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Excessive fluoride in mine water has become a major concern because it can cause detrimental effects to human health. Nevertheless, the removal efficiency of traditional adsorbents is far from satisfactory. Herein, La and Fe bimetallic supported zeolite was synthesized by co-precipitation method, for efficient defluoridation. The defluoridation performance of La-Fe zeolite was studied by a batch adsorption experiment and dynamic adsorption column test. Results indicated that the removal efficiency of F− was 99.04% under the optimal conditions (4 h, adsorbent dosage 8.0 g/L, agitation rate 200 rpm/min, temperature 298K and pH = 6 ± 1) that were determined through the batch adsorption experiments. CO32− and HCO3− can inhibit the defluorination effect of La-Fe zeolite. The adsorption of fluoride ions on La-Fe zeolite can be well described by the Langmuir adsorption model, and the maximum fluoride ion adsorption capacity is 2.64 mg/g. The test of dynamic adsorption column shows that the adsorption efficiency of F− by La-Fe zeolite on was higher than 85% for continuous adsorption of 9 h, indicating that La-Fe zeolite has good practical applications. The mechanism analysis indicated that the adsorption of fluoride ion by La-Fe modified zeolite involves both ion exchange and complexation, which belongs to the physicochemical process. [ABSTRACT FROM AUTHOR]

Acrylic manufacturing wastewater is characterized by high toxicity, poor biodegradability, high chemical oxygen demand (COD) and ammonia nitrogen. Herein, we exploited traditional Fenton technology to treat acrylic fiber manufacturing wastewater. The impacts of key operating variables including the initial concentration of H2O2 (CH2O2), the initial concentration of Fe2+ (DFe2+), and solution pH (pH) on the COD removal rate (RCOD) were explored and the treatment process was optimized by Response Surface Methodology (RSM). The results indicated that the optimum parameters are determined as pH 3.0, 7.44 mmol/L of Fe2+ and 60.90 mmol/L of H2O2 during Fenton process. For the actual acrylic manufacturing wastewater treatment shows that the removal rates for COD, TOC, NH4+-N and TN are 61.45%~66.51%, 67.82%~70.99%, 55.67%~60.97% and 56.45%~61.03%, respectively. It can meet the textile dyeing and finishing industry water pollutant discharge standard (GB4287-2012). During the Fenton reaction, the effective degradation and removal of organic matter is mainly achieved by HO• oxidation, supplemented by flocculation and sedimentation of Fe3+ complexes. This study will provide useful implications in the process parameters for the practical application of Fenton method in acrylic acid production wastewater. [ABSTRACT FROM AUTHOR]

Hazardous waste (HW) management is challenging because of their extreme toxicity to the environment and human beings. In the meantime, the occurrence of safety incidents that is caused by HW disclosed severe problems of HW management in China. However, there are no specific summaries of the HW management in China. Herein, we performed a systematic review of the identification method, management hierarchy, policy, disposal methods, and opening problems of HWs in China. The differences in HW identification between China and the United States were well discussed. The current status of HW production, management, and disposal in each province was summarized, and the possible development in HW production and management was proposed. The results in this review are expected to provide useful implications in the improvement of HW management. [ABSTRACT FROM AUTHOR]

Steel slag (SS) is one of byproduct of steel manufacture industry. The environmental concerns of SS may limit their re-use in different applications. The goal of this study was to investigate the leaching behavior of metals from SS before and after treated by microbially induced carbonate precipitation (MICP). Toxicity characteristic leaching procedure, synthetic precipitation leaching procedure and water leaching tests were performed to evaluate the leaching behavior of major elements (Fe, Mg and Ca) and trace elements (Ba, Cu and Mn) in three scenarios. The concentrations of leaching metals increased with the content of SS. After it reached the peak concentration, the leaching concentration decreased with the content of SS. The leachability of all elements concerned in this study was below 0.5%. The carbonate generated from the MICP process contributed to the low leachability of metals. After bio-modified by MICP process, the leaching concentrations of Ba from TCLP, SPLP and WLT tests were below 2.0 mg/L, which was the limit in drinking water regulated by U.S. EPA. The concentrations of Cu leached out from MICP-treated SS-sand samples were below 1.3 mg/L which is the limit regulated by national secondary drinking water. Compared with the regulations of U.S.EPA and Mississippi Department of Environment Quality (MDEQ), MICP-treated samples were classified as non-hazardous materials with respects to the leaching of metals. Meanwhile, maximum contaminant limits regulated by U.S.EPA states that MICP-treated SS are eco-friendly materials that can be reused as construction materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The leaching concentrations of different metals in stainless steel pickling residue (SSPR) were determined and the toxic metals were treated using Na 2 S∙ x H 2 O, FeSO 4 ∙6H 2 O, and phosphoric acid. A modified European Community Bureau of Reference (BCR) sequential extraction was used to identify the speciation of the concerned metals. Results showed that SSPR contains a large amount of Ca (58.41%), Fe (29.44%), Cr (3.83%), Ni (2.94%), Mn (2.82%) and some of Al, Cu, Mg, Zn. Among them, Cr and Ni were the most toxic metals in SSPR, thus the raw SSPR falls into hazardous waste category due to the leaching amount of Cr. In addition, the leached Cr was identified as Cr6+ (MgCrO 4) in the waste. BCR test revealed that risk assessment code (RAC) of Cr and Ni were 33.29% and 61.7%, indicating they posed "high" and "very high" risk to the environment, respectively. After fixing by Na 2 S∙ x H 2 O and FeSO 4 ∙6H 2 O, the leaching concentrations of Cr and Ni were less than 1.5 and 0.5 mg/L, respectively. After fixing by Na 2 S∙ x H 2 O and FeSO 4 ∙6H 2 O the treated SSPR can be safely reused as roadbed materials, concrete and cement aggregates. This study provides a useful implication in treatment and beneficial reuse of heavy metal-containing hazardous wastes. Image 1 [ABSTRACT FROM AUTHOR]

• Na 2 S∙xH 2 O was used to stabilize stainless steel pickling sludge. • Speciation and leaching behavior of heavy metals were examined. • The optimal pH range for stabilizing is 5.5-10. • With 7 days stabilization the products can be safely reused as roadbed materials and aggregates. This article presents an original study on stabilization of heavy metals in SSPS using sodium sulfide hydrate. The speciation and pH dependent leaching of the target heavy metals (Cr, Cu, Ni and Zn) based on GB 5085.3 and GB 16889 in both raw SSPS and stabilized products were examined. Results indicated that Cr and Ni are the two main toxic elements in SSPS. The BCR sequential extraction indicated that 55.2% of Cr in raw SSPS exist as Fe-Mn oxides, while water soluble Cr which is mainly consists of Cr(VI) accounts for 3.50%. After stabilization, the residual fraction Cr reached to more than 60% and Cr(VI) was not detected. The leaching concentration of Ni meets the limit of reuse SSPS, meanwhile, the sum proportion of sulfides and residual Ni increased from 8.68% to a maximum value of 31.82%. pH dependent leaching tests expound that the leaching concentrations of Cr, Ni, Cu and Zn are significantly high at pH = 2. The leaching concentrations of Cu, Ni and Zn are extremely low when pH varied from 7 to 13. The best stabilization pH span is from 5.5 to 10 for SSPS. The XRD and SEM-EDS analysis showed that the major compounds in treated SSPS were bassanite and plaster of Paris (POP). Since the extreme conditions such as pH = 2 or pH = 13 are infrequently, the stabilized SSPS can be safely reused in roadbed materials, bricks and concrete aggregates based on China HJ/T 301. [ABSTRACT FROM AUTHOR]

Studied were the adsorption-desorption and degradation of two widely used neonicotinoid insecticides clothianidin and thiamethoxam in three different agricultural soils in the state of Mississippi. The adsorptions of both the neonicotinoids fit a linear isotherm model. In different soils at different depths with different moisture contents, the adsorption distribution coefficients of clothianidin and thiamethoxam were found to be 0.62 to 1.94 and 0.59–2.03 L kg −1 , respectively. These distribution coefficients showed strong positive correlations with organic carbon content and pH of the soils. The desorptions of clothianidin and thiamethoxam also followed a linear isotherm, but were irreversible in respect to their adsorption isotherms. The desorption distribution coefficients ranged from 0.14 to 0.62 L kg −1 , increased with the decrease of organic carbon content. The degradations of clothianidin and thiamethoxam in the soils were found to be slow with half-lives ranged from 90 to 280 and 65 to 170 d for clothianidin and thiamethoxam respectively. The degradation rates increased with the increase of the organic carbon content in the soils. The moisture content in the soils had a positive effect on the degradation rates. The Groundwater Ubiquity Scores calculated from the adsorption distribution coefficient, organic content, and half-life suggest that clothianidin and thiamethoxam have moderate to high potential to leach to groundwater. [ABSTRACT FROM AUTHOR]

In this paper, Chayuan gully was used as a model to investigate initiation of groovetype debris flow via rainfall experiments. The results show that: (1) under condition of heavy rainfall, infiltration rate and water content in soil are inversely proportional with rainfall intensity at different depths. Heavy rainfall is conducive to overland flow, gully runoff and incised erosion, but does not favour water infiltration; (2) mode of slope failure and debris flow initiation mechanism are various under different rainfall and runoff conditions. The slope failure mode presents soil liquefaction and landslide with rainfall intensity of 60 mm/h. Accordingly, initiation mechanism of debris flow is close to landslide conversion. However, gully beds are easy to be eroded and slopes are prone to collapse with heavy rainfall and runoff. Then, debris flows occurred with initiation mechanism of entrainment; (3) the characteristic of debris flow is that several intermittent flows will appear. In addition, debris flow magnitude and flow viscosity are not consistent with rainfall intensity with heavy rainfall. On the contrary, mudslides viscosity is smaller, high sand torrent appears more in trials. The experimental results are well consistent with the natural debris flow occurrence at Chayuan gully. [ABSTRACT FROM AUTHOR]

The performance of electrocoagulation (EC) process in the treatment of geothermal water with high fluoride content was studied. The effect of applied current density, electrode plate number, electrode plate distance, and the temperature of geothermal water was investigated. The results show that EC can effectively reduce fluoride content to a low level, which can supply sanitary standard for drinking water in China (GB 5749-2006, 2006). With the increase in current density and electrode plate area, the removal efficiency of fluoride in geothermal water was also increased. However, with electrode plate distance increased from 0.5 to 2.0 cm, the fluoride removal efficiency decreased accordingly. The fluoride removal efficiency was improved when geothermal water temperature was increased from 18 to 38°C, while the fluoride removal efficiency changed little with geothermal water temperature from 38 to 62°C. [ABSTRACT FROM PUBLISHER]

A process for the determination of anaerobic-oxic biologically treated perfluoroalkyl substances (PFASs) in leachates from a landfill in Beijing, China, is provided. The applicability of electrocoagulation (EC) with aluminum electrodes for the remediation of PFASs in landfill leachates is investigated in detailed. With reaction time of 45 min, plate distance of 1 cm, current density of 35 mA/cm2 and plate amounts of four pairs, the EC reactor achieved the optimal removal efficiencies for chemical oxygen demand and PFASs. Perfluorooctane sulfonate was not detected in the treated leachates after the EC treatment. The average removal efficiencies of perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoate acid, perfluorononanoic acid and perfluorodecanoic acid were 65.1, 58.5, 75.2, and 33.8%, respectively. However, perfluoroundecanoic acid and perfluorododecanoic acid concentration increased by about 20.2 and 18.6% after the EC treatment process. [ABSTRACT FROM AUTHOR]

In this study, microbial induce carbonate precipitation (MICP) was introduced to immobilize chromium (Cr) in stainless steel pickling sludge (SSPS). Two methods were utilized to conduct the MICP process — Bacteria lysis liquor (BLL)-based MICP and bacteria-based MICP. BLL was obtained by breaking the cell walls with ultrasonic treatment. The urea hydrolyzation test illustrated that the BLL was better than bacteria solution. Both the treatments of bacteria lysis liquor-based MICP and bacteria-based MICP process can effectively entrap the Cr into mineral lattices, that reduce the potential environmental risk of SSPS. With 30 g/L urea and 7 days' treatment, BLL-based MICP presented better immobilization performance than bacteria-based MICP by lowering the bacteria concentration (OD 600) from 0.8 to 0.7. The excellent biosorption of BLL contributed to Cr removal. Nevertheless, the addition of calcium (Ca) significantly enhanced the immobilization performance of bacteria-based MICP process rather than BLL-based MICP process. pH-dependent leaching tests illustrated the leaching of Cr followed an amphoteric pattern, while the leaching of Ni and Ca followed the cation pattern. Geochemical modeling revealed that the leaching of Cr from bio-mineralized products was solubility-controlled by Cr(OH) 3 and Cr 2 O 3. [Display omitted] • Bacteria lysis liquor-based MICP presented better immobilization performances. • The addition of Ca improved the immobilization of Cr in bacteria-based MICP process. • Cr from bio-mineralized products showed strong pH-dependent leaching behavior. • Cr presented as Cr 2 O 3 and Cr(OH) 3 in the bio-mineralization products. [ABSTRACT FROM AUTHOR]

Leachate pollution in landfill sites is a major source of environmental concern. This study evaluates organics, nutrients and heavy metals in a landfill site in Beijing, and introduces a method combining coagulation–flocculation with filtration for the advanced treatment of leachate. The results confirm that CODCr, TN, NH4+−N, TP, Mn and As in leachate treated by an anaeobic–oxic biological method are unable to meet discharge or surface water quality standards. When treated with coagulation–flocculation combined with filtration under optimal conditions (cationic polyacrylamide dosage of 8.0 mg/L; polyaluminium chloride dosage of 350 mg/L; 0.4–0.6 mm ceramsite media in the filtration process), the residual NH4+− N, TN, Mn and As in the leachate meet the maximum allowed values for landfill leachate discharge or surface water quality standards in China; the exceptions are chemical oxygen demand and total phosphorus. Leachate treatment processes could be further strengthened or improved. [ABSTRACT FROM AUTHOR]

Cyanide (CN−) is extensively used in the process of plating devices and for surface treatment in the electroplating industry and is extremely hazardous to humans and the environment. Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) hold considerable promise for CN− removal. However, the activity of sulfate radical and hydroxyl radical generated in the PMS activation process is low in the base condition, leading to a drop in its efficiency in CN− removal. Thus, a photo-electrocatalytic system (PEC), developed using a TiO 2 photoanode and a carbon aerogel cathode, was used to activate PMS for the removal of CN− from wastewater through the generation of radicals and non-radicals. The PEC/PMS system could effectively remove CN−, with the removal efficiency reaching 98.5% within 2 min, when PMS concentration was at the 0.25 mmol/L level, and the applied bias voltage was -0.5 V. The main active species in the PEC/PMS system were superoxide radicals and singlet oxygen, which was proved through electron paramagnetic resonance detection and quenching experiments. Results obtained through in-situ Raman measurements, photocurrent tests, and electrochemical impedance spectroscopy measurements indicated that the TiO 2 could activate PMS to generate active species. Following many cycles of experimentation, it was discovered that the system displayed high catalytic performance and possessed satisfactory stability to remove CN− economically and efficiently. [Display omitted]. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both atomic H∗ and ∙OH were responsible for 2,4-DCP removal with Fe–P-CA cathode. • The release of iron ions with Fe–P-CA cathode was inhibited. • Hydrogen evolution potential with Fe–P-CA cathode was significantly decreased. [ABSTRACT FROM AUTHOR]

With the rapid economy and population growth, wastewater containing sulfate originated from industrial and human activities have gradually become a potential threat to the ecological security. As dominant microorganism responsible for treating high-sulfate wastewater, the sulfate-reducing bacteria (SRB) not only utilizes sulfate as the terminal electron acceptors, but also resists various harsh environments, so it was applied to a broader range of wastewater treatment. Based on previous studies, this study provides a comprehensive review of the metabolic mechanism and functional organisms of SRB. Further, the influence mechanism of environmental factors on the metabolic activity of SRB was analyzed from the perspective of pH, temperature, COD/SO 4 2− ratio, electron donors, oxidation reduction potential, hydraulic retention time, concomitant ions, and syntrophic/competitive effect. Additionally, applications and enhancing strategies for SRB were discussed based on above mechanism of action. Lastly, existing challenges and future development directions in environmental engineering applications are proposed. Future analysis should focus on functional genes and enzymes in assimilation sulfate reduction, research of SRB with complete oxidation capacity, the establishment of mathematical models simulating the metabolic activity and efficiency of SRB, the development of novel carbon sources fit for SRB, the potential value of heavy metals and S 0 recovery in sulfate reduction, and exploration of interaction mechanism between organohalides-respiring bacteria (OHRB) and SRB. [Display omitted] • The metabolic mechanism of SRB were summarized through metabolic pathways, functional organisms and key genes. • Eight key influencing factors affecting the metabolic activity of SRB were summarized. • SRB-mediated wastewater treatment technology is crucial in the process of water pollution control. • Further challenges and directions for SRB applications in environmental engineering are presented. [ABSTRACT FROM AUTHOR]

The pickling sludge produced from rolling process contains a large amount of Fe, Ca, Al as well as other metals. If these metals can be extracted and used, it will promote the recycling of pickling sludge. Herein, we proposed a two-step extraction method to extract Fe ions out from the pickling sludge, and then the extracted Fe was oxidized by H 2 O 2 and prepared into Fe-containing coagulant in the presence of Na 2 HPO 4 as stabilizer. The three main factors that affect the color removal efficiency and COD removal efficiency are identified as P:Fe ratio, H 2 O 2 adding amount, and curing time. Results show that the optimal preparation conditions are: P:Fe = 0.05, H 2 O 2 amount = 115%, and the curing time = 6 d, at which the color and COD removal efficiency reached 96.25% and 65.91%, respectively. The assessment of toxicity of the PPFC indicated that the content of harmful substances meets the thresholds in Chinese national standard GB141591-2016. The findings in this study are expected to provide new implications in treating different kinds of Fe-containing sludge. [Display omitted] • A two-stage extraction was developed for Fe extraction from pickling sludge. • P-doped polyferric chloride coagulant (PPFC) was prepared. • PPFC is no-toxic and effective coagulant for color and COD removal. [ABSTRACT FROM AUTHOR]

Cyclic volatile methylsiloxanes (cVMSs) are widely used in industrial processes and consumer products, which have been reported to be potentially toxic to human health due to their persistence and bioaccumulation. In this study, a novel photo-catalytic zinc oxide (ZnO)-coated aluminum (ZnO@Al) anode was prepared by a facile hydrothermal epitaxial process for the purpose of degrading cVMSs in practical wastewater. Morphological data and compositional analysis showed a compact coating layer that had the characteristic peaks of ZnO. To optimize the degradation process, central composite design combined with response surface methodology was applied to acquire the optimum parameters of cVMSs removal, and results indicated the cVMSs removal efficiency was approximately 63.3% at the conditions of current density = 17.3 mA/cm2, initial pH of electrolyte = 7.8, plate distance = 18 mm, UV intensity = 90 W, and reaction time = 80 min. Furthermore, the photo-electrocatalytic degradation of cVMSs obeys the pseudo-first order kinetic reaction, and the anode exhibited high durability as the attenuation of cVMSs removal efficiency was <6% after four times reuse. It was also observed that with the application period of the anode was extended, the electroflocculation reaction gradually occurred. The FT-IR of the generated flocs and the total ion gas chromatograms mass spectrometer analysis unraveled the methyl groups in Si-CH 3 could be easily attacked by hydroxyl radicals to form the intermediates of monohydroxy substituted products (m / z = 298, 372, and 446) and eventually short-chain carboxylic acids, alkyl radical and silicate. The effective removal of cVMSs by photo-electrocatalytic process using ZnO@Al anode provide significant implication in treatment of practical wastewater. Unlabelled Image • The ZnO-coated aluminum anode was prepared via a hydrothermal epitaxial method. • Photo-electrocatalytic method for the removal of cVMSs in wastewater was developed. • The kinetics, mechanism and reaction pathway of cVMSs degradation were proposed. [ABSTRACT FROM AUTHOR]

This study investigated the removal of chemical oxygen demand (COD), NH 4 -N, and perfluorinated compounds (PFCs) in the effluent from a wastewater treatment plant (WWTP) using ZnO coated activated carbon (ZnO/AC). Results suggested that the optimal dosage of the ZnO/AC was 0.8 g/L within 240 min of contact time, at which the maximum removal efficiency of COD was approximately 86.8%, while the removal efficiencies of PFOA and PFOS reached 86.5% and 82.1%. In comparison, the removal efficiencies of NH 4 -N, PFBA, and PFBS were lower, at approximately 47.9%, 44.0%, and 55.4%, respectively. In addition, COD was preferentially adsorbed before PFCs and NH 4 -N, when the contact time ranged from 0 to 180 min, and the order of PFCs removal showed a positive correlation with C-F chain length. The kinetic study revealed that the removal of COD, NH 4 -N, and PFCs could be better depicted and predicted by the Lagergren quasi-second order dynamic model with high correlation coefficients, which involved liquid membrane diffusion, intraparticle diffusion, and photocatalytic reactions. The saturated ZnO/AC was finally regenerated using ultrasound for 3 h and retained excellent performance, which proved it could be considered as an effective and alternative technology.

Toxicants like Pb in lead-based perovskite solar cells (PSCs) may become available to humans through leaching and transport through water, air, and soil. Here, we summarize the potential toxicity of different substances in PSCs and determine the leaching concentration of typical heavy metals used in PSCs through dynamic leaching tests (DLTs). Extraction fluids for the standard toxicity characteristic leaching procedure, synthetic precipitation leaching procedure, and deionized water were used as the DLT leaching solutions. Results indicated that the leaching concentration of Pb exceeded the hazardous waste limit of 5 mg/L. In addition, Pb was found to continuously leach out in the leaching cycles of water extraction. The findings confirmed that discarded PSCs may release Pb when subjected to water, rain, and landfill leachate. Total organic carbon and chemical oxygen demand analyses indicated that discarded PSCs could increase the oxygen consumption and may release CO 2 into the environment.

The present study investigated the preparation of nitric acid modified powder activated carbon (MPAC) and its adsorption of trace amounts of Ni(II) from aqueous solution. Results showed that raw powder activated carbon modified with 15% nitric acid (MPAC-15%) had the most developed pore structure and the highest adsorption efficiency for Ni(II) in aqueous solution. For MPAC-15%, the pore width was dominated by micropores with pore width about 1 nm and the total amount of chemical functional groups of MPAC-15% was 0.6630 mmol/g. Ni(II) adsorption tests indicated that the highest adsorption efficiency of MPAC-15% was 98%. The adsorption saturation time of MPAC-15% was about 120 min and the pH-dependent adsorption test showed that neutral conditions (6.5 < pH < 7.5) were suitable for Ni(II) adsorption. The adsorption kinetic analysis revealed that the pseudo-second order adsorption model fitted the adsorption process significantly. Thus, Ni(II) adsorption by MPAC-15% was dominated not only by physical adsorption via highly developed micropores but also by chemical adsorption between Ni(II) and surface functional groups. Adsorption isotherm analysis illustrated the Langmuir model was favorable for the adsorption of Ni(II), with R 2 = 0.9874.

The presence of perfluorinated compounds (PFCs) in the effluents of a wastewater treatment plant (WWTP) in Beijing was investigated in the current study. Perfluorooctanoate acid and perfluorooctane sulfonate were the predominant PFCs in wastewater, accounting for 19-27% and 18-31%, respectively. The concentrations of PFCs with long chains were much lower than those PFCs with short chains (≤C8). An electrochemical oxidation reactor was employed for advanced treatment of PFCs in WWTP effluents using stainless steel plates as anode and cathode electrodes. It was concluded that the removal efficiency of PFCs was improved accordingly with the increasing applied current density. The removal efficiencies of target PFCs ranged from 23.53 to 51.79% with a reaction time of 30 minutes, current density of 20 mA/cm(2), electrode plate distance of 1.0 cm and electrode plate amounts of five pairs.