Effects of biochars and MWNTs on biodegradation behavior of atrazine by Acinetobacter lwoffii DNS32

Metabolic insights into how multifunctional microbial consortium enhances atrazine removal and phosphorus uptake at low temperature

Agricultural soils in the black soil region of northeast China often face negative stress due to low temperatures, pesticide contamination, and inadequate nutrient supply. In this study, a new cold-tolerant strain of Peribacillus simplex C1 (C1) was selectively isolated from atrazine contaminated soil. The artificially constructed microbial consortium (CPD) [C1, phosphorus-solubilizing bacterium Enterobacter sp. P1, and atrazine-degrading bacterium Acinetobacter lwoffii DNS32] demonstrated the most effective performance in enhancing atrazine degradation and phosphorus-solubilizing capacity when the initial inoculation ratio of 5:1:2 at 15 °C. CPD enhanced energy-related metabolic pathways and increased choline production to regulate bacterial adaptation to temperature decrease. Additionally, the strains could selectively utilize carbon sources (low molecular weight organic acids) or nitrogen sources (some metabolites of atrazine) provided by each other to enhance growth. Furthermore, strain C1 enhanced membrane fluidity through increased expression of the unsaturated fatty acids. Pot experiments demonstrated that CPD assisted soybean seedlings in resisting dual stresses of low temperature and atrazine contamination by inducing the expression of genes related to photosynthesis, membrane permeability, phosphorus response, and cold tolerance.

New insight into the mechanism underlying the effect of biochar on phenanthrene degradation in contaminated soil revealed through DNA-SIP

Biochar has been widely used for the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil, but its mechanism of influencing PAH biodegradation remains unclear. Here, DNA-stable isotope probing coupled with high-throughput sequencing was employed to assess its influence on phenanthrene (PHE) degradation, the active PHE-degrading microbial community and PAH-degradation genes (PAH-RHD_α). Our results show that both Low-BC and High-BC (soils amended with 1 % and 4 % w/w biochar, respectively) treatments significantly decreased PHE biodegradation and bioavailable concentrations with a dose-dependent effect compared to Non-BC treatment (soils without biochar). This result could be attributed to the immobilisation of PHE and alteration of the composition and abundance of the PHE-degrading microbial consortium by biochar. Active PHE degraders were identified, and those in the Non-BC, Low-BC and High-BC microcosms differed taxonomically. Sphaerobacter, unclassified Diplorickettsiaceae, Pseudonocardia, and Planctomyces were firstly linked with PHE biodegradation. Most importantly, the abundances of PHE degraders and PAH-RHD_α genes in the ¹³C-enriched DNA fractions of biochar-amended soils were greatly attenuated, and were significantly positively correlated with PHE biodegradation. Our findings provide a novel perspective on PAH biodegradation mechanisms in biochar-treated soils, and expand the understanding of the biodiversity of microbes involved in PAH biodegradation in the natural environment.

The microorganism and biochar-augmented bioreactive top-layer soil for degradation removal of 2,4-dichlorophenol from surface runoff

Surface runoff is one of the major pollution sources impacting the quality of the surrounding waterbody. In this study, a highly-bioreactive top-layer soil incorporated with microorganism (BO) and peanut shell (PS) biochar or dairy manure (DM) biochar was proposed for removal of 2,4-dichlorophenol (2,4-DCP) from contaminated surface runoff. Both batch test and sandbox experiment consistently revealed that PS coupled with BO amendment (PS + BO) was most effective for sorption and degradation of 2,4-DCP, compared to BO and DM alone or in combination. About 77% of 6000 μg∙L^-1 2,4-DCP was absorbed within 36 h in the original low permeability bioreactive PS + BO soil layer (15 cm long×15 cm wide×4.5 cm deep) with the 0.33 L∙day^-1 processing capacity of surface runoff. Increasing the addition of quartz sand into the bioreactor soil layer by threefold the original bioreactor improved the processing capacity to 17.5 L∙day^-1. However, this permeability-optimized bioreactive layer was still not large enough to remove 2,4-DCP completely. The optimized scale by the multi-process coupling model of the convection, dispersion, adsorption, and degradation was 60 cm long × 60 cm wide × 18 cm deep where the processing capacity of 280 L·day^-1reached and 97.3% of 2,4-DCP was removed, correspondingly the 2,4-DCP concentration could meet the standard limit. In addition, the obtained model parameters showed that the biochar or microorganism significantly decreased the dispersion coefficient D of 2,4-DCP in the bioreactive layer. The 2,4-DCP distribution coefficient K_d, and first-order reaction rate λ in the PS+BO system significantly greater than that in the control, BO, and PS systems. Results from this study indicated that the top-layer soil incorporated with microorganisms and biochar is a feasible and effective approach for the surface runoff treatment.

The improved methods of heavy metals removal by biosorbents: A review

For decades, a vast array of innovative biosorbents have been found out and used in the removal of heavy metals, including bacteria, algae and fungi, etc. Although extensive biological species have been tried as a biosorbent for heavy metals removal, for removal efficiency or economy efficiency limited, it has failed to make a substantial breakthrough in practical application. Thus, many improved methods based on biosorbents emerged. In this review, based on the literature and our research results, we highlight three types of novel methods for biosorbents removal of heavy metals: chemical modification of biosorbents; biomass and chemical materials combination; multiple biomass complex systems. We mainly focus on their configuration, biosorption performance, their creation method, regeneration/reuse, their application and development in the future. Through the comparative analysis of various methods, we think that intracellular autogenous nanomaterials may open up another window in biosorption of heavy metals area. At the same time, the combination of various treatment methods will be the development tendency of heavy metal pollution treatment in the future.

Fabrication and characterization of a hierarchical porous carbon from corn straw-derived hydrochar for atrazine removal: efficiency and interface mechanisms

The excellent hierarchical porous carbon was fabricated from corn straw-derived hydrochar by chemical activation using potassium oxalate (K₂C₂O₄). SEM, BET, XPS, XRD, and Raman analysis were carried out for the characterization of the as-obtained samples. The morphology of the as-obtained porous carbon with hierarchical porous structures is made up of a large number of nano-particle aggregates and some nanosheet-like structures, possessing a super-large specific surface area (SSA, up to 2523 m² g^-1) with a large total pore volume of 1.464 cm³ g^-1. The as-fabricated carbon material rapidly removes atrazine in the first 3 h at the initial concentration of 20 mg L^-1 with an adsorption efficiency of 93.6%, which is faster and better than other representative materials reported previously. The acidic conditions are favorable for the atrazine adsorption onto the porous carbon. An efficient adsorbent was fabricated for environmental remediation, and in-depth insights into the interface mechanism between hierarchical porous carbon and atrazine are proposed. In addition, 95% of the adsorption capacity of MPC-1:3 can be recovered by simple annealing treatment.

A comparison of the characteristics and atrazine adsorption capacity of co-pyrolysed and mixed biochars generated from corn straw and sawdust

The biochar used in this study was prepared from corn straw and sawdust mixed in a ratio of 1:1 (m/m) at temperatures of 300 °C and 800 °C, which adopted the methods of co-pyrolysis (BC_300A and BC_800A) and mixing of single biochar (BC_300B and BC_800B). The obtained biochar was characterized by SEM, BET and FTIR analysis. Adsorption properties, including the atrazine adsorption kinetics and isotherms of the four kinds of biochar to atrazine, were investigated. The results showed that a pseudo-second order kinetic model was suitable for describing the adsorption of atrazine by BC_800B because its R² value is greater than the pseudo-first order model. The adsorption capacity (q_e) of BC_800B, blended from the two single biochars produced at 800 °C, is 37.2 mg g^-1, which is better than that of the other three species. This value is 4-6 times the q_e values of BC_300A, BC_300B and BC_800A, which are 6.74 mg g^-1, 7.77 mg g^-1 and 5.26 mg g^-1, respectively. At higher pyrolysis temperature, the pore structure of biochar is more developed, the specific surface area is larger, and the species and number of surface functional groups are also significantly different. At the same time, the results also showed that the order of mixing and pyrolysis affected the characteristics and adsorption capacity of biochar. This study reveals the atrazine adsorption mechanism of four kinds of biochar and provides information about the potential of these types of materials for the removal of atrazine in the aquatic environment.

Biodegradability of carbon nanotube/polymer nanocomposites under aerobic mixed culture conditions

The properties and commercial viability of biodegradable polymers can be significantly enhanced by the incorporation of carbon nanotubes (CNTs). The environmental impact and persistence of these carbon nanotube/polymer nanocomposites (CNT/PNCs) after disposal will be strongly influenced by their microbial interactions, including their biodegradation rates. At the end of consumer use, CNT/PNCs will encounter diverse communities of microorganisms in landfills, surface waters, and wastewater treatment plants. To explore CNT/PNC biodegradation under realistic environmental conditions, the effect of multi-wall CNT (MWCNT) incorporation on the biodegradation of polyhydroxyalkanoates (PHA) was investigated using a mixed culture of microorganisms from wastewater. Relative to unfilled PHA (0% w/w), the MWCNT loading (0.5-10% w/w) had no statistically significant effect on the rate of PHA matrix biodegradation. Independent of the MWCNT loading, the extent of CNT/PNC mass remaining closely corresponded to the initial mass of CNTs in the matrix suggesting a lack of CNT release. CNT/PNC biodegradation was complete in approximately 20 days and resulted in the formation of a compressed CNT mat that retained the shape of the initial CNT/PNC. This study suggests that although CNTs have been shown to be cytotoxic towards a range of different microorganisms, this does not necessarily impact the biodegradation of the surrounding polymer matrix in mixed culture, particularly in situations where the polymer type and/or microbial population favor rapid polymer biodegradation.

Magnetic bionanoparticles of Penicillium sp. yz11-22N2 doped with Fe3O4 and encapsulated within PVA-SA gel beads for atrazine removal

A novel magnetic bionanomaterial, Penicillium sp. yz11-22N2 doped with nano Fe₃O₄ entrapped in polyvinyl alcohol-sodium alginate gel beads (PFEPS), was successfully synthesized. The factors including nutrient substance, temperature, pH, initial concentrations of atrazine and rotational speeds were presented and discussed in detail. Results showed that the highest removal efficiency of atrazine by PFEPS was 91.2% at 8.00 mg/L atrazine. The maximum removal capacity for atrazine was 7.94 mg/g. Meanwhile, it has been found that most of atrazine were removed by metabolism and degradation of Penicillium sp. yz11-22N2, which could use atrazine as the sole source of either carbon or nitrogen. Degradation kinetics of atrazine conformed to first-order kinetics model. The intermediates indicated that the possible pathway for atrazine degradation by PFEPS mainly included hydrolysis dechlorination, dealkylation, side-chain oxidation and ring-opening.

Nitrogen-functionalization biochars derived from wheat straws via molten salt synthesis: An efficient adsorbent for atrazine removal

N-doped porous carbon sheets (NPCS) resulted from wheat straws are fabricated through using molten salts via the carbonization-functionalization progress, which show unique hierarchical structure, large pore volume and high surface area with affluent micropores. Results indicate that there exist many hierarchical pores consisting of the single carbon sheet with ultrathin nature, owing to the template role of molten salt mixtures at high temperature. Such superior structure can bring about desired performance of adsorption capacity of 82.8mg/g and quick adsorption rate of 1.43L/(gh) with an initial concentration of 35mg/L at 25°C. Langmuir and Freundlich models are adopted to interpret the adsorption behavior of atrazine and modified Freundlich and intraparticle diffusion (IPD) models are employed to characterize the dynamics of adsorption. Furthermore, nitrogen-functionalization biochars via molten salt synthesis should be further developed as a one-pot methodology to produce N-doped carbons, opening up a feasible approach for resource utilization of crop straws and other biomass wastes.

The enhancement of atrazine sorption and microbial transformation in biochars amended black soils

Generally, biochar plays an important role in controlling migration and accumulation of pollutants in soil. In this dissertation, biochars derived from wheat straws at various pyrolysis temperatures are used to investigate how biochar amendment affects adsorption and microbial degradation of atrazine (typical diffuse herbicide) in soils. In order to explore the influence of soil components, soil samples with different organic matter content are collected from typical agricultural sites, which are characterized as black soils in the northeast region of China. The basic sorption characteristics of biochars from wheat straws prepared at diverse pyrolysis temperature are analyzed, along with the comparisons of the sorption difference in the raw soil and soil amended with biochars at four levels of ratio (0.1%, 0.5%, 1.0% and 2.0%). By incubation experiments, atrazine degradation in non-sterile and sterile soils and effects of atrazine degradation rate after biochar amendment are also studied. Atrazine degradation is significantly enhanced in biochar amended soils, which may be because that biochar supplement can promote the growth and metabolism of microorganisms in the soil. Our findings reveal that wheatstraw- derived biochars may be effective remediation reagents for activating degradation of the soil functional microorganism and enhancing sorption of organic matter content, which can be applied to environmental-friendly accelerate the remediation of atrazine contaminated black soils.

Effects of multi-walled carbon nanotubes with various diameters on bacterial cellular membranes: Cytotoxicity and adaptive mechanisms

The effect of multi-walled carbon nanotubes (MWNTs) with different diameters on the destruction degree toward cellular membranes of bacterial has been explored by investigating the viability of bacteria and the change of composition and surface properties in cellular membranes with the exposure of MWNTs. The atrazine degrading bacteria Acinetobacter lwoffii DNS32 (DNS32) is chosen as the model species and Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) are selected as the comparison specie. Bacterial viability testing shows that MWNTs with smaller diameters generally display stronger toxicity to bacteria and also influenced by many factors including the electrostatic repulsion between MWNTs and bacteria and bacteria types. Interestingly, bacteria can self-regulate as an adaptive response to the toxicity of MWNTs, notably, DNS32 strain presents the adaptive responses when cultivated with MWNT_60-100 through modification of fatty acids in cell membranes, but does not exhibit similar responses when exposed to MWNT_10-20. This result may be related to the interference from MWNT_10-20, which exceeds the cellular ability to self-repair. Transmission electron microscopy (TEM) images and flow cytometric analysis of bacteria exposed to MWNTs reveal that the destruction of cell membrane in the DNS32 strain is more serious than that in the B. subtilis, indicating that electrostatic repulsion between the material and bacteria leading to the decrease of direct contact may be the primary factor that reduces the impacts from MWNTs.

Effect of static magnetic field on trichloroethylene removal in a biotrickling filter

A laboratory-scale biotrickling filter combined with a magnetic field (MF-BTF) and a single BTF (S-BTF) were set up to treat trichloroethylene (TCE) gas. The influences of phenol alone and NaAc-phenol as co-substrates and different MF intensities were investigated. At low MF intensity, MF-BTF displayed better performance with 0.20g/L of phenol, 53.6-337.1mg/m³ of TCE, and empty bed residence times of 202.5s. The performances followed the order MF-BTF (60.0mT)>MF-BTF (30.0mT)>S-BTF (0mT)>MF-BTF (130.0mT), and the removal efficiencies (REs) and maximum elimination capacities (ECs) corresponded to: 92.2%-45.5%, 2656.8mg/m³h; 89.8%-37.2%, 2169.1mg/m³h; 89.8%-29.8%, 1967.7mg/m³h; 76.0%-20.8%, 1697.1mg/m³h, respectively. High-throughput sequencing indicated that the bacterial diversity was lower, whereas the relative abundances of Acinetobacter, Chryseobacterium, and Acidovorax were higher in MF-BTF. Results confirmed that a proper MF could improve TCE removal performance in BTF.