Efficacy of in situ active capping Cd highly contaminated sediments with nano-Fe2O3 modified biochar

Comprehensive effects of sediment dredging on environmental risk and bioavailability of heavy metals from the sediment of Lake Taihu, China

The comprehensive effects of environmental dredging on heavy metals (HM) are still uncertain. This study comprehensively evaluates the long-term effects of dredging on the environmental risk and bioavailability of HM (Cu, Ni, Zn, Pb, Cd, Cr, and As) in Lake Taihu, China, by comparing simulated dredged treated (D) and undredged (UD) sediment cores under in-situ conditions for one year. Threshold effect level (TEL), geological accumulation index (Igeo), potential ecological risk index (RI), and ratios of secondary phase and primary phase (RSP) methods were used to assess the environmental risk of sediment HM; and the diffusive gradient in thin-films (DGT) technique was applied to assess the bioavailability of sediment HM. The results indicate that Cd was the most polluted metal assessed by the Igeo and RI method, and that dredging significantly reduced the total content of sediment HM, particularly for Cu, Zn, and Cd, and its Igeo and RI index, but caused a slight effect on its fractionation and distinct effect on RSP index. These indices changed independently and seasonally. Porewater analysis suggested higher HM concentrations in summer and winter may cause corresponding deterioration in overlying water. DGT analysis suggested a large proportion of metal-DOM complexes and showed that dredging reduced the bioavailability of Ni, Cd, and As but had a mixed impact (effective and/or ineffective impact varied with seasons) on other metals. These findings highlight the complexity of dredging effects on sediment HM dynamics, underscoring the importance of seasonal monitoring and multi-geoengineering techniques targeted at total and specific metals.

New insights into sustainable in-situ fixation of heavy metals in disturbed seafloor sediments

To address the issues of plume formation and heavy metal ion release during deep-sea mining operations, this study employed multi-sourced mineral composite roasting materials (MMCCM) of varying sizes. An in-situ capping technique was applied within a simulated system to immobilize heavy metals in contaminated sediments. The results demonstrated that capping with MMCCM of different sizes significantly suppressed the upward migration of Cu, Co, and Ni from sediments into the overlying seawater following disturbance. Ion diffusion was identified as a key mechanism driving heavy metal migration. By calculating the release rates of heavy metals during both the disturbed and undisturbed phases, it was found that the application of MMCCM induced a negative diffusion of heavy metals, indicating that the MMCCM-sediment layer functioned as a "sink" for heavy metals. FTIR and XPS analysis showed that the primary mechanisms for heavy metal removal by MMCCM were electrostatic attraction and complexation-precipitation. Additionally, capping with MMCCM facilitated the transition of heavy metals from labile to stable forms within the sediments. Through comprehensive evaluation, the long-term effectiveness of the fixed effects was demonstrated as follows: large MMCCM (L@MCM) > medium MMCCM (M@MCM) > small MMCCM (S@MCM) > powder MMCCM (P @ MCM). Finally, we proposed future research directions and introduced the DQSE framework for the sustainable application of MMCCM. Based on the above findings, this study provides new insights and research references for the in-situ immobilization of heavy metals and plume reduction during future deep-sea mining processes.

Green modification of biochar with poly(aspartic acid) enhances the remediation of Cd and Pb in water and soil

Biochar is a promising adsorbent for the remediation of heavy metals in water and soil. However, pristine biochar has a limited adsorption capacity for heavy metals, which restricts its application in the field of heavy metal immobilization. In the present study, the acidic amino acid-modified biochar was prepared, and its adsorption properties for cadmium (Cd) and lead (Pb) in aqueous solution were investigated. The results showed that poly(aspartic acid)-modified biochar (PASP-BC) was more effective in removing Cd(II) from water compared to biochar modified with poly(glutamic acid) (PGA-BC), aspartic acid (ASP-BC), and glutamic acid (GA-BC). The calculated maximum adsorption capacities, derived from Langmuir fitting parameters, for Cd(II) and Pb(II) by PASP-BC were 44.2 mg/g and 126.1 mg/g, respectively, which were 3.78 and 2.70 times higher than that for pristine BC. Based on the results from Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses, ion exchange, complexation, and electrostatic adsorption were identified as the mechanisms for Cd(II) and Pb(II) adsorption by PASP-BC. The results of the Toxicity Characteristic Leaching Procedure (TCLP) showed that PASP-BC effectively reduced the leachability of Cd and Pb by 91.2% and 84.7%, respectively, at a dosage of 3%. The pot experiment demonstrated that PASP-BC significantly reduced the bioavailability of heavy metals in Triticum aestivum L The maximum reduction in Cd and Pb content in roots was 76.3% and 72.6% when 3% PASP-BC was applied. Importantly, the application of PASP-BC decreased the translocation factor of heavy metals in wheat. Therefore, the green modification of biochar with poly(aspartic acid) has great potential in the heavy metals removal from wastewater and remediation in contaminated soil.

Contrasting fate and binding behavior of Mn and Cu with dissolved organic matter during in situ remediation using multicomponent capping in malodorous black water

The common use of peroxides in the remediation of malodorous black water may lead to the activation of heavy metals in sediment when eliminating black and odorous substances. The mechanisms of heavy metal interactions with dissolved organic matter (DOM) in response to in situ capping have not been elucidated, but this information could guide the optimization of capping materials. We developed a capping material consisting of hydrothermally carbonized sediment (HCS), hydrated magnesium carbonate (HMC) and sodium percarbonate (SPC) and used microcosm experiments to investigate the dynamics of Mn and Cu at the sediment-water interface in malodorous black water. The results showed that HCS, HMC and SPC contributed multiple functions of mechanical protection, chemical isolation and oxygen provision to the new caps. HMC promoted the conversion of Mn/Cu into carbonate minerals. The optimal mass proportions were 25 % HCS, 60 % HMC and 15 % SPC based on the mixture design. In situ capping altered the fate and transformation of metals in the sediment-overlying water profile in the short term through Mn immobilization and Cu activation. The complexation of Cu(II) ions was significantly stronger than that of Mn(II) ions. In situ capping had a significant effect on the order of complexation of different fluorescent DOM molecules with Mn(II)/Cu(II) ions: microbial byproducts and fulvic acid-like components were preferentially complexed with Cu(II) ions after capping, while phenolic and humic acid-like components preferentially interacted with Mn(II) ions. Humic-like components bound to Cu were affected the most by capping treatment, whereas protein-like components were relatively weakly affected. Our study provides valuable knowledge on the impact of in situ capping on DOM-metal complexes.

Aging properties and cadmium remediation mechanism of biochar in sediment from phosphorus-rich water

Cadmium (Cd) is the main heavy metal pollutant in sediments from East China. The biochar-sediment nexus can provide carbon sequestration and pollution control. In this work, an in situ study was conducted to investigate the long-term effects and control mechanism of biochar and the effect of biochar aging on Cd stabilization in overlying water-pore water-sediment. The Cd2+ concentration in the overlying water was positively correlated with total nitrogen (0.960, P < 0.05), total organic carbon (0.983, P < 0.05), and total phosphorus (0.993, P < 0.01) in pore water. Biochar stabilized Cd2+ by increasing the pH and oxidation-reduction potential of the sediment environment and promoting the formation of Cd1.25Ca0.75(P2O7) on the biochar surface in sediment from phosphorus-rich water. These changes were closely related to the Brunauer-Emmett-Teller surface area and average pore size of the biochar. Within 60 days, the biochar in the sediment underwent aging, which was closely related to the preparation temperature of the biochar. The organic composition of biochar prepared at a low temperature (≤ 300 °C) and the surface structure of biochar prepared at a high temperature (≥ 500 °C) were altered. The biochar parameter changes were in the order of pore volume > Brunauer-Emmett-Teller surface area > pore size. Our results show that biochar modification can enhance the remediation capacity of biochar, but may be unfavorable to biochar anti-aging. This knowledge will support policymakers and researchers when exploring long-term biochar use in contamination control and strengthen future research.

Phytoremediation of contaminated sediment combined with biochar: Feasibility, challenges and perspectives

The accumulation of contaminants in sediments is accelerated by human activities and poses a major threat to ecosystems and human health. In recent years, various remediation techniques have been developed for contaminated sediments. In this review, a bibliometric analysis of papers on sediment remediation indexed in the WOS database between 2009 and 2023 was conducted using VOSviewer. We describe the development of biochar and plants for sediment contaminant removal. However, the single processes of biochar remediation and phytoremediation can be impeded by (i) low efficiency, (ii) poor tolerance of plants towards pollutants, (iii) difficulty in biochar to degrade pollutants, and (iv) biochar aging causing secondary pollution. Fortunately, combination remediation, realized through the combination of biochar and plants, can overcome the shortcomings of their individual applications. Therefore, we suggest that the remediation of contaminants in sediments can be accomplished by combining biochar with macrophytes and considering multiple limiting factors. Here, we explore the challenges that co-remediation with biochar and macrophytes will face in achieving efficient and sustainable sediment remediation, including complex sediment environments, interaction mechanisms of biochar-macrophyte-microorganisms, emerging pollutants, and integrated life cycle assessments, which can provide references for combined biochar and plant remediation of sediments in the future.

New insights into the sustainable use of co-pyrolyzed dredged sediment for the in situ remediation of Cd polluted sediments in coastal rivers

The remediation of Cd-polluted sediment in coastal rivers is essential because of its potential hazards to river and marine ecosystems. Herein, a co-pyrolysis product of contaminated dredged sediment (S@BC) was innovatively applied to cap and immobilize Cd-contaminated sediment in coastal rivers in situ, and their remediation efficiencies, mechanisms, and microbial responses were explored based on a 360 d incubation experiment. The results showed that although S@BC immobilization and capping restrained sediment Cd release to the overlying water, S@BC capping presented a high inhibitory efficiency (66.0% vs. 95.3% at 360 d). Fraction analysis indicated that labile Cd was partially transformed to stable fraction after remediation, with decreases of 0.5%- 32.7% in the acid-soluble fraction and increases of 5.0%- 182.8% in the residual fraction. S@BC immobilization and capping had minor influences on the sediment bacterial community structure compared to the control. S@BC could directly adsorb sediment mobile Cd (precipitation and complexation) to inhibit Cd release and change sediment properties (e.g., pH and cation exchange capacity) to indirectly reduce Cd release. Particularly, S@BC capping also promoted Cd stabilization by enhancing the sediment sulfate reduction process. Comparatively, S@BC capping was a priority approach for Cd-polluted sediment remediation. This study provides new insights into the remediation of Cd-contaminated sediments in coastal rivers.

A comprehensive assessment to offer optimized remediation method for mercury contamination in Musa Bay by using hybrid Fuzzy AHP-VIKOR approach

Musa Bay, the largest wetland in Iran and one of the most important Hg-polluted media, plays a significant role in the ecosystem of the area and supports many forms of life. Mercury pollution has detrimental effects on the human body and at high levels leads to the loss of microorganisms in marine ecosystems. Hence, a comprehensive assessment for selecting an effective and sustainable remediation method is crucial to restoring the ecosystem promptly. The determination of a proper and practical treatment method not only is a case-based approach, but could be challenging due to its multi-criteria decision-making nature. Considering preferred crucial factors involved in the effectiveness of remedial actions, in this study a questionnaire is designed to assess the opinion of environmental experts, stakeholders, and some occupants of the area on remedial actions based on the importance weights of criteria. Subsequently, practical remediation and management strategies ranked by hybrid FVIKOR as a multi-criteria decision making (MCDM) method. Ranking results show that dredging and stabilization could offer a promising solution for the remediation of the case study. The results of the study demonstrate that the development of MCDM methods along with effective criteria and considering the analysis of the questionnaires, could offer the best remediation strategy for a specific contaminated site.

In Situ Remediation Technology for Heavy Metal Contaminated Sediment: A Review

Sediment is an important part of the aquatic ecosystem, which involves material storage and energy exchange. However, heavy metal pollution in sediment is on the increase, becoming an important concern for the world. In this paper, the state-of-art in situ remediation technology for contaminated sediment was elaborated, including water diversion, capping, electrokinetic remediation, chemical amendments, bioremediation and combined remediation. The mechanisms for these techniques to reduce/immobilize heavy metals include physical, electrical, chemical and biological processes. Furthermore, application principle, efficiency and scope, advantages and disadvantages, as well as the latest research progress for each restoration technology, are systematically reviewed. This information will benefit in selecting appropriate and effective remediation techniques for heavy metal-contaminated sediment in specific scenarios.

In Situ Synthesis of MnMgFe-LDH on Biochar for Electrochemical Detection and Removal of Cd2+ in Aqueous Solution

Herein, MnMgFe-layered double hydroxides/biochar (MnMgFe-LDHs/BC) composite was fabricated by immobilizing MnMgFe-LDHs on BC via the coprecipitation method, which was employed as an effective material for the detection and removal of Cd²⁺ from aqueous media. A lamellar structure of MnMgFe-LDHs with abundant surface-hydroxyl groups and various interlayer anions inside present a greater chance of trapping Cd²⁺. Meanwhile, the conductive BC with a porous structure provides numerous channels for the adsorption of Cd²⁺. Using the MnMgFe-LDHs/BC-based sensor, Cd²⁺ can be detected with a low limit of detection down to 0.03 ng/L. The feasibility of detecting Cd²⁺ in paddy water was also carried out, with satisfactory recoveries ranging from 97.3 to 102.3%. In addition, the MnMgFe-LDHs/BC material as an adsorbent was applied to remove Cd²⁺ from water with adsorption capacity of 118 mg/g, and the removal efficiency can reach 91%. These results suggest that the as-prepared MnMgFe-LDHs/BC can serve as a favorable platform for efficient determination and removal of Cd²⁺ in water.

Removal effect of enrofloxacin from mariculture sediments by bioelectrochemical system and analysis of microbial community structure

Based on the application of sediment microbial fuel cell (SMFC) in the bioremediation of sediment, this study used the sediment microbial fuel cell technology as the leading reactor. Modification of anode carbon felts (CF) by synthesis of PANI/MnO₂ composited to improve the electrical performance of the sediment microbial fuel cell. This study investigated the degradation effects, degradation pathways of the specific contaminant enrofloxacin and microbial community structure in sediment microbial fuel cell systems. The results showed that the sediment microbial fuel cell system with modified anode carbon felt (PANI-MnO₂/CF) prepared by in-situ chemical polymerization had the best power production performance. The maximum output voltage was 602 mV and the maximum power density was 165.09 mW m^-2. The low concentrations of enrofloxacin (12.81 ng g^-1) were effectively degraded by the sediment microbial fuel cell system with a removal rate of 59.52%.