Effect of attapulgite on heavy metals passivation and microbial community during co-composting of river sediment with agricultural wastes

The effects of different electrode materials on the electric field-assisted co-composting system for the soil remediation of heavy metal pollution

The electric field-assisted composting system (EACS) is an emerging technology that can enhance composting efficiency, but little attention has been given to electrode materials. Herein, an EACS was established to investigate the effects of electrode materials on humic substance formation and heavy metal speciation. Excitation-emission matrix analysis showed that carbon-felt and stainless-steel electrodes increased humic acid (HA) by 48.57 % and 47.53 %, respectively. In the EACS with the carbon-felt electrode, the bioavailability factors (BF) of Cu and Cr decreased by 18.00 % and 7.61 %, respectively. Despite that the stainless-steel electrodes decreased the BF of As by 11.26 %, the leaching of Cr, Ni, Cu, and Fe from the electrode itself is an inevitable concern. Microbial community analyses indicated that the electric field increased the abundance of Actinobacteria and stimulated the multiplication of heavy metal-tolerant bacteria. Redundancy analysis indicates that OM, pH, and current significantly affect the evolution of heavy metal speciation in the EACS. This study first evaluated the metal leaching risk of stainless-steel electrode, and confirmed that carbon-felt electrode is environment-friendly material with high performance and low risk in future research with EACS.

Phytostabilization of Heavy Metals and Fungal Community Response in Manganese Slag under the Mediation of Soil Amendments and Plants

The addition of soil amendments and plants in heavy metal-contaminated soil can result in a significant impact on physicochemical properties, microbial communities and heavy metal distribution, but the specific mechanisms remain to be explored. In this study, Koelreuteria paniculata was used as a test plant, spent mushroom compost (SMC) and attapulgite (ATP) were used as amendments, and manganese slag was used as a substrate. CK (100% slag), M0 (90% slag + 5% SMC + 5% ATP) and M1 (90% slag + 5% SMC + 5% ATP, planting K. paniculata) groups were assessed in a pilot-scale experiment to explore their different impacts on phytoremediation. The results indicated that adding the amendments significantly improved the pH of the manganese slag, enhancing and maintaining its fertility and water retention. Adding the amendments and planting K. paniculata (M1) significantly reduced the bioavailability and migration of heavy metals (HMs). The loss of Mn, Pb and Zn via runoff decreased by 15.7%, 8.4% and 10.2%, respectively, compared to CK. K. paniculata recruited and enriched beneficial fungi, inhibited pathogenic fungi, and a more stable fungal community was built. This significantly improved the soil quality, promoted plant growth and mitigated heavy metal toxicity. In conclusion, this study demonstrated that the addition of SMC-ATP and planting K. paniculata showed a good phytostabilization effect in the manganese slag and further revealed the response process of the fungal community in phytoremediation.

Characteristics of bacterial community structure in the sediment of Chishui River (China) and the response to environmental factors

Sediment microorganisms performed an essential function in the biogeochemical cycle of aquatic ecosystems, and their structural composition was closely related to environmental carrying capacity and water quality. In this study, the Chishui River (Renhuai section) was selected as the research area, and the concentrations of environmental factors in the water and sediment were detected. High⁃throughput sequencing was adopted to reveal the characteristics of bacterial community structures in the sediment. In addition, the response of bacteria to environmental factors was explored statistically. Meanwhile, the functional characteristics of bacterial were also analyzed based on the KEGG database. The results showed that the concentration of environmental factors in the water and sediment displayed spatial differences, with the overall trend of midstream > downstream > upstream, which was related to the wastewater discharge from the Moutai town in the midstream directly. Proteobacteria was the most dominant phylum in the sediment, with the relative abundance ranged from 52.06% to 70.53%. The distribution of genus-level bacteria with different metabolic activities varied in the sediment. Upstream was dominated by Massilia, Acinetobacter, and Thermomonas. In the midstream, Acinetobacter, Cloacibacterium and Comamonas were the main genus. Nevertheless, the abundance of Lysobacter, Arenimonas and Thermomonas was higher in the downstream. Redundancy analysis (RDA) showed that total nitrogen (TN) and total phosphorus (TP) were the main environmental factors which affected the structure of bacterial communities in sediment, while total organic carbon (TOC) was the secondary. The bacterial community was primarily associated with six biological pathway categories such as metabolism. Carbohydrate metabolism and amino acid metabolism were the most active functions in the 31 subfunctions. This study could contribute to the understanding of the structural composition and driving forces of bacteria in the sediment, which might benefit for the ecological protection of Chishui River.

Slow release of attapulgite based nano-enabled glyphosate improves soil phosphatase activity, organic P-pool and proliferation of dominant bacterial community

Glyphosate (Glp) was encapsulated onto the dopamine-modified attapulgite to develop an attapulgite-based nano-enabled Glp (DGlp) in this study with comparable weed control effects to pure Glp and commercial Glp solutions. Within 24 hours, the active Glp molecule was slowly released from DGlp at a maximum remaining rate of over 90%, and then degraded similarly to Glp solution in soil. The addition of DGlp improved soil available phosphorus (P) contents, phosphatase activity, and enzyme extractable P fraction. However, compared to Glp solution, DGlp addition had no effect on the transformation of soil inorganic P fractions. The 16S rRNA sequencing and co-occurrence network results revealed that DGlp had no significant effect on the soil bacterial diversity but diminished the complexity of soil bacterial network. According to the Mantel test, DGlp addition stimulated soil phosphatase activity and proliferation of dominant bacterial taxa (Proteobacteria and Firmicutes) capable of degrading Glp. Proteobacteria and Firmicutes that had been extensively recruited and enriched for their phosphatase activities may have mobilized reactive enzyme-P, significantly enhancing the transformation of reactive organic P and P-pool in soil. These results contributed to our understanding of the ecotoxicity and environmental impacts of nano-enabled Glp prior to its successful and sustainable application in agriculture.

Elaborating the mechanism of lead adsorption by biochar: Considering the impacts of water-washing and freeze-drying in preparing biochar

This paper examined the impacts of different pretreatments on the characteristics of biochar and its adsorption behavior for Pb2+. Biochar with combined pretreatment of water-washing and freeze-drying (W-FD-PB) performed a maximum adsorption capacity for Pb2+ of 406.99 mg/g, higher than that of 266.02 mg/g on water-washing pretreated biochar (W-PB) and 188.21 mg/g on directly pyrolyzed biochar (PB). This is because the water-washing process partially removed the K and Na, resulting in the relatively enriched Ca and Mg on W-FD-PB. And the freeze-drying pretreatment broke the fiber structure of pomelo peel, favoring the development of a fluffy surface and large specific surface area during pyrolysis. Quantitative mechanism analysis implied that cation ion exchange and precipitation were the driving forces in Pb2+ adsorption on biochar, and both mechanisms were enhanced during Pb2+ adsorption on W-FD-PB. Furthermore, adding W-FD-PB to Pb-contaminated soil increased the soil pH and significantly reduced the availability of Pb.

A combined passivator of zeolite and calcium magnesium phosphate fertilizer: Passivation behavior and mechanism for Cd (II) in composting

Passivation of heavy metals is one of the most efficient techniques to improve the quality of compost. Many studies confirmed the passivation effect of passivators (e.g., zeolite and calcium magnesium phosphate fertilizer) on cadmium (Cd), but passivators with single component could not effectively passivate Cd in the long-term operation of composting. In the present study, a combined passivator of zeolite and calcium magnesium phosphate fertilizer (ZCP) was used to explore its impacts of adding at different composting periods (heating period, thermophilic period, cooling period) on the Cd control, compost quality (e.g., temperature, moisture content and humification), microbial community structure as well as the compost available forms of Cd and addition strategy of ZCP. Results showed that Cd passivation rate could be increased by 35.70-47.92% under all treatments in comparison to the control treatment. By altering bacterial community structure, reducing Cd bioavailability and improving the chemical properties of the compost, the combined inorganic passivator could achieve high efficiency for Cd passivation. To sum up, the addition of ZCP at different composting periods has effects on the process and quality of composting, which could provide ideas for the optimization of the passivators addition strategy.

Characterization and Morphology of Nanocomposite Hydrogels with a 3D Network Structure Prepared Using Attapulgite-Enhanced Polyvinyl Alcohol

In this investigation, purified attapulgite (ATT) and polyvinyl alcohol (PVA) were utilized to fabricate nanocomposite hydrogels and a xerogel, with a focus on studying the impact of minor additions of ATT on the properties of the PVA nanocomposite hydrogels and xerogel. The findings demonstrated that at a concentration of 0.75% ATT, the water content and gel fraction of the PVA nanocomposite hydrogel reached their peak. Conversely, the nanocomposite xerogel with 0.75% ATT reduced its swelling and porosity to the minimum. SEM and EDS analyses revealed that when the ATT concentration was at or below 0.5%, nano-sized ATT could be evenly distributed in the PVA nanocomposite xerogel. However, when the concentration of ATT rose to 0.75% or higher, the ATT began to aggregate, resulting in a decrease in porous structure and the disruption of certain 3D porous continuous structures. The XRD analysis further affirmed that at an ATT concentration of 0.75% or higher, a distinct ATT peak emerged in the PVA nanocomposite xerogel. It was observed that as the content of ATT increased, the concavity and convexity of the xerogel surface, as well as the surface roughness, decreased. The results also confirmed that the ATT was evenly distributed in the PVA, and a combination of hydrogen bonds and ether bonds resulted in a more stable gel structure. The tensile properties exhibited that when compared with pure PVA hydrogel, the maximum tensile strength and elongation at break were achieved at an ATT concentration of 0.5%, indicating increases of 23.0% and 11.8%, respectively. The FTIR analysis results showed that the ATT and PVA could generate an ether bond, further confirming that ATT could enhance the PVA properties. The TGA analysis showed that the thermal degradation temperature peaked when the ATT concentration was at 0.5%, providing further evidence that the compactness of the nanocomposite hydrogel and the dispersion of the nanofiller was superior, contributing to a substantial increase in the mechanical properties of the nanocomposite hydrogel. Finally, the dye adsorption results displayed a significant rise in dye removal efficiency for methylene blue with the increase in the ATT concentration. At an ATT concentration of 1%, the removal efficiency rose by 103% compared with that of the pure PVA xerogel.

Investigation and comparative analysis of ecological risk for heavy metals in sediment and surface water in east coast estuaries of India

The sediments and surface water from 8 stations each from Dhamara and Paradeep estuarine areas were sampled for investigation of heavy metals, Cd, Cu, Pb, Mn, Ni, Zn, Fe, and Cr contamination. The objective of the sediment and surface water characterization is to find the existing spatial and temporal intercorrelation. The sediment accumulation index (I_sed), enrichment index (I_En), ecological risk index (I_EcR) and probability heavy metals (p-HMI) reveal the contamination status with Mn, Ni, Zn, Cr, and Cu showing permissible (0 ≤ I_sed ≤ 1, I_En ˂ 2, I_EcR ≤ 150) to moderate (1 ≤ I_sed ≤ 2, 40 ≤ R_f ≤ 80) contamination. The p-HMI reflects the range from excellent (p-HMI = 14.89-14.54) to fair (p-HMI = 22.31-26.56) in off shore stations of the estuary. The spatial patterns of the heavy metals load index (I_HMc) along the coast lines indicate that the pollution hotspots are progressively divulged to trace metals pollution over time. Heavy metal source analysis coupled with correlation analysis and principal component analysis (PCA) was used as a data reduction technique, which reveals that the heavy metal pollution in marine coastline might originate from redox reactions (FeMn coupling) and anthropogenic sources.

The driving mechanism of passivator islands adsorbing and immobilizing heavy metals during chicken manure composting

The aim of this study was to assess the effectiveness of biochar and montmorillonite islands on heavy metal adsorptive immobilization and identify crucial driving factors and pathways during chicken manure composting. Compared to montmorillonite (6.74 and 89.25 mg/kg), biochar exhibited an obviously higher ability of Cu and Zn enrichment (41.79 and 167.77mg/kg), might be attributed to its abundant active functional groups. Network analysis showed that compared to Cu, core bacteria positively and negatively related to Zn was obviously more and less in passivator islands, respectively, which might explain significantly higher Zn concentration. Structural Equation Model displayed that dissolved organic carbon (DOC), pH and bacteria were critical driving factors. Pretreatment of passivator packages, such as soaking in the solution being rich in DOC and inoculating specific microbial agents accumulating heavy metals via extracellular adsorption /intracellular interception would significantly improve the effectiveness of adsorptive passivation on heavy metals.

Improving the humification by additives during composting: A review

Humic substances (HSs) are key indicators of compost maturity and are important for the composting process. The application of additives is generally considered to be an efficient and easy-to-master strategy to promote the humification of composting and quickly caught the interest of researchers. This review summarizes the recent literature on humification promotion by additives in the composting process. Firstly, the organic, inorganic, biological, and compound additives are introduced emphatically, and the effects and mechanisms of various additives on composting humification are systematically discussed. Inorganic, organic, biological, and compound additives can promote 5.58-82.19%, 30.61-50.92%, 2.3-40%, and 28.09-104.51% of humification during composting, respectively. Subsequently, the advantages and disadvantages of various additives in promoting composting humification are discussed and indicated that compound additives are the most promising method in promoting composting humification. Finally, future research on humification promotion is also proposed such as long-term stability, environmental impact, and economic feasibility of additive in the large-scale application of composting. It is aiming to provide a reference for future research and the application of additives in composting.

Dietary supplementation modified attapulgite promote intestinal epithelial barrier and regulate intestinal microbiota composition to prevent diarrhea in weaned piglets

Attapulgite is a kind of natural clay mineral. Its unique pore structure makes it an ideal adsorption material and carrier material. However, the beneficial effect of modified attapulgites (SLK) in livestock is still unknown. The study was aimed to investigate the beneficial effect of modified attapulgites on diarrhea. 135 piglets were randomly divided into 5 groups and fed with control diet, traditional antibiotic substitute (TAS) supplementation diet, 0.5 mg/kg SLK supplementation diet, 1 mg/kg SLK supplementation diet, and 1.5 mg/kg SLK supplementation diet. This experiment lased two weeks. According to our result, 1.5 mg/kg SLK supplementation diet significantly decreased diarrhea score and diarrhea frequency, and effectively increased survival rate (P < 0.05). Dietary supplementation with 1.5 mg/kg SLK significantly increased high density lipoprotein cholesterol (HDLC), and choline esterase (CHE) concentration in serum (P < 0.05). AS compared with TAS group, 1.5 mg/kg SLK supplementation diet significantly decreased villus height and increased goblet number in jejunum, and increased villus height and decreased goblet number in ileum (P < 0.05). 1.5 mg/kg SLK supplementation diet also significantly changed cecal microbial community composition, including increased Limosilactobacillus abundance (P < 0.05). 1.5 mg/kg SLK supplementation diet significantly increased colonic microbial community composition, including decreased Escherichia-shigella abundance and increased Limosilactobacillus abundance (P < 0.05). Moreover, 1.5 mg/kg SLK supplementation diet significantly increased valerate, propionate, butyrate, and total short chain fatty acid contents in colon (P < 0.05). Valerate, propionate, butyrate, and total short chain fatty acid significantly associated with Lactobacillus. Fourerenilla and Fourerenilla.unclassfied significantly associated with acetate contents in colon (P < 0.05). In conclusion, dietary supplementation with modified apptapulgites significantly regulate intestinal microbial community composition and alleviate intestinal epithelial barrier to prevent diarrhea in piglets.