Concerns about the use of residues from municipal solid waste incinerators (MSWI) in construction materials usually focus on the potential for heavy metals and organic chemicals to leach into drainage waters under the influence of rain.We hypothesised that high level of salts in the MSWI leachates may cause more of a problem, particularly on soil physico-chemical properties. Both bottom ash (BA) and Solidified Air Pollution Control residue (SAPCr) leachates were added to experimental grassland plots. The amounts of Na+ increased by up to 13% in soils supplemented with each leachate. A decrease of the soil total porosity (−14%) was evidence of a subsequent adverse physical effect of this strong salinity. The potential for the grass cover type (species composition or density) to limit this adverse effect was discussed. Laboratory tests allowed us to determine that undiluted SAPCr induced slaking of aggregates accompanied by a strong decrease of aggregate stability, to 49% of control values. Undiluted BA induced dispersion of clays and others fine particles, which are then dislodged and transported into pores, causing blockage and decreasing total porosity. Clay dispersion followed by aggregate collapse occurred when soil solution contaminated by SAPCr was diluted by rainwater. This work stressed the importance of accounting for mineral contaminants, such as salts, when conducting an assessment of waste reuse scenarios.

We investigated the competitive effects of different fractions of wastewater treatment plant effluent organic matter (EfOM) on adsorption of an organic micro pollutant (OMP), propranolol (PRO), in a fixed bed column packed with magnetic tyre char (MTC). The results showed that the presence of EfOM inhibited PRO adsorption in wastewater leading to decreased PRO adsorption capacity from 5.86 to 2.03 mg/g due to competitive effects and pore blockage by smaller EfOM fractions. Characterization of EfOM using size exclusion chromatography (LC-OCD) showed that the principal factor controlling EfOM adsorption was pore size distribution. Low molecular weight neutrals had the highest adsorption onto MTC while humic substances were the least interfering fraction. Effect of important parameters such as contact time, linear velocity and bed height/diameter ratio on MTC performance was studied in large-lab scale columns. Linear velocity and contact time were found to be effective in increasing adsorption capacity of PRO on MTC and delaying breakthrough time. Increase in linear velocity from 0.64 cm/min to 1.29 cm/min increased mass transfer and dispersion, resulting in considerable rise of adsorbed amount (5.86 mg/g to 22.58 mg/g) and increase in breakthrough time (15.8–62.7 h). Efficiency of non-equilibrium Hydrus model considering dispersion and mass transfer mechanism was demonstrated for real wastewater and scale up purposes. Ball milling for degradation of adsorbed PRO and regeneration of MTC resulted in 79% degradation of PRO was achieved after 5 h milling (550 rpm), while the addition of quartz sand increased the efficiency to 92%.

Cadmium (Cd) is one dangerous and widespread heavy metal that of great environmental concern. To cost-efficiently adsorb aqueous Cd under influence of various factors, this study succeeded in fabricating goethite-modified biochar (GBC) derived from distillers’ grains (DGs) for Cd sorption of different concentrations (10–100 mg L⁻¹) at pH of 3, 6 and 8 with and without microcystin-LR (MC-LR). Sorption kinetics and isotherms data revealed that Cd sorption capacity of GBC and unmodified BC increased as pH elevated from 3 to 6 but stabilized when pH further elevated to 8. Pseudo-second-order and Langmuir models more accurately fitted to sorption data for both BCs, implying monolayer chemisorption of Cd onto BCs. GBC exhibited more robust sorption for each Cd concentration than unmodified BC, with the maximum sorption capacity of around 28 mg g⁻¹ at neutral and weak alkaline pH. Notably, goethite-modification obviously increased bulk polarity, specific surface area, porosity and surface oxygenic group abundance of BC, thus strongly enhancing Cd sorption by creating more sorption sites mainly via pore-filling, electrostatic attraction, and also via complexation and cation exchange. Co-existing MC-LR of 100 μg L⁻¹ did not obviously affect Cd sorption by both BCs for most Cd levels at each pH, mostly because sorption mechanisms diverged between MC-LR and Cd to largely avoid their competition for sorption sties. Thus, goethite could modify DG-BC as promising and cost-efficient sorbent for Cd even with co-existing MC-LR, especially at neutral and weak alkaline pH that common in the nature. This study was greatly implicated in modifying and applying DG-BC for Cd immobilization in MC-LR laden waters with various pH circumstances.

Vegetable soils with high nitrogen input are hotspots of nitrous oxide (N₂O) and nitric oxide (NO), and biochar amended to soil has been documented to effectively decrease N₂O and NO emissions. However, the aging effects of biochar on soil N₂O and NO production and the relevant mechanisms are not thoroughly understood. A¹⁵N tracing microcosm study was conducted to clarify the responses of N₂O and NO production pathways to the biochar aging process in vegetable soil. The results showed that autotrophic nitrification was the predominant source of N₂O production. Biochar aging increased the O-containing functional groups while lowering the aromaticity and pore size. Fresh biochar enhanced the AOB-amoA gene abundance and obviously stimulated N₂O production by 15.5% via autotrophic nitrification and denitrification. In contrast, field-aged biochar markedly weakened autotrophic nitrification and denitrification and thus decreased N₂O production by 17.0%, as evidenced by the change in AOB-amoA and nosZI gene abundances. However, the amendment with artificially lab-aged biochar had no effect on N₂O production. With the extension of aging time, biochar application reduced the soil NO production dominated by nitrification. Changes in the N₂O and NO fluxes were closely associated with soil NH₄⁺-N and NO₂⁻-N contents, indicating that autotrophic nitrification played a critical role in NO production. Overall, our study demonstrated that field-aged biochar suppressed N₂O production via autotrophic nitrification and denitrification by regulating associated functional genes, but not for lab-aged biochar or fresh biochar. These findings improved our insights regarding the implications of biochar aging on N₂O and NO mitigation in vegetable soils.

Recently, the adsorption-based environmental remediation techniques have gained a considerable attention, due to their economic viability and simplicity over other methods. Hence, detailed presentation and analysis were herein focused on describing the role of biochar in oil spill removal. Oil removal by utilizing biochar is assumed as a green-oriented concept. Biochar is a carbon-rich low-cost material with high porosity and specific surface chemistry, with a tremendous potentiality for oil removal from aqueous solutions. Oil sorption properties of biochar mainly depend on the biochar production/synthesis method, and the biomass feedstock type. In order to preserve the stability of functional groups in the structure, biochar needs to be produced/activated at low temperatures (<700 ᵒC). In general, biochar derived from biomass containing high lignin content via slow pyrolysis is more favorable for oil removal. Exceptional characteristics of biochar which intensify the oil removal capability such as hydrophobicity, oleophilicity or/and specific contaminant-surface interaction of biochar can be enhanced and be tuned by chemical and physical activation methods. Considering all the presented results, future perspectives such as the examination of biochar efficacy on oil removal efficiency in multi-element contaminated aqueous solutions to identify the best biomass feedstocks, the production protocols and large-scale field trials, are also discussed.

In order to solve the low sorption capacity of pristine biochar for anionic pollutants, e.g., reactive red 120 (RR120), a novel mesoporous Fe-biochar composite was fabricated in this study by combination of Fe-loading and ball-milling methods. The ball-milling Fe-biochar composite could effectively remove RR120 by up to 90.1 mg g⁻¹ at pH of 7.5, and slightly alkaline condition was preferred. Adsorption kinetics showed that ball-milling Fe-biochar composite could quickly sorb RR120 with the rate constant (k₂) of 2.07 g mg⁻¹ min⁻¹ (pH = 7.5). Positive surface charge and large surface area were responsible for the outstanding removal performance of RR120 by ball-milling Fe-biochar composite: (1) The adscititious Fe would be converted to β-FeOOH during pyrolysis, which significantly improved the zeta potential of biochar and thus facilitated the electrostatic adsorption for RR120, which contributed to 42.3% and 85.5% at pH of 3 and 7.5, respectively; (2) Ball-milling effectively increased the specific surface area and uniformed the pore size distribution, which could provide more sorption sites and expedite the diffusion of RR120 molecules, shortening the time from several hours to less than 15 min. Findings of this study not only provide a feasible modification method for biochar to adsorb anionic pollutants efficiently and rapidly, but also help to reveal the roles of Fe-loading and ball-milling in enhancing adsorption capacity.

Breaking of biochar during compaction of amended soil in roadside biofilters or landfill cover can affect infiltration and pollutant removal capacity. It is unknown how the initial biochar size affects the biochar breaking, clogging potential, and contaminant removal capacity of the biochar-amended soil. We compacted a mixture of coarse sand and biochar with sizes smaller than, similar to, or larger than the sand in columns and applied stormwater contaminated with E. coli. Packing columns with biochar pre-coated with a dye and analyzing the dye concentration in the broken biochar particles eluted from the columns, we proved that biochar predominantly breaks under compaction by disintegration or splitting, not by abrasion. Increases in biochar size decrease the likelihood of biochar breaking. We attribute this result to the effective dissipation of compaction energy through a greater number of contact points between a large biochar particle and the adjacent particles. Most of the broken biochar particles are deposited in the pore spaces of the background geomedia, resulting in an exponential decrease in hydraulic conductivity of amended sand with an increase in suspended sediment loading. The clogging rate was higher in the columns with small biochar. The columns with small biochar also exhibited high E. coli removal capacity, partly because of an increase in bacterial straining at reduced pore size after compaction. These results are useful in selecting appropriate biochar size for its application in soils and roadside biofilters for stormwater treatment.

Soil contains large amounts of humic acid (HA), iron ions and manganese ions, all of which affect U(VI) migration in the soil. HA interacts with iron and manganese ions to form HA salts (called HA-Fe and HA-Mn in this paper); however, the effects of HA-Fe and HA-Mn on the migration of U(VI) is not fully understood. In this study, HA-Fe and HA-Mn were compounded by HA interactions with ferric chloride hexahydrate and manganese chloride tetrahydrate, respectively. The influence of HA, HA-Fe and HA-Mn on U(VI) immobilization and migration was investigated by bath adsorption experiments and adsorption-desorption experiments using soil columns. The results showed that the presence of HA, HA-Fe and HA-Mn retarded the migration of U(VI) in soil. Supported by X-ray photoelectron spectroscopy (XPS) and BCR sequential extraction analyses, a plausible explanation for the retardation was that HA-Fe and HA-Mn could reduce hexavalent uranium to stable tetravalent uranium and increase the specific gravity of Fe/Mn oxide-bound uranium and organic/sulfide-bound uranium, which made it difficult for them to longitudinally migrate in soil. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and surface area and pore size analyses indicated that the complex formed between the hydroxyl, amino and carboxyl groups of HA-Fe and U(VI) increased the crystallinity of HA-Fe. The reaction between U(VI) and the hydroxyl, amino, aldehyde, keto and chlorine-containing groups of HA-Mn had no effect on the crystallinity of HA-Mn. Notably, the column desorption experiment found that the U(VI) immobilized in the soil remigrated under the effect of rain leaching, and acid rain promoted uranium remigration better than neutral rain. The findings provide some guidance for the decommissioning disposal of uranium contaminated site and it’s risk assessments.

This study examined arsenite [As(III)], arsenate [As(V)] and fluoride (F⁻) removal potential of bone char produced from sheep (Ovis aries) bone waste. Pyrolysis conditions tested were in the 500 °C–900 °C range, for a holding time of 1 or 2 h, with or without N₂ gas purging. Previous bone char studies mainly focused on either low or high temperature range with limited information provided on As(III) removal. This study aims to address these gaps and provide insights into the effect of pyrolysis conditions on bone char sorption capacity. A range of advanced chemical analyses were employed to track the change in bone char properties. As pyrolysis temperature and holding time increased, the resulting pH, surface charge, surface roughness, crystallinity, pore size and CEC all increased, accompanied by a decrease in the acidic functional groups and surface area. Pyrolysis temperature was a key parameter, showing improvement in the removal of both As(III) and As(V) as pyrolysis temperature was increased, while As(V) removal was higher than As(III) removal overall. F⁻ removal displayed an inverse relationship with increasing pyrolysis temperature. Bone char prepared at 500 °C released significantly more dissolved organic carbon (DOC) then those prepared at a higher temperature. The bone protein is believed to be a major factor. The predominant removal mechanisms for As were surface complexation, precipitation and interaction with nitrogenous functional groups. Whereas F⁻ removal was mainly influenced by interaction with oxygen functional groups and electrostatic interaction. This study recommends that the bone char pyrolysis temperature used for As and F⁻ removal are 900 °C and 650 °C, respectively.

Microplastics can adsorb chemical pollutants such as metals or pharmaceuticals, and transferred them along the food chain. In this work, an investigation of the adsorption of Cd, Co, Cr, Cu, Ni, Pb and Zn by five different types of microplastics was performed in Milli-Q water and natural waters (seawater, urban wastewater and irrigation water) via a series of batch adsorption experiments. The effects of concentration of metals and physicochemical characteristics of polymers were particularly studied. Results revealed a significant adsorption of lead, chromium and zinc on microplastics, especially on polyethylene and polyvinyl chloride. In the case of polyethylene terephthalate, it showed little adsorption capacity. Specific surface, porosity and morphology are characteristics that affect the molecular interactions. The adsorption isotherms were better described by Langmuir model, which indicates that the main adsorption mechanism might be chemical adsorption. Finally, results obtained in natural waters indicated that dissolved organic matter may play a major role on metal adsorption on microplastics. Results showed an enhancement of metal adsorption in waters with high chemical and biological oxygen demands as urban wastewater and irrigation water.