Circular economy based landfill leachate treatment with sulphur-doped microporous biochar

Mechanism and application of sulfhydryl-modified chitosan derivative for decontamination of Pb(II) and Cd(II) in water bodies

The accumulation of lead and cadmium in water bodies is a serious threat to environmental safety and human health, and they must be removed from wastewater. Based on this this study, a novel sulfhydryl-modified chitosan derivative (SHCS) was prepared by grafting method using chitosan as a substrate for the removal of Pb(II) and Cd(II) from polluted water bodies. The results showed that the SHCS derivative was a mesoporous biosorbent with a specific surface area of 0.0505 cm3/g. The adsorption kinetics of the adsorbent on the pollutants conformed to the pseudo-first-order and pseudo-second-order models (R2 > 0.99). The adsorption isotherms all followed the Langmuir model (Pb(II): R2 = 0.9388, Cd(II): R2 = 0.9592). The maximum adsorption capacities of SHCS were 209.27 mg/g and 64.19 mg/g for Pb(II) and Cd(II), respectively. The free energy of adsorption ΔGθ < 0 indicates that the adsorption process is a spontaneous reaction, in which the adsorption of lead is an adsorptive process (ΔHθ > 0) and the adsorption of cadmium is an exothermic process (ΔHθ < 0). The addition of NaNO3 and cations (K+, Ca2+, and Mg2+) did not affect the adsorption process of Pb(II) and Cd(II). The surface complexation and electrostatic attraction mechanisms controlled the decontamination of Pb(II) and Cd(II) by SHCS in water. Most importantly, the SHCS derivative was effective in removing low concentrations of Pb(II) and Cd(II) from three real wastewater samples as well as a simulated electroplating wastewater.

Sulfur-modified tea-waste biochar improves rice growth in arsenic contaminated soil and reduces arsenic accumulation

Arsenic (As) is a non-essential carcinogenic metalloid and an issue of concern for rice crops. This study investigated the effects of sulfur-loaded tea waste biochar (TWB) due to modification with sodium sulfide (SSTWB) or thiourea (TUTWB) on As stress and accumulation in rice plants. The results showed that sulfur-modified TWB improved plant morphology compared to plants grown in As-contaminated soil alone. Biochar amendments elevated the activity of antioxidant enzymes in rice plants harvested at 15 and 30 days after transplant (DAT). Additionally, SSTWB and TUTWB significantly reduced As content in shoots by 26% and 19% at 15 DAT, respectively, as compared to TWB. This trend continued at 30 DAT with SSTWB achieving the maximum decrease of 30%. Similar reductions were observed in plant roots. The study suggests that sulfur-modified biochar amendments offer a promising strategy to mitigate the negative effects of As on, and reduce its accumulation in, rice.

Exploring the Potential of Biochar Derived from Chinese Herbal Medicine Residue for Efficient Removal of Norfloxacin

One-step carbonization was explored to prepare biochar using the residue of a traditional Chinese herbal medicine, Atropa belladonna L. (ABL), as the raw material. The resulting biochar, known as ABLB4, was evaluated for its potential as a sustainable material for norfloxacin (NOR) adsorption in water. Subsequently, a comprehensive analysis of adsorption isotherms, kinetics, and thermodynamics was conducted through batch adsorption experiments. The maximum calculated NOR adsorption capacity was 252.0 mg/g at 298 K, and the spontaneous and exothermic adsorption of NOR on ABLB4 could be better suited to a pseudo-first-order kinetic model and Langmuir model. The adsorption process observed is influenced by pore diffusion, π-π interaction, electrostatic interaction, and hydrogen bonding between ABLB4 and NOR molecules. Moreover, the utilization of response surface modeling (RSM) facilitated the optimization of the removal efficiency of NOR, yielding a maximum removal rate of 97.4% at a temperature of 304.8 K, an initial concentration of 67.1 mg/L, and a pH of 7.4. Furthermore, the biochar demonstrated favorable economic advantages, with a payback of 852.5 USD/t. More importantly, even after undergoing five cycles, ABLB4 exhibited a consistently high NOR removal rate, indicating its significant potential for application in NOR adsorption.

One-step synthesis of ferrous disulfide and iron nitride modified hydrochar for enhanced adsorption and reduction of hexavalent chromium in Bacillus LD513 by promoting electron transfer and microbial metabolism

Microbial immobilization technology is effective in improving bioremediation efficiency and heavy metal pollution. Herein, Bacillus LD513 with hexavalent chromium (Cr(VI)) tolerance was isolated and immobilized on a novel ferrous disulfide (FeS2)/iron nitride (FeN) modified hydrochar (Fe3-SNHC) prepared from waste straws. The prepared Fe3-SNHC-based LD513 (FeLD) significantly improves Cr(VI) adsorption and reduction by 31.4 % and 15.7 %, respectively, compared to LD513 alone. Furthermore, the FeLD composite system demonstrates efficient Cr(VI) removal efficiency and good environmental adaptability under different culture conditions. Microbial metabolism and electrochemical analysis indicate that Fe3-SNHC is an ideal carrier for protecting LD513 activity, promoting extracellular polymer secretion, and reducing oxidative stress. Additionally, the carrier serves as an electron shuttle that accelerates electron transfer and promotes Cr(VI) reduction. Overall, FeLD is an environmentally friendly biocomposite that shows good promise for reducing Cr(VI) contamination in wastewater treatment.

Nitrogen Removal from Landfill Leachate Using Biochar Derived from Wheat Straw

Landfill leachate (LLCH) disposal poses challenges due to high pollutant concentrations. This study investigates the use of biochar (BC) derived from wheat straw for nitrogen content reduction. Laboratory experiments evaluated BC's adsorption capacity (qm) for nitrogen removal from ammonium chloride solution (NH4Cl) and LLCH, along with testing isotherm models. The results demonstrated that BC was more efficient (95.08%) than commercial activated carbon AC (93.11%), the blank, in adsorbing nitrogen from NH4Cl. This superior performance of BC may be attributed to its higher carbon content (57.74%) observed through elemental analysis. Lower results for BC/LLCH may be due to LLCH's complex chemical matrix. The Langmuir isotherm model best described BC/NH4Cl adsorption (qm = 0.5738 mg/g). The AC/NH4Cl data also fitted into the Langmuir (R2 ˃ 0.9) with a qm of 0.9469 mg/g, and 26.667 mg/g (R2 ˂ 0.9) was obtained for BC/LLCH; the BC/LLCH also gave higher qm (R2 ˃ 0.9) using the Jovanovich model (which also follows Langmuir's assumptions). The mean energy of the adsorption values estimated for the AC/NH4Cl, BC/NH4Cl, and BC/LLCH processes were 353.55, 353.55, and 223.61 kJ/mol, respectively, suggesting that they are all chemisorption processes and ion exchange influenced their adsorption processes. The Freundlich constant (1/n) value suggests average adsorption for BC/LLCH. The BC/LLCH data followed the Harkins-Jura model (R2: 0.9992), suggesting multilayered adsorption (or mesopore filling). In conclusion, biochar derived from wheat straw shows promising potential for landfill leachate remediation, offering efficient nitrogen removal capabilities and demonstrating compatibility with various adsorption models. This research also lays the groundwork for further exploration of other biochar-based materials in addressing environmental challenges associated with landfill leachate contamination.

Pb(ΙΙ), Cd(ΙΙ), and Mn(ΙΙ) adsorption onto pruning-derived biochar: physicochemical characterization, modeling and application in real landfill leachate

The aim of this study was to systemically evaluate how different pyrolysis temperatures (400, 550, and 700 °C) and particle sizes (1-2 mm and 63-75 µm) were influenced biochar evolution, made from urban pruning waste, during pyrolysis process and to establish their relationships with biochar potential for removal of lead (Pb), cadmium (Cd), and manganese (Mn) from real municipal solid waste landfill leachate. The effects of pH (2-7), contact time (30-300 min) and adsorbent dosage (0.1-5 g L-1) on heavy metals removal were also examined. The results showed that physicochemical properties of biochar were greatly influenced by pyrolysis temperature. Particle size, however, showed little influence on biochar characteristics (p > 0.05). The yield, volatile matter, hydrogen and oxygen contents, and surface functional groups decreased consistently with increasing pyrolysis temperature. An increase in the pH, electrical conductivity, ash, fixed carbon, and specific surface area values was also found. In biochar samples formed at high temperatures (i.e., 550 and 700 °C), Fourier transform infrared spectroscopy-FTIR studies confirmed the increase in aromaticity. Field emission scanning electron microscopy-FESEM images showed differences in the microporous structure and lower size pores at higher temperatures. Biochar pyrolyzed at 700 °C with a particle size of 63-75 µm (i.e., Lv700-63) showed the highest removal efficiency performance. Pb and Cd ions were completely removed (100%) by 0.2 g L-1 Lv700-63 at 7.0 pH and contact times of 120 and 90 min, respectively. The maximum percentage removal of Mn was 86.20% at optimum conditions of 0.2 g L-1 Lv700-63 dosage, 7.0 pH, and 180 min contact time. The findings suggests that the surface complexation, π-electron coordination, and cation exchange were the dominant mechanisms for the Pb, Cd, and Mn removal onto Lv700-63.

Recent trends and economic significance of modified/functionalized biochars for remediation of environmental pollutants

The pollution of soil and aquatic systems by inorganic and organic chemicals has become a global concern. Economical, eco-friendly, and sustainable solutions are direly required to alleviate the deleterious effects of these chemicals to ensure human well-being and environmental sustainability. In recent decades, biochar has emerged as an efficient material encompassing huge potential to decontaminate a wide range of pollutants from soil and aquatic systems. However, the application of raw biochars for pollutant remediation is confronting a major challenge of not getting the desired decontamination results due to its specific properties. Thus, multiple functionalizing/modification techniques have been introduced to alter the physicochemical and molecular attributes of biochars to increase their efficacy in environmental remediation. This review provides a comprehensive overview of the latest advancements in developing multiple functionalized/modified biochars via biological and other physiochemical techniques. Related mechanisms and further applications of multiple modified biochar in soil and water systems remediation have been discussed and summarized. Furthermore, existing research gaps and challenges are discussed, as well as further study needs are suggested. This work epitomizes the scientific prospects for a complete understanding of employing modified biochar as an efficient candidate for the decontamination of polluted soil and water systems for regenerative development.

Waste biomass derived highly-porous carbon material for toxic metal removal: Optimisation, mechanisms and environmental implications

Toxic elements, lead, and copper are often found in wastewater discharged from industries such as mining. The discharge of untreated effluent poses severe environmental challenges and sorption methods using agricultural waste materials are proposed as an efficient and cost-effective solution. For this research, activated sunflower material (ASM) was prepared from abundantly available agricultural sunflower waste residues and utilised to remove Pb2+ and Cu2+ ions from an aqueous medium. To begin, we examine variables that may have an impact on the adsorption process, such as pH, contact time, adsorbent dose, and initial concentration using Box-Behnken Design (BBD) to find optimal conditions. Maximum removal efficiency was found at a pH of 5, contact time of 180 min, and initial concentration of 50 mg/L for Pb2+ and 150 mg/L for Cu2+. Additionally, adsorbent dose differed by element, for Cu2+ it was 200 mg, whilst for Pb2+ it was 124 mg. Features of activated carbon such as morphology, elemental composition, textural properties, and surface functionalities were characterised using SEM-EDS, BET, FTIR, and XPS. The adsorption equilibrium data were analysed by Langmuir, Freundlich, and Dubinin-Radushkevich isotherm models. It was found that the obtained results for Pb2+ adsorption were better described with the Freundlich isotherm model. Maximum adsorption capacities for Pb2+ and Cu2+ were 91.8 mg/g and 20.5 mg/g, respectively. Furthermore, kinetic studies confirmed that the adsorption process followed a pseudo-first-order kinetic model for Pb2+, but for Cu2+ all applied kinetic models fitted experimental data with the same values of the correlation coefficient (R2 = 0.99). After comprehensive analysis using the methods mentioned above, ASM was tested for the removal of Cu2+ from mining wastewater sample, and the obtained removal efficiency was 98.6% ± 2.0%. The results of desorption experiments conducted, confirm that ASM has good potential to be reused for the purpose of removing Cu2+ from wastewater.

Removal of Pb(II) and phosphorus in water by γ-Al2O3/biochar

In this work, we synthesized activated alumina biochar composites (γ-Al₂O₃/BC) by sol-gel method, which improved the problem that the surface charge of γ-Al₂O₃ was not conducive to the removal of heavy metal cation in a neutral solution, and then explored the feasibility of removing Pb(II) by γ-Al₂O₃/BC as well as reusing Pb-laden waste sludge to remove phosphorus (P) and its micro-adsorption mechanisms. The results show that the maximum adsorption capacity of γ-Al₂O₃/BC for Pb(II) is 182.48 mg/g, and the removing capacity of recycled Pb-laden slag for P also reaches 87.13 mg/g. It was found that the presence of Pb in the slag makes P removal more effective. In addition, in the process of P removal, the Pb in the slag will not be released, which will not cause secondary pollution to the water. The micro-adsorption mechanism of Pb(II) and P on the composites was investigated by XPS, XRD, and FTIR. It demonstrates that special functional groups such as hydroxy-aluminum, hydroxyl, and carboxyl groups can remove Pb(II) through strong surface complexation and electrostatic attraction. Furthermore, the removal mechanism of P from Pb-laden sludge includes chemisorption and complexation, and the precipitation of P and Pb on the adsorbent surface is the main reason for the removal of P. Therefore, it is feasible to further effectively remove P by using the waste biochar containing Pb. The idea of this paper provides a potential method for the reuse of waste adsorbent.

Synergistic reduction of Cr(VI) by graphite N and thiophene S of N, S-co-doped hydrochar derived from waste straw

An efficient, simple, and inexpensive N, S-co-doped hydrochar (SNHC) was synthesized from waste straw by a one-pot hydrothermal process without calcination for the removal of Cr(VI). SNHC demonstrated excellent adsorption performance for Cr(VI) and high stability, achieving a high capacity of 171.33 mg/g (293 K, pH 2) and a capacity retention of 82.73 % after five cycles. The adsorption behavior was determined as a multilayer adsorption process based on chemisorption according to the simulation the results of Freundlich adsorption isotherms and pseudo-second-order models. The characterization of SNHC revealed that graphite N and thiophene S formed by the material were the effective active sites, functioning as electron donors to contribute a significant amount of electrons to reduce Cr(VI) to Cr(III). Therefore, next to electrostatic adsorption and complexation, the synergistic reduction of Cr(VI) by graphite N and thiophene S was the main mechanism for Cr(VI) removal. Additionally, density functional theory calculations indicated a low adsorption energy of thiophene S, which increased the attractive interaction between SNHC and Cr(VI) and played the most important role in reducing Cr(VI). The mechanism of the effect of graphite N and thiophene S on Cr(VI) removal not only offered a comprehensive perspective on the role of N, S co-doped mediation in hydrochar but also provided the basic theory for its practical application.

Recyclable nitrogen-doped biochar via low-temperature pyrolysis for enhanced lead(II) removal

Facile and low-cost preparation are essential in the conversation of agricultural waste into biochar. In this work, nitrogen-doped biochar (NBC-350-0.1) was prepared by thermal decomposition of urea (urea/biochar = 0.1:1 mass ratio) at a low temperature of 350 °C. NBC-350-0.1 showed good performance for Pb(II) removal with the maximum adsorption capacity of 130.87 mg g^-1 at 25 °C, which was five times that of pristine biochar (BC). Adsorption kinetics, isotherms and thermodynamics studies indicated that the adsorption of Pb(II) by NBC-350-0.1 or BC was the homogeneous monolayer adsorption with chemical action as the rate-limiting step, and was accompanied by spontaneous endothermic. Further analysis showed that the removal of Pb(II) on NBC-350-0.1 and BC depended on the complexation with unsaturated carbon bonds and ion exchange with Ca(II). Moreover, graphitic- and pyridinic-N in NBC-350-0.1 exerted a key part in the adsorption of Pb(II). NBC-350-0.1 regenerated by NaOH exhibited excellent recycling performance keeping the original removal efficiency at 84% after five cycles. In addition, this N doping method is suitable for improving the performance of coffee grounds, sawdust, and bagasse biochar. These results would provide an idea for obtaining recyclable N-doped biochar to treat the Pb(II) polluted wastewater.

Emerging materials and technologies for landfill leachate treatment: A critical review

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Co-composted Biochar Enhances Growth, Physiological, and Phytostabilization Efficiency of Brassica napus and Reduces Associated Health Risks Under Chromium Stress

Among heavy metals, chromium (Cr) contamination is increasing gradually due to the use of untreated industrial effluents for irrigation purposes, thereby posing a severe threat to crop production. This study aimed to evaluate the potential of compost, biochar (BC), and co-composted BC on the growth, physiological, biochemical attributes, and health risks associated with the consumption of Brassica grown on Cr-contaminated soil. Results revealed that Cr stress (Cr-25) significantly reduced the growth and physiological attributes and increased antioxidant enzyme activities in Brassica, but the applied amendments considerably retrieved the negative effects of Cr toxicity through improving the growth and physiology of plants. The maximum increase in plant height (75.3%), root length (151.0%), shoot dry weight (139.4%), root dry weight (158.5%), and photosynthetic rate (151.0%) was noted with the application of co-composted BC under Cr stress (Cr-25) in comparison to the control. The application of co-composted BC significantly reduced antioxidant enzyme activities, such as APX (42.5%), GP (45.1%), CAT (45.4%), GST (47.8%), GR (47.1%), and RG (48.2%), as compared to the control under Cr stress. The same treatment reduced the accumulation of Cr in grain, shoot, and roots of Brassica by 4.12, 2.27, and 2.17 times and enhanced the accumulation in soil by 1.52 times as compared to the control. Moreover, the application of co-composted BC significantly enhanced phytostabilization efficiency and reduced associated health risks with the consumption of Brassica. It is concluded that the application of co-composted BC in Cr-contaminated soil can significantly enhance the growth, physiological, and biochemical attributes of Brassica by reducing its uptake in plants and enhanced phytostabilization efficiency. The tested product may also help in restoring the soils contaminated with Cr.

Biochar application in organics and ultra-violet quenching substances removal from sludge dewatering leachate for algae production

Algae production in nutrient rich sludge dewatering leachate after biogas production is a promising option for wastewater treatment plants. However, the ultra-violet (UV) absorbing characteristic of UV-quenching substances (UVQS) existing in these waters can notably reduce the light transmission within the liquid body. The present work demonstrates a comparative adsorptive removal of UVQS, and other organic substances (expressed as COD and TOC) onto the "acid catalyst" functionalised adsorbent (PPhA) and commercial activated carbon (CAC) from leachate originating from leftover sludge dewatering after biogas production. Laboratory scale column studies were performed to investigate the adsorption performance of selected parameters. The PPhA increased the UV transmittance of leachate more than 4 times and outperformed CAC. Bed Depth Service Time and Yan models were used on the experimental data in order to estimate the maximum adsorption capacity and evaluate the characteristics of the fixed-bed. The PPhA equilibrium uptake of COD and TOC amounted to 5.7 mg/g and 0.9 mg/g, respectively. The postulated removal mechanism in environmentally relevant conditions (e.g., pH neutral) suggested a complex interaction between the biochar and organic macromolecules. Diluted phosphoric acid solution (0.01 mol/L) was successfully used for the column regeneration. Beside the UVQS, PPhA showed affinity towards toxic heavy metals (e.g., Pb, Ni, Co) pointing out the rich surface chemistry of the PPhA. Based on the obtained results and successfully implemented scale-up methodology, the low-cost PPhA adsorbent might effectively compete with the CAC as a highly efficient platform in wastewaters leachate processing.

Circularity of Brazilian silk: Promoting a circular bioeconomy in the production of silk cocoons

The bioeconomy is considered one of the three main sectors with the greatest opportunities for the development of the circular economy in Brazil, who is one of the largest silk producers in the world; and sericulture is an agribusiness that contributes greatly to the bioeconomy in Brazil. Therefore, this research aimed to identify opportunities for creating value by internalizing flows in the production of silk cocoons by promoting a circular bioeconomy. To that end, a tool was used to assess the circularity of the referred system. The current circularity of the production of silk cocoons, at the farm level, is 74.19 % for material, and 0 % for energy. A range of measures are proposed, based on (i) engaging with reverse logistics practices, (ii) establishing a local agroindustrial cooperative, and (iii) building community biodigesters, which aid a potential circularity of 85.51 % (material), and 100 % (energy) at the farm level, and 98.42 % (material) and 100 % (energy), at the cooperative level. On top of increasing circular value, the proposed measures might bring environmental benefits, such as lessening environmental impacts of logistics (by valuing local resources) and replacing non-renewable energy, and social impacts, through increased quality of life for sericulturists. Economic implications need further investigation and are suggested to be addressed in future research endeavors, along with policy implications for the development of a circular bioeconomy. Furthermore, an increased circularity can also contribute to a few of the sustainable development goals (SDGs) proposed by the United Nations, such as SDGs 2, 7, 9, 11, 12 and 13.