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Bromate formation has been found in the SO4•−-based oxidation processes, but previous studies primarily focused on the bromate formation in the homogeneous SO4•−-based oxidation processes. The kinetics and mechanisms of bromate formation are poorly understood in the heterogeneous SO4•−-based oxidation processes, although which have been widely studied in the eliminations of micropollutants. In this work, we found that the presence of CuO, a common heterogeneous catalyst of peroxymonosulfate (PMS), appreciably enhanced the bromate formation from the oxidation of bromide by PMS. The conversion ratio of bromide to bromate achieved over 85% within 10 min in this process. CuO was demonstrated to play a multiple role in the bromate formation: (1) catalyzed PMS to generate SO4•−, which then oxidizes bromide to bromate; (2) catalyzed the formed free bromine to disproportionate to bromate; (3) catalyzed the formed free bromine to decomposed back into bromide. In the CuO-PMS-Br system, bromate formation increases with increasing CuO dosages, initial CuO and bromide concentrations, but decreases with increasing bicarbonate concentrations. The presence of NOM (natural organic matter) resulted in a lower formed bromate accompanied with organic bromine formation. Notably, CuO catalyzes PMS to transform more than 70% of initial bromide to bromate even after recycled used for six times. The formation of bromate in the PMS catalysis by CuO system was also confirmed in real water.

To improve the resource utilization of chromium-containing solid waste in cement-based materials, the leaching rate, valence state, and microscopic morphology of hexavalent chromium in Portland cement-based materials were studied. The results indicate that the stabilization rate of hexavalent chromium in cement reaches 95% for specimens containing 0.5% potassium chromate by mass after 60 days. However, when the potassium chromate content is increased to 5%, the stabilization rate drops below 90%. Analysis through photoelectron spectroscopy elucidates that chromium mainly exists in two valence states within the cement paste: trivalent chromium, present as Cr(OH)3and CrOOH, and hexavalent chromium, existing in the forms of CaCrO4and K2CrO4. After curing for 28 days, the ratio of trivalent chromium to hexavalent chromium is approximately 7:13, with the main hexavalent chromium compound CaCrO4constituting about 21.4% of the total chromium content. Microscopic phase tests further intricate interactions between calcium ions and hexavalent chromium ions in a low water-cement ratio matrix, resulting in the additional CaCrO4whose quality steadily increased with age. The rise in ion content leads to a continuous augmentation in the diffraction peaks density of ettringite (AFt). This is attributed to the slightly larger spatial position of CrO42-compared to SO42-, facilitating its partial replacement in the columnar structure lattice of the ettringite hydration product.

Manganese is a transition metal derived primarily from parent materials in soil. Weathered manganese, predominantly present as manganese oxides, is widely applied in ecological restoration owing to its large specific surface area and high reduction potential. Recently, manganese oxide (MnOx) and its modified materials have been increasingly reported for environmental pollution remediation due to their low toxicity, eco-friendliness and abundance. This review summarizes the synthesis, preparation, application and prospects of MnOxand its modified manganese-based materials, highlighting their effects on contaminated soil, water and air. MnOxand its derivatives are believed to find broader applications and marketability in environmental protection in the future.

Electrochemically converting nitrate, a widely distributed nitrogen contaminant, into harmless N2is a feasible and environmentally friendly route to close the anthropogenic nitrogen-based cycle. However, it is currently hindered by sluggish kinetics and low N2selectivity, as well as scarce attention to reactor configuration. Here, we report a flow-through zero-gap electrochemical reactor that shows a high performance of nitrate reduction with 100% conversion and 80.36% selectivity of desired N2in the chlorine-free system at 100 mg-N·L–1NO3–while maintaining a rapid reduction kinetics of 0.07676 min–1. More importantly, the mass transport and current utilization efficiency are significantly improved by shortening the inter-electrode distance, especially in the zero-gap electrocatalytic system where the current efficiency reached 50.15% at 5 mA·cm–2. Detailed characterizations demonstrated that during the electroreduction process, partial Cu(OH)2on the cathode surface was reconstructed into stable Cu/Cu2O as the active phase for efficient nitrate reduction. In situ characterizations revealed that the highly selective *NO to *N conversion and the N–N coupling step played crucial roles during the selective reduction of NO3–to N2in the zero-gap electrochemical system. In addition, theoretical calculations demonstrated that improving the key intermediate *N coverage could effectively facilitate the N–N coupling step, thereby promoting N2selectivity. Moreover, the environmental and economic benefits and long-term stability shown by the treatment of real nitrate-containing wastewater make our proposed electrocatalytic system more attractive for practical applications.

Conventional biochemical processes have unsatisfactory effects on refractory wastewater treatment. Thus, a technically feasible and economical treatment should be established. In the conventional culture of microorganisms, adding exogenous nutrients to a medium can effectively promote micro-organism growth. Therefore, using exogenous nutrients in wastewater treatment may enhance microbial activity, subsequently speeding up the removal of contaminants. In this study, nutrients with different carbon and nitrogen (C/N) ratios were added to activated sludge and a chemical oxygen demand (COD) of 1000 mg/L was considered the benchmark for carbon source in the activated sludge process. Results showed that wastewater COD was reduced below 130 mg/L, and the removal rate reached 90% when the C/N ratio was 5:1. Along with the results from the study on F/M, dehydrogenase activity, content of extracellular polymeric substances, and microbial community in the wastewater treatment process, our findings indicated that adding exogenous nutrients increase microbial community diversity and promote the activity of microorganisms, thereby wastewater COD was reduced to 130 mg/L after 12 h and the removal rate reached approximately 90%. Simultaneously, analysis results on microbial community structure indicated that Proteobacteria, Firmicutes, and Bacteroidetes were the dominant species of bacteria. The addition of exogenous nutrients may increase the abundances of Pseudomonas and Bacillus species, which were essential in COD removal.

Polyphenols are organic substances commonly involved in a wide variety of industrial processes. They are prone to polymerize with other organic chemicals during production and subsequent wastewater treatment section, which yields various persistent and recalcitrant organic chemicals. To better understand the behavior of polyphenolic polymers in wastewater treatment processes and the effect on the biodegradability of wastewater, we explored the conversion of polyphenolic polymers during aerobic biochemical treatment and their relationship with extracellular polymeric substances (EPS). The CODCr(chemical oxygen consumption measured using potassium dichromate) removal efficiency of the polyphenolic polymers with high concentration was only 29.66% with CODCrof 437.5 mg/L, which was far from the wastewater discharge standard (60–100 mg/L, first class standard of GB 8978–1996). In the activated sludge system with stabilized organic matter as the substrate, the effluent had the highest degree of humification with the maximum SUVA value of 6.87 L/(mg∙m). The polyphenolic polymers caused a component variation in EPS, further affecting wastewater's humification degree and degradability. In particular, the content of humic acid-like substances in loose bound EPS (LB-EPS) was up to 4 times more than control, indicating higher aromatization and humification degree and of the waste. On the contrary, the content of polysaccharides in LB-EPS decreased by about 46.2–87.7% in treatments with different concentration of polyphenolic polymer. The high-concentration polyphenol polymers somehow stimulated the microbial production like proteins and humic-like substances. The direct conversion of polyphenol polymers also contributed to the increased humification of wastewater.

Supercapacitors fill the gap between batteries and conventional solid state and electrolytic capacitors. Polypyrrole (PPy) is a very important electrode material for supercapacitors. However, the repeated volume changes usually damage PPy structure and result in PPy poor stability during a long-term charging/discharging process. PPy/carbon material composites were prepared to overcome the defects of pure PPy electrodes, and significant enhancement for the specific capacitance, charging/discharging rate and electrodes stability was demonstrated thereafter. The development of composite electrodes based on PPy and carbon materials is reviewed in this paper.

With the rapid development of tanning industry, a noticeable number of chromium-containing tannery sludge (Cr-ITS) has been produced, which poses an impending threat to ecosystem and human health, and needs special disposal ahead of landfilling. In this study, an alternative method for thermally stabilizing Cr-ITS via employing ZnO and TiO2as dopants was developed. Oxidation of Cr(III), competitive formation of Cr-spinel, immobilization of Cr, and leaching toxicity of sintered products were investigated during Cr-ITS thermal treatment at the temperature range of 800–1200 ℃. Cr in Cr-ITS could be immobilized effectively through transforming Cr into spinel structure, as demonstrated by XRD analysis. Thus, the toxic Cr-ITS would be remedied and detoxified. Co-doping of ZnO and TiO2not only noticeable inhibited oxidation of Cr(III), but also accelerated conversion of Cr(III) to spinel dominated by ZnCr2O4. Increasing temperature was conducive to the formation of spinel. Most of Cr were incorporated into spinel phase when thermal treatment temperature was over 1000 ℃, where Cr(VI) leached was not detected, and leaching concentrations of Cr and Zn after prolonged leaching time of 25 d were 13.32 mg/L and 23.07 mg/L respectively, which all meet regulatory limits. When increasing temperature to 1100 ℃, their leaching risk was further reduced to 4.39 mg/L and 5.24 mg/L respectively, successfully achieving simultaneous stabilization of heavy metals. The overall results indicate that Cr-ITS immobilized with ZnO and TiO2is a promising and feasible strategy by incorporating Cr into spinel phases using sintering temperature reached in ceramic industry.

AbstractAdsorptive studies were carried out on four synthetic vinyl polymer tanning agents removal from aqueous phase onto wastewater activated sludge (AS). Batch experiments investigated the effects of contact time, dosage of adsorbate, extracellular polymeric substances (EPS), coexisted cations, and physical property of sludge flocs on the four vinyl polymers removal by AS to evaluate the kinetics, isotherms, and mechanisms. Almost 96% of polydiallyldimethylammonium chloride-acrylic-acrylamide (PDM-AA-AM), 90% of polydiallyldimethylammonium chloride-acrylic (PDM-AA), 82% of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate (PDM-AA-AM-HEA), and 56% of polydiallyldimethylammonium chloride (PDM) were removed from aqueous solutions. The kinetics process of adsorption can be described by the pseudo-second-order kinetic equation and the adsorption isotherms fitted to the Langmuir model very well. The adsorption capacity increases with the increase in initial vinyl polymers concentration. Coexisted cations (Ca2+, Na+) in aqueous solution restrained vinyl polymers adsorption on AS. The presence of Cr3+ions slightly improved the PDM-AA, PDM-AA-AM, and PDM-AA-AM-HEA removal, whereas retarded the PDM removal in some extent. AS are more effective than inactivated sludge in the removal of vinyl polymers. All the four vinyl polymers showed a decrease in the degree of removal when EPS was partial extracted from the biomass. The adsorption mechanisms of AS for vinyl polymers included hydrophobic interaction, surface binding, and electrostatic force. Surface binding may play a major role in PDM-AA, PDM-AA-AM, and PDM-AA-AM-HEA adsorption, while electrostatic interaction may play a major role in PDM removal. This study provided strong evidence that AS can be employed for an effective solution for vinyl polymers syntans removal.

Adsorptive studies were carried out on four synthetic vinyl polymer tanning agents removal from aqueous phase onto wastewater activated sludge (AS). Batch experiments investigated the effects of contact time, dosage of adsorbate, extracellular polymeric substances (EPS), coexisted cations, and physical property of sludge flocs on the four vinyl polymers removal by AS to evaluate the kinetics, isotherms, and mechanisms. Almost 96% of polydiallyldimethylammonium chloride-acrylic-acrylamide (PDM-AA-AM), 90% of polydiallyldimethylammonium chloride-acrylic (PDM-AA), 82% of polydiallyldimethylammonium chloride-acrylic-acrylamide-hydroxyethyl acrylate (PDM-AA-AM-HEA), and 56% of polydiallyldimethylammonium chloride (PDM) were removed from aqueous solutions. The kinetics process of adsorption can be described by the pseudo-second-order kinetic equation and the adsorption isotherms fitted to the Langmuir model very well. The adsorption capacity increases with the increase in initial vinyl polymers concentration. Coexisted cations (Ca2+, Na+) in aqueous solution restrained vinyl polymers adsorption on AS. The presence of Cr3+ions slightly improved the PDM-AA, PDM-AA-AM, and PDM-AA-AM-HEA removal, whereas retarded the PDM removal in some extent. AS are more effective than inactivated sludge in the removal of vinyl polymers. All the four vinyl polymers showed a decrease in the degree of removal when EPS was partial extracted from the biomass. The adsorption mechanisms of AS for vinyl polymers included hydrophobic interaction, surface binding, and electrostatic force. Surface binding may play a major role in PDM-AA, PDM-AA-AM, and PDM-AA-AM-HEA adsorption, while electrostatic interaction may play a major role in PDM removal. This study provided strong evidence that AS can be employed for an effective solution for vinyl polymers syntans removal.

AbstractHexavalent chromium in aqueous environment may result in severe environmental and public health problems. In this study, short-chain polyaniline/palygorskite composites (PANI/PA) were prepared and developed to remove aqueous Cr(VI). Characterized results showed that short-chain polyaniline was successfully incorporated on the surface of PA. The maximum Cr(VI) adsorption amount was found to be 11.54, 14.34, and 16.22 mg/g at 15, 25, and 35°C, respectively, and polyaniline on the adsorbent surface may account for the enhanced Cr(VI) adsorption. Cr(VI) adsorption was highly dependent on both solution pH and ionic strength, which indicates that electrostatic force and anion exchange may account for the increased Cr(VI) adsorption onto PANI/PA. Cr(VI) saturated PANI/PA can be easily desorbed in alkaline solution and regenerated adsorbents still possess high adsorption amount for aqueous Cr(VI). The current study shows that PANI/PA can be used as an effective and recyclable adsorbent for the removal of Cr(VI) in water and wastewater treatment.

Hexavalent chromium in aqueous environment may result in severe environmental and public health problems. In this study, short-chain polyaniline/palygorskite composites (PANI/PA) were prepared and developed to remove aqueous Cr(VI). Characterized results showed that short-chain polyaniline was successfully incorporated on the surface of PA. The maximum Cr(VI) adsorption amount was found to be 11.54, 14.34, and 16.22 mg/g at 15, 25, and 35°C, respectively, and polyaniline on the adsorbent surface may account for the enhanced Cr(VI) adsorption. Cr(VI) adsorption was highly dependent on both solution pH and ionic strength, which indicates that electrostatic force and anion exchange may account for the increased Cr(VI) adsorption onto PANI/PA. Cr(VI) saturated PANI/PA can be easily desorbed in alkaline solution and regenerated adsorbents still possess high adsorption amount for aqueous Cr(VI). The current study shows that PANI/PA can be used as an effective and recyclable adsorbent for the removal of Cr(VI) in water and wastewater treatment.

AbstractIn this study, the removal potential of vinyl polymer/ZnO nanocomposite (PDM/ZnO) by activated sludge (AS) biomass was investigated. PDM/ZnO was effectively removed by AS adsorption (90.3% of total PDM/ZnO removed). The effects of contact time, temperature, pH of the solution, PDM/ZnO production method, initial adsorbate concentration, and properties of the adsorbent were studied. The experimental results are fitted with the Langmuir and Freundlich equations. The adsorption kinetics closely followed the pseudo-second-order model. Thermodynamic parameters (ΔH°, ΔS°, ΔG°) indicate that the adsorption of PDM/ZnO onto AS was feasible, spontaneous, and endothermic. The effects of PDM/ZnO production method and pH value both indicate that electrostatic force may main mechanism in PDM/ZnO adsorption process. The decrease in the adsorption capacity of inactivated sludge suggests that the increase of adsorbent surface area also plays a significant role in the removal process.

In this study, the removal potential of vinyl polymer/ZnO nanocomposite (PDM/ZnO) by activated sludge (AS) biomass was investigated. PDM/ZnO was effectively removed by AS adsorption (90.3% of total PDM/ZnO removed). The effects of contact time, temperature, pH of the solution, PDM/ZnO production method, initial adsorbate concentration, and properties of the adsorbent were studied. The experimental results are fitted with the Langmuir and Freundlich equations. The adsorption kinetics closely followed the pseudo-second-order model. Thermodynamic parameters (ΔH°, ΔS°, ΔG°) indicate that the adsorption of PDM/ZnO onto AS was feasible, spontaneous, and endothermic. The effects of PDM/ZnO production method and pH value both indicate that electrostatic force may main mechanism in PDM/ZnO adsorption process. The decrease in the adsorption capacity of inactivated sludge suggests that the increase of adsorbent surface area also plays a significant role in the removal process.

AbstractPolyaniline adsorbent prepared by chemical oxidation was developed to remove the humic acid (HA) in aqueous solution. The adsorbents showed the high adsorption capacity for aqueous HA with the maximum adsorption amount 126.58 mg g−1, and the adsorption isotherm obeyed the Langmuir model. The adsorption kinetics followed an initial diffusion-controlled and then an attachment-controlled adsorption process. The HA adsorption was not much impacted in the presence of Na+, K+, while Ca2+ion in aqueous solution can evidently enhance the HA adsorption. The HA adsorption on polyaniline decreased with increasing solution pH owing to the electrostatic interaction between imine and amine of polyaniline and disassociated HA. The HA molecules adsorbed on the polyaniline can be effectively desorbed in 0.1 M NaOH solution, and regenerated adsorbent can be repeatedly used in the subsequently adsorption–regeneration cycles.

Polyaniline adsorbent prepared by chemical oxidation was developed to remove the humic acid (HA) in aqueous solution. The adsorbents showed the high adsorption capacity for aqueous HA with the maximum adsorption amount 126.58 mg g-1, and the adsorption isotherm obeyed the Langmuir model. The adsorption kinetics followed an initial diffusion-controlled and then an attachment-controlled adsorption process. The HA adsorption was not much impacted in the presence of Na+, K+, while Ca2+ion in aqueous solution can evidently enhance the HA adsorption. The HA adsorption on polyaniline decreased with increasing solution pH owing to the electrostatic interaction between imine and amine of polyaniline and disassociated HA. The HA molecules adsorbed on the polyaniline can be effectively desorbed in 0.1 M NaOH solution, and regenerated adsorbent can be repeatedly used in the subsequently adsorption–regeneration cycles.

Conventional methods for investigating heavy metal contamination in soil are time consuming and expensive. In this study, we (i) explored reflectance spectroscopy as an alternative method for assessing heavy metals, and (ii) further explored the physicochemical mechanism that allows estimation of heavy metals with the reflectance spectroscopy method. We first investigated the spectral response of changing concentrations of heavy metals in soils. The results indicated that only at very high concentration can transition elements exhibit their inherent absorption features. In spite of this observation, we successfully predicted low levels of heavy metals in agricultural soils. The best prediction accuracies were obtained for the siderophile elements Ni, Cr, and Co. The poorest prediction was for Cd. The order of prediction accuracy for metals was approximately the same as the order of their correlation coefficients with Fe. Complementary to some previous studies that found that the intercorrelation between heavy metals and active soil components (such as Fe oxides, organic matter, and clay) is the major predictive mechanism, in the present study we concluded that the correlation with total Fe (including active and residual Fe) is the major mechanism. This conclusion was further supported by both correlation analysis and chemical sequential extraction. Correlation analysis showed that all metals are negatively correlated with reflectance while positively correlated with the absorption depth at about 500 nm, a feature resulting from goethite. The chemical forms of heavy metals, which showed that besides the crystalline Fe oxide and organic matter fractions, heavy metals have significant amounts in the residual fraction, also strengthened the conclusion.

AbstractAn investigation was carried out into the crop uptake of Cr(III) and its accumulation in two alkaline soils that have received tannery sludge as organic fertilizer for many years. The Cr(III) concentrations in the soils did not exceed the safe levels. However, Cr content in wheat and rice straw was up to 17 mg kg-1in recently sludge-applied soils, and Cr content in wheat grain exceeded the hygienic standard of China for food. After the sludge application, Cr(III) remained in top soil in the first few years and its transfer to a depth of 60cm was discovered in the soils with application of the sludge for over 15 years. Asequential extraction procedure and seedling culture experiment were used to assess the Cr(III) chemical forms and their phytoavailability. The results showed that Cr in straw and wheat grain was significantly correlated with total Cr(III), H2O-NH4OAc and DPTA extractable Cr(III). 2 mol L-1HCl extractable Cr(III) was an important source of soil Cr available to the crops. In the seedling culture experiment, it was discovered that 1 mol L-1NH4OAc and 0.05 mol L-1DPTA exhibited higher extraction capacities for Cr(III) than plant uptake at lower soil Cr(III) concentration, while they were coincident at higher Cr(III) concentration. Cr content in wheat seedlings reached a maximum of 23.5 mg kg-1, which was hardly attainable under field conditions.