The mechanism differences between sulfadiazine degradation and antibiotic resistant bacteria inactivation by iron-based graphitic biochar and peroxydisulfate system.

In this study, the activation of peroxydisulfate (PS) by K2FeO4-activation biochar (KFeB) and acid-picking K2FeO4-activation biochar (AKFeB) was investigated to reveal the mechanism differences between iron site and graphitic structure in sulfadiazine (SDZ) degradation and ARB inactivation, respectively. KFeB/PS and AKFeB/PS systems had similar degradation property towards SDZ, but only KFeB/PS system showed excellent bactericidal property. The mechanism study demonstrated that dissolved SDZ was degraded through electron transfer pathway mediated by graphitic structure, while suspended ARB was inactivated through free radicals generated by iron-activated PS, accompanied by excellent removal on antibiotic resistance genes (ARGs). The significant decrease in conjugative transfer frequency indicated the reduced horizontal gene transfer risk of ARGs after treatment with KFeB/PS system. Transcriptome data suggested that membrane protein channel disruption and adenosine triphosphate synthesis inhibition were key reasons for conjugative transfer frequency reduction. Continuous flow reactor of KFeB/PS system can efficiently remove antibiotics and ARB, implying the potential application in practical wastewater purification. In conclusion, this study provides novel insights for classified and collaborative control of antibiotics and ARB by carbon-based catalysts driven persulfate advanced oxidation technology.

From waste corn straw to graphitic porous carbon: A trade-off between specific surface area and graphitization degree for efficient peroxydisulfate activation.

Electron transfer pathways have been verified as overriding regimes when peroxydisulfate (PDS) was activated by porous carbon. The incorporation of graphitic structure into carbon matrix was favorable to the rapid electron transfer, but excessive graphitization would deteriorate the specific surface area (SSA), weakening the catalytic performance. The reasonable trade-off between SSA and graphitization degree was necessary and challenging for the preparation of efficient carbon based PS-activators. Herein, a series of graphitic porous carbon with discrepant SSA and graphitic structure were fabricated. The incorporation of graphitization tracks into ultra-thin edges on porous carbon film was verified by multifarious structural characterization. After trade-off, the optimum catalyst exhibited superior catalytic performance with degradation rate constant (kobs) exceeding that of ungraphitized precursor by up to 16.0 times. Mechanistic investigations substantiated that the sufficient SSA of catalyst provided favorable conditions for its affinity towards PDS and sulfadiazine (SDZ), resulting in the formation of PDS* complexes and SDZ adsorption, while the appropriate graphitization degree ensured the reinforced electron transfer rate, which collectively accelerated SDZ oxidation through electron-transfer pathway. The multivariate linear regression model linking kobs to SSA and graphitization degree was established providing basis to construct efficient catalysts for PDS activation.

Hierarchically porous magnetic biochar as an amendment for wheat (Triticum aestivum L.) cultivation in alkaline Cd-contaminated soils: Impacts on plant growth, soil properties and microbiota.

Hierarchically porous magnetic biochar (HMB) had been found to act as an effective amendment to remediate cadmium (Cd) in water and soil in a previous study, but the effects on wheat growth, Cd uptake and translocation mechanisms, and soil microorganisms were unknown. Therefore, soil Cd form transformation, soil enzyme activity, soil microbial diversity, wheat Cd uptake and migration, and wheat growth were explored by adding different amounts of HMB to alkaline Cd-contaminated soil under pot experiments. The results showed that application of HMB (0.5 %-2.0 %) raised soil pH, electrical conductivity (EC) and available Fe concentration, decreased soil available Cd concentration (35.11 %-50.91 %), and promoted Cd conversion to less bioavailable Cd forms. HMB treatments could reduce Cd enrichment in wheat, inhibit Cd migration from root to stem, rachis to glume, glume to grain, and promote Cd migration from stem to leaf and stem to rachis. HMB (0.5 %-1.0 %) boosted antioxidant enzyme activity, reduced oxidative stress, and enhanced photosynthesis in wheat seedlings. Application of 1.0 % HMB increased wheat grain biomass by 40.32 %. Besides, the addition of HMB (0.5 %-1.0 %) could reduce soil Cd bioavailability, increase soil enzyme activity, and increase the abundance and diversity of soil bacteria. Higher soil EC brought forth by HMB (2.0 %) made the wheat plants and soil bacteria poisonous. This study suggests that applying the right amount of HMB to alkaline Cd-contaminated soil could be a potential remediation strategy to decrease Cd in plants' edible parts and enhance soil quality.

Mechanism of additional carrier with seasonal temperature changes enhanced ecological floating beds for non-point source pollution water treatment.

The continuous performance and denitrification characteristics of carriers were investigated in two modified enhanced ecological floating beds (EFBs), one with only ceramsite and the other with ceramsite and extra additional stereo-elastic packing. Over a period of more than 414 days, the extra carrier was found to improve nitrogen removal while enhancing the system's resistance to seasonal temperature variations. The denitrification of all carriers in EFBs was inhibited in practice by seasonal temperature change, especially temperature rose from below 20 °C to above 20 °C and the inhibition rate of nitrous nitrogen (NO2--N) reduction was consistently above 91%, which was higher than that of nitrate nitrogen (NO3--N). However, the denitrification process including the rate and the resistance to temperature changes of ceramsite in the same EFBs with stereo-elastic packing at different temperatures, was consistently improved. The removal rate of NO3--N and NO2--N increased by up to 23.5% and 19.5%, respectively. The potential denitrification rates of all carriers increased with time which was also evidenced by in PICRUSt results, which showed that the abundances of predicted functional genes encoding NO3--N and NO2--N reductase increased over time. The dominant denitrifier also differed over time due to seasonal temperature changes.

Visible light-driven C/O-g-C3N4 activating peroxydisulfate to effectively inactivate antibiotic resistant bacteria and inhibit the transformation of antibiotic resistance genes: Insights on the mechanism.

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) dissemination within water pose a serious threat to public health. Herein, C and O dual-doped g-C3N4 (C/O-g-C3N4) photocatalyst, fabricated via calcination treatment, was utilized to activate peroxydisulfate (PDS) to investigate the disinfection effect on tetracycline-resistant Escherichia coli and the transformation frequency of ARGs. As a result, approximately 7.08 log E. coli were inactivated, and 72.36 % and 53.96 % of antibiotics resistance gene (tetB) and 16 S rRNA were degraded respectively within 80 min. Futhermore, the transformation frequency was reduced to 0.8. Characterization and theoretical results indicated that C and O doping in g-C3N4 might lead to the electronic structure modulation and band gap energy reduction, resulting in the production of more free radicals. The mechanism analysis revealed that C/O-g-C3N4 exhibited a lower adsorption energy and reaction energy barrier for PDS compared to g-C3N4. This was beneficial for the homolysis of O-O bonds, forming SO4•- radicals. The attack of the generated active species led to oxidative stress in cells, resulting in damage to the electron transport chain and inhibition of ATP production. Our findings disclose a valuable insight for inactivating ARB, and provide a prospective strategy for ARGs dissemination in water contamination.

Unrecognized Role of Organic Acid in Natural Attenuation of Pollutants by Mackinawite (FeS): The Significance of Carbon-Center Free Radicals.

Organic acid is prevalent in underground environments and, against the backdrop of biogeochemical cycles on Earth, holds significant importance in the degradation of contaminants by redox-active minerals. While earlier studies on the role of organic acid in the generation of reactive oxygen species (ROS) primarily concentrated on electron shuttle or ligand effects, this study delves into the combined impacts of organic acid decomposition and Mackinawite (FeS) oxidation in contaminant transformation under dark aerobic conditions. Using bisphenol A (BPA) as a model, our findings showed that oxalic acid (OA) notably outperforms other acids in enhancing BPA removal, attaining a rate constant of 0.69 h-1. Mass spectrometry characterizations, coupled with anaerobic treatments, advocate for molecule-O2 activation as the principal mechanism behind pollutant transformation. Comprehensive results unveiled that carbon center radicals, initiated by hydroxyl radical (•OH) attack, serve as the primary agents in pollutant oxidation, accounting for at least 93.6% of the total •OH generation. This dynamic, driven by the decomposition of organic acids and the concurrent formation of carbon-centered radicals, ensures a steady supply of electrons for ROS generation. The obtained information highlights the importance of OA decomposition in the natural attenuation of pollutants and offers innovative strategies for FeS and organic acid-coupled decontamination.

Production of biochar from squeezed liquid of fruit and vegetable waste: Impacts on soil N2O emission and microbial community.

The squeezed liquid from fruit and vegetable waste (LW) presents a unique wastewater challenge, marked by recalcitrance in treatment and amplified design risks with the application of conventional processes. Following coagulation of the squeezed liquid, the majority of particulate matter precipitates. The resulting precipitated floc (LWF) is reclaimed and subsequently utilized for the synthesis of biochar. The present study primarily explores the viability of repurposing LWF as biochar to enhance soil quality and mitigate N2O emissions. Findings indicate that the introduction of a 2% proportion of LWFB led to a remarkable 99.5% reduction in total N2O emissions in contrast to LWF. Concurrently, LWFB substantially enhanced nutrients content by elevating soil organic carbon (SOC) and nitrogen levels. Utilizing high-throughput sequencing in conjunction with qPCR, the investigation unveiled that the porous structure and substantial specific surface area of LWFB potentially fostered microbial adhesion and heightened diversity within the soil microbial community. Furthermore, LWFB notably diminished the relative abundance of AOB (Nitrosospira, Nitrosomonas), and NOB (Candidatus_Nitrotoga), thereby curbing the conversion of NH4+ into NO3-. The pronounced elevation in nosZ abundance implies that LWFB holds the potential to mitigate N2O emissions through a conversion to N2.

Temporal and spatial changes of water quality in intensively developed urban rivers and water environment improvement: a case study of the Longgang River in Shenzhen, China.

The water quality status, spatial and temporal change processes, and water environment improvement process of urban rivers are valuable lessons to be learned under the sustainable development strategy. This study aims to reveal the water environment improvement process of intensively developed urban rivers, elucidate the spatial and temporal distribution characteristics of major pollutants, and provide recommendations for their water environment management. Water quality data from eight monitoring sites (2007-2020) in the Longgang River basin in Shenzhen, China, and comprehensive pollution index method (CPI), modified comprehensive pollution index method (M-CPI), and Pearson correlation analysis method were used for comprehensive analysis. The study shows that TN, TP, NH3-N, and COD have the greatest influence on the water quality of Longgang River, with the average pollution contribution of 53.39%, 14.49%, 11.66%, and 4.92%, in order. In 2015-2020, the water quality of the main stream of the Longgang River in the wet season was worse than that in the dry season, while the water quality of the tributaries Dingshan River and the Huangsha River in the dry season was worse than the wet season. The spatial distribution characteristics based on M-CPI indicate that the water quality of the lower reaches of Longgang River, the tributaries Dingshan River and Huangsha River, is relatively poor. In addition, the water environment improvement process of Longgang River can be divided into 3 stages: engineering stage (2007-2013, rating changed from heavily polluted to basically qualified), bottleneck stage (2013-2017, rating fluctuated slightly above and below basically qualified), and ecological restoration stage (2017-2020, rating reached qualified in 2019).

Silica mitigated calcium mineral scaling in brackish water reverse osmosis.

Although the autopsies of reverse osmosis (RO) membranes from full-scale, brackish water desalination plants identify the co-presence of silica and Ca-based minerals in scaling layers, minimal research exists on their formation process and mechanisms. Therefore, combined scaling by silica and either gypsum (non-alkaline) or amorphous calcium phosphate (ACP, alkaline) was investigated in this study for their distinctive impacts on membrane performance. The obtained results demonstrate that the coexistence of silica and Ca-based mineral salts in feedwaters significantly reduced water flux decline as compared to single type of Ca-based mineral salts. This antagonistic effect was primarily attributed to the silica-mediated alleviation of Ca-based mineral scaling. In the presence of silica, silica skins were immediately established around Ca-based mineral precipitates once they emerged. Sheathing by the siliceous skins hindered the aggregation and thus the morphological evolution of Ca-based mineral species. Unlike sulfate precipitates, ACP precipitates can induce the formation of dense and thick silica skins via an additional condensation reaction. Such a phenomenon rationalized the notion concerning a stronger mitigating effect of silica on ACP scaling than gypsum scaling. Meanwhile, coating by silica skins altered the surface chemistries of Ca-based mineral precipitates, which should be fully considered in regulating membrane surface properties for combined scaling control. Our findings advance the mechanistic understanding on combined mineral scaling of RO membranes, and may guide the appropriate design of membrane surface properties for scaling-resistant membrane tailored to brackish water desalination.

Characterization of a novel nornicotine-degrading strain Mycolicibacterium sp. SMGY-1XX from a nornicotine-degrading consortium and preliminary elucidation of its biodegradation pathway by multi-omics analysis.

Nicotine and nornicotine are all toxic alkaloids involved in the formation of carcinogenic tobacco-specific nitrosamines. Microbes play an important role in removing these toxic alkaloids and their derivatives from tobacco-polluted environments. By now, microbial degradation of nicotine has been well studied. However, limited information is available on the microbial catabolism of nornicotine. In the present study, a nornicotine-degrading consortium was enriched from a river sediment sample and characterized by metagenomic sequencing using a combination of Illumina and Nanopore technologies. The metagenomic sequencing analysis demonstrated that Achromobacter, Azospirillum, Mycolicibacterium, Terrimonas, and Mycobacterium were the dominant genera in the nornicotine-degrading consortium. A total of 7 morphologically distinct bacterial strains were isolated from the nornicotine-degrading consortium. These 7 bacterial strains were characterized by whole genome sequencing and examined for their ability to degrade nornicotine. Based on a combination of 16 S rRNA gene similarity comparisons, 16 S rRNA gene-based phylogenetic analysis, and ANI analysis, the accurate taxonomies of these 7 isolated strains were identified. These 7 strains were identified as Mycolicibacterium sp. strain SMGY-1XX, Shinella yambaruensis strain SMGY-2XX, Sphingobacterium soli strain SMGY-3XX, Runella sp. strain SMGY-4XX, Chitinophagaceae sp. strain SMGY-5XX, Terrimonas sp. strain SMGY-6XX, Achromobacter sp. strain SMGY-8XX. Among these 7 strains, Mycolicibacterium sp. strain SMGY-1XX, which has not been reported previously to have the ability to degrade nornicotine or nicotine, was found to be capable of degrading nornicotine, nicotine as well as myosmine. The degradation intermediates of nornicotine and myosmine by Mycolicibacterium sp. strain SMGY-1XX were determined and the nornicotine degradation pathway in strain SMGY-1XX was proposed. Three novel intermediates, myosmine, pseudooxy-nornicotine, and γ-aminobutyrate, were identified during the nornicotine degradation process. Further, the most likely candidate genes responsible for nornicotine degradation in Mycolicibacterium sp. strain SMGY-1XX were identified by integrating genomic analysis, transcriptomic analysis, and proteomic analysis. The findings in this study will help to expand our understanding on the microbial catabolism of nornicotine and nicotine and provide new insights into the nornicotine degradation mechanism by consortia and pure culture, laying a foundation for the application of strain SMGY-1XX for the removal, biotransformation, or detoxification of nornicotine.

The fate of phthalate acid esters in wastewater treatment plants and their impact on receiving waters.

Phthalates (PAEs) are gaining attention and being researched as an endocrine disruptor as global plastic use surge. There is an urgent need to explore the key factors affecting the removal of PAEs from wastewater and the impact of wastewater effluent on receiving water. Here we investigated the levels and distribution patterns of 16 typical PAEs in surface water and five wastewater treatment plants (WWTPs) along the Dongyang River from Yiwu, China, collecting 42 surface water and 31 wastewater samples. We found that influent PAEs concentration and treatment process were the key factors affecting the degradation efficiency of PAEs in primary and secondary treatment, respectively. In primary treatment, long-chain PAEs were more easily removed (and sometimes less likely to accumulate) than short-chain PAEs, regardless of the influent PAEs concentration (a key factor in primary treatment), while in secondary treatment, short-chain PAEs were easily removed regardless of the treatment process (a factor in secondary treatment). This was not the case for long-chain PAEs, which were only more readily removed in the A/A/O process. In addition, by comparing the significant differences between wastewater and surface water, we found that the total PAEs in the treated effluent were significantly lower than in surface water upstream and in built-up urban areas, indicating that wastewater discharges in the study area did not increase PAEs in the receiving water. Finally, river in the city center and artificial treatment facilities in the study area were identified as requiring priority attention. The results of this study can serve as a model for controlling PAEs in other similar developing cities in China and provide valuable information on the fate of endocrine disruptor from wastewater treatment in China and their impact on surface water.

Purification performance from bypass ecological treatment systems treating WWTPs effluents and improvement of water quality in receiving rivers: A case study in southern China.

Effluents from wastewater treatment plants (WWTPs) is the main source of pollution in rivers in developing countries. In this case study, three bypass ecological treatment systems along urban rivers achieved high removal efficiencies for chemical oxygen demand (COD; 55.7-64.0%), ammonium N (NH4+-N; 63.1-89.4%) and total phosphorous (TP; 27.6-76.7%). 16 S rRNA gene sequencing analysis confirmed that Proteobacteria was the main bacterial phylum (44.4%) in the ecological treatment system, and members were enriched significantly in the non-aeration area (59.3%). The relative abundance of Nitrospirae was highest in the inflow area (25.0%), but restrained in the non-aeration area (5.7%). 18 S rRNA gene annotation results indicated that phylum Rotifer was gradually inhibited with the direction of water flow and diffusion, while phylum Rhodophyta displayed the opposite trend. After implementation of bypass ecological treatment systems, receiving rivers were improved significantly from Grade Ⅴ to Ⅳ, and the biodiversity of zooplankton, zoobenthos and fish communities was greatly improved.

Microbial community structure analyses and cultivable denitrifier isolation of Myriophyllum aquaticum constructed wetland under low C/N ratio.

With the rapid expansion of livestock production, the amount of livestock wastewater accumulated rapidly. Lack of biodegradable organic matter makes denitrification of livestock wastewater after anaerobic digestion more difficult. In this study, Myriophyllum aquaticum constructed wetlands (CWs) with efficient nitrogen removal performance were established under different carbon/nitrogen (C/N) ratios. Analysis of community composition reveals the change of M. aquaticum CWs in microbial community structure with C/N ratios. The proportion of Proteobacteria which is one of the dominant phyla among denitrifier communities increased significantly under low C/N ratio conditions. Besides, to obtain cultivable denitrifier that could be added into CWs in situ, 33 strains belonging to phylum Proteobacteria were isolated from efficient M. aquaticum CWs, while the best-performing denitrification strain M3-1 was identified as Bacillus velezensis JT3-1 (GenBank No. CP032506.1). Redundancy analysis and quadratic models showed that C/N ratio had significant effects on disposal of nitrate (NO3--N) and the strains isolated could perform well in denitrification when C/N ratio is relatively low. In addition, they have relatively wide ranges of carbon sources, temperature and a high NO3- removal rate of 9.12 mg/(L·hr) at elevated concentrations of 800 mg/L nitrate. Thus, strains isolated from M. aquaticum CWs with low C/N ratio have a practical application value in the treatment of nitrate-containing wastewater. These denitrifying bacteria could be added to CWs to enhance nitrogen removal efficiency of CWs for livestock wastewater with low C/N ratio in the future.

Monitoring and control methods of harmful algal blooms in Chinese freshwater system: a review.

Harmful algal blooms (HABs) are a worldwide problem with substantial adverse effects on the aquatic environment as well as human health, which have prompted researchers to study measures to stem and control them. Meanwhile, it is key to research and develop monitoring methods to establish early warning HABs. However, both the current monitoring methods and control methods have some shortcomings, making the field application limited. Thus, we need to improve current approaches for monitoring and controlling HABs efficiently. Based on the freshwater system features in China, we review various monitoring and control methods of HABs, summarize and discuss the problems with these methods, and propose the future development direction of monitoring and control HABs. Finally, we envision that it can combine physical, chemical, and biological methods to inhibit HAB expansion in the future, complementing each other with advantages. Further, we promise to establish a long-term strategy of controlling HABs with various algicidal bacteria co-cultivate for field applications in China. Efforts in studying algicidal bacteria must be increased to better control HABs and mitigate the risks of aquatic ecosystems and human health in China.

Soybean straw biochar activating peroxydisulfate to simultaneously eliminate tetracycline and tetracycline resistance bacteria: Insights on the mechanism.

Tetracycline (TC) has been frequently detected in various environments, thus promoting the occurrence of resistance in bacterial populations. In this study, a suite of soybean straw biochars (SSBs) were fabricated under different pyrolysis temperatures (600-1000 °C), which were utilized as peroxydisulfate (PS) activators for TC degradation and TC resistant Escherichia coli (E. coli) disinfection. The purification effect of SSBs/PS systems manifested obvious positive dependence on pyrolysis temperature of SSBs with SSB1000/PS system obtained the superior TC degradation, E. coli disinfection and coexisting TC and E. coli elimination capacity. The leakage of intracellular DNA and the degradation of total DNA and extracellular DNA was revealed no matter in alone E. coli or combined pollution which can also be supported by the gradual ruptured bacterial morphology and attenuated internal components. It can be found that TC adsorption in SSBs played a significant role on TC degradation, while the electrostatic repulsion always existed between E. coli and SSB1000. Furthermore, a battery of solid evidences collectively demonstrated the significant different purification mechanism of TC and E. coli. The TC degradation was achieved dominantly by surface-bound radicals, while bactericidal activity should be attributed to free SO4·- in bulk solutions. In contrast to other SSBs, the largest mesopore volumes, highest C=O content, lowest interfacial charge transfer resistance and strongest electron donating capacity explained the outperformed catalytic performance of SSB1000.

Recovery and utilization of phosphorus from fruit and vegetable wastewater.

Excessive discharge of phosphorus into the water bodies is the key factor to cause eutrophication. The fruit and vegetable wastewater contains large amounts of phosphorus, and it may be directly discharged into water bodies, which has a great burden on the municipal sewage pipe network. Therefore, coagulation was used to remove phosphorus, recovered the phosphorus from the wastewater into the precipitate, and then the precipitate was pyrolyzed as an efficient adsorbent for phosphate removal. By comparing the adsorption effects of adsorbents (XT-300, XT-400, and XT-500) with pyrolysis temperatures of 300 °C, 400 °C, and 500 °C on phosphate in actual phosphorus-containing wastewater and simulated phosphorus-containing wastewater at different adsorbent dosage (4 g/L, 7 g/L, and 10 g/L), it was found that XT-300 had the best performance of adsorption, and the adsorption of phosphate was endothermic and obeyed the Langmuir isotherms and Elovich kinetics. The influence of pH, coexisting anions, and the structure of XT-300 revealed that the removal of phosphate was associated with electrostatic attraction, pore filling, but could not be determined whether it was related to surface precipitation. This study provides a way and method for the recovery and utilization of phosphorus in fruit and vegetable wastewater and proves that the synthetic adsorbent was an efficient phosphorus adsorbent. In the long term, we can try to use the adsorbent after phosphorus adsorption to promote plant growth in agricultural systems.

Covalent organic framework-based porous materials for harmful gas purification.

Covalent organic frameworks (COFs) with 2D or 3D networks are a class of novel porous crystalline materials, and have attracted more and more attention in the field of gas purification owing to their attractive physicochemical properties, such as high surface area, adjustable functionality and structure, low density, and high stability. However, few systematic reviews about the application statuses of COFs in gas purification are available, especially about non-CO2 harmful gases. In this review, the recent progress of COFs about the capture, catalysis, and detection of common harmful gases (such as CO2, NOx, SO2, H2S, NH3 and volatile pollutants) were comprehensively discussed. The design strategies of COF functional materials from porosity adjustment to surface functionalization (including bottom-up approach, post-synthetic approach, and blending with other materials) for certain application were summarized in detail. Furthermore, the faced challenges and future research directions of COFs in the harmful gas treatment were clearly proposed to inspire the development of COFs.

Insights on the electron transfer pathway of phenolic pollutant degradation by endogenous N-doped carbonaceous materials and peroxymonosulfate system.

In this study, chitosan, a low-price and easily obtainable natural polymerized sugar containing abundant nitrogen element, was employed as a precursor for preparing hierarchically porous carbon (PC) to activate peroxymonosulfate (PMS). The PC fabricated at 800 °C obtained the optimum catalytic performance with complete removal of p-hydroxybenzoic acid (HBA) in 30 min. The selective degradation toward phenolic pollutants with different substituent groups and the resistance over the interference of typical anions and natural organic matter implied a non-radical pathway contributed most for HBA degradation. The investigation of structure-activity relationship suggested a positive linear correlation between graphitic N content and HBA removal. The chemical quenching experiment and electron paramagnetic resonance (EPR) excluded the crucial role of radicals and 1O2. Solid evidence based on electrochemical techniques demonstrated the essential contribution of electron transfer pathway achieved by three successive processes including the first close adsorption of PMS by PC800 to form metastable intermediates, then an internal electron transfer from active graphitic N to PMS within metastable intermediates and finally external electron transfer from HBA to metastable intermediates. This study provided insightful mechanism understanding of a promising organics elimination strategy by PMS activation through N-doped carbonaceous materials utilizing chitosan as a simultaneous carbon and nitrogen precursor.

Hierarchically porous magnetic biochar as an efficient amendment for cadmium in water and soil: Performance and mechanism.

Three types of hierarchically porous magnetic biochars (HMBs) were prepared by pyrolyzing low-cost wheat straw and potassium ferrate (K2FeO4) under a nitrogen atmosphere at 600, 700 and 800 °C, respectively, which could be used as amendments for cadmium (Cd) in water and soil. HMB fabricated at 700 °C (HMB700) had the best remediation performance for Cd in water and soil, which was mainly due to its largest specific surface area and micropore volume. Batch sorption experiments showed that Cd(II) sorption onto HMBs were well-described by a pseudo-second-order model and Sips (Freundlich-Langmuir) model, indicating that HMBs removed Cd(II) mainly through chemical adsorption. MINTEQ modeling evidenced that HMBs adsorbed Cd(II) mainly through precipitation rather than surface complexation. The adsorption behavior of HMB700 to Cd(II) could be explained by surface complexation (-OCd, -COOCd), precipitation (Cd(OH)2 and CdCO3), physical adsorption (rich pore structure) and ion exchange (K+, Ca2+, Mg2+). Furthermore, adding HMBs (1 wt%) (incubation 60 days) could also significantly increase soil pH and electrical conductivity (EC), and significantly reduce the available Cd content in soil (47.97%-61.38%). Adding HMBs could promote the conversion of bioavailable to less bioavailable Cd forms. These results provided a new idea for fabricating agricultural waste-based HMBs to remediate Cd in water and soil.

Activation of peroxymonosulfate by iron-biochar composites: Comparison of nanoscale Fe with single-atom Fe.

A convenient and efficient method to fabricate isolated Fe single-atom catalysts deposited on Myriophyllum aquaticum-based biochar (ISA-Fe/MC) is reported for peroxymonosulfate-based organics degradation. Firstly, the Fe nanoparticles anchored on the hierarchical porous biochar (nano-Fe/MC) can be obtained by utilizing K2FeO4 as a synchronous activation and graphitization agent. Subsequently, ISA-Fe/MC was achieved by HCl etching of nano-Fe/MC to remove the excess Fe nanoparticles. Compared with nano-Fe/MC, ISA-Fe/MC demonstrated outperformed catalytic capacity towards PMS activation for phenol degradation. The combination of super high surface area, hierarchical porous structure, graphitization structure and atomically dispersed Fe species should be responsible for prominent catalytic oxidation ability and outstanding resistance to common anions and humic acid. Based on the chemical scavengers, EPR experiments and electrochemistry tests, the SO4•- dominated radical degradation pathway for nano-Fe/MC and electron transfer reigned non-radical degradation pathway for ISA-Fe/MC was revealed. In contrast to nano-Fe/MC, density functional theory calculations demonstrated the enhanced density of states around Fermi level in ISA-Fe/MC meaning the increased catalytic performance and more electron transfer between single-atom Fe to adjacent graphitic C and N which could serve as electron transfer channel for PMS activation.