The biosorption capacity of biochar for 4-bromodiphengl ether: study of its kinetics, mechanism, and use as a carrier for immobilized bacteria

Techniques and mechanisms of bacteria immobilization on biochar for further environmental and agricultural applications

Bacteria immobilization on biochar is a promising approach to achieve high concentration and stability of microbial cells for several applications. The present review addressed the techniques utilized for bacteria immobilization on biochar, discussing the mechanisms involved in this process, as well as the further utilization in bioremediation and agriculture. This article presents three immobilization techniques, which vary according to their procedures and conditions, including cell growth, adsorption, and adaptation. The mechanisms for cell immobilization are primarily adsorption and biofilm formation on biochar. The favorable characteristics of biochar immobilization depend on the pyrolysis methods, raw materials, and properties of biochar, such as surface area, pore size, pH, zeta potential, hydrophobicity, functional groups, and nutrients. Scanning electron microscope (SEM) and colony forming unit (CFU) are the analyses commonly carried out to verify the efficiency of bacteria immobilization. The benefits of applying biochar-immobilized bacteria include soil decontamination and quality improvement, which can improve plant growth and crop yield. Therefore, this emerging technology represents a promising solution for environmental and agricultural purposes. However, it is important to evaluate the potential adverse impacts on native microbiota by introducing exogenous microorganisms.

Biochar-immobilized Bacillus spp. for heavy metals bioremediation: A review on immobilization techniques, bioremediation mechanisms and effects on soil

Heavy metals contamination present risks to ecosystems and human health. Bioremediation is a technology that has been applied to minimize the levels of heavy metals contamination. However, the efficiency of this process varies according to several biotic and abiotic aspects, especially in environments with high concentrations of heavy metals. Therefore, microorganisms immobilization in different materials, such as biochar, emerges as an alternative to alleviate the stress that heavy metals have on microorganisms and thus improve the bioremediation efficiency. In this context, this review aimed to compile recent advances in the use of biochar as a carrier of bacteria, specifically Bacillus spp., with subsequent application for the bioremediation of soil contaminated with heavy metals. We present three different techniques to immobilize Bacillus spp. on biochar. Bacillus strains are capable of reducing the toxicity and bioavailability of metals, while biochar is a material that serves as a shelter for microorganisms and also contributes to bioremediation through the adsorption of contaminants. Thus, there is a synergistic effect between Bacillus spp. and biochar for the heavy metals bioremediation. Biomineralization, biosorption, bioreduction, bioaccumulation and adsorption are the mechanisms involved in this process. The application of biochar-immobilized Bacillus strains results in beneficial effects on the contaminated soil, such as the reduction of toxicity and accumulation of metals in plants, favoring their growth, in addition to increasing microbial and enzymatic activity in soil. However, competition and reduction of microbial diversity and the toxic characteristics of biochar are reported as negative impacts of this strategy. More studies using this emerging technology are essential to improve its efficiency, to elucidate the mechanisms and to balance positive and negative impacts, especially at the field scale.

Combined maize straw-biochar and oxalic acids induced a relay activity of abundant specific degraders for efficient phenanthrene degradation: Evidence based on the DNA-SIP technology

Biochar-oxalic acid composite application (BCOA) have shown to be efficient in the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil, but the functional degraders and the mechanism of improving biodegradation remains unclear. In this study, with the help of stable isotope probing technology of phenanthrene (Phe), we determined that BCOA significantly improved Phe mineralization by 2.1 times, which was ascribed to the increased numbers and abundances of functional degraders. The BCOA increased contents of dissolved organic carbon and available nutrients and decreased pH values in soil, thus promoting the activity, diversity and close cooperation of the functional Phe-degraders, and stimulating their functions associated with Phe degradation. In addition, there is a relay activity among more and diverse functional Phe-degraders in the soil with BCOA. Specifically, Pullulanibacillus persistently participated in Phe-degradation in the soil with BCOA throughout the incubation period. Moreover, Pullulanibacillus, Blastococcus, Alsobacter, Ramlibacter, and Mizugakiibacter were proved to be potential Phe-degraders in soil for the first time. The specific Phe degraders and their relay and cooperation activity in soils as impacted by BCOA were first identified with DNA-stable isotope probing technology. Our findings provided a novel perspective to understand the efficient degradation of PAH in the BCOA treatments, revealed the potential of soil native microbes in the efficient bioremediation of PAH-contaminated natural soil, and provided a basis for the development of in-situ phytoremediation technologies to remediate PAH pollution in future.

Biochar-microorganism interactions for organic pollutant remediation: Challenges and perspectives

Numerous harmful chemicals are introduced every year in the environment through anthropogenic and geological activities raising global concerns of their ecotoxicological effects and decontamination strategies. Biochar technology has been recognized as an important pillar for recycling of biomass, contributing to the carbon capture and bioenergy industries, and remediation of contaminated soil, sediments and water. This paper aims to critically review the application potential of biochar with a special focus on the synergistic and antagonistic effects on contaminant-degrading microorganisms in single and mixed-contaminated systems. Owing to the high specific surface area, porous structure, and compatible surface chemistry, biochar can support the proliferation and activity of contaminant-degrading microorganisms. A combination of biochar and microorganisms to remove a variety of contaminants has gained popularity in recent years alongside traditional chemical and physical remediation technologies. The microbial compatibility of biochar can be improved by optimizing the surface parameters so that toxic pollutant release is minimized, biofilm formation is encouraged, and microbial populations are enhanced. Biocompatible biochar thus shows potential in the bioremediation of organic contaminants by harboring microbial populations, releasing contaminant-degrading enzymes, and protecting beneficial microorganisms from immediate toxicity of surrounding contaminants. This review recommends that biochar-microorganism co-deployment holds a great potential for the removal of contaminants thereby reducing the risk of organic contaminants to human and environmental health.

Application of biochar immobilized microorganisms for pollutants removal from wastewater: A review

Microbial immobilization technology (MIT) has been rapidly developed and used to remove pollutants from water/wastewater in recent years, owing to its high stability, rapid reaction rate, and high activity. Microbial immobilization carrier with low cost and high removal efficiency is the key of MIT. Biochar is considered to be an efficient carrier for microbial immobilization because of its high porosity and good adsorption effect, which can provide a habitat for microorganisms. The use of biochar immobilized microorganisms to treat different pollutants in wastewater is a promising treatment method. Compared with the other biological treatment technology, biochar immobilized microorganisms can improve microbial abundance, repeated utilization ratio, microbial metabolic capacity, etc. However, current research on this method is still in its infancy. Little attention has been paid to the interaction mechanisms between biochar and microorganisms, and many studies are only carried out in the laboratory. There are still problems such as difficult recovery after use and secondary pollution caused by residual pollutants after biochar adsorption, which need further clarification. To have comprehensive digestion and an in-depth understanding of biochar immobilized microorganisms technology in wastewater treatment, the wastewater treatment methods based on biochar are firstly summarized in this review. Then the mechanisms of immobilized microorganisms were explored, and the applications of biochar immobilized microorganisms in wastewater were systematically reviewed. Finally, suggestions and perspectives for future research and practical application are put forward.

A Review of the Dynamic Mathematical Modeling of Heavy Metal Removal with the Biosorption Process

Biosorption has great potential in removing toxic effluents from wastewater, especially heavy metal ions such as cobalt, lead, copper, mercury, cadmium, nickel and other ions. Mathematically modeling of biosorption process is essential for the economical and robust design of equipment employing the bioadsorption process. However, biosorption is a complex physicochemical process involving various transport and equilibrium processes, such as absorption, adsorption, ion exchange and surface and interfacial phenomena. The biosorption process becomes even more complex in cases of multicomponent systems and needs an extensive parametric analysis to develop a mathematical model in order to quantify metal ion recovery and the performance of the process. The biosorption process involves various process parameters, such as concentration, contact time, pH, charge, porosity, pore size, available sites, velocity and coefficients, related to activity, diffusion and dispersion. In this review paper, we describe the fundamental physical and chemical processes involved in the biosorption of heavy metals on various types of commonly employed biosorbents. The most common steady state and dynamic mathematical models to describe biosorption in batch and fixed-bed columns are summarized. Mathematical modeling of dynamic process models results in highly coupled partial differential equations. Approximate methods to study the sensitivity analysis of important parameters are suggested.

An old story with new insights into an ignored issue of metabolites in biochar-amended soil: Effect of biochar on dissipation of carbosulfan as an example

Carbofuran (CAS) is one of extensively used carbamate pesticides, which is considered as a derivative or a candidate of carbofuran (CAN) for its lower toxicity and persistence. Nevertheless, CAS could be degraded into its toxic metabolites, imposing potential risks on ecological safety. In this paper, biochars, derived from rice straw (RS), chicken manure (CM), corn straw (CS) and tire rubber (TR), were applied in CAS-contaminated soil to explore their effects on the dissipation of CAS and its metabolites. The dissipation rate of CAS was depressed by the amendment of biochar, mainly because biochar inhibited the hydrolysis of CAS by elevating soil pH value. Nevertheless, CS has efficiently enhanced the dissipation of CAN by almost 2-times for its promotion in hydrolysis and biodegradation. CS and CM improved biodegradation by altering the composition and structure of the microbial communities, exhibiting potential for facilitating bioremediation of CAS and CAN. Moreover, steam activated biochar accelerated the dissipation rate by 1.7-2.9 times and 1.3-2.4 times for CAS and CAN, respectively. This study investigated the effects of biochar on CAS and its toxic metabolites as well as possible governing mechanisms, providing rational instruction for biochar application in ambient atmosphere.

Synergetic effects of biochars and denitrifier on nitrate removal

Nitrate is one of the most common water contaminants and has caused severe environmental problems. This work aimed to investigate the effects of integration of denitrifier with biochars on nitrate removal and understand the underlying mechanisms. The results showed that physiochemical properties of biochars varied according to different feedstocks, which influenced bacteria attachment and nitrate removal through adsorption. However, bacteria could colonize on biochars no matter biochars surface were favorable for bacteria attachment or not. Immobilization of denitrifier on biochars significantly improved nitrate removal efficiencies and reduced lag time. Underlying mechanisms investigation showed that the integration of denitrifier with biochars had synergetic effects on promoting nitrate removal, which improved not only the expression and activity of nitrate reductase, but also the electron transport system activity.

Enhanced removal of cadmium from wastewater with coupled biochar and Bacillus subtilis

Shortcomings of individual biochar or microbial technologies often exist in heavy metal removal from wastewater and may be circumvented by coupled use of biochar and microorganisms. In this study, Bacillus subtilis and each of three biochars of different origins (corn stalk, peanut shell, and pine wood) were coupled forming composite systems to treat a cadmium (Cd, 50 mg/L) wastewater formulated with CdCl₂ in batch tests. Biochar in composite system enhanced the activity and Cd adsorption of B. subtilis. Compared with single systems with Cd removal up to 33%, the composite system with corn stalk biochar showed up to 62% Cd removal, which was greater than the sum of respective single B. subtilis and biochar systems. Further analysis showed that the removal of Cd by the corn stalk composite system could be considered to consist of three successive stages, that is, the biochar-dominant adsorption stage, the B. subtilis-dominant adsorption stage, and the final biofilm formation stage. The final stage may have provided the composite system with the ability to achieve prolonged steady removal of Cd. The biochar-microorganism composite system shows a promising application for heavy metal wastewater treatment.

Combination of biochar and immobilized bacteria accelerates polyacrylamide biodegradation in soil by both bio-augmentation and bio-stimulation strategies

Polyacrylamide (PAM) has been used extensively due to its well-known stable chemical properties, but limited information is available on the biodegradation of soil-containing PAM. In this work, sufficient degradation of PAM was achieved via the addition of the Klebsiella sp. PCX-biochar composite to PAM-containing soil, due to the synergic effect of bio-augmentation and bio-stimulation. The optimal degradation rate of 69.1% over 30-day period was observed under the following conditions: the addition of immobilized bacteria at 0.07 g/g, pH 6.6, and temperature at 38.0 °C. In this study, we showed that PAM was successfully hydrolyzed by amidase, and ammonia in the hydrolysis product was then oxidized by the nitrifying bacteria. The decrease of water-extractable organic carbon (WEOC) also demonstrated the chain cleavage in PAM. PAM was utilized as a carbon source not only by Klebsiella sp. PCX but also by some taxa from indigenous bacteria. Last but not least, it was shown in this study that biochar, even though immobilized with exogenous microorganisms, actually enhanced bacterial diversity and stimulated the growth of some indigenous PAM-degrading taxa. Based on the above observations, we concluded that PAM biodegradation via the addition of bacteria-immobilized biochar was a synergy of both bio-augmentation and bio-stimulation strategies.

Insights into the mechanisms underlying efficient Rhizodegradation of PAHs in biochar-amended soil: From microbial communities to soil metabolomics

The combined effects of biochar amendment and the rhizosphere on the soil metabolic microbiome during the remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil remain unknown. In this study, we attempted to characterize a PAH degradation network by coupling the direct PAH degradation with soil carbon cycling. From microbial community structure and functions to metabolic pathways, we revealed the modulation strategies by which biochar and the rhizosphere benefited PAH degradation in soil. Firstly, some PAH degraders were enriched by biochar and the rhizosphere, and their combination promoted the cooperation among these PAH degraders. Simultaneously, under the combined effects of biochar and the rhizosphere, the functional genes participating in upstream PAH degradation were greatly upregulated. Secondly, there were strong co-occurrences between soil microbial community members and metabolites, in particular, some PAH degraders and the metabolites, such as PAH degradation products or common carbon resources, were highlighted in the networks. It shows that the overall downstream carbon metabolism of PAH degradation was also greatly upregulated by the combined effects of biochar and plant roots, showing good survival of the soil microbiome and contributing to PAH biodegradation. Taken together, both soil carbon metabolism and direct contaminant biodegradation are likely to be modulated by the combined effects of biochar and plant roots, jointly benefitting to PAH degradation by soil microbiome. Our study is the first to link PAH degradation with native carbon metabolism by coupling sequencing and soil metabolomics technology, providing new insights into a systematic understanding of PAH degradation by indigenous soil microbiome and their networks.

Effects of biochar properties on the bioremediation of the petroleum-contaminated soil from a shale-gas field

The characteristics of biochar carriers prepared from different biomass (corncob, straw, and sawdust) were investigated, and the bioremediation performance of the biochar through microbial immobilization was analyzed. Corncob biochar had the highest specific surface area (157.11-312.30 m² g^-1) among the different biomass, and the specific surface area and total pore volume reached the maximum at 500 °C. The pore size was primarily micropore, which aided to the fixation of microorganisms and the adsorption of petroleum pollutants. With increased pyrolysis temperature, the polar functional groups in biochar decreased, and the aromatic functional groups gradually increased, thereby benefiting the adsorption of hydrophobic organic compounds. Corncob biochar had the highest zeta potential, i.e., from - 30.95 to - 6.43 mV, conducive to the electrostatic adsorption between carrier and microorganism. The highest oil-removal and microbial-immobilization rates of biochar CC500 (with corncob pyrolyzed at 500 °C) were about 70.7% and 71.2%, respectively. A strong recovery of microbial growth activity was also observed; recovery was 83.38% compared with free bacteria, and the fixed microorganisms reached logarithmic-growth period at 8-18 h.

Biochar as simultaneous shelter, adsorbent, pH buffer, and substrate of Pseudomonas citronellolis to promote biodegradation of high concentrations of phenol in wastewater

Microbial degradation is an elimination method for removal of organic contaminants from soil and water. However, the main factor limiting its practical application is high bacterial sensitivity to environmental factors such as pH, toxicity, and mass transfer. In this study, biochar was produced pyrolytically from peanut shells at 350 °C, 550 °C, and 750 °C (referred to as BC350, BC550, and BC750, respectively) and their promotion on phenol biodegradation in wastewater by the bacterium Pseudomonas citronellolis was investigated. Higher initial phenol concentration (>400 mg L^-1) showed obvious inhibition on biodegradation with the removal efficiencies being less than 46%, and even the bacterium failed to survive at the phenol concentrations of higher than 1000 mg L^-1. With biochar incorporated, the removal efficiencies of phenol increased from below 46% to up to 99% at the initial concentrations of 400-1200 mg L^-1. Immobilization of strains in biochar by calcium alginate further increased the microbial tolerance to high concentrations of phenol (i.e., 63% removal at 1200 mg L^-1). Scanning electron microscopy demonstrated that biochar acted as shelter to support the bacterium to struggle with extreme conditions. The initial adsorption of phenol by biochar alleviated the initial toxicity of phenol to bacterium and the subsequent gradual desorption controlled the bioavailability of phenol. In this regard, BC350 showed a comparable sorption capacity with BC550 and BC750, while a higher desorption potential than them, thus balanced better the toxicity and bioavailability of phenol to microbes. Alkalinity of BC550 and BC750 played important roles in rescuing the microbes from being damaged by pH shock via neutralizing the fast generation of acidic intermediates. The extractable organic substances in BC350 could be consumed by bacterium as substrates, which was confirmed by incubating the strains in water-extractable solution. Results of this study indicate that incorporation of microbes with biochar could promote the biodegradation of high concentration organic wastewater.

Use of Bacillus-siamensis-inoculated biochar to decrease uptake of dibutyl phthalate in leafy vegetables

Dibutyl phthalate (DBP) is a frequently detected farmland contaminant that is harmful to the environment and human health. In this study, a DBP-degrading endophytic Bacillus siamensis strain T7 was immobilized in rice husk-derived biochar for bioremediation of DBP-polluted agricultural soils. The effects of this microbe-biochar composite on the soil prokaryotic community and the mechanism by which it regulates DBP degradation, were also investigated. A supplement of T7-biochar composite not only significantly boosted DBP biodegradation in soil by raising the DBP degradation rate constant and half-life from 0.1979 d^-1 and 2.3131 d to 0.2434 d^-1 and 2.1062 d, respectively, but also impeded DBP uptake by leafy vegetables. The general bioremediation effect of T7-biochar alliance excelled pure T7 suspensions and biochar, by trapping more DBP and boosting its complete degradation in soil. Besides, the combination of strain T7 and biochar can increase the proportion of some beneficial bacteria and boost the functional diversity of soil prokaryotic community, then to a certain extent may reverse the negative effect of DBP pollution on the agricultural soils. These results indicate that the rice-husk-derived biochar is a proper media when utilizing functional microbes into environmental treatment. Overall, T7-biochar composite is a promising soil modifier for soil bioremediation and the production of DBP-free crops.

Adsorption of indigo carmine on Pistia stratiotes dry biomass chemically modified

Pistia stratiotes is a common aquatic plant of the northern region of the state of Rio de Janeiro, and its use as adsorbent material was studied in the present work. The preparation process included washing, drying, grinding, and acid activation. The sorption potential for removal of the indigo carmine dye from aqueous solutions was tested under various conditions, such as initial concentration, contact time, and temperature. The tests showed that the obtained biosorbent showed good performance for dye removal with a maximum capacity of 41.2 mg/g. The kinetic studies revealed that the pseudo-second-order equation provided the best fit of the experimental data. The Freundlich isotherm provided the best fit of the experimental sorption data for the system under study. The results obtained show that Pistia stratiotes has great potential to be used as biosorbent for the removal of dyes from aqueous solutions.

Adsorption and degradation in the removal of nonylphenol from water by cells immobilized on biochar

To investigate the role of adsorption by biochar and biodegradation by bacteria in the wastewater treatment system of microorganisms immobilized on biochar, Nonylphenol (NP) removal (adsorption + degradation) rates and degradation rates from water by NP degrading bacteria immobilized on bamboo charcoal (BC) and wood charcoal (WC) were examined in a short-term and long-term. Results showed that cells immobilized on different biochar had different NP removal effects, and cells immobilized on bamboo charcoal (I-BC) was better. After eight rounds of long-term reuse, the cumulative removal rate and the degradation rate of NP in water by I-BC were 93.95% and 41.86%, respectively, significantly higher than those of cells immobilized on wood charcoal (69.60%, 22.78%) and free cells (64.79%, 19.49%) (P < 0.01). The rise in the ratio of the degradation rate to the removal rate indicated that the long-term NP removal effect is more dependent on biodegradation. The amount of residual NP in I-BC still accounted for about 50%, indicating that the secondary pollution in the disposal of carrier could not be ignored. In addition, promotion effect of biochar on microorganisms were observed by SEM, quantitative PCR and 16S rRNA. Pseudomonas, Achromobacter, Ochrobactrum and Stenotrophomonas were predominant bacteria for NP degradation. The addition of biochar (especially bamboo charcoal) also effectively delayed the transformation of their community structure.

Kinetic and isothermal adsorption-desorption of PAEs on biochars: effect of biomass feedstock, pyrolysis temperature, and mechanism implication of desorption hysteresis

Biochar has the potential to sequester biomass carbon efficiently into land, simultaneously while improving soil fertility and crop production. Biochar has also attracted attention as a potential sorbent for good performance on adsorption and immobilization of many organic pollutants such as phthalic acid esters (PAEs), a typical plasticizer in plastic and presenting a current environmental issue. Due to lack of investigation on the kinetic and thermodynamic adsorption-desorption of PAEs on biochar, we systematically assessed adsorption-desorption for two typical PAEs, dimethyl phthalate (DMP) and diethyl phthalate (DEP), using biochar derived from peanut hull and wheat straw at different pyrolysis temperatures (450, 550, and 650 °C). The aromaticity and specific surface area of biochars increased with the pyrolysis temperature, whereas the total amount of surface functional groups decreased. The quasi-second-order kinetic model could better describe the adsorption of DMP/DEP, and the adsorption capacity of wheat straw biochars was higher than that of peanut hull biochars, owing to the O-bearing functional groups of organic matter on exposed minerals within the biochars. The thermodynamic analysis showed that DMP/DEP adsorption on biochar is physically spontaneous and endothermic. The isothermal desorption and thermodynamic index of irreversibility indicated that DMP/DEP is stably adsorbed. Sorption of PAEs on biochar and the mechanism of desorption hysteresis provide insights relevant not only to the mitigation of plasticizer mobility but also to inform on the effect of biochar amendment on geochemical behavior of organic pollutants in the water and soil.

Roles of polar groups and aromatic structures of biochar in 1-methyl-3-octylimidazolium chloride ionic liquid adsorption: pH effect and thermodynamics study

Adsorption mechanisms of 1-methyl-3-octylimidazolium chloride ([OMIM]Cl) on rice straw-derived biochars produced at 400, 500, and 700 °C (referred as RB400, RB500, and RB700, respectively) were evaluated. Adsorption affinity followed the order of RB700 > RB400 > RB500. Electrostatic attraction and hydrogen bond controlled adsorption of [OMIM]Cl on RB400, while π-π EDA interaction between [OMIM]Cl and the aromatic rings of biochar dominated adsorption of RB500 and RB700. With increasing solution pH, -COOH and -OH on biochar became deprotonated. Consequently, [OMIM]Cl binding to these sites changed from hydrogen bond to electrostatic attraction. Adsorption capacity of [OMIM]Cl increased with increasing pH during the adsorption process. Solid concentration induced by -OH of [OMIM]Cl was higher than that of -COOH. Thermodynamics study indicated that adsorption process was spontaneous and endothermic. ∆H ⁰ values indicated that [OMIM]Cl adsorption on biochars was a physisorption.

Lead adsorption by biochar under the elevated competition of cadmium and aluminum

Competitive adsorption studies are important to accurately estimate the lead adsorption capacity on biochar in soil. The structure of biochars was evaluated by Fourier-Transform Infrared Spectroscopy and X-ray Diffraction, and the competitive of Cadmium (Cd) and Aluminum (Al) with Lead (Pb) adsorption were determined by kinetic experiments and pH effects. Adsorption kinetics indicated that the adsorption amount (mg g⁻¹) of Pb by biochar was in the decreasing order of CM400 (90.9) > BB600 (56.5) > CM100 (29.2), the presence of the oxygen-containing functional groups, Si-containing mineral, PO₄³⁻ and CO₃²⁻ significantly contributed to Pb adsorption by biochars. With the presence of Cd, Pb adsorption amount was reduced by 42.6%, 23.7% and 19.3% for CM100, CM400 and BB600, respectively. The Si-containing mineral, PO₄³⁻ and CO₃²⁻ that were rich in CM400 and BB600 has led to less competition by Cd. In addition, Al showed a strong competition with Pb leading to the adsorption being reduced by 95.8%, 82.3% and 80.6%, respectively for CM100, CM400 and BB600. This was mainly attributed to the additional acidification effect by Al resulting in a counteractive of biochar’s liming effect. Results from this study are important for accurately estimating the heavy metal adsorption by biochar in soil.

Characteristics of uranium biosorption from aqueous solutions on fungus Pleurotus ostreatus

Uranium(VI) biosorption from aqueous solutions was investigated in batch studies by using fungus Pleurotus ostreatus biomass. The optimal biosorption conditions were examined by investigating the reaction time, biomass dosage, pH, temperature, and uranium initial concentration. The interaction between fungus biomass and uranium was confirmed using Fourier transformed infrared (FT-IR), scanning electronic microscopy energy dispersive X-ray (SEM-EDX), and X-ray photoelectron spectroscopy (XPS) analysis. Results exhibited that the maximum biosorption capacity of uranium on P. ostreatus was 19.95 ± 1.17 mg/g at pH 4.0. Carboxylic, amine, as well as hydroxyl groups were involved in uranium biosorption according to FT-IR analysis. The pseudo-second-order model properly evaluated the U(VI) biosorption on fungus P. ostreatus biomass. The Langmuir equation provided better fitting in comparison with Freundlich isotherm models. The obtained thermodynamic parameters suggested that biosorption is feasible, endothermic, and spontaneous. SEM-EDX and XPS were additionally conducted to comprehend the biosorption process that could be described as a complex process involving several mechanisms of physical adsorption, chemisorptions, and ion exchange. Results obtained from this work indicated that fungus P. ostreatus biomass can be used as potential biosorbent to eliminate uranium or other radionuclides from aqueous solutions.

Characterization of anthropogenic impacts in a large urban center by examining the spatial distribution of halogenated flame retardants

Anthropogenic impacts have continuously intensified in mega urban centers with increasing urbanization and growing population. The spatial distribution pattern of such impacts can be assessed with soil halogenated flame retardants (HFRs) as HFRs are mostly derived from the production and use of various consumer products. In the present study, soil samples were collected from the Pearl River Delta (PRD), a large urbanized region in southern China, and its surrounding areas and analyzed for a group of HFRs, i.e., polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane, bis(hexachlorocyclopentadieno)cyclooctane (DP) and hexabromobenzene. The sum concentrations of HFRs and PBDEs were in the ranges of 0.66-6500 and 0.37-5700 (mean: 290 and 250) ng g(-1) dry weight, respectively, around the middle level of the global range. BDE-209 was the predominant compound likely due to the huge amounts of usage and its persistence. The concentrations of HFRs were greater in the land-use types of residency, industry and landfill than in agriculture, forestry and drinking water source, and were also greater in the central PRD than in its surrounding areas. The concentrations of HFRs were moderately significantly (r(2) = 0.32-0.57; p < 0.05) correlated with urbanization levels, population densities and gross domestic productions in fifteen administrative districts. The spatial distribution of DP isomers appeared to be stereoselective as indicated by the similarity in the spatial patterns for the ratio of anti-DP versus the sum of DP isomers (fanti-DP) and DP concentrations. Finally, the concentrations of HFRs sharply decreased with increasing distance from an e-waste recycling site, indicating that e-waste derived HFRs largely remained in local soil.