Leachate Concentrations Research Articles

Mobility and crop uptake of Zn in a legacy sludge-enriched agricultural soil amended with biochar or compost: insights from a pot and recirculating column leaching test

The application of organic amendments to contaminated soils is a remediation method to regulate metal(loid) leaching to waters and uptake to crops. Here, wood-derived biochar and/or green waste compost was amended to a Zn-rich agricultural soil (~ 450mgkg-1 total Zn, derived from legacy sludge application). A pot experiment grew barley and pea crops in amended soil for 100days, simultaneously measuring Zn, pH, and dissolved organic carbon (DOC) in pore waters and Zn uptake to plants. An assessment was made of leaching of Zn via a linked column test that recirculated soil leachates to amendments multiple times to chart the confounding impacts of pH and DOC on Zn mobility. Concentrations of Zn in pore waters in the pot test were reduced from 2mgl-1 in soil without amendment to 1mgl-1 following the addition of 5% (vol.) biochar and compost, which was reduced further (0.5mgl-1) in the presence of crops. DOC appeared largely unaffected by soil amendment when mixed into soil, though was universally increased by the presence of the barley crop, whilst pH was variable (pH 4-6) and not clearly correlated with any intervention. Barley head mass was significantly increased after 5% biochar and both doses of compost amendment. Barley Zn content was maintained or enhanced by all soil amendments. The leaching column test revealed that biochar raised pH above that of the soil and compost amendment. Zn leachate concentrations were also reduced from after biochar amendment. Notably, compost resulted in net mobilisation of Zn from soil. This study demonstrates that the addition of biochar and compost to a Zn-rich agricultural soil was able to reduce pore water Zn considerably, especially in the presence of a barley crop. Compared to compost, biochar was the more efficient sorbent of Zn.

Improving the specificity of E. coli acetate/propionate exclusion biosensors via iterative engineering

Real-time monitoring of key performance indicator analytes such as acetate and propionate within anaerobic digestors (AD) is required for optimum biogas production. In this paper the further refinement of acetate and propionate whole cell (E. coli) exclusion biosensors is reported following an iterative process in which key metabolites that might interfere with O2-uptake measurements are identified and genes required for their catabolism are knocked out (exclusion). Analysis of biological leachate from an AD reactor treating lignocellulosic material revealed the presence of formate, which was subsequently shown to elicit a response in previously developed E. coli biosensor strains. P1 phage transduction was employed to delete two genes encoding formate dehydrogenase, fdoH and fdnH, to eliminate formate catabolism. Deletion of these genes from the propionate biosensor strain W:ldgyepak abolished interference from formate and enabled accurate determination of propionate concentrations in biological leachate. However, the acetate biosensing strain E1/pGDR11-acs, despite not having any response to formate, responded to propionate. It was likely that this was a result of the promiscuity of the wild type acetyl CoA synthetase, which was replaced with Acs2 from Saccharomyces cerevisiae, resolving the problem and enabling acetate determination with the biosensor. Acetate and propionate concentrations in authentic leachate influent were estimated to be 26.5 mM and 65.5 mM, respectively, using the biosensor, and 26.6 and 70 mM, respectively, by HPLC, demonstrating the accuracy and specificity of the refined biosensor.

Impact of volcanic ash from Cotopaxi-2015 and Tungurahua-2016 eruptions on the dielectric characteristics of suspension insulators, Ecuador

In Ecuador, a country with several active volcanoes and with four eruptions in the last decade in the continental arc, it is very likely that high-voltage transmission lines cross volcanic hazard zones on their routes. Here, we quantify the impact of fresh volcanic ash from the hydromagmatic Cotopaxi-2015 and the magmatic Tungurahua-2016 eruptions on the dielectric characteristics of ANSI 52–3 suspension insulators made of porcelain and glass, under moist conditions. The experiments include two methodologies to measure the performance of the insulators in real-time: the minimum insulator flashover voltage (FOVmin) and the dielectric loss factor angle. Both allow quantifying i) the critical voltage that the insulators can withstand prior to flashover occurrence and, ii) the strong fluctuating behavior that the insulators undergo in an ashy environment. Based on six contamination scenarios, we found that there is a higher chance of flashover if the insulators are completely blanketed (top and bottom) even with a fine ash layer (1 mm), than if they are covered just at the top. Our results further show that the ash of Cotopaxi-2015 eruption has a higher chance of leading to insulator failure because of its higher conductivity (i.e. higher leachate content) than that of Tungurahua-2016. Additionally, we identify two critical voltages prior to electrical flashover on the insulators of 28.25 kV and 17.01 kV for the 230 kV and 138 kV Ecuadorian transmission lines, respectively. Finally, we present a simple impact evaluation for the main Ecuadorian transmission lines based on the outcomes of this research and the official volcanic hazard maps for Cotopaxi and Tungurahua volcanoes.

Drought Reduces Release of Plant Matter Into Dissolved Organic Matter Potentially Restraining Ecosystem Recovery

Future climate scenarios indicate increasing drought intensity that threatens ecosystem functioning. However, the behavior of ecosystems during intense drought, such as the 2018 drought in Northern Europe, and their respective response following rewetting is not fully understood. We investigated the effect of drought on four different vegetation types in a temperate climate by analyzing dissolved organic matter (DOM) concentration and composition present in soil leachate, and compared it to two accompanying years. DOM is known to play an important role in ecosystem recovery and holds information on matter flows between plants, soil microorganisms and soil organic matter. Knowledge about DOM opens the possibility to better disentangle the role of plants and microorganisms in ecosystem recovery. We found that the average annual DOM concentration significantly decreased during the 2018 drought year compared to the normal year. This suggests a stimulation of DOM release under normal conditions, which include a summer drought followed by a rewetting period. The rewetting period, which holds high DOM concentrations, was suppressed under more intense drought. Our detailed molecular analysis of DOM using ultrahigh resolution mass spectrometry showed that DOM present at the beginning of the rewetting period resembles plant matter, whereas in later phases the DOM molecular composition was modified by microorganisms. We observed this pattern in all four vegetation types analyzed, although vegetation types differed in DOM concentration and composition. Our results suggest that plant matter drives ecosystem recovery and that increasing drought intensity may lower the potential for ecosystem recovery.

Optimizing nitrogen management reduces mineral nitrogen leaching loss mainly by decreasing water leakage in vegetable fields under plastic-shed greenhouse

Excessive fertilization leads to high nitrogen (N) leaching under intensive plastic-shed vegetable production systems, and thereby results in the contaminations of ground or surface water. Therefore, it is urgent to develop cost-effective strategies of nitrogen management to overcome these obstacles. A 15-year experiment in annual double-cropping systems was conducted to explore impacts of N application rate and straw amendment on mineral N leaching loss in plastic-shed greenhouse. The results showed that seasonal mineral N leaching was up to 103.4–603.4 kg N ha−1, accounting for 12%–41% of total N input under conventional N fertilization management. However, optimized N application rates by 47% and straw addition obviously decreased mineral N leaching by 4%–86%, while had no negative impacts on N uptake and tomato yields. These large decreases of N leaching loss were mainly due to the reduced leachate amount and followed by N concentration in leachate, which was supported by improved soil water holding capacity after optimizing N application rates and straw addition. On average, 52% of water leachate and 55% of mineral N leaching simultaneously occurred within 40 days after planting, further indicating the dominant role of water leakage in regulating mineral N leaching loss. Moreover, decreasing mineral N leaching was beneficial for reducing leaching loss of base cations. Therefore, optimized N application rates and straw amendment effectively alleviates mineral N leaching losses mainly by controlling the water leakage without yield loss in plastic-shed greenhouse, making this strategy promising and interesting from environmental and economical viewpoints.

Laboratory batch representation of PFAS leaching from aged field soils: Intercomparison across new and standard approaches

Relating laboratory leaching methods to partitioning and transport of per- and poly-fluoroalkyl substances (PFAS) in field soils is challenging, making estimation of fluxes to groundwater and surface water uncertain. Existing laboratory leaching methods have limitations when assessing field leaching. For 37 aged field soils from five sites historically contaminated with PFAS over decades, we assess PFAS leaching using new and existing laboratory leaching methods to provide alternative methods better reflecting PFAS risks posed by its leaching and movement. Dominant PFAS in the soils were perfluorooctane sulfonic acid, perfluorohexane sulfonic acid, and perfluorohexanoic acid and to a lesser extent perfluorooctanoic acid. Leaching from intact soil cores (Exp 1) was taken to reflect field conditions. These were compared to two new laboratory batch tests, saturate-spin (Exp 2) and saturate-tumble-spin (Exp 3), and two standard approaches; Australian Standard Leaching Procedure (ASLP, Exp 4) and the Leaching Environmental Assessment Framework (LEAF, Exp 5). The tests varied in terms of liquid:soil ratio, tumbling time and pH of the starting solution, with LEAF-1313 conducted across seven pHs (2−12). Correlations between leachate and soil concentrations were highest for Exp 4 and Exp 5 (R2 = 0.72–0.98) and lowest for Exp 3 (R2 = 0.53). The PFAS mass leached as a fraction of the total increased such that: soil core leaching (27 %) < saturate-spin (30 %) < saturate-tumble-spin (65 %) ≤ LEAF-1313 (65 to 88 % at pH 5–9) < ASLP (90 %). As a fraction of individual PFAS compounds in leachate compared with soil, the shorter chain PFAS (e.g., perfluorobutanoic acid) were higher in the leachate in all tests. Across all tests, the saturate-spin batch test most closely represented intact soil core leaching and therefore potentially provides a measure more analogous of in situ soil leaching at field sites. Other methods would apply to broader applications such as landfill disposal.

A feasibility study of municipal solid waste leachate utilisation in concrete

Water was replaced with raw municipal solid waste leachate in a concrete mix. Compared with the control specimen (prepared with freshwater), the hardened concrete specimen made with 100% leachate and cured in freshwater for 28 days showed reductions of 20% in ultrasonic pulse velocity and 45% in unconfined compressive strength. Scanning electron microscopy revealed that an increase in leachate content increased the microscopic pores and cracks within concrete owing to organic matter in the leachate. Heavy metals are contaminants in leachate and can leak from leachate-produced concrete. The toxicity characteristic leaching procedure revealed that the heavy metal leakage of the 100% leachate specimen was lower than the maximum permissible range. Furthermore, the use of leachate in fresh cement paste induced a 56 min delay in initial setting compared with the control specimen. Slump measurements performed 0, 30 and 60 min after concrete fabrication indicated that leachate addition could double the concrete slump as compared with the control specimen. This research provides basic information for the use of raw leachate in concrete mixes. Fresh and hardened concrete properties decreased with an increase in the percentage of leachate in the mix design. Replacement of tap water with 10% leachate satisfied the US standard for ready-mixed concrete. Further investigations are recommended to approve the use of leachate as a part of concrete mixing water.

Oxidation of As(III) by pressurized oxygen and the simultaneous precipitation of As(V) as scorodite in acidic sulfate solutions

Due to the lack of affordable and green disposal technologies, high arsenic-containing waste acid from the heavy nonferrous metallurgical smelter causes serious environmental pollution and threatens human health. In this study, a cost-effective and environmentally-friendly solution for simultaneous oxidation and precipitation of arsenic as well as formation of scorodite by adding ferrous sulfate as an iron source is proposed under elevated temperature (170 °C) and pressurized oxygen (1 MPa) conditions. And that the total reaction can be interpreted as 4Fe2+ + 4HAsO2 + 3O2 + 10H2O → 4FeAsO4·2H2O + 8H+. Consequently, the final oxidation and removal efficiency of arsenic reached 98.95% and 97.42%, respectively, resulting in scorodite with an arsenic leaching concentration of 1.4 mg/L in the TCLP leaching test. The results prove that the HO•, Fe(III) and Fe(IV) produced by the oxidation of Fe(II) is of capable oxidizing As(III) to As(V). Most importantly, the synthetic transformation mechanism of scorodite via a four-stage process is revealed, including the oxidation of As(III), formation of a mixture of amorphous hydronium jarosite and iron arsenate as precursors, partial dissolution of the precursor as well as nucleation and growth of scorodite particles.

Ex situ soil washing to remove PFAS adsorbed to soils from source zones

AbstractThis article presents the results of an Environmental Security Technology Certification Program (ESTCP) demonstration conducted at Eielson Air Force Base in Fairbanks, Alaska: Ex situ soil washing to remove per‐ and polyfluoroalkyl substances (PFAS) adsorbed to soils from source zones. The ESTCP project information can be found here: https://www.serdp-estcp.org/Program-Areas/Environmental-Restoration/Risk-Assessment/ER20-5258. The final report is expected to be published in September 2022. The objective of the project was to demonstrate and validate soil washing as a cost‐effective mass removal technology that can be applied to treat soil in source zones impacted by PFAS. The approach focused on the treatment of coarse soil fractions (sand and gravel) and separation of fines (silt/clay) for potential treatment by other means such as landfilling, thermal desorption, or stabilization. The goal was to optimize the treatment process to minimize wastes requiring more expensive treatment so that the cost would be competitive with landfilling in the continental United State. The treatment process was designed and optimized at the bench‐scale and demonstrated at the field‐scale by conducting a treatment trial at the Eielson Air Force Base using a mobile soil washing plant. Approximately 180 tons of PFAS‐contaminated soil was treated with untreated perfluorooctane sulfonate (PFOS) concentrations ranging from 4.5 to 560 μg/kg. The technology was validated by measuring PFAS mass removal efficiencies based on soil concentrations of PFAS compounds measured via Department of Defense Quality Standards Manual 5.3 Table B‐14 and PFAS leachate concentrations as measured by synthetic precipitation leaching procedure testing. PFAS concentrations in treated soils were compared to Alaska Department of Environmental Conservation soil screening levels for the migration to groundwater pathway through leaching for perfluorooctanoic acid (PFOA), PFOS, and perfluorobutane sulfonate (PFBS). PFAS concentrations in soil leachate were compared to US Environmental Protection Agency groundwater screening criteria for PFOA, PFOS, and PFBS. The results of the treatability testing and pilot tests confirmed that coarse grained sand and gravel were successfully treated to meet performance goals and the fines were segregated for alternative treatment. The benefit of the waste minimization approach is that more cost‐effective means can be applied to treat most of the impacted soil volume while limiting expensive residuals disposal or more expensive means of treatment such as incineration or thermal desorption. Treated soils can be beneficially reused on‐site and fines could also be stabilized to meet leaching‐based standards, as an alternative to off‐site disposal or treatment. This flexible approach allows one to tailor the combined remedy strategy to meet clients' objectives and risk tolerance through a sustainable, least‐cost remedial approach.

Effect of Municipal Solid Waste Incineration Fly Ash on the Mechanical Properties and Microstructure of Geopolymer Concrete.

Geopolymers are environmentally friendly materials made from industrial solid waste with high silicon and aluminum contents, and municipal solid waste incineration fly ash (MFA) contains active ingredients such as Si, Al and Ca. According to this fact, a green and low-carbon geopolymer concrete was prepared using MFA as a partial replacement for metakaolin in this study. The mechanical properties of the MFA geopolymer concrete (MFA-GPC) were investigated through a series of experiments, including a compressive strength test, splitting tensile strength test, elastic modulus test and three-point bending fracture test. The effect of the MFA replacement ratio on the microstructure of MFA-GPC was investigated by SEM test, XRD analysis and FTIR analysis. MFA replacement ratios incorporated in GPC were 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40% by replacing metakaolin with equal quality in this study. In addition, toxic leaching tests of MFA and MFA-GPC were performed by ICP-AES to evaluate the safety of MFA-GPC. The results indicated that the mechanical properties of MFA-GPC decreased with the increase of the MFA replacement ratio. Compared with the reference group of GPC without MFA, the maximum reduction rates of the cubic compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, initiation fracture toughness, unstable fracture toughness and fracture energy of MFA-GPC were 83%, 81%, 78%, 93%, 77%, 73% and 61%, respectively. The microstructure of MFA-GPC was porous and carbonized; however, the type of hydrated gel products was still a calcium silicoaluminate-based silicoaluminate gel. Moreover, the leaching content of heavy metals from MFA-GPC was lower than that of the standard limit. In general, the appropriate amount of MFA can be used to prepare GPC, and its mechanical properties can meet the engineering requirements, but the amount of MFA should not be too high.

Enhanced Weathering Using Basalt Rock Powder: Carbon Sequestration, Co-benefits and Risks in a Mesocosm Study With Solanum tuberosum

Enhanced weathering (EW) of silicate rocks can remove CO2 from the atmosphere, while potentially delivering co-benefits for agriculture (e.g., reduced nitrogen losses, increased yields). However, quantification of inorganic carbon sequestration through EW and potential risks in terms of heavy metal contamination have rarely been assessed. Here, we investigate EW in a mesocosm experiment with Solanum tuberosum growing on alkaline soil. Amendment with 50 t basalt/ha significantly increased alkalinity in soil pore water and in the leachate losses, indicating significant basalt weathering. We did not find a significant change in TIC, which was likely because the duration of the experiment (99 days) was too short for carbonate precipitation to become detectable. A 1D reactive transport model (PHREEQC) predicted 0.77 t CO2/ha sequestered over the 99 days of the experiment and 1.83 and 4.48 t CO2/ha after 1 and 5 years, respectively. Comparison of experimental and modeled cation pore water Mg concentrations at the onset of this experiment showed a factor three underestimation of Mg concentrations by the model and hence indicates an underestimation of modeled CO2 sequestration. Moreover, pore water Ca concentrations were underestimated, indicating that the calcite precipitation rate was overestimated by this model. Importantly, basalt amendment did not negatively affect potato growth and yield (which even tended to increase), despite increased Al availability in this alkaline soil. Soil and pore water Ni increased upon basalt addition, but Ni levels remained below regulatory environmental quality standards and Ni concentrations in leachates and plant tissues did not increase. Last, basalt amendment significantly decreased nitrogen leaching, indicating the potential for EW to provide benefits for agriculture and for the environment.

Occurrence of per- and polyfluoroalkyl substances (PFAS) in municipal solid waste landfill leachates from western China.

Landfill leachate has been documented as a significant source of trace organic pollutants, comprising an expansive family of per- and polyfluoroalkyl substances (PFAS). This study presents the findings on the distribution of 13 perfluoroalkyl carboxylates (PFCAs) and 4 perfluoroalkyl sulfonates (PFSAs) in leachates from 6 municipal solid waste (MSW) landfills in western China. The total concentrations of 17 PFAS in sampled leachates ranged from 1805 to 43,310ng/L, and 15 compounds were detected in all samples. The short-chain compounds perfluorobutane sulfonate (PFBS, mean mass fraction 23.1%) and perfluorobutyric acid (PFBA, mean mass fraction 20.6%) were dominant. There were higher PFAS concentrations in leachates from operating landfills (mean: 12,194ng/L) compared to closed landfills (mean: 2747ng/L), but there was no significant difference between young (< 10years) and old landfills (> 10years). Moderate to weak correlations were observed between PFAS concentrations and leachate properties, e.g., TN, NH4+-N, TOC, and pH. This is the first report on the distribution of PFAS in landfill leachates from western China. The results have identified landfill leachate as an underestimated source of PFAS in the environment and have contributed to a more comprehensive evaluation on PFAS presence across China.

Leaching Remediation of Dredged Marine Sediments Contaminated with Heavy Metals

There are more than 150 ports in China and a considerable proportion of dredged sediments in ports and waterways are contaminated with heavy metals as the typical contaminants. It is mandatory to remediate the contaminated dredged sediments prior to further resource utilization. The over-arching objective of this study was to use natural organic acids (oxalic acid, citric acid, tartaric acid, and malic acid) as leaching agents to remove heavy metals (Cu, Cd, and Pb) from contaminated dredged sediments. Batch experiments were conducted to investigate the factors governing the removal rate of heavy metals and leaching kinetics. Citric acid had the best leaching effect on heavy metals Cu, Cd, and Pb with an optimal leaching concentration of 20 mmol/L and a solid-to-liquid ratio of 1:20. The average removal rates of Cu, Cd, and Pb were 85%, 73%, 56%, and 35% for citric acid, malic acid, tartaric acid, and oxalic acid, respectively. The leaching kinetics showed that the removal of heavy metals increased rapidly with time and then gradually reached the maximum value which was best described by the Elovich equation model. The outcomes of this study suggest that citric acid is an effective and environmentally friendly leaching agent for removing heavy metals from marine dredged sediments.

Numerical modeling and simulation of leachate transport in MSW contaminated soil: Impact on seasonal changes

A municipal solid waste (MSW) disposal site with an area of 200 m2 and a depth of 0.3, 0.6 and 0.9 m is studied to assess and control the environmental impacts of leachate discharge on the inner layers of soil. The numerical model was developed under rainy and dry seasonal conditions. The soil properties and leachate concentration data were used for the finite element modelling considering time steps and diffusion coefficient. The effect of seasonal variations in leachate transport is dependent on soil properties such as hydraulic conductivity, moisture content and porosity. Results obtained from numerical computations were compared with the experimental values. However, the comparison demonstrates a good agreement between experimental and numerical calculations.

Xenobiotic Organic Compounds in a Landfill Leachate

Landfilling is a predominant method of waste disposal in most of the countries. Amongst the disadvantages of landfills use is the generation of gas and leachate which can possibly lead to the contamination of groundwater. Thus, examining of hazardous constituents of leachate such as xenobiotic organic compounds (XOCs) is essential to contain any unwanted impacts on the environment. In this study, leachate samples were collected from Al Amirat un engineered landfill in Muscat in order to examine the presence of XOCs. The results have showed the presence of some kinds of polychlorinated biphenyls (PCBs), pesticides, BTEX (benzene, toluene, ethyl benzene, xylene) and phthalates in low quantities. The concentrations of XOCs were only a small fraction of the total carbon content of leachate, but environmentally relevant leachate pollution levels were estimated to persist for decades to centuries. Thus, leachate should be collected regularly by means of newly constructed boreholes to avoid any risk to the environment. Such old un engineered landfills need to be well capped and rehabilitated to minimize their impacts on the environment.

Control of N-NH4+ and K+ leaching in potato using a carrageenan hydrogel

Potato cultivation requires fertilizers to sustain crop yields, but a significant percentage of added nutrients is lost by leaching. The use of coating materials for fertilizers is currently being considered to reduce these losses. The objective of this study was to determine if a carrageenin based hydrogel (CBH), used to coat fertilizer, decreases NH4+ and K+ leaching from a potato crop without affecting growth, specific gravity, and tuber yield. The CBH was tested in a diploid potato crop, cultivar Criolla Colombia (Solanum tuberosum L., Phureja Group) using a randomized full block design including the treatments noncoated fertilizer (T1), CBH coated fertilizer (T2), and no fertilizer (T3). Mineral nutrients in soil leachates together with dry biomass, foliar area, chlorophyll, tuber specific gravity, and yield were quantified. The nutrient content in leachates from T2 were below those from T1. No significant differences between treatments were observed for growth factors, yield, and tuber specific gravity. This study confirms the controlling effect of the CBH, ensuring the retention of the nutrients added in the fertilizer and preventing them from easily leaching. Future field studies are worthwhile to establish the amount of fertilizer this coating could save.

Interaction of diesel oil contaminants with laterite soil and bentonite treated by sawdust -landfill liner

ABSTRACT Landfill liners blended with industrial by-product seems to outperform the conventional liners. This paper presents the influence of sawdust (SD) admixed with bentonite and locally available lateritic soil on consistency limits, free swell index (FSI), compaction characteristics, unconfined compressive strength (UCS), hydraulic conductivity and leachate characteristics. SD content was varied as 10%, 15% and 20%. Diesel oil contaminants (DOC) and deionised water (DIW) were used as the test fluids. From the test results, consistency limits, FSI, maximum dry density, leachate concentration of heavy metals and UCS decreased, whereas optimum moisture content and hydraulic conductivity increased with increasing sawdust content. Furthermore, the energy-dispersive X-ray spectrometer revealed the absence of calcium in the blends which have resulted in poor cementation and decreased the UCS. X-ray diffraction showed that the presence of cellulose in sawdust and montmorillonite in bentonite adsorb the heavy metals in DOC. Based on the test results, 15% Saw dust content in the blends proves to be the optimum in retaining the heavy metal concentrations, improving the geotechnical properties and qualifying as a landfill liner material.

Tritium as a Tracer of Leachate Contamination in Groundwater: A Brief Review of Tritium Anomalies Method

Environmental isotopes are essential in hydrogeological studies, thanks to their contribution to the understanding of aquifers dynamics, vulnerability, water resources assessment, and management issues. The environmental isotopic approach plays a vital role in tracing the hydrological cycle and identifying various sources of contamination in the environment and gives independent information concerning what can be determined by a traditional hydrogeological study. Even in the framework of COP-26, isotopes have been indicated as fingerprints of climate change and therefore suitable for the evaluation of water balance and assessment of processes involved therein; in pollution studies they are used as fundamental support of traditional geochemical measures. Tritium, in particular, has been used since the 1960s to identify potential leaks in the containment walls of waste disposal sites, since its presence in the leachate (at very high levels in some cases) depends on the incorrect waste disposal of some peculiar items. Its use as a tracer of pollution by landfills is highlighted and emphasized by the very low concentrations of tritium in the natural environment. By comparing tritium content of leachate to that of water downflow from the waste disposal site, it is therefore possible to establish with a good success rate whether leachate have migrated or not out of the landfill, in the surrounding environment. An additional potential of tritium is to give a prompt indication of pollution risk in the environment indicating leaching even before the chemical indicator of pollution can be detected. This article wants to provide a contribution to the scientific community, collecting all the existing research in this field and providing data and benchmarks about this method, in particular stressing the role of tritium as an indicator of leachate transfer out of waste disposal sites.

A pilot-process for calcium hydroxide production from iron slag by low-temperature precipitation

The production of Ca(OH)2 via thermal decomposition of limestone is an energy intensive process resulting in significant CO2 emissions. However, if produced in a manner that obviates the need for the thermal decomposition of limestone, Ca(OH)2 could be a “CO2-negative” material. Herein, we design and demonstrate the operation of a continuous, low-temperature (< 100 °C), aqueous-phase pilot-process to produce Ca(OH)2 using calcium extracted from alkaline industrial wastes. The three-step process encompasses unit operations including: (i) calcium leaching from basic oxygen furnace BOF slag, (ii) leachate concentration by reverse osmosis (RO), and (iii) Ca(OH)2 precipitation by temperature swing. This process presents several advantages compared to the traditional route. First, it advances the recycling of waste from the steel industry. Second, it operates significantly below the temperature used in conventional lime production (900 °C) as it bypasses limestone calcination, responsible for ~65% of the CO2 emissions from the current process. Thus, the new process has a lower CO2 footprint and enables the use of industrial waste heat. The mass and energy balances were quantified to reveal that increasing the calcium concentration of the feed solution and the precipitation temperature, decrease the energy demands of the RO step, thereby reducing the process’s overall CO2 footprint. The pilot system operated continuously and achieved a production rate of nearly 1 kg per day of Ca(OH)2 with a purity greater than 95 wt%. The average particle size of the precipitates depended on the residence time in the precipitation reactor, demonstrating an ability to produce size-controlled particulates. Importantly, the process achieved full water recirculation/reutilization level indicative of a low-consumable water demand. The outcomes offer new insights and understanding relevant to developing and upscaling low-CO2 processes for cement, lime, and portlandite.

Stabilization of arsenic and antimony Co-contaminated soil with an iron-based stabilizer: Assessment of strength, leaching and hydraulic properties and immobilization mechanisms

Soils with relatively high concentrations of arsenic (As) and antimony (Sb) in mining areas would impose significant risks to human health and ecosystem. A new stabilizer PFSC composed of polymerized ferric sulfate (PFS) and calcium hydroxide (Ca(OH)2) is proposed to stabilize the soil with co-existed As and Sb sampled at an abandoned arsenic factory site. The effects of stabilizer dosage on the properties of the stabilized soil including leached concentrations of As and Sb, unconfined compressive strength (UCS), and hydraulic conductivity (kw) were investigated. The mechanisms of As and Sb immobilization in the soils were interpreted by Tessier's sequential extraction procedure (SEP), scanning electron microscope (SEM), and X-ray diffraction (XRD) results. The results showed increasing PFSC dosage was effective for reducing leached concentrations of As and Sb. When the PFSC dosage increased from 2% to 10%, the UCS and kw increased from 84 to 206 kPa and decreased from 6.48 × 10−8 to 6.33 × 10−9 m s−1, respectively. Tessier's SEP results showed that the leachable As and Sb fractions decreased from 12% to 5.6% and 7.5% to 3.8%, while the Fe–Mn oxides bound fractions increased from 22.3% to 29.4% and 13.2% to 19.5%. The SEM images and XRD patterns of untreated and PFSC stabilized contaminated soils indicated that hematite and calcite (CaCO3) were the main products of PFSC stabilization processes. Adsorption on ferrihydrite, entrapment in hematite lattices, and co-precipitate with calcite might were the main mechanisms of As and Sb immobilization.