The solidification/stabilization (S/S) method is a common technique for the remediation of soils polluted by heavy metal. This study, thus, evaluated the long-term effectiveness, in term of the stabilization of lead in the solidified/stabilized soils, under freeze-thaw cycles, which are important physical processes that lead to material weathering. Three types of compound binders were obtained by mixing the three most commonly used binders (cement, quicklime, and fly ash) in varying proportions for the remediation of lead-contaminated soils. The leachability, chemical forms, and microstructure characteristics of the solidified/stabilized samples after various numbers freeze-thaw cycles (i.e., 0, 30, 90, and 180 times) were examined by utilizing the toxicity characteristic leaching procedure (TCLP) test, chemical speciation analysis, and scanning electron microscopy (SEM). The results showed that the long-term freeze-thaw cycles lead to decreased leachate pH and increased lead concentration in the leachate. The larger the total mix quantities of cement and quicklime, the lower the concentration of lead was presented in the leachate, however, indicating that cement and quicklime are more effective in immobilizing lead ions than fly ash. Chemical speciation analysis revealed that the long-term freeze-thaw cycles did, however, reduce the content of carbonate-bound form lead while the quantity of the ion-exchange forms. SEM further confirmed the observed leaching characteristics and chemical speciation characteristics. In addition, it indicated that, at the same number of freeze-thaw cycles, high initial lead concentrations substantially delayed the hydration process of cement in solidified lead-contaminated soil.

Pomelo peel has been reported as an efficient biosorbent for lead removal from wastewater treatment processes. The current work aimed to examine the amounts of lead desorption from the biosorbent waste in amended soil samples for up to 3 months (10% w/w). The desorption experiments were performed under two widely used techniques, single extraction and column leaching. Lead desorption was evaluated using two common eluents, which were 0.01-M Ca(NO₃)₂ and 0.04-M EDTA solutions. Under the single extraction method, using Ca(NO₃)₂, the highest amounts of Pb desorption were observed at 1 month (18.0 to 33.7% of total soil Pb), followed by a decrease attributed to re-adsorption of Pb released from the pomelo waste onto the soil. Much higher percentages of the soil Pb were desorbed using the EDTA solution throughout the period of the experiment (83.5 to 110.4% of total soil Pb). Soil pH appeared to have no effect on Pb desorption at this stage. The results from the column leaching study were similar although much smaller amounts of Pb were desorbed. Sequential fractionation data indicated that the bulk of the Pb released from the pomelo waste ended up associated with the soil oxide fraction with lesser amounts associated with the soil carbonate fraction. The results of this study suggest that land disposal of lead-contaminated biowastes such as pomelo peel could release Pb by desorption into the environment. Such material should therefore be treated as Solid waste should be treated as hazardous waste and only be disposed of in safe environmentally friendly ways.

Clean energy transition has been considered as an indispensable way to attain sustainable development for China, where the coal-to-gas initiative plays a vital role towards the goal. This paper takes Beijing, China’s political and economic center as well as a national pioneer in the energy transition, as a case to systematically analyze the co-mitigation of air pollution (PM₂.₅) and carbon emissions (CO₂) achieved by the policy-driven natural gas-coal consumption substitution. Firstly, a qualitative analysis of the relationship of Beijing’s coal-to-gas policies and its air quality has been conducted. Then, VAR and ARDL models are employed to quantitatively analyze the impacts of coal-to-gas policies on PM₂.₅ and CO₂, respectively. Results show that (i) an innovation of natural gas/coal consumption ratio will reduce PM₂.₅ concentrations, and the effect decreases over time; and (ii) an increase of 1% in natural gas/coal consumption ratio in Beijing will cause a decrease of 0.0784% in CO₂ emissions in the long run. Therefore, the coal-to-gas policies do increase the usage of natural gas and improve Beijing’s air quality. The assessment methods and conclusions can be regarded as a reference for not only China’s policymakers, but also other countries, especially nowadays when air quality is becoming more valued and GHGs are being tightly controlled.

A greenhouse microcosm study investigated the impacts of recovered iron oxyhydroxide mine drainage residuals (MDRs) on phosphorus (P) and trace metal distributions at the sediment layer/water column interface in Grand Lake o’ the Cherokees, a large reservoir receiving waters impacted by both historic mining and current agricultural land uses. Each mesocosm included 5 kg of lake sediment and 20 L of on-site groundwater. Three treatments were examined in triplicate: control (C) with no additions, low MDR (LM) with 0.3 kg added MDR, and high MDR (HM) with 0.9 kg added MDR. In the first 10 days, aqueous soluble reactive phosphorous (SRP) concentrations decreased likely due to colonizing biomass uptake with no significant differences among the three treatments. LM and HM treatments showed delayed peaks in dissolved oxygen (DO) and lesser peaks in chlorophyll-a (Chl-a) concentrations compared to the C treatment, indicating MDR addition may suppress biomass growth. During days 11 to 138, the C treatment demonstrated increasing pH, decreasing ORP, and biomass decay resulting in significantly increased SRP concentrations. In LM and HM treatments, sufficient P sorption by the MDR maintained low SRP concentrations. Although the MDRs are derived from metal-rich mine waters, all aqueous concentrations were below both hardness-adjusted acute and chronic criteria, except for Pb with regard to the chronic criterion. Metal concentrations in sediments were below the Tri-State Mining District (TSMD)–specific Sediment Quality Guidelines (SQGs). MDR additions may serve as stable long-term P sinks to prevent P release from dead biomass, decrease internal P cycling rates, and mitigate eutrophication, with limited concern for trace metal release. Graphical Abstract

Outward foreign direct investment (OFDI) plays a pivotal role in the strategy to build a high-level and open economy. This research used spatial panel models and data from 30 provinces in China from 2004 to 2017 to empirically analyse the relationship between OFDI and air pollution. The results revealed that, first, China’s air pollution showed two spatial clustering areas: the eastern coastal area (e.g. Zhejiang) and the north-western area (e.g. Xinjiang). Second, with the increase in OFDI, the direct effect on the concentration of respirable suspended particulate matter (PM₁₀) and sulphur dioxide (SO₂) was negative, and the direct effect on nitrogen dioxide (NO₂) was positive; however, the total effect was negative. An increase of 1% in OFDI would directly decrease the concentrations of PM₁₀ and SO₂ by 0.024% and 0.096%, respectively, while NO₂ would directly increase by 0.061%, but the total effect of OFDI on the three air pollutants was negative. Third, the environmental Kuznets curve hypothesis existed between economic growth and SO₂ and NO₂ but not between economic growth and PM₁₀. The spatial panel model results revealed that the spatial spillover effects of air pollutants (i.e. PM₁₀, SO₂, and NO₂) were 0.494, 0.447 and 0.314, respectively. Moreover, the impact of OFDI on air pollution had significant temporal heterogeneity. To make the results robust, this research conducted a robustness test by replacing the spatial weight matrix and dependent variables. Finally, the conclusion of this article demonstrates the importance of OFDI in improving air pollution, and we could benefit from OFDI. Our research conclusions provide an important reference for policymakers in implementing trade policies and improving air pollution.

The pretreatment of wheat straw has been recognized to be an essential step prior to anaerobic digestion, owing to the high abundance of lignocellulosic materials. In order to choose economical and effective techniques for the disposal of wheat straw, effects of five pretreatment methods including acid, alkali, co-pretreatment of acid and alkali, CaO₂, and liquid digestate of municipal sewage sludge on anaerobic digestion of wheat straw were investigated by analyzing biogas production and organic matter degradation in the study. The results showed that among these pretreatment methods, the methane yield was highest in the liquid digestate pretreated-wheat straw with 112.6 mL gTS⁻¹, followed by the acid, alkali, and CaO₂ pretreatments, and the lowest was observed in the co-pretreatment of acid and alkali. Illumina MiSeq sequencing of the microbial communities in the anaerobic digesters revealed that the genera Ruminiclostridium including Ruminiclostridium and Ruminiclostridium 1, Hydrogenispora, and Capriciproducens were the main hydrolytic bacteria, acidogenic bacteria, and acetogenic bacteria, respectively, in the anaerobic digesters. Capriciproducens and Hydrogenispora dominated in the first and the later stages, respectively, in the anaerobic digesters, which could work as indicators of the anaerobic co-digestion stage of sludge and wheat straw. The total solid and SO₄²⁻-S contents of the solid digestate and the NH₄⁺-N concentration of the liquid digestate had a significant influence on the microbial community in the digesters. These findings indicated that liquid digestate pretreatment was a potential option to improve the anaerobic digestion of wheat straw, due to the low cost without additional chemical agents.

Synthetic musks (SMs) are fragrance additives widely used in personal care products. SMs and their transformation by-products may reach the environment even after wastewater treatment, resulting in ecological and health concerns. The identification and toxicity assessment of SM by-products generated from different chemical and biological treatment processes have been rarely studied. This study established a 3D-QSAR model based on SMs’ molecular structures (independent variable) and their lethal concentration (LC₅₀) of mysid (dependent variable). The developed model was further used to predict the LC₅₀ of SMs transformation by-products. Fifty-eight by-products of six common SMs (i.e., galaxolide (HHCB), tonalide (AHTN), phantolide (PHAN), traseolide (TRASE), celestolide (ADBI), and musk ketone (MK)) generated from biodegradation, photodegradation, advanced oxidation, and chlorination were identified through literature review and lab experiment as the model inputs. Predicted LC₅₀ results indicated that the toxicity of 40% chlorination by-products is higher than their precursors. Biodegradation is an effective method to treat AHTN. The advanced oxidation may be the best way to treat HHCB. This is the first study on biotoxicity of SM transformation by-products predicted by the 3D-QSAR model. The research outputs helped to provide valuable reference data and guidance to improve management of SMs and other emerging contaminants.

In this present work, the performance of a semifluidized bed adsorption column has been evaluated for the removal of Pb²⁺ and Cd²⁺ in a semi-continuous mode. The composite adsorbents have been synthesized from waste biomass–based biochar and alginate-based biopolymer. Synthesized adsorbent characterized and finally tested its effectiveness in the removal of both Pb²⁺ and Cd²⁺ metal ions by batch and semifluidized bed column adsorption studies. The adsorptive removal efficiencies were found to be dependent on solution pH, initial metal ion concentration, adsorbent dose or initial bed height, static bed height, system temperature and inlet flow rate of semifluidized bed operation. Pseudo-second-order kinetic model was fitted to the batch adsorption experimental data by non-linear and linear regression method and it was found that the non-linear method gives a better way of obtaining the various kinetic parameters and its applicability. A solute phase mass transfer–based dynamic model has been developed to explain the adsorptive behaviour of metal ions onto adsorbents during the semi-continuous mode of operation of a semifluidized bed system. Various mass transfer parameters and degree of dispersion coefficients for the individual packed and fluidized section were obtained from the developed model.

Anthropogenic action in nature has increased the concentrations of particulates and other pollutants in water sources. The generation of water quality data requires sample collection, transport, and analysis, which incurs high costs. As a consequence, the water quality of remote and underserved areas is often not well monitored. In addition, when monitoring is available, data may come to water managers too late for on time decision-making. An effective and low-cost monitoring system that captures the signature of a water source has been developed in this research. A water signature is a unique or distinguishing measurement of patterns, or a collection of data sets, created from sensors monitoring the water source of interest, and providing compact and computationally efficient representations of the data acquired. The goal of this research was to develop a system that captures the signature of the water source and has low-cost monitoring, as well as sufficient accuracy and resolution to ensure that the measured variables can be used in the monitoring. The system is composed of an arduino-based micro-controller (Artmega328 ®); a 3D-printed measurement chamber, with optical and conductivity sensors; a self-priming pump; and a wireless telecommunication system. All electric and electronic devices are powered by a solar-powered system. The system was deployed in the field in different locations, and was able to respond qualitatively to water changes. The system was responsive in the range of 100 to 200 NTU for optical phenomena and responsive in the range of 0 to 2 μS/cm for electrical conductivity phenomena. The estimated cost of the system is $370. The results of this research are important for the development of non-analytical water quality monitoring sensors for remote, underserved regions.