Multistage optimizations of slow pyrolysis synthesis of biochar from palm oil sludge for adsorption of lead

A novel magnetic sludge biochar was prepared by making full use of internal iron in sludge combining KMnO4-NaOH modification to enhance the adsorption of Pb (Ⅱ), Cu (Ⅱ) and Cd (Ⅱ)

This study synthesized novel magnetic biochar (PCMN600) by KMnO4-NaOH combined modification using iron-containing pharmaceutical sludge to remove toxic metals from wastewater effectively. Various characterization experiments of engineered biochar showed that the modification process introduced ultrafine MnOx particles on the carbon surface and resulted in higher BET surface area and porosity along with more oxygen-containing surface functional groups. Batch adsorption studies indicated that the maximum adsorption capacities of PCMN600 for Pb2+, Cu2+ and Cd2+ were 181.82 mg/g, 30.03 mg/g and 27.47 mg/g, respectively, at a temperature of 25 °C and pH of 5.0, which were much higher than that of pristine biochar (26.46 mg/g, 6.56 mg/g and 6.40 mg/g). The adsorption datums of three toxic metal ions fitted well to the pseudo-second-order model and Langmuir isotherm, and the sorption mechanisms were identified as electrostatic attraction, ion exchange, surface complexation, cation-π interaction and precipitation. The strong magnetic properties of the engineered biochar endowed the adsorbent with remarkable reusability, and after five cycles of recycling, PCMN600 still retained nearly 80% of its initial adsorption capacities.

Crawfish shell- and Chinese banyan branch-derived biochars reduced phytoavailability of As and Pb and altered community composition of bacteria in a contaminated arable soil

Globally, soil contamination with arsenic (As) and lead (Pb) has become a severe environmental issue. Herein, a pot experiment was conducted using pak choi (Brassica chinensis L.) to investigate the effects of biochars derived from crawfish (Procambarus clarkia) shells (CSB) and Chinese banyan (Ficus microcarpa) branches (CBB) on the phytoavailability of As and Pb, and bacterial community composition in soils. Our results showed that the application of CSB and CBB decreased the concentrations of DTPA-extractable Pb in soils ranging from 26.8 % to 28.8 %, whereas CSB increased the concentration of NH₄H₂PO₄-extractable As in soils, compared to the control. Application of both biochars reduced the uptake of As and Pb in the edible part of pak choi. In addition, application of CBB significantly (P < 0.05) increased the activities of α-glucosidase, β-glucosidase, cellobiohydrolase, and acid phosphomonoesterase by 55.0 %, 54.4 %, 195.1 %, and 76.7 %, respectively, compared to the control. High-throughput sequencing analysis revealed that the predominant bacteria at the phyla level in both biochar-treated soils were Firmicutes, Proteobacteria, and Actinobacteriota. Redundancy and correlation analyses showed that the changes in bacterial community composition could be related to soil organic carbon content, As availability, and nutrient availability in soils. Overall, the Chinese banyan branch biochar was more suitable than the crawfish shell biochar as a potential amendment for the remediation of soils co-contaminated with As and Pb.

Biochar derived carbonaceous material for various environmental applications: Systematic review

Biochar is the solid material produced from the carbonization of organic feedstock biomass. This material has several unique characteristics such as greater carbon content, good electrical conductivity, high stability and large surface area, which can be applied in several research areas such as generation of power and wastewater treatment. In connection with this, recently, the investigations on biochar significantly focus on the removal of toxic heavy metals since the biochar material is easily available and environmentally friendly. According to an environmental analytical device, biochar-derived carbonaceous material has been additionally applied to the synthesis of an effective, sensitive, and low-cost electrochemical sensor. Biochar with an assessment of electrochemical properties has engaged with different redox reactions in water. In this survey, electrochemical ways of behaving of biochar in light of the electrochemical structures were analytically compiled as well as the impact from biomass sources and manufacturing process including carbonization strategies, pre-treatment/changed techniques. This review emphasizes the various synthesis methods of biochar form organic feedstock, properties and different modulations of biochar for the bioremediation of heavy metals. This review study emphasizes the utilization of biochar as sensing platform and supercapacitor for electrode fabrication in electrochemical biosensor to enhance the remediation of toxic contaminants from water streams and by switching the less ecological traditional materials. Brief information on the techniques employed for packaging biochar as carbon electrode is summarized. Scope in the aspect of environmental concern of biochar, future challenges and prospects are proposed in detail.

Engineered macroalgal and microalgal adsorbents: Synthesis routes and adsorptive performance on hazardous water contaminants

Colourants, micropollutants and heavy metals are regarded as the most notorious hazardous contaminants found in rivers, oceans and sewage treatment plants, with detrimental impacts on human health and environment. In recent development, algal biomass showed great potential for the synthesis of engineered algal adsorbents suitable for the adsorptive management of various pollutants. This review presents comprehensive investigations on the engineered synthesis routes focusing mainly on mechanical, thermochemical and activation processes to produce algal adsorbents. The adsorptive performances of engineered algal adsorbents are assessed in accordance with different categories of hazardous pollutants as well as in terms of their experimental and modelled adsorption capacities. Due to the unique physicochemical properties of macroalgae and microalgae in their adsorbent forms, the adsorption of hazardous pollutants was found to be highly effective, which involved different mechanisms such as physisorption, chemisorption, ion-exchange, complexation and others depending on the types of pollutants. Overall, both macroalgae and microalgae not only can be tailored into different forms of adsorbents based on the applications, their adsorption capacities are also far more superior compared to the conventional adsorbents.

Artificial intelligence (AI) applications in adsorption of heavy metals using modified biochar

The process of removal of heavy metals is important due to their toxic effects on living organisms and undesirable anthropogenic effects. Conventional methods possess many irreconcilable disadvantages pertaining to cost and efficiency. As a result, the usage of biochar, which is produced as a by-product of biomass pyrolysis, has gained sizable traction in recent times for the removal of heavy metals. This review elucidates some widely recognized harmful heavy metals and their removal using biochar. It also highlights and compares the variety of feedstock available for preparation of biochar, pyrolysis variables involved and efficiency of biochar. Various adsorption kinetics and isotherms are also discussed along with the process of desorption to recycle biochar for reuse as adsorbent. Furthermore, this review elucidates the advancements in remediation of heavy metals using biochar by emphasizing the importance and advantages in the usage of machine learning (ML) and artificial intelligence (AI) for the optimization of adsorption variables and biochar feedstock properties. The usage of AI and ML is cost and time-effective and allows an interdisciplinary approach to remove heavy metals by biochar.

Adsorptive removal of cationic methylene blue and anionic Congo red dyes using wet-torrefied microalgal biochar: Equilibrium, kinetic and mechanism modeling

This study aims to investigate the adsorption behavior of cationic and anionic dyes of methylene blue (MB) and Congo red (CR) onto wet-torrefied Chlorella sp. microalgal biochar respectively, as an approach to generate a waste-derived and low-cost adsorbent. The wet-torrefied microalgal biochar possessed microporous properties with pore diameter less than 2 nm. The optimum adsorbent dosage of wet-torrefied microalgal biochar for MB and CR dyes removal were determined at 1 g/L and 2 g/L, respectively, with their natural pHs as the optimum adsorption pHs. The determined equilibrium contact times for MB and CR were 120 h and 4 h, respectively. Based on the equilibrium modeling, the results revealed that Langmuir isotherm showed the best model fit, based on the highest R² coefficient, for both the adsorption processes of MB and CR using the wet-torrefied microalgal biochar, indicating that the monolayer adsorption was the dominant process. From the modeling, the maximum adsorption capacities for MB and CR were 113.00 mg/g and 164.35 mg/g, respectively. The kinetic modeling indicated the adsorption rate and mechanism of the dyes adsorption processes, which could be crucial for future modeling and application of wet-torrefied microalgal biochar. From the results, it suggests that the valorization of microalgae by utilizing wet-torrefied microalgal biochar as the effective adsorbent for the removal of toxic dyes with an approach of microalgal biorefinery and value-added application to the environment is feasible.

Crayfish shell biochar for the mitigation of Pb contaminated water and soil: Characteristics, mechanisms, and applications

Biochar has been widely used in the mitigation of soil potentially toxic metals due to its high efficiency and low cost. Crayfish shell biochar (CSBC) was prepared at 300, 500, and 700 °C (referred to as CS300, CS500, and CS700, respectively) and the performance and mechanism of CSBC for mitigating Pb polluted water and soil was investigated. The results indicated that CSBC prepared at higher temperatures possessed higher pH value and ash content, more abundant pore structure, and higher stability. Pb²⁺ adsorption onto CSBC fitted well with the pseudo second order and intraparticle diffusion models. The maximum adsorption capacity of Pb²⁺ increased with the pyrolysis temperature, being 599.70, 1114.53, and 1166.44 mg·g^-1 for CS300, CS500 and CS700, respectively. Compared with the control soil samples, the content of available Pb after applying 0.05%-5% CSBC was reduced by 1.87%-16.48% in acidic soils and 1.00%-11.09% in alkaline soils. Moreover, the fractionation of exchangeable Pb was converted to stable organic matter bound, Fe-Mn oxide bound, and residue fractions. XRD, SEM-EDS, and FTIR analysis showed that ion exchange, complexation, precipitation, and C-π interaction are the dominant interaction mechanisms. Therefore, CSBC can employ as an effective immobilizing agent for the mitigation of Pb contaminated water and soil.

Oxalic acid modified copper tailings as an efficient adsorbent with super high capacities for the removal of Pb2

Comprehensive utilization of tailings is not only conducive to ensuring the sustainable use of resources but also can reduce the related environmental pollution. In the present work, a new utilization way of copper tailings was proposed and a novel composite (OMT-6) was prepared by modification of tailings with oxalic acid. The composite had super high Pb²⁺ adsorption capacity with the maximal Pb²⁺ removal capacity of 862.07 mg/g. Its Pb²⁺ removal behaviours followed pseudo-second-order kinetic equation and Langmuir model, suggesting that Pb²⁺ removal depended on monolayer adsorption. The surface of OMT-6 was rough and a lot of nanospheres were loaded on its surface. The composite had mesoporous structure and a larger specific surface area compared with tailings, the above characteristics of which facilitated Pb²⁺ removal. The major crystal structures of OMT-6 were transformed to CaC₂O₄•H₂O and FeC₂O₄•2H₂O after oxalic acid modification and Pb²⁺ could be removed by the ions exchange between Ca²⁺, Fe²⁺ and Pb²⁺. Pb²⁺ removal mechanisms of OMT-6 involved ion exchange, surface complexation and electrostatic attraction interaction, among which ion exchange played a key role. These results indicated that the prepared OMT-6 composite from copper tailings was an ideal material for Pb²⁺ removal from aqueous solution.

A novel composite of SiO2 decorated with nano ferrous oxalate (SDNF) for efficient and highly selective removal of Pb2+ from aqueous solutions

Developing a material with high adsorption capacity and selectivity to remove lead from Pb²⁺ polluted wastewater is of vital importance for environment protection and resources utilization. In this study, a novel composite, SiO₂ decorated with nano ferrous oxalate (SDNF), was prepared from natural biotite containing ores to remove Pb²⁺. Pseudo-first-order kinetic (R² = 0.99) and Langmuir models (R² = 0.99) fitted the data well, manifesting that Pb²⁺ adsorption process was monolayer adsorption. The maximum Pb²⁺ adsorption capacity was identified as 446.98 mg/g. SEM and TEM images showed that nano ferrous oxalate with average size of 11.51 nm was coated on the surface of ores, and their distributions were uniform. Results of XRD, XPS, FTIR and zeta potential indicated that ion exchange, surface complexation and electrostatic attraction interaction were involved in the remvoal of Pb²⁺, and the ion exchange between Fe²⁺ and Pb²⁺ played a major role. Moreover, both Cd²⁺ and Zn²⁺ removal efficiency are less than 2 % in Pb-Cd or Pb-Zn coexisted solution, indicating the composite possessed high selectivity for Pb²⁺ removal. All above results indicated that the composite was a material with high adsorption capacity and selectivity for Pb²⁺, which was suitable for remediation of Pb²⁺ pollution from Pb²⁺ containing wastewater.

Preparation and characterization of activated carbons obtained from the waste materials impregnated with phosphoric acid(V)

In the paper spent coffee grounds were used as a precursor to obtain activated carbons. The raw material was impregnated with phosphoric acid(V) at the different impregnations ratios: 0.5, 1, 1.5, 2. Carbonization was carried out according to two procedures differing in activation atmosphere (N2 or CO2). The obtained activated carbons were characterized on the basis of low-temperature nitrogen adsorption/desorption, thermal analysis, potentiometric titration method, X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Carbons obtained according to procedure 2 (activation in CO2) were characterized by better developed porosity, e.g. surface (SBET to 720.9 m2/g) and pore volume (Vp to 0.334 cm3/g). All obtained carbons had surface acidic (mainly carboxyl) groups and exhibited the amorphous structure. The thermal analysis showed that the obtained materials were thermally stable up to the temperature ~ 420 °C.

Biochar derived from corn stalk and polyethylene co-pyrolysis: characterization and Pb(ii) removal potential

Biochar is widely used as adsorbents for gaseous or liquid pollutants due to its special pore structure.

Optimization of activated palm oil sludge biochar preparation for sulphur dioxide adsorption

Palm oil sludge (POS) is an organic waste generated from the palm oil industry. POS causes environmental pollution if it is improperly disposed. In this study, the potential of activated POS biochar, as an adsorbent for the removal of SO₂ gas was tested. POS biochar was physically activated using CO₂ gas. The effects of activation preparation variables i.e. activation temperature (300-700 °C), activation time (30-150 min) and CO₂ flow rate (100-500 ml/min) were investigated using design expert version 8.0.7.1 software. Central Composite Design (CCD) was used to develop a quadratic model to correlate the operating variables with the activated biochar adsorption capacity. Analysis of variance (ANOVA) was performed to identify the significant factors on the experimental design response. The optimum preparation conditions of activated POS biochar were found to be at activation temperature of 442 °C, activation time of 63 min and CO₂ flow rate of 397 ml/min. The maximum adsorption capacity at the optimum conditions was recorded as 16.65 mg/g. The adsorption capacity increased significantly after the activation process. Characteristics of the activated POS biochar proposed that SO₂ was physically adsorbed. Furthermore, it was found that the adsorption capacity can be further enhanced by increasing the reaction temperature to 100 °C or with 15% of relative humidity in the inlet gas. The prepared adsorbents can be regenerated by thermal treatment.

The effect of biochar mild air oxidation on the optimization of lead(II) adsorption from wastewater

In the present study, the effects of mild air oxidation of a biochar produced by the Pyrovac Inc. pyrolysis process, on the adsorption of lead(II) from synthetic wastewater under batch experimental conditions have been investigated. The adsorption experiments were performed under several conditions suggested by the response surface methodology, which allowed finding the optimal conditions, in order to maximize the adsorption capacity (Q(mgg^-1)), as well as the extraction efficiency (E (%)). The optimal conditions of lead ions adsorption were as follows: pH = 5, agitation time = 300 min, adsorbent mass = 0.5 g (per 50 cm³ of solution), and lead initial concentration = 100gm^-3, resulted in an adsorption capacity of 7.9 mg g^-1. Equilibrium adsorption was then obtained by keeping pH and adsorbent mass at the optimal values and changing the lead initial concentration for a sufficient agitation time. Results showed that mild air oxidation increased the equilibrium adsorption capacity of biochar from 2.5 to 44 mg g^-1. Oxidized biochar after equilibrium adsorption was submitted to SEM/EDX and XPS analysis. From SEM it was found that lead particles were distributed heterogeneously after adsorption. From XPS analysis, it was revealed that the external surface of oxidized biochar particles becomes saturated for the initial point of equilibrium diagram, obtained at lead initial concentration of 100gm^-3, suggesting that for a higher concentration, the internal surfaces of particles participate in the cations adsorption. The participation of surface functional groups in the adsorption process showed that carbonyl, carboxylic, and aromatic rings of oxidized biochar were involved in the adsorption. This work suggests that the very simple process of mild air oxidation can be used instead of the usual costly chemical activation, in order to improve biochar cation exchange capacity.

Highly efficient nickel (II) removal by sewage sludge biochar supported α-Fe2O3 and α-FeOOH: Sorption characteristics and mechanisms

A novel approach was employed to load α-Fe₂O₃ and α-FeOOH onto sewage sludge biochar (SBC) with the purpose of efficient nickel (Ni) removal. A high Ni(II) adsorption capacity of 35.50 mg·g^-1 in 100 ppm Ni(II) solution with 10 mg modified sewage sludge biochar (MSBC) was achieved. The adsorption kinetic and isotherm were fitted well by the pseudo-second-order model and the Langmuir model, respectively. The optimal pH was found around a neutral pH of 7. The adsorption mechanisms of Ni(II) onto MSBC were described as the synergistic effects of electrostatic attraction, ion exchange, inner-sphere complexation and co-precipitation. The initial rapid adsorption phenomenon could be attributed to electrostatic attraction and ion exchange, and then inner-sphere complexation and co-precipitation acted as a crucial role in the following step. The remarkable performance of MSBC provides an effective waste utilization approach to simultaneous sewage sludge recycle and Ni removal from aqueous solution.

Ice-templated graphene oxide/chitosan aerogel as an effective adsorbent for sequestration of metanil yellow dye

Graphene oxide/chitosan aerogel (GOCA) was prepared by a facile ice-templating technique without using any cross-linking reagent for metanil yellow dye sequestration. The adsorption performance of GOCA was investigated by varying the adsorbent mass, shaking speed, initial pH, contact time, concentration and temperature. The combined effects of adsorption parameters and the optimum conditions for dye removal were determined by response surface methodology. GOCA exhibited large removal efficiencies (91.5-96.4%) over a wide pH range (3-8) and a high adsorption capacity of 430.99 mg/g at 8 mg adsorbent mass, 400 mg/L concentration, 35.19 min contact time and 175 rpm shaking speed. The adsorption equilibrium was best represented by the Langmuir model. GOCA could be easily separated after adsorption and regenerated for re-use in 5 adsorption-desorption cycles thereby maintaining 80% of its adsorption capability. The relatively high adsorption and regeneration capabilities of GOCA render it an attractive adsorbent for treatment of azo dye-polluted water.

Surface grafting techniques on the improvement of membrane bioreactor: State-of-the-art advances

Membrane bioreactor (MBR) is regarded as the state-of-the-art technology in separation processes. Surface modification techniques play a critical role in improving the conventional membrane system which is mostly hydrophobic in nature. The hydrophobic nature of membranes is known to cause fouling, resulting in high maintenance costs and shorter lifespan of MBR. Thus, surface grafting aims to improve the hydrophilicity of bio-based membrane systems. This review describes the major surface grafting techniques currently used in membranes, including photo induced grafting, plasma treatment and plasma induced grafting, radiation induced grafting, thermal induced grafting and ozone induced grafting. The advantages and disadvantages of each method is discussed along with their parametric studies. The potential applications of MBR are very promising, but some integral membrane properties could be a major challenge that hinders its wider reach. The fouling issue could be resolved with the surface grafting techniques to achieve better performance of MBRs.