Synthesis of amino-functionalized magnetic aerobic granular sludge-biochar for Pb(II) removal: Adsorption performance and mechanism studies

Green modification of biochar with poly(aspartic acid) enhances the remediation of Cd and Pb in water and soil

Biochar is a promising adsorbent for the remediation of heavy metals in water and soil. However, pristine biochar has a limited adsorption capacity for heavy metals, which restricts its application in the field of heavy metal immobilization. In the present study, the acidic amino acid-modified biochar was prepared, and its adsorption properties for cadmium (Cd) and lead (Pb) in aqueous solution were investigated. The results showed that poly(aspartic acid)-modified biochar (PASP-BC) was more effective in removing Cd(II) from water compared to biochar modified with poly(glutamic acid) (PGA-BC), aspartic acid (ASP-BC), and glutamic acid (GA-BC). The calculated maximum adsorption capacities, derived from Langmuir fitting parameters, for Cd(II) and Pb(II) by PASP-BC were 44.2 mg/g and 126.1 mg/g, respectively, which were 3.78 and 2.70 times higher than that for pristine BC. Based on the results from Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses, ion exchange, complexation, and electrostatic adsorption were identified as the mechanisms for Cd(II) and Pb(II) adsorption by PASP-BC. The results of the Toxicity Characteristic Leaching Procedure (TCLP) showed that PASP-BC effectively reduced the leachability of Cd and Pb by 91.2% and 84.7%, respectively, at a dosage of 3%. The pot experiment demonstrated that PASP-BC significantly reduced the bioavailability of heavy metals in Triticum aestivum L The maximum reduction in Cd and Pb content in roots was 76.3% and 72.6% when 3% PASP-BC was applied. Importantly, the application of PASP-BC decreased the translocation factor of heavy metals in wheat. Therefore, the green modification of biochar with poly(aspartic acid) has great potential in the heavy metals removal from wastewater and remediation in contaminated soil.

Repurposing spent biomass of vetiver grass used for stormwater treatment to generate biochar and ethanol

Stormwater pollution is a key factor contributing to water quality degradation, posing substantial environmental and human health risks. Although stormwater retention ponds, also referred to as wet ponds, are commonly implemented to alleviate stormwater challenges by reducing peak flow and removing suspended solids, their effectiveness in removing heavy metals and nutrients is limited. This study evaluated the performance of floating treatment platforms (FTPs) featuring vetiver grass (Chrysopogon zizanioides), a non-invasive, nutrient- and metal-accumulating perennial grass, in removing heavy metals (Cu, Pb, and Zn) and nutrients (P and N) in stormwater retention ponds. Furthermore, the potential for utilizing the spent vetiver biomass for generating biochar and bioethanol was investigated. The study was conducted in a greenhouse setup under simulated wet and dry weather conditions using pond water collected from a retention pond in Stafford Township, New Jersey, USA. Two FTPs with vetiver (vegetated FTPs) were compared with two FTPs without vetiver (non-vegetated FTPs), which served as controls. Results showed that the removal of heavy metals and nutrients by the FTPs with vetiver was significantly higher (p < 0.05) than the FTPs without vetiver. Notably, vetiver showed resilience to stormwater pollutants and hydroponic conditions, displaying no visible stress symptoms. The biochar and bioethanol generated from the spent vetiver exhibited desirable yield and quality, without raising concerns regarding pollutant leaching, indicated by very low TCLP and SPLP concentrations. This study provides compelling evidence that the implementation of vetiver-based FTPs offers a cost-effective and environment-friendly solution for mitigating stormwater pollution in retention ponds. Furthermore, the utilization of vetiver biomass for biofuel and biochar production supports clean production and fostering circular economy efforts.

Screening and performance optimization of fungi for heavy metal adsorption in electrolytes

The resource recovery and reuse of precious metal-laden wastewater is widely recognized as crucial for sustainable development. Superalloy electrolytes, produced through the electrolysis of superalloy scrap, contain significant quantities of precious metal ions, thereby possessing substantial potential for recovery value. This study first explores the feasibility of utilizing fungi to treat Superalloy electrolytes. Five fungi resistant to high concentrations of heavy metals in electrolytes (mainly containing Co, Cr, Mo, Re, and Ni) were screened from the soil of a mining area to evaluate their adsorption characteristics. All five fungi were identified by ITS sequencing, and among them, Paecilomyces lilacinus showed the best adsorption performance for the five heavy metals; therefore, we conducted further research on its adsorption characteristics. The best adsorption effect of Co, Cr, Mo, Re, and Ni was 37.09, 64.41, 47.87, 41.59, and 25.38%, respectively, under the conditions of pH 5, time 1 h, dosage 26.67 g/L, temperature 25-30°C, and an initial metal concentration that was diluted fivefold in the electrolyte. The biosorption of Co, Mo, Re, and Ni was better matched by the Langmuir model than by the Freundlich model, while Cr displayed the opposite pattern, showing that the adsorption process of P. lilacinus for the five heavy metals is not a single adsorption mechanism, but may involve a multi-step adsorption process. The kinetics study showed that the quasi-second-order model fitted better than the quasi-first-order model, indicating that chemical adsorption was the main adsorption process of the five heavy metals in P. lilacinus. Fourier transform infrared spectroscopy revealed that the relevant active groups, i.e., hydroxyl (-OH), amino (-NH2), amide (- CONH2), carbonyl (-C = O), carboxyl (-COOH), and phosphate (PO43-), participated in the adsorption process. This study emphasized the potential application of P. lilacinus in the treatment of industrial wastewater with extremely complex background values.

Fabrication of two novel amino-functionalized and starch-coated CuFe2O4-modified magnetic biochar composites and their application in removing Pb2+ and Cd2+ from wastewater

Novel magnetic biochar composites (SFeCu@SBCO and FeCu@SBCO-NH2) were fabricated by modifying oxidized sawdust biochar (SBCO) with Fe/Cu loading, starch-coating/amination, characterized (FTIR, XRD, BET, SEM-EDS and XPS) and applied in capturing Pb2+ and Cd2+ from wastewater. Adsorption experiments revealed that SFeCu@SBCO and FeCu@SBCO-NH2 exhibited extraordinary adsorption performance toward Pb2+/Cd2+ with the maximum adsorption capacity reaching 184.26/173.35 mg g-1 and 201.43/190.81 mg g-1, respectively, which were >5 times higher than those of SBC. The great increase in adsorption capacity of the two adsorbents was ascribed to the introduction of CuFe2O4 and starch/amino groups. Pb2+ and Cd2+ adsorption was an endothermic reaction controlled by monolayer chemisorption. Complexation and electrostatic attraction were the two predominant mechanisms. Besides, ion exchange together with physical adsorption also occurred during the adsorption. Additionally, the both adsorbents displayed favorable stability and reusability as well as desirable anti-interfering ability to other metal cations. Taken together, the both adsorbents could be utilized as reusable magnetic adsorbents with promising prospect in the effective remediation of Pb2+/Cd2+ contaminated water. The study not only contributed to the better understanding of biochar modification strategy and the application of modified biochar in heavy metals pollutants removal, but also realized resource utilization of biomass waste.

Stability of aerobic granular sludge for simultaneous nitrogen and Pb(II) removal from inorganic wastewater

ABSTRACTIn this paper, we proposed a strategy for the establishment of an aerobic granular sludge (AGS) system for simultaneous nitrogen and Pb(II) removal from inorganic wastewater. AGS was stored in lead nitrate solution to select functional bacteria resistant to lead poison, and then an AGS system for ammonia nitrogen (180-270 mg/L) and Pb(II) (15-30 mg/L) removal was established based on carbon dosing and a two-stage oxic/anoxic operational mode. After storage for 40 days, the stability of AGS decreased because specific oxygen uptake rate, nitrification rate and abundance of Nitrosomonas decreased to different degrees compared with those before storage. During the first 70 days of the recovery process, AGS in R1 (the blank reactor) and R2 (the control reactor) both experienced a first breakage and then regranulation process. The main properties of AGS in reactors R1 and R2 tended to be stable after days 106 and 117, respectively, but the structure of steady-state AGS in R2 was more compact. The total inorganic nitrogen (TIN) in effluent from R1 and R2 basically remained below 25 mg/L after days 98 and 90, respectively. The Pb(II) concentration in effluent from R2 was always below 0.3 mg/L. On day 140, the relative abundance of Nitrosomonas in R2 (6.17%) was significantly lower than that in R1 (12.15%), whereas the relative abundance of denitrifying bacteria was significantly higher than that in R1 (62.44% and 46.79%). The system removed 1 kg of influent TIN only consuming approximately 1.85 kg of carbon source, demonstrating clear advantages in energy savings.

A critical review on sustainable hazardous waste management strategies: a step towards a circular economy

Globally, industrialisation and urbanisation have led to the generation of hazardous waste (HW). Sustainable hazardous waste management (HWM) is the need of the hour for a safe, clean, and eco-friendly environment and public health. The prominent waste management strategies should be aligned with circular economic models considering the economy, environment, and efficiency. This review critically discusses HW generation and sustainable management with the strategies of prevention, reduction, recycling, waste-to-energy, advanced treatment technology, and proper disposal. In this regard, the major HW policies, legislations, and international conventions related to HWM are summarised. The global generation and composition of hazardous industrial, household, and e-waste are analysed, along with their environmental and health impacts. The paper critically discusses recently adapted management strategies, waste-to-energy conversion techniques, treatment technologies, and their suitability, advantages, and limitations. A roadmap for future research focused on the components of the circular economy model is proposed, and the waste management challenges are discussed. This review stems to give a holistic and broader picture of global waste generation (from many sources), its effects on public health and the environment, and the need for a sustainable HWM approach towards the circular economy. The in-depth analysis presented in this work will help build cost-effective and eco-sustainable HWM projects.

Enhanced Chromium (VI) Adsorption onto Waste Pomegranate-Peel-Derived Biochar for Wastewater Treatment: Performance and Mechanism

Surface chemical modification allows for the rational construction of biochar with desirable structures and functionalities for environment purification. Fruit-peel-derived adsorbing material has been well studied in the adsorption of heavy-metal removal due to its abundance and non-toxicity, but its precise mechanism in removing chromium-containing pollutants remains unclear. Herein, we explored the potential application of engineered biochar prepared from fruit waste via chemical modification to remove chromium (Cr) from an aqueous solution. By synthesizing two types of agricultural residue-derived adsorbents, including pomegranate peel adsorbent (PG) and its modified product, pomegranate-peel-derived biochar (PG-B), via chemical and thermal decomposition methods, we elucidated the adsorption property of Cr(VI) on the studied materials and identified the cation retention mechanism of the adsorption process. Batch experiments and varied characterizations demonstrated that superior activity was exhibited in PG-B, which can contribute to the porous surfaces caused by pyrolysis and effective active sites resulting from alkalization. The highest Cr(VI) adsorption capacity is obtained at pH 4, a dosage of 6.25 g L^-1, and a contact time of 30 min. The maximum adsorption efficiency of 90.50% in a short period (30 min) was obtained on PG-B, while PG reached a removal performance of 78.01% at 60 min. The results from kinetic and isotherm models suggested that monolayer chemisorption dominated the adsorption process. The Langmuir maximum adsorption capacity is 16.23 mg g^-1. This study shortened the adsorption equilibrium time of pomegranate-based biosorbents and presents positive significance in designing and optimizing waste fruit-peel-derived adsorption materials for water purification.

Adsorption of Rhodamine B from an aqueous solution by acrylic-acid-modified walnut shells: characterization, kinetics, and thermodynamics

A batch experiment was used in studying the effect of acrylic-acid-modified walnut shell (MWNS) as a low-cost adsorbent for removing Rhodamine B (RB) cationic dye in aqueous solutions. The adsorbent dosage, initial dye concentration, contact time, temperature, pH, and supporting electrolyte concentration on the adsorption behaviour of the adsorbent were explored. The adsorbent was characterized using the point of zero charge (pH_PZC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), automatic specific surface analysis (BET), and X-ray photoelectron spectroscopy (XPS). Results showed that MWNS had abundant active groups and rough surface, which is conducive to the adsorption process. The kinetics and equilibrium data of MWNS-to-RB adsorption were in accordance pseudo-second-order kinetic and Freundlich isotherm models, respectively. Under optimal adsorption conditions, the maximum adsorption capacity of RB was 48.87 mg·g^-1. Thermodynamic results showed spontaneously and exothermically the adsorption process. Moreover, the addition of electrolyte had a negative effect on equilibrium adsorption capacity and adsorption rate.HIGHLIGHTS Acrylic-acid-modified walnut shells was used as an adsorbent for the removal of Rhodamine B (RB).The adsorption of RB by modified walnut shells was greatly affected by pH.Pseudo-second-order kinetic and Freundlich model fit the experimental data.The modified walnut shell can remove RB through electrostatic attraction, hydrogen bonding, and electron donor-acceptor interaction.

Pb(II) bioremediation using fresh algal-bacterial aerobic granular sludge and its underlying mechanisms highlighting the role of extracellular polymeric substances

Lead (Pb) discharged from rural industries poses a significant threat to the environment and human health. Algal-bacterial aerobic granular sludge (A-B AGS) is a promising alternative for sewage treatment with high efficiency and good settleability. In this study, Pb(II) biosorption using fresh A-B AGS was investigated for the first time. The important role of extracellular polymeric substances (EPS) was revealed with the involved mechanisms being clarified. The desorbents for Pb recovery from Pb-loaded A-B AGS were also screened. Results showed that A-B AGS has an excellent maximum Pb adsorption capacity of 72.4 mg·g^-1 at pH 6.0. EPS plays an important role in keeping microbial activity, Pb bonding, and providing metal ions (Ca, Na and Mg) for Pb ion exchanges. Electrostatic interaction, ion exchange, and bonding to functional groups may occur orderly in the Pb biosorption process and the formation of pyromorphite (Pb₅(PO₄)₃Cl) contributes to Pb biosorption. About 66 % of the adsorbed Pb was accumulated in the A-B AGS microbial cells. Na₂EDTA (0.05 M) can recover 60.3 % of the loaded Pb with the highest microbial activity of granules being remained. All the findings will provide the theoretical basis for the large-scale application of A-B AGS to bioremediate Pb(II)-containing wastewater.

Effect of dissolved humic acids and coated humic acids on tetracycline adsorption by K2CO3-activated magnetic biochar

Humic acids (HAs) widely exist in water environment, and has an important impact on the adsorption of pollutants. Herein, HAs (both dissolved and coated) was employed to assess the effect on the removal of the organic contaminant tetracycline (TC) by K₂CO₃ modified magnetic biochar (KMBC). Results showed that low concentration of dissolved HAs promoted TC removal, likely due to a bridging effect, while higher concentration of dissolved HAs inhibited TC adsorption because of the competition of adsorption sites on KMBC. By characterization analysis, coated HAs changed the surface and pore characteristics of KMBC, which suppressed the TC removal. In a sequential adsorption experiment involving dissolved HAs and TC, the addition of HAs at the end of the experiment led to the formation of HAs-TC ligands with free TC, which improved the adsorption capacity of TC. TC adsorption by KMBC in the presence of dissolved HAs and coated HAs showed a downward trend with increasing pH from 5.0 to 10.0. The TC adsorption process was favorable and endothermic, and could be better simulated by pseudo-second-order kinetics and Freundlich isotherm model. Hydrogen bonds and π-π interactions were hypothesized to be the underlying influencing mechanisms.

Adsorption performance of tetracycline by the biomass ash derived from the pyrolysis of FeCl3-activated municipal sludge without gas protection

The municipal sludge activated by FeCl3 solution was pyrolyzed at 500 °C without gas protection, and the pyrolysis products, named as biomass ash, could effectively adsorb tetracycline (TC) from aqueous solution. Different FeCl3 concentrations could directly affect the physicochemical properties of the biomass ash, so that the biomass ash as adsorbent showed different adsorption efficiency toward TC. The activation of FeCl3 increased the oxygen-containing functional groups and surface polarities of the biomass ash. When the concentration of FeCl3 solution was 0.5 mol/L, the biomass ash behaved the maximum specific surface area (37.74 m2/g) and the best adsorption efficiency. The pseudo-second-order kinetics model and the Freundlich multi-molecule model could fully explain the TC adsorption process by the biomass ash pyrolyzed from municipal sludge activated by FeCl3. Moreover, the adsorption mechanism was mainly attributed to the chemical adsorption.

Functionalized biochars: Synthesis, characterization, and applications for removing trace elements from water

Biochar (BC) has been recognized as an effective adsorbent to remove trace elements (TEs) from water. However, low surface functionality and small pore size can limit the adsorption ability of pristine biochar. These limitations can be addressed by using functionalized biochars which are developed by physical, chemical, or biological activation of biochar to improve their physico-chemical properties and adsorption efficiency. Despite the large amount of research concerning functionalized biochars in recent decades, to our knowledge, no comprehensive review of this topic has been published. This review focuses solely on the synthesis, characterization, and applications of functionalized/engineered biochars for removing TEs from water. Firstly, we evaluate the synthesis of functionalized biochars by physical, chemical, and biological strategies that yield the desired properties in the final product. The following section describes the characterization of functionalized biochars using various techniques (SEM, TEM, EDS, XRD, XANES/NEXAFS, XPS, FTIR, and Raman spectroscopy). Afterward, the role of functionalized biochars in the adsorption of different TEs from water/wastewater is critically evaluated with an emphasis on the factors affecting sorption efficiency, sorption mechanisms, fate of sorbed TEs from contaminated environments and associated challenges. Finally, we specifically scrutinized the future recommendations and research directions for the application of functionalized biochar. This review serves as a comprehensive resource for the use of functionalized biochar as an emerging environmental material capable of removing TEs from contaminated water/wastewater.

Optimization of target biochar for the adsorption of target heavy metal ion

The purpose of this work is to study the pyrolysis conditions of target biochar suitable for target heavy metal ion, to characterize the optimized target biochar, and to study the adsorption performance of biochar. With Cu²⁺ and Zn²⁺ as the target pollutants, the pyrolysis conditions involved in the preparation process as pyrolysis temperature, pyrolysis time, and heating rate were evaluated and optimized from Box–Behnken Design (BBD), response surface methodology (RSM) and desirability function, the optimized pyrolysis conditions of target biochar for Cu²⁺ (Cu-BC) and Zn²⁺ (Zn-BC) were obtained. The optimum pyrolysis parameters for Cu-BC and Zn-BC were pyrolysis time of 3.09 and 2.19 h, pyrolysis temperature of 425.27 and 421.97 °C, and heating rate of 19.65 and 15.88 °C/min. The pseudo-second-order kinetic and Langmuir isotherm model proved to be the best fit for the equilibrium data, with a maximum adsorption capacity (Q_max) fitted by Langmuir model were 210.56 mg/g for Cu²⁺ by Cu-BC and 223.32 mg/g for Zn²⁺ by Zn-BC, which were both higher than the Q_max of unoptimized biochar (BC) for Cu²⁺ (177.66 mg/g) and Zn²⁺ (146.14 mg/g). The physical properties, chemical structure, surface chemistry properties of Cu-BC and Zn-BC were characterized by Zeta potential meter, Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). This study puts forward a new perspective for optimizing target biochar production for special environmental application.

Hybrid Metal Oxide/Biochar Materials for Wastewater Treatment Technology: A Review

This paper discusses the properties of metal oxide/biochar systems for use in wastewater treatment. Titanium, zinc, and iron compounds are most often combined with biochar; therefore, combinations of their oxides with biochar are the focus of this review. The first part of this paper presents the most important information about biochar, including its advantages, disadvantages, and possible modification, emphasizing the incorporation of inorganic oxides into its structure. In the next four sections, systems of biochar combined with TiO₂, ZnO, Fe₃O₄, and other metal oxides are discussed in detail. In the next to last section probable degradation mechanisms are discussed. Literature studies revealed that the dispersion of a metal oxide in a carbonaceous matrix causes the creation or enhancement of surface properties and catalytic or, in some cases, magnetic activity. Addition of metallic species into biochars increases their weight, facilitating their separation by enabling the sedimentation process and thus facilitating the recovery of the materials from the water medium after the purification process. Therefore, materials based on the combination of inorganic oxide and biochar reveal a wide range of possibilities for environmental applications in aquatic media purification.

Synthesis and characterization of lanthanum-based metal organic framework decorated polyaniline for effective adsorption of lead ions from aqueous solutions

The novel La-MOF@x%PANI composite was synthesized via a two-step procedure with ultra-sonication, and the adsorption mechanism of Pb²⁺ ions from synthetic aqueous solutions was systematically studied. The Pb²⁺ adsorption on the La-MOF@x%PANI was evaluated by the Fourier transform infrared spectroscopy, powder X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray analysis, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy, and elemental mapping analyses. The effects of the adsorption-influencing parameters, including contact time, solution pH, and co-existing cations on the maximum adsorption capacity of Pb²⁺ onto the prepared composite material were investigated. Moreover, the adsorption of Pb²⁺ ions could be eliminated with rapid adsorption kinetics using the water-stable La-MOF@x%PANI composite. The as-synthesized La-MOF@50%PANI exhibited excellent adsorption performance toward Pb²⁺ ions with an extraordinary adsorption capacity of 185.19 mg/g at pH 6. The Pb²⁺ adsorption onto the La-MOF@x%PANI composite follows the pseudo-second-order kinetics and fits well with the Langmuir isotherm model, indicating the Pb²⁺ adsorption depended on the solution pH as the adsorption mechanism was mainly governed by the electrostatic attraction. Notably, La-MOF@x%PANI composite possesses outstanding regeneration ability and stability after up to four successive cycles. The satisfactory findings reflect that the La-MOF@50%PANI hybrid composite holds a great promise for remediating Pb²⁺ ions from aqueous environments.

Fabrication, application, and mechanism of metal and heteroatom co-doped biochar composites (MHBCs) for the removal of contaminants in water: A review

The potential risk of various contaminants in water has recently attracted public attention. Biochars and modified biochars have been widely developed for environmental remediation. Metal and heteroatom co-doped biochar composites (MHBCs) quickly caught the interest of researchers with more active sites and higher affinity for contaminants compared to single-doped biochar by metal or heteroatoms. This study provides a comprehensive review of MHBCs in wastewater decontamination. Firstly, the main fabrication methods of MHBCs were external doping and internal doping, with external doping being the most common. Secondly, the applications of MHBCs as adsorbents and catalysts in water treatment were introduced emphatically, which mainly included the removal of metals, antibiotics, dyes, pesticides, phenols, and other organic contaminants. Thirdly, the removal mechanisms of contaminants by MHBCs were deeply discussed in adsorption, oxidation and reduction, and degradation. Furthermore, the influencing factors for the removal of contaminants by MHBCs were also summarized, including the physicochemical properties of MHBCs, and environmental variables of pH and co-existing substance. Finally, futural challenges of MHBCs are proposed in the leaching toxicity of metal from MHBCs, the choice of heteroatoms on the fabrication for MHBCs, and the application in the composite system and soil remediation.

Waste-to-Resource Strategy to Fabricate Functionalized MOFs Composite Material Based on Durian Shell Biomass Carbon Fiber and Fe3O4 for Highly Efficient and Recyclable Dye Adsorption

Recently, metal–organic frameworks (MOFs), which are porous inorganic–organic hybrid materials consisting of metal ions (clusters or secondary building units) and organic ligands through coordination bonds, have attracted wide attention because of their high surface area, huge ordered porosity, uniform structural cavities, and excellent thermal/chemical stability. In this work, durian shell biomass carbon fiber and Fe₃O₄ functionalized metal–organic framework composite material (durian shell fiber-Fe₃O₄-MOF, DFM) was synthesized and employed for the adsorption removal of methylene blue (MB) from wastewater. The morphology, structure, and chemical elements of the DFM material were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscope (XPS) techniques. Adsorption conditions such as pH, adsorption time, and temperature were optimized. The adsorption isotherm and kinetics results show that the adsorption process of DFM material to MB is more in line with the Freundlich model and pseudo-second-order kinetic model. Using these models, the maximum adsorption capacity of 53.31 mg/g was obtained by calculation. In addition, DFM material could be easily reused through an external magnet and the removal rate of MB was still 80% after five adsorption cycles. The obtained results show that DFM composite material, as an economical, environmentally friendly, recyclable new adsorbent, can simply and effectively remove MB from wastewater.

Desorption characteristics of phosphate and ammonium from sludge-based biochar

It is effective to adsorb phosphate and ammonium from water by sludge-based biochar, while the desorption performance has not been studied systematically. Biochar in this study was prepared through the co-pyrolysis of sludge and walnut shells to remove NH4+ and PO43- from water. The desorption characteristics of NH4+ and PO43- from the post-adsorption sludge-based biochar were investigated. The effects of the adsorption condition (concentration of adsorption solution) and desorption conditions (pH value of desorption solution and desorption temperature and time) on desorption performance were examined. Several techniques were performed to characterise the properties of the post-adsorption sludge-based biochar. The adsorption amount of the pure sewage sludge biochar (SBC) for PO43- and the biochar derived from the co-pyrolysis of sewage sludge and walnut shell with the mixing ratio of 3:1 (MBC3-1) for NH4+ were 14.19/ 23.75 mg/g and 9.28/ 16.23 mg/g, respectively, when the concentrations of the adsorbates were 100 and 500 mg/L. The desorption experiments showed that the acidic condition (pH = 2) was beneficial for PO43- and NH4+ desorption. The highest desorption ratio reached 7.58% for PO43- and 2.18% for NH4+. The desorption of PO43- was endothermic, whereas that of NH4+ was exothermic. The desorption amounts of PO43- and NH4+ decreased and increased, respectively, with the increase in desorption time. This study of the desorption characteristics of PO43- and NH4+ in sludge-based biochar provides a theoretical basis for the subsequent utilisation of sludge-based biochar.

Improved Pb(II) removal in aqueous solution by sulfide@biochar and polysaccharose-FeS@ biochar composites: Efficiencies and mechanisms

Novel biochars, namely nano iron sulfide@ walnut shell biochar (FeS@WNS), Starch-FeS@WNS and Chitosan-FeS@WNS, were prepared by WNS loaded with nano FeS and starch (or chitosan). Nano FeS can be effectively improved lead ions (Pb(II)) removal and starch (or chitosan) improved the stability of FeS and the defect of easy agglomeration. The materials were characterized by SEM, EDS, FTIR and XRD, and the preparation was successful. The adsorption capacity of Pb(II) reached 63.5, 80.0, 84.7 mg g^-1 under 0.5 g L^-1 of FeS@WNS, Starch-FeS@WNS and Chitosan-FeS@WNS. The adsorption of Pb(II) on the materials was more consistent with the pseudo-second-order kinetic model (K₂ = 0.001-0.005 g (mg·min)^-1, R² = 0.980-0.999) and Langmuir model (R² = 0.974-1.00), indicating that the adsorption of Pb(II) was mainly monolayer adsorption dominated by chemical adsorption. △G < 0 (-3.7~-6.97) and △H > 0 (1.56-20.49) indicated that the reaction was a spontaneous endothermic process. The mechanisms of Pb(II) removal from aqueous solutions involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange and oxidoreduction. Additionally, stability and reusability of FeS@WNS, Starch-FeS@WNS and Chitosan-FeS@WNS was good. The novel sorbents of Starch-FeS@WNS and Chitosan-FeS@WNS can be used in Pb(II) wastewater treatment.

Degradation of Rhodococcus erythropolis SY095 modified with functional magnetic Fe3O4 nanoparticles

Alkali-surfactant-polymer flooding technology is widely employed to extract crude oil to enhance its production. The bacterial strain Rhodococcus erythropolis SY095 has shown high degradation activity of alkane of crude oil. In the past, many treatment strategies have been implemented to reduce oil concentration in wastewater. Previous studies mainly focused on the extracellular products of Erythrococcus rather than its degradation properties. In the current study, we designed an immobilization method to modify the surface of R. erythropolis SY095 with functional Fe₃O₄ nanoparticles (NPs) for biodegradation of crude oil and separation of the immobilized bacteria after degradation. We characterize the synthesized NPs through various methods, including scanning electron microscope energy-dispersive spectrometer, Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and a vibrating sample magnetometer. We found that the size of the synthesized NPs was approximately 100 nm. Our results showed that R. erythropolis SY095 was successfully coated with functional magnetic NPs (MNPs) that could be easily separated from the solution via the application of an external magnetic field. The coated cells had a high tolerance for heavy metals. Our findings demonstrated that the immobilization of MNPs to bacterial surfaces is a promising approach for the degradation of crude oil.

High capacity Pb(II) adsorption characteristics onto raw- and chemically activated waste activated sludge

The Pb(II) adsorption characteristics of chemically activated waste activated sewage sludge (WAS) were compared to raw WAS. Adsorption kinetics and equilibrium isotherm parameters were fit using classic adsorption models. HCl and H₂SO₄ activation terminated any significant sludge-based adsorption. Raw and ZnCl₂ activated WAS displayed Langmuir adsorption capacities of 307 mg/g and 274 mg/g, respectively. Surface characterization revealed that chemical activation with ZnCl₂ increased the BET surface area for raw WAS from 0.97 m²/g to 1.78 m²/g, but did not significantly change the surface structure. FTIR analyzes and XPS were used to further investigate the nature of lead binding. The relationships between equilibrium ion concentration and Pb(II) adsorption suggest cationic exchange with hydrogen, calcium, and zinc as a significant mechanism of Pb(II) removal alongside electrostatic attraction. The pH_PZC was determined as 2.58 and 2.30 for ZnCl₂ activated WAS and raw WAS respectively. HNO₃ and Ca(NO₃)₂ demonstrated sufficient elution properties for WAS recovery. For authentic industrial effluent both raw and ZnCl₂ activated WAS displayed Pb(II) removal behavior comparable to simulated Pb(II) solutions. In comparison with modified and unmodified sludges from literature, this study demonstrates the auspicious potential of raw WAS as an effective Pb(II) adsorbent independent of pyrolytic or chemical activation.

Recycle of Fenton sludge through one-step synthesis of aminated magnetic hydrochar for Pb2+ removal from wastewater

In order to achieve proper disposal of Fenton sludge, a new recycle method for preparing adsorbents based on one-step hydrothermal carbonization synthesis of aminated hydrochar from Fenton sludge (AHFS) was developed. It was found that AHFS prepared at 340 °C for 60 min showed Pb²⁺ adsorption capacity as high as 359.83 mg g^-1. Adsorption kinetics and thermodynamics results indicated that chemical interaction, intra-particle diffusion and monolayer homogeneous surface of AHFS dominated in adsorption process. The contribution proportion of different mechanisms, including cation-exchange (43.15%), acidic groups complexation (28.17%) and amino groups complexation (24.06%) to overall Pb²⁺ adsorption, demonstrated that complexation of surface functional groups played the dominated role in the adsorption process. Especially, the addition of amino was conducive to the increased adsorption capacity of hydrochar. In addition, according to the regeneration test, the magnetic AHFS exhibited a satisfactory reproducibility and recyclability. These findings illustrated that the synthesis of aminated magnetic hydrochar not only provided an innovative and efficient heavy metal adsorbent to remove Pb²⁺ from wastewater, but also explored a new method for the resource utilization of Fenton sludge.

Application of Ni0.5Zn0.5Fe2O4 magnetic nanoparticles for diclofenac adsorption: isotherm, kinetic and thermodynamic investigation

Ni_0.5Zn_0.5Fe₂O₄ magnetic nanoparticles were synthesized to obtain a new efficient adsorbent for diclofenac sodium (DF) removal. Fourier Transform Infrared (FTIR), Energy Dispersive Spectrometer (EDS), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) and vibrating sample magnetometer (VSM) were applied to characterize the prepared adsorbent. These analyses revealed that adsorbent was successfully prepared with average particle diameter of about 50 nm and a BET surface area of 168.09 m²/g. The saturation magnetization value of magnetic nanoparticles (MNPs) was found to be 24.90 emu/g, thus, adsorbent was efficiently separated from the solution by a facile and rapid magnetic separation process. The effect of adsorption time, amount of adsorbent, initial pH of the solution, initial diclofenac concentration and temperature on the removal of DF were evaluated. Also, the adsorption data were best fitted to the pseudo-first-order kinetic model and Langmuir isotherm model. The thermodynamics studies suggested spontaneous and exothermic adsorption. The maximum diclofenac adsorption amount of the synthesized nanoadsorbent was 52.91 mg/g, which is higher than many recently studied adsorbents.

Conversion of sewage sludge into biochar: A potential resource in water and wastewater treatment

Production of biochar from sewage sludge (SS) is consistent with the goal of sustainable resource recovery and promotes a wastewater-based circular economy. Thermochemical conversion of SS to biochar resolves two major issues simultaneously as it minimizes the cost of disposal and acts as a resource to eliminate the toxic contaminants from water and wastewater. The reusability and ready availability of the biochar, irrespective of the season, makes it an economically viable material for wastewater treatment. In this review, explicit insights into the production, modification and usage of SS derived biochar are provided including (i) the production yield, (ii) characteristic features such as physical, chemical, electrochemical and morphological aspects, and (iii) impact on contaminant removal through adsorption, catalytic and electrochemical processes. Particular attention is given to the use of SS derived biochar as an adsorbent for contaminants present in wastewaters, the potential use of biochar as a catalyst and support material in advanced oxidation processes and the use of biochars as an electrode material. The effect of pyrolysis conditions and co-pyrolysis with other materials on biochar properties is explored and insight is provided into the toxicity of biochar components present at different process conditions.

High efficiency removal of Pb(ii) in aqueous solution by a biochar-supported nanoscale ferrous sulfide composite

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution. The experimental results of SEM, EDS, XRD, and FT-IR spectroscopy clearly implied that the biochar was successfully modified with nanoscale ferrous sulfide composite. The maximum adsorption capacity of Pb(ii) ions by FeS@biochar reached 88.06 mg g⁻¹. Compared with other reported adsorbents, the removal rate of Pb(ii) ions by FeS@biochar was higher. The pseudo-second-order kinetic model and Langmuir isotherm model could better fit the experimental adsorption results. The removal rate of Pb(ii) ions by FeS@biochar was controlled by the chemical reaction and monolayer adsorption on the surface of FeS@biochar. The mechanisms of Pb(ii) removal from aqueous solutions by biochar involved electrostatic attraction, hydrogen bonding, physical adsorption, ion exchange, and chemical precipitation. Additionally, the chemical stability and reusability of FeS@biochar were good. It is also an environment-friendly material for low-cost wastewater treatment.

A biochar-supported nanoscale ferrous sulfide composite was prepared and applied for the treatment of Pb(ii) ions in aqueous solution.

Efficient removal of Pb(II) through recycled biochar-mineral composite from the coagulation sludge of swine wastewater

Zeolite-Mg/Fe chloride dual enhanced coagulation is a cost-effective method for advanced treatment of swine wastewater, but the sludge generated after the enhanced coagulation remains to be a problem. In this study, the precipitate from a swine wastewater coagulation unit was regenerated by pyrolysis treatment in an O₂-limited environment to develop a high efficient adsorbent (biochar-mineral composite, BMC) for the removal of Pb(II) from wastewater. SEM images indicate that complex Mg/Fe oxides and sludge biochar gathered around zeolite particles. Effects of different influencing factors such as Pb(II) initial concentration, pH, adsorption time and ion concentration on the adsorption performance were investigated. The results show that the Langmuir isotherm model can better express the adsorption of Pb(II) on BMC than Freundlich model and Temkin model. BMC pyrolyzed at 500 °C showed the maximum adsorption capacity of 450.58 mg/g under experimental condition of 25 °C, 100 mg/L Pb(II) initial concentration and the initial pH of 5.6. The adsorption mechanisms on BMC mainly include ion exchange, electrostatic interaction. Therefore, it is a cost-effective and environmental-friendly strategy to obtain biochar-mineral composite from recycled sludge, which can efficiently remove Pb(II) from wastewater.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

Waste-to-resources: Green preparation of magnetic biogas residues-based biochar for effective heavy metal removals

The agricultural wastes disposal and polluted water purification are always the key issues of environmental restoration. In this work, a magnetic biogas residue-based biochar (mBR-C) by direct pyrolysis and sonochemical method was prepared from biogas residue (BR). Response design methodology based on Box-Behnken design was used for the preparation parameters optimization. The characterization results identified that mBR-C had well-developed pore structure and surface area, which was beneficial to diffuse and capture heavy metal ions. Traces of toxic heavy metal in mBR-C was leached (˂0.04 mg/L) through TCLP method, indicating the environmental safety of the magnetic biochar. Meanwhile, the mBR-C exhibited excellent solid-liquid separation efficiency because of its strong magnetism. The series of adsorption experiments indicated that mBR-C could capture Cu²⁺ and Pb²⁺ rapidly, and the maximum adsorption capacity for Cu²⁺ and Pb²⁺ was 75.76 and 181.82 mg/g, respectively, which was higher than some other biochars previously reported. mBR-C was further applied in the synthetic wastewater treatment, which could effectively purify at least 600 mL (150 BV) to meet emission standards. After several column adsorption-desorption cycles, the adsorption capacity could still reach 85%, implying that mBR-C has good reusability and stability. Overall, the mBR-C can be used as an eco-friendly, desirable, economic and recyclable biosorbent in heavy metal polluted water treatment, providing a new idea for a combination of biogas residue recycle and wastewater treatment.

Coadsorption behaviors and mechanisms of Pb(ii) and methylene blue onto a biodegradable multi-functional adsorbent with temperature-tunable selectivity

An entirely bio-degradable adsorbent based on lignin was synthesized by a crosslinking method and the adsorption of methyl blue (MB) and Pb(ii) onto the adsorbent were comparatively investigated, with adsorption behavior and mechanism of the two pollutants on the adsorbent (SLS) being assessed in single and binary systems. According to the results, SLS was capable of effective adsorption using MB and Pb(ii). The adsorption behavior of MB and Pb(ii) followed Langmuir and pseudo-first order models and showed temperature-dependent preferences. At 298 K MB was more preferred while at 318 K Pb(ii) adsorption was more favorable, which means that the selectivity of SLS can be tuned by changing the temperature. From a mechanism aspect, the adsorption of MB and Pb(ii) were both achieved through more than one route. Pb(ii) mainly interacts with sulfonate and hydroxyl groups on SLS, while MB can be bound on both anionic and aromatic groups due to its aromatic nature. Recycling and reuse experiments showed that used SLS can be readily reactivated and stably reused. The findings will guide adsorbent applications in wastewater containing heavy metals and aromatic compounds.

In situ preparation of magnetic hydrochar by co-hydrothermal treatment of waste vinasse with red mud and its adsorption property for Pb(II) in aqueous solution

Herein, a new magnetic hydrochar was prepared through co-hydrothermal treatment of vinasse with red mud, two abundant industrial wastes, and its adsorption property was evaluated on Pb(II), selected model ion in aqueous solution. During co-hydrothermal process, Fe₂O₃ species in red mud was reduced to Fe₃O₄ form, hereby, in situ magnetization of hydrochar was achieved, which was confirmed by characterization studies. Produced hydrochar with porous structure (V_total = 0.071 cm³/g and BET surface area = 23 m²/g) had saturation magnetization (44.7 emu/g), providing easier separation from water by a magnet. Maximum Pb(II) adsorption was favored at pH ≥ 5.0 within 120 min of equilibrium time and Freundlich isotherm model was preferable. The contribution percentage of different mechanisms including cation-exchange (40.8 %), (electrostatic attraction + "cation-π" interaction) (31.2 %), precipitation (25.4 %) and complexation (2.6 %) to overall Pb(II) adsorption indicated that cation-exchange was the dominant mechanism. Finally, application to fortified real water demonstrated that in situ magnetic hydrochar produced by suggested approach was successful at adsorptive removal of Pb(II) from water with no matrix effects.

Synthesis of amino-functionalized biochar/spinel ferrite magnetic composites for low-cost and efficient elimination of Ni(II) from wastewater

Novel amino-modified rice bran biochar/MgFeAlO₄ (RB@MgFeAlO₄-NH₂) magnetic composites were synthesized via a simple one-step solvothermal approach and applied for removing toxic Ni(II) from wastewater. The elimination process and sorption performance of Ni(II) on RB@MgFeAlO₄-NH₂ were analyzed by combining batch experiments and spectral techniques. The sorption isotherms and kinetic data indicated that Ni(II) sorption on RB@MgFeAlO₄-NH₂ was monolayer and rapid. The experimental results confirmed that the obtained RB@MgFeAlO₄-NH₂ magnetic composite had high sorption capacity for Ni(II). The maximum sorption capacity of Ni(II) on RB@MgFeAlO₄-NH₂ was 201.62 mg g^-1. The researches based on the sorption mechanism showed that the ion exchange mechanism accounted for 76.51% of Ni(II) sorption. In addition, the amino, carboxyl and hydroxyl functional groups were also involved in the complexation with Ni(II). In view of its multiple advantages of environmental friendliness, low cost, easy magnetic separation and high sorption capacity, RB@MgFeAlO₄-NH₂ will be an excellent adsorbent for low-cost and efficient elimination of Ni(II) from aqueous solutions.

Fabrication of L-cysteine stabilized α-FeOOH nanocomposite on porous hydrophilic biochar as an effective adsorbent for Pb2+ removal

Lead (Pb) pollution has caused worldwide attention as it can cause hazards to humans and the environment. Chemical properties and structures of the adsorbent greatly influence the Pb²⁺ removal efficiency. L-cysteine (L-cy) stabilized porous hydrophilic biochar-supported α-FeOOH nanocomposites (L-cy/FeOOH@PHB) are prepared as an efficient adsorbent via a cheap and simple one-step hydrothermal method for removing Pb²⁺ from aqueous solution. Characterizations of the synthesized L-cy/FeOOH@PHB revealed that the iron particles distributed uniformly on the surface of porous hydrophilic biochar. The equilibrium adsorption capacity of the L-cy/FeOOH@PHB reaches up to 103.04 mg g^-1for Pb²⁺ removal, higher than other typical materials reported preiously. The adsorption kinetics and isotherms were fitted well with the pseudo-second-order model and the Freundlich model, respectively, suggesting chemical adsorption on the heterogeneous surface and pores of L-cy/FeOOH@PHB. The introduction of L-cysteine provides abundant surface N- and S-containing functional groups as active sites for Pb²⁺ adsorption and also plays an important role in altering the porous structure, distribution of α-FeOOH nanoparticles, affinity of iron species to biochar, and surface functional groups, which determined the performance of the resultant composites. Notably, regeneration experiments show that Pb²⁺ adsorption capacity still maintains at 77.3 mg g^-1 on L-cy/FeOOH@PHB after five successive utilizations, indicating the potential applicability for removing Pb²⁺ from aqueous solution.

Effect of deashing on activation process and lead adsorption capacities of sludge-based biochar

To explore the effect of inorganic minerals on activation process and lead adsorption of sludge-based biochar, sludge-based biochar was pre-deashed using hydrochloric acid or hydrofluoric acid followed by potassium acetate activation. The results indicate that hydrochloric or hydrofluoric acid deashing can improve the pore parameters of sludge-based biochars and promote subsequent activation effect of potassium acetate. The specific surface area of biochar activated by potassium acetate after hydrochloric acid and hydrofluoric acid pretreatment increased from 583.36 m²/g to 718.70 m²/g and 991.55 m²/g, respectively. The enhancement of pore structure is conducive to enhancing the physical adsorption of lead on sludge-based biochar, while the chemical adsorption is not significantly affected at the same time. Thereby, the biochar and activated biochar pretreated with hydrofluoric acid showed better lead adsorption capacities (16.70 and 49.47 mg/g) than untreated biochar (7.56 and 38.49 mg/g).

Removal of aqueous-phase lead ions by dithiocarbamate-modified hydrochar

Hydrochar produced from agricultural and forestry wastes and its application into the environment are very attractive. Herein, a high-efficiency dithiocarbamate-modified hydrochar (DTHC) was prepared successfully and then applied to eliminate Pb(II) from aqueous solutions. DTHC was characterized by various techniques. It was found that dithiocarbamate and amine groups were successfully grafted onto the surface of hydrochar. The surface area of DTHC was 7.94 m²·g^-1, which was four folds less than pristine hydrochar (31.60 m²·g^-1), but its adsorption capacity obviously increased. Adsorption experiments showed that the Pb(II) adsorption process onto DTHC well accorded with pseudo-2nd-order kinetics and Langmuir isotherms. The highest Pb(II) uptake by DTHC at 293 K determined from the Langmuir model was 151.51 mg·g^-1. Fourier transform infrared spectra and X-ray photoelectron spectroscopy verified that dithiocarbamate, carboxylate, amine and sulfonate groups all facilitated the Pb(II) adsorption. The adsorption mechanism was ascribed to the inner-sphere surface complexation of Pb(II) by these groups and to the ion exchange between Pb(II) and Na(I). Thus, DTHC is an effective adsorbent for Pb(II) removal from water.

Carbon-silica mesoporous composite in situ prepared from coal gasification fine slag by acid leaching method and its application in nitrate removing

Coal gasification fine slag (CGFS) was produced in the coal gasification process which was classified as an industrial solid waste. It was featured with naturally formed amorphous structures and an abundance of silicon, carbon and metal oxides. In this study, on the basis of the composition and structure characteristics of CGFS, a simple hydrochloric acid (HCl) leaching technology was applied to in situ prepare carbon-silica mesoporous composites (CSMCs) from CGFS by fully considering the value of the residual carbon. Special focus was put on the novel mechanism of pore formation in amorphous silica glass microspheres (SGM) during acid leaching. Experimental evidences showed that the metal oxides were uniformly distributed in SGM thus the dissolution of the metal oxides were starting from the surface of SGM, then gradually extending to the interior, and finally leading to form "tree branch" mesoporous channels. In addition, a response surface method was used to predict the optimal reaction conditions and the optimal sample (named as CGFS-O) was successfully prepared. CGFS-O possessed a prominent specific surface area (SSA) (337.51 m²/g) as well as an excellent pore volume (0.341 cm³/g). CGFS-O also exhibited a desirable capacity for NO₃^- removing and the adsorption process was studied detailed by changing different adsorption conditions. Adsorption results proved that CSMCs have the potential to purify wastewater in an economically and environmentally way. Therefore, combined with a proof-of-concept adsorption performance experiment, our study has not only provided a cost-effective strategy to industrially prepare CSMCs, reutilizing CGFS in an environmentally friendly way, but also contributed to the future applications of CSMCs with valuable insights into the pore formation mechanism in SGM during acid leaching process.

Adsorption Behavior and Relative Distribution of Cd2+ Adsorption Mechanisms by the Magnetic and Nonmagnetic Biochars Derived from Chicken Manure

The present study investigated the adsorption of Cd²⁺ by nonmagnetic and magnetic biochars (CMB and M-CMB) derived from chicken manure, respectively. The adsorption characteristics were investigated as a function of initial pH, contact time, initial Cd²⁺ concentration and magnetic separation. Adsorption process of both biochars were better described by Pseudo-second-order kinetic equation and Freundlich isotherm model, which were spontaneous and endothermic in nature. It was found that maximum capacities were 60.69 and 41.07 mg/g obtained at the initial Cd²⁺ concentration of 180 mg/L for CMB and M-CMB, and the turbidity of adsorption-treated solution was reduced from 244.3 to 11.3 NTU after magnetic separation of 0.5 min. These indicated that M-CMB had lower adsorption capacity of Cd²⁺ than CMB, though it was successfully separated from the treated solutions. Furthermore, both biochars before and after adsorption were analyzed by SEM-EDS, XRD and FTIR. Adsorption mechanisms mainly included precipitation, ion-exchange, complexation and Cπ-coordination, in which precipitation and ion-exchange dominated the adsorption process by CMB, while in M-CMB, precipitation was always predominant mechanism, followed by ion-exchange. The two other mechanisms of complexation and Cπ-coordination were trivial in both biochars, jointly contributing 7.21% for CMB and 5.05% for M-CMB to total adsorption. The findings deepen our understanding of the mechanisms governing the adsorption process, which are also important for future practical applications in the removal of heavy metals from wastewater by the biochars.

Understanding the role of extracellular polymeric substances in the rheological properties of aerobic granular sludge

The gel-properties of aerobic granular sludge could sustain the mechanical strength and stability of granules during the operation of wastewater treatment. The contributing extracellular polymeric substances to the gel strength of aerobic granular sludge were verified from the perspective of rheological properties in this study. Moreover, the correlations between the molecular structure and gel properties of extracellular polymeric substances were established by analyzing rheological properties and spectrum results of extracellular polymeric substances extracted by various extraction methods. The results indicated that protein and polysaccharide were indispensable to maintain the cross-linking structure of extracellular polymeric substances. The gel strength of extracellular polymeric substances was positively correlated with the amount of α-helix of natural protein and intermolecular hydrogen bond between each component. The cation exchange resin method which retained the relatively higher ratio of α-helix of natural protein and intermolecular hydrogen bond could better preserve the gel properties of the original aerobic granular sludge. This study could provide a theoretical reference for the cultivation of aerobic granular sludge and the optimization of operating conditions of the reactor.

Removal of Pb(II) Ions from Wastewater by Using Polyethyleneimine-Functionalized Fe3O4 Magnetic Nanoparticles

A class of polyethyleneimine (PEI)-functionalized Fe3O4 magnetic nanoparticles (MNPs) has been facilely produced through a solvothermal process. The synthetic MNPs have been characterized by multiple technologies and then used for Pb(II) ion sorption from the aqueous media in different conditions. It was found the Pb(II) adsorption behaviors could be well fitted by the pseudo second-order kinetic and Langmuir isotherm models. The maximum Pb(II) adsorption capacity at 25 °C and pH 5.0 was calculated to be 60.98 mg/g. Moreover, effects of temperature, pH, and electrolyte of aqueous phase on the Pb(II) adsorption capacity of MNPs have been carefully examined. The Pb(II) adsorbing capacity was enhanced with temperature or pH rising, but reduced with the addition of various electrolytes. Additionally, the recyclability of synthetic MNPs has been also assessed. The prepared PEI-functionalized MNPs could still maintain good adsorption performance after five cycles of Pb(II) removal. These results indicated that the PEI-functionalized Fe3O4 MNPs could be readily synthesized and served as a desirable and economic adsorbent in Pb(II)-contaminated wastewater treatment.