Remediation Performance and Mechanism of Heavy Metals by a Bottom Up Activation and Extraction System Using Multiple Biochemical Materials

Microbial-inoculated biochar for remediation of salt and heavy metal contaminated soils

Numerous harmful contaminants (i.e. salt and heavy metals) have become major threats to soil and are being introduced into the soil through human and geological activities. These contaminants are raising global concerns about their toxic effects on food safety, human health and reclamation mechanisms. Microbial-inoculated biochar can improve soil environment by immobilizing and transforming contaminants in soil and altering the physico-chemical and biochemical properties of soil. In this review we will discuss the positive effects of microbial-modified biochar on physicochemical properties of contaminated soil. It can decrease the pH, EC while increase CEC, OM and other biochemical properties of soil. Additionally, we discuss the efficacy of biochar as a microbial carrier for salt and heavy metals-contaminated soil and plant growth in those soils. This review provides a better understanding of the potential of microbial biochar can be used for bioremediation of contaminated soil, which will help the researcher to modify biochar in a targeted way for specific applications.

Biochar enhances Cd mineralization through microbially induced carbonate precipitation as a soil remediation strategy for rice paddies

Microbial induced carbonate precipitation (MICP) is a promising technique for remediating Cd-contaminated soils. However, the high cost and potential disruption to soil micro-ecology due to the excessive urea addition remain significant challenges, limiting the broader application of MICP technology in agricultural soils. This study aims to improve the efficiency of Cd immobilization by MICP under low urea levels by investigating the stimulatory effect of porous materials on urease secretion by ureolytic bacteria. Results demonstrate that these materials, including biochar, activated carbon, zeolite, and oyster shell, can stimulate the growth of ureolytic bacteria strain kp-22, but not diatomite. Urease activity was greatly improved within 12 h, and the Cd removal rate reached over 82.12% within 0.5 h. Notably, biochar supported urealytic bacterium strain kp-22 (BCM) can steadily remove Cd in solution, with the Cd removal rate remaining close to 99% even after multiple additions of Cd. XRD analysis shows that Cd was removed by BCM due to the formation of CdCO3. Soil experiment reveals that BCM significantly decreased the bioavailable Cd content in both flooded and unflooded paddy soils, even when the urea addition was at a dosage suitable for agricultural production. 16S rRNA gene sequencing shows that the disturbance caused by BCM to the soil bacterial community was lower than that caused by strain kp-22 alone. These findings offer new insights into enhancing the efficiency of MICP for Cd remediation, increasing the potential for broader application of MICP technology in sustainable agriculture.

Feasibility and mechanism of adsorption and bioreduction of hexavalent chromium using Rhodopseudomonas palustris immobilized on multiple materials

Rhodopseudomonas palustris immobilized on multiple materials was used to invistigate Cr(VI) adsorption and bioreduction. The highest Cr(VI) removal (97.5%) was achieved at 276h under the opitimed conditions of 2.5% SA, 8% PVA, and 50% filling degree. The highest adsorption capacity was obtained at 11.75 mg g-1 under 300 mg L-1 Cr(VI). Results from adsorption kinetics and isotherms indicated that Cr(VI) adsorption of immobilized photosynthetic bacteria (IPSB) was consistent with the Freundich model and the pseudo-second-order kinetic model (qe = 14.00 mg g-1). SEM and FTIR analyses verified that the porous multilayer network structure of IPSB provided more adsorption sites and functional groups for the removal of Cr(VI). Furthermore, the maximum Cr(VI) reduction efficiency of IPSB was achieved at 10.80 mg g-1, which correlated with the up-regulation of chrR gene expressions at 100 mg L-1 Cr(VI). This study demonstrated the dual mechanisms of Cr(VI) removal in IPSB-treated Cr wastewater, involving both chemisorption and bioreduction working synergistically.

Remediation of Cr(VI)-contaminated soil by CS/PPy coupling with Microbacterium sp. YL3

In this research, a new material, chitosan/polypyrrole (CS/PPy), was synthesized and linked with the Cr(VI)-reducing bacterial strain YL3 to treat Cr(VI)-polluted soil. The findings demonstrated that the synergistic application of strain YL3 and CS/PPy achieved the greatest reduction (99.6 %). During the remediation process, CS/PPy served as a mass-storage and sustained release agent in the soil, which initially decreased the toxic effects of high concentrations of Cr(VI) on strain YL3, thereby enhancing the Cr(VI) reduction efficiency of strain YL3. These combined effects significantly mitigated Cr(VI) stress in the soil and restored enzyme activities. Furthermore, wheat growth in the treated soil also significantly improved. High-throughput sequencing of the microorganisms in the treated soil revealed that CS/PPy was not only effective at removing Cr(VI) but also at preserving the original microbial diversity of the soil. This suggests that the combined treatment using strain YL3 and CS/PPy could rehabilitate Cr(VI)-contaminated soil, positioning CS/PPy as a promising composite material for future bioremediation efforts in Cr(VI)-contaminated soils.

Enhanced degradation of phthalate esters (PAEs) by biochar-sodium alginate immobilised Rhodococcus sp. KLW-1

In this study, a new strain of bacteria, named Rhodococcus sp. KLW-1, was isolated from farmland soil contaminated by plastic mulch for more than 30 years. To improve the application performance of free bacteria and find more ways to use waste biochar, KLW-1 was immobilised on waste biochar by sodium alginate embedding method to prepare immobilised pellet. Response Surface Method (RSM) predicted that under optimal conditions (3% sodium alginate, 2% biochar and 4% CaCl2), di (2-ethylhexyl) phthalate (DEHP) degradation efficiency of 90.48% can be achieved. Under the adverse environmental conditions of pH 5 and 9, immobilisation increased the degradation efficiency of 100 mg/L DEHP by 16.42% and 11.48% respectively, and under the high-stress condition of 500 mg/L DEHP concentration, immobilisation increased the degradation efficiency from 71.52% to 91.56%, making the immobilised pellets have strong stability and impact load resistance to environmental stress. In addition, immobilisation also enhanced the degradation efficiency of several phthalate esters (PAEs) widely existing in the environment. After four cycles of utilisation, the immobilised particles maintained stable degradation efficiency for different PAEs. Therefore, immobilised pellets have great application potential for the remediation of the actual environment.

Rhodopseudomonas palustris shapes bacterial community, reduces Cd bioavailability in Cd contaminated flooding paddy soil, and improves rice performance

Photosynthetic bacteria (PSB) are suitable to live and remediate cadmium (Cd) in the slightly oxygenated or anaerobic flooding paddy field. However, there is currently limited study on the inhibition of Cd accumulation in rice by PSB, and the relevant mechanisms has yet to be elucidated. In the current study, we firstly used Rhodopseudomonas palustris SC06 (a typical PSB) as research target and combined physiology, biochemistry, microbiome and metabolome to evaluate the mechanisms of remeding Cd pollution in paddy field and inhibiting Cd accumulation in rice. Microbiome analysis results revealed that intensive inoculation with R. palustris SC06 successfully survived and multiplied in flooding paddy soil, and significantly increased the relatively abundance of anaerobic bacteria including Desulfobacterota, Anaerolineaceae, Geobacteraceae, and Gemmatimonadaceae by 46.40 %, 45.00 %, 50.12 %, and 21.30 %, respectively. Simultaneously, the structure of microbial community was regulated to maintain relative stability in the rhizosphere soil of rice under Cd stress. In turn, these bacteria communities reduced bioavailable Cd and enhanced residual Cd in soil, and induced the upregulation of sugar and organic acids in the rice roots, which further inhibited Cd uptake in rice seedlings, and dramatically improved the photosynthetic efficiency in the leaves and the activities of antioxidative enzymes in the roots. Finally, Cd content of the roots, stems, leaves, and grains significantly decreased by 38.14 %, 69.10 %, 83.40 %, and 37.24 % comparing with the control, respectively. This study provides a new strategy for the remediation of Cd-contaminated flooding paddy fields and the safe production of rice.

In situ mycoremediation of acid rain and heavy metals co-contaminated soil through microbial inoculation with Pleurotus ostreatus

The combined pollution of acid rain and heavy metals in soil is a pressing environmental problem, especially in the regions with large-scale heavy industrial production activities. Low remediation efficiency and weak long-lasting stability are major challenges when disposing the heavy metals contaminated soil in acid rain polluted sites. Herein, a specific microbe, strain CT13 was isolated and domesticated to exhibit high tolerance to both acid rain and cadmium (Cd). Then, an in situ mycoremediation method by adopting a bioaugmentation technology of strain CT13 inoculation with Pleurotus ostreatus was developed. The remediation performance was investigated in acidic conditions with Cd concentrations in soil ranging from 0 to 15 mg/kg. While most of the bacteria strains (e.g. strain CT6/13) significantly improved the dry weight of mushroom and Cd accumulation in neutral environment, the performance of strain CT6 was remarkably deteriorated in acid rain environment. In contrast, strain CT13 maintained its behavior in acidic conditions, displaying ∼30 % and 150 % enhancements (vs the neutral environment) in the dry weight of mushroom and Cd accumulation, respectively. In addition, inoculation of strain CT13 led to significant reductions in the content of superoxide dismutase, peroxidase and lipid peroxidation in the fruiting body of P. ostreatus, indicating an improvement in the mushroom's tolerance to both acid rain and heavy metals. The synergistic effect of strain CT13 and P. ostreatus realized the significant improvement in soil remediation efficiency and long-lasting stability in acidic conditions, providing valuable insights into the remediation of heavy metal contaminated soil in the regions affected by acid rain.

Screening of cadmium-chromium-tolerant strains and synergistic remediation of heavy metal-contaminated soil using king grass combined with highly efficient microbial strains

The present study involved the isolation of two cadmium (Cd) and chromium (Cr) resistant strains, identified as Staphylococcus cohnii L1-N1 and Bacillus cereus CKN12, from heavy metal contaminated soils. S. cohnii L1-N1 exhibited a reduction of 24.4 % in Cr6+ and an adsorption rate of 6.43 % for Cd over a period of 5 days. These results were achieved under optimal conditions of pH (7.0), temperature (35 °C), shaking speed (200 rpm), and inoculum volume (8 %). B. cereus strain CKN12 exhibited complete reduction of Cr6+ within a span of 48 h, while it demonstrated a 57.3 % adsorption capacity for Cd over a period of 120 h. These results were achieved under conditions of optimal pH (8.0), temperature (40 °C), shaking speed (150 rpm), and inoculum volume (2-3 %). Additionally, microcharacterization and ICP-MS analysis revealed that Cr and Cd were accumulated on the cell surface, whereas Cr6+ was mainly reduced extracellularly. Subsequently, a series of pot experiments were conducted to provide evidence that the inclusion of S. cohnii L1-N1 or B. cereus CKN12 into the system resulted in a notable enhancement in both the plant height and biomass of king grass. In particular, it was observed that the presence of S. cohnii L1-N1 or B. cereus CKN12 in king grass led to a significant reduction in the levels of Cd and Cr in the soils (36.0 % and 27.8 %, or 72.9 % and 47.4 %, respectively). Thus, the results of this study indicate that the combined use of two bacterial strains can effectively aid in the remediation of tropical soils contaminated with moderate to light levels of Cd and Cr.

Potential bioremediation of lead and phenol by sunflower seed husk and rice straw-based biochar hybridized with bacterial consortium: a kinetic study

Environmental pollution is a global phenomenon and troublesome fact that poses a grave risk to all living entities. Via coupling carbonaceous feedstocks with outstanding microbial activity, kinetic experiments were established using the consortium of Proteus mirabilis and Raoultella planticola, biochar-derived sunflower seed husk (SHB) and rice straw (RSB), and their composites, which investigated at 30 °C (150 rpm) to eliminate 700 mg L-1 lead (120 h) and phenol (168 h) from synthetic wastewater. The derived biochars physicochemical properties of were studied. According to adsorption capacity (qe), consortium-SHB composites and consortium-RSB composites removed lead completely (70 mg g-1) within 48 h and 66 h, respectively. Besides, phenol was remediated entirely after 42 h and 48 h by both composite systems (69.90 mg g-1), respectively, comparing with bacterial consortium only or parent SHB and RSB. Moreover, four kinetic models were studied to describe the bioremediation process. Fractional power and Elovich models could be recommended for describing the adsorption kinetics for lead and phenol removal by the studied biomaterials with high correlation coefficient (R2 ≥ 0.91 for Pb2+ and ≥ 0.93 for phenol) and lower residual root mean square error (RMSE) and chi-square (X2). Overall, bacterial consortium-biochar composites exhibited greater remediation of lead and phenol than the sum of each single bacterial consortium and biochar systems; reflecting synergistic interaction of adsorptive capability of biochar and metabolic performance of bacterial consortium, as denoted by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The current study addressed the successful design of employing functional remediating consortium immobilized on waste biomass-derived biochar as a conducive alternative eco-sorbent and economic platform to detoxify organic and inorganic pollutants.

Enhanced cadmium phytoextraction efficiency of ryegrass (Lolium perenne L.) by porous media immobilized Enterobacter sp. TY-1

Although studies on immobilized microorganisms have been conducted, their performance remains unclear for enhancing plants to remediate cadmium (Cd)-contaminated soil. In this study, a Cd-resistant strain TY-1 with good plant growth promotion traits was immobilized by biochar (BC) or oyster shell (OS) power to strengthen ryegrass to remediate Cd-contaminated soil. SEM-EDS combined with FTIR showed that TY-1 could tolerate Cd toxicity by surface precipitation, and functional groups such as hydroxyl and carbonyl groups might be involved. In the biocomposite treatments, soil pH increased, and the activity of fertility-related enzymes such as dehydrogenase increased by 109.01%-128.01%. The relative abundance of genus Saccharimonadales decreased from 7.97% to 3.35% in BS-TY and 2.61% in OS-TY, respectively. Thus, a suitable environment for ryegrass growth was created. The fresh weight, dry weight, plant height and Cd accumulation of ryegrass in TY treatment increased by 122.92%, 114.81%, 42.08% and 8.05%, respectively, compared to the control. Cd concentration in ryegrass was further increased in BC-TY and OS-TY by 24.14% and 40.23%, respectively. The improvement in soil microcosm and plant biomass forms an ongoing virtuous cycle, demonstrating that using carrier materials to improve the efficiency of microbial-assisted phytoremediation is realistic and feasible.

Application potential of Vaccinium ashei R. for cadmium migration retention in the mining area soil

Despite numerous reports on phytoremediation of heavy metals contaminated soil, there are few reports on plant retention of heavy metals in the mining area slope. This study was the first of its kind to explore the cadmium (Cd) retention capacity of the blueberry (Vaccinium ashei Reade). Firstly, we investigated the stress response of blueberry to different soil Cd concentrations (1, 5, 10, 15, 20 mg/kg) to assess its potential for phytoremediation by pot experiments. The results showed that the blueberry biomass exposed to 10 and 15 mg/kg Cd was significantly increased compared with the control (1 mg/kg Cd); the blueberry crown increased by 0.40% and 0.34% in 10 and 15 mg/kg Cd-contaminated soil, respectively, compared with control; the blueberry heigh did not even change significantly in each treatment group; the total chlorophyll content, peroxidase and catalase activity of blueberry were enhanced in 5-20 mg/kg Cd treatments. Furthermore, the Cd contents of blueberry in the root, stem and leaf increased significantly as the Cd concentration of soil increased. We found that more Cd accumulated in blueberry root: the bioaccumulation concentration factor was root > stem > leaf for all groups; the residual-Cd (Cd speciation) in soil increased by 3.83%-411.11% in blueberry-planted versus unplanted groups; blueberry improved the Cd-contaminated soil micro-ecological environment including soil organic matter, available K and P, as well as microbial communities. Then, to investigate the effect of blueberry cultivation on Cd migration, we developed a bioretention model and revealed that soil Cd transport along the model slope was significantly weakened by blueberry cultivation, especially at the bottom of the model. In a word, this research suggests a promising method for the phytoremediation of Cd-contaminated soil and the reduction of Cd migration in mining areas.

Construction of bifunctional bacterial community for co-contamination remediation: Pyrene biodegradation and cadmium biomineralization

Polycyclic aromatic hydrocarbons and heavy metals are typical pollutants in the non-ferrous metal smelting industry. The combination of biodegradation and biomineralization has great development potential for co-contamination removal as an environmentally friendly method. Pyrene (Pyr) and cadmium (Cd) were regarded as model pollutants of co-contamination in this study. A bifunctional bacterial community named Ycp was screened from a non-ferrous smelting slag field soil. The 16S rRNA gene high throughput sequencing analysis showed that Enterobacter was the dominant genus (99.1%). Ycp had adaptability under a wide range of environmental conditions (pH 3-9, salinity 0-10 g L^-1 NaCl, Pyr concentration 0-50 mg L^-1, Cd concentration 0-100 mg L^-1), and the removal rate of Pyr and Cd reached 41.8%-76.9%, 82.8%-98.8%, respectively. It was found that compound carbon sources had promoting effect on the removal of Pyr and Cd, with the maximum removal rate of 88.3% and 98.0%. According to the degradation products of Pyr by LC-MS analysis and the mineralized products of Cd²⁺ by XRD and SEM-EDS analysis, the mechanism of Ycp for co-contamination remediation was: Ycp biodegraded Pyr through salicylic acid and phthalic acid metabolic pathways, and biomineralized Cd²⁺ into CdCO₃ through microbially induced carbonate precipitation. This study provided a basis for microbial remediation of co-contamination.

Strategy for enhancing Cr(VI)-contaminated soil remediation and safe utilization by microbial-humic acid-vermiculite-alginate immobilized biocomposite

Bioreduction is an efficient approach to in-situ remediate Cr(VI)-contaminated soil, but further strengthening methods are still urgently needed. Herein, a novel immobilized biocomposite (B-HA-VE-SA) was successfully synthesized by embedding a efficient strain Bacillus sp. CRB-7 with humic acid (HA) combined vermiculite (VE) and sodium alginate (SA). The performance and enhancement mechanism of the immobilized biocomposite on remediating Cr(VI)-contaminated soil were also investigated by analyzing the whole-genome of CRB-7, Cr(VI) detoxification, soil microecological regulation, and subsequent crop growth response. Genomic annotation demonstrated that CRB-7 contains multiple genes contributed to Cr(VI) tolerance, Cr(VI) reduction and other metals resistance. Results showed that embedded CRB-7 biocomposites exhibited more effective reduction of Cr(VI) in soil compared with control and free CRB-7 treatment, especially B-HA-VE-SA achieved the highest Cr(VI) removal efficiency (96.18%) and the residual Cr proportion (49.04%) via multiple mechanisms including carrier effects, nutrient sustained-release, and electron-shuttle effect enhanced the bioremediation process. Furthermore, the synergies of CRB-7 and immobilizers (HA, VE and SA) significantly improved soil microecology (soil enzyme activities, microbial quantity and diversity), and engendered the evolution of microbial community composition and functional pathways. Consequently, pot experiments (Brassica napus L.) verified the plant-growth-promoting (12.00-18.00% and 43.82-69.00% higher in emergence rate and biomass) and Cr-accumulation-reducing effects (19.47-91.09% and 29.11-89.80% lower in root and aerial parts) of free and immobilized CRB-7. Taken together, these findings highlighted the superiority of B-HA-VE-SA in simultaneous remediation, microecological improvement and safe utilization of Cr(VI)-contaminated soil.

Characterization of soil microbial community activity and structure for reducing available Cd by rice straw biochar and Bacillus cereus RC-1

The combination of biochar and specific bacteria has been widely applied to remediate Cadmium-contaminated soil. But little is known about how such composites affect the dynamic distribution of metal fractions. This process is accompanied by the alternations of soil properties and microbial community structures. Composite of rice straw biochar and Bacillus cereus RC-1 were applied to investigate its impacts on Cd alleviation and soil microbial diversity and structure. The bacterial/biochar composite treatment decreased the fraction of HOAc-extractable Cd by 38.82%, and increased residual Cd by 23.95% compared to the untreated control. Moreover, compared with the untreated control, the composite treatment significantly increased the soil pH by about 1.5 units, and the activities of catalase, urease and invertase enzymes were increased by 42.39%, 30.50% and 31.20%, respectively. Composite treatment increased soil bacterial and fungal alpha diversity, the relative abundance of Bacillus, Streptomyces, Arthrobacter, and Aspergillus species were also increased. Mantel test and correlation analysis indicated that the effects associated with fungal communities in influencing soil properties were lower than that those of bacterial communities by different treatment. Aggregated boosted tree (ABT) models analysis showed that soil chemical proprieties (as determined by SOM, CEC, AN, etc.,) contributed over 50% of the changes in bacterial and fungal communities by the composite treatment. The co-occurrence network results showed that all treatments enhanced the correlation between OUT groups and improved the possible relationships in the bacterial and fungal communities, especially the interrelationships between bacteria and fungi after the Cd fractions stabilized. These findings provide a new insight to optimal strategies for the remediation of Cd-contaminated soil.

The effects of biochar and its applications in the microbial remediation of contaminated soil: A review

The amendment of biochar for soil bioremediation can improve soil conditions, influence soil microbial community, and achieve co-application of biochar-microbe to promote the removal of pollutants. This paper summarizes the positive effects of biochar on microorganisms, including acting as a shelter, providing nutrients, and improving soil conditions (soil aggregation, pH, cation exchange capacity (CEC), and enzymatic activity). These effects will cause variations in microbial abundance, activity, and community structure. Biochar can act as an electron mediator to promote electron transfer in the process of microbial degradation. And the application of biochar in soil bioremediation is also introduced. Nevertheless, toxic substances carried by biochar that may threaten microbial community shouldn't be overlooked. With this review, we can better understand biochar's involvement in soil bioremediation, which will help us choose and modify biochar in a targeted manner for the desired purpose in practical applications.

Micro-dynamic process of cadmium removal by microbial induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) is a technique used extensively to address heavy metal pollution but its micro-dynamic process remains rarely explored. In this study, A novel Cd-tolerant ureolytic bacterium DL-1 (Pseudochrobactrum sp.) was used to study the micro-dynamic process. With conditions optimized by response surface methodology, the removal efficiency of Cd²⁺ could achieve 99.89%. Three components were separated and characterized in the reaction mixture of Cd²⁺ removal by MICP. The quantitative-dynamic distribution of Cd²⁺ in different components was revealed. Five synergistic effects for Cd²⁺ removal were found, including co-precipitation, adsorption by precipitation, crystal precipitation on the cell surface, intracellular accumulation and extracellular chemisorption. Importantly, during Cd²⁺ removal by MICP, the phenomenon that crystalline nanoparticles adhere to the cell surface, but without any micrometer-sized precipitation encapsulated bacterial cells was observed. This indicated that the previously studied model of bacterial cells as nucleation sites for metal cation precipitation and crystal growth is oversimplified. Our findings provided valuable insights into the mechanism of heavy metals removal by MICP, and a more straightforward method for studying biomineralization-related dynamic process.

The potential effectiveness of mixed bacteria-loaded biochar/activated carbon to remediate Cd, Pb co-contaminated soil and improve the performance of pakchoi plants

Cadmium (Cd) and lead (Pb) are toxic heavy metals that cause severe soil pollution and pose health risks to humans. It is urgent to develop feasible strategies for Pb and Cd remediation. In this study, a bacteria consortium (Enterobacter asburiae G3, Enterobacter tabaci I12 and Klebsiella variicola J2 in a 1:3:3 proportion) with optimal Cd, Pb adsorption ability was constructed and immobilized on biochar (BC)/activated carbon (AC) via physisorption and sodium alginate encapsulation. The effects of mixed bacteria-loaded BC/AC on Cd and Pb remediation were investigated. The results indicated that their application reduced the DTPA-extractable Cd, Pb in soil by 22.05%-55.84% and 31.64%-48.13%, respectively. The residual Pb, Cd were increased while the exchangeable fractions were decreased. Soil urease, catalase and phosphatase activities were enhanced and soil bacterial community was improved, indicating a soil quality improvement. Consequently, the biomass of pakchoi plants was significantly increased. Cd and Pb in the shoots of pakchoi plants were decreased by 28.68%-51.01% and 24.18%-52.87%, respectively. Collectively, the bacteria-loaded BC/AC showed superior performance than free bacteria, BC and AC alone. Our study may provide a better understanding of the development of green and sustainable materials for remediation of heavy metal by the combination of BC/AC and functional bacteria.

Novel Control Strategy for Membrane Biofouling by Surface Loading of Aerobically and Anaerobically Applicable Photocatalytic Optical Fibers Based on a Z-Scheme Heterostructure Zr-MOFs/rGO/Ag3PO4 Photocatalyst

The high replacement cost of modified membranes in antibiofouling application is inevitable. Here, surface-loaded photocatalytic optical fibers (POFs) were developed as antibiofouling strategies to replace membrane modification. To prepare aerobically and anaerobically applicable POFs, novel visible light-driven zirconium-based metal-organic framework/reduced graphene oxide/Ag₃PO₄ (Zr-MOFs/rGO/Ag₃PO₄) Z-scheme heterojunctions were constructed and coated on optical fibers. After loading the POFs on the membrane surface, the antibiofouling capability of the POFs was demonstrated during membrane filtration of bacteria and foulants under visible light irradiation. The disinfection efficiencies of the POFs against Escherichia coli and Staphylococcus aureus reached 95.7 and 92.4%, respectively, by aerobic treatment and 90.3 and 85.5%, respectively, by anaerobic treatment. For the inactivated bacteria, cell membrane and membrane-associated functions were destroyed, accompanied by antioxidant enzyme decomposition, loss of cell respiration and adenosine triphosphate (ATP) synthesis capacity, and leakage and oxidation of protein, lipid, potassium, DNA, and RNA. During membrane filtration of model foulants and membrane bioreactor sludge, the POFs significantly alleviated the membrane flux decline by foulant disintegration. By qualitative and quantitative detection and quenching tests of reactive species, aerobically generated ^•O₂^- and ^•OH and anaerobically generated ^•OH from POFs played dominant roles in the antibiofouling process. This work provides unique insights into membrane fouling control based on environmentally friendly and efficient photocatalytic technology.

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.

Cadmium Exposure Alters Rhizospheric Microbial Community and Transcriptional Expression of Vetiver Grass

Vetiver grass (Chrysopogon zizanioides L.) has been used to remediate cadmium (Cd)-contaminated soil, while there have been few studies on the influence of Cd exposure on the rhizospheric microbial community and transcriptional expression of C. zizanioides. In this study, we investigated the response of the rhizospheric microbial community and transcriptional expression of C. zizanioides in 20 mg/kg Cd-contaminated soil. The results showed that Cd levels in the roots and shoots of C. zizanioides reached 250.80 and 73.40 mg/kg, respectively. The Cd exposure changed the rhizospheric bacterial community, resulting in the significant enrichment of Sphingomonas, Lysobacter, and Gemmatimonadetes in Cd-contaminated soil. In addition, 880 and 3,419 differentially expressed genes were identified in the plant roots and shoots, respectively, in response to Cd stress. Among these, the overexpressed genes associated with redox homeostasis, glutathione (GSH) metabolism, cell wall biosynthesis, and transmembrane transport pathways were found to participate in Cd detoxification in C. zizanioides. These findings could be useful for understanding the selective variation of the rhizospheric microbial community and the detoxification mechanisms of C. zizanioides in Cd phytoremediation.

Lipid degrading microbe consortium driving micro-ecological evolvement of activated sludge for cooking wastewater treatment

In this study, a lipid degrading microbe consortium (LDMC) was assembled to improve the performance of activated sludge (AS) on cooking wastewater purification. LDMC can rapidly degrade high-level oil (efficiency beyond 93.0% at 5.0 g/L) as sole carbon source under various environmental conditions (10.0-45.0 °C, pH 2.0-12.0). With LDMC inoculation, AS' water treatment performance was significantly enhanced, which removed 36.10 and 48.93% more chemical oxygen demand (COD) and ammonia nitrogen from wastewater than control. A better settling property and smaller bulking risk were found with LDMC inoculation, indicated by a lower SV₃₀ and SVI index but a higher MLSS. By GC/MS analysis, a gradual degradation on the end of the fatty acid chain was suggested. LDMC inoculation significantly changed AS's microbial community structure, improved its stability, decreased the microbial community diversity, facilitated the enrichment of lipid degraders and functional genes related to lipid bio-degradation. Lipid degraders including Nakamurella sp. and Stenotrophomona sp., etc. played a crucial role during oil degradation. Sludge structure maintainers such as Kineosphaera sp. contributed largely to the stability of AS under exogenous stress. This study provided an efficient approach for cooking wastewater treatment along with the underlying mechanism exploration, which should give insights into oil-containing environmental remediation.

Enhanced degradation of petroleum hydrocarbons by immobilizing multiple bacteria on wheat bran biochar and its effect on greenhouse gas emission in saline-alkali soil

In this study, an immobilization method for forming and keeping dominant petroleum degradation bacteria was successfully developed by immobilizing Pseudomonas, Acinetobacter, and Sphingobacterium genus bacteria on wheat bran biochar pyrolyzed at 300, 500, and 700 °C. The removal efficiency indicated that the highest TPHs (total petroleum hydrocarbons) removal rate of BC500-4 B (biochar pyrolyzed at 500 °C with four kinds of petroleum bacteria) was 58.31%, which was higher than that of BC500 (36.91%) and 4 B (43.98%) used alone. The soil properties revealed that the application of biochar increased the content of organic matter, available phosphorus, and available potassium, but decreased pH and ammonium nitrogen content in soil. Bacterial community analysis suggested that the formation of dominant degrading community represented by Acinetobacter played key roles in TPHs removal. The removal rate of alkanes was similar to that of TPHs. Besides, biochar and immobilized material can also mediate greenhouse gas emission while removing petroleum, biochar used alone and immobilized all could improve CO₂ emission, but decrease N₂O emission and had no significant impact on CH₄ emission. Furthermore, it was the first time to found the addition of Acinetobacter genus bacteria can accelerate the process of forming a dominant degrading community in wheat bran biochar consortium. This study focused on controlling greenhouse gas emission which provides a wider application of combining biochar and bacteria in petroleum soil remediation.

Biochemical composite material using corncob powder as a carrier material for ureolytic bacteria in soil cadmium immobilization

Corncob powder possessing its superiority in environmental sustainability and cost, was approved with strong capability of being a replacement of biochar in facilitating the microbial carbonate precipitation process. In this study, the ureolytic bacterial strain Bacillus sp. WA isolated from a pre-acquired metal contaminated soil in Guiyu, China, was showed to be well attached on the surfaces of corncob powder, indicating the carrier's role as a durable shelter for bacterial cells. The efficient immobilization helped develop biochemical composite material (BCM) and proven to function better the calcite precipitation. Afterwards, the mechanism and multi-directional benefits of BCM in edaphic cadmium remediation were examined through pot experiment and compared with corncob powder/bacterial strain/nutrient media as control groups. Integrated lab-scale analyses emphasized the advantages of BCM by the maximum soil urease activity (up to 3.440 U/mg and increased by 214% in 28 days), maximal bacterial propagation (most abundant population in fluorescence microscopy), richest surface functional group (most remarkable OC bond and CO bond in FTIR result), notable calcite precipitation (clear calcite crystals on the surface of BCM compared to control group under SEM-EDS), and highest Cd immobilization rate (exchangeable Cd decreased by 68.54%), among all treatments. The pH and electroconductivity measurements additionally led to the mechanism of corncob powder and NBU promoting pre-existed ureolytic bacteria in soil, which demonstrated the added value of corncob to be fine carbon source and residence shelter for soil microorganism, revealing its potential in developing agricultural materials.

Effect of biochar-immobilized Sphingomonas sp. PJ2 on bioremediation of PAHs and bacterial community composition in saline soil

This study aimed to investigate the bioremediation efficiency and bacterial regulation mechanism of biochar-immobilized bacterium (BM) in polycyclic aromatic hydrocarbon (PAH)-contaminated saline soil by conducting pot experiments. In BM treatment, PAH-degrading strain Sphingomonas sp. PJ2 was inoculated into biochar produced at 400 °C and 600 °C using the pine needles (BM400 and BM600). The removal rates of PAHs, soil physicochemical properties, abundance of PAH-ring hydroxylating dioxygenase (PAH-RHD), and bacterial community composition were determined. After 60 days of bioremediation, BM treatment significantly (P < 0.05) increased the removal rate of PAHs compared with biochar and PJ2 alone (15.94% and 37.3%, respectively). BM treatment clearly improved the physicochemical properties of saline soil. Moreover, the amount of Gram-positive PAH degraders increased in BM-treated soils compared with other treatments, and their gene abundance had a strong positive correlation with the removal rates of PAHs in soils (r = 0.896; P < 0.01). Furthermore, BM treatment increased the abundance of Sphingomonas genus, indicating that the strain PJ2 could survive and colonize in PAH-contaminated saline soil under the protection of biochar. This study provided an effective and green approach for the remediation and improvement of the PAH-contaminated saline soil.

Comparative study on different organic acids for promoting Solanum nigrum L. hyperaccumulation of Cd and Pb from the contaminated soil

Organic acids-assisted phytoremediation is a promising strategy to remove metal pollutants from the soil. However, few reports have focused on the mechanisms of organic acids promoting the uptake of heavy metals by hyperaccumulators. In this study, 5 types of organic acids, namely polybasic carboxylic acids, acidic amino acids, acidic plant growth regulators, phosphoric and gluconic acids, were comprehensively investigated the effects on the solubility of Cd and Pb in the soil along with their uptake by Cd hyperaccumulator Solanum nigrum L. The results indicated that the addition of Hydroxyethylidene-1,1-diphosphonic acid (HEDP) and d-Gluconic acid (D-GA) effectively extracted the most of acid-extractable and some of reducible and oxidizable fractions of Cd and Pb in the soil, with the extraction rates of 64.8% and 34.4% for total Cd and 53.6% and 30.0% for total Pb, respectively. HEDP and D-GA significantly increased the accumulations of Cd (57.1% and 35.0%) and Pb (43.4% and 31.9%) by S. nigrum without the inhibition of its biomass, making the great removal efficiencies of Cd (1.35% and 1.16%) and Pb (0.039% and 0.036%) from the soil. The enhanced phytoremediation efficiency of S. nigrum was due to the increase of the extractable Cd and Pb in the rhizosphere but little changes of soil pH and enzyme activities (catalase and urease). Among all of organic acids, HEDP may be an alternative to EDTA because of its characteristics of environmental friendliness and high efficiency.

Effects of magnetic biochar-microbe composite on Cd remediation and microbial responses in paddy soil

There is growing global interest in the bioremediation of cadmium (Cd) using combinations of biochar and microorganisms. However, the interactions among biochar, introduced and indigenous microorganisms remain unclear. Accordingly, a 90 day microcosm experiment was conducted to investigate this by adding Bacillus sp. K1 strain inoculated rice straw biochar (SBB) and magnetic straw biochar (MBB) into a Cd contaminated paddy soil from Hunan, China. All treatments were incubated aerobically (60% water holding capacity) or anaerobically for 90 d. During both soil incubations, Bacillus sp. K1 successfully colonized in soil with composites applications. Soil pH was significantly increased from acid to neutral, and available Cd decreased with the addition of both composites. The better remediation efficiency of MBB than SBB under anerobic conditions was attributed to the transformation of acetic acid-extractable Cd into the residual fraction, caused by Cd²⁺ bonding with crystal Fe₃O₄. The application of the two kinds of composites caused similar changes to both microbial communities. There was a slight decrease in indigenous microbial alpha diversity with the MBB aerobic application, while the total population number of bacteria was increased by 700%. Both the redundancy analysis and Mantel analyses indicated that pH and microbial biomass C contributed to the colonization of Bacillus sp. K1 with SBB under aerobic conditions, and with MBB under anerobic conditions, respectively. The research provides a new insight into interactive effects and investigates immobilization mechanisms involved of bacterial/biochar composites in anaerobic and aerobic soils.

Performance and mechanisms for remediation of Cd(II) and As(III) co-contamination by magnetic biochar-microbe biochemical composite: Competition and synergy effects

Contaminations by heavy metals in the environment always exist as a mixture of both metal and metalloid. Thus, it is a challenge to simultaneously remove both components due to their adverse chemical behaviors. Herein, effective cadmium (Cd) and arsenic (As) removal in aqueous solution was achieved by use of a novel composite, which was synthesized by Bacillus sp. K1 loaded onto Fe₃O₄ biochar (MBB). The combination with Bacillus sp. K1 provided new biosorption sites such as amine and hydroxyl groups in the composite surface, which significantly increasing the removal capability of Cd(II) by 230% when compared with the raw magnetic biochar. Both competition and synergy effects were found in binary system. Adsorption of As(III) extended active sites for capturing Cd(II), which appeared on the surface of the MBB as type B ternary surface complexes. The maximum adsorption capacity of Cd(II) and As(III) reached 25.04 and 4.58 mg g^-1 in a binary system, respectively. In summary, this environmentally friendly composite is promising for simultaneous Cd(II) and As(III) remediation.

Performance of microbial induced carbonate precipitation for immobilizing Cd in water and soil

Microbial induced carbonate precipitation (MICP) is known as a significant process for remediating heavy metals contaminated environment. In this study, a novel Cd-resistant ureolytic bacteria was isolated and identified as Enterobacter sp. Its performances for immobilizing Cd in solution and soil were systematically discussed at different treatment conditions. Results showed that initial pH and Cd concentration were important parameters to influence Cd removal rate. The maximal Cd removal rate in solution reached 99.50 % within 7 days by MICP. The precipitation produced in Cd removal process were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer to understand the removal mechanism. Analyses showed that Cd removal mechanism of CJW-1 was predominately via biominerals including calcites and vaterites to absorb Cd2+. Cd immobilization tests demonstrated that the highest Cd-immobilization rate in soil could reach 56.10 %. Although all treatments contribute to soil pH, fertility, and enzyme activities improvement, oyster shell wastes (OS) had a better effect on soil cation exchange capacity. All treatments had negative effects on soil respiration and bacterial community, but OS can alleviate such adverse influence. Our results emphasized that Cd-resistant ureolytic bacteria strain CJW-1 combined with OS had excellent ability and reuse value to remediate Cd-contaminated environment.

Change in phytoextraction of Cd by rapeseed (Brassica napus L.) with application rate of organic acids and the impact of Cd migration from bulk soil to the rhizosphere

Adding exogenous low-molecular weight organic acids is an effective technique to improve phytoremediation of Cd-contaminated soil and has been well documented, but how acid application rate affects remediation efficiency and its underlying limiting factors remains elusive. We investigated this using pot experiments with rapeseed (Brassica napus L.) as the model plant. Plastic pots packed with a sandy loam contaminated by Cd at 4.838 mg/kg were amended with acetic acid, oxalic acid, citric acid, malic acid and tartaric acid, respectively, at an application rate gradient varying from 0.0 to 12.0 mmol/kg. Plants in each pot were harvested after growing for five months, and we then measured the exchangeable, carbonate, Fe-Mn oxide, organic and residual Cd in the rhizosphere, as well as Cd in both roots and shoots. The results showed that all organic acids improved plant uptake of Cd and, compared with the control without acid addition, they could improve Cd uptake by more than 100%. The enhanced Cd extraction was due to the increase in exchangeable Cd in the rhizosphere. Plant Cd was weakly correlated to the amount of Cd lost from a unit volume of the rhizosphere due to root extraction (R² = 0.06), but a good negative correlation was found between them after normalizing the lost Cd by root biomass (R² = 0.36). Mass balance analysis revealed that the average Cd content in soil (rhizosphere and bulk soils combined) was much higher than the Cd content in the rhizosphere, and the improved Cd mobility after acid addition was thus due to the increased chelation. As diffusion of ligands in water is one order in magnitude smaller than diffusion of Cd ions, our results suggested that Cd migration from the bulk soil into the rhizosphere was a major factor limiting Cd phytoextraction by rapeseed after adding the exogenous organic acids.

24-Epibrassinolide combined with heavy metal resistant bacteria enhancing phytoextraction of Amaranthus hypochondriacus L. in Cd-contaminated soil

The remediation efficiency of phytoextraction on heavy metal could be influenced by metal bioavailability and plant growth. Hence, we applied a synergistic intensification system with plant hormone (24-Epibrassinolide, EBR) and metal-resistant bacterium (Serratia sp. CTZ4) to enhance Cd extraction of Amaranthus hypochondriacus L. in contaminated soil. Results demonstrated that the combination of CTZ4 and EBR promoted soil microecology through decreasing soil pH, improving soil enzymatic activity (dehydrogenase, invertase, acid phosphate, urease). Besides, microbial community structure was evaluated to understand the diversity and relative abundance of microbe in soil after remediation. Moreover, the maximum extraction of Cd was 5.91 mg kg-1 and increased about 60.16 % to CK. Meanwhile, the antioxidant system (SOD, CAT activities) of plant was improved significantly as well as plants biomass increasing by 46.02 % with the combination of EBR and CTZ4. Thus, our results proved that the utilization of EBR and CTZ4 is an alternated method to enhance phytoextraction efficiency of A. hypochondriacus in Cd-contaminated soil.

Responsiveness change of biochemistry and micro-ecology in alkaline soil under PAHs contamination with or without heavy metal interaction

Co-presence of organic pollutants and heavy metals in soil is causing increasing concerns, but the lack of knowledge of relation between soil ecology and pollutant fate is limiting the developing of specific control strategy. This study investigated soil change under pyrene stress and its interaction with cadmium (Cd). Soil physicochemical properties were not seriously influenced. However, pollutants' presence easily varied soil microbial activity, quantity, and diversity. Under high-level pyrene, Cd presence contributed to soil indigenous microorganisms' adaption and soil microbial community structure stability. Soils with both pyrene and Cd presented 7.11-12.0% higher pyrene degradation compared with single pyrene treatment. High-throughput sequencing analysis indicated the proportion of Mycobacterium sp., a commonly known PAHs degrader, increased to 25.2-48.5% in treatments from 0.52% in control. This phenomenon was consistent with the increase of PAHs probable degraders (the ratio increased to 2.86-6.57% from 0.24% in control). Higher Cd bioavailability was also observed in soils with both pollutants than that with Cd alone. And Cd existence caused the elevation of Cd resistant bacterium Limnobacter sp. (increased to 12.2% in CdCK from 2.06% in control). Functional gene prediction also indicated that abundance of genes related to nutrient metabolism decreased dramatically with pollutants, while the abundances of energy metabolism, lipid metabolism, secondary metabolites biosynthesis-related genes increased (especially for aromatic compound degradation related genes). These results indicated the mutual effect and internal-interaction existed between pollutants and soils resulted in pollutants' fate and soil microbial changes, providing further information regarding pollutants dissipation and transformation under soil microbial response.

High-effectively degrade the di-(2-ethylhexyl) phthalate via biochemical system: Resistant bacterial flora and persulfate oxidation activated by BC@Fe3O4

Di-(2-ethylhexyl) phthalate (DEHP) has been classified as a priority pollutant which increased the healthy risk to human and animals dramatically. Hence, a novel biochemical system combined by DEHP-resistant bacterial flora (B) and a green oxidant of persulfate (PS) activated by Nano-Fe₃O₄ was applied to degrade DEHP in contaminated soil. In this study, the resistant bacterial flora was screened from activated sludge and immobilized by sodium alginate (SAB). Nano-Fe₃O₄ was coated on biochar (BC@Fe₃O₄) to prevent agglomerating in soil. X-ray diffraction (XRD) and scanning electron microscope (SEM) were utilized to characterize BC@Fe₃O₄. Results demonstrated that the treatment of biochemical system (SAB + BC@Fe₃O₄ + PS) presented the maximum degradation rate about 92.56% within 24 days of incubation and improved soil microecology. The 16S rDNA sequences analysis of soil microorganisms showed a significantly different abundance and a similar diversity among different treatments. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional genes difference analysis showed that some metabolic pathways, such as metabolism of cofactors and vitamins, energy metabolism, cell growth and death, replication and repair, were associated with the biodegradation of DEHP. Besides, DEHP was converted to MEHP and PA by biodegradation, while DEHP was converted to DBP and PA by persulfate and BC@Fe₃O₄, and then ultimately degraded to CO₂ and H₂O.

The influence of corncob-based biochar on remediation of arsenic and cadmium in yellow soil and cinnamon soil

Biochar plays a significant role in soil remediation. However, the simultaneous immobilization mechanism and relationship of biochar to cations and anions have never been clear. We designed a batch incubation experiment to investigate the impact of corncob-based biochars to cadmium (Cd) and arsenic (As) contaminations in yellow soil and cinnamon soil, and analyze the relationships among biochars physicochemical characteristics (surface area: SA, total pore volume: TV, average pore size: AV and the C/O rate), soil properties, metals immobilization and microbial diversity indices. Results showed that the modified biochars (inorganic-modified biochar: BCTD) had a good effect on heavy metals immobilization and transformed acid extractable and reducible fraction into the residual fraction. Total nitrogen, organic matter and available potassium increased in both soils after biochar application. The principal component analysis presented that the smaller C/O rate was favorable to As stabilization; the SA and TV of biochar were negatively correlated with the leaching concentration of Cd. The larger surface area, higher porosity and organic matters of biochar were more beneficial to soil microbial diversity. This work not only can demonstrate remediation mechanisms of heavy metals contaminated soil by biochars, but also gain an application of biochars technology in the recycling and reutilize of agricultural waste, and provide a clear strategy for heavy metals contaminated soil, especially As and Cd.

Bioremediation of cadmium polluted soil using a novel cadmium immobilizing plant growth promotion strain Bacillus sp. TZ5 loaded on biochar

Bioremediation of cadmium polluted soil using biochar (BC) and plant growth promotion bacteria (PGPB) have been widely concerned. In our study, a novel Cd immobilizing PGPB strain TZ5 was isolated based on the Cd immobilizing potential and plant growth promotion (PGP) traits. Further, changes of surface morphology and functional groups of TZ5 cells were observed after exposed to Cd²⁺ by SEM-EDS and FTIR analyses. Then, the strain TZ5 was successfully loaded on BC as biochemical composites material (BCM). Pot experiment indicated that the percentage of acetic acid-extractable Cd in BCM treatments significantly decreased by 11.34 % than control. Meanwhile, BCM significantly increased the dry weight of ryegrass by 77.78 %, and decreased the Cd concentration of ryegrass by 48.49 %, compared to control. Microbial counts and soil enzyme activities in rhizosphere were both significantly improved by BCM. Furthermore, the proportion of relative abundance of Bacillus genus was enhanced after treated by BCM, which indicated that the strain TZ5 was successfully colonized in the rhizosphere. This study provided a practical strategy for bioremediation of Cd contaminated soil.

Characteristics and in situ remediation effects of heavy metal immobilizing bacteria on cadmium and nickel co-contaminated soil

Cadmium (Cd) and nickel (Ni) in soil have caused serious environmental problems and increased healthy risks to humans and biota, it is vital important and necessary to develop effective methods to resolve the combined contaminated problems. In this study, strains L5 and L6 with good heavy metal resistant and immobilizing capacities were isolated from Cd and Ni contaminated soil. Bacterial characteristic experiment illustrated that many functional groups (-OH, -NH2 and -COO et al.) were distributed on the surface of L5 and L6. Under the stress of heavy metals, bacterial appearances were distorted. The pot experiment indicated that the concentrations of HOAc-extractable Cd and Ni in soil reduced 6.26-15.33% and 13.31-19.53% with the inoculation of L5 and L6. In addition, the immobilization rates on Cd and Ni improved 61.27-128.50% and 23.69-39.66% with re-inoculation of strains L5 and L6 at 30 days, respectively. After inoculation of strains L5 and L6 for 60 days, the activities of FDA hydrolysis, acid phosphatase, urease, invertase and dehydrogenase in soil increased obviously. Furthermore, bacterial diversity indexes and community structure of soil were also improved. Thus, given the beneficial remediation effects of the isolated strains, L5 and L6 have great potentials for heavy metals contaminated soil remediation.

Insight into the mechanisms of plant growth promoting strain SNB6 on enhancing the phytoextraction in cadmium contaminated soil

Plant growth-promoting rhizobacteria (PGPR) assisted accumulator has been proposed as a phytoextraction method to clean cadmium (Cd) in contaminated soil, while the mechanisms were few studied regrading PGPR-soil-accumulator as an assemble. In this study, we revealed the possible mechanisms of the plant growth-promotion strain SNB6 on enhancing the Cd phytoextration of vetiver grass by the analysis of the whole genome of SNB6, soil biochemical properties and plant growth response. Results showed that SNB6 encoded numerous genes needed for Cd tolerance, Cd mobilization and plant growth promotion. SNB6 increased HOAc-extractable Cd that showed a positive correlation with Cd uptake in accumulator. In addition, SNB6 improved the biochemical activities (bioavailability of nutritional substances, bacterial count, soil respiration and enzyme activity) in rhizosphere soil. Moreover, the antioxidative enzymes activities of accumulator were significantly enhanced by SNB6. Consequently, SNB6 promoted Cd uptake and biomass of accumulator, thus enhancing the Cd phytoextraction. The maximum Cd extractions in root, stem and leaf reached to 289.47 mg/kg, 88.33 mg/kg and 59.38 mg/kg, respectively. Meanwhile, the total biomass of accumulator was increased by 9.68-45.99% in SNB6 treatment. These findings could be conducive to the understanding the mechanisms of PGPR on enhancing the Cd phytoextraction of accumulator.

Effect of Serratia sp. K3 combined with organic materials on cadmium migration in soil-vetiveria zizanioides L. system and bacterial community in contaminated soil

Phytoremediation is an economical strategy to harvest cadmium (Cd) from contaminated soil, but the efficiency of phytoremediation was affected by many factors. This study investigated the potential of Serratia sp. K3 (K3) assisted with straw biogas residue (SBR) or leavening fertilizer (LF) on improving the Cd migration efficiency and micro-environment in soil-vetiveria zizanioides L. system. The results showed that the acid soluble Cd in soil was increased by 2.83-29.79% in treatments compared with control (CK). In addition, Cd accumulation in the roots and shoots of vetiveria zizanioides were significantly enhanced by the combination of K3 and SBR/LF. Especially, the translocation factor of Cd increased by 21.53-62.37% in groups with K3 compared with the groups without K3, correspondingly. Furthermore, SBR/LF effectively changed bacterial community structure, and improved bacterial abundance. Relative abundance of functional genes related with carbohydrate/energy/amino acid metabolism were increased in groups of SBRB/LFB rhizosphere compared with CK. These results provide insight into the change of phytoremediation efficiency and soil bacterial communities in the vetiveria zizanioides rhizosphere after inoculation. This study may provide a promising method for improving phytoremediation in Cd contaminated soil.

Remediation of hexavalent chromium contaminated soil by nano-FeS coated humic acid complex in combination with Cr-resistant microflora

A novel nano-composite material (CMC-FeS@HA) combining the advantages of humic acid (HA) and FeS was synthesized to remediate hexavalent chromium (Cr(VI)) contaminated soil along with chromium (Cr) resistant microflora. The characteristic analysis confirmed the successful synthesis of the nano-composite, which provided further mechanism evidence of its detoxification effect on polluted soil. Energy Dispersive System analysis proved the adsorption of the microbe consortium (MC) for Cr. After remediation, Cr(VI) in all treatments was dramatically reduced and the leachable Cr in soil treated by CMC-FeS@HA and MC decreased 89.14% compared with control. The result of BCR sequential extraction showed that Cr was stabilized, whose form changed to oxidizable and residual from HOAC-extractable. Besides, CMC-FeS@HA, as a sustained-release acid with high biocompatibility, could continuously decrease the pH of strongly alkaline soil and created a suitable micro-ecological environment for soil microorganisms. Moreover, CMC-FeS@HA dramatically improved soil physicochemical property, soil microbial activity (dehydrogenase, hydrolase, urease, and invertase activities), and soil microecological diversity. In total, this study provided a useful technology for soil remediation, which innovatively combined chemical remediation and microbial-remediation with a positive effect on soil quality, providing a good approach for the multiple technology combination in the environmental cause.

Mechanism study of Chromium influenced soil remediated by an uptake-detoxification system using hyperaccumulator, resistant microbe consortium, and nano iron complex

A soil heavy metal decontamination system was developed based on the immobilization of bioavailable metal fraction by iron-biochar nano-complex (BC@Fe₃O₄) and the uptake by Chromium (Cr) hyperaccumulator Leersia hexandra (L. hexandra) under the assistance of metal resistant microbe consortium (MC). In this system, L. hexandra was able to accumulate 485.1-785.0 mg kg^-1 in root and 147.5-297.2 mg kg^-1 of Cr in its aerial part. With MC assistance, more Cr could be translocated to the aerial part of L. hexandra, which dramatically improved its remediation potential. Meanwhile, BC@Fe₃O₄ application decreased bioavailable Cr in soil and reduced soil toxicity, which contributed to soil microbial community adaption and L. hexandra performance under high level of Cr concentration (elevated microbial activity, decreased plant stress response, enhanced L. hexandra growth and accumulation) without negative influence on accumulation efficiency. Moreover, details of the possible mechanistic insight into metal removal were discussed, which indicated a negative correlation of the extractable Cr with soil microecology and hyperaccumulator performance. Furthermore, the resistant bacteria successfully altered soil microbial community, enhanced its diversity, which was in favor of the soil quality improvement.

Impacts of a novel strain QY-1 allied with chromium immobilizing materials on chromium availability and soil biochemical properties

In-situ passivation of soil chromium (Cr) contamination based on chemical and biological passivators has been widely concerned, however, the cooperative effect of two types of passivators on Cr passivation and soil properties was little investigated. In this study, nano zero valent iron (nZVI) and humic acid (HA) as the chemical passivators were selected and were combined with a novel Cr resistant strain QY-1 to study these two points. Results demonstrated that the combination was more effective in Cr immobilization, among which, HA + QY-1 had the highest passivation rate (82.83%), followed by nZVI + QY-1. HA + QY-1 alleviated soil Cr stress most efficiently as its soil relevant fertility indicators, microbial quantity, respiration and seed gemination rate significantly increased. On the contrary, nZVI decreased soil respiration and microbial abundance, but the addition of QY-1 could relieve this phenomenon. The results highlighted the ability of HA + QY-1 to remediate Cr contaminated soil and improve soil stability.

Photocatalytic Bacterial Inactivation by a Rape Pollen-MoS2 Biohybrid Catalyst: Synergetic Effects and Inactivation Mechanisms

A novel and efficient 3D biohybrid photocatalyst, defective MoS₂ nanosheets encapsulated carbonized rape pollen, was fabricated and applied to water disinfection. The rape pollen-MoS₂ (PM) biohybrid showed excellent dispersibility, high stability, and efficient charge-carrier separation and migration ability, resulting in the highly enhanced photocatalytic inactivation performance toward various waterborne bacteria under different light sources. The inactivation mechanisms were systematically investigated. Reactive species (RSs), including electrons, holes, and reactive oxygen species (•O₂^- and •OH), played major roles in inactivating bacteria. The antioxidant system of bacteria exhibited a self-protection capacity by eliminating the photogenerated RSs from PM biohybrid at the early stage of inactivation. With the accumulation of RSs, the cell membrane and membrane-associated functions were destroyed, as suggested by the collapse of cell envelope and subsequent loss of cell respiration and ATP synthesis capacity. The microscopic images further confirmed the destruction of the bacterial membrane. After losing the membrane barrier, the oxidation of cytoplasmic proteins and lipids caused by invaded RSs occurred readily. Finally, the leakage of DNA and RNA announced the irreversible death of bacteria. These results indicated that the bacterial inactivation began with the membrane rupture, followed by the oxidation and leakage of intracellular substances. This work not only provided a new insight into the combination of semiconductors with earth-abundant biomaterials for fabricating high-performance photocatalysts, but also revealed the underlying mechanisms of photocatalytic bacterial inactivation in depth.

Elucidation of the mechanisms into effects of organic acids on soil fertility, cadmium speciation and ecotoxicity in contaminated soil

The remediation effect of organic acids in heavy metal contaminated soil was widely studied. However, the comprehensive evaluation of organic acids on micro-ecological environment in heavy metal contaminated soil was less known. Herein, this experiment was conducted to investigate the impact of malic acid, citric acid and oxalic acid on soil fertility, cadmium (Cd) speciation and ecotoxicity in contaminated soil. Especially, to evaluate the ecotoxicity of Cd, high-throughput sequencing was used to investigate the soil bacterial community structure and diversity after incubation with organic acids. The results showed that obvious changes in soil pH were not observed. Whereas, the contents of available phosphorus (Olsen-P) and alkali hydrolysable nitrogen (Alkeline-N) evidently increased with a significant difference. Furthermore, compared to control, the proportion of acetic acid-extractable Cd increased by 3.06-6.63%, 6.11-9.43% and 1.91-6.22% respectively in the groups amended with malic acid, citric acid and oxalic acid, which indicated that citric acid did better in improving the availability of Cd than malic acid and oxalic acid. In terms of biological properties, citric acid did best in bacteria count increase, enzyme activities and bacterial community structure improvement. Accordingly, these results provided a better understanding for the influence of organic acids on the micro-ecological environment in Cd contaminated soil, based on physicochemical and biological analysis.

The activation and extraction systems using organic acids and Lentinus edodes to remediate cadmium contaminated soil

To develop a high efficient and eco-friendly approach to remediate cadmium (Cd) contaminated soil, we designed the activation and extraction systems, on the basis of combined effects between the ability of organic acids to activate Cd and the ability of mushroom accumulator (Lentinus edodes) to extract Cd. The results showed that the proportion of acetic acid-extractable Cd significant increased with the application of exogenous organic acids. Additionally, soil microecology analysis indicated that exogenous organic acids evidently enhanced the numbers of microbial cells and the activities of soil enzymes. Besides, high throughput sequencing analysis revealed exogenous organic acids improved the diversity and structure of soil bacterial community after remediation. Particularly, the combination application of mushroom and exogenous citric acid had highest accumulation efficiency of Cd, and its efficiency was 59.19% higher than single mushroom treatment. Hence, exogenous organic acids could alleviate soil microecology and increase mycoextraction efficiency, which suggested it was a feasible route to remediate Cd contaminated soil by the activation and extraction systems.

The performance of biochar-microbe multiple biochemical material on bioremediation and soil micro-ecology in the cadmium aged soil

Biochar (BC) and plant growth promoting bacteria (PGPR) have been widely applied to improve the qualities of heavy metal contaminated soil, while the synergy effect of BC and PGPR on the bioremediation of cadmium (Cd) contaminated soil was less studied. In this study, a novel PGPR strain SNB6 was isolated and then immobilized on BC as the multiple biochemical material (BCM) as well as combined with vetiver grass (Chrysopogon zizanioides L.) to form BC-PGPR-accumulator system. The promoting effects of BCM on bioremediation and soil micro-biology were comprehensively investigated. SEM and FTIR analysis indicated that the strain SNB6 was successfully fixed on BC and the functional groups between BC and SNB6 surface contributed to the immobilization effect. The BCM significantly enhanced the Cd content and bioaccumulation factor (BCF) of accumulator, about 412.35% and 403.41% higher than that of control, respectively. Meanwhile, the biomass of fresh and dry accumulator in the BCM treatment was 227.27% and 178.33% higher than that of control. In addition, the system significantly increased the proportion of HOAc-extractable Cd and soil micro-ecology. Microbial counts and soil enzyme activities in rhizosphere were both significantly improved by the interaction of BCM and C. zizanioides. Furthermore, the strain SNB6 in the rhizosphere interface was successfully colonized, and soil microbial community was evaluated to understand the microbial diversity after bioremediation. Our study indicated that the BCM could significantly enhance the bioremediation efficiency and drive the soil micro-ecology, and the BC-PGPR-accumulator system provided a feasible pathway to remediate heavy metal contaminated sites.

The effect of two different biochars on remediation of Cd-contaminated soil and Cd uptake by Lolium perenne

Biochar can be widely used to reduce the bioavailability of heavy metals in contaminated soil because of its adsorption capacity. But there are few studies about the effects of biochar on cadmium uptake by plants in soil contaminated with cadmium (Cd). Therefore, an incubation experiment was used to investigate the effects of rice straw biochar (RSBC) and coconut shell biochar (CSBC) on Cd immobilization in contaminated soil and, subsequently, Cd uptake by Lolium perenne. The results showed that the microbial counts and soil enzyme activities were significantly increased by biochar in Cd-contaminated soil, which were consistent with the decrease of the bioavailability of Cd by biochar. HOAc-extractable Cd in soil decreased by 11.3-22.6% in treatments with 5% RSBC and by 7.2-17.1% in treatments with 5% CSBC, respectively, compared to controls. The content of available Cd in biochar treatments was significantly lower than in controls, and these differences were more obvious in treatment groups with 5% biochar. The Cd concentration in L. perenne reduced by 4.47-26.13% with biochar. However, the biomass of L. perenne increased by 1.35-2.38 times after adding biochar amendments. So, Cd uptake by whole L. perenne was augmented by RSBC and CSBC. Accordingly, this work suggests that RSBC and CSBC have the potential to be used as a useful aided phytoremediation technology in Cd-contaminated soil.

Bioreduction of hexavalent chromium using a novel strain CRB-7 immobilized on multiple materials

In this study, a novel Cr(VI) tolerant strain CRB-7 identified as Bacillus sp., was isolated and characterized for its high Cr(VI) reduction. The strain CRB-7 grew well and effectively reduced Cr(VI) under various conditions including pH (7-9), temperature (30-40 °C) and Cr(VI) concentrations (50-250 mg L^-1). It almost completely reduced 120 mg L^-1 Cr(VI) within 48 h under optimized condition of pH 7 and 37 °C. Further characterization by SEM-EDS and FTIR analyses indicated Cr(VI) removal mechanism of CRB-7 was predominately via bioreduction with little amount of bioadsorption. Furthermore, the strain CRB-7 based immobilized biobeads were successfully synthesized using five different porous materials as bacterial loading carrier respectively to ascertain the optimal immobilization biocomposite for Cr(VI) removal. CRB-7 cells immobilized with 3% sodium alginate (SA) and 5% humic acid (HA) exhibited the highest Cr(VI) removal efficiency. Moreover, immobilized biobeads have the advantages over free cells in being more stable and easier to reuse. High Cr(VI) reducing ability of the free and immobilized CRB-7 cells suggest the strain CRB-7, especially the B-HA-SA biocomposite is promising for remediating Cr(VI)-contaminated sites.

Mechanisms into the removal and translocation of cadmium by Oudemansiella radicata in soil

This study investigated the removal and translocation mechanism of cadmium (Cd) by Oudemansiella radicata (O. radicata) in mushroom-soil rhizosphere and the fruiting body of mushroom. For this, the biomass, physiochemical parameters, and Cd distribution of O. radicata were examined in the soil spiked with 0, 10, 20, and 30 mg kg^-1 Cd. The soil microecology and the Cd fractionation in the soil rhizosphere were also measured. Results showed that, O. radicata possesses high capability to tolerate Cd, although its surface phenotypic structure was influenced by high concentrations of Cd. The observed concentrations of Cd in O. radicata were in the following order: root (the part of stipe in soil) > pileus > stipe. The presence of Cd led to an increase in the production of antioxidant enzymes and glutathione (GSH). These results suggested that antioxidant enzymes and GSH assisted detoxification and accumulation of Cd within the mushroom. Meanwhile, in the soil rhizosphere, the concentrations of oxalic, citric, and malic acids were enhanced with the treatment of Cd, indicating that the production of these acids was closely related to the presence of Cd in soils. Additionally, the proportion of acid-soluble Cd was increased and the soil microecology (microbial counts, urease, and acid phosphatase activities) also enhanced with the inoculation of O. radicata. Overall, this study demonstrated that O. radicata is a promising candidate for the remediation of Cd-contaminated soil.

Effects of amendments on heavy metal immobilization and uptake by Rhizoma chuanxiong on copper and cadmium contaminated soil

An improved method was applied for remediating cadmium and copper co-contaminated soil and reducing the metal concentration in Rhizoma chuanxiong. Pot experiments were conducted with six amendments (composed with bentonite, phosphate, humic acid, biochar, sepiolite powder, etc.). The results showed that soil pH, biological activities (soil enzymatic activities and microbial counts) and R. chuanxiong biomass were greatly improved with the addition of amendments in all treatments, especially in T3 and T6. Also, amendments effectively decreased the concentration of malondialdehyde and H₂O₂ in R. chuanxiong. In the T3 treatment, the bio-available Cd and Cu in soil were significantly decreased by 0.53 and 0.41 mg kg^-1, respectively. Meanwhile, the amendment in T3 reduced Cd and Cu accumulation in R. chuanxiong about 45.83 and 39.37%, respectively, compared to T0. Moreover, the Fourier transform infrared spectroscopy spectra showed the surface functional groups of every amendment. To conclude, this study offers an effective and environmental method to reduce metal accumulation in R. chuanxiong on heavy metal co-contaminated soil.