Electrochemical reduction is currently one of promising methods for nitrate removal from water, yet most treatment approaches have problems of high cost and energy consumption. In this work, a low current density was applied in electrochemical reduction of nitrate. Copper-modified titanium (Cu/Ti) electrodes with optimal electrochemical activity and fastest kinetics were firstly screened. Thirty minutes of electrodeposition time and neutral pH were found to have the greatest nitrate reduction rate of 83.14%. To further improve the removal of nitrate, activated carbon (AC) and copper-modified activated carbon (Cu/AC) particles were applied to construct three-dimensional reaction systems, with removal rates of nitrate of 88.72% and 96.05%, respectively. The average conversion rates of nitrate to ammonia nitrogen increased from 15.28% to 42.68% and 62.64% in AC- and Cu/AC-based reaction systems, respectively. Oxidation of Cu(0) on surfaces of Cu/Ti cathode and Cu/AC particles to Cu(I) was revealed by X-ray photoelectron spectroscopy (XPS) and Cu LMM spectra analysis. Besides, results of water chemistry characteristics indicated the conversion of AC to carbonate ion. It could be concluded that enhanced nitrate reduction of Cu/Ti-based reaction system was attributed by Cu particle- and AC-mediated electron transfer. This study provided a reference for low-cost electrochemical reduction of nitrate.

Epoxiconazole (EPX) is a triazole fungicide commonly used in agriculture and for domestic purposes around the world. The excessive application of this pesticide may result in a variety of adverse effects on non-target organisms, including humans. Since, the liver and kidneys are the target organs of this fungicide, potential hepatotoxic and nephrotoxic effects are of high relevance. Thus, our study aimed to investigate the toxic effects of EPX on the liver and kidney of Wistar rats. The exposure of rats to EPX at these concentrations (8, 24, 40, 56 mg/kg bw representing, respectively, NOEL (no observed effect level), NOEL × 3, NOEL × 5, and NOEL × 7) for 28 days significantly enhances hepatic and renal lipid peroxidation which is accompanied by an increase in the level of protein oxidation. Furthermore, the results of the present study clearly indicated that EPX administration induces an increase in the levels of DNA damage in a dose-dependent manner. In addition, the activities of liver and kidney antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione S-transferase (GST) are increased significantly in EPX-treated rats at concentrations of 8, 24, and 40 mg/kg bw. However, with the dose NOEL × 7 (56 mg/kg bw of EPX), the activities of CAT, GPx, and GST are decreased. Indeed, EPX-intoxicated rats revealed a significant reduction in acetylcholinesterase (AChE) activity in both liver and kidney compared with the control group. Also, our results demonstrated that the EPX administration leads to a disruption of the hepatic (aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH)) and renal (uric acid and creatinine) functions. The biochemical perturbations obtained in the present study are corroborated with the histopathological modifications. Since EPX treatment caused severe damage in the overall histo-architecture of liver and kidney tissues, these results suggest that administration of EPX induced a marked deregulation of liver and kidney functions. Graphical abstract

Cadmium (Cd) is a heavy metal that poses a huge potential threat to human and animal health. Therefore, it is necessary to study its damage mechanism. In the present study, we have examined the protective effects of Ganoderma lucidum triterpenoids on oxidative stress and apoptosis in the spleen of chickens induced by Cd. One hundred and twenty healthy Hailan white chickens (7-day-old) were randomly divided into the following four groups: control group, Cd group, triterpenoid group, and Cd–triterpenoid group. The chickens were euthanized on the 20th, 40th, and 60th days, and the spleens were removed. Cd and malondialdehyde (MDA) content, antioxidant enzyme (superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px)) activities, and inflammatory factor (tumor necrosis factor alpha (TNF-α) and interleukin (IL-1β and IL-6)) and apoptotic factor (caspase-3, BAX, and Bcl-2) expressions were detected. The results showed that Ganoderma lucidum triterpenoids could reduce the content of Cd and MDA; increase the antioxidant enzyme activities (SOD and GSH-Px); decrease the expression of inflammatory factors (TNF-α) and interleukin (IL-1β and IL-6); increase the expression of apoptotic factor (Bcl-2); and decrease the expression of apoptotic factors (caspase-3 and Bax). It showed that the triterpenoids of Ganoderma lucidum had significant protective effects on oxidative stress and apoptosis of chicken spleen, which provided a theoretical basis for further prevention and treatment of cadmium poisoning.

A waste–struvite/diatomite compound (MAP@Dia) recovered from nutrient-rich wastewater treated by MgO-modified diatomite (MgO@Dia) was provided to immobilize lead in aqueous solution and contaminated soil. The mechanism and effectiveness of lead immobilization was investigated, and the pHₛₜₐₜ leaching test and fixed-bed column experiments were carried out to assess the risk of MAP@Dia reuse for lead immobilization. The results showed that MAP@Dia were effective in immobilizing lead in aqueous solution with adsorption capacity of 832.47–946.50 mg/g. The main mechanism of Pb immobilization by MAP@Dia could be contributed by surface complexation and dissolution of struvite followed by precipitation of hydroxypyromorphite Pb₁₀(PO₄)₆(OH)₂. Lead(II) concentration reduced from 269.61 to 78.26 mg/kg, and residual lead(II) increased to 53.14% in contaminated soil when the MAP@Dia application rate was 5%. The increased neutralization capacity (ANC) and lower lead extraction yields in pHₛₜₐₜ leaching test in amended soil suggested 5 times of buffering capacity against potential acidic stresses and delayed triggering of “chemical time bombs.” The results of column studies demonstrated that amendment with MAP@Dia could reduce the risk of lead and phosphorus (P) leaching. This study revealed that MAP@Dia could provide an effective solution for both P recycling and lead immobilization in contaminated soil.

Municipal solid waste incineration (MSWI) generates bottom ash, fly ash (FA), and air pollution control (APC) residues as by-products. FA and APC residues are considered hazardous due to the presence of soluble salts and a high concentration of heavy metals, and they should be appropriately treated before disposal. Physicochemical characterization using inductively coupled plasma mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) have shown that FA and APC have potential for reuse after treatment as these contain CaO, SiO₂, and Al₂O₃. Studies conducted on treatment of FA and APC are categorized into three groups: (i) separation processes, (ii) solidification/stabilization (S/S) processes, and (iii) thermal processes. Separation processes such as washing, leaching, and electrochemical treatment improve the quality and homogeneity of the ash. S/S processes such as chemical stabilization, accelerate carbonation, and cement solidification modify hazardous species into less toxic constituents. Thermal processes such as sintering, vitrification, and melting are effective at reducing volume and producing a more stable product. In this review paper, the treatment processes are analyzed in relation to ash characteristics. Issues concerning mixing FA and APC residues before treatment, true treatment costs, and challenges are also discussed to provide further insights on the implications and possibilities of utilizing FA and APC as secondary materials.

Considerable researches on removal of azo dyes have been reported in recent years, but few researchers have documented adsorption and/or transformation of anthraquinone dyes by physical, chemical, or biological treatment methods due to their fused aromatic structures. In this study, tea residue was found to have significant enhancement effect on the decolorization of anthraquinone dye reactive blue 19. This effect worked on different dye decolorizing bacterial florae and the natural bacterial flora from surface water and exhibited universal feature. Six single bacterial strains were isolated from bacterial flora DDMY2. Unexpectedly, all of them had poor decolorization capacity. High-throughput sequencing results revealed the community evolution of bacterial flora DDMY2 cultured with tea residue after 6 months and 12 months. It was found that the community structure changed dramatically because the influence of tea residue and the dominant functional genera, such as unclassified_o_Pseudomonadales, Stenotrophomonas, Bordetella, and Brevibacillus, was significantly enriched. Meanwhile, the evolved community structure could keep stable for a long time, resulting in the decolorization effect stabilized for a long time. This study provides the tea residue as the bioactivator that can be applied to boost the decolorization of dyes by various potential bacterial florae. It also enlarges our knowledge of making full use of biowaste in biological wastewater treatment.

Phosphorus is a dominant environmental factor in fostering eutrophication, and its biogeochemical behavior has attracted much attention. This study investigated the distribution of phosphorus fractions and the adsorption-desorption characteristic in the soils of wetlands converted from paddy fields with a restoration duration of 1, 2, 3, 5, 13, or 19 years. The results demonstrated the content of total phosphorus (TP) first increased, which was then reversed until the process stabilized after 5 restoration years. Labile inorganic phosphorus (L-Pi), labile organic phosphorus (L-Po), iron-aluminum–bound phosphorus (Fe.Al-P), and humic phosphorus (Hu-P) peaked at 1–3 restoration years, respectively, while moderately labile organic phosphorus (Ml-Po), calcium-magnesium–bound phosphorus (Ca.Mg-P), and residual phosphorus (Re-P) decreased within 0–5 restoration years. During the 5th to 19th restoration years, the contents of all phosphorus fractions stabilized within a minor fluctuating range. Redundancy analysis (RDA) results indicated that total nitrogen (TN) and soil organic matter (SOM) are the important environmental factors controlling redistribution of phosphorus fractions. The capability of restored wetlands to retain phosphorus increased first and then decreased with the extension of the restoration duration. Path analysis (PA) results demonstrated that pH, TN, and Fe are the primary factors for the capacity of soil to retain phosphorus, followed by SOM, Mn, and electrical conductivity(EC). Fe.Al-P and Hu-P had a higher release risk with approximate amounts of 197.25–337.25 and 113.28–185.72 mg/kg during the first stage of restoration, which needs to be focused.

The reduction of wet desulfurization wastewater is one of the important tasks of coal-fired power plants, and it is important for achieving “zero emissions.” Evaporation and concentration (E&C) with waste heat is an effective way to reduce wastewater. Here, two typical types of industrial desulfurization wastewater are used to study the change rule of pH and total dissolved solids during wastewater concentration in a circulating evaporation tower. The results indicate that with the increase of concentration ratio, the pH of desulfurization wastewater is decreased rapidly and then is gradually stabilized at 2–3 when SO₂ or SO₃ is contained in flue gas, and the increase in conductivity is less for wastewater with higher SO₄²⁻ content. The characteristics of various ions are also analyzed, and the composition and microscopic morphology of the precipitates are characterized during concentration. The growth pattern of Ca²⁺ concentration is dependent on the ratio of Ca²⁺ and SO₄²⁻ in raw wastewater. When the concentration ratio is 7.21, the insoluble and slightly soluble substances undergo precipitation and the solid content is approximately 20%, which can help realize the concentration and reduction of desulfurization wastewater.

With the adding of tourist volume in China, carbon emissions from hotel sector increased greatly. Environmental efficiency of hotel sector considering technology heterogeneity is mainly analyzed across different regions of China from 2000 to 2013. Metafrontier global Malmquist-Luenberger (ML) is implemented to evaluate environmental efficiency of hotel sector. Furthermore, we analyze whether technology heterogeneity of different regions increased or not through technological gap ratio. The empirical analysis revealed that the east had the highest environmental efficiency under metafrontier after 2009. After 2009, technological gap ratio (TGR) in the east ranked highest among four regions in China. Environmental regulation positively impacts environmental efficiency under group frontier of hotel sector in the model of nation, east, and middle. Urbanization has U-shaped link with environmental efficiency of hotel sector for the east. It is important to strengthen environmental regulation to reduce carbon emissions. Last, it is important to enhance consciousness of energy abating and carbon emissions reduction of hotel customers.

The aim of this study was to investigate the impact of incorporating Walnut leaves (WL) and their biochars produced at three temperatures (200, 400, and 600 °C) on fractionation, availability and maize indices in a naturally calcareous highly contaminated soil of Central Iran. A pot experiment was conducted considering soils treated with 0, 0.5, 1, and 2% (w/w) of WL and their derived biochars. After maize (Zea mays L.) planting, shoot and root dry matter and Pb and Zn concentration in shoots and roots and DTPA-extractable and fractions of Zn and Pb in soils were determined. Results showed showed that biochar amendments substantially modified the partitioning of Zn and Pb from easily available forms to less available forms. The results showed that DTPA-extractable of Zn and Pb and their bioaccumulation were reduced upon the addition of biochars produced at different temperatures and application rates in a calcareous soil. Treating soil with 2% biochar produced at 600 °C increased significantly shoot and root dry matter by 131.4% and 116.7%, respectively and reduced the bioavailability of Zn and Pb (DTPA-TEA extraction) by 49.1%, and 34.9%, respectively (P < 0.05) in comparison to the control. Therefore, biochars were able to reduce metals contamination in treatments and increase maize dry matter. Biochar decreased Zn and Pb concentration in plant tissues and promoted gradual maize growth responses through changing metals fractions. Therefore, biochar as a sorbent for contaminants can assist in maize to mitigate and phytostabilize Zn and Pb in highly contaminated soils.