Iron anode was employed to enhance the degradation of Orange G (OG) by permanganate (EC/KMnO₄). Continuously generated Fe²⁺ from iron anode facilitated the formation of fresh MnO₂, which plays a role in catalyzing permanganate oxidation. The EC/KMnO₄ system also showed a better performance to remove OG than Fe²⁺/KMnO₄, indicating the importance of in situ formed fresh MnO₂. Besides, the effects of applied current, KMnO₄ dosage, solution pH, and natural organics were evaluated and results demonstrated that high current and oxidant dosage are favorable for OG removal. And the application of iron anode has a promoting effect on the KMnO₄ oxidation over a wide pH range (5.0–9.0), while the Fe²⁺/KMnO₄ process does not. For natural organics, its presence could inhibit OG removal due to its competitive role. And the promoting effect of OG removal by the EC/KMnO₄ process in natural water was confirmed. At last, the EC/KMnO₄ process showed a satisfying performance on the decolorization and mineralization of OG. This study provides a potential technology to enhance permanganate oxidation and broadens the knowledge of azo dye removal.

Extracellular polymeric substances (EPS) are key components of the cyanobacterium Microcystis aeruginosa and play an important role in cyanobacteria blooms formation. Here, we analyzed the effects of 48-h exposure to nanosized CeO₂ (n-CeO₂), CuO (n-CuO), and ZnO (n-ZnO) on the production and composition of EPS of M. aeruginosa. Toxicity experiments revealed that soluble nanoparticles (NPs) (n-ZnO, n-CuO) demonstrated higher toxicity to cells and caused membrane damage. The production of LB-EPS increased by 34.48, 20.09, and 46.33 %, and TB-EPS increased by −5.78, 22.3, and −2.67 % in the presence of n-CeO₂, n-CuO, and n-ZnO NPs, respectively, and polysaccharides are the main incremental portion compared with protein and humic acids. Three-dimensional excitation–emission fluorescence spectra revealed the enhancement of fulvic–humic-like and disappearance of tyrosine aromatic substances in TB-EPS compared with the slight changes observed in LB-EPS. Fourier-transform infrared spectroscopy illustrated the susceptibility of −NH₂ and double-bonded carbon and oxygen in amides to three types of NPs. These results improve our understanding of the potential influence of NPs on the aggregation behaviors of cyanobacteria and formation process of cyanobacteria blooms. Graphical abstract ᅟ

In this study, performance of hydrolysis acidification process treating simulated dyeing wastewater containing azo and anthraquinone dyes in different stages was investigated. The decolorization ratio, CODCᵣ removal ratio, BOD₅/CODCᵣ value, and volatile fatty acids (VFAs) production were almost better in stage 1 than that in stage 2. Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) confirmed the biodegradation of Reactive Black 5 (RB5) and Remazol Brilliant Blue R (RBBR) in hydrolysis acidification process. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analyses revealed that significant difference of microbial community structures existed in stage 1 and 2. The dominant species in stage 1 was related to Bacteroidetes group, while the dominant species in stage 2 was related to Bacteroidetes and Firmicutes groups. From the results, it could be speculated that different dyes’ structures might have significant influence on the existence and function of different bacterial species, which might supply information for bacteria screening and acclimation in the treatment of actual dyeing wastewater.

The stability of nanoparticles (NPs) in aquatic environments is important to evaluate their adverse effects on aquatic ecosystems and human health. Nanoparticle stability is known to be influenced by coexisting ions and dissolved organic matter. This study was designed to investigate the effects of coexisting low-level Cd(II) on the stability of humic acid-coated nano-TiO₂ (HA-TiO₂) particles in aquatic environments by measuring their aggregation kinetics through time-resolved dynamic light scattering (DLS) and monitoring suspended HA-TiO₂ concentrations via optical absorbance changes over time. The particles exhibited aggregation behavior consistent with the classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The results showed that Cd(II) concentration, pH, and ionic strength had various effects on the aggregation kinetics of the HA-TiO₂ NPs. The HA-TiO₂ particles aggregated faster as the Cd(II) concentration increased whereas the stability of the nanoparticles increased as the solution pH increased or ionic strength decreased regardless of the Cd(II) concentration. At the fixed pH and ionic strength conditions, the addition of Cd(II) promoted aggregation of nanoparticles, leading to higher attachment efficiencies. The enhanced aggregation of the HA-TiO₂ NPs in the presence of coexisting cadmium ions in aqueous solutions indicated that the fate and transport of nanoparticles could be greatly affected by heavy metals in aquatic environments.

Natural surface drinking water sources with the increasing chromophoric dissolved organic matter (CDOM) have profound influences on the aquatic environment and drinking water safety. Here, this study investigated the spatiotemporal variations of CDOM in Fengshuba Reservoir and its catchments in China. Twenty-four surface water samples, 45 water samples (including surface water, middle water, and bottom water), and 15 pore water samples were collected from rivers, reservoir, and sediment of the reservoir, respectively. Then, three fluorescent components, namely two humic-like components (C1 and C2) and a tryptophan-like component (C3), were identified from the excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) for all samples. For spatial distributions, the levels of CDOM and two humic-like components in the reservoir were significantly lower than those in the upstream rivers (p < 0.01), indicating that the reservoir may act as a reactor to partly reduce the levels of exogenous input including CDOM and humic-like matters from the surrounding catchment. For temporal variations, the mean levels of CDOM and three fluorescent components did not significantly change in rivers, suggesting that perennial anthropic activity maybe an important factor impacting the concentration and composition of river CDOM but not the precipitation and runoff. However, these mean values of CDOM for the bulk waters of the reservoir changed markedly along with seasonal variations, indicating that the hydrological processes in the reservoir could control the quality and quantity of CDOM. The different correlations between the fluorescent components and primary water parameters in the river, reservoir, and pore water samples further suggest that the reservoir is an important factor regulating the migration and transformation of FDOM along with the variations of different environmental gradients.

A novel laboratory-scale bioelectrode and anaerobic sludge coupled system was established for the enhancement of p-chloronitrobenzenes (p-ClNB) reductive transformation with addition of magnetite nanoparticles. In this coupled system, the bioelectrodes were supplied with a voltage of 0.8 V and the amount of magnetite nanoparticles was set at 7.4 mL/400 mL. Results showed that high p-ClNB transformation rate of 0.284 h⁻¹ and high p-chloroaniline (p-ClAn) dechlorination rate of 0.082 h⁻¹ were achieved in the coupled system at p-ClNB initial concentration of 30 mg L⁻¹, and p-ClAn is one of the reductive products of p-ClNB. The cyclic voltammetry curve showed that when the potential was −1000 mV, the magnetite-biocathode current was about 10.7 times of the abiotic cathode. Also, a shift in the reductive peak potential and a dramatic increase in reductive peak current were observed. These findings suggest that magnetite nanoparticles could enhance the electrocatalytic activity and may act as electron conduits between microorganisms or between electrodes and microorganisms to promote the extracellular electron transfer.

Colloidal particles have an ability to sorb heavy metals, metalloids, and organic compounds (e.g. biosurfactants) present in soil and groundwater. The pH and ionic strength changes may promote release of such particles causing potential contaminant transport. Therefore, it is very important to know how a colloid particle-mineral particle and colloid-mineral-biosurfactant system behaves in the natural environment. They can have negative impact on the environment and human health. This study highlighted the influence of biosurfactants produced by Pseudomonas aeruginosa on the transport of colloidal hematite (α-Fe₂O₃) through porous bed (materials collected from the Szklary and Zloty Stok solid waste heaps from Lower Silesia, Poland). Experiments were conducted using column set in two variants: colloid solution with porous bed and porous bed with adsorbed biosurfactants, in the ionic strengths of 5 × 10⁻⁴ and 5 × 10⁻³ M KCl. The zeta potential of mineral materials and colloidal hematite, before and after adsorption of biosurfactant, was determined. Obtained results showed that reduction in ionic strength facilitates colloidal hematite transport through the porous bed. The mobility of colloidal hematite was higher when the rhamnolipid adsorbed on the surface of mineral grain.

Comprehensively evaluating water quality with a single method alone is challenging because water quality evaluation involves complex, uncertain, and fuzzy processes. Moreover, water quality evaluation is limited by finite water quality monitoring that can only represent water quality conditions at certain time points. Thus, the present study proposed a dynamic fuzzy matter–element model (D–FME) to comprehensively and continuously evaluate water quality status. D–FME was first constructed by introducing functional data analysis (FDA) theory into a fuzzy matter–element model and then validated using monthly water quality data for the Poyang Lake outlet (Hukou) from 2011 to 2012. Results showed that the finite water quality indicators were represented as dynamic functional curves despite missing values and irregular sampling time. The water quality rank feature curve was integrated by the D–FME model and revealed comprehensive and continuous variations in water quality. The water quality in Hukou showed remarkable seasonal variations, with the best water quality in summer and worst water quality in winter. These trends were significantly correlated with water level fluctuations (R = −0.71, p < 0.01). Moreover, the extension weight curves of key indicators indicated that total nitrogen and total phosphorus were the most important pollutants that influence the water quality of the Poyang Lake outlet. The proposed D–FME model can obtain scientific and intuitive results. Moreover, the D–FME model is not restricted to water quality evaluation and can be readily applied to other areas with similar problems.

Copper wastewater from industry is detrimental to plants and environment. There are some problems in the aspects of high efficiency and energy saving during treatment of wastewater. In present work, the novel double iron electrodes technique of pulse-alternating current was applied to flocculate copper in wastewater. The process parameters of the copper removal in wastewater were studied in the developed electrochemical reactors. Scanning electron microscopy, X-ray diffraction, and energy-dispersive spectroscopy were used to characterize the electrocoagulations. The copper residue in the effluent was measured by UV spectrophotometry. The adsorption mechanism was described through the isothermal adsorption curves of copper during flocculation processes. The simulated wastewater containing 100 mg dm⁻³ Cu²⁺ and 100 mg dm⁻³ NaCl as conductive salt was adjusted to pH 7.8–8 with ammonia or sulfuric acid. At room temperature of 20–25 °C, controlling the flow rate of 3 dm³ min⁻¹, and applying pulse-alternating current of 40 μA gFₑ ⁻¹, the copper residue in the effluent passing through four-series reactors was reduced to 0.118 mg dm⁻³, which was far lower than 0.3 mg dm⁻³ (from GB20900–2008). The removal rate of copper could reach 99.882%. The removal of copper in the wastewater treated via our electrocoagulation technique was far more efficient than the conventional DC current coagulation and chemical flocculation. The double iron electrodes were used to reduce the concentration polarization and improved the current efficiency. The significant economic and good social benefit will be promisingly produced if our developed technique is applied in the treatment of industrial wastewater.

We analyze the heavy metals concentrations in muscle samples of milk shark (Rhizoprionodon acutus) from Persian Gulf. The metals distribution was Zn > Cu > Pb > Cd > Hg. No statistical differences were observed among size or weight by sex (p < 0.05). Metals concentrations in the population de R. acutus from Larak and Lavan islands are homogeneous along the coastal study area. Our study suggest that the results reflect the natural contents of trace metals in this species, and the health risk associated to milk shark consumption in Persian Gulf is relatively low.