Biochar loaded with ferrihydrite and Bacillus pseudomycoides enhances remediation of co-existed Cd(II) and As(III) in solution

Bioremediation is one of the effective ways for heavy metal remediation. Iron-modified biochar (F@BC) loaded with Bacillus pseudomycoides (BF@BC) was synthesized to remove the coexistence of cadmium (Cd) and arsenic (As) in solutions. The results showed that B. pseudomycoides significantly increased the removal rate of Cd(II) by enhancing the specific surface area and Si-containing functional groups of biochar (BC). The surface of F@BC was enriched with Fe-containing functional groups, significantly improving As(III) adsorption. The combination of ferrihydrite and strains on BF@BC enhanced the removal of Cd(II) and As(III). It also promoted the oxidation of As(III) by producing an abundance of hydroxyl radicals (·OH). The maximum saturated adsorption capacity of BF@BC for Cd(II) and As(III) increased by 52.47% and 2.99 folds compared with BC, respectively. This study suggests that biochar loaded with Fe and bacteria could be sustainable for the remediation of the coexistence of Cd(II) and As(III) in solutions.

Distinct chromium removal mechanisms by iron-modified biochar under varying pH: Role of iron and chromium speciation

Iron-modified biochar (Fe-biochar) has been widely developed to attenuate Cr(VI) pollution in both acid and alkaline environments. However, there are few comprehensive studies on how the iron speciation in Fe-biochar and chromium speciation in solution influencing the removal of Cr(VI) and Cr(III) under varying pH. Here, multiple Fe-biochar containing Fe3O4 or Fe(0) were prepared and applied to remove aqueous Cr(VI). Kinetics and isotherms suggested that all Fe-biochar could efficiently remove Cr(VI) and Cr(III) via adsorption-reduction-adsorption. The Fe3O4-biochar immobilized Cr(III) by forming FeCr2O4, while amorphous Fe-Cr coprecipitate and Cr(OH)3 was formed when using Fe(0)-biochar. Density functional theory (DFT) analysis further indicated that pH increase caused more negative adsorption energies between Fe(0)-biochar and the pH-dependent Cr(VI)/Cr(III) species. Consequently, the adsorption and immobilization of Cr(VI) and Cr(III) species by Fe(0)-biochar was more favored at higher pH. In comparison, Fe3O4-biochar exhibited weaker adsorption abilities for Cr(VI) and Cr(III), which were in consistent with their less negative adsorption energies. Nonetheless, Fe(0)-biochar merely reduced ∼70% of adsorbed Cr(VI), while ∼90% of adsorbed Cr(VI) was reduced by Fe3O4-biochar. These results unveiled the importance of iron and chromium speciation for chromium removal under varying pH, and might guide the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.

Enhanced benzofluoranthrene removal in constructed wetlands with iron- modified biochar: Mediated by dissolved organic matter and microbial response

Polycyclic aromatic hydrocarbons (PAHs) pose a high risk to ecosystems owing to their adverse environmental effects. The use of biochar in constructed wetlands (CWs) to remove PAH has received increased interest, but is frequently challenging because of saturation adsorption. To enhance the microbial degradation, electron acceptors are provided. This study aimed to remove a representative PAH, benzofluoranthrene (BbF), using iron-modified biochar as a supplement to the CW substrate. Results revealed that iron-mediated biochar based CWs increased the removal of BbF by 20.4 % and ammonium by 25.6 %. The BbF retained in substrate with biochar (36.6 % higher content) and further removed with iron modification (40.6 % lower content). Iron-modified biochar increased dissolved organic carbon content, particularly low-aromaticity, and low-molecular-weight organic matters (25.7 % higher tryptophan-like material), which contributed to PAH degradation by microorganisms. Microbial analysis confirmed that iron-mediated biochar enriched the abundance of microbes (e.g., Cellulomonas, Actinotalea, and Sphingomonas) and key enzymes (e.g., catA, lipV, and sdhA) that are involved in PAH degradation. Higher proportion of iron-reducing bacteria (e. g., Thiobacillus, Rhodobacter) played a significant role in driving microbial iron cycle, which was beneficial for PAHs removal. Based on the results, we confirmed that the use of iron-modified biochar in CWs enhance PAH removal.

Remediation of arsenic-contaminated paddy field by a new iron oxidizing strain (Ochrobactrum sp.) and iron-modified biochar

Iron-oxidizing strain (FeOB) and iron modified biochars have been shown arsenic (As) remediation ability in the environment. However, due to the complicated soil environment, few field experiment has been conducted. The study was conducted to investigate the potential of iron modified biochar (BC-FeOS) and biomineralization by a new found FeOB to remediate As-contaminated paddy field. Compared with the control, the As contents of G_B (BC-FeOS), G_F (FeOB), G_FN (FeOB and nitrogen fertilizer), G_BF (BC-FeOS and FeOB) and G_BFN (BC-FeOS, FeOB and nitrogen fertilizer) treatments in pore water decreased by 36.53%-80.03% and the microbial richness of iron-oxidizing bacteria in these treatments increased in soils at the rice maturation stage. The concentrations of available As of G_B, G_F, G_FN, G_BF and G_BFN at the tillering stage were significantly decreased by 10.78%-55.48%. The concentrations of nonspecifically absorbed and specifically absorbed As fractions of G_B, G_F, G_FN, G_BF and G_BFN in soils were decreased and the amorphous and poorly crystalline hydrated Fe and Al oxide-bound fraction was increased. Moreover, the As contents of G_B, G_F, G_FN, G_BF and G_BFN in rice grains were significantly decreased (*P < 0.05) and the total As contents of G_FN, G_BF and G_BFN were lower than the standard limit of the National Standard for Food Safety (GB 2762-2017). Compared with the other treatments, G_BFN showed the greatest potential for the effective remediation of As-contaminated paddy fields.

Mechanistic investigation of mercury removal by unmodified and Fe-modified biochars based on synchrotron-based methods

Improved surface characteristics and incorporated Fe, S, and Cl species are reported in Fe-modified biochar, which makes it a prospective material for Hg(II) removal. In this study, aqueous Hg(II) was removed from solution by unmodified, FeCl₃-modified, and FeSO₄-modified biochars pyrolyzed at 300, 600, or 900 °C. Higher pyrolytic temperature resulted in higher removal efficiency, with the biochars pyrolyzed at 900 °C removing >96% of Hg(II). Fe-modification enhanced Hg(II) removal for biochars pyrolyzed at 600 °C (from 88% to >95%) or 900 °C (from 96% to 99%). Based on synchronous extended X-ray absorption fine structure (EXAFS) analysis, Hg coordinated to S in modified and unmodified biochars pyrolyzed at 900 °C, where thiol was reported, and in FeSO₄-modified biochars pyrolyzed at 600 or 900 °C, where sulfide was recognized; in other biochars, Hg bound to O or Cl. Additionally, confocal micro-X-ray fluorescence imaging (CMXRFI) demonstrated Hg was distributed in agreement with S in biochars where HgS was formed; otherwise, Hg distribution was influenced by Hg species in solution and the pore characteristics of the biochar. This investigation provides information on the effectiveness and mechanisms of Hg removal that is critical for evaluating biochar applications and optimizing modification methods in groundwater remediation.

Bioretention cell incorporating Fe-biochar and saturated zones for enhanced stormwater runoff treatment

Nitrogen (N) and phosphorus (P) removal in conventional bioretention systems is highly variable. Therefore, five novel experimental columns with different media configurations and constituents, and incorporating a saturated zone were developed and assessed to optimize the removal of N, P and other nutrients. Three types of media composed of the conventional mixed sand and soil media (T₁), biochar-amended media (T₂), and iron-coated biochar (ICB)-amended media (T₃) were evaluated. Two of the experimental columns were designed with double-layer configurations, while the other three were of a single-layer structure. Removal efficiencies of nutrients in the experimental columns were evaluated and compared using simulated runoff. Also, the effect of media depth on the retention of P and denitrifying enzyme activity (DEA) in the bioretention columns were evaluated. The experimental column only filled with T₃ showed the best performance for COD, ammonia (NH₄⁺-N) and total phosphorus (TP) removal (94.6%, 98.3% and 93.70%, respectively), whereas columns filled with T₂ performed poorly for TP removal (57.36%). For the removal of nitrate (NO₃^--N) and total nitrogen (TN), the columns using a single-layer and only filled with either T₃ or T₂ exhibited the best performance (93% and 97% TN removal, respectively). Overall, this study demonstrates that our proposed single-layered bioretention cell only filled with T₃ and incorporating a saturated zone effectively improves the runoff quality, and can provide a new bioretention cell configuration for efficient stormwater treatment.

Efficient removal of atrazine by iron-modified biochar loaded Acinetobacter lwoffii DNS32

In order to efficiently remove commonly used herbicide atrazine in farmland, an iron-modified biochar (FeMBC) was fabricated via chemical co-precipitation of Fe³⁺ onto corn stalks biochar. The composites of FeMBC and Acinetobacter lwoffii DNS32 (bFeMBC) effectively accelerated the degradation rate of atrazine (100 mg L^-1) in inorganic salt culture solution. TEM，XRD，XPS and FTIR were used to study the basic properties of the Materials. FeMBC promoted the formation of bacterial biofilm, -NH functional group on the surface of bacterial extracellular polymers (EPS) and FeMBC could interact with the aromatic ring of atrazine through Hbonding, which were conducive for microbial capture of atrazine. Meanwhile, the pores (2-10 μm) of FeMBC facilitated the passage of the DNS32 strain and the atrazine molecule, which contributed to the efficient capture and degradation of atrazine by DNS32 strain. BFeMBC amendment helped to maintain the bacterial diversity in the atrazine contaminated soil. The increase of rare bacteria (relative abundance of 0.01%-0.05%) richness plays a certain role in stabilizing nutrient cycling, thereby promoting microbial nutrient utilization activities and has the function of pollutant degradation. This may contribute to the digestion of atrazine and its intermediate metabolites，reducing the stress of microbial in atrazine contaminated soil. bFeMBC amendment may be a promising in situ remediation technique for soil atrazine contamination.

A paddy field study of arsenic and cadmium pollution control by using iron-modified biochar and silica sol together

Under flooded conditions in paddy soil, the mobility of As increases while the mobility of Cd decreases. The opposite geochemical behavior of As and Cd makes it difficult to reduce their mobilities simultaneously. Our recent study found that combined applications of biochar and zero-valent iron successfully reduced the mobilities of As and Cd simultaneously. On this basis, in the present study, an iron-modified biochar (Fe-BC) was developed, and its effect on decreasing the accumulations of As and Cd in rice was verified in a 2-year field trial. In addition, previous studies indicated that silicon fertilizer can also reduce As and Cd accumulation in rice grain. Hence, the effect of the combined or separate application of Fe-BC and silica sol on As and Cd accumulation in rice grain was investigated. Over the 2-year field trial, the grain yields decreased in the following order: iron-modified biochar plus silica sol (Fe-BC plus Si) > silica sol (Si) > Fe-BC > control (CK). Concentrations of As and Cd in brown rice were in the order: Fe-BC plus Si < Si ≈ Fe-BC < CK. The treatments of Fe-BC and Fe-BC plus Si significantly increased the soil pH and thus decreased available As and available Cd in the soil. In addition, significantly positive correlations between available As and As in brown rice and between available Cd and Cd in brown rice were found. In conclusion, co-application of iron-modified biochar and silica sol should be a recommended strategy to reduce the accumulation of As and Cd in rice grains.

Remediation of arsenic-contaminated paddy soil by iron-modified biochar

Arsenic contamination in paddy soils has aroused global concern due to its threats to food security and human health. Biochar modified with different iron materials was prepared for arsenic (As) immobilization in contaminated soils. Soil incubation experiments were carried to investigate the effects of biochar modified with Fe-oxyhydroxy sulfate (Biochar-FeOS), FeCl₃ (Biochar-FeCl₃), and zero-valent iron (Biochar-Fe) on the pH, NaHCO₃-extractable As concentrations, and the As fractions in soils. The scanning electron microscope and X-ray diffraction analysis demonstrated that iron was successfully loaded onto the surface or embedded into the pores of the biochar. Addition of Biochar-FeOS, Biochar-FeCl₃, and Biochar-Fe had no significant effects on the soil pH but significantly decreased the contents of NaHCO₃-extractable As in soils by 13.95-30.35%, 10.97-28.39%, and 17.98-35.18%, respectively. Biochar-FeOS, Biochar-FeCl₃, and Biochar-Fe treatments decreased the concentrations of non-specifically sorbed and specifically sorbed As fractions in soils, and increased the amorphous and poorly crystalline, hydrated Fe, Al oxide-bound, and residual As fractions. Compared with the other iron-modified biochars, Biochar-FeOS showed the most effective immobilization and has the potential for the remediation of As-contaminated paddy soils.