Biochar has a large specific surface area, well-developed pore structure, abundant surface functional groups, and superior nutrient supply capacity, which is widely available and environmentally ...friendly with its advantages in waste resource utilization, heavy metal(loid) remediation, and carbon storage. This review focuses on the interactions between biochar (including raw biochar, functional biochar (modified/ engineered/ designer biochar), and composite biochar) and rhizosphere during the remediation of soil contaminated with heavy metal(loid)s (Pb, As, Cd, Hg, Co, Cu, Ni, Zn, Cr, etc.) and the effects of these interactions on the microbial communities and root exudates (enzymes and low-molecular-weight organic acids (LMWOAs)). In terms of microorganisms, biochar affects the composition, diversity, and structure of microbial communities through the supply of nutrients, provision of microbial colonization sites, immobilization of heavy metal(loid)s, and introduction of exogenous microorganisms. With regard to root exudates, biochar provides electron transfer support between the microorganisms and exudates, regulates the secretion of enzymes to resist the oxidative stress stimulated by heavy metal(loid)s, ameliorates rhizosphere acidification caused by LMWOAs, and promotes the activity of soil enzymes. The roles and mechanisms of biochar on rhizosphere soils are discussed, as well as the challenges of biochar in the remediation of heavy metal(loid)-contaminated soils, and the issues that need to be addressed in future research are foreseen.
Graphical Abstract
Highlights
The interactions between biochar and rhizosphere in the remediation of soil with heavy metal(loid)s have been focused
Biochar affects rhizosphere microorganisms by changing population diversity and community structure
Biochar regulates root exudates secretion and promotes soil enzyme activity in contaminated soil
Effects of biochar (BC) and ferrous iron (Fe2+) additions on hydrogen (H2) production from glucose were investigated. Results showed that suitable Fe2+ concentration could enhance Fe-Fe-hydrogenase ...activity, while BC addition could facilitate hydrogen-producing bacteria growth. Both of them could synergistically improve H2 production, indicating a simple, cost effective and practical process.
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•Suitable ferrous iron (Fe2+) could improve Fe-Fe-hydrogenase activity.•Biochar (BC) addition could facilitate hydrogen-producing bacteria growth.•Maximum H2 yield of 234.4ml/g glucose was obtained at 3:1 of BC/Fe2+.•Fe2+ and BC showed synergistic effects on biohydrogen production.•BC value chain was expanded by the use as additive in hydrogen fermentation.
Effects of biochar (BC) and ferrous iron (Fe2+) additions on hydrogen (H2) production from glucose were investigated using batch experiment. The glucose with both BC and Fe2+ additions were incubated at 37°C for H2 production. As compared with the control group (without BC and Fe2+ additions), the synergic effects of BC and Fe2+ make the lag phase time decease from 4.25 to 2.12h, and H2 yield increase from 158.0 to 234.4ml/g glucose. Moreover, suitable concentrations of BC and Fe2+ serve to enhance volatile fatty acid generation during H2 evolution. These results indicate that H2 production is improved by BC and Fe2+ regulations, where synergic mechanisms are described as follows: BC acts as support carriers of anaerobes and system pH buffers, which promotes the biofilm formation and maintains suitable pH environment; Appropriate Fe2+ concentration can improve hydrogenase activity in H2 production.
This review highlights scientific and advances of carbon-based functional materials, such as graphene, biochar, activated carbon, carbon cloth and nano-tube, maghemite and magnetite carbons in ...improving anaerobic digestion performance. Moreover, it focuses on some important mechanisms like microbial immobilization, syntrophic communities, interspecies electron transfer, buffering capacity, biogas upgrading, and nutrient retention, as well as current challenges and future perspectives of different carbon materials in bio-H2 and CH4 processes. Further attention should be paid to carbon-microbe interactions and the effects in continuous-feed digesters.
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•Carbon supplementation improves anaerobic digestion performance.•Carbons favor microbial activity and electron transfer among anaerobes.•Carbons facilitate microbial immobilization and metabolism.•Carbons may raise fertilizer nutrient retention and biogas quality.•Future perspectives and challenges for carbon-amended digestion are enlightened.
Carbon-based materials such as graphite, graphene, biochar, activated carbon, carbon cloth and nano-tube, and maghemite and magnetite carbons are capable for adsorbing chemicals onto their surfaces. Currently, this review is to highlight the relevance of carbons in enhancing hydrogen or methane production. Some key roles of carbons in improving cell growth, enrichment and activity, and accelerating their co-metabolisms were elaborated with regard to their effects on syntrophic communities, interspecies electron transfer, buffering capacity, biogas upgrading, and fertilizer nutrient retention and land application. Carbons can serve as a habitation for microbial immobilization, and a provision for bioelectrical connections among cells, and provide some essential elements for anaerobes. Besides, an outlook on the possible options towards the large scale and improvement solutions has been provided. Further studies in this area could be encouraged to intend and operate continuous mode by designing carbon-amended bioreactor with stability and reliability.
Hydrogen (H2) gas represents renewable resource candidate to traditional energy resource. Methods to promote the H2 evolution rate attract increasing attentions. In the present research, ferric ...oxide/carbon nanoparticles (FOCNPs) were synthesized and evaluated the feasibility to enhance the production rate of H2 gas from glucose through anaerobic fermentation by mixed bacteria. The results demonstrated that appropriate dose of FOCNPs promoted, while excessive concentration of FOCNPs suppressed the production of H2. Addition of 200 mg/L FOCNPs resulted in the highest yield of 218.63 ml H2/g glucose, 33.7% higher than 163 ml H2/g glucose of the control test without addition of FOCNPs. However, 400 mg/L of FOCNPs inhibited the H2 evolution to 154 ml/g glucose, 5.5% lower than the control. It was revealed that the H2 evolution followed the acetic pathways. The FOCNPs had a specific surface area of 27.63 m2/g, and thus addition of FOCNPs could provide more attachment sites for the growth of anaerobes. Moreover, FOCNPs could promote the activity of hydrogenase and electron transfer efficiency, beneficial for the bio-H2 evolution. However, excessive addition of FOCNPs could be toxic to microbes, and further suppressing the H2 production. The present research provided an effective method to promote the evolution rate of H2 gas.
Ferric oxide/carbon nanoparticles (FOCNPs) was synthesized and subsequently utilized in hydrogen (H2) fermentation via glucose-fed anaerobic mixed bacteria at 37 °C. FOCNPs served as not only a support carrier of anaerobes to improve cell growth, but also a biocatalyst to promote hydrogenase activity and electron transfer efficiency in the H2 production. Display omitted
•Fe2O3/C nanoparticles (FOCNPs) was used in hydrogen (H2) fermentation.•Suitable FOCNPs could enhance hydrogenase activity and electron transfer.•FOCNPs could facilitate hydrogen-producing bacteria growth and richness.•Both Gompertz and logistic models fitted well the H2 fermentation process.•Addition of 200 mg/L FOCNPs improved H2 production by 33.7%.
The annual microplastic (MP) release into soils is 4-23 times higher than that into oceans, significantly impacting soil quality. However, the mechanisms underlying how MPs impact soil properties ...remain largely unknown. Soil-MP interactions are complex because of soil heterogeneity and varying MP properties. This lack of understanding was exacerbated by the diverse experimental conditions and soil types used in this study. Predicting changes in soil properties in the presence of MPs is challenging, laborious, and time-consuming. To address these issues, machine learning was applied to fit datasets from peer-reviewed publications to predict and interpret how MPs influence soil properties, including pH, dissolved organic carbon (DOC), total P, NO
-N, NH
-N, and acid phosphatase enzyme activity (acid P). Among the developed models, the gradient boost regression (GBR) model showed the highest R
(0.86-0.99) compared to the decision tree and random forest models. The GBR model interpretation showed that MP properties contributed more than 50% to altering the acid P and NO
-N concentrations in soils, whereas they had a negligible impact on total P and 10-20% impact on soil pH, DOC, and NH
-N. Specifically, the size of MPs was the dominant factor influencing acid P (89.3%), pH (71.6%), and DOC (44.5%) in soils. NO
-N was mainly affected by the MP type (52.0%). The NH
-N was mainly affected by the MP dose (46.8%). The quantitative insights into the impact of MPs on soil properties of this study could aid in understanding the roles of MPs in soil systems.
Magnetic activated carbon (MAC) was fabricated to improve biohydrogen (bio-H
2
) production. The MAC exhibited higher biocatalytic capability and better microbial immobilization than activated carbon ...(AC) during the bio-H
2
process. Glucose supplemented with 200 mg/L MAC obtained the highest H
2
yield of 214 mL/g glucose, much higher than that (130 mL/g glucose) of the control group without MAC. Suitable dosage such as 300 mg/L AC or 200 mg/L MAC promoted volatile fatty acid (VFA) formation and H
2
generation. Besides, the metabolites showed that AC or MAC did not change the bio-H
2
evolution pathway. Some possible biochemical mechanisms were as follows: MAC served as a microbial carrier to promote cell colonization and electron transfer rate, and it released Fe
3+
to enhance glucose acidogenesis and Fe
2+
to increase microbial concentration and activity in the bio-H
2
evolution.
Graphical Abstract
Magnetic activated carbon (MAC) was fabricated and subsequently used in bio-H
2
process through glucose-fed anaerobic mixed bacteria at 37 °C. The MAC acted as a carrier of anaerobes to promote cell growth and electron transfer rate, and released Fe
3+
to increase glucose acidogenesis and Fe
2+
to improve microbial concentration and activity in the bio-H
2
evolution process.
Incidental oral ingestion is considered to be an important exposure route for humans to soil contaminants, such as fluoride (F). For 25 soil samples containing 4000 mg F/kg from aluminium smelting ...site in southwestern China, this study investigated F bioaccessibility in the human gastrointestinal tract in vitro. Fluoride bioaccessibility (2.4–48.8%) in the gastric phase was primarily caused by the dissolution of F-Ca and F-Al compounds (assigned to residual phase), identified by X-ray photoelectron spectroscopy and sequential extraction. Following modification to the small intestinal phase, the variation in F bioaccessibility (2.5–38.8%) should be the result of concurrent processes, including the formation of F complexes and competitive adsorption, and inversely the precipitation of fluorite and surface adsorption of formed F–Al complexes. The colon incubation with human gut microbiota yielded a 1.3-fold increase in F bioaccessibility (3.9–45.7%), probably due to the dissolution of F bound to Fe (hydr)oxides. Bioaccessibility adjustment can reduce hazard quotient of fluoride, and non-carcinogenic risk for children should be noted that soil F intake contributed 21.7% on average, up to 76.6% of oral reference dose. This will result in better understanding of human health risk assessment associated with F exposures.
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•Soil fluoride bioaccessibility was determined by combining PBET and SHIME.•Dissolution of F-Ca and F-Al compounds was primary source of gastric bioaccessibility.•The precipitation of fluorite with low solubility was observed in small intestine.•Increased colon bioaccessibility was due to dissolution of F-bearing Fe (hydr)oxides.•Highest contribution of soil F intake to oral reference dose was 76.6% for children.
Manganese doped magnetic carbon (MDMC) was synthesized to enhance bio-hydrogen (H2) process under the mesophilic and thermophilic conditions. MDMC characterization showed that MnFe2O4, Fe2O3 and few ...MnCO3 were adhered to activated carbon and formed MDMC whose specific surface area and average pore size were 110.92 m2·g−1 and 3.2 nm, respectively. Suitable concentration of MDMC promoted while high dosage suppressed the H2 production of glucose through anaerobic fermentation by heat-treated sludge. The highest yields of 211 and 148 ml H2/g glucose were obtained at 400 mg/L (37 °C) and 600 mg/L MDMC (55 °C), being 55.8% and 19.3% higher than that of the control groups, respectively. Some possible mechanisms were proposed as follows: appropriate concentration of MDMC provided considerable and favorable sites for microbial colonization, released trace elements (e.g. Mn, Fe) into liquid for the microbial growth, and promoted the direct inter-species electron transfer. Moreover, MDMC could be recycled by magnetic separation after bio-H2 process due to its magnetism.
MnFe2O4, Fe2O3 and few MnCO3 were adhered to activated carbon, fabricating the manganese doped magnetic carbon (MDMC) that was employed to stimulate bio- hydrogen (H2) production. Results showed that suitable amount of MDMC increased H2 yield through providing a composite carrier and trace elements like Fe and Mn for H2 production bacteria. MDMC could be also recycled via magnetic separation after the bio-process due to its magnetism. Display omitted
•MDMC was synthesized, containing MnFe2O4, Fe2O3, MnCO3 and AC.•Suitable addition of MDMC obtained the highest H2 yield in bio-H2 process.•The H2 yields amended with MDMCs increased by 9.6–55.8 %.•MDMC enriched bacteria and promoted their growths and H+ transfer rates.•MDMC could be recycled by magnetic separation after bio-H2 production.
INFOGEST is a standardized in vitro digestion method suitable for foods, but rarely used to study the bioaccessibility of heavy metals in food. This study aimed to explore the differences between ...INFOGEST and the extensively used Physiologically Based Extraction Test (PBET) and Unified Bioaccessibility Research Group of Europe Method (UBM) methods for determining the bioaccessibility of As and Cd in rice. Intestinal As (79.3 ± 8.5 %, 75.8 ± 12.7 %, and 72.3 ± 12.2 % for INFOGEST, PBET, and UBM, respectively) and Cd (47.0 ± 6.4 %, 40.7 ± 13.8 %, and 38.1 ± 15.7 % for INFOGEST, PBET, and UBM, respectively) bioaccessibilities in the rice samples determined by the three methods were generally similar (p > 0.1, except for As bioaccessibility between INFOGEST and UBM). Furthermore, PBET was significantly correlated with INFOGEST for As bioaccessibility (R
= 0.416) and with UBM for Cd bioaccessibility (R
= 0.879). Additionally, PBET indicated that the bioaccessibilities of As and Cd in the polished rice were 17.0 % and 19.8 % higher, respectively, than that in the unpolished rice. This study highlights the influence of in vitro methods and rice matrices on heavy metal bioaccessibility values, necessitating a more accurate assessment of health risks associated with rice consumption.
The oxidation and immobilization of arsenic (As) by manganese oxides have been shown to reduce As toxicity and bioavailability under abiotic conditions. In this study, we investigate the impact of ...manganese oxide (δ-MnO2) on the fate of different Fe-minerals-adsorbed As in the presence of As(V)-reducing bacteria Bacillus sp. JQ. Results showed that in the absence of δ-MnO2, As release in goethite was much higher than in ferrihydrite and hematite during microbial reduction. Adding 3.1 mM Mn reduced As release by 0.3%, 46.3%, and 6.7% in the ferrihydrite, goethite, and hematite groups, respectively. However, aqueous As was dominated by As(III) in the end, because the oxidation effect of δ-MnO2 was limited and short-lived. Additionally, the fraction of solid-phase As(V) increased by 9.8% in ferrihydrite, 39.4% in goethite, and 7.4% in hematite in the high-Mn treatments, indicating that δ-MnO2 had the most significant oxidation and immobilization effect on goethite-adsorbed As. This was achieved because goethite particles were evenly distributed on δ-MnO2 surface, which supported As(III) oxidation by δ-MnO2; while ferrihydrite strongly aggregated, which hindered the oxidation of As(III). Our study shows that As-oxidation and immobilization by manganese oxides cannot easily be assessed without considering the mineral composition and microbial conditions of soils.
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•The As(III) oxidation by δ-MnO2 is limited under biotic-reducing conditions.•The oxidation and immobilization of δ-MnO2 on As in Gt is higher than Fh and Hm.•Fe-minerals aggregation extent and their interactions with δ-MnO2 controls As fate.•The remediation effect of δ-MnO2 on As may be more predominant in soils rich in Gt.
