The effects of rice straw biochar on indigenous microbial community and enzymes activity in heavy metal-contaminated sediment

Unveiling the long-term dynamic effects: Biochar mediates bacterial communities to modulate the petroleum hydrocarbon degradation in oil-contaminated sediments

Sediment, as the destination of marine pollutants, often bears much more serious petroleum pollution than water. Biochar is increasingly utilized for remediating organic pollutant-laden sediments, yet its long-term impacts on oil-contaminated sediment remain poorly understood. In this study, simulation experiments adding 2.5 wt% biochars (corn straw and wood chips biochar at different pyrolysis temperatures) were conducted. The effects on petroleum hydrocarbon attenuation, enzyme activities, and microbial community structure were systematically investigated. Results showed enhanced degradation of long-chain alkanes in certain biochar-treated groups. Biochar species and PAH characteristics together lead to the PAHs' attenuation, with low-temperature corn straw biochar facilitating the degradation of phenanthrene, fluorene, and chrysene. Initially, biochars reduced polyphenol oxidase activity but increased urease and dehydrogenase activities. However, there was a noticeable rise in polyphenol oxidase activity for a long time. Biochars influenced bacterial community succession and abundance, likely due to nutrient release stimulating microbial activity. The structural equations model (SEM) reveals that DON affected the enzyme activity by changing the microbial community and thus regulated the degradation of PAHs. These findings shed light on biochar's role in bacterial communities and petroleum hydrocarbon degradation over extended periods, potentially enhancing biochar-based remediation for petroleum-contaminated sediments.

Recalcification stabilizes cadmium but magnifies phosphorus limitation in wastewater-irrigated calcareous soil

Long-term wastewater irrigation leads to the loss of calcium carbonate (CaCO3) in the tillage layer of calcareous land, which irreversibly damages the soil's ability to retain cadmium (Cd). In this study, we selected calcareous agricultural soil irrigated with wastewater for over 50 years to examine the recalcification effects of sugar beet factory lime (SBFL) at doses of 0%, 2.5%, 5%, and 10%. We found that SBFL promoted Cd transformation in the soil from active exchangeable species to more stable carbonate-bonded and residual species, which the X-ray diffraction patterns also confirmed results that CdSO4 reduced while CdS and CaCdCO3 increased. Correspondingly, the soil bioavailable Cd concentration was significantly reduced by 65.6-84.7%. The Cd concentrations in maize roots and shoots were significantly reduced by 11.7-50.6% and 13.0-70.0%, respectively, thereby promoting maize growth. Nevertheless, SBFL also increased the proportion of plant-unavailable phosphorus (P) in Ca8-P and Ca10-P by 4.3-13.0% and 10.7-25.9%, respectively, reducing the plant-available P (Olsen P) content by 5.2-22.1%. Consequently, soil P-acquiring associated enzyme (alkaline phosphatase) activity and microbial (Proteobacteria, Bacteroidota, and Actinobacteria) community abundance significantly increased. Our findings showed that adding SBFL to wastewater-irrigated calcareous soil stabilized Cd, but exacerbated P limitation. Therefore, it is necessary to alleviate P limitations in the practice of recalcifying degraded calcareous land.

Use of selected amendments for reducing metal mobility and ecotoxicity in contaminated bottom sediments

The aims of the study were 1) to assess the suitability of selected amendments for reducing the mobility of metals in sediments by evaluating their effects on metal sorption capacity, and 2) to assess the ecotoxicity of sediment/amendment mixtures. Three different amendments were tested: cellulose waste, biochar, and dolomite. The efficiency of metal immobilization in mixtures was dependent on pH, which increased with concentrations of amendment. The higher negative charge observed for dolomite and cellulose waste corresponded with greater attraction of cations and enhanced metal sorption. For cellulose waste, the highest values of the Q parameter were attributed to the presence of OH groups, which corresponded with the highest immobilization of metals. Biochar reduced the negative surface charge, which highlights the importance of additional factors such as high specific surface area and volume of pores in metal immobilization. All amendments increased the SSA and VN2, indicating a higher number of sorption sites for metal immobilization. Most bioassays established a reduction of the ecotoxicity for amendments. Mixtures with dolomite (25%, 45% doses) and biochar (45% dose) were low toxic. Mixtures with cellulose waste were toxic or highly toxic. The mobility of metals from contaminated sediments can be limited by reused industry side products, which could contribute to further closing the circular economy loop.

Co-influence of biochar-supported effective microorganisms and seasonal changes on dissolved organic matter and microbial activity in eutrophic lake

DOM (dissolved organic matter) play a crucial role in lakes' geochemical and carbon cycles. Eutrophication evolution would influence nutrient status of waters and investigating the DOM variation helps a better understanding of bioremediation on environmental behavior of DOM in eutrophic lakes. In our study, the contents, compositions and characteristics of systematic DOM&SOM (sediment organic matter) were greatly influenced by seasonal changes. But the effective bioremediations obviously reduced the DOM concentration and thus mitigated the eutrophication outbreak risks in water bodies due to the increased MBC (microbial biomass carbon), microbial activity and metabolism. In early summer, the overall DOM in each treatment were readily low levels and derived from both autochthonous and exogenous origins, dominated by fulvic acid-like. In midsummer, the DOM contents and characteristics in each treatment increased significantly as phytoplankton activity improved, and the majority of DOM were humic acid-like and mainly of biological origin. The greatest differences of enzymes, MBC, microbial metabolism and DOM&SOM removal among different treatments were observed in summer months. In autumn, the systematic DOM&SOM slightly reduced due to the deceased microbial activity, in which the microbial humic acids were main component and derived from endogenous sources. Additionally, the gradually decreased SOM with cultivated time in each treatment was a result of microbiological conversion of SOM into DOM. For various treatments, BE, BE.A, BE.C and BE.E increased the MBC, enzymatic and microbial activities due to the application of biochar-supported EMs. Among these, BE and BE.A, especially BE.A with oxygen supplement, achieved the most desirable effect on reducing systematic DOM&SOM levels and increasing enzymatic and microbial activities. The group of EM also reduced the levels of DOM&SOM as improved degradation of EMs for DOM. However, BC, BE.C and BE.E finally did not achieved the desirable effect on reducing DOM&SOM due to the suppression of microbial activities, respectively, from high dose of biochar, weakening of dominant species and additional introduction of EMs in low liveness.

Mechanisms of biochar assisted di-2-ethylhexyl phthalate (DEHP) biodegradation in tomato rhizosphere by metabolic and metagenomic analysis

The intensive accumulation of di-2-ethylhexyl phthalate (DEHP) in agricultural soils has resulted in severe environmental pollution that endangers ecosystem and human health. Biochar is an eco-friendly material that can help in accelerating organic pollutant degradation; nevertheless, its roles in enhancing DEHP removal in rhizosphere remain unclear. This work investigated the impacts of biochar dosage (0%-2.0%) on DEHP degradation performance in tomato rhizosphere by comprehensively exploring the change in DEHP metabolites, bacterial communities and DEHP-degrading genes. Our results showed a significant increase of rhizosphere pH, organic matter and humus by biochar amendment, which achieved a satisfactorily higher DEHP removal efficiency, maximally 77.53% in treatments with 1.0% of biochar. Biochar addition also remarkably changed rhizosphere bacterial communities by enriching some potential DEHP degraders of Nocardioides, Sphingomonas, Bradyrhizobium and Rhodanobacter. The abundance of genes encoding key enzymes (hydrolase, esterase and cytochrome P450) and DEHP-degrading genes (pht3, pht4, pht5, benC-xylZ and benD-xylL) were increased after biochar amendment, leading to the change in DEHP degradation metabolism, primarily from benzoic acid pathway to protocatechuic acid pathway. Our findings evidenced that biochar amendment could accelerate DEHP degradation by altering rhizosphere soil physicochemical variables, bacterial community composition and metabolic genes, providing clues for the mechanisms of biochar-assisted DEHP degradation in organic contaminated farmland soils.

Physiological characteristics, rhizosphere soil properties, and root-related microbial communities of Trifolium repens L. in response to Pb toxicity

Trifolium repens L. (T. repens) is considered a potential phytoremediation species due to its large biomass and ability to accumulate and tolerate heavy metals. Lead (Pb) is an important heavy metal pollutant that can affect plant growth, photosynthesis, and enzyme activity. However, response mechanism of microorganisms in three root niches of metal tolerant plants to Pb is not completely understood. Therefore, in this study, a Pb poisoning model of T. repens was established with a Pb gradient (0, 1000 mg/kg, 2000 mg/kg, and 3000 mg/kg), and was used to evaluate growth and physiological responses, as well as enrichment and transport coefficients in T. repens, and explore the characteristics of rhizosphere soil and microbial composition of three root niches. We found that Pb stress caused oxidative injury, and inhibited photosynthesis in T. repens. 16S rDNA sequencing analysis showed that the richness of microbial communities in bulk soil was higher than that in rhizosphere soil both under Pb stress and Pb nonstress conditions. Moreover, Proteobacteria was dominant phylum in bulk and rhizosphere soils, and Proteobacteria and Cyanobacteria were dominant phylum in endophytic bacteria. For the first time, we systematically investigated the response of Pb from bulk soil to plant leaves. The results showed that microbial interaction existed between bulk and rhizosphere soil. Rhizosphere bacterium Haliangium was positively correlated with urease activity and soil nutrients. Endophytic bacterium Pseudomonas was positively correlated with plant biomass and played an important role in Pb tolerance of T. repens. In addition, endophytic bacteria formed complex correlation networks with growth and physiological indexes of both root and shoot, moreover the network in root was more complicated. Taken together, Pb stress dose-dependently inhibited the growth of plants. This study provided a theoretical basis for the further development of microbial cooperation with plant remediation of heavy metal contaminated soil.

Microbial Responses to Biochar Soil Amendment and Influential Factors: A Three-Level Meta-Analysis

Biochar is a multifunctional soil conditioner capable of enhancing soil health and crop production while reducing greenhouse gas emissions. Understanding how soil microbes respond to biochar amendment is a vital step toward precision biochar application. Here, we quantitatively synthesized 3899 observations of 24 microbial responses from 61 primary studies worldwide. Biochar significantly boosts microbial abundance [microbial biomass carbon (MBC) > colony-forming unit (CFU)] and C- and N-cycling functions (dehydrogenase > cellulase > urease > invertase > nirS) and increases the potential nitrification rate by 40.8% while reducing cumulative N2O by 12.7%. Biochar derived at lower pyrolysis temperatures can better improve dehydrogenase and acid phosphatase and thus nutrient retention, but it also leads to more cumulative CO2. Biochar derived from lignocellulose or agricultural biomass can better inhibit N2O through modulating denitrification genes nirS and nosZ; repeated biochar amendment may be needed as inhibition is stronger in shorter durations. This study contributes to our understanding of microbial responses to soil biochar amendment and highlights the promise of purpose-driven biochar production and application in sustainable agriculture such that biochar preparation can be tuned to elicit the desired soil microbial responses, and an amendment plan can be optimized to invoke multiple benefits. We also discussed current knowledge gaps and future research needs.

Promoting plant resilience against stress by engineering root microenvironment with Streptomyces inoculants

Plant growth is directly influenced by biotic and abiotic stress factors resulting from environmental changes. Plant growth-promoting rhizobacteria (PGPR) have become a crucial area of research aimed at addressing these challenges. However, a knowledge gap exists regarding how PGPR impacts the microenvironments surrounding plant roots. The purpose of this study is to elucidate the effects of two distinct PGPR strains, Streptomyces griseorubiginosus BTU6 (known for its resistance to smut disease) and S. chartreusis WZS021, on sugarcane roots. Additionally, we compare the resultant modifications in the physicochemical characteristics of the rhizospheric soil and root architecture. The results reveal that following the inoculation of S. chartreusis WZS021, there was a significant increase in the active chemicals associated with nitrogen metabolism in sugarcane roots. This enhancement led to a substantial enrichment of nitrogen-cycling microbes like Pseudomonas and Gemmatimona. This finding supports earlier research indicating that S. chartreusis WZS021 enhances sugarcane's capacity to utilize nitrogen effectively. Furthermore, after treatment with S. chartreusis, Aspergillus became the predominant strain among endophytic fungi, resulting in alterations to their community structure that conferred drought resistance. In contrast, the relative abundance of Xanthomonas in the root environment decreased following inoculation with S. griseorubiginosus. Instead, Gemmatimona became more prevalent, creating a favorable environment for plants to bolster their resistance against disease. Notably, inoculations with S. chartreusis WZS021 and S. griseorubiginosus BTU6 led to substantial changes in the chemical composition, enzymatic activity, and microbial community composition in the soil surrounding sugarcane roots. However, there were distinct differences in the specific alterations induced by each strain. These findings enhance plant resilience to stress by shedding light on PGPR-mediated modifications in root microenvironments.

Garbage to Gains: The role of biochar in sustainable soil quality improvement, arsenic remediation, and crop yield enhancement

Threats of soil quality deterioration and metal pollution have inflicted several parts of the world, apart from the need for surplus crop production. The investigation used biochar prepared from waste biomasses such as wheat and rice straw, kitchen waste, leaf litter, Lantana camara, orange peel, and walnut shell to improve soil quality, reduce As pollution, and enhance plant growth. Biochars were amended at doses of 0%, 2.5%, 5%, and 7.5% and conditioned for 3 months. At a 7.5% dose, the maximum improvements in cation exchange capacity (a 62% increase), anion exchange capacity (a two-fold increase), bulk density (a 31% decrease), porosity (a 32% increase), water holding capacity (an 86% increase), soil respiration (a 32% increase), total carbon (a two-and-a-half-fold increase), total nitrogen (an eleven-fold increase), total phosphorus (3 times rise), total potassium (a two-and-a-half-fold increase), mobile As (a 38% decrease), leachable As (a 53% decrease), and bio-available As (a 56% decrease) were observed. Further, pot experiments revealed augmented biomass growth (61% and 177%), increased length (71% and 209%), and decreased As accumulation (56% and 55%) in the above-ground parts of Bengal gram and coriander plants, respectively. Therefore, the application of biochar was found to enhance the physico-chemical properties of soil, reduce As contamination levels, and improve crop growth. The study recommends using waste biomasses to prepare eco-friendly biochars, which could contribute to advancing sustainable agriculture and the circular economy.

Application of biochar in microbial fuel cells: Characteristic performances, electron-transfer mechanism, and environmental and economic assessments

Biochar is a by-product of thermochemical conversion of biomass or other carbonaceous materials. Recently, it has garnered extensive attention for its high application potential in microbial fuel cell (MFC) systems owing to its high conductivity and low cost. However, the effects of biochar on MFC system performance have not been comprehensively reviewed, thereby necessitating the evaluation of the efficacy of biochar application in MFCs. In this review, biochar characteristics were outlined based on recent publications. Subsequently, various applications of biochar in the MFC systems and their probable processes were summarized. Finally, proposals for future applications of biochar in MFCs were explored along with its perspectives and an environmental evaluation in the context of a circular economy. The purpose of this review is to gain comprehensive insights into the application of biochar in the MFC systems, offering important viewpoints on the effective and steady utilization of biochar in MFCs for practical application.

Investigation of heavy metal and micro-macro element speciation in biomass ash enriched sewage sludge compost

The objective of this study was to enrich the nutrient content of compost and to investigate the passivation and solubilization of plant micronutrients (Fe, Al, Cu, Ni, Zn, Na, Mn), macroelements (P, K, Mg, Ca), and heavy metals (Cr, Cd, Pb) during sewage sludge composting with nutrient-rich biomass ash additives. T0: 0%, T1: 3.5%, T2: 7.0%, and T3: 14.0% dry weight (DW), weight/weight (w/w) biomass ash was added to the sewage sludge + sawdust mixture (volume, 1:1) to obtain the final NPK content and monitored over a 45-day period. Sawdust was used as auxiliary material. The sequential extraction method was used to determine the elemental species. Cr, Cd and Pb showed higher affinity to the residual fraction and occluded in the oxide fraction, which decreased the bioavailability factor (BF) (<1% BF-Cr, 21% BF-Cd and 9% BF-Pb) compared to the control treatment (46% BF-Cr, 47% BF-Cd and 80% BF-Pb). As the amount of biomass ash increased (T1-T3), the percentages of residual Cr (Res-Cr) (10-65%), exchangeable Cd (Exc-Cd) and organically bound Cd (Org-Cd) (14% and 21%), and oxides-Pb (Oxi-Pb) (20-61%) increased. In all composts, Fe, Al, and Cu were associated with organically bound and oxides-entrapped fractions. More than 50% of total Mn and Mg were concentrated mainly in exchangeable fractions, suggesting high mobility and bioavailability (42% BF-Mn and 98% BF-Mg). Ni, Zn, and Na tended to be present in oxide-bound, organically bound, and residual fractions, while K and P were associated with exchangeable and organically bound fractions. The overall results suggest that composting sewage sludge with biomass ash may be the best strategy and technique to overcome soil application bottlenecks because it passivates heavy metals and improves the bioavailability of plant nutrients.

Magnetic loofah sponge biochar facilitates microbial interspecies cooperation in surface and subsurface sediments for enhanced PAH biodegradation

Magnetic biochar had been used for the bioremediation of polycyclic aromatic hydrocarbon (PAH)-contaminated sediments. However, the long-term remediation pattern of vertical stratification driven by the application of magnetic biochar and the assembly of microbes had received little attention. In this study, magnetic loofah sponge biochar (MagLsBC), magnetic iron oxide (MagOx) and magnetic coconut shell activated carbon (MagCoAC) were applied for the 900-day remediation of contaminated sediments. Significant (p < 0.05) PAH biodegradation was observed in both the surface and subsurface sediments with MagLsBC addition. However, enhanced PAH biodegradation was observed only in the surface sediments with MagOx and MagCoAC treatments. Magnetotactic bacteria (Magnetococcus) was dominant genera in surface sediments and indigenous PAH degradation bacteria were more abundant in subsurface sediments of MagLsBC relative to other bacterial communities. The network interaction between microbes in surface and subsurface sediments with MagLsBC treatments was a less complex and tighter than those with MagCoAC, MagOx or Control treatments. Long-distance electron transfer rates could be enhanced through cooperation between magnetotactic bacteria and indigenous degradation bacteria, thus accelerating PAH degradation in sediment with MagLsBC treatment, especially in the underlying sediment.

Differential effects of cow dung and its biochar on Populus euphratica soil phosphorus effectiveness, bacterial community diversity and functional genes for phosphorus conversion

Introduction

Continuous monoculture leading to soil nutrient depletion may cause a decline in plantation productivity. Cow dung is typically used as a cheap renewable resource to improve soil nutrient status. In this study, our purpose was to compare the effects of different cow dung return methods (direct return and carbonization return) on soil microbial communities and phosphorus availability in the root zone (rhizosphere soil and non-rhizosphere soil) of P.euphratica seedlings in forest gardens and to explore possible chemical and microbial mechanisms.

Methods

Field experiments were conducted. Two-year-old P.euphratica seedlings were planted in the soil together with 7.5 t hm-2 of cow dung and biochar made from the same amount of cow dung.

Results

Our findings indicated that the available phosphorus content in soil subjected to biochar treatment was considerably greater than that directly treated with cow dung, leading to an increase in the phosphorus level of both aboveground and underground components of P.euphratica seedlings. The content of Olsen-P in rhizosphere and non-rhizosphere soil increased by 134% and 110%, respectively.This was primarily a result of the direct and indirect impact of biochar on soil characteristics. Biochar increased the biodiversity of rhizosphere and non-rhizosphere soil bacteria compared with the direct return of cow dung. The Shannon diversity index of carbonized cow manure returning to field is 1.11 times and 1.10 times of that of direct cow manure returning to field and control, and the Chao1 diversity index is 1.20 times and 1.15 times of that of direct cow manure returning to field and control.Compared to the direct addition of cow dung, the addition of biochar increased the copy number of the phosphorus functional genes phoC and pqqc in the rhizosphere soil. In the biochar treatment, the abundance of the phosphate-solubilizing bacteria Sphingomonas and Lactobacillus was significantly higher than that in the other treatments, it is relative abundance was 4.83% and 2.62%, respectively, which indirectly improved soil phosphorus availability.

Discussion

The results indicated that different cow dung return methods may exert different effects on phosphorus availability in rhizosphere and non-rhizosphere soils via chemical and microbial pathways. These findings indicated that, compared to the direct return of cow dung, biochar return may exert a more significant impact on the availability of phosphorus in both rhizosphere and non-rhizosphere soils, as well as on the growth of P.euphratica seedlings and the microbial community.

Biochar improves the growth and physiological traits of alfalfa, amaranth and maize grown under salt stress

Purpose

Salinity is a main factor in decreasing seed germination, plant growth and yield. Salinity stress is a major problem for economic crops, as it can reduce crop yields and quality. Salinity stress occurs when the soil or water in which a crop is grown has a high salt content. Biochar improve plant growth and physiological traits under salt stress. The aim of the present study, the impact of biochar on growth, root morphological traits and physiological properties of alfalfa, amaranth and maize and soil enzyme activities under saline sands.

Methods

We studied the impact of biochar on plant growth and the physiological properties of alfalfa, amaranth and maize under salt stress conditions. After 40 days, plant growth parameters (plant height, shoot and root fresh weights), root morphological traits and physiological properties were measured. Soil nutrients such as the P, K and total N contents in soil and soil enzyme activities were analyzed.

Results

The results showed that the maize, alfalfa, and amaranth under biochar treatments significantly enhanced the plant height and root morphological traits over the control. The biochar on significantly increased the total root length, root diameter, and root volume. Compared to the control, the biochar significantly increased the chlorophyll a and b content, total chlorophyll and carotenoid content under salt stress. Furthermore, the biochar significantly increased enzyme activities of soil under salt stress in the three crops.

Conclusions

Biochar treatments promote plant growth and physiological traits of alfalfa, amaranth, and maize under the salt stress condition. Overall, biochar is an effective way to mitigate salinity stress in crops. It can help to reduce the amount of salt in the soil, improve the soil structure, and increase the availability of essential nutrients, which can all help to improve crop yields.

Exploring biochar and fishpond sediments potential to change soil phosphorus fractions and availability

Phosphorus (P) availability in soil is paradoxical, with a significant portion of applied P accumulating in the soil, potentially affecting plant production. The impact of biochar (BR) and fishpond sediments (FPS) as fertilizers on P fixation remains unclear. This study aimed to determine the optimal ratio of BR, modified biochar (MBR), and FPS as fertilizer replacements. A pot experiment with maize evaluated the transformation of P into inorganic (Pi) and organic (Po) fractions and their contribution to P uptake. Different percentages of FPS, BR, and MBR were applied as treatments (T1-T7), T1 [(0.0)], T2 [FPS (25.0%)], T3 [FPS (25.0%) + BR (1%)], T [FPS (25%) +MBR (3%)], T5 [FPS (35%)], T6 [FPS (35%) +BR (1%)], and T7 [FPS (35%) + MBR (1%)]. Using the modified Hedley method and the Tiessen and Moir fractionation scheme, P fractions were determined. Results showed that various rates of MBR, BR, and FPS significantly increased labile and moderately labile P fractions (NaHCO3-Pi, NaHCO3-Po, HClD-Pi, and HClC-Pi) and residual P fractions compared with the control (T1). Positive correlations were observed between P uptake, phosphatase enzyme activity, and NaHCO3-Pi. Maximum P uptake and phosphatase activity were observed in T6 and T7 treatments. The addition of BR, MBR, and FPS increased Po fractions. Unlike the decline in NaOH-Po fraction, NaHCO3-Po and HClc-Po fractions increased. All Pi fractions, particularly apatite (HClD-Pi), increased across the T1-T7 treatments. HClD-Pi was the largest contributor to total P (40.7%) and can convert into accessible P over time. The T5 treatment showed a 0.88% rise in residual P. HClD-Pi and residual P fractions positively correlated with P uptake, phosphatase activity, NaOH-Pi, and NaOH-Po moderately available fractions. Regression analysis revealed that higher concentrations of metals such as Ca, Zn, and Cr significantly decreased labile organic and inorganic P fractions (NaHCO3-Pi, R 2 = 0.13, 0.36, 0.09) and their availability (NaHCO3-Po, R 2 = 0.01, 0.03, 0.25). Excessive solo BR amendments did not consistently increase P availability, but optimal simple and MBR increased residual P contents in moderately labile and labile forms (including NaOH-Pi, NaHCO3-Pi, and HClD-Pi). Overall, our findings suggest that the co-addition of BR and FPS can enhance soil P availability via increasing the activity of phosphatase enzyme, thereby enhancing plant P uptake and use efficiency, which eventually maintains the provision of ecosystem functions and services.

Biochar Derived from Post-Adsorbent for Immobilizing Cu and Cd in Sediment: The Effect on Heavy Metal Species and the Microbial Community Composition

Many biomass wastes or their modified forms have been investigated as heavy metal adsorbents. However, less emphasis has been placed on post-adsorbent management or possible further utilization. In this study, biochar (BC) derived from modified bamboo adsorbent after the adsorption of Cu from an aqueous solution was used for the in situ remediation of lake sediment contaminated with Cd and Cu. The results indicated that the Cu concentration was extremely low (≤0.015 mg/L), while Cd was not detected in the overlying water or the interstitial water after the 90-day BC treatment. The pH value (7.5-8.1) slightly increased, and the toxicity characteristic leaching procedure (TCLP) leachability of the Cu and Cd in the sediment decreased overall. Cu and Cd were preferentially transformed into more stable species. The findings highlighted the potential possibility of BC derived from post-adsorbent being used for sediment remediation. However, the BC addition produced significant effects on the sediment microbial activity and community structure. In general, with an increase in BC, the urease activity increased, while the alkaline phosphatase and invertase activity decreased, which could be attributed to the BC itself. In addition, significant changes in both bacterial and fungal genera were observed. Hence, a cautious approach should be taken in the practical application of BC.

Biochar supported nanoscale zero-valent iron for the kinetics removal and mechanism of decabromodiphenyl ethane in the sediment

The extensive applications of decabromodiphenyl ethane (DBDPE), a novel brominated flame retardant, have induced its accumulation in sediment, which may have a great negative impact on the ecological environment. In this work, the biochar/nano-zero-valent iron materials (BC/nZVI) were synthesized to remove DBDPE in the sediment. Batch experiments were carried out to investigate the influencing factors of the removal efficiency, and kinetic model simulation and thermodynamic parameter calculation were performed. The degradation products and mechanisms were probed. The results indicated that the addition of 0.10 g·g-1 BC/nZVI to the sediment with an initial concentration of 10 mg·kg-1 DBDPE could remove 43.73% of DBDPE during 24 h. The water content of the sediment was a critical factor in the removal of DBDPE, which was optimal at 1:2 of sediment to water. The removal efficiency and reaction rate were enhanced by increasing dosage, water content, and reaction temperature or decreasing initial concentration of DBDPE based on the fitting results of the quasi-first-order kinetic model. Additionally, the calculated thermodynamic parameters suggested that the removal process was a spontaneously and reversibly endothermic reaction. The degradation products were further determined by GC-MS, and the mechanisms were presumed that DBDPE was debrominated to produce octabromodiphenyl ethane (octa-BDPE). This study provides a potential remediation method for highly DBDPE-contaminated sediment by using BC/nZVI.

Bioremediation system consisted with Leclercia adecarboxylata and nZVI@Carbon/Phosphate for lead immobilization: The passivation mechanisms of chemical reaction and biological metabolism in soil

Bioremediation is one of the most promising strategies for heavy metal immobilization. A new remediation system was demonstrated in this research, which combined phosphate solubilizing bacteria (PSB) with nZVI@Carbon/Phosphate (nZVI@C/P) composite to remediate lead contaminated soil. Experimental results indicated that the new system (nZVI@C/P + PSB) could effectively convert the labile Pb into the stable fraction after 30 days of incubation, which increased the maximum residual fraction percentage of Pb by 70.58%. The characterization results showed that lead may exist in the forms of Pb₅(PO₄)₃Cl, PbSO₄ and 3PbCO₃·2Pb(OH)₂·H₂O in the soil treated with nZVI@C/P + PSB. Meanwhile, soil enzyme activities and Leclercia abundance were enhanced in the treated soil compared with CK during the incubation time. In addition, the specialized functions (e.g. ABC transporters, siderophore metabolism, sulfur metabolism and phosphorus metabolism) in PSB and nZVI@C/P + PSB group were also enhanced. These phenomena proved that the key soil metabolic functions may be maintained and enhanced through the synergistic effect of incubated PSB and nZVI@C/P. The study demonstrated that this new bioremediation system provided feasible way to improve the efficacy for lead contaminated soil remediation.

The Difference between Rhizosphere and Endophytic Bacteria on the Safe Cultivation of Lettuce in Cr-Contaminated Farmland

Chromium (Cr) is a major pollutant affecting the environment and human health and microbial remediation is considered to be the most promising technology for the restoration of the heavily metal-polluted soil. However, the difference between rhizosphere and endophytic bacteria on the potential of crop safety production in Cr-contaminated farmland is not clearly elucidated. Therefore, eight Cr-tolerant endophytic strains of three species: Serratia (SR-1~2), Lysinebacillus (LB-1~5) and Pseudomonas (PA-1) were isolated from rice and maize. Additionally, one Cr-tolerant strain of Alcaligenes faecalis (AF-1) was isolated from the rhizosphere of maize. A randomized group pot experiment with heavily Cr-contaminated (a total Cr concentration of 1020.18 mg kg^-1) paddy clay soil was conducted and the effects of different bacteria on plant growth, absorption and accumulation of Cr in lettuce (Lactuca sativa var. Hort) were compared. The results show that: (i) the addition of SR-2, PA-1 and LB-5 could promote the accumulation of plant fresh weight by 10.3%, 13.5% and 14.2%, respectively; (ii) most of the bacteria could significantly increase the activities of rhizosphere soil catalase and sucrase, among which LB-1 promotes catalase activity by 224.60% and PA-1 increases sucrase activity by 247%; (iii) AF-1, SR-1, LB-1, SR-2, LB-2, LB-3, LB-4 and LB-5 strains could significantly decrease shoot the Cr concentration by 19.2-83.6%. The results reveal that Cr-tolerant bacteria have good potential to reduce shoot Cr concentration at the heavily contaminated soil and endophytic bacteria have the same or even better effects than rhizosphere bacteria; this suggests that bacteria in plants are more ecological friendly than bacteria in soil, thus aiming to safely produce crops in Cr-polluted farmland and alleviate Cr contamination from the food chain.

Carbon content determines the aggregation of biochar colloids from various feedstocks

The aggregation kinetics of biochar colloids (BCs) play a crucial role in the fate and transport of contaminants, as well as the carbon (C) cycle in the environment. However, the colloidal stability of BCs from various feedstocks is very limited. In this study, the critical coagulation concentration (CCC) of twelve standard biochars pyrolyzed from various feedstocks (municipal source, agricultural waste, herbaceous residue, and woody feedstock) at 550 °C and 700 °C were investigated, and the relationship between the physicochemical characteristics of biochar and the colloidal stability of BCs was further analyzed. The CCC of BCs in the NaCl solution followed the trend of municipal source < agricultural waste < herbaceous residue < woody feedstock, which was similar to the order of C content in biochar. The CCC of BCs showed a strong positive correlation with the C content of various biochars, especially pyrolyzed at a higher temperature of 700 °C. The BCs derived from lignin-rich feedstock (e.g., woody feedstock) had the highest colloidal stability, followed by cellulose-rich feedstock (e.g., agricultural waste and herbaceous residue). The BCs derived from organic matter-rich feedstock (municipal source) were easy to aggregate in the aqueous environment. This study quantitatively provides new insights into the relationship between BCs stability and biochar characteristics from various feedstocks, which is critical to assess biochar environmental behavior in aqueous environments.

Comparative study on plant growth-promoting bacterial inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium-contaminated soil

A field study was conducted to compare FM-1 inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium (Cd)-contaminated soil. Cascading relationships between bacterial inoculation by irrigation and spraying and soil properties, plant growth-promoting traits, plant biomass and Cd concentrations in Bidens pilosa L. were explored based on the partial least squares path model (PLS-PM). The results indicated that inoculation with FM-1 not only improved the rhizosphere soil environment of B. pilosa L. but also increased the Cd extracted from the soil. Moreover, Fe and P in leaves play vital roles in promoting plant growth when FM-1 is inoculated by irrigation, while Fe in leaves and stems plays a vital role in promoting plant growth when FM-1 is inoculated by spraying. In addition, FM-1 inoculation decreased the soil pH by affecting soil dehydrogenase and oxalic acid in cases with irrigation and Fe in roots in cases with spraying. Thus, the soil bioavailable Cd content increased and promoted Cd uptake by Bidens pilosa L. To address Cd-induced oxidative stress, Fe in leaves helped to convert GSH into PCs, which played a vital role in ROS scavenging when FM-1 was inoculated by irrigation. The soil urease content effectively increased the POD and APX activities in the leaves of Bidens pilosa L., which helped alleviate Cd-induced oxidative stress when FM-1 was inoculated by spraying. This study compares and illustrates the potential mechanism by which FM-1 inoculation can improve the phytoremediation of Cd-contaminated soil by Bidens pilosa L., suggesting that FM-1 inoculation by irrigation and spraying is useful in the phytoremediation of Cd-contaminated sites.

Treatment of produced water using Mn oxide nanoparticales loaded on walnut shells

Sorption of ²²⁶Ra from produced water with oil production on manganese oxide nanoparticles loaded on walnut shell media was investigated using batch-type technique. The results showed that ²²⁶Ra is effectively adsorbed onto the adsorbent with equilibrium time of approximately 30 min. Removal efficiency of ²²⁶Ra from produced water depends mainly on the adsorbent dose and concentration of associated ions; removal efficiency decreased when their concentrations increase. The maximum adsorption capacity is reached 58 Bq g^-1. The adsorbent is effective and suitable for removing ²²⁶Ra ions from the produced water under the studied conditions in this work.

Remediation of Cu and As contaminated water and soil utilizing biochar supported layered double hydroxide: Mechanisms and soil environment altering

Preparing materials for simultaneous remediation of anionic and cationic heavy metals contamination has always been the focus of research. Herein a biochar supported FeMnMg layered double hydroxide (LDH) composites (LB) for simultaneous remediation of copper and arsenic contamination in water and soil has been assembled by a facile co-precipitation approach. Both adsorption isotherm and kinetics studies of heavy metals removal by LB were applied to look into the adsorption performance of adsorbents in water. Moreover, the adsorption mechanisms of Cu and As by LB were investigated, showing that Cu in aqueous solution was removed by the isomorphic substitution, precipitation and electrostatic adsorption while As was removed by complexation. In addition, the availability of Cu and As in the soil incubation experiments was reduced by 35.54%-63.00% and 8.39%-29.04%, respectively by using LB. Meanwhile, the addition of LB increased the activities of urease and sucrase by 93.78%-374.35% and 84.35%-520.04%, respectively, of which 1% of the dosage was the best. A phenomenon was found that the richness and structure of microbial community became vigorous within 1% dosage of LB, which indirectly enhanced the passivation and stabilization of heavy metals. These results indicated that the soil environment was significantly improved by LB. This research demonstrates that LB would be an imaginably forceful material for the remediation of anionic and cationic heavy metals in contaminated water and soil.

CaFe-layered double hydroxide corn straw biochar reduced heavy metal uptake by Brassica campestris L. and Ipomoea aquatic F.: Rhizosphere effects and oxidative stress alleviation

In the present study, CaFe-layered double hydroxide corn straw biochar (CaFe-LDH@CSB) was applied to the rhizosphere soil of both pakchoi (Brassica campestris L. ssp. Chinensis Makino, B. campestris L.) and water spinach (Ipomoea aquatic F., I. aquatic F.) to explore and clarify the potential mechanism by which CaFe-LDH@CSB helps vegetables reduce heavy metal (HM) uptake and alleviate oxidative stress. Pot experiments were conducted with CaFe-LDH@CSB applied at four levels: control (CK), T1 (5 g kg^-1), T2 (10 g kg^-1) and T3 (20 g kg^-1). The results indicated that the application of CaFe-LDH@CSB significantly increased pH and decreased the acid-soluble forms of Cd, Pb, Zn and Cu in the rhizosphere soil of both B. campestris L. and I. aquatic F.; decreases of 39.4%, 18.0%, 10.0% and 33.3% in B. campestris L. and of 26.6%, 49.1%, 13.2% and 36.8% in I. aquatic F., respectively, were observed at the T3 level. Moreover, CaFe-LDH@CSB application reduced HM uptake by B. campestris L. and decreased HM-induced oxidative stress through the regulation of soil physicochemical properties and microbial abundance. For B. campestris L., variations in Sordariomycetes helped alleviate the accumulation of HMs in the aerial part, while GSH and -SH from the nonenzymatic system played an important role in scavenging H₂O₂ in leaves, thus helping B. campestris L. alleviate HM-induced oxidative stress. For I. aquatica F., variations in Vicinamibacteria and Mortierellomycetes helped alleviate the accumulation of HMs in plants, while GSH and PCs from nonenzymatic systems played an important role in removing ·O₂^- in leaves, thereby helping I. aquatica F. alleviate HM-induced oxidation stress. Our study indicated that the application of CaFe-LDH@CSB improved the rhizosphere soil environment and rebuilt the soil microbial community, helping B. campestris L. and I. aquatica F. alleviate HM-induced oxidative stress and promoting the growth of both vegetables.

Insight into the Speciation of Heavy Metals in the Contaminated Soil Incubated with Corn Cob-Derived Biochar and Apatite

Soil heavy metal contamination is a severe issue. The detrimental impact of contaminated heavy metals on the ecosystem depends on the chemical form of heavy metals. Biochar produced at 400 °C (CB400) and 600 °C (CB600) from corn cob was applied to remediate Pb and Zn in contaminated soil. After a one month amendment with biochar (CB400 and CB600) and apatite (AP) with the ratio of 3%, 5%, 10%, and 3:3% and 5:5% of the weight of biochar and apatite, the untreated and treated soil were extracted using Tessier's sequence extraction procedure. The five chemical fractions of the Tessier procedure were the exchangeable fraction (F1), carbonate fraction (F2), Fe/Mn oxide fraction (F3), organic matter (F4), and residual fraction (F5). The concentration of heavy metals in the five chemical fractions was analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). The results showed that the total concentration of Pb and Zn in the soil was 3023.70 ± 98.60 mg kg^-1 and 2034.33 ± 35.41 mg kg^-1, respectively. These figures were 15.12 and 6.78 times higher than the limit standard set by the United States Environmental Protection Agency (U.S. EPA 2010), indicating the high level of contamination of Pb and Zn in the studied soil. The treated soil's pH, OC, and EC increased significantly compared to the untreated soil (p > 0.05). The chemical fraction of Pb and Zn was in the descending sequence of F2 (67%) > F5 (13%) > F1 (10%) > F3 (9%) > F4 (1%) and F2~F3 (28%) > F5 (27%) > F1 (16%) > F4 (0.4%), respectively. The amendment of BC400, BC600, and apatite significantly reduced the exchangeable fraction of Pb and Zn and increased the other stable fractions including F3, F4, and F5, especially at the rate of 10% of biochar and a combination of 5:5% of biochar and apatite. The effects of CB400 and CB600 on the reduction in the exchangeable fraction of Pb and Zn were almost the same (p > 0.05). The results showed that CB400, CB600, and the mixture of these biochars with apatite applied at 5% or 10% (w/w) could immobilize lead and zinc in soil and reduce the threat to the surrounding environment. Therefore, biochar derived from corn cob and apatite could be promising materials for immobilizing heavy metals in multiple-contaminated soil.

Biochar-mediated abiotic and biotic degradation of halogenated organic contaminants - A review

Prevailing global increases in population, urbanization, and agricultural production are causing increased pressures on water resources, especially as the use of chemicals in agriculture, industry, and medicine provide new challenges for water treatment and reuse. Organohalogen compounds are persistent contaminants that often evade current wastewater treatment technologies, resulting in their accumulation in the environment and posing a serious threat to ecosystem health. Recent advances in understanding pyrogenic carbons as electron shuttling and storing materials have exposed their potential for enhancing the dehalogenation and overall degradation of organohalide contaminants in soil, sediment, surface water, and wastewater systems. Biochar is a porous carbonaceous material produced during the thermochemical decomposition of biomass feedstock in the presence of little or no oxygen (pyrolysis). Interest in biochar for application towards environmental remediation is largely based on its three distinct benefits: I) carbon sequestration to offset greenhouse gas emissions, II) adsorption of (in-) organic contaminants and nutrients, and III) a strong electron exchange capacity. Due to the innate complexity of biochar materials, several electron transfer mechanisms exist by which biochar may mediate contaminant degradation. These electron transfer pathways include electron-accepting and donating cycles through redox-active functional groups and direct electron transfer via conductive carbon matrices. These mechanisms are responsible for biochar's participation in multiple redox-driven biogeochemical transformations with proven consequences for effective organohalogen remediation. This literature review summarizes the current knowledge on the mechanisms and processes through which biochar can directly or indirectly mediate the transformation of organohalogen compounds under various environmental conditions. Perspectives and research directions for future application of biochars for targeted remediation strategies are also discussed.

Removing Lead from Contaminated Sediment Using Indium-Based Perovskite Precursor

Heavy metal pollution in river and lake sediments seriously damages river ecological safety and indirectly affects human health. The existing research mainly focuses on how to adsorb pollutants and repair sediment, and how the reuse of these pollutants may be a new technology to control sediment pollutants. The rapid development of perovskite solar cells in recent years has attracted a lot of attention, among which lead (Pb) halide perovskites have very excellent photoelectric performance. In this study, we propose a novel idea of introducing indium (In)-based perovskite to replace Pb (II) ions dispersed in river and lake sediment. Three sediment samples from a river in Shanghai Peace Park were collected to analyze the distribution of heavy metal Pb. We mixed the digestion solution of sediment with the prepared CH₃NH₃(MA)InICl₂ solution and found that indium (In) in perovskite precursor solution would be gradually replaced by Pb in sediments. An in situ synchrotron radiation XRD experiment was performed to reveal the reaction mechanism of solutions and provide a good research platform for the comprehensive reuse of sediment in the future. This study provides a new method of remediation of heavy metal pollution in river and lake sediments.

A critical review on biochar-based catalysts for the abatement of toxic pollutants from water via advanced oxidation processes (AOPs)

Proper waste disposal is a key towards sustainable development. Wastewater treatment is delineated by the application of efficient, economic and novel catalysts. Biochar is derived from the thermochemical conversion of biomass or any carbonaceous materials and is considered as one of the most eco-friendly substitute for activated carbon. Owing to its large surface area, porosity, crystallinity and active functional groups, the biochar-based catalysts has been extensively applied for the abatement of toxic pollutants from wastewater streams. While most of the reviews focus on the adsorptive properties of the biochar, this review critically analyses the recent development of biochar-based catalysts in the field of advanced oxidation processes (Fenton-like systems, photocatalytic and sonocatalytic systems). The presence of persistent free radicals and oxygen-containing functional groups renders biochar to act as catalyst. The mechanisms accompanying catalytic performance of biochar-based catalysts have also been reviewed. However, the research in this area is quite at an initial phase, and many advancements schemes are essential prior to scale-up and commercialization. Future researches should be devoted to more efficient and rigorous understanding of the structural properties of biochar to engineer the catalytic degradation of targeted pollutants in wastewater treatment.

The Influence of the Reduction in Clay Sediments in the Level of Metals Bioavailability-An Investigation in Liujiang River Basin after Wet Season

The seasonal elevation of metals' bioavailability can aggravate the threat of metal contamination in the aquatic environment. Nevertheless, their regulations have rarely been studied, particularly the connections between metals' transformation and environmental variations. Therefore, the catchment area of Liujiang River was taken as an example in this study, their seasonal variations in metals' bioavailability in sediments, especially during the wet season, was investigated to recover the processes associated with metals' speciations and multiple environmental factors. The results revealed that the concentration of metals in sediments were high overall in the wet season, but low in the dry season. The significantly reduced ratio of metals in non-residual forms was largely related to the overall reduction in metals in oxidizable and reducible forms after the wet season. However, the elevated BI indexes of most metals suggested their increased bioavailability in the dry season, which should be closely related to their corresponding elevations in carbonate-bound and exchangeable forms after the wet season. The variations in metals' bioavailability were primarily related to their predominance of exchangeable and carbonate-bound form. The higher correlation coefficients suggested the destabilization of the oxidizable form should be treated as a critical approach to the impact of metals' bioavailability after the wet season. In view of that, sediments' coarsening would pose the impacts on the destabilization of exogenous metals in sediments, the reduction in clay sediments should be responsible for the elevation of metals bioavailability after the wet season. Therefore, the monitoring of metals' bioavailability in sediments should be indispensable to prevent metal contamination from enlarging the scope of their threat to the aquatic environment of the river, especially after the wet season.

The profiles of chiral pesticides in peri-urban areas near Yangtze River: Enantioselective distribution characteristics and correlations with surface sediments

Chiral pesticides account for 30% of pesticides. Pesticides are inevitably leached into the groundwater by runoff. At the watershed level, the distribution characteristics of enantiomers in sediments collected from the river network of an agricultural area near the middle and lower reaches of the Yangtze River were tested, and their potential correlations with the physicochemical properties and microbial communities of the sediments were analyzed. The sediment pollution was serious at sites 8 and 9, with their pollution source possibly being agricultural or industrial sewage. Moreover, there were higher cumulative contents of pesticide residues at sites 4, 8, and 9. Specifically, Cycloxaprid was the most detected chiral pesticide in the study area, followed by Dinotefuran and Diclofop-methyl. Additionally, Ethiprole and Difenoconazole had strong enantioselectivity in the study area. Interestingly, the enantiomers of some chiral pesticides, such as Tebuconazole, had completely different distributions at different sites. Pearson correlation analysis showed that sediment catalase and microbial biomass carbon were important factors for enantioselectivity of chiral pesticides. The effect of sediment physicochemical properties on enantioselective distribution was achieved by influencing the microorganisms in the sediment. Furthermore, the enantioselective distribution of Tebuconazole was closely related to the genus Arenimonas. Overall, the enantioselective distribution of most of the chiral pesticides was positively correlated with the prokaryotic microbial community. This study provides empirical support for agricultural non-point source pollution caused by chiral pesticides, and also lays a research foundation for exploring the factors that affect the fate of chiral pesticides in the environment.

Effect of nanohydroxyapatite/biochar/sodium humate composite on phosphorus availability and microbial community in sandy soils

Phosphorus (P) is essential for crop growth as an indispensable nutrient; however, there has been growing concern over the low use efficiency of P used in current fertilizers. We synthesized and characterized a potential P fertilizer nanohydroxyapatite/biochar/sodium humate (nHAP/BC/HANa) composite. To study the impact of the composite on soil chemical properties and microbial community in sandy soils, we set up four treatments as follows: (1) biochar (BC), (2) nanohydroxyapatite (nHAP), (3) nHAP/BC/HANa composite, and (4) sodium humate (HANa) was added separately into soils amended with nHAP/BC (nHAP/BC + HANa) to compare its performance with that of the nHAP/BC/HANa composite. A key finding was that the nHAP/BC/HANa composite not only significantly increased the soil available P content and alkaline phosphatase activity but also the increased organic matter content compared to the control. Additionally, leaching losses of P in soils amended with the nHAP/BC/HANa composite were lower than those in soils amended with the nHAP/BC + HANa, which suggested that the nHAP/BC/HANa composite had great potential to decrease P loss in sandy soils. Moreover, bacterial communities were more sensitive than fungal communities to all treatments. The bacterial communities showed the most significant changes in the nHAP/BC/HANa treatments. Results from Mantel tests further indicated that the strongest correlation between bacterial communities and soil properties occurring in the nHAP/BC/HANa treatments. Random forest analysis was conducted to identify the dominant microbial taxa, such as Proteobacteria, Acidobacteria, and Gemmatimonadetes, for predicting changes in soil properties. There was an asymptotical transition in bacterial community assembly processes from stochastic to deterministic in the nHAP/BC/HANa treatments. In conclusion, we demonstrated that nHAP/BC/HANa composite had the remarkable contribution to soil P availability in sandy soils, and simultaneously promoted the bacterial functions potential for P cycling, which present valuable insights to the development of potential P fertilizer.

Microbial-assisted soil chromium immobilization through zinc and iron-enriched rice husk biochar

Soil chromium toxicity usually caused by the tannery effluent compromises the environment and causes serious health hazards. The microbial role in strengthening biochar for its soil chromium immobilization remains largely unknown. Hence, this study evaluated the effectiveness of zinc and iron-enriched rice husk biochar (ZnBC and FeBC) with microbial combinations to facilitate the chromium immobilization in sandy loam soil. We performed morphological and molecular characterization of fungal [Trichoderma harzianum (F1), Trichoderma viride (F2)] and bacterial [Pseudomonas fluorescence (B1), Bacillus subtilis (B2)] species before their application as soil ameliorants. There were twenty-five treatments having ZnBC and FeBC @ 1.5 and 3% inoculated with bacterial and fungal isolates parallel to wastewater in triplicates. The soil analyses were conducted in three intervals each after 20, 30, and 40 days. The combination of FeBC 3%+F2 reduced the soil DTPA-extractable chromium by 96.8% after 40 days of incubation (DAI) relative to wastewater. Similarly, 92.81% reduction in chromium concentration was achieved through ZnBC 3%+B1 after 40 DAI compared to wastewater. Under the respective treatments, soil Cr(VI) retention trend increased with time such as 40 > 30 > 20 DAI. Langmuir adsorption isotherm verified the highest chromium adsorption capacity (41.6 mg g⁻¹) with FeBC 3% at 40 DAI. Likewise, principal component analysis (PCA) and heat map disclosed electrical conductivity-chromium positive, while cation exchange capacity-chromium and pH-organic matter negative correlations. PCA suggested the ZnBC-bacterial while FeBC-fungal combinations as effective Cr(VI) immobilizers with >70% data variance at 40 DAI. Overall, the study showed that microbes + ZnBC/FeBC resulted in low pH, high OM, and CEC, which ultimately played a role in maximum Cr(VI) adsorption from wastewater applied to the soil. The study also revealed the interrelation and alternations in soil dynamics with pollution control treatments. Based on primitive soil characteristics such as soil metal concentration, its acidity, and alkalinity, the selection criteria can be set for treatments application to regulate the soil properties. Additionally, FeBC with Trichoderma viride should be tested on the field scale to remediate the Cr(VI) toxicity.

Dynamics of fungal and bacterial communities in different types of soil ageing with different dosages of cadmium

This study investigated the structure of fungal and bacterial communities in different types of Cd-contaminated soils. The results showed that obvious variations in microbial structure between contaminated alkaline soils and acidic soils. Proteobacteria, Gemmatimonadetes, Bacteroidetes and Basidiomycota dominated the studied communities in the alkaline soils, whereas Actinobacteria, Chloroflexi, Firmicutes, Acidobacteria, Saccharibacteria and Ascomycota were more abundant in the acidic soils. Additionally, Cd tolerant (Proteobacteria, Bacteroidetes, Ascomycota) and sensitive (Actinobacteria, Acidobacteria, Basidiomycota) in alkaline soils and JL-soils, Cd tolerant (Actinobacteria, Acidobacteria, Basidiomycota) and sensitive (Saccharibacteria, Proteobacteria, Bacteroidetes, Ascomycota, Mucoromycota) in the acidic soils were identified. Redundancy analysis and correlation analysis demonstrated that it was significantly affected by different environment parameters in alkaline soils and acidic soils. Varied bacterial community structures in all soils were dominantly influenced by pH and SOM. The similarities among different groups indicated the effect of soil type on microbial community structure was greater than that of Cd level. The above conclusions may provide a new perspective for the bio-remediation of Cd in different types of soils.

Co-application of biochar and nitrogen fertilizer promotes rice performance, decreases cadmium availability, and shapes rhizosphere bacterial community in paddy soil

Cadmium (Cd) contamination in soil has posed a great threat to crop safety and yield as well as soil quality. Biochar blended with nitrogen fertilizer have been reported to be effective in remediating Cd-contaminated soil. However, the influence of co-application of biochar and nitrogen fertilizer on the Cd bioavailability, rice yield and soil microbiome remains unclear. In this study, eight different treatments including control (CK), 5% biochar (B), 2.6, 3.5, 4.4 g/pot nitrogen fertilizers (N1, N2 and N3), and co-application of biochar and nitrogen fertilizers (BN1, BN2, BN3) were performed in a pot experiment with paddy soil for observations in an entire rice cycle growth period. Results showed single N increased soil available Cd content and Cd uptake in edible part of rice, while the soil available Cd content significantly decreased by 14.8% and 7.4%-11.1% under the B, BN treatments, and the Cd content in edible part of rice was significantly reduced by 35.1% and 18.5%-26.5%, respectively. Besides, B, N and BN treatments significantly increased the yield of rice by 14.3%-86.6% compared with CK, and the highest yield was gained under BN3 treatment. Soil bacterial diversity indices (Shannon, Chao1, observed species and PD whole tree index) under N2, N3 were generally improved. Cluster analysis indicated that bacterial community structures under BN treatments differed from those of CK and single N treatments. BN treatments enhanced the abundances of key bacterial phylum such as Acidobacteria, positively associated with yield, and increased the abundance of Spirochaetes, negatively correlated to soil available Cd and Cd uptake of rice. Furthermore, the regression path analysis (RPA) revealed that pH, organic matter (OM), alkaline hydrolysis of nitrogen (AHN) and available Cd were the major properties influencing Cd content in edible part of rice. Redundancy analysis (RDA) revealed that pH and available Cd played key role in shaping soil bacterial community. Thus, BN is a feasible practice for the improvements of rice growth and remediation of Cd-polluted soil.

Sulfur enhances cadmium bioaccumulation in Cichorium intybus by altering soil properties, heavy metal availability and microbial community in contaminated alkaline soil

Cadmium (Cd) contamination seriously threatens the soil health and food safety. Combination of amendment and accumulator plant is a green and effective technique to improve phytoremediation of Cd-contaminated alkaline soil. In this study, a potting experiment was conducted to investigate the effect of sulfur on Cd phytoextraction by Cichorium intybus (chicory). Soil chemical and microbial properties were determined to reveal the mechanism of sulfur-assisting Cd phytoremediation by chicory. Soil pH decreased from 7.77 to the lowest 7.30 with sulfur addition (0.6, 0.9 and 1.2 g kg-1, LS, MS and HS treatment); Electric conductivity, sulfate anion and available cadmium concentration increased gradually with increasing sulfur doses. Cd concentration of shoot and root significantly increased from 1.47 to 4.43 mg kg-1, 6.15 to 20.16 mg kg-1 by sulfur treatment relative to CK, which were attributed to increased available Cd concentration induced by decreased pH. Sulfur treatments significantly increased the Cd bioconcentration factor by 64.1%, 118.6%, 201.0% for shoot, 76.3%, 145.6% and 227.7% for root under LS, MS and HS relative to CK treatment, respectively (P < 0.05). However, only MS treatment significantly improved the Cd removal efficiency by 82.9% in comparison of CK treatment (P < 0.05). Microbial community diversity measured by 16SrRNA showed that Thiobacillus and Actinobacteria were the key and dominant strains of soil microbial communities after sulfur addition, which played a pivotal role in the process of sulfur oxidation involved in decrease of soil pH and the transformation of Cd forms. Correlation analysis and path analysis by structural equation model indicated that soil sulfate anion and Thiobacillus directly affected Cd removal efficiency by chicory in Cd-contaminated alkaline soil. This suggests that combination of sulfur and chicory may provide a way to promote Cd bioaccumulation for phytoremediation of Cd-contaminated alkaline soil.

Effect of rice straw biochar on three different levels of Cd-contaminated soils: Cd availability, soil properties, and microbial communities

Biochar can be effective in immobilizing soil cadmium (Cd), but the difference in its immobilization mechanisms for different levels of Cd-contaminated soils was overlooked. In this study, rice straw biochar (BC) was added to three Cd-contaminated soils following 180 days of incubation, in the process of which the dynamic changes of Cd speciation, soil properties and microbial community diversity were determined. BC could significantly reduce the ratio of acid-soluble in the three soils, especially in light and medium Cd-contaminated soils by more than 20%. The addition of biochar could significantly increase the soil pH, soil organic matter, cation exchange capacity, and the activities of catalase, but decrease the richness and diversity of bacterial communities in all soils. The associations between microbial communities were inhibited in light and medium Cd-contaminated soils, but promoted in heavy Cd-contaminated soils. Furthermore, the main pathway of BC effect on soil Cd availability was also analyzed by partial least squares model (PLS-PM), which indicated that BC indirectly reduced Cd availability mainly by regulating the microbial community in light Cd-contaminated soil, whereas BC directly reduced Cd availability primarily by its own adsorption in medium and heavy Cd-contaminated soils. This research deepened understanding of the mechanisms of stabilization of Cd by biochar for agricultural soils.

Soil bacteria around a derelict tailings pile with different metal pollution gradients: community composition, metal tolerance and influencing factors

Bacteria play a vital role in ecological processes of soil contaminated by heavy metals. Here, soil sampling was carried out around a tailings pile contaminated to different degrees by cadmium (Cd), lead (Pb) and arsenic (As). The bacteria in the soil were cultured, separated and purified on Luria-Bertani medium, and the changes in bacterial communities in soils with different pollution levels were analysed with 16S rRNA sequencing. Bacillus pacificus strain MZ520364 was found to be highly tolerant to Cd, Pb and As, and single-metal and multimetal tolerance experiments were further conducted with this strain. The results obtained from alpha diversity and operational taxonomic unit (OTU) statistical analyses showed a significant difference in bacterial composition among soils with different metal pollution levels, and the highest bacterial diversity was found at the most severely polluted site. Evidence from variance partitioning analysis (VPA) and the Spearman correlation heatmap analysis showed that the leading factors affecting bacterial community composition were cation exchange content (CEC), pH, total Zn, total As, and available As concentrations in soil. Additionally, in the single-metal treatments, B. pacificus MZ520364 could tolerate 600 mg/L Cd²⁺, 1000 mg/L Pb²⁺ or 700 mg/L As³⁺. When Cd, Pb and As coexisted, the best growth of B. pacificus MZ520364 was present at 120 mg/L Cd²⁺, 200 mg/L Pb²⁺ and 150 mg/L As³⁺. The effect of Cd, Pb and As on the growth of the strain followed the order of Cd > As > Pb, and the heavy metal combination showed more toxicity than single metals. In summary, our results revealed the ecological impact of soil physicochemical properties on the diversity and richness of soil bacterial communities and suggested that B. pacificus MZ520364 may be used for the remediation of Cd-Pb-As co-contaminated soil.

Development of phosphorus composite biochar for simultaneous enhanced carbon sink and heavy metal immobilization in soil

As a porous and carbon material, biochar is focused on respectively in sequestrating carbon and stabilizing metals in soil, while few studies attempted to design biochar for simultaneously achieving these two targets. This study proposed to produce phosphorus-composite biochar for synchronously enhancing carbon sequestration and heavy metals immobilization. Two phosphorus materials from tailings, Ca(H₂PO₄)₂ and Ca₅(PO₄)₃(OH), were selected as modifier to load into biomass prior to pyrolysis. Results showed that incorporating P not only increased pyrolytic C retention in biochar by 36.1-50.1%, but also obtained biochar with higher stability by chemically formation of COP, C-PO₃ and C₂-PO₂. After 90-day incubation with soil, more C was sequestrated in the P-biochar amended soil (59.6-67.0%) than those pristine biochar (43.2-46.6%). Highly soluble Ca(H₂PO₄)₂ was more efficient than Ca₅(PO₄)₃(OH) in this regard. Meanwhile, these P-composite biochar exhibited more Pb/Cd immobilization (31.3-92.3%) compared with the pristine biochar (9.5-47.2%), which was mainly due to the formation of stable precipitates Pb₅(PO₄)₃Cl and Cd₃(PO₄)₂, especially for Ca₅(PO₄)₃(OH) modification. Additionally, P-composite biochar "intelligently" altered soil microbial community, i.e., they suppressed Actinobacteria proliferation, which is correlated to carbon degradation, while promoted Proteobacteria growth, facilitating phosphate dissolution for ready reaction with heavy metals to form precipitate, benefiting the Pb and Cd immobilization. A dual functions biochar was engineered via simply loading phosphorous prior to pyrolysis and simultaneously enhanced carbon sequestration and heavy metal immobilization.

Biochar/vermicompost promotes Hybrid Pennisetum plant growth and soil enzyme activity in saline soils

Soil salinity has become a major threat to land degradation worldwide. The application of organic amendments is a promising alternative to restore salt-degraded soils and alleviate the deleterious effects of soil salt ions on crop growth and productivity. The aim of present study was to explore the potential impact of biochar and vermicompost, applied individually or in combination, on soil enzyme activity and the growth, yield and quality of Hybrid Pennisetum plants suffered moderate salt stress (5.0 g kg^-1 NaCl in the soil). Our results showed that biochar and/or vermicompost promoted Na⁺ exclusion and K⁺ accumulation, relieved stomatal limitation, increased leaf pigment contents, enhanced electron transport efficiency and net photosynthesis, improved root activity, and minimized the oxidative damage in Hybrid Pennisetum caused by soil salinity stress. In addition, soil enzymes were also activated by biochar and vermicompost. These amendments increased the biomass and crude protein content, and decreased the acid detergent fiber and neutral detergent fiber contents in salt-stressed Hybrid Pennisetum. Biochar and vermicompost addition increased the biomass and quality of Hybrid Pennisetum due to the direct effects related to plant growth parameters and the indirect effects via soil enzyme activity. Finally, among the different treatments, the use of vermicompost showed better results than biochar alone or the biochar-compost combination did, suggesting that the addition of vermicompost to the soil is an effective and valuable method for reclamation of salt-affected soils.

Effects of sediment physicochemical factors and heavy metals on the diversity, structure, and functions of bacterial and fungal communities from a eutrophic river

Urbanization has destroyed river ecosystems, leading to eutrophication. Heavy metals are frequently observed in urban rivers, and the joint effects of eutrophication and heavy metals on microbial communities, especially on fungal communities, have not been adequately explored. In this study, we explored the effect of sediment physicochemical factors and heavy metals on the microbial diversity, community structure, and functions of bacterial and fungal communities from a black-odorous river in Wuhu, China. Twenty-four samples were collected, and the diversity and structure of fungal and bacterial communities were determined by high-throughput sequencing. Proteobacteria and Rozellomycota were the main phyla in the bacterial and fungal communities, respectively. The results showed different distribution patterns of bacterial and fungal communities along the river. Physicochemical factors and heavy metals exhibited different effects on microbial variation. Specifically, pH and Cr negatively affected bacterial α-diversity, whereas total phosphorus and Cr significantly affected fungal α-diversity. Variance partitioning analysis revealed that physicochemical factors explained more of the bacterial community structure than heavy metals (49.5% vs. 36.6%), with pH and total phosphorus being the dominant factors. Opposite patterns were observed for fungal community structure, with heavy metals contributing the most (48.0%). A similar influence pattern was observed for the predicted functions of the two communities. This study suggests that heavy metals in eutrophication rivers are essential factors that shift the microbial variation and should be considered in urban river evaluation and remediation.

Enhanced Cr(VI) stabilization in soil by chitosan/bentonite composites

In this study, chitosan/bentonite composites (CSBT) was synthesized and applied to the immobilization of chromium in the soil. The influence of passivating agents on various forms of chromium was investigated by batch experiment. The results showed that CSBT could reduce the content of exchangeable form and oxidizable form, while increase the content of residual form of chromium. The addition of 0.2 g·kg^-1 CSBT had the best effect, with the concentration of exchangeable, reducible and oxidizable form decreased by 46.74%, 8.15%, and 14.46%, respectively. During the experiment time, the passivation effect increased rapidly within 14 days, and the content of residual form in the total Cr increased from 0.76% to 14.23%, the equilibrium was reached at the 28th day and was basically maintained in the subsequent period. CSBT had little impact on soil pH, and soil pH maintained constant during the experiment period. The amino, carboxyl and hydroxyl groups of CSBT promoted the conversion of available chromium to residual state in soil, and reduced the bioavailability of chromium in soil.

Effects of wetland plant biochars on heavy metal immobilization and enzyme activity in soils from the Yellow River estuary

The purpose of this study was to assess the effects of wetland plant biochars on the enzyme activity in heavy metal contaminated soil. The biochars were produced from Phragmites australis (PB), Suaeda salsa (SB), and Tamarix chinensis (TB) under different pyrolysis temperatures and times. The detected pyrolysis products showed that the ash, pH, electrical conductivity, and carbon content of the biochars increased significantly, while the production rate of the biochars decreased with increasing pyrolysis temperature and time. The results of the adsorption experiments indicated that biochar addition could effectively reduce the concentration of Pb and/or Cd in the Pb²⁺/Cd²⁺ single or mixed solutions, but the Pb²⁺ and Cd²⁺ in the mixed solution indicated a competitive adsorption. A 30-day incubation experiment was conducted using salt marsh soil amended with different biochar application rates to investigate the short-term effects of biochar addition on Pb and Cd immobilization. The PB and SB significantly immobilized Pb within the first 15 days, but Pb remobilized within the next 15-day period. In contrast, TB addition did not significantly fix Pb. Moreover, biochar addition promoted the conversion of Cd from the residue to the less immobile fractions. The addition of three types of plant biochar had no significant effect on the urease activity in wetland soil but significantly increased soil sucrase activity. PB and SB significantly promoted catalase activity, while TB significantly inhibited soil catalase activity. According to the adsorption effect, the fixation effect, and the promotion of enzyme activities, the Suaeda salsa biochars are suitable for the remediation of heavy metal pollution in wetland soils.

Toxic Metals in a Paddy Field System: A Review

The threat of toxic metals to food security and human health has become a high-priority issue in recent decades. As the world’s main food crop source, the safe cultivation of rice has been the focus of much research, particularly the restoration of toxic metals in paddy fields. Therefore, in this paper, we focus on the effects of toxic metals on rice, as well as the removal or repair methods of toxic metals in paddy fields. We also provide a detailed discussion of the sources and monitoring methods of toxic metals pollution, the current toxic metal removal, and remediation methods in paddy fields. Finally, several important research issues related to toxic metals in paddy field systems are proposed for future work. The review has an important guiding role for the future of heavy metal remediation in paddy fields, safe production of rice, green ecological fish culture, and human food security and health.

Integrative analyses of geochemical parameters-microbe interactions reveal the variation of bacterial community assembly in multiple metal(loid)s contaminated arable regions

Soil microbes play crucial roles in biochemical and geochemical processes in contaminated arable ecosystems. However, what factors determine the assembling process of soil bacterial community under multiple heavy metal (loid)s (HMs) stress and how communities respond to geochemical changes have rarely been understood. Therefore, a number of contaminated soils were sampled to explore the interactions among geochemical parameters, HMs and innate bacterial community. The results showed that soil biochemical activities were inhibited obviously with the increase of HMs. Significant differences were observed in bacterial composition and abundance in studied areas, with Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria and Firmicutes governing the bacterial community structure. Redundancy analysis and variation partition analysis revealed that about 67.33% of the variation in bacterial assemblages could be explained by physiochemical parameters (21.59%), biochemical parameters (11.64%), toxic metal (loid)s (9.11%) and the interaction effect of these variables (24.99%), among which total-arsenic and moisture were the main factors. Spearman correlation analysis also demonstrated that dehydrogenase, moisture and TOC have a positive correlation with bacterial community structure with As-Cd-Pb gradient. Altogether, this study would provide a comprehensive relationship between major environmental factors and bacterial assemblages, which could offer some baseline data to investigate the mechanisms of how communities respond to physiochemical changes.

Calorific Value of Festuca rubra Biomass in the Phytostabilization of Soil Contaminated with Nickel, Cobalt and Cadmium Which Disrupt the Microbiological and Biochemical Properties of Soil

The choice of optimal plant species for phytoremediation and organic fertilization plays an important role in stabilizing the functions of soils contaminated with heavy metals. The influence of nickel, cobalt and cadmium on the biomass yield and calorific value of Festuca rubra, heavy metal concentrations in soil and plants and the microbiological, biochemical and physicochemical proprieties of soil were analyzed in a pot experiment. The tolerance index (TI) describing Festuca rubra’s ability to tolerate heavy metals, as well as the translocation (TF), accumulation (AF) and bioaccumulation (BF) factors of heavy metals in Festuca rubra were calculated. The experiment was conducted in two series: In soil fertilized and not fertilized with compost. Nickel and cobalt significantly inhibited the growth and development of Festuca rubra. The experiment demonstrated that this plant species can be grown on soil contaminated with heavy metals. Festuca rubra contained on average 46.05% C, 34.59% O, 5.91% H, 3.49% N, 0.19% S and 9.76% ash. Festuca rubra has a stable calorific value which is not affected by heavy metals; therefore, biomass harvested from heavy metal-polluted soil can be used for energy generation. The calorific value of Festuca rubra ranged from 15.924 to 16.790 MJ kg−1 plant d.m., and the heat of combustion from 17.696 to 18.576 MJ kg−1. It has a stable calorific value which is not affected by heavy metals, therefore biomass harvested from heavy metal-polluted soil can be used for energy generation. Festuca rubra is particularly useful for the phytostabilization of soil contaminated with cadmium and cobalt. Compost minimizes the adverse effects of heavy metal pollution on the microbiological, biochemical and physicochemical properties of soil.

Simultaneous elimination of black-odor and stabilization of heavy metals in contaminated sediment using calcium peroxide/hydroxyapatite: Microbial responses and ecotoxicological effects

In this study, laboratory-scale experiments were conducted to investigate the feasibility of the combined use of calcium peroxide and hydroxyapatite (CaO₂/HAP) for simultaneous black-odor sediment remediation and heavy metal stabilization. The ecotoxicological effects of remediated sediment were also evaluated based on biological toxicity. Results showed that CaO₂/HAP effectively eliminated the black-odor and simultaneously stabilized heavy metals in the sediment. Under the optimal dosage ratio of CaO₂/HAP (1:2), the acid volatile sulfides decreased to approximately 20 mg/kg (dry weight, dw) and oxidation-reduction potential increased from - 165 mV to approximately - 90 mV. The leaching of heavy metals meets the strictest standards (Level I) of the "Technical Specification for Output Disposal of Contaminated Sediment Treatment Plant of River and Lake" (SZDB/Z 236-2017). The indigenous microbial community succession occurred (p < 0.01), Proteobacteria and Firmicutes accounting for 75.54% and 20.19%, respectively, were the predominant bacteria in the remediated sediment. Additionally, CaO₂/HAP remediated sediments were safer and more environmentally friendly than raw sediments, and were not biotoxic to the benthic environment (p < 0.01). This study provides new insights into the combined use of the beneficial amendments remediating heavy metal-contaminated black-odor river sediment.

Influence of biochar remediation on Eisenia fetida in Pb-contaminated soils

In this study, the remediation influence of maize straw biochar on earthworms (Eisenia fetida) in contaminated soils (with Pb at 0, 300, 700, and 1000 mg kg^-1) amended with different amounts of biochar (0%, 1%, 3%, and 5%) was investigated. The results showed that applying biochar to metal-polluted soils effectively reduced the mobility of Pb, promoting the transformation of Pb from exchangeable (EXC) and bound-to-carbonate (Carb) fractions to Fe/Mn oxide (FeMnOx), organic bound (ORG) and residual (RES) fractions. Consequently, a reduction in the mortality and weight loss of earthworms was also achieved by biochar. The accumulation amount of Pb in earthworms steadily increased with exposure time, and with the increasing dosage of biochar, the accumulated Pb decreased by 50.8-78.0% (300 mg kg^-1), 30.9-67.3% (700 mg kg^-1), and 17.4-55.1% (1000 mg kg^-1), which was significantly positively correlated with the mortality of earthworms. Simultaneously, the application of biochar increased the soil pH (0.05-0.23 units), cation exchange capacity (CEC) (0.26-4.54 cmol kg^-1), and content of organic matter (0.54-11.66%). There were higher soil enzyme activities (including sucrase activity, urease activity, and alkaline phosphatase activity) in the treatments with a biochar addition of 3%. Through remediation, Proteobacteria (50.82%), Actinobacteriota (32.37%), Firmicutes (4.83%) and Bacteroidota (1.88%) were the most important phyla in the microbiota communities. Furthermore, soil pH value and leaching toxicity concentration showed the most striking effects on earthworms. Therefore, the influence of earthworms must be taken into account in the remediation of Pb-contaminated soil with biochar.

Chitosan-modified biochar: Preparation, modifications, mechanisms and applications

The chitosan-modified biochar composite, as a carbohydrate polymer, has received increasing attention and becomes a research hotspot. It is a promising impurity adsorption material, which has potential application value in the agricultural environment fields such as soil improvement and sewage purification. The composite can combine the advantages of biochar with chitosan, and the resulting composite usually exhibits a great improvement in its surface functional groups, adsorption sites, stability, and adsorption properties. In addition, compared to other adsorbents, the composite truly achieves the concept of "waste control by waste". In this paper, the preparation method, composite classification, adsorption mechanism, and models of biochar modified by chitosan are introduced, meanwhile, we also review and summarize their effects on the decontamination of wastewater and soil. In addition to common heavy metal ions, we also review the adsorption and removal of some other organic/inorganic pollutants, including (1) drug residues; (2) dyes; (3) phosphates; (4) radionuclides; (5) perfluorochemicals, etc. Moreover, challenges and prospects for the composite are presented and further studies are called for the chitosan-biochar composite. We believe that the composite will lead to further achievements in the field of environmental remediation.