Coexistence of polyethylene microplastics and biochar increases ammonium sorption in an aqueous solution

Microplastics in granular sequencing batch reactors: Effects on pollutant removal dynamics and the microbial community

This study investigated the relationship between microplastic (MP) presence and pollutant removal in granular sludge sequencing batch reactors (GSBRs). Two types of MPs, polyethylene (PE) and polyethylene terephthalate (PET), were introduced in varying concentrations to assess their effects on microbial community dynamics and rates of nitrogen, phosphorus, and organic compound removal. The study revealed type-dependent variations in the deposition of MPs within the biomass, with PET-MPs exhibiting a stronger affinity for accumulation in biomass. A 50 mg/L dose of PET-MP decreased COD removal efficiency by approximately 4 % while increasing P-PO4 removal efficiency by around 7 % compared to the control reactor. The rate of nitrogen compounds removal decreased with higher PET-MP dosages but increased with higher PE-MP dosages. An analysis of microbial activity and gene abundance highlighted the influence of MPs on the expression of the nosZ and ppk1 genes, which code enzymes responsible for nitrogen and phosphorus transformations. The study also explored shifts in microbial community structure, revealing alterations with changes in MP dose and type. This research contributes valuable insights into the complex interactions between MP, microbial communities, and pollutant removal processes in GSBR systems, with implications for the sustainable management of wastewater treatment in the presence of MP.

Effects of biodegradable microplastics coexistence with biochars produced at low and high temperatures on bacterial community structure and phenanthrene degradation in soil

The increasing use of biodegradable plastics may result in more serious pollution of microplastics which often coexist with biochar in soil, this will affect how organic pollutants move and transform in the soil. This work investigated the effect of biodegradable polybutylene adipate-co-terephthalate (PBAT) coexistence with biochars produced at temperatures of 400 and 700 °C (W4 and W7) on soil bacterial communities and phenanthrene degradation. The results showed that coexistence of PBAT and biochar paticles greatly boosted the relative abundance of Nocardioides while decreased the relative abundance of Sphingomonas as compared to soils with a single addition of PBAT or biochar. Changes in soil Eh values were the most influential factor in bacterial communities (more than 40% contribution). The degradation ratio of phenanthrene when PBAT coexisted with W7 (39.6 ± 3.6%) was not significantly different from the treatment with a single W7 addition (35.0 ± 2.3%, P＞0.05), and was related to phenanthrene degradation in the adsorbed state of W7 in soil. In contrast, the degradation ratio of phenanthrene in PBAT coexisting with W4 (35.1 ± 3.5%) was intermediate between that of single PBAT (49.8 ± 0.9%) and W4 (13.7 ± 5.8%) treatments. This was primarily due to changes in the experiment's initial bioavailable phenanthrene content. Furthermore, after the introduction of earthworms, phenanthrene degradation ratio in coexistence treatments were very similar to that described above in the absence of earthworms. Except for two treatments that contain W7, phenanthrene degradation ratio in the other treatments was increased by the presence of earthworms (up to 23%), which is related to the enhanced relative abundance of polycyclic aromatic hydrocarbon-degraders. Our findings indicated that PBAT coexistence with high-temperature or low-temperature biochar had a completely different impact on bacterial communities and phenanthrene degradation in soil.

Microplastics and biochar interactively affect nitrous oxide emissions from tobacco planting soil

Biochar application to amend acidified tobacco-soils can enhance tobacco quality and reduce nitrous oxide (N2O) emissions. Microplastics from agricultural mulch are commonly found in cash-crop farmland soils and, together with biochar, affect soil N2O emissions. In this study, we applied three types of microplastics (polyethylene, PE; polylactic acid, PLA; polybutylene adipate terephthalate, PBAT) and rice biochar alone or in combination to acidified tobacco planting soil in central China to investigate their effects on soil N2O emissions, soil chemical properties, nitrogen-cycle-related functional genes, and microbial functional diversity during a 35-day laboratory incubation period. Significant increases in N₂O emissions were observed with PE and PLA, which raised emissions by 15.96 % and 21.52 %, respectively. Additionally, different microplastics affected soil N₂O emissions through distinct regulatory pathways. Co-application of microplastics and biochar suppressed N2O emissions compared to microplastics alone. Biochar mitigates N2O emissions mainly by increasing the abundance of the nosZ gene. It can remediate soil contaminated by microplastics and reduce their negative impacts on the soil environment. This study provides deeper insight into the effects of microplastics on soil nitrogen cycling and biochar-mitigated remediation of microplastic-contaminated soil.

Ammonium ion removal from aqueous solutions in the presence of organic compounds, using biochar from banana leaves. Competitive isotherm models

Industrial, e.g. food industrial and domestic wastewaters contain huge amount of compounds causing eutrophication, and should be removed with high cost during wastewater treatment. However, these compounds could be utilized as fertilizers too. Biochar can remove a wide range of pollutants from water, such as ammonium, which can be found in relatively high concentration in dairy wastewaters. However, adsorption performance may be affected by the presence of other wastewater pollutants. Thus, this study aims to determine the efficiency of biochar as an adsorbent of ammonium in aqueous solutions in the presence of some selected organic compounds of typical dairy wastewaters such as bovine serum albumin (BSA), lactose, and acetic acid. Methods: The biochar was produced from banana leaves at 300 °C, modified with NaOH, and characterized by Scanning Electron Microscope - Energy Dispersive X-Ray Spectroscopy (SEM-EDX), Fourier-transform infrared spectra (FTIR) analysis, and specific surface area measurements. Batch experiments were carried out to investigate the ammonium adsorption capacity and the ion competitive adsorption mechanism. Significant Findings: Results show that the surface structure of the biochar derived from banana leaves is different from other biochars previously studied; although the specific surface area is not very considerable and despite having nitrogen within the elemental composition, the biochar studied is capable of adsorbing 2.60 mg NH4+/m2, the highest ammonium removal in 2 h occurs at pH 9 and 500 mg biochar dose. Langmuir model in the monolayer phase analysis fits better for all scenarios and the maximum NH4+ adsorption capacity was 0.97 mg/g without organic compounds. In the multilayer adsorption phase, the isotherm model that best fits the data obtained is the Harkins-Jura model without organic compounds. The presence of organic compounds in the aqueous solution significantly impacts the adsorption of ammonium by biochar since it improves the adsorption capacity (1.132 mg/g BSA, 0.975 mg/g lactose, and 1.874 mg/g acetic acid). The Aranovich-Donohue isotherm model fitted the data obtained during ion competitive adsorption experiments well.

Microplastic Has No Effect on Rice Yield and Gaseous N Emission from an Infertile Soil with High Inorganic N Inputs

Microplastic might affect the crop yield, nitrogen (N) use efficiency and reactive N losses from agricultural soil systems. However, evaluation of these effects in infertile soil planted with different rice cultivars is lacking. We conducted a soil column experiment to determine the influence of a typical microplastic polyethylene (PE) input into an infertile soil with 270 kg N ha-1 and planted with two rice cultivars, i.e., a common rice Nangeng 5055 (NG) and a hybrid rice Jiafengyou 6 (JFY). The results showed that JFY produced a significantly (p < 0.05) greater grain yield than NG (61.6-66.2 vs. 48.2-52.5 g pot-1) but was not influenced by PE. Overall, PE hardly changed the N use efficiency of NG and JFY. Unexpectedly, PE significantly (p < 0.05) increased the total amino acid content of NG. Compared with JFY, NG volatilized significantly (p < 0.05) more ammonia (NH3) (0.84-0.92 vs. 0.64-0.67 g N pot-1) but emitted equal nitrous oxide (N2O). PE exerted no effect on either NH3 volatilization or the N2O emission flux pattern and cumulative losses of the rice growth cycle, whether with NG or JFY. Some properties of tested soils changed after planting with different rice cultivars and incorporating with microplastic. In conclusion, the rice production, N use efficiency, NH3 volatilization and N2O emission from the N-fertilized infertile soil were pronouncedly influenced by the rice cultivar, but not the PE. However, PE influenced the grain quality of common rice and some properties of tested soils with both rice cultivars.

Microplastic inhibits the sorption of trichloroethylene on modified biochar

Biochar (BC) was used to remove trichloroethylene (TCE) from soil and water phases, and BC modification changed the sorption behavior of pollutants. Microplastics are emerging pollutants in the soil and water phases. Whether microplastics can affect the sorption of TCE by modified BC is not clear. Thus, batch sorption kinetics and isotherm experiments were conducted to elucidate the sorption of TCE on BC, and BC combined with polyethylene (PE) or polystyrene (PS). The results showed that HCl and NaOH modification increased TCE sorption on BC, while HNO3 modification inhibited TCE sorption on BC. When PE/PS and BC coexisted, the TCE sorption capacity decreased significantly on BC-CK + PE, BC-HCl + PE, BC-HNO3 + PE, BC-NaOH + PE, and BC-NaOH + PS, which was likely due to the preferential sorption of PE/PS on BC samples. We concluded that microplastics can change TCE sorption behavior and inhibit TCE sorption on BC samples. Thus, the interaction of BC and microplastics should be considered when BC is used for TCE removal in soil and water remediation.

Nano-biochar as a potential amendment for metal(loid) remediation: Implications for soil quality improvement and stress alleviation

Metal(loid) contamination of agricultural soils has become an alarming issue due to its detrimental impacts on soil health and global agricultural production. Therefore, environmentally sustainable and cost-effective solutions are urgently required for soil remediation. Biochar, particularly nano-biochar, exhibits superior and high-performance capabilities in the remediation of metal(loid)-contaminated soil, owing to its unique structure and large surface area. Current researches on nano-biochar mainly focus on safety design and property improvement, with limited information available regarding the impact of nano-biochar on soil ecosystems and crop defense mechanisms in metal(loid)-contaminated soils. In this review, we systematically summarized recent progress in the application of nano-biochar for remediation of metal(loid)-contaminated soil, with a focus on possible factors influencing metal(loid) uptake and translocation in soil-crop systems. Additionally, we conducted the potential/related mechanisms by which nano-biochar can mitigate the toxic impacts of metal(loid) on crop production and security. Furthermore, the application of nano-biochar in field trials and existing challenges were also outlined. Future studies should integrate agricultural sustainability and ecosystem health targets into biochar design/selection. This review highlighted the potential of nano-biochar as a promising soil amendment for enhancing the remediation of metal(loid)-contaminated agricultural soils, thereby promoting the synthesis and development of highly efficient nano-biochar towards achieving environmental sustainability.

Small microplastic particles promote tetracycline and aureomycin adsorption by biochar in an aqueous solution

Biochar (BC) has been used to remove antibiotics from wastewater. Microplastics are emerging contaminants of wastewater. The capacities of microplastics for adsorbing antibiotics and the effects of microplastics of different types and particle sizes on antibiotic adsorption by BC have not been studied. Here, adsorption isotherm and kinetics experiments were performed to investigate tetracycline and aureomycin adsorption to polyvinyl chloride particles with diameters of 10, 100, 500, and 2000 μm, polylactic acid particles with diameters of 30, 100, 500, and 2000 μm (PLA30, PLA100, PLA500, and PLA2000, respectively), and wheat straw BC. The highest tetracycline adsorption capacity (25.00 mg g-1) was found for a PLA30 + BC. The tetracycline adsorption capacities of the other microplastic particles were 20.44-24.57 mg g-1. The highest aureomycin adsorption capacity (39.50 mg g-1) was found for 10 μm polyvinyl chloride particles and BC. The aureomycin adsorption capacities of the other microplastic particles were 32.21-38.42 mg g-1. The tetracycline adsorption capacities were 13.69%, 6.28%, 5.49%, and 4.54% higher for PLA30 + BC, PLA100 + BC, PLA500 + BC, and PLA2000 + BC, respectively, than for only BC. This may have been because there were more sites available per unit mass of microplastic for adsorbing tetracycline and dissolved organic carbon on small microplastic particles than large microplastic particles. The results indicated that microplastics can adsorb antibiotics and increase the amounts of antibiotics adsorbed by BC. Therefore, it is essential to consider potential interactions between BC and microplastics when BC is used to remove antibiotics from wastewater.

Polyethylene microplastics alter soil microbial community assembly and ecosystem multifunctionality

Although pervasive microplastics (MPs) pollution in terrestrial ecosystems invites increasing global concern, impact of MPs on soil microbial community assembly and ecosystem multifunctionality received relatively little attention. Here, we manipulated a mesocosm experiment to investigate how polyethylene MPs (PE MPs; 0, 1%, and 5%, w/w) influence ecosystem functions including plant production, soil quality, microbial community diversity and assembly, enzyme activities in carbon (C), nitrogen (N) and phosphorus (P) cycling, and multifunctionality in the maize-soil continuum. Results showed that PE MPs exerted negligible effect on plant biomass (dry weight). The treatment of 5% PE MPs caused declines in the availability of soil water, C and P, whereas enhanced soil pH and C storage. The activity of C-cycling enzymes (α/β-1, 4-glucosidase and β-D-cellobiohydrolase) was promoted by 1% PE MPs, while that of β-1, 4-glucosidase was inhibited by 5% PE MPs. The 5% PE MPs reduced the activity of N-cycling enzymes (protease and urease), whereas increased that of the P-cycling enzyme (alkaline phosphatase). The 5% PE MPs shifted soil microbial community composition, and increased the number of specialist species, microbial community stability and networks resistance. Moreover, PE MPs altered microbial community assembly, with 5% treatment decreasing dispersal limitation proportion (from 13.66% to 9.96%). Overall, ecosystem multifunctionality was improved by 1% concentration, while reduced by 5% concentration of PE MPs. The activity of α/β-1, 4-glucosidase, urease and protease, and ammonium-N content were the most important predictors of ecosystem multifunctionality. These results underscore that PE MPs can alter soil microbial community assembly and ecosystem multifunctionality, and thus development and implementation of practicable solutions to control soil MPs pollution become increasingly imperative in sustainable agricultural production.

Microplastic-Assisted Removal of Phosphorus and Ammonium Using Date Palm Waste Derived Biochar

Microplastics (MPs) are emerging environmental pollutants worldwide, posing potential health risks. Moreover, MPs may act as vectors for other contaminants and affect their fate, transport, and deposition in the environment. Therefore, efficient and economical techniques are needed for the removal of contemporary MPs and contaminants from the environment. The present research study investigated the sorption of phosphorus (P) and ammonium (NH4+) onto date palm waste-derived biochar (BC) from an aqueous solution in the presence of polyamide (PA) and polyethylene (PE) MPs. The BC was prepared at 600 °C, characterized for physio-chemical properties, and applied for P and NH4+ removal via isotherm and kinetic sorption trials. The results of the sorption trials demonstrated the highest removal of NH4+ and P was obtained at neutral pH 7. The highest P sorption (93.23 mg g-1) by BC was recorded in the presence of PA, while the highest NH4+ sorption (103.76 mg g-1) was found with co-occurring PE in an aqueous solution. Sorption isotherm and kinetics models revealed that P and NH4+ removal by MP-amended BC followed chemisorption, electrostatic interaction, precipitation, diffusion, and ion exchange mechanisms. Overall, co-existing PA enhanced the removal of P and NH4+ by 66% and 7.7%, respectively, while co-existing PE increased the removal of P and NH4+ by 55% and 30%, respectively, through the tested BC. Our findings suggested that converting date palm waste into BC could be used as a competent and economical approach to removing P and NH4+ from contaminated water. Furthermore, microplastics such as PE and PA could assist in the removal of P and NH4+ from contaminated water using BC.

Cation-π mechanism promotes the adsorption of humic acid on polystyrene nanoplastics to differently affect their aggregation: Evidence from experimental characterization and DFT calculation

Multiple water-chemistry factors determine nanoplastics aggregation and thus change their bioavailability and ecological risks in natural aquatic environments. However, the dominant factors and their interactive mechanisms remain elusive. In this study, polystyrene nanoplastics (PSNPs) showed greater colloidal stability in Li Lake water compared to ultrapure water. The RDA and PARAFAC results suggested that dissolved organic carbon, humic acid (HA) in particular, Ca2+, and pH are critical factors influencing PSNPs aggregation. Batch experiments showed that the critical coagulation concentration (CCC) of PSNPs was increased with pH increase; HA increased the CCC of PSNPs in NaCl by 2.6-fold but decreased that in CaCl2 by 1.8-fold. Moreover, cations increased the adsorption of HA on PSNPs. The DFT results suggested that HA-cations complexes (EAE = -1.10 eV and -0.51 eV for HA-Ca2+ and HA-Na+, respectively) but not HA alone (EAE = -0.33 eV) are the main scenarios for their adsorption on PSNPs, and a cation-π mechanism between PSNPs and HA-cations complexes dominates PSNPs aggregation in this scenario. The findings are significant for better understanding the environmental process and fate of nanoplastics in aquatic environments. ENVIRONMENTAL IMPLICATION: Nanoplastics are kinds of emerging contaminants. Nanoplastic aggregation determines their bioavailability and toxic risks to ecological health. Herein, the hydrodynamic sizes of PSNPs in local Li Lake water was tested and a redundancy analysis was performed to examine the key water-chemistry factors driving PSNPs aggregation. Moreover, the mechanisms in PSNPs aggregation driven by multiple dominant water-chemistry factors including cations, pH, and DOC were firstly unveiled by combining experimental characterization and theoretical computations. This work improves our understanding of the environmental fate of nanoplastics and provides a theoretical basis for the risk assessment and control of nanoplastics in real aquatic environments.

Microplastics in water: types, detection, and removal strategies

Microplastics are one of the most concerning groups of contaminants that pollute most of the surroundings of the Earth. The abundance of plastic materials available in the environment moved the scientific community in defining a new historical era known as Plasticene. Regardless of their minuscule size, microplastics have posed severe threats to the life forms like animals, plants, and other species present in the ecosystem. Ingestion of microplastics could lead to harmful health effects like teratogenic and mutagenic abnormalities. The source of microplastics could be either primary or secondary in which the components of microplastics are directly released into the atmosphere and the breakdown of larger units to generate the smaller molecules. Though numerous physical and chemical techniques are reported for the removal of microplastics, their increased cost prevents the large-scale applicability of the process. Coagulation, flocculation, sedimentation, and ultrafiltration are some of the methods used for the removal of microplastics. Certain species of microalgae are known to remove microplastics by their inherent nature. One of the biological treatment strategies for microplastic removal is the activated sludge strategy that is used for the separation of microplastic. The overall microplastic removal efficiency is significantly high compared to conventional techniques. Thus, the reported biological avenues like the bio-flocculant for microplastic removal are discussed in this review article.

Interactions between white and black carbon in water: A case study of concurrent aging of microplastics and biochar

Microplastics and biochar, as particulate matter that is prevalent in the water environment, will inevitably encounter and interact with each other during environmental aging. The potential interaction of microplastics and biochar, and the associated impact on their environmental behavior remains largely unknown. In this study, we exposed microplastics and biochar concurrently to ultraviolet light to mimic the aging process, investigated the release and fluorescence characteristics of dissolved organic matter (DOM) in water, and analyzed the effects of co-existing microplastics and biochar on their sorption of organic contaminants. We demonstrate that early-stage interactions of microplastics and biochar could entangle to promote the release of DOM from biochar, while their long-term interactions after light irradiation resulted in the sorption of hydrophobic and small molecules of microbial byproduct-like DOM. Simultaneously, early-stage interactions of microplastics and biochar showed a promotion for sorption of organic contaminants with an increase of 5.3-17.7%. After aging, however, long-term interactions between microplastics and biochar made it no longer promote the sorption of organic contaminants due to the influence of heterogeneous aggregation. Our results provide new insights into the time-dependent interactions between microplastics and biochar and highlight the need to incorporate their interactions into future environmental risk assessments for microplastics in the water environment.

Aging, characterization and sorption behavior evaluation of tire wear particles for tetracycline in aquatic environment

Accounting for more than half of the total primary microplastic (MP) emissions, and one-sixth of the total marine MP pollution in China in 2015, tire wear particles (TWP) are inevitable to age and interact with co-existing species, thus pose a potential risk to the surroundings. The impacts of simulated ultraviolet radiation weathering and liquid-phase potassium persulfate oxidation of TWP on the surface physicochemical properties were comparatively explored. The characterization results demonstrated that the content of carbon black, particle size and specific surface area of the aged TWP all decreased, while the changes of the hydrophobicity and polarity were inconsistent. The interfacial interactions with tetracycline (TC) in aqueous were investigated, the well fitted pseudo-second-order kinetics, Dual-mode Langmuir and Scatchard isotherm models indicated the attachment of TC dominated by surface adsorption at lower concentration, and there's a positive synergistic effect among the main sorption domains. Moreover, the results of the influences of co-existing salts and natural organic matter revealed that the potential risks of TWP elevated by the adjacent media in natural compartment. This work provides new insights into the way that TWP interact with contaminants in the real environment.

Biochar alleviated the toxic effects of PVC microplastic in a soil-plant system by upregulating soil enzyme activities and microbial abundance

Plastics have become an emerging pollutant threatening the sustainability of agroecosystems and global food security. Biochar, a pro-ecosystem/negative carbon emission technology can be exploited as a circular approach for the conservation of plastics contaminated agricultural soils. However, relatively few studies have focused on the effects of biochar on plant growth and soil biochemical properties in a microplastic contaminated soil. This study investigated the effects of a cotton stalk (Gossypium hirsutum L.) biochar on plant growth, soil microbes, and enzyme activity in PVC microplastic (PVC-MPs) contaminated soil. Biochar amendment increased shoot dry matter production in PVC-MPs contaminated soil. However, PVC-MPs alone significantly reduced the soil urease and dehydrogenase activity, soil organic and microbial biomass carbon, bacterial/fungal community percentage, and their abundance (16S rRNA and 18S rRNA genes, respectively). Interestingly, biochar amendment with PVC-MPs significantly alleviated the hazardous effects. Principal component and redundancy analysis of the soil properties, bacterial 16S rRNA genes, and fungal ITS in the biochar-amended PVC-MPs treatments revealed that the observed traits formed an obvious cluster compared to non-biochar treatments. To sum up, this study indicated that PVC-MPs contamination was not benign, while biochar shielded the hazardous effects and sustained soil microbial functionality.

Surface change of microplastics in aquatic environment and the removal by froth flotation assisted with cationic and anionic surfactants

Microplastics (MPs) are increasingly released into the environment due to the widespread usage and improper management of plastics. Considerable research efforts have been devoted to the remediation of MPs. Froth flotation has been demonstrated as an effective method to remove MPs in water and sediment. However, there is a lack of knowledge on the regulation of the hydrophobicity/hydrophilicity of MPs surfaces. We found that exposure to the natural environment resulted in the increased hydrophilicity of MPs. The flotation efficiencies of polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), and polyethylene glycol terephthalate (PET) MPs decreased to zero after six months of natural incubation in rivers. According to various characterizations, the hydrophilization mechanism is mainly correlated with surface oxidation and the deposition of clay minerals. Inspired by surface wettability conversion, we applied surfactants (collectors) to enhance MPs hydrophobicity and flotation efficiency. Anionic sodium oleate (NaOL) and cationic dodecyl trimethyl ammonium chloride (DTAC) were used to regulate surface hydrophobicity. The effects of collector concentration, pH, conditioning time, and metal ions on MPs flotation were thoroughly elucidated. Characterizations and adsorption experiments were performed to describe the heterogeneous adsorption of surfactants on MPs surfaces. The interaction between surfactants and MPs was explained through density functional theory (DFT) simulations. The dispersion energy between hydrophobic hydrocarbon chains attracts collectors on the MPs surface, and the collector molecules wrap and laminate to MPs surfaces. Flotation using NaOL exhibited a higher removal efficiency, and NaOL was environmentally friendly. Subsequently, we investigated the activation of Ca²⁺, Fe³⁺, and Al³⁺ to further improve the collecting efficiency of NaOL. Under the optimized conditions, MPs in natural rivers could be removed by froth flotation. This study shows the great promise of froth flotation for the application of MPs removal.

Pyrolytic biochar from plastic film waste addition on farmland for maize growth improvement: Process and effect study

Pyrolyzing and returning to farmland is one of the potential methods for farmland plastic film waste. This study explored both pyrolyzation and activation optimum conditions of a mixture of plastic film (polyethylene) and maize straw (MPS) in a 1:5 ratio to produce MPS-char, investigated the action of the char on the maize seedling stage (for 30 days). The results showed that the char promoted the root to be more advanced than aboveground part, therefore, this study experimentally clarified the role MPS-char played when added to the soil. The functional groups of the char were varied by the participation of polyethylene. Carbon-based groups were observed, such as carbonyl or carboxyl groups, which could constitute an NH₄⁺ absorption release system to increase the existence of urea in soil, therefore the average nitrogen concentration was improved by 16.18 %. However, the shallow soil temperature increased by 2.03 °C, and the deep soil temperature slightly decreased with the effect of MPS-char. While, the soil moisture content was slightly reduced in the second half of the experiment, and the soil oxygen content increased by 7.64 % throughout the whole experiment. Overall, returning MPS-char to farmland showed a positive effect on maize growth, which was caused by the variation of both chemical and physical properties. This variation provides opportunities for further promotion of rhizosphere development.

Comparative analysis of the sorption behaviors and mechanisms of amide herbicides on biodegradable and nondegradable microplastics derived from agricultural plastic products

Coexisting of microplastics (MPs) and residual herbicides has received substantial attention due to concerns about the pollutant vector effect. Here, the widely used amide herbicides were examined for their sorption behaviors on the priority biodegradable and nondegradable MPs identified in intensive agriculture. The fitting results indicated that the interactions between napropamide (Nap)/acetochlor (Ace) and the MPs, i.e., poly (butyleneadipate-co-terephthalate) microplastic (PBATM), polyethylene microplastic (PEM), and polypropylene microplastic (PPM), may be dominated by hydrophobic absorptive partitioning on the heterogeneous surfaces. Additionally, chemisorption cannot be ignored for the sorption of Nap/Ace on the biodegradable MPs. The sorption capacities of Nap/Ace on the MPs followed the order of PBATM > PEM > PPM. The differences in sorption capacity which varied by the MP colors were not significant. The hydrophobicity of the herbicides and the MPs, the rubber regions, surface O-functional groups, benzene ring structures and large specific surface area of the biodegradable MPs played key roles in the better performance in sorbing amide herbicides. Moreover, MPs, especially biodegradable MPs, might lead to a higher vector effect for residual amide herbicides than some other common environmental media. This study may provide baseline insights into the great potential of biodegradable MPs to serve as carriers of residual amide herbicides in intensive agrosystems.

Efficient removal of microplastics from aqueous solution by a novel magnetic biochar: performance, mechanism, and reusability

Microplastics' (MPs) pollution removal from water bodies has become an urgent task to ensure water quality safety and water ecological security on a global scale. In this work, coprecipitation was employed to investigate the adsorption of MPs by magnetic biochar (MRB) prepared from agricultural waste rice husks in an aquatic system. The results showed that MRB can adsorb up to 99.96% of MPs in water; acidic conditions were favorable for the effective MPs' adsorption reaction, and competing anions had a greater effect on adsorption. The adsorption mechanism results revealed that the adsorption of MPs by MRB was a spontaneous process, and electrostatic attraction, surface complexation, hydrogen bonding and π-π interactions were present in the adsorption process. Furthermore, after the adsorption of MPs, MRB can be recovered by thermal treatment (500 °C) and still exhibits up to 90% MPs adsorption (after four uses). This work reveals that MRB is an inexpensive, efficient, and reusable nanoscale adsorbent for MPs pollution removal in water, which may provide new ideas for microplastic pollution control in the aqueous environment.

Environmental risk of microplastics after field aging: Reduced rice yield without mitigating yield-scale ammonia volatilization from paddy soils

Microplastics (MPs, <5 mm) are enriched in paddy ecosystems as emerging environmental pollutants. Biochar (BC) is a controversial recalcitrant carbon product that poses potential environmental risks. The presence of these two exogenous organic substances has been demonstrated to have impacts on soil nitrogen cycling and crop production. However, the after-effects of MPs and BC on soil ammonia (NH₃) volatilization and rice yield after field aging remain unexplored. In this study, two common MPs, including polyethylene (PE) and polyacrylonitrile (PAN), and BC were selected for rice growing season observations to study the impacts on soil NH₃ volatilization and rice yield after field aging. The results showed that the reduction of cumulative soil NH₃ losses by MPs was around 45% after one-year field aging, which was within the range of 40-57% in the previous rice season. Abatement of NH₃ volatilization by MPs mainly occurred in basal fertilization and was related to floodwater pH. Besides, the reduction rate of NH₃ volatilization by BC and MPs + BC was enhanced after field aging (63% and 50-57%) compared to that in the previous rice season (5% and 11-19%), with the abatement process occurring in the first supplementary fertilization. There was a significant positive correlation between cumulative NH₃ volatilization and soil urease activity. Notably, field aging removed the positive effect of MPs and MPs + BC in reducing yield-scale NH₃ losses in the previous rice season (∼62%). Furthermore, despite BC affecting rice yield insignificantly after field aging, the presence of MPs led to a significant 17-19% reduction in rice yield. Our findings reveal that differences in the after-effects of BC and MPs in field aging emerge, where the negative impacts of MPs on soil NH₃ abatement and crop yield are progressively becoming apparent and should be taken into serious consideration.

Atmospheric microplastics and nanoplastics as vectors of primary air pollutants - A theoretical study on the polyethylene terephthalate (PET) case

Polyethylene terephthalate (PET) microplastics and nanoplastics are ubiquitously present in the atmosphere as atmospheric and airborne forms (PET-aMPs). Using first-principles calculations, we analyze the uptake of primary air pollutants onto PET-aMPs, focusing on their stabilities, adsorption mechanisms, and thermochemistry. The results show that PET-aMPs are selective for the spontaneous adsorption of CO, CO₂, NO, N₂O, NO₂, NH_3, and SO₂, reaching stable adsorption energies of 6-20 kcal/mol per molecule, with comparable uptake ability than carbon-based materials, metals/metalloids, and metal oxide surfaces. Then, PET-aMPs become a vector for coexisting air pollutants in the atmosphere, which adsorb by inner or outer adsorption depending on the molecular polarity (dipole moment) and atomic constitution (electronegativity) of gaseous molecules. Also, atmospheric H₂O and O₂ are not competitive molecules, and ozone could enhance adsorption due to surface oxidation and structure breakdown. The interplay of electrostatic (46-61%) and dispersion forces (21-58%) drives the adsorption mechanism, where low-polar pollutants display almost a balanced electrostatic vs. dispersion contribution, while high polar molecules display a higher electrostatic stabilization. The outer adsorption is reached by strong dispersion, hydrogen bonding, and dipole-dipole-induced pairs, while lone-pair-π interactions appear in the inner adsorption regime. These results expand the understanding of the hazards and risks of atmospheric and airborne microplastics/nanoplastics, their impacts, co-transport ability, and interaction with the environment.

Adsorptive behavior of micro(nano)plastics through biochar: Co-existence, consequences, and challenges in contaminated ecosystems

The abundance of micro(nano)plastics in natural ecosystems is a crucial global challenge, as these small-sized plastic particles originate from land-based and marine-based activities and are widely present in marine, freshwater, and terrestrial ecosystems. Micro(nano)plastics can significantly be reduced through various methods, such as biological, chemical, and physical techniques. Biochar is a low-cost adsorbent and is considered an efficient material and its application is ecologically effective carbon-negative for remediation of organic and inorganic pollutants. Therefore, this review critically discusses the fate and transport of micro(nano)plastics and their interactions with different biochar in aqueous and column porous media. This review outlines the implications of biochar with the co-existence of micro(nano)plastics in efforts to understand their coupled effects on soil physicochemical properties, microbial communities, and plant growth, along with the removal of heavy metals and other toxic contaminants. In batch experiments, biochar synthesized from various biomasses such as corn straw, hardwood, pine and spruce bark, corncob, and Prosopis juliflora had shown high level of removal efficiency (>90 %) for microplastic adsorption under varying environmental conditions viz., pH, temperature, ionic strength, particle size, and dose due to chemical bonding and electrostatic attractions. Increased temperature of the aqueous solutions encouraged higher adsorption, while higher pH and dissolved organic matter and nutrients may show decreased adsorption capacities for micro(nano)plastics using biochar. Compared to other available physical, chemical, and biological methods, biochar-amended sand filters in column experiments have been very efficient in removing micro(nano)plastics. In saturated column porous media, various microplastics could be inhibited using biochar due to decreased electrostatic repulsion, steric hindrance, and competitive sorption due to humic acid, ionic strength, and cations. Finally, this review provides in-depth insights on further investigations and recommendations for overall micro(nano)plastics removal using biochar-based materials.

Adsorption Characteristics and Mechanism of Methylene Blue in Water by NaOH-Modified Areca Residue Biochar

To solve the water pollution problem caused by methylene blue (MB), areca residue biochar (ARB) was prepared by pyrolysis at 600 °C, and modified areca residue biochar (M-ARB) was obtained by modifying ARB with 1.5 mol/L NaOH, and they were utilized to adsorb and eliminate MB from water. The structural characteristics of ARB and M-ARB were examined, and the main influencing factors and adsorption mechanism of MB adsorption process were investigated. The outcomes demonstrated an increase in M-ARB’s specific surface area and total pore volume of 66.67% and 79.61%, respectively, compared with ARB, and the pore structure was more abundant, and the content of oxygen element was also significantly increased. When the reaction temperature was 25 °C, starting pH of the mixture was 10, the initial MB concentration was 50 mg/L, the ARB and M-ARB dosages were 0.07 g/L and 0.04 g/L, respectively, the adsorption equilibrium was achieved at about 210 min, and the elimination rate for MB exceeded 94%. The adsorption behaviors of ARB and M-ARB on MB were more in line with the Langmuir isotherm model (R2 > 0.95) and the quasi-secondary kinetic model (R2 > 0.97), which was characterized by single-molecule layer chemisorption. The highest amount of MB that may theoretically be absorbed by M-ARB in water ranging from 136.81 to 152.72 mg/g was 74.99–76.59% higher than that of ARB. The adsorption process was a spontaneous heat absorption reaction driven by entropy increase, and the adsorption mechanism mainly involved electrostatic gravitational force, pore filling, hydrogen bonding, and π–π bonding, which was a complex process containing multiple mechanisms of action. NaOH modification can make the ARB have more perfect surface properties and more functional group structures that can participate in the adsorption reaction, which can be used as an advantageous adsorption material for MB removal in water.

Polyethylene microplastic and biochar interactively affect the global warming potential of soil greenhouse gas emissions

Emerging microplastic pollution and biochar application result in their coexistence in the soil. In this study, a polyethylene microplastic, a straw biochar, and a manure biochar were applied alone or in combination to an agricultural soil to explore their interactive effects on microbial biomass carbon and nitrogen, bacterial community composition, structure and function, and the resultant greenhouse gas emissions in a 45-day laboratory incubation. At the end of incubation, the co-application of microplastic and biochar suppressed the global warming potential of cumulative greenhouse gas emissions compared with the sum of their application alone. Specifically, coexisting with microplastics increased N₂O emissions by 37.5% but decreased CH₄ emissions by 35.8% in the straw biochar added soil, and decreased N₂O, CO₂ and CH₄ emissions by 24.8, 6.2, and 65.2%, respectively, in the manure biochar added soil. A correlation network analysis illustrated that the increased global warming potential was related to the changed bacterial function and microbial biomass carbon and nitrogen in the treatments with straw biochar and/or polyethylene microplastic added, and by the changed bacterial community structure and function in the treatments with manure biochar and/or polyethylene microplastic added. Bacterial functions associated with tricarboxylic acid cycle contributed to CO₂ emissions. Bacterial functions associated with the nitrogen cycle such as nosZ and AOBamoABC were negatively and positively correlated with N₂O emissions, respectively. The interaction between different types of microplastics and soil amendments and the resultant effects on ecosystem function deserve further research.

The weathering process of polyethylene microplastics in the paddy soil system: Does the coexistence of pyrochar or hydrochar matter?

This study is based on a particular test site to simulate the weathering process of microplastics (MPs) in paddy soil. A substantial amount of plastic waste, especially MPs, inevitably accumulates in agricultural soil due to the high consumption and short average use of plastics. Recently, MP pollution has become a global environmental concern. However, insight into the soil weathering process of MPs in paddy soil, particularly in the presence of biochar, is lacking. In this study, the physicochemical properties of polyethylene (PE) MPs were determined through a 24-week weathering system conducted in paddy soil, paddy soil with pyrochar, or hydrochar. Moreover, the sorption of original and weathered PE MPs toward three typical pollutants (cadmium/Cd, bisphenol A/BPA, and dimethyl phthalate/DMP) was investigated. The surface of PE MPs was fractured, 1.1-fold rougher, yellow-colored (11.7 units), and 1.8-fold more oxidized after paddy soil weathering. In addition, the crystallinity, negative charge, and stronger hydrophilicity of weathered PE MPs increased compared to original PE MPs. Weathering in a pyrochar or hydrochar system caused fissures, extensive destruction of amorphous areas, and accelerated chemical or bio-oxidation processes for PE MPs, resulting in a more noticeable change in roughness (1.4-2.2-fold), yellow color (12.7-13.7), crystallinity (1.2-1.5-fold), and oxygen content (2.5-3.6-fold). Weathered PE MPs facilitated the sorption with Cd and BPA, attributed to larger specific surface area, abundant polar functional groups, and increased negatively charged sites. However, sorption of DMP to PE MPs was highly influenced by their hydrophobicity, resulting in decreased hydrophobic partition sorption on weathered PE MPs. Overall, paddy soil weathering affected the properties of PE MPs and enhanced sorption of Cd and BPA but reduced sorption of DMP. The coexistence of biochar exacerbated the paddy soil weathering effect. The insight gained from this study assists in better understanding the weathering process of PE MPs in agricultural soils.

Every coin has two sides: Continuous and substantial reduction of ammonia volatilization under the coexistence of microplastics and biochar in an annual observation of rice-wheat rotation system

Microplastics (MPs) are verified to affect the fate of ammonia (NH₃) in agricultural soils. However, the impacts and mechanisms of MPs coupled with biochar (BC), a widely used agricultural conditioner, on NH₃ losses are mostly untapped. The aim of this study was to investigate the mechanisms of common MPs (i.e., polyethylene, polyester, and polyacrylonitrile) and straw-derived BC on NH₃ volatilization in rice-wheat rotation soils. Results showed that BC alone and MPs with BC (MPs + BC) reduced 5.5 % and 11.2-26.6 % cumulative NH₃ volatilization than the control (CK), respectively, in the rice season. The increased nitrate concentration and soil cation exchange capacity were dominant contributors to the reduced soil NH₃ volatilization in the rice season. BC and MPs + BC persistently reduced 44.5 % and 60.0-62.6 % NH₃ losses than CK in the wheat season as influenced by pH and nitrate concentration. Moreover, BC and MPs + BC increased humic acid-like substances in soil dissolved organic matter by an average of 159.1 % and 179.6 % than CK, respectively, in rice and wheat seasons. The increased adsorption of soil NH₄⁺ and the promotion of crop root growth were the main mechanisms of NH₃ reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH₃ mitigation in rice-wheat rotational ecosystems.

Understanding and mitigating the distinctive stresses induced by diverse microplastics on anaerobic hydrogen-producing granular sludge

This work comparatively studied the different stress responses of anaerobic hydrogen-producing granular sludge (HPG) to several typical MPs in wastewater, i.e., polyethylene (PE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) MPs. A new approach to mitigating the inhibition caused by MPs based on biochar was then proposed. The results displayed that microbe in HPG had diverse tolerances to PE-MPs, PET-MPs and PVC-MPs, with the hydrogen production downgraded to 82.0 ± 3.2 %, 72.3 ± 2.5 % and 66.6 ± 2.3 % (p < 0.05) of control respectively, due to the distinct leachates toxicities and oxidative stress level induced by different MPs. The discrepant mitigation reflected in the hydrogen yields of biochar-based HPGs raised back to 88.7 ± 1.4 %, 85.3 ± 3.8 % and 88.5 ± 3.5 % of control. The MPs induced disintegrated granule morphology, fragile microbial viability and impaired defensive function of extracellular polymeric substances were restored by biochar. The effective mitigation was revealed to be due to the strong adsorption of MPs by biochar, reducing direct contact between microbes and MPs. Biochar addition also enhanced protection for HPG by increasing EPS secretion and weakened the oxidative damage to anaerobes induced by MPs. Biochar manifested the disparate adsorption properties of three MPs. The most superior mitigation in HPG contaminated by PVC-MPs was attributed to the strongest affinity of biochar to PVC-MPs and effective alleviation of PVC leachates toxicity.

Preparation, adsorption performance and mechanism of MgO-loaded biochar in wastewater treatment: A review

Biochar is a low cost, porous and solid material with an extremely high carbon content, various types of functional groups, a large specific surface area and many other desirable characteristics. Thus, it is often used as an adsorbent or a loading matrix. Nano-magnesium oxide is a crystalline material with small particles and strong ion exchangeability. However, due to the high surface chemical energy, it easily forms agglomerates of particles. Therefore, to combine the advantages of biochar and magnesium, metal magnesium nanoparticles can be loaded onto the surface of biochar with different modification techniques, resulting in biochars with low cost and high adsorption performance to be used as an adsorption matrix (collectively referred to as Mg@BC). This review presents the effects of different Mg@BC preparation methods and synthesis conditions and summarizes the removal capabilities and adsorption mechanisms of Mg@BC for different types of pollutants in water. In addition, the review proposes the prospects for the development of Mg@BC to solve various problems in the future.

Adsorption of Different Pollutants by Using Microplastic with Different Influencing Factors and Mechanisms in Wastewater: A Review

The studies on microplastics are significant in the world. According to the literature, microplastics have greatly specific surface areas, indicating high adsorption capacities for highly toxic pollutants in aquatic and soil environments, and these could be used as adsorbents. The influencing factors of microplastic adsorption, classification of microplastics, and adsorption mechanisms using microplastics for adsorbing organic, inorganic, and mixed pollutants are summarized in the paper. Furthermore, the influence of pH, temperature, functional groups, aging, and other factors related to the adsorption performances of plastics are discussed in detail. We found that microplastics have greater advantages in efficient adsorption performance and cost-effectiveness. In this paper, the adsorptions of pollutants by microplastics and their performance is proposed, which provides significant guidance for future research in this field.

Recent advancements on biochars enrichment with ammonium and nitrates from wastewaters: A critical review on benefits for environment and agriculture

During the last decade, biochars have been considered as attractive and eco-friendly materials with various applications including wastewater treatment, energy production and soil amendments. However, the important nitrogen losses during biochars production using the pyrolysis process have limited their potential use in agriculture as biofertilizer. Therefore, it seems necessary to enrich these biochars with nitrogen sources before their use in agricultural soils. This paper is the first comprehensive review on the assessment of biomass type and the biochars' properties effects on N recovery efficiency from aqueous solutions as well as its release and availability for plants when applying the N-enriched chars in soils. In particular, the N recovery efficiency by raw biochars versus the type of the raw feedstock is summarized. Then, correlations between the adsorption performance and the main physico-chemical properties are established. The main mechanisms involved during ammonium (NH₄-N) and nitrates (NO₃-N) recovery process are thoroughly discussed. A special attention is given to the assessment of the biochars physico-chemical modification impact on their N recovery capacities improvement. After that, the application of these N-enriched biochars in agriculture and their impacts on plants growth as well as methane and nitrous oxide greenhouse gas emissions reduction are also discussed. Finally, the main future development and challenges of biochars enrichment with N from wastewaters and their valorization as biofertilizers for plants growth and greenhouse gas (GHG) emissions reduction are provided. This systematic review is intended to promote the real application of biochars for nutrients recovery from wastewaters and their reuse as eco-friendly fertilizers.

Presence of microplastics alone and co-existence with hydrochar unexpectedly mitigate ammonia volatilization from rice paddy soil and affect structure of soil microbiome

Microplastics (MPs), as an emerging pollutant, may cause deleterious changes to the nitrogen cycle in terrestrial ecosystems. However, single impact of MPs and synergistic effects of MPs with hydrochar on ammonia (NH₃) volatilization and soil microbiome in paddy fields has been largely unexplored. In this study, polyethylene (PE), polyacrylonitrile (PAN) and straw-derived hydrochar (HBC) were selected for observations in an entire rice cycle growth period. Results showed that under the condition of 0.5% (w/w) MPs concentration, presence of MPs alone and co-existence of MPs and HBC (MPs + HBC) unexpectedly mitigated cumulative NH₃ volatilization from paddy soil compared with the control with no MPs or HBC addition. MPs + HBC increased NH₃ volatilization by 37.8-46.2% compared with MPs alone, indicating that co-existence of MPs and HBC weaken the mitigation effect of MPs on NH₃ volatilization. Additionally, results of nitrogen cycle related microorganisms closely related to NH₃ volatilization demonstrated that MPs + HBC altered the bacterial community structure and species diversity. These findings provide an important opportunity to advance our understanding of the impacts of MPs in agricultural environment and soils, and provide a sound theoretical basis for rationalizing the application of HBC in soil with MPs.

Combined Effects of Microplastics and Biochar on the Removal of Polycyclic Aromatic Hydrocarbons and Phthalate Esters and Its Potential Microbial Ecological Mechanism

Microplastics (MPs) have been attracting wide attention. Biochar (BC) application could improve the soil quality in the contaminated soil. Currently, most studies focused on the effect of MPs or BC on the soil properties and microbial community, while they neglected the combined effects. This study investigated the combined effects of BC or ball-milled BC (BM) and polyethylene plastic fragments (PEPFs) and degradable plastic fragments (DPFs) on the removal of polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) from the PAH-contaminated soil and the potential microbial ecological mechanisms. The results showed that BC or BM combined with PEPF could accelerate the removal of PAHs and PAEs. PEPF combined with BM had the most significant effect on the removal of PAHs. Our results indicating two potential possible reasons contribute to increasing the removal of organic pollutants: (1) the high sorption rate on the PEPF and BC and (2) the increased PAH-degrader or PAE-degrader abundance for the removal of organic pollutants.