Reverse osmosis (RO) technique plays an important role in the treatment of secondary biochemical effluent. However, the reverse osmosis concentrate (ROC) with high salinity and organic pollutants generated from this process remains a challenge to be tackled. The O₃-assisted UV-Fenton advanced oxidation process (AOP) as a pretreatment for the nanofiltration (NF) was used to treat the ROC of industrial wastewater. The optimal removal rates of COD and UV₂₅₄ were 80.4 and 77.4%, respectively. In the NF process, four types of commercial NF membranes (NF90 (Dow, USA), DK (GE, USA), NT101, and NT103 (NADIR, Germany)) were used to treat the AOP effluent. The effects of operating pressure and feed temperature on ion rejection were investigated. The results show that NF90 and NT103 membranes had better rejections to monovalent ions, while DK and NT101 membranes could effectively separate monovalent and divalent ions and their ion rejections decreased with the increase of feed temperature. With the NF90 membrane, the highest TDS removal rate of 89.65% was obtained at the operating pressure of 1.2 MPa.

Adsorption plays an important role in removing cadmium (Cd²⁺) from water, and magnetic adsorbents are increasingly being used due to their ease of separation and recovery. Magnetic Fe₃O₄–coated hydroxyapatite (HAP) nanoparticles (nHAP-Fe₃O₄) were developed by co-precipitation and then used for the removal of Cd²⁺ from water. The properties of these nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and magnetization curves. Experiments were conducted to investigate the effects of adsorption and mechanisms. Results illustrated that kinetic data were well fitted by a pseudo-second-order model. The adsorption capacity of nHAP-Fe₃O₄ was 62.14 mg/g. The mechanisms for the adsorption of Cd²⁺ on nHAP-Fe₃O₄ included rapid surface adsorption, intraparticle diffusion, and internal particle bonding, with the ion exchange with Ca²⁺ and chemical complexation being the most dominant. The regeneration efficiency and recovery rate of nHAP-Fe₃O₄ eluted by EDTA-Na₂ after the fifth cycle were 63.04% and 40.2%, respectively. Results revealed that the feasibility of nHAP-Fe₃O₄ as an adsorbent of Cd²⁺ and its environmental friendliness make it an ideal focus for future research.

For a long-period comparative analysis of air pollution in coastal and inland cities, we analyzed the continuous Morlet wavelet transform on the time series of a 5274-day air pollution index in Shanghai and Lanzhou during 15 years and studied the multi-scale variation characteristic, main cycle, and impact factor of the air pollution time series. The analysis showed that (1) air pollution in the two cities was non-stationary and nonlinear, had multiple timescales, and exhibited the characteristics of high in winter and spring and low in summer and autumn. (2) The monthly variation in air pollution in Shanghai was not significant, whereas the seasonal variation of air pollution in Lanzhou was obvious. (3) Air pollution in Shanghai showed an ascending tendency, whereas that in Lanzhou presented a descending tendency. Overall, air pollution in Lanzhou was higher than that in Shanghai, but the situation has reversed since 2015. (4) The primary cycles of air pollution in these two cities were close, but the secondary cycles were significantly different. The aforementioned differences were mainly due to the impact of topographical and meteorological factors in Lanzhou, the weather process and the surrounding environment in Shanghai. These conclusions have reference significance for Shanghai and Lanzhou to control air pollution. The multi-timescale variation and local features of the wavelet analysis method used in this study can be applied to varied aspects of air pollution analysis. The identification of cycle characteristics and the monitoring, forecasting, and controlling of air pollution can yield valuable reference.

Degradation of humic acid (HA) in heterogeneous electro-Fenton/chlorine processes was investigated using a catalyst of Mn-Cu bimetallic oxides supported on Al-containing MCM-41. The catalyst was synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂ adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The bimetallic oxide catalyst exhibited a higher activity compared to monometallic one. Adding Al in the bimetallic oxide catalyst enhanced the stability of the catalyst, reduced metal ion leaching, increased the initial ratio of Mn³⁺/Mn⁴⁺ and Cu⁺/Cu²⁺, and slightly enhanced the degradation efficiency of HA and corresponding chemical oxygen demand (COD). The effect of Mn and Cu content in MCM-41, catalyst dosage, pH value, and initial concentration of HA and salinity on degradation efficiency were investigated. A high COD reduction about 91.5% and general current efficiency (GCE) about 41.7% have been achieved under the optimal conditions of pH 6, salinity 1000 mg/L, catalyst dosage 0.5 g/L, HA sodium salt concentration 200 mg/L, and reaction time 60 min. A possible mechanism for the reaction was suggested. Kinetic analysis showed that HA degradation in the electro-Fenton/chlorine processes was fit with first-order kinetics.

The study investigated the sorption capacity of biosorbent-raphia sp. against ammonia. Raphia fibers were used without and with the modification of its surface with NaCl, NaNO₃, and K₂SO₄. The data was analyzed in the state of equilibrium using four isotherm models such as Langmuir, Freudlich, Temkin, and Dubinin-Radushkevich. The equilibrium of ammonia sorption for all studied systems was best described by the Freudlich isotherm model. On its basis, it can be assumed that the studied process is of chemical nature, which results from the value of the coefficient 1/n < 1. In order to confirm the sorption mechanism, analysis of the kinetics of the ammonia sorption process on raphia fibers was performed. Four kinetic models of sorption were calculated: pseudo-first-order model, pseudo-second-order model, Elovich model, and Webber-Morris intermolecular diffusion model. The sorption kinetics of the modeled ammonia waste were carried out using unmodified palm fibers and all kinds of surface modification. This process was best described by the pseudo-second-order sorption model, which can be considered as a confirmation of the chemical nature of ammonia sorption on raphia sp. fibers.

Thermal processing of materials is used in a very broad sense to cover all sets of technologies and processes for a wide range of industrial sectors and it refers to material development with a specific application potential due to its advantages over conventional synthesis methods. By applying hydrothermal technique, the development of advanced materials has been pursued, in order to retain heavy metals from wastewater. This research refers to nanosilica-based materials, specifically mesoporous silica, for which the heavy metal retention properties were improved by using nano-TiO₂ and nano-CeO₂, considering the properties of titanium and cerium. Advanced methods have been used to characterize the materials obtained as X-ray fluorescence (XRF) and energy-dispersive X-ray spectroscopy (EDS) for chemical composition; X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for microstructural properties and BET analyser for pores and specific surface area characterization. The results showed higher retention efficiencies for the doped nanosilica.

In this study, the treatment of wastewater coming from a river highly polluted with domestic and industrial effluents was evaluated. For this purpose, series of photocatalysts obtained by ZnO and TiO₂ modification were evaluated. The effect of metal addition and Ti precursor (in the case of the titania series) over the physicochemical and photocatalytic properties of the materials obtained was also analyzed. The evaluation of the photocatalytic activity showed that semiconductor modification and precursor used in the materials synthesis are important factors influencing the physicochemical and therefore the photocatalytic properties of the materials obtained. The water samples analyzed in the present work were taken from a highly polluted river, and it was found that the effectiveness of the photocatalytic treatment increases when the reaction time increases and for both, wastewater samples and isolated Escherichia coli strain follow the next order Pt/TiO₂ << ZnO. It was also observed that biochemical and chemical demand oxygen and turbidity significantly decrease after treatment, thus indicating that photocatalysis is a non-selective technology, which can lead to recover wastewater containing different pollutants.

In this study, the novel adsorbent PVA-TA-βCD was synthesized via thermal cross-linking between polyvinyl alcohol and β-cyclodextrin. The characterization methods SEM-EDS, FTIR, and XPS were adopted to characterize the adsorbent. The effect of pH, contact time, initial concentrations, and temperature during the adsorption of Pb(II), Cd(II), and Mn(II) onto the PVA-TA-βCD was also investigated. In a single-component system, the data fitted well to pseudo-second-order, and film diffusion and intra-particle diffusion both played important roles in the adsorption process. As for isotherm study, it showed a heterogeneous adsorption capacity of 199.11, 116.52, and 90.28 mg g⁻¹ for the Pb(II), Cd(II), and Mn(II), respectively. Competition between the ions existed in a multi-component system; however, owing to the stronger affinity of the PVA-TA-βCD for Pb(II) relative to Cd(II) and Mn(II), the Pb(II) adsorption onto the PVA-TA-βCD was less affected by the addition of the other metals, which could be effectively explained by the hard and soft acid and base theory (HSAB). Furthermore, PVA-TA-βCD showed good reusability throughout regeneration experiments.

Manganese dioxide nanoparticles/activated carbon (MnO₂/AC) composites and manganese dioxide nanoparticles (MnO₂ NPs) are prepared through chemical reduction method. Morphological study shows that MnO₂ NPs had cylindrical and spherical shape. The morphological study also revealed that MnO₂ NPs were well dispersed on AC while neat Mn NPs present both in dispersed and in agglomerated form. The FT-IR study confirms the synthesis of MnO₂ NPs. Zetasizer study presented that the Mn NPs had uniform size and below 100 nm in size and had zeta potential of − 20 mV, which represent its stability in the suspension form. The synthesized Mn/AC composite and Mn NPs were utilized as photocatalysts for the photodegradation of Congo red (CR) dye. The degradation study shows that MnO₂/AC composite degraded CR dye more efficiently than MnO₂ NPs under UV and normal light irradiation. The efficient degradation of dye by Mn/AC composite is due to the synergistic effect between dye adsorption on AC and rapid photodegradation by supported MnO₂ NPs. The results revealed that Mn/AC composite degraded about 98.53% of CR dye within 5 min while MnO₂ NPs degraded 66.57% of dye within the same irradiation time. The recycled catalyst also significantly degraded dye which verifies its sustainability. The effect of catalyst dosage and initial dye concentration was conducted. The degradation rate of dye was found drastically faster in tap water (in presence of catalyst), which might be due to the presence of various mineral ions in the tap water.

Perfluorinated and polyfluorinated substances (PFASs) are widely found in freshwater ecosystems because of their resistance to degradation and their ability to accumulate in aquatic organisms. While water temperature controls many physiological processes in fish, knowledge of the effects of this factor on PFAS toxicokinetic is still limited. This study presents experimental results of internal distribution and elimination rates of two perfluorinated acid compounds, namely perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) in adult rainbow trout (Oncorhynchus mykiss) exposed to three temperatures. Dietary exposure experiments were conducted at 7 °C, 11 °C, and 19 °C and liver, blood, muscle, brain, and kidney were sampled for analysis. PFOS concentrations were comparable to or exceeded those of PFHxS, while PFHxS was eliminated faster than PFOS, whatever the temperature. Internal distribution changed significantly for both substances when fish were exposed to a range of temperatures from 7 to 19 °C. Indeed, PFOS and PFHxS relative distribution increased in blood, liver, and brain while they decreased in muscle when the water temperature rose. The water temperature variation affected the elimination half-lives, depending on the substances and organs.