Sediment metals adhering to biochar enhanced phosphorus adsorption in sediment capping

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.

Effect of Modified Biochar Prepared by Co-pyrolysis of MgO on Phosphate Adsorption Performance and Seed Germination

Biochar is currently used as a phosphate adsorbent in water and subsequently as a soil amendment. In this study, modified biochar was prepared directly by co-pyrolysis of MgO and rice straw, and a preliminary ecotoxicological assessment was performed before the application of modified biochar to soil. The effects of single factors, such as pyrolysis temperature, dosage, pH, and coexisting ions, on phosphate adsorption performance were investigated. In addition, after phosphate adsorption, the effects of modified biochar leachate on the germination of corn and rice seeds were examined. The results showed that phosphate adsorption by the modified biochar first increased and then decreased as the pyrolysis temperature increased, with modified biochar prepared at 800 °C showing the greatest adsorption. In addition, a comprehensive cost analysis showed that the best phosphate adsorption effect of modified biochar was achieved at a dosage of 0.10 g and a solution pH of 3. In contrast, the presence of competitive coexisting ions, Cl- , NO3 - , CO3 2- , and SO4 2- , reduced the phosphate adsorption capacity of the modified biochar. The adsorption kinetics results revealed that the process of phosphate adsorption by the modified biochar was more in line with the pseudo-second-order model and dominated by chemisorption. Moreover, the adsorption isotherm results indicated that the process was more in line with the Langmuir model and dominated by monomolecular layer adsorption, with a maximum adsorption of 217.54 mg/g. Subsequent seed germination tests showed that phosphate-adsorbed modified biochar leachate had no significant effect on the germination rate of corn seeds, whereas it improved the germination rate of rice seeds. Together, these results provide guidance for the application of modified biochar firstly as an adsorbent of phosphate and subsequently as a soil remediator.

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

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

Simultaneous immobilization of heavy metals and nutrient elements in contaminated sediment using a novel composite agent product

In this research, an innovative type of sediment resource treatment agent (SRA) was synthesized successfully, which could immobilize ammonia nitrogen (NH₃-N), total phosphorus (TP), potassium (K), and simultaneously stabilize cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) in dredged sediment. The effects of SRA dosage on stabilizing the nutrient elements and heavy metals were investigated. The results demonstrated that the increase of SRA dosage significantly enhanced the stabilization of nutrients and heavy metals. The 14-day rainwater infiltration and rainwater scouring experiments were carried out. With the simulation test of rainwater infiltration, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH₃-N, TP, and K with 2% SRA addition reached 80.8%, 76.8%, 80.3%, 77.5%, 78.0%, 72.7%, 64.3%, 73.9%, and 73.9%, respectively. Under the action of rainwater scouring, the stabilization ratios of Cr, Cu, Ni, Pb, Zn, Cd, NH3-N, TP, and K with 6.4% SRA addition reached 84.6%, 84.0%, 77.6%, 87.3%, 80.0%, 61.5%, 76.2%, 77.8%, and 91.7%, respectively. Therefore, the results demonstrate that SRA is an excellent composite material in stabilizing heavy metals while reserving the nutrients in dredged sediment, thus showing great potential in the application for dredged sediment resource treatment.

Nano-Zero-Valent Zinc-Modified Municipal Sludge Biochar for Phosphorus Removal

Municipal sludge biochar (MSBC) can be used to absorb phosphorus in water for waste treatment. Nano-zero-valent zinc (nZVZ) was uniformly attached to MSBC to obtain a highly efficient phosphorus-absorbing composite material, nZVZ–MSBC. Characterization by FTIR, XPS, XRD, and BET showed that nZVZ was uniformly dispersed on the surface of the MSBC. Zinc loading was able to greatly improve the adsorption performance of MSBC for phosphorus. Adsorption experiments illustrated that the adsorption process conformed to the Langmuir model, and the maximum adsorption amount was 186.5 mg/g, which is much higher than that for other municipal sludge biochars. The adsorption process reached 80% of the maximum adsorption capacity at 90 min, and this gradually stabilized after 240 min; adsorption equilibrium was reached within 24 h. The optimum pH for adsorption was 5. The main adsorption mechanism was chemical adsorption, but physical adsorption, external diffusion, internal diffusion, and surface adsorption also played roles. The potential for application as an efficient adsorbent of phosphorus from water was confirmed. In addition, a novel strategy for municipal sludge disposal and resource utilization is provided.

Impacts of anions on activated persulfate oxidation of Fe(II) - Rich potassium doped magnetic biochar

The potassium-doped magnetic biochar (KMBC) preparation was inevitably introduced the different anions in the process of modifying magnetic biochar (MBC) with different potassium salts, but the effect and mechanism of different anion on KMBC activation properties has not been reported. Therefore, in this paper, five different KMBCs were prepared using several common potassium salts under the same dosage of K⁺ and Fe²⁺, and then was added in the presence of persulfate (PS) for the removal of metronidazole (MNZ). The removal rate of metronidazole was ordered as KMBC_K2SO4 (98.40%) > KMBC_KNO3 (76.84%) > KMBC_KCl (20.79%) > KMBC_K2CO3 (19.02%) > KMBC_K2C2O4 (14.23%). However, the semi-quantitative of Fe(II) experiments results confirmed that the effectively increase of Fe(II) content by potassium salts modification played the dominant role in improvement of KMBC activation performance. The Fe(II) content of KMBC were ordered as KMBC_K2CO3 > KMBC_K2SO4 > KMBC_KNO3 > KMBC_KCl > KMBC_K2C2O4, with the Fe(II) content of KMBC of 36.74, 17.70, 8.79, 5.24 and 4.85 mg/g, respectively. The indicated that the introduction of different anions would lead to different optimal Fe(Ⅱ) content in KMBC modified with different potassium salts, which was most directly reflected in ¹O₂ content in different KMBC/PS systems, and account for the difference in MNZ degradation efficiency. Meanwhile, when the Fe(II) content in KMBC reached the range of 13.7-28.8 mg/g, KMBC had the better performance of activating PS.

Control of Endogenous Phosphorus Release at the Sediment–Water Interface by Lanthanum-Modified Fly Ash

This study optimizes the modification and granulation of fly ash to make it more stable at the sediment–water interface. Through laboratory simulations, the modified fly ash pellets were optimally granulated to cover the sediment–water interface, and its control effect and mechanism were evaluated. The results showed that the phosphorus adsorption effect of lanthanum-modified fly ash was 34% and 40% higher compared with those of acid-modified and alkali-modified fly ash, respectively, with the phosphorus adsorption effect reaching 85%. The best dosing ratio was about 0.3 g/L. Adsorption was affected by pH and was more effective under weak alkalinity, close to the Langmuir adsorption model, which was consistent with the unimolecular layer adsorption characteristics and the presence of chemisorption and physical adsorption. The saturation adsorption amount of phosphate by lanthanum-modified fly ash was 8.89 mg/g. The optimized granulation conditions for lanthanum-modified fly ash pellets were a fly ash/montmorillonite ratio of 7:3, a roasting temperature of 900 °C, a roasting time of 4 h, and a particle size of 3 mm. After 20 days, the orthophosphate removal rate was more than 60% higher than that of the control group, with a total phosphorus removal rate of 43%. After covering for 60 days, active phosphorus in the surface layer of the sediment was gradually transformed into a stable phosphorus form, with calcium phosphorus accounting for 70% of the total inorganic phosphorus. The ability of the sediment to release phosphorus to the overlying water body was also significantly weakened. Meanwhile, the total phosphorus removal rate in the overlying water at the sediment–water interface reached more than 40%, and orthophosphate removal reached more than 60%, indicating an obvious phosphorus control effect. Transmission electron microscopy analysis showed that lanthanum was present at locations enriched with elemental phosphorus and was adsorbed onto the material surface. Therefore, lanthanum-modified fly ash pellets are a promising in situ phosphorus control agent with good endogenous phosphorus pollution control abilities in eutrophic water bodies.

Adsorption of copper, and zinc onto novel Ca-alginate-biochar composite prepared by biochars produced from pyrolysis of groundnut husk

Alginate-based composites have been studied for adsorption technology as adsorbents due to their biocompatible, non-toxic, and cost-effective properties. In this work, groundnut husk biochar (GHB), calcium alginate (CA), and groundnut husk biochar/calcium alginate novel composites (%10) (CA-GHB1) and (% 20) (CA-GHB2) are synthesized and characterized using BET, SEM, EDX, FTIR, TGA. Adsorption performance is compared among GHB, CA, CA-GHB1, and CA-GHB2 composites to remove Cu(II), Zn (II) from aqueous solutions. Factors affecting adsorption, as well as kinetics, equilibrium, and thermal properties of adsorption, were studied using conventional equations. Adsorption isotherm models were used for two and three-parameter isotherm models to understand the interaction between the adsorbent and the adsorbate. 24.3, 44.6, 45.6, and 40.73 mg g^-1 for removal of Cu(II) on GHB, CA, CA-GHB1, and CA-GHB2 and 32.16, 25.07, 36.09, and 40.55 mg g^-1 for removal of Zn(II) on GHB, CA, CA-GHB1, and CA-GHB2 found maximum adsorption capacity (Qm) calculated from Langmuir isotherm. According to D-R isotherm data, the adsorption process is classified as physical adsorption. Thermodynamically, the adsorption process is non-spontaneous and endothermic.