Search

Purposively designing environmental advanced materials and elucidating the underlying reactivity mechanism at the atomic level allows for the further optimization of the removal performance for contaminants. Herein, using well facet-controlled I-Cu2WS4 single crystals as a model transition metal chalcogenide sorbent, we investigated the adsorption performance of the exposed facets toward gaseous elemental mercury (Hg0). We discovered that the decahedron exhibited not only facet-dependent adsorption properties for Hg0 but also recrystallization along the preferential [001] growth direction from a metastable state to the steady state. Besides, the metastable crystals with a predominant exposure of {101} facets dominated the promising adsorption efficiency (about 99% at 75 °C) while the saturated adsorption capacity was evaluated to be 2.35 mg·g-1. Subsequently, comprehensive characterizations and X-ray adsorption fine structure (XAFS), accompanied by density functional theory (DFT) calculations, revealed that it might be owing to the coordinatively unsaturated local environment of W atoms with S defects and the surface relative stability of different facets, which could be affected by the change in surface atom configuration. Hence, the new insight into the facet-dependent adsorption property of transition metal chalcogenide for Hg0 may have important implications, and the atomic-level study directly provides instructions for development and design of highly efficient functional materials.

Mercury (Hg) removal is crucial to the safety of water resources, yet it lacks an effective removal technology, especially for emergency on-site remediation. Herein, multilayered oxygen-functionali...

Reducing energy use is crucial to commercialize electrochemical oxidation technologies. We developed a three-dimensional (3-D) electrochemical system that can significantly reduce the applied voltage and effectively degrade organic contaminants in low-ionic-strength wastewaters. The 3-D system consisted of a composite wire mesh anode (composed of blue TiO2 nanotubes covered with SnO2-Sb2O3), a proton exchange membrane, and a stainless-steel wire mesh cathode, which were compressed firmly together. For the 3-D system, we placed the anode of a 3-D electrode toward the wastewater that flowed past the anode. Both the two-dimensional (2-D) and 3-D systems had the same anode and cathode. We found that the 3-D system could reduce the applied voltage by 75.7% and reduce the electrical efficiency per log order reduction (EE/O) by 73% for 0.001 M Na2SO4. For Na2SO4 concentrations greater than 0.05 M, the 2-D system had a slightly lower EE/O. We also compared the EE/O of electrochemical advanced oxidation processes (EAOPs) with that of other advanced oxidation processes (UV/H2O2, UV/persulfate, O3/H2O2, UV/ TiO2, and UV/chlorine). We found that EAOPs have a much higher EE/O for low BA concentrations (20 mg/L) and a much lower EE/O for high BA concentrations (2000 mg/L).

An understanding of the impacts regarding different phases of inorganic materials on heavy metal removal is indispensable, owing to the intrinsic structure of materials that can affect its properties. In this study, the distinct adsorption behaviors of heavy metals (Pb(II) and Cu(II)) on different phases of MoS2 (metallic phase (1T) and semiconducting phase (2H)) were theoretically and experimentally investigated. According to the computational results, both Pb(II) and Cu(II) have formed more stable complexes on 1T-MoS2 compared to those on 2H-MoS2 due to the lower adsorption energy (Ead). This phenomenon indicates that Pb(II) and Cu(II) were more preferably adsorbed onto 1T-MoS2. Based on the results of the computational studies, two-dimensional (2D) MoS2 nanosheets with identical 1T and 2H phases were synthesized via a facile hydrothermal reaction. As we surmised, 1T-MoS2 achieved excellent Pb(II) and Cu(II) adsorption capacities, which were 147.09 and 82.13 mg/g at 298 K, respectively, compared to those of 2H-MoS2 (i.e., 64.16 and 50.74 mg/g at 298 K). Moreover, 1T-MoS2 has shown other superior properties, such as (i) ultrafast adsorption kinetics and (ii) great anti-interference activity toward other existing cations, compared to 2H-MoS2. Extensive computations and characterizations of MoS2-Pb and -Cu adsorption complexes illustrated that the active S sites were indispensable for heavy metal adsorption. Overall, for the first time, we provide evidence that 1T-MoS2 is more functional in heavy metal removal compared to 2H-MoS2, which can guide and expand the applications of MoS2-based adsorbents in environmental remediation.

Benzophenone derivatives, including benzophenone-1 (C13H10O3, BP1), benzophenone-3 (C14H12O3, BP3) and benzophenone-8 (C14H12O4, BP8), that used as UV filters are currently viewed as emerging contaminants. Degradation behaviors on co-exposure benzophenone derivatives using UV-driven advanced oxidation processes under different aqueous environments are still unknown. In this study, the degradation behavior of mixed benzophenone derivatives via UV/H2O2 and UV/peroxydisulfate (PDS), in different water matrices (surface water, hydrolyzed urine and seawater) were systematically examined. In surface water, the attack of BP3 by hydroxyl radicals (HO∙) or carbonate radicals (CO3∙-) in UV/H2O2 can generate BP8, which was responsible for the relatively high degradation rate of BP3. Intermediates from BP3 and BP8 in UV/PDS were susceptible to CO3∙-, bringing inhibition of BP1 degradation. In hydrolyzed urine, Cl− was shown the negligible effect for benzophenone derivatives degradation due to low concentration of reactive chlorine species (RCS). Meanwhile, BP3 abatement was excessively inhibited during co-exposure pattern. In seawater, non-first-order kinetic behavior for BP3 and BP8 was found during UV/PDS treatment. Based on modeling, Br− was the sink for HO∙, and the co-existence of Br− and Cl− was the sink for SO4∙-. The cost-effective treatment toward target compounds removal in different water matrices was further evaluated using EE/O. In most cases, UV/H2O2 process is more economically competitive than UV/PDS process.

Increasing numbers of cement furnaces have applied selective catalytic reduction (SCR) units for advanced treatment of NO in the flue gas. However, the SCR catalysts may face various poisons, such as acidic, alkaline, and heavy metal species, in the fly ash. In this work, we studied the deactivation mechanisms of multipoisons (Ca, Pb, and S) on the CeO

Recently, the UV/free chlorine process has gained attention as a promising technology for destroying refractory organic contaminants in the aqueous phase. We have developed a kinetic model based on first-principles to describe the kinetics and mechanisms of the oxidation of organic contaminants in the UV/free chlorine process. Substituted benzoic acid compounds (SBACs) were chosen as the target parent contaminants. We determined the second-order rate constants between SBACs and reactive chlorine species (RCS; including [Formula: see text], [Formula: see text] and [Formula: see text]) by fitting our model to the experimental results. We then predicted the concentration profiles of SBACs under various operational conditions. We analyzed the kinetic data and predicted concentration profiles of reactive radicals ([Formula: see text] and RCS), we found that [Formula: see text] was the dominant radicals for SBACs destruction. In addition, we established quantitative structure activity relationships (QSARs) that can help predict the second-order rate constants for SBACs destruction by each type of reactive radicals using SBACs Hammett constants. Our first-principles-based kinetic model has been verified using experimental data. Our model can facilitate a design for the most cost-effective application of the UV/free chlorine process. For example, our model can determine the optimum chlorine dosage and UV light intensity that result in the lowest energy consumption.

A novel electrocatalytic system was developed to realize one-pot conversion of organic pollutants into liquid fuels such as methanol (CH3OH) and ethanol (C2H5OH). The process combines the catalytic oxidation of organic pollutants with electrocatalytic reduction of CO2. We first coupled the electrocatalytic process with SO4•−-based advanced oxidation processes (AOPs) for the degradation of 4-nitrophenol (4-NP) using a 3D-hexagonal Co3O4 anode. In this step, 4-NP was mineralized to CO2, and then the CO2 was converted to CH3OH and C2H5OH by electrocatalytic reduction using a flower-like CuO cathode. The experimental results show the destruction of 4-NP (60 mL, 10 mg/L) can be as high as 99%. In addition, the yields of CH3OH and C2H5OH were 98.29 μmol/L and 40.95 μmol/L, respectively, which represents a conversion of 41.8% of 4-NP into liquid fuels; the electron efficiency was 73.1%. In addition, we found that 3D-hexagonal arrays of Co3O4 with different morphologies can be obtained by adding different amounts of urea. We also investigated the formation mechanism of novel 3D-hexagonal Co3O4 arrays for the first time. A mechanism was proposed to explain the electrocatalytic steps involved in the conversion of 4-NP to CH3OH and C2H5OH and the synergetic effects between AOPs and electrocatalysis.

The increasing anthropogenic inputs of Pb and Cd into China’s Nen River (Qiqihar section) owing to rapid urbanization in the past 50 years may pose ecological risks to the river’s aquatic system. To confirm this hypothesis, we determined the Pb and Cd concentrations in the sediments of the Nen River flowing across Qiqihar City by comparing the control group (samplings in the Nen River branch bypassing the city) and bioaccumulation along the food chain. We found significantly higher Pb concentrations in the sediments than in the control group (39.21 mg kg−1 dry weight [dw] vs. 22.44 mg kg−1 dw; p

Oxcarbazepine (OXC) is ubiquitous in the aqueous environment. And due to its ecotoxicological effects and potential risks to human, an effective way to eliminate OXC from aqueous environment has aroused public concerns in recent years. Radical-based reactions have been shown to be an efficient way for OXC destruction, but the reactions of OXC with reactive oxygen species (ROS) and carbonate radical (CO3•−) are still unclear. In this study, we focused the degradation of OXC and ROS, CO3•− generation mechanism, and their roles in OXC degradation via UV and UV/H2O2. The triplet state of oxcarbazepine (3OXC∗) was found to play an important role in OXC degradation via UV. And hydroxyl radicals (•OH) and singlet oxygen (1O2) were found to be the dominant ROS in OXC degradation. Superoxide radical (O2•−) did not react with OXC directly, but it may react with intermediate byproducts. Generation of CO3•− played a positive role on OXC degradation for both UV and UV/H2O2. In addition to •OH, 3OXC* also contribute to CO3•− production. The second-order rate constants of OXC with •OH and CO3•− were 1.7 × 1010 M−1 s−1 and 8.6 × 107 M−1 s−1, respectively. Potential OXC degradation mechanisms by •OH were proposed and included hydroxylation, α-ketol rearrangement, and benzylic acid rearrangement. Compared with non-selective •OH, the reactions involving CO3•− are mainly electron transfer and hydrogen abstraction. And the acute toxicity of OXC was lower after UV/H2O2 and UV/H2O2/HCO3− treatments, which was confirmed by luminescent bacterial assay (Vibrio fischeri bacterium).

Based on the local T-S model, the switching control method for the nonlinear response of the seismic surface is studied, and the stiffness matrix of the composite interlayer element of viscoelastic damper and herringbone support is derived. The high-order single step 6 method is applied to the nonlinear seismic response analysis and the instantaneous optimal active switching control. The local T-S model and controller are designed, and the approach and control of global nonlinear responses are realized through the multi-model switching control. The results show that the proposed method can accurately reflect the reduction of seismic ground load and the switching control of the main structure when the viscoelastic damper is installed. The switching control effect of the maximum spatial displacement becomes more and more obvious with the change of time history, and the control effect of all layers applying the switching control force is the most significant. Whether the controller is disturbed or not, it is always good and stable performance. RESUMEN Este artículo estudia el método de control de conmutación para la respuesta no lineal de la superficie sísmica con base en el modelo local T-S, y deriva la matriz de rigidez del elemento compuesto de capa intermedia del amortiguador viscoelástico y el soporte de espiga. El método 6 de un solo paso de alto orden se aplica al análisis de respuesta sísmica no lineal y al control de conmutación activo óptimo instantáneo. El modelo local T-S y el controlador están diseñados, y el enfoque y el control de la respuesta global no lineal se realizan a través del control de conmutación multimodelo. Los resultados muestran que el método propuesto puede reflejar con precisión la reducción de la carga de tierra sísmica y el control de conmutación de la estructura principal cuando se instala el amortiguador viscoelástico. El efecto de control de cambio del desplazamiento espacial máximo se vuelve cada vez más obvio con el cambio del historial de tiempo, y el efecto de control de todas las capas que aplican la fuerza de control de cambio es el más significativo. Ya sea que el controlador esté alterado o no, siempre es un rendimiento bueno y estable.

Phenicol antibiotics (PABs) degradation by UV/H2O2 is important because we need to determine the reduction in toxicity and disinfection byproducts for post-chlorine. In this study, the degradation of PABs, including florfenicol (FLO), chloramphenicol (CAP) and thiamphenicol (THA), was examined. The pseudo-first order degradation rate constants of PABs were 3 times higher in ultrapure water (UW) than that in synthetic wastewater (SW) for these conditions: [PABs]0 = 1 μM, [H2O2] = 0.1 mM, and I0 = 1.985 × 10−6 E L−1 s−1. Fulvic acid (FA) and HCO3– inhibited PABs degradation, Cl− and NO3– concentrations of up to 5 mM and 10 mM had a negligible impact. The impact of water matrix on PABs degradation was successfully predicted using pseudo-steady-state kinetic model. The degradation of PABs was triggered via hydroxylation and/or hydrogen abstraction. The treatment of PABs via UV/H2O2 could decrease their antimicrobial properties, while the byproducts of FLO and THA showed higher acute toxicity in Vibrio fischeri. In addition, two identification products (TP-276 and TP-354) of FLO had higher ecotoxicity toxicity (using ECOSAR) in fish, daphnid and green algae. The trichloromethane formation potential (TCMFP) for PABs with post-chlorination in UW and SW can be reduced after UV/H2O2 compared to UV, and is related to the corresponding decrease of dissolved organic carbon (DOC).

Although noble metal electrocatalysts are highly efficient in the dehalogenation of halogenated antibiotics, the prohibitive cost hinders their practical applications. In this study, a cobalt-phosphorous/oxide (Co P/O) composite prepared via a one-step electrodeposition was for the first time applied in electroreductive dechlorination of halogenated antibiotics (HA), including chloramphenicol (CAP), florfenicol (FLO) and thiamphenicol (TAP). Co P/O had a higher FLO dechlorination efficiency (91%) than Pd/C (69.3%) (t = 60 min, C0 = 20 mg L−1, applied voltage of −1.2 V vs. saturated calomel electrode (SCE)). Furthermore, the dechlorination efficiencies of Co P/O for CAP and TAP reached to 98.7 and 74.2%, respectively. The electron spin resonance and in situ Raman characterizations confirmed that atomic H* was produced via the Co P and the formation of Co Cl bonds occurred on the Co O in Co P/O. The Co Cl bond formation could trap HA molecules onto Co P/O and weaken the C Cl bond strength. The synergistic effect of H* attack and Co Cl bond was responsible for the high dechlorination efficiency. This study offers new insights into the interface mechanism of electroreductive dehalogenation process, and shows a great potential for the remediation of halogenated antibiotics contaminated wastewater.

While the widely used β-lactam antibiotics, such as cephalosporins, are known to be susceptible to oxidation by sulfate radical (SO4-), comprehensive study about SO4--induced oxidation of cephalosporins is still limited, such as the impact of water matrices, and the structure and antibacterial activity of transformation products. Herein, the oxidation of cefalexin (CFX), a most frequently detected cephalosporin, was systematically investigated by thermally activated persulfate (PS). CFX oxidation followed pseudo-first-order kinetics, and SO4- dominantly contributed to the overall oxidation of CFX. The impact of water matrices, such as Cl-, HCO3- and natural organic matter, on CFX degradation was predicted using a pseudo-steady-state kinetic model. The secondary reactive species, such as chlorine and carbonate radicals, were found to contribute to CFX degradation. Product analysis indicated oxidation of CFX to six products (molecular weight of 363), with two stereoisomeric sulfoxides as the primary oxidation products. It was thus suggested that the primary amine on the side chain, and the thioether sulfur and double bond on the six-membered ring were the reactive sites of CFX towards SO4- oxidation. Antibacterial activity assessment showed that the biological activity of CFX solution was significantly diminished after treatment by the thermally activated PS.

Chloride ion (Cl–) is one of the most common anions in the aqueous environment. A mathematical model was developed to determine and quantify the impact of Cl– on the oxidization rate of organic compounds at the beginning stage of the UV/persulfate (PS) and UV/H2O2 processes. We examined two cases for the UV/PS process: (1) when the target organic compounds react only with sulfate radicals, the ratio of the destruction rate of the target organic compound when Cl– is present to the rate when Cl– is not present (designated as rRCl–/rR) is no larger than 1.942%; and (2) when the target organic compounds can react with sulfate radicals, hydroxyl radicals and chlorine radicals, rRCl–/rR, can be no larger than 60%. Hence, Cl– significantly reduces the organic destruction rate in the UV/PS process. In the UV/H2O2 process, we found that Cl– has a negligible effect on the organic-contaminant oxidation rate. Our simulation results agree with the experimental results very well. Accordingly, our mathematical model is ...

The design and synthesis of metalloid imprinted materials is a challenge due to lack of a feasible functional monomer. A novel cyclic functional monomer (CFM) was used to develop Sb(III)-ion imprinted polymer (CFM-IIP) for efficient and selective removal Sb(III). CFM possesses positively charged imidazolium moiety and specific cyclic size matching with Sb(III). CFM-IIP has a maximum Sb(III) adsorption capacity of 79.1 mg·g–1, while that of a noncyclic functional monomer imprinted polymer (NCFM-IIP) is only 30.9 mg Sb(III)·g–1. The relative selectivity coefficients of CFM-IIP compared to NCFM-IIP for Sb(III)/Cl–, Sb(III)/NO3–, Sb(III)/PO43–, Sb(III)/SO42–, and Sb(III)/Cr2O72– were 6.6, 78.4, 5.9, 3.0, and 3.2, respectively. Kinetic data fitted well with pseudo-second-order model. The adsorption between Sb(III) and CFM-IIP was identified to be feasible, spontaneous, and endothermic. ζ-Potential, X-ray photoelectron spectroscopic analysis, and density functional theory calculations revealed the mechanism of ...

Advanced oxidation processes (AOPs) have been widely used for the destruction of organic contaminants in the aqueous phase. In this study, we introduce an AOP on activated peroxymonosulfate (PMS) by using ascorbic acid (H2A) to generate sulfate radicals (SO4•–). Sulfate radicals, hydroxyl radicals (HO•), and ascorbyl radicals (A•–) were found using electron spin resonance (ESR). But we found A•– is negligible in the degradation of microcystin-LR (MCLR) due to its low reactivity. We developed a first-principles kinetic model to simulate the MCLR degradation and predict the radical concentrations. The MCLR degradation rate decreased with increasing pH. The scavenging effect of natural organic matter (NOM) on SO4•– was relatively small compared to that for HO•. Considering both energy consumption and MCLR removal, the optimal H2A and PMS doses for H2A/PMS process were determined at 1.0 × 10–6 M and 1.6 × 10–5 M, respectively. In addition, we determined the toxicity using the protein phosphatase 2A (PP2A) tes...

In this study, nanoscale zero-valent iron (nZVI) with a considerably high surface area (182.97 m2·g−1) and featured morphology of chain structure has been synthesized and well characterized. The as-prepared nZVI on can totally remove Cr(VI) under anoxic condition after 20 min reaction, whereas only 43% of Cr(VI) was removed after 60 min reaction under oxic condition. Noteworthily, the nZVI exhibits excellent removal capacity of Cr(VI) (123.85 mg/g) and fast removal rate (0.017 g·mg−1·min−1), much better than those reported in the literatures except for that reported by Li et al. (2008) [1] . Experimental results have confirmed that only FeCr2O4 with low compactness was generated under anoxic and acidic conditions in the new process. And it is evident that the formation of the passivation layer which contains oxides and hydroxides (or (oxy)hydroxides) of iron and chromium were well hindered. Furthermore, the as-prepared nZVI has shown fast removal of traced Cr(VI) from the Cr-spiked drinking water or actual Cr-contaminated lake water. Accordingly, we proposed a new reaction process of Cr(VI) reduction by nZVI under anoxic condition. And we firstly make clear the detailed process of Cr(VI) removal by the as-prepared nZVI via X-ray photoelectron spectrometer (XPS) analysis in time scale. Meanwhile, the excellent Cr(VI) removal performance of the as-prepared nZVI could be attributed to (i) the high surface area, (ii) large quantity of active sites of nZVI, and (iii) fast electron transfer from the nZVI/FeCr2O4 to Cr(VI). The present work not only provides the potential materials for the application to the rapid and high-efficient removal of Cr(VI) from aqueous solution, but also proposed a new avenue for hindering the passivation of Fe0. And a detailed mechanism of the Cr(VI) removal by nZVI was proposed for the first time.

High adsorption capacity, fast adsorption kinetics, good reusability and low cost are highly demanded for adsorbents used in practical adsorption process. In this study, a porous double network Jute/Polyacrylic acid (Jute/PAA) gel was prepared using simple free-radical polymerization of acrylic acid in Jute aqueous solution. The high permeability of Jute/PAA hydrogel with about 80 wt% water made internal adsorption sites fully expose to metal ions. The Jute/PAA gel adsorbent could efficiently adsorb heavy metals in melting wastewater, especially Cd2+ and Pb2+. The adsorbent showed very high adsorption capacities of 401.7 mg/g for Cd2+ and 542.9 mg/g for Pb2+. Moreover, the adsorption equilibrium reached within only 10 min for 40 mg/L of Cd2+ and Pb2+ using 1 g/L adsorbent. Meanwhile, the removal efficiencies reached 81.0% for Pb (C0 = 3.825 mg/L), 79.3% for Cd (C0 = 6.075 mg/L), 83.4% for Cu (C0 = 9.325 mg/L), 29.8% for Zn (C0 = 188.6 mg/L), 22.3% for Mn (C0 = 17.05 mg/L), 96.2% for Cr (C0 = 0.25 mg/L) and 99.8% for Fe (C0 = 9.75 mg/L) in melting wastewater using 1 g/L adsorbent in 2 h. In particular, the concentrations of Pb, Cd and Cr decreased below 0.001 mg/L using 4 g/L adsorbent. In the fixed-bed column experiments, the treatment volume of melting wastewater reached 2900 BV (32.8 L) only producing 50 BV (565 mL) eluent. This work develops a highly practical adsorption process based on hydrogel adsorbents for the removal of heavy metals in actual wastewater.

A systematic study of the interaction between adsorbents and potentially toxic metal ions in multicomponent systems is of great significance due to the coexistence of multiple potentially toxic metal ions in the real water environment. In this study, a new humic substance-based double network hydrogel (PAA/HS gel) was produced by a radical polymerization method and applied to Pb(II), Cu(II) and Cd(II) removal in both individual and multicomponent systems under various conditions. The macroporous network structure (aperture ≈ 10 μm) and high water permeability of the PAA/HS gel could fully facilitate the active site exposure and increase the potentially toxic metal ion diffusion rate. The PAA/HS gel exhibited high theoretical adsorption capacities of 360.50, 151.00 and 412.76 mg g−1 for Pb(II), Cu(II) and Cd(II) in individual systems. Noticeably, both interference and promotion of adsorption behaviors were identified in multicomponent systems. In binary systems, the adsorption capacity and rate were decreased for Pb(II) and Cu(II), while increased for Cd(II). In ternary systems, the adsorption capacity and rate for Pb(II), Cu(II) and Cd(II) were decreased. The adsorption isotherms and kinetics were well fitted by Langmuir–Freundlich and Elovich models, respectively, indicating that the PAA/HS gel possessed a heterogeneous surface and various types of binding sites. The FTIR and XPS studies confirmed that both nitrogen- and oxygen-containing functional groups (i.e., amino, phenolic hydroxyl and carboxyl groups) were involved in the adsorption process, while the interactions between functional groups and Pb(II), Cu(II) and Cd(II) were different.

The adsorption behavior of arsenic (As) on specific crystalline phases of manganese dioxide (MnO2) remains unclear. In this study, we evaluated the ability of α-MnO2 nanofibers (MO-2) to remove both arsenite (As(III)) and arsenate (As(V)), using experimental and computational methods. The maximum adsorption capacity values of As(III) and As(V) on MO-2 were 117.72 and 60.19 mg/g, respectively, which is higher than values reported for α-MnO2, β-MnO2 and γ-MnO2. In particular, because MO-2 has much higher adsorption capacity for As(III) than As(V), it can be effectively applied in removal of As(III) from groundwater, and a pre-oxidation process is not required. Fixed-bed tests showed that about 800 mL As(III)- or 480 mL As(V)-contaminated water could be treated before breakthrough, and MO-2 can be effectively regenerated using only 12 mL of eluent. This means we can concentrate the As(III) and As(V) by factors of 66.6 and 40.0, respectively. According to density functional theory (DFT) calculations, As(III) and As(V) form stable complexes on (1 0 0) and (1 1 0) of α-MnO2. Moreover, the surface complexes of As(III) and As(V) on (1 0 0) are more stable than (1 1 0). Electron transfer from As(III) on (1 0 0) is greater than (1 1 0). These phenomenon are may due to the fact that (1 0 0) has lower surface energy than (1 1 0). Partial density of state (PDOS) analysis further confirmed that As(III, V) are chemisorbed on MO-2, which agreed with the Dubinin-Radushkevich model.

The trophic relations of the red-crowned crane in Zhalong wetland, northeastern China may significantly be altered due to the rapid decrease in accessible food resources. To confirm this hypothesis, we determined the trophic status of this vulnerable species by using stable isotope (carbon (δ13C) and nitrogen (δ15N) methods. The δ13Cand 15Nsignatures in the red-crowned crane species were in the range of −17.8‰to −18.5‰and 6.9‰to 8.1‰, respectively. The majority of the ecosystem of Zhalong wetland has an average food-chain length of 3.9, and the trophic level of the examined species, i.e., red-crowned crane, was approximately 3.1. The trophic relations of red-crowned cranes have changed over the period of 2004 to 2014, as the biological species in the bottom trophic level significantly exhausted in the past years. The conflict of food demand by red-crowned cranes versus the livelihood demand of local wetland residents should be resolved to ensure sustainability of food supply sustainable for rare and extinguishable species.

The concentrations of Pb and Cd, and trace elements (Cu and Zn) in the urban topsoil, rook (Corvus frugilegus) feces and feathers and human scalp hair were analyzed to examine the potential ecological risk posed by Pb and Cd on local residents of Qiqihar City, northeastern China. Results revealed that the Cd concentrations in the topsoil were ranged from 0.14 to 3.55 mg kg−1 dry weight (dw). The maximal geoaccumulation indices [a value from logarithmic (a measured metal content/1.5 × background content of the metal in this region), introduced by Muller] of Cd exceeded 3.5, which suggested that this region was seriously contaminated by Cd. The corresponding average detectable concentrations in C. frugilegus feathers and feces were 1.38 and 3.97 mg kg−1 dw for Pb and 1.04 and 0.69 mg kg−1 dw for Cd. High Pb and Cd concentrations, respectively, ranging from 7.46 to 24.9 mg kg−1 dw and from 0.35 to 0.92 mg kg−1 dw were also detected in the human scalp hair samples. These high Pb and Cd concentrations ...

Surface modification of adsorbents plays a crucial role in its adsorption performance. Furthermore, the most important step in modification is to design the modification groups based on target pollutants. In this study, the phosphate adsorption performance of zirconium hydroxide was enhanced by different ammonium modification as a result of increasing utilization efficiency of adsorption site. The maximum capacity is 155.04 mg/g from the zirconium hydroxide modified by dimethylamine. In comparison with undecorated zirconium hydroxide, the selectivity factors for Cl–, SO42–, and NO3– are all raised by almost 2 times by dimethylamine modification. The mass transfer rate K2 also increase 6 times using N-methylaniline and N-ethylmethylamine. Results from zeta-potential and FT-IR revealed that the enhanced adsorption capacity for phosphate were directly related to the inner-sphere complex and electrostatic interactions (quaternary ammonium groups and phosphate) and ligand exchange (the hydroxyl groups of zirco...

In this work, we investigated the abatement of highly concentrated 1H-Benzotriazole (BTA) in aqueous solution by ozonation. Focusing on the COD removal and BTA degradation, the effects of different operational factors were explored, including different initial BTA concentrations (100–1000 mg/L), ozone dosages (16–48 mg/min) and initial pH values (3–11). It was found that the degradation of BTA was obviously affected by the initial concentration of BTA, pH value and O3 dosage. And the optimized pH value was observed at 11. The increasing of ozone dosage and the pH value would accelerate the degradation efficiency of BTA and COD removal, while the increasing of initial BTA concentration would hamper this process. Based on the effects of ozone dosage, initial BTA concentration and initial pH value, a kinetic model was established with the function of C = C0exp(−8.68QO32.4997C0−2.1262[OH−]0.0444t).

Two types of lignin-based carbon fibers were prepared by electrospinning method. The first was activated with Fe3O4 (LCF-Fe), and the second was not activated with Fe3O4 (LCF). Gas phase adsorption isotherms for toluene on LCF-Fe and LCF were studied. The gas phase adsorption isotherm for 0% RH showed LCF-Fe have about 439 mg/g adsorption capacity which was close to that of commercially available activated carbon (500 mg/g). The Dubinin-Radushkevich equation described the isotherm data very well. Competitive adsorption isotherms between water vapor and toluene were measured for their RH from 0 to 80%. The effect of humidity on toluene gas-phase adsorption was predicted by using the Okazaki et al. model. In addition, a constant pattern homogeneous surface diffusion model (CPHSDM) was used to predict the toluene breakthrough curve of continuous flow-packed columns containing LCF-Fe, and its capacity was 412 mg/g. Our study, which included material characterization, adsorption isotherms, kinetics, the impact of humidity and fixed bed performance modeling, demonstrated the suitability of lignin-based carbon fiber for volatile organic compound removal from gas streams.

Sulfide is a toxic and corrosive odorant generated in various sludge treatment and disposal systems. We developed an electrochemical pretreatment (EPT) approach to eliminate sludge sulfide production without adding chemicals. Biochemical sulfide potential (BSP) test was used to evaluate the effectiveness of EPT on sludge sulfide production. The sulfide control was effective with EPT, and we determined the underlying mechanism of EPT. EPT which was operated at 12 V for 720 s eliminated 99% of dissolved sulfide and 100% of gaseous H2S(g). In comparison, the dissolved sulfide reached 104 ± 1 mg S/L in the control BSP test. A sulfur mass balance analysis in the BSP test showed that 90% of the produced sulfide was removed via metal precipitation. Metal distribution results confirmed that metals (i.e., Fe, Mn, and Ni) in the sludge became soluble after EPT and were released from their residual and organically bound fractions. EPT which was operated at 15 V solubilized around 73, 92, and 72% of Fe, Mn, and Ni, and these metals precipitated the sulfide that was produced from biological sulfate reduction. Sludge analysis revealed that EPT disintegrated sludge flocs and disrupted metal-binding functional groups. Specifically, reduction of 17% C═O functional groups in the sludge was found, which could be associated with metal release. The impact of oxidants (e.g., chlorine) generated from EPT on sulfide oxidation was minimal. The findings of this study broadened up our understanding of the electrochemical process for sulfide control during saline sludge digestion.

Efficient elimination of antibacterial activity of halogenated antibiotics by dehalogenation pretreatment is desired for a biochemical treatment process. In this study, crystalline cobalt phosphide nanosheet arrays on a Ti plate (C-CoP/Ti) are fabricated by a simple electrodeposition and phosphorization process. The crystalline structure greatly promotes atomic hydrogen (H*) generation. Moreover, the nanosheet arrays can provide abundant active sites and accelerate electron transfer and mass transport. As a result, the dehalogenation rate of florfenicol (FLO, an emerging organic pollutant) on C-CoP/Ti is 11.1, 2.97, and 13.6 times higher than that on amorphous CoP/Ti, Pd/Ti, and bare Ti, respectively. The C-CoP/Ti electrode achieves 97.4% dehalogenation of FLO (20 mg L-1) within 30 min at -1.2 V (vs Ag/AgCl). Nearly 100% of Cl and 20% of F are broken away within 120 min, showing the highest electrocatalytic defluorination efficiency reported so far. Both experimental results and theoretical calculations reveal that the dehalogenation of FLO on C-CoP/Ti is synergistically accomplished via direct reduction of electron transfer and indirect reduction of H*. This study develops a highly efficient non-noble metal electrode material for dehalogenation of halogenated organic compounds.

Structural tunability and surface functionality of layered two-dimensional (2-D) iron oxychloride (FeOCl) nanosheets are critical for attaining exceptional adsorption properties. In this study, we combine computational and experimental tools to elucidate the distinct adsorption nature of Pb(II) on 2-D FeOCl nanosheets. After finding promising Pb(II) adsorption characteristics by bulk FeOCl sheets (B-FeOCl), we applied computational quantum mechanical modeling to mechanistically explore Pb(II) adsorption on representative FeOCl facets. Results indicate that increasing the exposure of FeOCl oxygen and chlorine sites significantly enhances Pb(II) adsorption. The (110) and (010) facets of FeOCl possess distinct orientations of oxygen and chlorine, resulting in different Pb(II) adsorption energies. Consequently, the (110) facet was found to be more selective toward Pb(II) adsorption than the (010) facet. To exploit this insight, we exfoliated B-FeOCl to obtain ultrathin FeOCl nanosheets (U-FeOCl) possessing unique chlorine- and oxygen-enriched surfaces. As we surmised, U-FeOCl nanosheets achieved excellent Pb(II) adsorption capacity (709 mg g-1 or 3.24 mmol g-1). Moreover, U-FeOCl demonstrated rapid adsorption kinetics, shortening adsorption equilibration time to one-third of the time for B-FeOCl. Extensive characterization of FeOCl-Pb adsorption complexes corroborated the simulation results, illustrating that increasing the number of Pb-O and Pb-Cl interaction sites led to the improved Pb(II) adsorption capacity of U-FeOCl.

The estimated daily intakes (EDIs) of six trace elements (Cu, Zn, Pb, Cd, Hg, and As) in vegetables (leafy vegetable, i.e., bok choy, fruit vegetables, i.e., cucumber and tomato, and other categories, i.e., mushroom, kidney bean, and potato), cereals (rice and wheat flour), and meats (pork, mutton, and beef) most commonly consumed by adult inhabitants of Qiqihar, Northeastern China, were determined to assess the health status of local people. The average EDIs of Cu, Zn, Pb, Cd, Hg, and As were with 20.77 μg (kg bw)−1 day−1 of Cu, 288 μg (kg bw)−1 day−1 of Zn, 2.01 μg (kg bw)−1 day−1 of Pb, 0.41 μg (kg bw)−1 day−1 of Cd, 0.01 μg (kg bw)−1 day−1 of Hg, and 0.52 μg (kg bw)−1 day−1 of As, respectively, which are below the daily allowance recommended by FAO/WHO. However, the maximum EDIs of Pb and Cd were 4.56 μg (kg bw)−1 day−1 and 1.68 μg (kg bw)−1 day−1, respectively, which are above the recommended levels [i.e., 3.58 μg (kg bw)−1 day−1 for Pb and 1.0 μg (kg bw)−1 day−1 for Cd] by FAO/WHO. This finding indicates that the potential health risk induced by daily ingestion of Pb and Cd for the local residents should receive a significant concern. Similarly, we detected elevated Pb and Cd concentrations, i.e., with average of 13.58 and 0.60 mg kg−1 dw, respectively, in the adult scalp hairs. Consumption of rice, potato, bok choy, and wheat flour contributed to 75 and 82% of Pb and Cd daily intake from foodstuffs. Nevertheless, human scalp hair is inappropriate biological material for determination of the nutritional status of trace elements in this region.

Highly porous, three-dimensional (3D) nanostructured composite adsorbents of reduced graphene oxides/Mn3O4 (RGO/Mn3O4) were fabricated by a facile method of a combination of reflux condensation and solvothermal reactions and systemically characterized. The as-prepared RGO/Mn3O4 possesses a mesoporous 3D structure, in which Mn3O4 nanoparticles are uniformly deposited on the surface of the reduced graphene oxide. The adsorption properties of RGO/Mn3O4 to antimonite (Sb(III)) and antimonate (Sb(V)) were investigated using batch experiments of adsorption isotherms and kinetics. Experimental results show that the RGO/Mn3O4 composite has fast liquid transport and superior adsorption capacity toward antimony (Sb) species in comparison to six recent adsorbents reported in the literature and summarized in a table in this paper. Theoretical maximum adsorption capacities of RGO/Mn3O4 toward Sb(III) and Sb(V) are 151.84 and 105.50 mg/g, respectively, modeled by Langmuir isotherms. The application of RGO/Mn3O4 was demonstrated by using drinking water spiked with Sb (320 μg/L). Fixed-bed column adsorption experiments indicate that the effective breakthrough volumes were 859 and 633 mL bed volumes (BVs) for the Sb(III) and Sb(V), respectively, until the maximum contaminant level of 5 ppb was reached, which is below the maximum limits allowed in drinking water according to the most stringent regulations. The advantages of being nontoxic, highly stable, and resistant to acid and alkali and having high adsorption capacity toward Sb(III) and Sb(V) confirm the great potential application of RGO/Mn3O4 in Sb-spiked water treatment.

The dietary uptake of Cd and Pb may contribute to the decline of migratory red-crowned cranes (Grus japonensis) on the Asian mainland. To uncover the relevance of this hypothesis, we determined the concentrations of Pb and Cd as well as further macro and trace elements (Ca, Mg, Cu, Zn, Hg and As) in the gastric contents, gastric wall, intestinal wall, liver, kidney, muscle, and feathers of two individuals found dead in Zhalong Wetland in Northeastern China. Indeed, the Pb concentrations in the liver and kidney tissues was with 31.4 and 60.3 mg kg(-1) dry weight (dw), respectively, above concentrations considered as potentially toxic level in common birds (i.e. 30 mg kg(-1)). These Pb concentration may have possibly been associated with lethal toxicosis in this endangered species suggesting Pb as major threat for G. japonensis populations. Thus, the inputs of Pb into Zhalong Wetland should be reduced to maintain and reestablish environmental conditions supporting the population development of these migratory red-crowned cranes in the Zhalong Wetland, a critical crane habitat for the long-term sustainability of this species.

This study examined Tessier's fractions of Pb, Cd, and As in the sediments and their potential toxic effects on four aquatic animals, i.e., Enchytraeus of Lumbricidae, Cipangopaludina chinensis of Viviparidae, Cybister japonicus Sharp of Dytiscidae, and Perccottus glenii Dybowski of Odontobutidae in Zhalong Wetland, Northeastern China. Results show that Cd poses a high risk to the biota in Zhalong Wetland. The geo-accumulation indices indicate that the region only has background concentrations of As, although it is slightly polluted by Pb and is seriously polluted by Cd. The exchangeable fraction receives minor contributions from these metals: 0.8% for Pb, 2.8% for Cd, and 4% for As. Three reed organs and four aquatic animal groups contain detectable concentrations of Pb, Cd, and As, with the following order of increasing concentrations: stem < rhizome < root < Viviparidae < Odontobutidae < Dytiscidae < Lumbricidae. Relatively low bioaccumulation factor (BAF) of As occurred in four aquatic organis...

The concentrations of six elements (Ca, Mg, Zn, Cu, Pb and Cd) in the eggshells of breeding red-crowned cranes (Grus japonensis) in China’s Zhalong Wetland were examined. Two macronutrients, namely, Ca and Mg, were predominant in the eggshells, with corresponding concentrations varying from 127 g kg−1 to 323 g kg−1 and 0.33 g kg−1 to 5.51 g kg−1 (dry weight, dw), respectively. The Cu and Zn contents were in the range of below the detection limit (ND) to 8.05 mg kg−1 and ND to 511 mg kg−1 dw, respectively. The maximal Pb and Cd concentrations in the eggshells of the red-crowned crane exceeded a level considered to be potentially toxic in birds (i.e., 1.7 mg kg−1 for Pb and 0.34-0.91 mg kg−1 dw for Cd), ranging from ND-3.20 mg kg−1 dw for Pb and ND-1.20 mg kg−1 dw for Cd. The principal components analysis results revealed the complex chemical associations between two essential (Cu and Zn) and nonessential (Pb and Cd) elements in the eggshells of G. japonensis in China. Increased Pb and Cd levels in the bodies and eggshells of the red-crowned cranes suggest this species in their colonies are exposed to these contaminants, although which had not induced to obvious eggshell thinning in the examined species.

This paper reports on the development of macroporous flow-through anodes. The anodes comprised an enhanced TiO2 nanotube array (ENTA) that was grown on three macroporous titanium substrates (MP-Ti) with nominal pore sizes of 10, 20, and 50 µm. The ENTA was then covered with SnO2-Sb2O3. We refer to this anode as the MP-Ti-ENTA/SnO2-Sb2O3 anode. The morphology, pore structure, and electrochemical properties of the anode were characterized. Compared with the traditional NTA layer, we found that the MP-Ti-ENTA/SnO2-Sb2O3 anode has a service lifetime that was 1.56 times larger than that of MP-Ti-NTA/SnO2-Sb2O3. We used 2-methyl-4-isothiazolin-3-one (MIT), a common biocide, as the target pollutant. We evaluated the impact of the operating parameters on energy efficiency and the oxidation rate of MIT. Furthermore, the apparent rate constants were 0.38, 1.63, and 1.24 min−1 for the 10, 20, and 50 μm nominal pore sizes of the MP-Ti substrates, respectively, demonstrating the different coating–loading mechanisms for the porous substrate. We found that hydroxyl radicals were the dominant species in the MIT oxidation in the HO radical scavenging experiments. The radical and nonradical oxidation contributions to the MIT degradation for different current densities were quantitatively determined as 72.1%–74.8% and 25.2%–27.9%, respectively. Finally, we summarized the oxidation performance for MIT destruction for (1) the published literature on various advanced oxidation technologies, (2) the published literature on various anodes, and (3) our flow-by and -through anodes. Accordingly, we found that our flow-through anode has a much lower electrical efficiency per order value (0.58 kWh m−3) than the flow-by anodes (6.85 kWh m−3).

In arid and semi-arid regions, identifying and monitoring of soil alkalinity and salinity are in urgently need for preventing land degradation and maintaining ecological balances. In this study, physicochemical, statistical, and spectral analysis revealed that potential of hydrogen (pH) and electrical conductivity (EC) characterized the saline-alkali soils and were sensitive to the visible and near infrared (VIS-NIR) wavelengths. On the basis of soil pH, EC, and spectral data, the partial least squares regression (PLSR) models for estimating soil alkalinity and salinity were constructed. The R2 values for soil pH and EC models were 0.77 and 0.48, and the root mean square errors (RMSEs) were 0.95 and 17.92 dS/m, respectively. The ratios of performance to inter-quartile distance (RPIQ) for the soil pH and EC models were 3.84 and 0.14, respectively, indicating that the soil pH model performed well but the soil EC model was not considerably reliable. With the validation dataset, the RMSEs of the two models were 1.06 and 18.92 dS/m. With the PLSR models applied to hyperspectral data acquired from the hyperspectral imager (HSI) onboard the HJ-1A satellite (launched in 2008 by China), the soil alkalinity and salinity distributions were mapped in the study area, and were validated with RMSEs of 1.09 and 17.30 dS/m, respectively. These findings revealed that the hyperspectral images in the VIS-NIR wavelengths had the potential to map soil alkalinity and salinity in the Songnen Plain, China.

Sulfadiazine (SDZ) has been frequently detected in surface waters in recent years. We evaluated the kinetics, mechanisms, intermediate products and bacterial community structure that result from the reaction of SDZ with free chlorine (HOCl/OCl−). We examined this in a pilot-scale water distribution system. Neutral pH had the fastest rate of destruction of SDZ. A second-order reaction constant for the destruction of SDZ by chlorine increased with increasing concentration of free chlorine (FC). For different pipe materials, the rate of SDZ degradation decreased as follows: stainless steel (SS) pipe > polyethylene (PE) pipe > ductile iron (DI) pipe. Based on the less complex bacterial diversity and more chlorine-resistant by 16S ribosomal ribonucleic acid (rRNA) gene analysis, SS pipe and PE pipe were more suitable in SDZ degradation in water distribution system (WDS) than DI pipe. In addition, the transformation products from SDZ chlorination were identified by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry, and the products included SO2 extrusion products, haloacetic acids and trihalomethanes. Toxicity tests further confirmed that the toxicity of SDZ chlorination was higher both in low FC (0.7 mg/L) and high FC (1.3 mg/L) in WDS.

Ternary CoFeNi-layered double hydroxide (CoFeNi-LDH) was synthesized and initially applied to activate peroxymonosulfate (PMS) for the degradation of Congo red (CR) and Rhodamine B (RhB). The results show that the CoFeNi-LDH/PMS system can efficiently degrade nearly 100% of 20 mg/L CR or 20 mg/L RhB within 6- and 10-min reaction times, respectively. And the catalyst exhibits higher degradation efficiency on CR than on RhB under identical conditions, which is confirmed by electron clouds of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) performed by DFT calculations. Quenching tests reveal that SO4− is the dominant active species participating in the degradation process. Mechanism investigation demonstrates that Co(II)-Co(III)-Co(II) cycle is responsible for activating PMS to generate radicals for dyes degradation. A dynamic kinetic model is successfully developed to simulate the concentration profiles of CR and RhB degradation in CoFeNi-LDH/PMS system. The empirical second order rate constants between SO4− and CR (kSO4− /CR), HO and CR (k OH/CR), SO4− and RhB (kSO4− /RhB), HO and RhB (kHO /RhB) are determined to be 2.47 × 107, 3.44 × 106, 8.39 × 106 and 2.62 × 107 M−1s−1, respectively. In addition, toxic assessment using ECOSAR program suggests that the overall toxicity of CR and RhB decreased after treatment with CoFeNi-LDH/PMS system. Repeating tests and application of CoFeNi-LDH in different water sources give us adequate confidence that the as-synthesized CoFeNi-LDH is favorable for the purification of dye-contaminanted waters in practical.

Development of high capacity material for antimonite (Sb(III)) and antimonate (Sb(V)) removal is the key to solving water antimony contamination. Three-dimensional Cu(II)-specific metallogels (Cu-MG), which are considered to have high density adsorption sites for antimony (Sb), were first applied to adsorb Sb(III) and Sb(V). Batch assays resulted in adsorption capacities of Cu-MG for Sb(III) and Sb(V) at 102.4 mg/g and 264.1 mg/g, respectively. In addition, the adsorption capacity for Sb(III) was up to 225.7 mg/g using in situ oxidation. Kinetic assays resulted in more than 90% removal of Sb in 30 min. X-ray photoelectron spectroscopy (XPS) revealed the adsorption of Sb depended mainly on coordination interactions of vacant orbitals of the Cu atom with the lone-pairs of the O atom of Sb ( O H ) 3 or Sb ( OH ) 6 − . Adsorption energy based on density functional theory (DFT) confirmed that Sb(III) adsorbed as a single layer whereas Sb(V) adsorbed as a multi-layer. These findings are consistent with experimental results. In addition, DFT calculations revealed that the Cu-MG theoretical capacity for Sb(V) adsorption is higher than for Sb(III). Cu-MG is a new and promising class of adsorbents for the removal of Sb(III) and Sb(V) from contaminated water.

Arsenic (As) is a pervasive environmental toxin and carcinogenic metalloid. It ranks at the top of the US priority List of Hazardous Substances and causes worldwide human health problems. Wetlands, including natural and artificial ecosystems (i.e. paddy soils) are highly susceptible to As enrichment; acting not only as repositories for water but a host of other elemental/chemical moieties. While macro-scale processes (physical and geological) supply As to wetlands, it is the micro-scale biogeochemistry that regulates the fluxes of As and other trace elements from the semi-terrestrial to neighboring plant/aquatic/atmospheric compartments. Among these fine-scale events, microbial mediated As biotransformations contribute most to the element’s changing forms, acting as the ‘switch’ in defining a wetland as either a source or sink of As. Much of our understanding of these important microbial catalyzed reactions follows relatively recent scientific discoveries. Here we document some of these key advances, with focuses on the implications that wetlands and their microbial mediated transformation pathways have on the global As cycle, the chemistries of microbial mediated As oxidation, reduction and methylation, and future research priorities areas.

High sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1 mg/g for Pb(II) and 153.8 mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3-6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736 mL) for Pb(II) and 200 BV (2262 mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351 mL) for Pb(II) and 250 BV (8483 mL) for Cd(II), producing only 4 BV (136 mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103 mL), all metal ions in the actual industrial effluent could be effectively removed (