Impact of biochar supported nano zero-valent iron on anaerobic co-digestion of sewage sludge and food waste: Methane production, performance stability and microbial community structure

Boosting sewage sludge safety with nano-biochar for polycyclic aromatic hydrocarbons immobilization and ecotoxicity reduction

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in sewage sludge (SSL), posing environmental and health risks. Stabilizing these contaminants is crucial for improving the ecological safety and reuse potential of SSL. This study investigated the effectiveness of nano-biochars (n-BC) and bulk biochars (b-BC) derived from willow (WL) and rice husk (RH) in reducing freely dissolved (Cfree) PAHs in SSL and mitigating its ecotoxicity. RH-derived biochars demonstrated superior performance, achieving 1.5- to 4.7-fold greater reductions in Cfree PAH content compared to WL-derived variants. Notably, n-BC proved more effective than b-BC, with n-BC-RH and n-BC-WL showing up 1.2- to 2.0-fold greater reductions, respectively. The optimal BC's dose range was 2.5-5 %, with diminishing returns observed at higher concentrations (10 %). The n-BC treatment also showed enhanced toxicity reduction, improving Aliivibrio fischeri luminescence and Lepidium sativum root growth by up to 109 % and 369 % compared to b-BC. Analysis revealed that inorganic minerals (present in ash) in both BC types played a key role in PAH immobilization. These results highlight n-BC's potential as an innovative solution for sustainable SSL management. This research addresses a critical gap in sludge management by proposing practical, scalable, and sustainable solutions for PAH contamination.

Promoting caproate production using anaerobically digested sludge-derived biochar: Performances, mechanisms, and environmental impacts

Carbon chain elongation offers a promising pathway for converting waste resources into caproate. However, challenges in yield and selectivity have limited its broader application. To address these limitations, anaerobically digested sludge-derived biochar (ADS-B) was incorporated into the carbon chain elongation process. The findings reveal that the addition of 20 g/L ADS-B resulted in the highest net caproate yield (6.5 g/L) and selectivity (61.1%). Further analysis highlighted that ADS-B's superior physicochemical properties enhanced the conversion of butyrate to caproate and facilitated the colonization of key microorganisms, such as Terrisporobacter and Clostridium, essential for caproate production. Additionally, a life cycle assessment indicated that ADS-B addition effectively reduced the environmental impact of caprate production, with additional potential for further mitigation through feedstock substitution. This study provides critical insights into the application of anaerobically digested sludge-derived biochar for enhancing carbon chain elongation, presenting an alternative approach for waste reutilization.

Characteristic study of biological CaCO3-supported nanoscale zero-valent iron: stability and migration performance

nZVI has attracted much attention in the remediation of contaminated soil and groundwater, but the application is limited due to its aggregation, poor stability, and weak migration performance. The biological CaCO3 was used as the carrier material to support nZVI and solved the nZVI agglomeration, which had the advantages of biological carbon fixation and green environmental protection. Meanwhile, the distribution of nZVI was characterised by SEM-EDS and TEM carefully. Subsequently, the dispersion stability of bare nZVI and CaCO3@nZVI composite was studied by the settlement experiment and Zeta potential. Sand column and elution experiments were conducted to study the migration performance of different materials in porous media, and the adhesion coefficient and maximum migration distances of different materials in sand columns were explored. SEM-EDS and TEM results showed that nZVI could be uniformly distributed on the surface of biological CaCO3. Compared with bare nZVI, CaCO3@nZVI composite suspension had better stability and higher absolute value of Zeta potential. The migration performance of nZVI was poor, while CaCO3@nZVI composite could penetrate the sand column and have good migration performance. What's more, the elution rates of bare nZVI and CaCO3@nZVI composite in quartz sand columns were 5.8% and 51.6%, and the maximum migration distances were 0.193 and 0.885 m, respectively. In summary, this paper studies the stability and migration performance of bare nZVI and CaCO3@nZVI composite, providing the experimental and theoretical support for the application of CaCO3@nZVI composite, which is conducive to promoting the development of green remediation functional materials.

Porous hollow microspheres based on industrial solid waste enhance biomethane recovery from corn straw

The increasing production of industrial solid waste requires better disposal solutions. Porous hollow microspheres (PHM) are small inorganic materials with high surface area and adsorption capacity, but their potential for use in anaerobic digestion (AD) has not been explored. With PHM as additive, the effects of different industrial solid wastes (waste glass, steel slag, and fly ash) with different loadings (2 %-8 %), respectively, on the AD of corn straw were investigated in this study. The results showed that PHM could supplement trace elements and promote biofilm formation, which effectively shortened the lag period (25.00-60.87 %) and increased the methane yield (4.75 %-16.28 %). The 2 % PHM loading based on steel slag gave the highest methane yield (300.16 NmL/g VSadd). Microbial and PICRUSt2 analyses indicated that PHM enriched hydrolytic and acidogenic bacteria, increased the abundance of methanogenesis-related enzyme genes. This study provides a theoretical basis for the comprehensive utilization of coupled industrial and agricultural wastes.

Complete 2,4,6-trichlorophenol degradation by anaerobic sludge acclimated with 4-chlorophenol: Synergetic effect of nZVI@BMPC and sodium lactate as an external nutrient

Ball-milled plastic char supported nano zero-valent iron (nZVI@BMPC) and their application combined with anaerobic sludge for microbial dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) were investigated. The XRD and FTIR analysis proved composition of zero valent states of iron, and the BET and SEM analysis showed that nZVI was uniformly distributed on the surface of BMPC. Successive addition of 1000 mg/L sodium lactate and nZVI@BMPC enhanced the acclamation of anaerobic sludge and resulted in the degradation of 4-CP within 80 days. The acclimated consortium with nZVI@BMPC completely degraded 2,4,6-TCP into CH4 and CO2, and the key dechlorination route was through 4-CP dechlorinaion and mineralization. The degradation rate of 2,4,6-TCP with nZVI@BMPC was 0.22/d, greater than that without nZVI@BMPC. The dechlorination efficiency was enhanced in the Fe2+/Fe3+ system controlled by nZVI@BMPC and iron-reducing bacteria. Metagenomic analysis result showed that the dominant de-chlorinators were Chloroflexi sp., Desulfovibrio, and Pseudomonas, which could directly degrade 2,4,6-TCP to 4-CP, especially, Chloroflexi bacterium could concurrently be used to mineralize 4-CP. The relative abundance of the functional genes cprA, acoA, acoB, and tfdB increased significantly in the presence of the nZVI@BMPC. This study provides a new strategy can be a good alternative for possible application in groundwater remediation.

Global performance and trends of research on emerging contaminants in sewage sludge: A Bibliometric Analysis from 1990 to 2023

The pervasive occurrence of emerging contaminants (ECs) in sewage sludge (SWS) poses significant safety challenges concerning the processing, disposal, and secure application, ultimately jeopardizing both human health and the ecological environment. To comprehensively comprehend the evolutionary trajectories, present state, and research advancements in the field of ECs in SWS, a systematic was conducted, scrutinizing the annual publication quantity, disciplinary distribution, core authors, involved nations/regions, pertinent keywords, and citation status of 2082 research publications related to ECs in SWS from 1990 to 2023. The results indicate a substantial upward trajectory in the research literature pertaining to ECs in SWS. The study of ECs in SWS encompasses 78 disciplines, including Environmental Sciences, Environmental Engineering, and Water Resources. China, Spain, and the USA ranked among the top three countries in terms of both total publications and citation frequency. The majority of publications were published in reputable high-impact journals such as Science of the Total Environment, Chemosphere, and Bioresource Technology. Based on high-frequency keywords, co-occurrence networks of keywords, and keywords burst analysis, it is found that the occurrence and environment behavior of ECs in SWS (ARGs, microplastics, PPCPs, and POPs), the detection and analytical methods, the impact on SWS treatment and disposal processes, and the accumulation and ecological risks in plants and soil during SWS land utilization, are the main research directions and hot topics in this field. In the future, the study of the impact of SWS treatment technologies on ECs removal is expected to receive increased research attention.

Metagenomic analysis reveals the mechanisms of biochar supported nano zero-valent iron in two-phase anaerobic digestion of food waste: microbial community, CAZmey, functional genes and antibiotic resistance genes

The mechanisms of biochar supported nano zero-valent iron (BC/nZVI) on two-phase anaerobic digestion of food waste were investigated. Results indicated that the performance of both acidogenic phase and methanogenic phase was effectively facilitated. BC/nZVI with the amount of 120 mg/L increased methane production by 32.21%. In addition, BC/nZVI facilitated direct interspecies electron transfer (DIET) between Geobacter and methanogens. Further analysis showed that BC/nZVI increased the abundance of most CAZymes in acidogenic phase. The study also found that BC/nZVI had positive effects on metabolic pathways and related functional genes. The abundances of acdA and ackA in acidogenic phase were increased by 151.75% and 36.26%, respectively, and the abundances of pilA and TorZ associated with DIET were also increased. Furthermore, BC/nZVI mainly removed IMP-12, CAU-1, cmeB, ErmR, MexW, ErmG, Bla2, vgaD, MuxA, and cpxA from this system, and reduced the antibiotic resistance genes for antibiotic inactivation resistance mechanisms.

A novel biochar-augmented enzymatic process for conversion of food waste to biofertilizers: Planting trial with leafy vegetable

The present study developed a novel biochar-augmented enzymatic approach for fast conversion of food waste to solid and liquid biofertilizers. By augmented with 10 % of biochar and mediated with 5 % of food waste-derived hydrolytic enzymes mixture (i.e. fungal mash), 100 kg of food waste could be converted into 22.3 kg of solid biofertilizer with a water content of 30 % and 55.0 kg of liquid biofertilizer, which fulfilled Chinese national standards for solid and liquid organic biofertilizers, respectively. Field plantation results showed that the Pak Choi grown on food waste-derived biofertilizers was comparable with that on commercial ones, in terms of the vegetable productivity and nutrient contents. It was further revealed that the application of food waste-derived biofertilizers did not change soil chemical properties but enriched microbial diversity. This study clearly indicated that the biochar-augmented enzymatic approach for food waste conversion to biofertilizers was technically feasible and economically viable towards circular agriculture economy.

Influence of adding strategy of biochar on medium-chain fatty acids production from sewage sludge

Production of medium-chain fatty acids (MCFAs) from sewage sludge has dual effects on valuable sludge disposal and renewable energy generation, while low efficiency limits its application. Biochar addition is considered an effective method to improve MCFAs production. In this study, the influence of biochar adding strategies (i.e., adding biochar in acidification or chain elongation (CE) processes) on MCFAs production was explored. Results showed that by adding biochar in the acidification process, MCFAs accumulation increased by over 114%, accompanied by the highest carbon conversion efficiency (134.66%) and electron transfer efficiency of MCFAs (94.22%) by the terminal CE. Adding biochar before the acidification process better enriched CE bacteria (e.g., Paraclostridium) and strengthened the dominant metabolic pathway. In contrast, the biochar added before the CE process priorly enriched the bacteria capable of degrading organics, like unclassified_f__Dysgonomonadaceae, norank_f__norank_o__OPB41, and Acetobacterium. The differences in excessive ethanol oxidation and short-chain fatty acids accumulation induced by varied adding strategies might be responsible for this.

Mechanisms of anaerobic treatment of sulfate-containing organic wastewater mediated by Fe0 under different initial pH values

The anaerobic treatment of sulfide-containing organic wastewater (SCOW) is significantly affected by pH, causing dramatic decrease of treatment efficiency when pH deviates from its appropriate range. Fe0 has proved as an effective strategy on mitigating the impact of pH. However, systematic analysis of the influence mechanism is still lacking. To fill this gap, the impact of different initial pH values on anaerobic treatment efficiency of SCOW with Fe0 addition, the change of fermentation type and methanogens, and intra-extracellular electron transfer were explored in this study. The results showed that Fe0 addition enhanced the efficacy of anaerobic treatment of SCOW at adjusted initial pH values, especially at pH 6. Mechanism analysis showed that respiratory chain-related enzymes and electron shuttle secretion and resistance reduction were stimulated by soluble iron ions generated by Fe0 at pH 6, which accelerated intra-extracellular electron transfer of microorganisms, and ultimately alleviated the impact of acidic pH on the system. While at pH 8, Fe0 addition increased the acetogenic bacteria abundance, as well as optimized the fermentation type and improved the F420 coenzyme activity, resulting in the enhancement of treatment efficiency in the anaerobic system and remission of the effect of alkaline pH on the system. At the neutral pH, Fe0 addition had both advantages as stimulating the secretion of respiratory chain and electron transfer-related enzymes at pH 6 and optimizing the fermentation type pH 8, and thus enhanced the treatment efficacy. This study provides important insights and scientific basis for the application of new SCOW treatment technologies.

Applications and synergistic degradation mechanisms of nZVI-modified biochar for the remediation of organic polluted soil and water: A review

Increasing organic pollution in soil and water has garnered considerable attention in recent years. Nano zero-valent iron-modified biochar (nZVI/BC) has been proven to remediate the contaminated environment effectively due to its abundant active sites and unique reducing properties. This paper provides a comprehensive overview of the application of nZVI/BC in organic polluted environmental remediation and its mechanisms. Firstly, the review introduced primary synthetic methods of nZVI/BC, including in-situ synthesis (carbothermal reduction and green synthesis) and post-modification (liquid-phase reduction and ball milling). Secondly, the application effects of nZVI/BC were discussed in remediating soil and water polluted by antibiotics, pesticides, polycyclic aromatic hydrocarbons (PAHs), and dyes. Thirdly, this review explored the mechanisms of the adsorption and chemical degradation of nZVI/BC, and synergistic degradation mechanisms of nZVI/BC-AOPs and nZVI/BC-Microbial interactions. Fourth, the factors that influence the removal of organic pollutants using nZVI/BC were summarized, encompassing synthesis conditions (raw materials, pyrolysis temperature and aging of nZVI/BC) and external factors (reagent dosage, pH, and coexisting substances). Finally, this review proposed future challenges for the application of nZVI/BC in environmental remediation. This review offers valuable insights for advancing technology in the degradation of organic pollutants using nZVI/BC and promoting its on-site application.

Effects of Fe-N co-modified biochar on methanogenesis performance, microbial community, and metabolic pathway during anaerobic co-digestion of alternanthera philoxeroides and cow manure

The performance of anaerobic digestion (AD) is susceptible to disturbances in feedstock degradation, intermediates accumulation, and methanogenic archaea activity. To improve the methanogenesis performance of the AD system, Fe-N co-modified biochar was prepared under different pyrolysis temperatures (300,500, and 700 °C). Meanwhile, pristine and Fe-modified biochar were also derived from alternanthera philoxeroides (AP). The aim was to compare the effects of Fe-N co-modification, Fe modification, and pristine biochar on the methanogenic performance and explicit the responding mechanism of the microbial community in anaerobic co-digestion (coAD) of AP and cow manure (CM). The highest cumulative methane production was obtained with the addition of Fe-N-BC500 (260.38 mL/gVS), which was 42.37 % higher than the control, while the acetic acid, propionic acid, and butyric acid concentration of Fe-N-BC were increased by 147.58 %, 44.25 %, and 194.06 % compared with the control, respectively. The co-modified biochar enhanced the abundance of Chloroflexi and Methanosarcina in the AD system. Metabolic pathway analysis revealed that the increased methane production was related to the formation and metabolism of volatile fatty acids and that Fe-N-BC500 enhanced the biosynthesis of coenzyme A and the cell activity of microorganisms, accelerating the degradation of propionic acid and enhancing the hydrogenotrophic methanogenesis pathway. Overall, Fe-N co-modified biochar was proved to be an effective promoter for accelerated methane production during AD.

Anaerobic co-digestion of sewage sludge pretreated by thermal hydrolysis and food waste: gas production, dewatering performance, and community structure

Anaerobic co-digestion can effectively break the limitations of mono-digestion. However, there are still some problems such as long residence time, unsatisfactory methane yield, and unstable performance for co-digestion of sewage sludge (SS) and food waste (FW). Therefore, the SS in the reactor treating co-digestion of SS and FW is considered to be pretreated by thermal hydrolysis. In this work, the anaerobic co-digestion of SS of thermal hydrolysis pretreatment (THP) and FW significantly improved the stability, methane production of the digestive reactor, and dewaterability of the digested sludge. The R6 obtained the most cumulative methane production (315.76 mL/g VS). In addition, compared to R3, the cumulative methane production and maximum methane production rate of R5 increased by 9.93% and 14.56%, respectively. The dewaterability of R4, R5, and R6 was improved, while the dewatering performance of the R3 decreased to a greater extent. The results of the kinetic model fitting were consistent with the experimental results. Among them, the hydrolysis constants (Kh) of anaerobic co-digestion of THP-SS and FW were 0.121, 0.130, and 0.114 d-1, respectively, which were higher than those of other groups. And the estimated lag time (λ) of co-digestion was also lower than that of mono-digestion groups. Microbial community analysis indicated that the bacterial diversity and richness of anaerobic co-digested groups of THP-SS and FW were enhanced, while the methanogens with acetoclastic pathway became the main methanogenic microorganisms. This work provides essential information on anaerobic co-digestion containing different THP-SS contents.

Functional biochar in enhanced anaerobic digestion: Synthesis, performances, and mechanisms

Anaerobic digestion technology is crucial in bioenergy recovery and organic waste management. At the same time, it often encounters challenges such as low organic digestibility and inhibition of toxic substances, resulting in low biomethane yields. Biochar has recently been used in anaerobic digestion to alleviate toxicity inhibition, improve the stability of anaerobic digestion processes, and increase methane yields. However, the practical application of biochar is limited, for the properties of pristine biochar significantly affect its application in anaerobic digestion. Although much research focuses on understanding original biochar's fundamental properties and functionalization, there are few reviews on the applications of functional biochar and the effects of critical properties of pristine biochar on anaerobic digestion. This review systematically reviewed functionalization strategies, key performances, and applications of functional biochar in anaerobic digestion. The properties determining the role of biochar were reviewed, the synthesis methods of functional biochar were summarized and compared, the mechanism of functional biochar was discussed, and the factors affecting the function of functional biochar were reviewed. This review provided a comprehensive understanding of functional biochar in anaerobic digestion processes, which would be helpful for the development and applications of engineered biochar.

A review of application of combined biochar and iron-based materials in anaerobic digestion for enhancing biogas productivity: Mechanisms, approaches and performance

Strengthening direct interspecies electron transfer (DIET), via adding conductive materials, is regarded as an effective way for improving methane productivity of anaerobic digestion (AD). Therein, the supplementation of combined materials (composition of biochar and iron-based materials) has attracted increasing attention in recent years, because of their advantages of promoting organics reduction and accelerating biomass activity. However, as far as we known, there is no study comprehensively summarizing the application of this kind combined materials. Here, the combined methods of biochar and iron-based materials in AD system were introduced, and then the overall performance, potential mechanisms, and microbial contribution were summarized. Furthermore, a comparation of the combinated materials and single material (biochar, zero valent iron, or magnetite) in methane production was also evaluated to highlight the functions of combined materials. Based on these, the challenges and perspectives were proposed to point the development direction of combined materials utilization in AD field, which was hoped to provide a deep insight in engineering application.

Iron-modified biochar boosts anaerobic digestion of sulfamethoxazole pharmaceutical wastewater: Performance and microbial mechanism

The accumulation of volatile fatty acids (VFAs) caused by antibiotic inhibition significantly reduces the treatment efficiency of sulfamethoxazole (SMX) wastewater. Few studies have been conducted to study the VFAs gradient metabolism of extracellular respiratory bacteria (ERB) and hydrogenotrophic methanogen (HM) under high-concentration sulfonamide antibiotics (SAs). And the effects of iron-modified biochar on antibiotics are unknown. Here, the iron-modified biochar was added to an anaerobic baffled reactor (ABR) to intensify the anaerobic digestion of SMX pharmaceutical wastewater. The results demonstrated that ERB and HM were developed after adding iron-modified biochar, promoting the degradation of butyric, propionic and acetic acids. The content of VFAs reduced from 1166.0 mg L^-1 to 291.5 mg L^-1. Therefore, chemical oxygen demand (COD) and SMX removal efficiency were improved by 22.76% and 36.51%, and methane production was enhanced by 6.19 times. Furthermore, the antibiotic resistance genes (ARGs) such as sul1, sul2, intl1 in effluent were decreased by 39.31%, 43.33%, 44.11%. AUTHM297 (18.07%), Methanobacterium (16.05%), Geobacter (6.05%) were enriched after enhancement. The net energy after enhancement was 0.7122 kWh m^-3. These results confirmed that ERB and HM were enriched via iron-modified biochar to achieve high efficiency of SMX wastewater treatment.

Toxicity of Nanoscale Zero-Valent Iron to Soil Microorganisms and Related Defense Mechanisms: A Review

Soil pollution is a global environmental problem. Nanoscale zero-valent iron (nZVI) as a kind of emerging remedial material is used for contaminated soil, which can quickly and effectively degrade and remove pollutants such as organic halides, nitrates and heavy metals in soil, respectively. However, nZVI and its composites can enter the soil environment in the application process, affect the physical and chemical properties of the soil, be absorbed by microorganisms and affect the growth and metabolism of microorganisms, thus affecting the ecological environment of the entire soil. Because of the potential risks of nZVI to the environment and ecosystems, this paper summarizes the current application of nZVI in the remediation of contaminated soil environments, summarizes the various factors affecting the toxic effects of nZVI particles and comprehensively analyzes the toxic effects of nZVI on microorganisms, toxic mechanisms and cell defense behaviors to provide a theoretical reference for subsequent biosafety research on nZVI.

Enhanced elimination of Cr(VI) from aqueous media by polyethyleneimine modified corn straw biochar supported sulfide nanoscale zero valent iron: Performance and mechanism

A novel polyethyleneimine modified corn straw biochar supported sulfide nanoscale zero-valent iron (S-nZVI@PBC) was developed to enhance Cr(VI) removal from aqueous media. The characteristics of morphology, chemical composition, and functional groups of S-nZVI@PBC, as well as its kinetics and mechanism for Cr(VI) removal were explored. Characterization verified S-nZVI was successfully loaded onto PEI modified biochar. The adsorption process was well represented pseudo-second-order model (R² = 0.990) and Langmuir isotherm model (R² = 0.962), indicating it was a monolayer chemical adsorption process. The Cr(VI) removal was affected by pH and achieved the maximum when pH = 3.0, which may be ascribed to the better corrosion of nZVI and release of Fe(II) from the S-nZVI@PBC in acidic condition. The primary mechanisms were adsorption, reduction, and co-precipitation. S-nZVI@PBC exhibited higher stability and reusability than nZVI, which makes it more promising in environmental application. Overall, S-nZVI@PBC is of great potential for treating Cr(VI)-containing wastewater.

Enhanced stability of food waste anaerobic digestion under low inoculum to substrate ratio by using biochar

The influence of biochar on anaerobic digestion (AD) of organic waste have been widely studied. However, the effect of biochar on the mitigation of acidification and subsequently the stimulation of methanogenesis recovery during mono food waste (FW) digestion process under a low inoculum to substrate (I/S) ratio (i.e. a high organic loading) is rarely investigated. In this study, the benefit of biochar with respect to methane production from FW was explored in a mono FW AD system with four different additional amounts of biochar, i.e. 0, 5, 10 and 15 g/L. Results revealed that biochar boosted methane production in AD at a low I/S ratio by 390-530% through stimulating methanogenic activity, improving organics removal and enhancing process stability. The biochar dosage of 10 g/L demonstrated the highest biodegradability of 92.3% and the highest specific methane production of 553.0 mL/g VSremoved among all groups. Without biochar addition, volatile fatty acids (VFAs) accumulated to 20 g/L and the highest total ammonium-N (TAN) was > 1200 mg/L. The suppression of methanogenesis was significantly correlated with VFA and TAN (p < 0.05). Therefore, biochar addition presented a positive effect on VFAs degradation and buffering capacity which could be an effective approach to enhance methane production from FW digestion at a low inoculum to substrate ratio without the fear of system failure.

Effect of biochar on antibiotic resistance genes in the anaerobic digestion system of antibiotic mycelial dreg

To address the problem of antibiotic mycelial dreg (AMD) treatment and removal of antibiotic resistance genes (ARGs), this study adopted anaerobic digestion (AD) technology, and added biochar (BC) and biochar loaded with nanosized zero-valent iron (nZVI-BC) to promote the AD of AMD and enhance the removal of ARGs. Results showed that nZVI-BC was better than BC in promoting AD due to the hydrogen evolution corrosion and the synergistic effect of nZVI and BC. In addition, BC and nZVI-BC can enhance the oxidative stress response and reduce ammonia stress phenomenon, which significantly reduces the abundance of aadA, ant(2″)-Ⅰ, qacEdelta1 and sul1. In conclusion, the enhance effect of nZVI-BC is greater than BC. The removal efficiency rates of nZVI-BC on the above-mentioned four ARGs were improved by 33%, 9%, 24% and 11%.

Electron shuttles enhanced the removal of antibiotics and antibiotic resistance genes in anaerobic systems: A review

The environmental and epidemiological problems caused by antibiotics and antibiotic resistance genes have attracted a lot of attention. The use of electron shuttles based on enhanced extracellular electron transfer for anaerobic biological treatment to remove widespread antibiotics and antibiotic resistance genes efficiently from wastewater or organic solid waste is a promising technology. This paper reviewed the development of electron shuttles, described the mechanism of action of different electron shuttles and the application of enhanced anaerobic biotreatment with electron shuttles for the removal of antibiotics and related genes. Finally, we discussed the current issues and possible future directions of electron shuttle technology.

Recent advances in conductive materials amended anaerobic co-digestion of food waste and municipal organic solid waste: Roles, mechanisms, and potential application

Recently, conductive materials (i.e., carbon-based and iron-based materials) as a feasible and attractive approach have been introduced to anaerobic co-digestion (ACoD) system for promoting its performance and stability through direct interspecies electron transfer. Owing to the key roles of conductive materials in ACoD process, it is imperative to gain a profound understanding of their specific functions and mechanisms. Here, this review critically examined the state of the art of conductive materials assisted ACoD of food waste and common municipal organic solid waste. Then, the fundamental roles of conductive materials on ACoD enhancement and the relevant mechanisms were discussed. Last, the perspectives for co-digestate treatment, reutilization, and disposal were summarized. Moreover, the main challenges to conductive materials amended ACoD in on-site application were proposed and the future remarks were put forward. Collectively, this review poses a scientific basis for the potential application of conductive materials in ACoD process in the future.

Ball milling sulfur-doped nano zero-valent iron @biochar composite for the efficient removal of phosphorus from water: Performance and mechanisms

This study successfully prepared a novel sulfur-doped nano zero-valent iron @biochar (BM-SnZVI@BC) by modifying corn stover biochar with Fe⁰ and S⁰ using a mechanical ball milling method for effective phosphorus (P) adsorption in the waterbody. Batch experiments revealed that BM-SnZVI@BC (BC/S⁰/Fe⁰ = 3:1:1) reached a Q_max of 25.00 mg P/g and followed PFO and Langmuir models. This work had shown that electrostatic attraction, surface chemical precipitation, hydrogen bonding, and ligand effects all contributed to P removal. Since the FeS layer mitigated the oxidation-induced surface passivation of nZVI, sulfidation significantly extended the lifetime of BM-SnZVI@BC, removing 84.4% of P even after 60 d aging in air. The regeneration experiments of composites showed that re-ball milling destroyed the surface iron oxide layer to improve the properties of the recovered material. This is an essential step in the design of P-removal agents to implement anti-aging and commercialization of adsorbents for engineering applications.

Marine Biomass-Supported Nano Zero-Valent Iron for Cr(VI) Removal: A Response Surface Methodology Study

Heavy metal ions such as Cr(VI) pose great hazards to the environment, which requests materials and methods for decontamination. Nano zero-valent iron (nZVI) has emerged as a promising candidate for Cr(VI) removal. Herein, harnessing the merits of marine biomass, a heterogeneous water treatment system for the decontamination of Cr(VI) is developed based on the in situ immobilization of nZVI on the seashell powder (SP)-derived porous support. A response surface methodology (RSM) study involving three independent factors is designed and conducted to direct material synthesis and reaction design for products with optimal performances. Under optimal synthetic conditions, the nZVI-loaded seashell powder (SP@nZVI), which is characterized in detail by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), results in a 79% increase in the removal efficiency of Cr(VI) compared to free nZVI. Mechanism studies show that the removal of Cr(VI) by SP@nZVI conforms to the Langmuir adsorption model with a quasi-second order kinetic equation, in which redox reactions between nZVI and Cr(VI) occurred at the SP surface. The results of this work are expected to benefit the reuse of bioresource waste in developing environmental remediation materials.

Iron-based biochar derived from waste-activated sludge enhances anaerobic digestion of synthetic salty organic wastewater for methane production

Herein, synthetic iron-based biochar was used in anaerobic digestion of synthetic salty organic wastewater for methane production. The iron-based biochar synthesized at different pyrolysis temperatures improved methane production. An optimal methane production of 551 ± 4.0 mL/L was achieved by adding iron-based biochar prepared at 700℃. The rate of hydrolysis-acidification and methanogenesis was promoted by iron-based biochar as the NaCl concentration was less than 20 g/L. However, the catalytic effect of iron-based biochar on methane production of saline wastewater failed during the NaCl concentration of 40 g/L due to the complete suppression of methanogenesis. Analyzing the methanogenic activity of iron-based biochar modified anerobic systems and characterizing the physical-chemical properties of iron-based biochar demonstrated that the iron oxides and/or zero-valent iron generated on the biochar surface increased methane production. This study highlights the potential benefits of iron-rich sludge-based biochar on enhanced anaerobic digestion and treatment of salty organic wastewater.