efficiency reached 55.8% and 68.7% by coagulation-UV/O₃ process after 60 min oxidation, respectively. Five main components of pharmaceutical tail wastewater (PTW) were identified by SFS. Spectral analysis revealed that UV/O₃ was selective for the removal of different fluorescent components, especially fulvic acid-like fluorescent (FLF) component and humus-like fluorescent (HLF) component. Synchronous fluorescence/UV-visible two-dimensional correlation spectra analysis showed that the degradation of organic matter occurred sequentially in the order of HLF, FLF, microbial humus-like fluorescence component (MHLF), tryptophan-like fluorescent component (TRLF), tyrosine-like fluorescent component (TYLF). The UV/O₃ process removed 95.6% of HLF, 80.0% of FLF, 56.0% of TRLF, 50.8% of MHLF and 44.4% of TYLF. Therefore, the coagulation-UV/O₃ process was proven to be an attractive way to reduce the environmental risks of PTW.