Controlling the concentration of free radicals in polymerization systems is advantageous for preparing cationic polyacrylamide (CPAM) with a high molecular weight and acceptable dissolvability. In this study, a novel ultraviolet (UVA)-initiated system characterized by an adjustable light intensity and a redox-azo complex initiator was used to synthesize a CPAM flocculant named NP. Comparatively, another CPAM flocculant named SP with a stable UVA light intensity and a single initiator was prepared. Their chemical structure, morphology, and thermal stability were analyzed through instrumental analysis. ¹H NMR indicated that NP was successfully prepared, and a small fraction of a cationic homopolymer was mixed in the product. Polymerization conditions of NP were optimized, and polymerization mechanism was determined by investigating the effects of various parameters on intrinsic viscosity, conversion, and dissolvability. Results showed that the best performance was obtained at indices of 0.45 wt‰ redox initiator concentration, 0.2 wt‰ azo initiator concentration, 40.0 wt% cationic monomer, 3 wt‰ urea, and first- and second-stage light intensities of 8.5 and 13 mW/cm², respectively. The sludge conditioning performances of NP and SP were comparatively evaluated, and the mechanism was determined by examining sedimentation behavior and floc size distribution. High intrinsic viscosity, porous morphology structure, and mixed NP cationic homopolymer contributed to the improvement of sludge conditioning performance.

To control eutrophication caused by agricultural non-point sources, integrated riparian wetlands were constructed and operated to intercept and treat the polluted water flowing into the Fuxian Lake. The influent and effluent mass loadings of total nitrogen (TN), total phosphorus (TP), suspended solid (SS), and chemical oxygen demand (COD) of riparian wetland systems were monitored for nearly one year. In addition, influent and effluent samples of each riparian wetland treatment unit were collected and analyzed for nitrogen (nitrate, nitrite, ammonia, and organic nitrogen) and phosphorus (organic phosphorus and phosphate). Results showed that the wetland systems removed various pollutants. There was a little seasonal change on the COD, SS, TN, and TP removal efficiency. There was no flow in the wetland during the winter. Therefore, the pollutant removal efficiency could not be determined. The nitrogen analysis results showed that ammonia nitrogen and nitrate nitrogen were the main nitrogen species present in the influent and effluent of each wetland functioning unit. Information obtained from this study is helpful in providing a design basis for similar wetland systems to control agricultural non-point source pollution.

The widespread occurrence of nano-plastics (NPs) in aquatic environments poses emerging challenges to the pollutant removal performance and ecological stability of constructed wetlands (CWs). This study investigates the performance of calcium-modified (Ca-MBF) and manganese-modified basalt fiber (Mn-MBF) bio-nests as novel substrates to mitigate NP-induced inhibition of CWs. Laboratory-scale CWs were operated for 180 days to evaluate substrate-associated enzyme activities, microbial community structure, and functional gene profiles. Results showed that Mn-MBF bio-nests enhanced the activities of dehydrogenase (DHA), urease (UR), ammonia monooxygenase (AMO), nitrite oxidoreductase (NOR), nitrate reductase (NAR), nitrite reductase (NIR), and phosphatase (PST) by 86.2%, 65.5%, 127.0%, 62.8%, 131.5%, 65.3%, and 107.0%, respectively, compared with the control. In contrast, Ca-MBF bio-nests increased these enzyme activities by 48.6%, 53.5%, 67.0%, 30.6%, 95.0%, 45.3%, and 54.6%, respectively. MBF bio-nests also enhanced microbial diversity, enriched denitrifying and phosphorus-removing bacteria (e.g., Thauera, Plasticicumulans), and promoted extracellular polymeric substance secretion. Functional gene prediction indicated elevated abundances of nitrogen cycle-related genes, thereby enhancing nitrification, denitrification, and phosphorus removal processes. These synergistic effects collectively improved nitrification, denitrification, and phosphorus removal efficiency, with Mn-MBF showing superior performance. This study highlights MBF bio-nests as a sustainable strategy to enhance the resilience and long-term operational stability of CWs in environments impacted by nano-plastic pollution.

Iron–carbon micro-electrolysis and combined processes were used to treat simulated dyeing wastewater containing direct Big Red 4BE dye (concentration of 1500 mg/L, chromaticity of 80,000 times, and salt content of 20 g/L). Through single-factor experiments, the optimal reaction conditions were determined as follows: reaction time of 110 min, initial pH of 5, and iron and carbon mass ratio of 1:2. Under the optimal conditions, the concentration was reduced to 14.51 mg/L, the chromaticity was reduced to 3000 times, and the decolorization rate reached 99.03%. In order to further decrease the wastewater chromaticity, coagulation and Fenton oxidation were respectively employed for in-depth treatment after iron–carbon micro-electrolysis. The total decolorization rate of the dye wastewater exceeded 99.7%, with the treated effluent meeting the specified chromaticity discharge standard (80-fold). The integrated processes of iron–carbon micro-electrolysis combined with either coagulation sedimentation or Fenton oxidation demonstrated superior performance in treating direct Big Red 4BE dye wastewater.

IIron-carbon micro-electrolysis and combined process were used to treat printing and dyeing wastewater, which was formulated with direct Big Red 4BE dye (concentration of 1500mg/L, chromaticity of 80,000 times, and salt content of 20g/L). The optimal conditions were determined by one-factor experiments, with a reaction time of 110 min, an initial pH of 5, and an iron and carbon mass ratio of 1:2. Under the optimal conditions, the concentration was reduced to 14.51mg/L, the chromaticity was reduced to 3,000 times, and the decolourization rate reached 99.03%. In order to further reduce the chromaticity of the wastewater, coagulation and Fenton oxidation were used to treat the wastewater in depth after the iron-carbon micro-electrolysis, respectively. The total decolorization rate of the dye wastewater reached more than 99.7%, and the treated wastewater met the emission standard of 80 times the chromaticity in the "Discharge Standard of Water Pollutants for Textile Dyeing and Finishing Industry" (GB4287-2012). The combination of iron-carbon micro-electrolysis and coagulation sedimentation or Fenton oxidation had a good effect on the treatment of direct Big Red 4BE dye wastewater.

This research investigated the pollutant removal efficiency by two constructed wetlands located on the north shore of the Fuxian Lake, Yunnan Province, China. We conducted continuous monitoring for a storm to examine residence time variations in pollutants (nitrogen and phosphorus) under local hydrologic conditions. During storm events, water samples with an interval of a few hours from the beginning of the rain at the inlet and outlet of the wetland were collected and analyzed for nitrogen (total nitrogen, ammonium, nitrate, and nitrite) and phosphorus (total phosphorus (TP)). The results have implications for stormwater management. While concentrations of nitrogen species are variable, they are not strongly related to flow conditions, so treatment systems must be designed to cope with stochastic inflow concentrations at all times. Principal components analysis of water quality parameters using data collected during non-storm periods at the Yaonigou wetland (Phase I) and the Yaonigou wetland (Phase II) was conducted. The greatest loadings of the first principal component, the second, and the third principal component of inflow in Yaonigou wetland (Phase I) are ammonia, TP, and nitrate, respectively.