Does biochar in combination with compost effectively promote phytostabilization of heavy metals in soil under different temperature regimes?

Reclamation of co-pyrolyzed dredging sediment as soil cadmium and arsenic immobilization material: Immobilization efficiency, application safety, and underlying mechanisms

The safe management of toxic metal-polluted dredging sediment (DS) is imperative owing to its potential secondary hazards. Herein, the co-pyrolysis product (DS@BC) of polluted DS was creatively applied to immobilize soil Cd and As to achieve DS resource utilization, and the efficiency, safety, and mechanism were investigated. The results revealed that the DS@BC was more effective at reducing soil Cd bioavailability than the DS was (58.9-73.2% vs. 21.8-27.4%), except for the dilution effect, whereas the opposite phenomenon occurred for soil As (25.5-35.7% vs. 35.7-42.8%). The DS@BC immobilization efficiency was dose-dependent for both Cd and As. Soil labile Cd and As were transformed to more stable fractions after DS@BC immobilization. DS@BC immobilization inhibited the transfer of soil Cd and As to Brassica chinensis L. and did not cause excessive accumulation of other toxic metals in the plants. The appropriate addition of the DS@BC (8%) sufficiently alleviated the oxidative stress response of the plants and enhanced their growth. These findings indicate that the DS@BC was safe and effective for soil Cd and As immobilization. DS@BC immobilization decreased the diversity and richness of the rhizosphere soil bacterial community because of the dilution effect. The DS@BC immobilized soil Cd and As via direct adsorption, and indirect increasing soil pH, and regulating the abundance of specific beneficial bacteria (e.g., Bacillus). Therefore, the use of co-pyrolyzed DS as a soil Cd and As immobilization material is a promising resource utilization method for DS. Notably, to verify the long-term effects and safety of DS@BC immobilization, field trials should be conducted to explore the effectiveness and risk of harmful metal release from DS@BC immobilization under real-world conditions.

Understanding of manganese-sulfur functionalized biochar: Bridging effect enhanced specific passivation of lead in soil

Widespread contamination of soils by neurotoxic lead ions (Pb) posed a serious risk to food security, but efficient treatment in soil remained a challenge. For the adsorption of Pb, DFT calculations were firstly performed to predict the synergistic effect of sulfhydryl-hydroxyl groups as well as the ability of sulfur ions to strengthen Pb-OH bonding. Consequently, Mn-S functionalized coffee ground biochar (MSBC) was then synthesized utilizing precipitation and impregnation methods. In the soil experiment, the removal efficiency of Pb reached 82.92%, exceeding the previous research results. In addition, it successfully restored the polluted farmland near the mining area and increased the plant height of Swiss chard by 186.23%. Subsequently, synergistic effect of sulfhydryl-hydroxyl groups was confirmed by XPS, FT-IR, and DFT calculations. Furthermore, the factors affecting the structural stability of O-Pb-S were discussed by regression analysis. These reflected that MSBC can enhance the removal efficiency of Pb in soil by mitigating the competition of impurity ions to adsorption sites. These findings may provide new insights into the development of the specific passivation materials for other heavy metals.

How to make lunar soil suitable for cultivation? - A review

The investigation of lunar soil encompasses extensive periods, employs many improvement methods, and has generated several simulants. The improvement of lunar soil has recently garnered growing interest as an aspect of In-Situ Resource Utilization (ISRU) for regolith. It is crucial to clarify the challenges of utilizing lunar soil as a planting substrate to develop more effective techniques. This review presents a comprehensive analysis of research on improving lunar soil properties, highlights the disparities in mineral composition between real lunar soil (also called regolith) and simulated lunar soil, then details their deficiencies as planting substrates. Following an investigation of existing improvement methods, a dilemma of metals、salt precipitation and high pH caused by adding organic matter alone was noted, while the function of microbes (bacteria, algae, and lichens) in improvement processes was assessed. Finally, we present a perspective on future the lunar soil plantable research development based on the Bioregenerative Life Support System (BLSS). This review aims to promote the engineering application of lunar soil improvements and sustainable development. We hope that one day, regolith will enable plants to flourish on the Moon.

Unveiling biochar potential to promote safe crop production in toxic metal(loid) contaminated soil: A meta-analysis

Biochar application emerges as a promising and sustainable solution for the remediation of soils contaminated with potentially toxic metal(loid)s (PTMs), yet its potential to reduce PTM accumulation in crops remains to be fully elucidated. In our study, a hierarchical meta-analysis based on 276 research articles was conducted to quantify the effects of biochar application on crop growth and PTM accumulation. Meanwhile, a machine learning approach was developed to identify the major contributing features. Our findings revealed that biochar application significantly enhanced crop growth, and reduced PTM concentrations in crop tissues, showing a decrease trend of grains (36.1%, 33.6 to 38.6%) > shoots (31.1%, 29.3 to 32.8%) > roots (27.5%, 25.7 to 29.2%). Furthermore, biochar modifications were found to amplify its remediation potential in PTM-contaminated soils. Biochar application was observed to provide favorable conditions for reducing PTM uptake by crops, primarily through decreasing available PTM concentrations and improving overall soil quality. Employing machine learning techniques, we identified biochar properties, such as surface area and C content as a key factor in decreasing PTM bioavailability in soil-crop systems. Furthermore, our study indicated that biochar application could reduce probabilistic health risks associated with of the presence of PTMs in crop grains, thereby contributing to human health protection. These findings highlighted the essential role of biochar in remediating PTM-contaminated lands and offered guidelines for enhancing safe crop production.

Rice husk and its derived biochar assist phytoremediation of heavy metals and PAHs co-contaminated soils but differently affect bacterial community

In order to evaluate the feasibility of rice husk and rice husk biochar on assisting phytoremediation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) co-contaminated soils, a 150-day pot experiment planted with alfalfa was designed. Rice husk and its derived biochar were applied to remediate a PAHs, Zn, and Cr co-contaminated soil. The effects of rice husk and biochar on the removal and bioavailability of PAHs and HMs, PAH-ring hydroxylating dioxygenase gene abundance and bacterial community structure in rhizosphere soils were investigated. Results suggested that rice husk biochar had better performance on the removal of PAHs and immobilization of HMs than those of rice husk in co-contaminated rhizosphere soil. The abundance of PAH-degraders, which increased with the culture time, was positively correlated with PAHs removal. Rice husk biochar decreased the richness and diversity of bacterial community, enhanced the growth of Steroidobacter, Bacillus, and Sphingomonas in rhizosphere soils. However, Steroidobacter, Dongia and Acidibacter were stimulated in rice husk amended soils. According to the correlation analysis, Steroidobacter and Mycobacterium may play an important role in PAHs removal and HMs absorption. The combination of rice husk biochar and alfalfa would be a promising method to remediate PAHs and HMs co-contaminated soil.

Effect of biochar with various pore characteristics on heavy metal passivation and microbiota development during pig manure composting

Understanding the porosity of biochar (BC) that promotes the heavy metal (HM) passivation during composting can contribute to the sustainable management of pig manure (PM). The current work aimed to explore the influence of BC with varying pore sizes on the physicochemical properties and morphological changes of HMs (including Zn, Cu, Cr, As, and Hg), and microbiota development during PM composting. The various pore sizes of BC were generated by pyrolyzing pine wood at 400 (T1), 500 (T2), 600 (T3) and 700 (T4) °C, respectively. The results revealed a positive correlation between specific surface area of BC and pyrolysis temperature. BC addition contributed to a significantly extended compost warming rate and duration of high-temperature period, as well as HM passivation, reflected in the decrease in Exc-Zn (63-34%) and Red-Cu (28-13%) content, and the conversion of Oxi-Cr (29-21%) and Red-Hg (16-5%) to more stable forms. Moreover, BC at T4 exhibited the best effect on Zn and Cu passivation due to the highest specific surface area (380.03 m2/g). In addition to its impact on HM passivation, BC addition improved the microbial environment during PM composting, leading to enhanced microbial diversity and richness. Notably, Chloroflexi and Bacteroidota played key roles in promoting the transformation of Exc-Cu and Red-Hg into stable forms. This phenomenon further stimulated the enhanced decomposition of organic matter (OM) when BC prepared at 600-700 °C was added. Therefore, it can be concluded that the regulation of BC porosity is an effective strategy to improve HM passivation and the overall effectiveness of PM composting.

Effect of freeze-thaw manipulation on phytostabilization of industrially contaminated soil with halloysite nanotubes

The latest trends in improving the performance properties of soils contaminated with potentially toxic elements (PTEs) relate to the possibility of using raw additives, including halloysite nanotubes (HNTs) due to eco-friendliness, and inexpensiveness. Lolium perenne L. was cultivated for 52 days in a greenhouse and then moved to a freezing-thawing chamber for 64 days. HNT addition into PTE-contaminated soil cultivated with grass under freezing-thawing conditions (FTC) was tested to demonstrate PTE immobilization during phytostabilization. The relative yields increased by 47% in HNT-enriched soil in a greenhouse, while under FTC decreased by 17% compared to the adequate greenhouse series. The higher PTE accumulation in roots in HNT presence was evident both in greenhouse and chamber conditions. (Cr/Cd and Cu)-relative contents were reduced in soil HNT-enriched-not-FTC-exposed, while (Cr and Cu) in HNT-enriched-FTC-exposed. PTE-immobilization was discernible by (Cd/Cr/Pb and Zn)-redistribution into the reducible fraction and (Cu/Ni and Zn) into the residual fraction in soil HNT-enriched-not-FTC-exposed. FTC and HNT facilitated transformation to the residual fraction mainly for Pb. Based on PTE-distribution patterns and redistribution indexes, HNT's role in increasing PTE stability in soils not-FTC-exposed is more pronounced than in FTC-exposed compared to the adequate series. Sphingomonas, Acidobacterium, and Mycobacterium appeared in all soils. HNTs mitigated FTC's negative effect on microbial diversity and increased Planctomycetia abundance.