Fluorine contamination, mobility, and risks in soils at a phosphate-gypsum waste landfill: a new analytical method and comparison with previous methods

This study used a new X-ray fluorescence (XRF)-based analytical method with better precision and sensitivity to evaluate the fluorine concentrations in soil. It was hypothesized that the XRF method with a pellet-synthesizing procedure may effectively analyze the fluorine concentrations in soil with ease and reliability. The total fluorine concentrations determined using XRF were compared with those determined using three different types of analytical protocols-incineration/distillation, alkaline fusion, and aqua regia extraction procedures. Among the three procedures, the incineration/distillation procedure did not show reliable precision and reproducibility. In contrast, the total fluorine concentrations determined using the XRF analysis were linearly correlated with those determined using the alkaline fusion and aqua regia extraction procedures. Based on the results of the Korean waste leaching procedure and toxicity characteristics leaching procedure, the leachability of fluorine from soil and waste was not directly related to total fluorine concentrations in soil. Risk assessment also revealed that the fluorine-rich soils did not show non-carcinogenic toxic effects, despite exceeding the regulation level (800 mg/kg) in South Korea for total fluorine concentrations in soil. Our results suggest that XRF analysis in combination with the newly developed pretreatment method may be a promising alternative procedure for easily and rapidly determining the total fluorine concentration in soil. However, further efforts are needed to evaluate fluorine leachability and its associated risks in fluorine-contaminated soils.

Bioleaching of sewage sludge for copper extraction using Acidithiobacillus thiooxidans: Optimization and ecological risk assessment

In this study, Acidithiobacillus thiooxidans was used for the bioleaching of copper (Cu) from sewage sludge. In order to find optimization conditions, three factors including solid-to-liquid ratio (S/L) (0.01-0.2 %(w/v)), initial element sulfur (S0) (1-10 g/L), and initial pH (1-3) have been investigated. Based on response surface methodology (RSM) determined a significant reduced quadratic model with a p-value of 0.0022 (<0.05 significant level). The maximum Cu recovery was 85.3% in the optimum condition of S/L = 0.16% (w/v), S0 = 8.2 g/L, and pH = 1.4. Furthermore, a kinetic study based on a shrinking core model was performed and the result showed that chemical reaction was rate limiting in the extraction. Toxicity Characteristic Leaching Procedure (TCLP) results after bioleaching showed the bioleaching process detoxified sludge and the bioleached sludge residue was well within the regulatory limits for disposal. The germination seed with adding bioleached and unbioleached sludge to the soil was determined. Various parameters such as Germination Index (GI), Tolerance Index (TI), Vigor Index (VI), and stem length showed that the sewage sludge indices significantly increased than the sample soil with unbioleached sludge.

A review of toxicity assessment procedures of solar photovoltaic modules

Environmental management of solar photovoltaic (PV) modules is attracting attention as a growing number of field-operated PV modules approach end of life (EoL). PV modules may contain small amounts of toxic metals, and the procedures for assessing and regulating the toxic metal content and release of such materials at EoL differ widely across nations. This paper provides an overview of the metal composition of PV modules and common procedures for toxicity assessment through extensive research and review of technical literature and legislative documents. This review focuses on three primary aspects: first, it explores the distribution of toxic elements within current and emerging PV module designs, with a specific focus on obtaining representative samples for proportional toxicity testing within different module laminate areas. Second, it examines a sampling standard and the diverse toxicity testing methods and regulations employed in various regions, encompassing standards like the Environmental Protection Agency (EPA) Test Method 1311 (Toxicity Characteristic Leaching Procedure, TCLP) in the U.S., Restriction of Hazardous Substances (RoHS) in Europe, and the Waste Extraction Test (WET) in California. Third, the review examines the sources of variability in toxicity testing outcomes, including techniques for securing homogeneous samples from non-uniform PV modules, selecting particle sizes representative of landfill conditions in extracted samples, determining appropriate leachate characteristics such as leaching agents and pH levels, and considering factors like test duration and temperatures. In summary, this review summarizes relevant regulations and offers a comprehensive overview of the strengths and limitations associated with several toxicity assessment procedures currently in practice.

Characterization of textile effluent treatment plant sludge and its industrial application in fired clay bricks with health risk assessment

The textile industry in Bangladesh faces environmental and health challenges due to the disposal of solid waste from Effluent Treatment Plants (ETPs). To address this issue, a study was conducted using soil from a brick industry near Dhaka, amending it with varying amounts of dry sludge to create clay bricks. The original soil had a loam texture and medium plasticity. The research found that adding 9 wt% of sludge resulted in Grade A commercial bricks with a compressive strength of 15.33 MPa and water absorption of 13.33 wt%, meeting BDS 208 standards. However, these sludge-incorporated bricks experienced more shrinkage during the burning process due to organic content, requiring additional soil to maintain conventional dimensions. Also, to assess the health hazards of these sludge-incorporated bricks, a leaching test was performed, revealing that no toxic heavy metals (Pb, Cd, Cr, Cu, Ni, and Zn) in the leachate exceeded the limits set by the United States Environmental Protection Agency (USEPA). The study indicates that textile ETP sludge can serve as a sustainable raw material for bricks, potentially reducing the environmental burden caused by textile sludge disposal by 28.75%. This innovative approach offers a promising solution to both environmental and health concerns associated with textile waste in Bangladesh's industrial sector.

Synergistic utilization of industrial waste red mud and rice husk ash for eco-friendly geopolymer preparation: enhancing strength and mitigating hazardous leaching

The prolonged stacking of substantial volumes of industrial waste red mud (RM) can have significantly hazardous effects on the environment. In order to address this critical problem, this study proposes the synergistic preparation of geopolymers utilizing RM in conjunction with another industrial waste, rice husk ash (RHA). Geopolymers with varying incorporation of RHA were prepared using sodium hydroxide and sodium silicate composite alkaline activator. The mechanical properties, microstructure, and environmental characteristics of geopolymers were investigated. The incorporation of RHA significantly enhanced the strength of RM-based geopolymers, with the highest strength of 25.40 MPa achieved at 40% incorporation. According to XRD patterns and FTIR spectra, C-(A)-S-H and N-(A)-S-H were generated during the geopolymerization, thereby enhancing the strength of geopolymers. From SEM micrographs of geopolymers, it was evident that the geopolymer matrix was constituted by the encapsulation of unreacted inert particles of RM and residual fragments of RHA with C-(A)-S-H and N-(A)-S-H. The leaching levels of trace elements and heavy metals in geopolymers are both below the regulatory thresholds, thereby effectively mitigating the presence of hazardous substances in raw materials. These findings proved that the reuse of RM and RHA for the synergistic preparation of environmentally friendly geopolymers is a promising approach to address the issue of substantial RM stacking.

Self-consumed strategy to reuse cathode residue for Zn stabilization in spent batteries: Structural properties and metal stabilization effect

Due to ecotoxicity, zinc (Zn) as a heavy metal from electronic waste (e-waste) has been a source of pollution to soil and water for several decades. This study proposes a solution to this serious environmental problem via a self-consumed strategy to stabilize Zn in anode residues. This unique method uses cathode residues from spent zinc-manganese oxide (Zn-Mn) batteries as a stabilized matrix via thermal treatment. More specifically, the strategy incorporates zinc metal into a chemically durable matrix comprised of a lattice of AB2O4 compounds. Results demonstrate that 5-20 wt% of anode residue were fully incorporated into the cathode residue to form a Mn3-xZnxO4 solid solution after sintering at 1300 ℃ for 3 h. The lattice parameters of the Mn3-xZnxO4 solid solution reveal an approximately linear decreasing evolution with the addition of anode residue. To determine the occupancy of Zn in the crystal structure of the products, we used Raman and Rietveld refinement processes; the results reveal that Mn2+ in the 4a site was gradually replaced by Zn2+. We then used a prolonged toxicity leaching procedure to evaluate the Zn stabilization effect after phase transformation; this showed that the Zn leachability of sintered anode-doped cathode sample was over 40 folds lower than that of untreated anode residue. Therefore, this study presents an economical and effective strategy for mitigating the presence of heavy metal pollutants derived from e-waste.

Utilization of gasification slag and petrochemical incineration fly ash for glass ceramic production

This study investigated glass ceramics produced using coal gasification slag (CGS) and petrochemical incineration fly ash (PIFA) to immobilize hazardous heavy metals such as Cr and As. However, the crystallization kinetics and stabilization behavior mechanism of different heavy metals in the petrochemical incineration fly ash-derived glass-ceramics remains unclear. And X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and inductively coupled plasma mass spectrometry were used to characterize glass and crystalline products. In this paper, we reported the crystallization kinetics and chemical leaching characteristics of the glass ceramic. A low crystallization activation energy of 121.49 kJ/mol was achieved from crystallization peak of several different heating rates around 850°C, implying that it is easier to produce the glass ceramics at that temperature. The Avrami parameter of the former crystallization was determined to be 1.23 ± .12, which indicated two-dimensional crystal growth with heterogeneous nucleation. The toxicity characteristic leaching procedure results indicated that the heavy metals were well solidified, and that the leaching concentration was significantly lower than the limit specified by governmental agencies. The potentially toxic element index of the parent glass and the two glass ceramics were 11.7, 5.8, and 3.6, respectively. Therefore, the conversion of hazardous petrochemical incineration fly ash and other solid waste into environmentally friendly glass ceramics shows considerable potential and reliability.

Review of the impact of stormwater and leaching from pavements on the environment

The intensive growth of roadway infrastructure worldwide leads to growing concerns over the health impacts of stormwater runoff and leachate from roadway materials. This comprehensive review combines various sources of information from the last 30 years of research on the impact of pavement stormwater runoff and leaching on the environment. Of the 95 papers found in library searches, 42 papers add significantly to the body of literature around this subject after review of content and quality. Normally constructed asphalt and concrete pavements were found to release low levels of contaminants during their life. However, deposition from atmospheric pollutants and materials dispersed by vehicles on pavements do have a measurable impact on the quality of stormwater runoff. These tend to be expressed in initial flush from stormwater events. Reuse of old pavements at end of life tend to have little environmental impact when recycled. However, because of deposition of pollutants over their life these materials can have an impact when used in unbound layers of the pavement or in storage before reuse. Water quality can be improved by porous pavements, which allow infiltration of water and drainage to lower layers, thereby filtering many pollutants in stormwater runoff. The challenge is preventing the high initial pavement porosity from plugging over time. Pavement sealers containing coal tar pitch have high levels of polycyclic aromatic compounds and have been shown to impact aquatic life negatively and produce sediment buildup in ponds and streams. Recent studies have investigated photooxidation of pavements and its influence on leaching, but these remain as laboratory-scale studies. Tables outline materials tested, analytical parameters measured, and methodologies to allow readers to easily identify studies most relevant to their focus on impact of stormwater and leaching from pavements on the environment.

Novel GO/Fe-Mn hybrid for the adsorptive removal of Pb(II) ions from aqueous solution and the spent adsorbent disposability in cement mix: compressive properties and leachability study for circular economy benefits

GO/Fe-Mn hybrids were prepared by a single-pot chemical precipitation method and were characterized using FTIR, XRD, Raman, zeta potential, and FESEM, which confirmed the impregnation of Fe/Mn onto GO sheets. The synthesized hybrids were successively applied in removing the Pb(II) ions from aqueous solution and later utilizing the spent adsorbent to increase the properties of cement. The adsorption capability of the synthesized hybrid was seen in a set of batch studies to find out that about 15 min of contact time was required to remove 99% of the contaminant at a pH of 5 ± 0.2 and a dose of 0.83 g/L. The mechanism of the adsorption process for the synthesized hybrid was well described by Elovich kinetic model with an R² of 0.99 and Langmuir isotherm model, also with an R² of 0.99. The desorption studies conducted using 0.1 M HCl solution showed significant stability of the hybrid with a drop of 12% in the removal efficiency of Pb after up to five adsorption-desorption cycles. This points to an efficient adsorbent having potential for economical use. Later, the spent adsorbent was mixed with cement at ratios of 0.05%, 0.1%, and 0.5%, and compressive strength tests were performed, which showed an increase in the strength by 7.62%, 16.11%, and 26.82% at 28 days of curing time. The TCLP and SPLP tests performed on the hybrid and cement-spent adsorbent mix showed all the leaching parameters were well within the permissible limits. This development shows the potential for the use of spent adsorbent in a circular economy model.

Removal of arsenic in acidic wastewater using Lead-Zinc smelting slag: From waste solid to As-stabilized mineral

High-arsenic wastewater has long been considered a major threat to ecological balance and human health because of its strong toxicity and high mobility. Herein, an environmentally friendly process was proposed for As removal and fixation in the form of As-stabilized mineral, using Lead-Zinc smelting (LZS) slag as the in situ Fe donor, neutralizer, and crystal seed. The slag was dissolved in the wastewater and released Fe and Ca ions, while simultaneously increasing the pH value of the solution to help scorodite synthesis. The dissolved Ca²⁺ ion preferentially reacted with SO₄^2- ion in the form of CaSO₄·2H₂O precipitate as in situ "seeds" for As precipitation. The dissolved Fe(II) and As(III) ions were oxidized to Fe(III) and As(V) ions by H₂O₂, and later reacted with each other to generated amorphous ferric arsenate on the surface of CaSO₄·2H₂O, and then evolved into scorodite crystals with high stability. With a Fe/As molar ratio of 2, a reaction temperature of 90 °C, and a reaction time of 12 h, 98.42% of As was effectively precipitated from the wastewater with an initial As concentration of 7530.00 mg/L. Moreover, the leached As concentration of the As-bearing precipitate in the TCLP test was 3.46 mg/L. The concentration of the residual As and heavy metals ions in the final filtrate was lower than local wastewater discharge standards, successfully realizing the treatment of smelting wastewater. In summary, a prospective process successfully shows a great potential for co-treatment of LZS wastewater and slag, which could advance the large-scale disposal of LZS plants.

Arsenite removal from drinking water by bark-based magnetic iron oxide particle (BMIOP): a column study

The removal of arsenite [As(III)] from drinking water was investigated in a column at flow rates of 2.0 and 5.0 mL/min (up-flow direction) using bark-based magnetic iron oxide particles (BMIOP) prepared by coating (Fe(NO₃)₃.9H₂O) over Tamarindus Indica bark. The BMIOP was compared with regenerated BMIOP, commercial activated carbon, commercial activated alumina (Al₂O₃). At 2.0 mL/min, empty bed contact time (EBCT), breakthrough time (BT), the volume of treated water and breakthrough capacity (BC) on fresh BMIOP were found to be 6.8 min, 33.15 h, 4.380 L and 0.742 mg/g, respectively, and at 5.0 mL/min, were found to be 4.1 min, 13 h, 3.675 L and 0.453 mg/g respectively. EBCT, BT and BC were increased by 65.85%, 155% and 63.79%, respectively, as the flow rate was reduced from 5.0 to 2.0 mL/min. After regeneration of BMIOP, EBCT, BT, saturated time, BC and saturation capacity (SC) were reduced by 21.95%, 15.38%, 55.15%, 16.78% and 29.71%, respectively. The BC of fresh BMIOP was increased by factors 4.15, 3.60 and 1.20 and SC by factors 9.51, 7.88 and 1.42 compared to commercial activated carbon, commercial activated Al₂O₃ and regenerated BMIOP, respectively. Logit model could be used for the design of the adsorption column. Thomas model and artificial neural network (ANN) were applied to predict the characteristic column parameters useful for process design. Quality of treated water meets BIS requirements. Toxicity Characteristic Leaching Procedure (TCLP) and semi-dynamic tests show that the exhausted BMIOP is safe for disposal in a secure landfill; hence, BMIOP has been proved to separate As(III) from water.

A feasibility study on production of concrete blocks using treated municipal solid waste leachate

Increased water demand due to population growth and industrialization has led to increased water consumption. Hence, it is required to find an alternative to water in different industries. Concrete represents a remarkable water-consuming industry. The present study investigates whether the treated leachate of municipal landfills can be employed as a substitute for water in the concrete mixing scheme. For this purpose, concrete samples fabricated at different concentrations of treated leachates were compared to the control sample containing distilled water in terms of unconfined compressive strength (UCS) at the ages of 7 and 28 days. The experimental results revealed treated leachate accelerated the cement setting time by nearly 15 min and increased concrete slumping by 16%. The complete replacement of distilled water with treated leachate decreased UCS by 25% (from 50 to 38 MPa). The scanning electron microscope (SEM) and ultrasonic results showed that a rise in the treated leachate content of concrete increased porosity. Increased porosity would reduce UCS. Leaking of heavy metals existing in the leachate should be also investigated for the solidified matrices. The toxicity characteristic leaching procedure (TCLP) revealed that heavy metals leaching in all the samples are in the acceptable range. Results have shown that the use of leachate up to a concentration of 20% can be used in concrete, and the solidified product can also stabilize the pollutants, successfully. It is a valuable finding because using treated leachate as a practical additive in the concrete can prevent environmental contamination.

The treatment of electroplating wastewater using an integrated approach of interior microelectrolysis and Fenton combined with recycle ferrite

Heavy metal ions in chelated forms have aroused great concerns because of their high solubility, poor biodegradation and extreme stability. In this research, an efficient strategy, interior microelectrolysis-Fenton-recycle ferrite (IM-Fenton-RF), was developed to treat simulated electroplating wastewater containing chelated copper at room temperature. The decomplexation of chelated copper was carried out by both interior microelectrolysis and Fenton reactions. IM process can not only partly degrade the complexes of chelated copper via the microelectrolysis reaction but also it produces Fe²⁺ ions for the Fenton reaction. After decomplexation, the IM-Fenton effluent directly flowed into the RF reactor for copper ions removal. Under optimum reaction conditions (reflux ratio = 0.37, Fe²⁺ concentration = 9.20 g/L at pH 10.18), 99.9% copper was removed by the IM-Fenton-RF system. The produced IM-Fenton-RF sludge is based on ferrite precipitate and has several advantages over metal hydroxides sludge. Ferrite sludge is stable owing to the stability of ferrite's crystal structure, while the toxicity characteristic leaching procedure (TCLP) test meets relevant standards. The sedimentation rate and volume of ferrite sludge were 3.86 times faster and 11.0 times lower than those of metal hydroxides sludge. Furthermore, the yielding sludge of ferrite can be recovered and utilized for the synthesis of Fe-C metallic species, the main compound of IM packing for interior microelectrolysis reaction. All these results show that a combination of IM-Fenton and RF is an effective approach to treat wastewater containing chelated copper, showing great potential for industrial applications.

Study on Tailings Covering System Constructed by Geological Polymerization of Mine Waste, Part 1: Material Characterization and Cover Construction

Acid mine drainage (AMD) is a serious and persistent environmental pollution problem. At present, many studies have focused on the tailings pond's cover systems. This paper introduced the research results of using tin tailings from Laili mountain to make the covering layer of tailings pond. The first part included a detailed description of tailings characterization and acid production potential. On this basis, the hard layer (HL) was prepared and its feasibility as oxidation barrier was evaluated. It was found that when the proportion of tailings waste was 70%, the immobilization efficiency of heavy metals can reach more than 99.45%, and the pH of leaching solution was about 10.8. Moreover, the beneficial effect of solid waste addition on the HL was also verified. This suggests that HL as a post-mining restorative strategy has strong positive influence on pollution control.

Conversion of chromium-containing solid wastes into value-added products through a plasma-assisted aluminothermic process

Chromium-containing solid wastes have been generated by chemical and leather/tanning industries, and the management and proper disposal of the same wastes have been challenging tasks. A significant fraction of these wastes contains chromium compounds with chromium present in the hexavalent (Cr⁺⁶) form, which is hazardous to human beings, animals, and ecosystems. Since these wastes are discarded largely without proper treatments, soil and groundwater get contaminated and they can cause several health issues to human beings. Conventional methods developed to convert hazardous Cr⁶⁺ to Cr³⁺/Cr metal either generate secondary toxic wastes and unwanted by-products and/or are time-consuming processes. In this work, a plasma-assisted aluminothermic process is developed to convert the toxic waste into non-toxic products. The waste was mixed with aluminium powder and subjected to transferred arc plasma treatment in a controlled air atmosphere. Chemical analysis and Cr leachability studies of the waste material prior to plasma treatment have shown that it is highly toxic. Analysis of the products obtained from the plasma treatment showed that Cr and Fe present in the waste could be recovered as a metallic mixture as well as oxide slag, which were found to be non-toxic. Easy separation of the metallic fraction and the slag from the treated product is one of the merits of this process. Besides converting chromium-containing toxic waste to non-toxic materials, the process is rapid and recovers the metals from the waste completely.

Urban mining of obsolete computers by manual dismantling and waste printed circuit boards by chemical leaching and toxicity assessment of its waste residues

Waste residues and acidic effluents (post-processing of E-waste) released into the local surroundings cause perilous environmental threats and potential risks to human health. Only limited research and information are available toward the sustainable management of waste residues generated post resource recovery of E-waste components. In the present study, the manual processing of obsolete computer (keyboard, monitor, CPU, and mouse) and chemical leaching of waste printed circuit boards (WPCBs) (motherboard, hard drive, DVD drive, and power supply) were performed for urban mining. The toxicity characteristics of typical pollutants in the residues of the WPCBs (post chemical leaching) were studied by toxicity characteristics leaching procedure (TCLP) test. Manual dismantling techniques resulted in an efficient urban mining concept with an overall average profit estimation of INR 2513.73/US$ 34.59. The chemical leaching of WPCBs showed a high concentration of metal leaching like Cu (229662 ± 575.3 mg/kg) and Pb (36785.67 ± 13.07 mg/kg) in the motherboard after stripping epoxy coating. The toxicity test revealed that the concentration of Cu (245.746 ± 0.016 mg/l) in the treated waste residue and Cu (430.746 ± 0.0015 mg/l) and Pb (182.09 ± 0.0035 mg/l) in the non-treated waste residue exceeded the threshold limit. The concentrations of other elements As, Cd, Co, Cr, Ag, Mn, Zn, Ni, Fe, Se, and In were within the permissible limit. Hence, the waste residue stands non-hazardous except Cu and Pb. Stripping out the epoxy coating of WPCBs enhances the metal leaching concentrations. The study highlighted that efficient and appropriate E-waste urban mining has immense potential in tracing the waste scrap into secondary resources. This study also emphasized that the final processed waste residue (left unattended or discarded due to lack of appropriate skill and technology) can be taken into consideration and exploited for value-added materials.

Evaluation of heavy metal leaching under simulated disposal conditions and formulation of strategies for handling solar panel waste

With the steady growth in the worldwide solar installed capacity, there is an immediate concern about the fate of the solar panels at the end of their life. Solar panel waste is often disposed of indiscriminately, exposing the environment to chemical hazards. The major objective of the current study was to evaluate the leaching potential of the polycrystalline solar panel waste under different simulated disposal conditions through toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and pH static leaching procedure tests. Moreover, the study evaluates the effects of ageing and the breakage of the Glass Laminate Encapsulation (GLE) of solar panels on their leaching potential. Among the metals studied (silver (Ag), aluminium (Al), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), lead (Pb), and zinc (Zn)), the concentrations of Pb were as high as 9.3 mg/L, 1.4 mg/L, 6.7 mg/L in the TCLP, SPLP, and pH static test respectively. This indicated the hazardous nature of the waste with leaching potential of Pb above the permissible limits stipulated by various regulatory bodies. The presence of GLE reduced the mobility of Pb by a factor of 4.1-8.8 in the TCLP test, thereby rendering the waste as non-hazardous for its disposal in a landfill. However, the indiscriminate disposal of solar panel waste in the natural environment as simulated by the SPLP test indicated its harmful nature irrespective of the physical condition. Ageing of the solar panels before disposal and acidic pH conditions also positively influenced the leaching potential of the selected metals subjected to their reactivity and the accessibility of internal layers of waste to the leaching solution. Strategies such as extended producer responsibilty, advance-recycling fee, and incentivizing the recycling industry will lead to both economic benefit creation and effective waste management of this waste stream.

Biological attenuation of arsenic and nitrate in a suspended growth denitrifying-sulphidogenic bioreactor and stability check of arsenic-laden biosolids

Co-occurrence of arsenic and nitrate in groundwater sources at a wide range of concentrations is reported. In this work, performance of suspended growth semi-batch reactor was assessed for co-removal of arsenic and nitrate from simulated groundwater to meet the drinking water standards in the absence of iron. The bioreactor was inoculated with mixed bacterial culture and operated in the absence of oxygen for more than 450 days under varying influent arsenate (200-800 µg/L), nitrate concentrations (50-250 mg/L), and hydraulic retention time of 3-6 days. Complete nitrate removal was observed at all tested concentrations. Arsenic removal was found to meet drinking water standards from initial concentrations and up to 600 µg/L. The extended toxicity characteristic leaching procedure leaching experiments indicated that arsenic-laden biosolids would not constitute a hazardous waste. The arsenic leaching was found to increase with an increase in dissolved oxygen and the final leachate concentrations of arsenic were below 150 µg/L. The leaching experiments suggested maintaining non-alkaline conditions for minimum arsenic release from arsenic biosolids formed under sulphidogenic conditions. This study is the first to report that nitrate and arsenic can be simultaneously removed to meet drinking standards in a suspended growth bioreactor.

Understanding metal dissolution from solar photovoltaics in MSW leachate under standard waste characterization conditions for informing end-of-life photovoltaic waste management

The upcoming end-of-life solar photovoltaics (PV) waste stream is a huge concern before solid waste professionals due to presence of hazardous metals like lead or cadmium. The objective of present study was to understand the metal dissolution from PVs under four standard waste characterization regulatory tests of U.S., Germany, and Japan and their representativeness with actual landfill leachate. Modules were exposed to real municipal solid waste (MSW) landfill leachate for extended extraction duration, agitation and diluted leachate to investigate the effect of various parameters on metal dissolution. The results indicated that extractions using landfill leachates resulted in lower metal release than standard methods. The leached metal concentrations were found to be within the threshold limits except for cadmium, copper, lead and selenium, with maximum lead release from amorphous-PV of 8.68 mg/L and 6.91 mg/L with respect to TCLP and WET tests, respectively. Arsenic showed negligible release with maximum concentration of 0.046 mg/L from copper indium gallium de-selenide(CIGS) PV. Regardless of small size (1-2 cm pieces) and agitation, Germany and Japan's standard tests resulted in minimal release except of copper from copper indium gallium de-selenide PV. Leaching without agitation, showed negligible release from all photovoltaics whereas when agitation is applied to diluted leachate, significant release was observed with aluminum and copper leached up to 145.32 mg/L (multi-crystalline silicon) and 139.01 mg/L (amorphous-PV), respectively. CIGS was found to be most hazardous with a Metal Hazard Score (calculated on the basis of magnitude of leached metals with respect to their threshold limit and subsequent health effects) of 23.19, when exposed to standard tests. For all scenarios, increased metal release was observed with decrease in sample size and increase in leachate dilution and thus, leaching in highly acidic conditions are by no means representative for modules dumping in realistic conditions.

Oyster Shell Powder, Zeolite and Red Mud as Binders for Immobilising Toxic Metals in Fine Granular Contaminated Soils (from Industrial Zones in South Korea)

Low-cost absorbent materials have elicited the attention of researchers as binders for the stabilisation/solidification technique. As, there is a no comprehensive study, the authors of this paper investigated the performance of Oyster shell powder (OS), zeolite (Z), and red mud (RM) in stabilising heavy metals in three types of heavy metal-contaminated soils by using toxicity characteristic leaching procedure (TCLP). Samples were collected from surroundings of an abandoned metal mine site and from military service zone. Furthermore, a Pb-contaminated soil was artificially prepared to evaluate each binder (100× regulatory level for Pb). OS bound approximately 82% of Pb and 78% of Cu in real cases scenario. While Z was highly effective in stabilizing Pb in highly polluted artificial soil (>50% of Pb) at lower dosages than OS and RM, it was not effective in stabilising those metals in the soils obtained from the contaminated sites. RM did not perform consistently stabilising toxic metals in soils from contaminated sites, but it demonstrated a remarkable Pb-immobilisation under dosages over than 5% in the artificial soil. Further, authors observed that OS removal efficiency reached up to 94% after 10 days. The results suggest that OS is the best low-cost adsorbent material to stabilize soils contaminated with toxic metals considered in the study.

Environmental monitoring of toxic metals in roadside soil and dust in Ulsan, South Korea: pollution evaluation and distribution characteristics

This study investigated toxic metal distribution in roadside soil and dust in the metropolitan city of Ulsan, South Korea, and the factors affecting distribution, using Korean waste-leaching tests, determination of total concentrations, sequential extraction, and statistical analysis. Composite grab samples were collected from high-traffic roads (7 sites), low-traffic roads (2 sites), and an uncontaminated control area (2 sites) in Ulsan. The pH of roadside soil and dust was slightly alkaline. The concentrations of copper, lead, and zinc in soil as determined by Korean waste-leaching tests decreased as soil depth increased, while those of arsenic, nickel, and chromium increased. Leaching concentrations in dust were lower than in soil, with the exception of copper. Total concentrations decreased as soil depth increased, and total concentrations of metals in dust were higher than in soil. The sampling sites that exceeded the regulation levels of soil contamination in South Korea were 7 points in topsoil, 3 points in middle soil, and 9 points in dust. TCLP tests showed that the concentrations of arsenic, cadmium, and lead in topsoil and dust at Duwang and Myeongchon intersections were higher than regulatory levels. The maximum correlation coefficient among two metals in soil and dust was 0.987 (p < 0.01), for cadmium and lead. Concentrations of cadmium, copper, arsenic, lead, nickel, and mercury, mostly from tire and brake-pad abrasion, were highly correlated. The strong positive correlation between traffic volume and metals in dust suggests that vehicle emissions may be responsible for metal contamination of soil and dust. Pollution indices of topsoil at 4 sites and all dust at 7 high-traffic sites were higher than 1.0, which is consistent with an effect of vehicle traffic on metal contamination in soil and dust.

Influence of redox potential on leaching behavior of a solidified chromium contaminated soil

Cement-based solidification/stabilization (S/S) technology is often used to remediate chromium (Cr) contaminated soils. The valence state and mobility of Cr in soils are closely related with redox potential (E_H). However, Cr mobilization from the solidified soils influenced by E_H has received little attention. In this study, semi-dynamic leaching tests and the toxicity characteristic leaching procedure (TCLP) were performed on a S/S treated Cr contaminated soil under various E_H conditions. The effective diffusion coefficient and leachability index were obtained from the leaching data to investigate the leaching behavior of Cr from the S/S treated soil. Speciation of Cr remained in the sample after the leaching process was obtained through the sequential extraction procedures. The results show that an increase in E_H increases the effective diffusion coefficient of Cr and, therefore, the amount of Cr leached. This result is attributed to immobile Cr(III) being oxidized to highly mobile Cr(VI). The leachability index results indicate that the cement solidification of Cr contaminated soil may not be appropriate under oxidizing conditions. For the TCLP and sequential extraction procedures, the leached amount of Cr exhibits a strong dependence on E_H. As E_H increases, the content of Cr remaining in the soil in unstable phases reduced, and more Cr was released to leachant.

Effect of partially replacing ordinary Portland cement with municipal solid waste incinerator ashes and rice husk ashes on pervious concrete quality

Pervious concrete (PC) provides multiple benefits, including reducing stormwater runoff, purifying water, recharging groundwater, and reducing the heat island effect. This study aims to determine an effective way to reuse municipal solid waste incinerator (MSWI) fly ash (FA), MSWI bottom ash (BA), and rice husk ash (RHA) as single or binary partial replacements for ordinary Portland cement (OPC) in PC. The ashes and PC specimens were characterized via X-ray fluorescence spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the PC quality. The main components of the ashes were similar to those of OPC, suggesting that the ashes could be reused as cement materials; however, the cementitious activity of the ashes, especially MSWI FA, was relatively low. All ashes except 1100 °C MSWI FA met the standard requirements and can be applied as pozzolanic materials. The three PC specimens with binary replacements containing RHA (550, 700, and 900 °C) and MSWI BA (1100 °C) showed a synergistic effect and exhibited a higher 90-day compressive strength than the other specimens with single and binary ash replacements containing RHA (550 and 900 °C). The water permeability ranged between 0.106 and 0.391 cm/s, and the TCLP-released metal concentrations from all specimens met the regulatory standards of Taiwan. The results indicated that replacement with MSWI BA and RHA in cement materials provides an acceptable compressive strength and water permeability.

NTA-enhanced Pb remediation efficiency by the phytostabilizer Athyrium wardii (Hook.) and associated Pb leaching risk

Nitrilotriacetic acid (NTA), a biodegradable chelant, has been promoted to effectively assist Pb phytoextraction, while a few researches available on the phytostabilizer of Athyrium wardii (Hook.). In this study, two incubation experiments and a subsequent column experiment were conducted to investigate the effects of application of NTA on Pb availability in soils and Pb accumulation in A. wardii and associated leaching risk. The application of NTA significantly increased the exchangeable Pb and Pb bound to carbonates along with a decreased pH, leading to enhanced Pb availability in soils. It was more effective in enhancing Pb availability in soils by adding 2 mmol kg^-1 NTA into soils at once for 7 d, thus demonstrating potential for enhancing Pb uptake by A. wardii. After the addition of 2 mmol kg^-1 NTA for 7 d, Pb concentrations in roots of A. wardii was enhanced by 23.8%, along with 10.6% of increase for Pb accumulation in roots. No significant changes were observed for the biomass of A. wardii. Meanwhile, the available Pb and TCLP-extractable Pb in 0-20 cm soils increased by 11.1-23.4% and 7.1-31.2%, thus promoting Pb leaching in 0-20 cm soils. However, there were no changes for Pb leaching risk levels of 20-40 cm soils. No Pb was detected in the leachates from all columns. The application of 2 mmol kg^-1 NTA at once for 7 d is therefore proved to show greater potential in enhancing Pb remediation efficiency by the phytostabilizer of A. wardii without increasing Pb leaching risk into groundwater.

Stability of metal-rich residues from laboratory multi-step treatment system for ferriferous acid mine drainage

Passive systems are often used for the treatment of acid mine drainage (AMD) on closed and abandoned mine sites. Metal-rich residues (solid precipitates) with variable chemical composition and physical properties can be generated. Their characterization is required to better anticipate the potential fate, including stability for disposal, potential recovery, or reuse. The present study evaluated the leaching potential of solids from a laboratory passive multi-step treatment for Fe-rich AMD (2350 ± 330 mg/L Fe_tot, 0.7 ± 0.4 mg/L Ni, 0.2 ± 3.0 mg/L Zn, and 5073 ± 407 mg/L SO₄^2-, at pH 3.04 ± 0.45). To do so, post-treatment solids from three units (Fe-pretreatment reactor (50% wood chips and 50% wood ash, WA50), passive biochemical reactor, PBR for SO₄^2- treatment (30% inorganic materials, 70% organic substrate), and polishing reactor (50% calcite and 50% wood chips, C50)) of a pilot laboratory treatment system were sampled. Physicochemical and mineralogical characterization, as well as static leaching tests were then performed. Results showed that all solids had high neutralizing potential, while high inorganic carbon was found in C50. Moreover, high metal concentrations were found in WA50. Metals and sulfates in all solids precipitated in the form of oxyhydroxides, oxy-hydroxy-sulfates, carbonates, sulfides, sulfate, and native sulfur. The Fe was not found as problematic contaminant in solids, but it was in AMD. However, a probable generation of contaminated neutral drainage by Ni and Zn could occur from WA50. The C50 had the highest acid neutralizing capacity and could better resist to acid aggression relative to solids from PBR and WA50. The PBR and C50 solids were considered as non-hazardous towards regulation's limits and a potential co-disposal with municipal wastes could be a storage option. Further studies should be undertaken by testing other leaching and kinetic tests to assess long-term metal stability.