Sorptive removal of toluene and m-xylene by municipal solid waste biochar: Simultaneous municipal solid waste management and remediation of volatile organic compounds

Engineered lignocellulosic based biochar to remove endocrine-disrupting chemicals: Assessment of binding mechanism

The safety and health of aquatic organisms and humans are threatened by the increasing presence of pollutants in the environment. Endocrine disrupting chemicals are common pollutants which affect the function of endocrine and causes adverse effects on human health. These chemicals can disrupt metabolic processes by interacting with hormone receptors upon consumptions by humans or aquatic species. Several studies have reported the presence of endocrine disrupting chemicals in waterbodies, food, air and soil. These chemicals are associated with increasing occurrence of obesity, metabolic disorders, reproductive abnormalities, autism, cancer, epigenetic variation and cardiovascular risk. Conventional treatment processes are expensive, not environment friendly and unable to achieve complete removal of these harmful chemicals. In recent years, biochar from different sources has gained a considerable interest due to their adsorption efficiency with porous structure and large surface areas. biochar derived from lignocellulosic biomass are widely used as sustainable catalysts in soil remediation, carbon sequestration, removal of organic and inorganic pollutants and wastewater treatment. This review conceptualizes the production techniques of biochar from lignocellulosic biomass and explores the functionalization and interaction of biochar with endocrine-disrupting chemicals. This review also identifies the further needs of research. Overall, the environmental and health risks of endocrine-disrupting chemicals can be dealt with by biochar produced from lignocellulosic biomass as a sustainable and prominent approach.

Biochar as an effective material for acetone sorption and the effect of surface area on the mechanism of sorption

Walnut shells and apricot pits were used to produce non-activated, air-activated and steam-activated biochar. The specific surface area decreased in the order steam-activated (500-727 m 2.g-1), air-activated (59-514 m2.g-1) and non-activated biochars (1.71-236 m2.g-1). The results indicated that water steam created a multi-layer block structure with a well-developed porous structure, especially at 900 °C, while activation with air resulted in a more fragmented structure with a higher amount of coarse pores, leading to lower specific surface values. Acetone sorption experiments were performed in order to determine the acetone sorption capacity and to evaluate the acetone sorption kinetics of the biochars, as well as to identify the possible mechanism of sorption. The maximum sorption capacity estimated from the adsorption isotherms up to a relative pressure of 0.95 ranged from 60.3 to 277.3 mg g-1, and was highest in the steam-activated biochar with the largest surface area. The acetone adsorption isotherms were fitted with different adsorption models, where the Fritz-Schlunder model showed the best fitting results. The adsorption kinetics was evaluated using two kinetics models - pseudo first order and pseudo second order. The results indicated that the biochars with a large surface area exhibited physical sorption through van der Waals forces as the dominant mechanism, while acetone sorption on samples with a smaller surface area can be attributed to a mixed dual sorption mechanism, which combines physical sorption and chemisorption on oxygen functional groups. The perfect reusability of the biochars was confirmed by four consecutive adsorption-desorption cycles.

Photocatalytic Degradation of Xylene by Carbon Quantum Dots/Clinoptilolite Composites

In this work, a series of clinoptilolite composites decorated with carbon quantum dots (CQDs/clinoptilolite) with hierarchical pore structures was demonstrated that exhibits good photocatalytic performance for the removal of xylene. The technique for the attachment of carbon quantum dots to clinoptilolite was prepared by a hydrothermal method in this study. The structural features were confirmed by SEM, TEM, EDS, XRD, BET, XPS, and solid diffuse reflection measurements, while the degradation mechanism was investigated by adding a trapping agent into the nanocomposites. The introduction of CQDs promoted the separation of photogenerated electrons and holes as well as the generation of reactive radicals, which effectively improved the light utilization and even increased the degradation rate of xylene by 73% at the optimal state. The photocatalytic test was conducted under a different dwell time, catalyst dosage, initial concentration, and illumination intensity. The results showed that the degradation rate of xylene by the CQDs/clinoptilolite catalyst reached 97.4% under the optimal reaction conditions (the catalyst was Catalyst No. 2, the residence time was 90 s, the initial concentration was 2.5 g/m3, the light intensity was three lamps for irradiation, and the catalyst dosage was 0.05 g). In addition, the degradation efficiency of the CQDs/clinoptilolite photocatalyst still reached 78% after eight consecutive catalytic regeneration cycles. This work sheds new light on the degradation of xylene.

Chicken Cartilage-Derived Carbon for Efficient Xylene Removal

Chicken cartilage was used for the first time as a raw material for the microwave-assisted synthesis of biochar and activated carbon. Various microwave absorbers, i.e., commercial active carbon, scrap tyres, silicon carbide, and chicken bone-derived biochar, as well as various microwave powers, were tested for their effect on the rate of pyrolysis and the type of products formed. Biochars synthesised under 400 W in the presence of scrap tyres and chicken bone-derived biochar were activated with KOH and K₂CO₃ with detergent to produce activated carbon with a highly developed porous structure that would be able to effectively adsorb xylene vapours. All carbons were thoroughly characterised (infrared spectroscopy, X-ray fluorescence spectrometry, nitrogen adsorption/desorption, Raman spectroscopy, proximate and ultimate analysis) and tested as xylene sorbents in dynamic systems. It was found that the activation causes an increase of up to 1042 m²·g^-1 in the specific surface area, which ensures the sorption capacity of xylene about 300 mg·g^-1. Studies of the composition of biogas emitted during pyrolysis revealed that particularly valuable gaseous products are formed when pyrolysis is carried out in the presence of silicon carbide as a microwave absorber.

Efficient aqueous molybdenum removal using commercial Douglas fir biochar and its iron oxide hybrids

Molybdenum (Mo) is a naturally-occurring trace element in drinking water. Most commonly, molybdate anions (MoO₄^2-) are in well water and breast milk. In addition, it is used in medical image testing. Recently, the EPA classified Mo as a potential contaminant, as exposure can lead to health effects such as gout, hyperuricemia, and even lung cancer. We have assessed the sorptive removal of aqueous molybdate using Douglas fir biochar (DFBC) and a hybrid DFBC/Fe₃O₄ composite containing chemically-coprecipitated iron oxide (Fe₃O₄). Adsorption was studied at various: pH values, equilibrium times (5 min-24 h), initial Mo concentrations (2.5-1000 mg/L), and temperatures (5, 25, and 40 °C) using batch sorption and fixed-bed column equilibrium methods. Langmuir capacities for DFBC and DFBC/Fe₃O₄ (at pH 3, 2 hrs equilibrium) were within 459.3-487.9 mg/g and 288-572 mg/g, respectively. These adsorbents and their Mo-laden counterparts were characterized by elemental analysis, BET, PZC, SEM, TEM, EDS, XRD, and XPS. MoO₄^2- adsorption on DFBC is thought to be governed primarily via electrostatic attraction. Adsorption by DFBC/Fe₃O₄ is primarily governed by chemisorption onto magnetite surface hydroxyl groups, while electrostatics prevail in the DFBC-exposed phase. Stoichiometric precipitation of iron molybdates triggered by iron dissolution was also considered. The data suggest that DFBC and DFBC/Fe₃O₄ are promising candidates for molybdate sorption.

Biochar application for greenhouse gas mitigation, contaminants immobilization and soil fertility enhancement: A state-of-the-art review

Rising global temperature, pollution load, and energy crises are serious problems, recently facing the world. Scientists around the world are ambitious to find eco-friendly and cost-effective routes for resolving these problems. Biochar has emerged as an agent for environmental remediation and has proven to be the effective sorbent to inorganic and organic pollutants in water and soil. Endowed with unique attributes such as porous structure, larger specific surface area (SSA), abundant surface functional groups, better cation exchange capacity (CEC), strong adsorption capacity, high environmental stability, embedded minerals, and micronutrients, biochar is presented as a promising material for environmental management, reduction in greenhouse gases (GHGs) emissions, soil management, and soil fertility enhancement. Therefore, the current review covers the influence of key factors (pyrolysis temperature, retention time, gas flow rate, and reactor design) on the production yield and property of biochar. Furthermore, this review emphasizes the diverse application of biochar such as waste management, construction material, adsorptive removal of petroleum and oil from aqueous media, immobilization of contaminants, carbon sequestration, and their role in climate change mitigation, soil conditioner, along with opportunities and challenges. Finally, this review discusses the evaluation of biochar standardization by different international agencies and their economic perspective.

Review on carbon-based adsorbents from organic feedstocks for removal of organic contaminants from oil and gas industry process water: Production, adsorption performance and research gaps

Large amounts of process water with considerable concentrations of recalcitrant organic contaminants, such as polycyclic aromatic hydrocarbon (PAHs), phenolic compounds (PCs), and benzene, toluene, ethylbenzene, and xylene (BTEX), are generated by several segments of oil and gas industries. These segments include refineries, hydraulic fracturing (HF), and produced waters from the extraction of shale gas (SGPW), coalbed methane (CBMPW) and oil sands (OSPW). In fact, the concentration of PCs and PAHs in process water from refinery can reach 855 and 742 mg L^-1, respectively. SGPW can contain BTEX at concentrations as high as 778 mg L^-1. Adsorption can effectively target those organic compounds for the remediation of the process water by applying carbon-based adsorbents generated from organic feedstocks. Such organic feedstocks usually come from organic waste materials that would otherwise be conventionally disposed of. The objective of this review paper is to cover the scientific progress in the studies of carbon-based adsorbents from organic feedstocks that were successfully applied for the removal of organic contaminants PAHs, PCs, and BTEX. The contributions of this review paper include the important aspects of (i) production and characterization of carbon-based adsorbents to enhance the efficiency of organic contaminant adsorption, (ii) adsorption properties and mechanisms associated with the engineered adsorbent and expected for certain pollutants, and (iii) research gaps in the field, which could be a guidance for future studies. In terms of production and characterization of materials, standalone pyrolysis or hybrid procedures (pyrolysis associated with chemical activation methods) are the most applied techniques, yielding high surface area and other surface properties that are crucial to the adsorption of organic contaminants. The adsorption of organic compounds on carbonaceous materials performed well at wide range of pH and temperatures and this is desirable considering the pH of process waters. The mechanisms are frequently pore filling, hydrogen bonding, π-π, hydrophobic and electrostatic interactions, and same precursor material can present more than one adsorption mechanism, which can be beneficial to target more than one organic contaminant. Research gaps include the evaluation of engineered adsorbents in terms of competitive adsorption, application of adsorbents in oil and gas industry process water, adsorbent regeneration and reuse studies, and pilot or full-scale applications.

Experimental analysis on products distribution and characterization of medical waste pyrolysis with a focus on liquid yield quantity and quality

The massive generation of medical waste (MW) poses a serious risk to the natural environment and human health. The pyrolysis technique is proposed as a potential treatment for MW to tackle the associated environmental issues and produce value-added products. In this work, medical waste pyrolysis has been conducted at various temperatures using a fixed bed reactor with a 20 °C·min^-1 heating rate and nitrogen was used as a career gas with a flow rate of 100 ml·min^-1. In addition, the effect of temperature on products yield and chemical composition of MW pyrolysis have been investigated. The maximum yield of 57.1% for liquid oil was observed from the mixed MW pyrolysis at 500 °C. The gas and char yield were found between 26.5-37.3% and 24.2-12.4%, respectively, for the pyrolysis temperature of 450 °C to 600 °C. According to GC analysis, the concentration of the main gaseous products such as CH₄, H₂, and C₂H₄ was increased with increasing temperature, while CO and CO₂ experienced a decreasing trend. The results of GC-MS analysis revealed that the main components of MW pyrolysis oil were aromatic hydrocarbons, cyclic hydrocarbons, aliphatic hydrocarbons, alcohol, carboxylic acids, and their derivatives. The aromatic and cyclic hydrocarbons content increased up to 38.2% at a pyrolysis temperature of 600 °C. As pyrolysis oil tends to have more long-chain hydrocarbons therefore carbon distributions from C₇ to C₃₅ were observed. The ultimate analysis of oil and char revealed that the increased temperature enhanced the carbon content up to 78.6% and 68.0%, respectively. Furthermore, the higher heat values of 41.8, 24.4, and 52.7 MJ·kg^-1 were reported for oil, char, and gas, respectively.

Comparison of 17β-Estradiol Adsorption on Corn Straw- and Dewatered Sludge-Biochar in Aqueous Solutions

Removal of steroid hormones from aqueous environment is of prevailing concern because of their adverse impact on organisms. Using biochar derived from biomass as adsorbent to remove pollutants has become more popular due to its low cost, effectiveness, and sustainability. This study evaluated the feasibility of applying corn straw biochar (CSB) and dewatered sludge biochar (DSB) to reduce 17β-estradiol (E2) from aquatic solutions by adsorption. The experimental results showed that the adsorption kinetics and isotherm behavior of E2 on the two biochars were well described by the pseudo-second-order (R2 > 0.93) and Langmuir models (R2 > 0.97). CSB has higher E2 adsorption capacity than DSB, and the maximum adsorption capacity was 99.8 mg/g obtained from Langmuir model at 298 K, which can be attributed to the higher surface area, porosity, and hydrophobicity of this adsorbent. Higher pH levels (>10.2) decreased the adsorption capacities of biochar for E2, while the ionic strength did not significantly affect the adsorption process. The regeneration ability of CSB was slightly better than that of DSB. The possible adsorption mechanism for E2 on biochar is suggested as π−π interactions, H−bonding, and micropores filling. These results indicated that CSB has more potential and application value than DSB on reducing E2 from aqueous solutions when considering economy and removal performance.

Petrochemical Wastewater Treatment by Eggshell Modified Biochar as Adsorbent: Atechno-Economic and Sustainable Approach

Petrochemical industrial wastewater (PIW)contains toluene and xylene (TX), and various organic and inorganic pollutants, causing severe risks to human health if improperly released into the environmental matrices. For the long-term reliability of environmental conservation, this study illustrates the interlinkage between PIW treatment and the three pillars of sustainable development. Sewage sludge biochar was modified with eggshell, showing a relatively high fixed C content (increase in carbonization degree), and small O/C and N/C ratios. The prepared biochar was employed for TX adsorption in mono-component solutions, giving removal efficiencies of 79.1% (T) and 86.6% (X), at pH =10, adsorbent dosage =2 g/L, and Co =40 mg/L within 60 min. The main adsorption mechanism was physisorption, including precipitation/pore-filling, π-π dispersive interaction, and van der Waals force. The modified biochar also treated real PIW under five adsorption/regeneration cycles, providing essential steps toward large-scale applications. According to an economic feasibility estimation, the biochar application for treating 1 m3 of PIW would offer a payback period of 6.9 yr. The study outputs could be linked to the restoration of water-related ecosystems, biochar modification for industrial applications, and climate change mitigation, adopting the 2030 agenda and its sustainable development goals (SDGs).

Progress and prospects in mitigation of landfill leachate pollution: Risk, pollution potential, treatment and challenges

The escalating loads of municipal solid waste (MSW) end up in open dumps and landfills, producing continuous flows of landfill leachate. The risk of incorporating highly toxic landfill leachate into environment is important to be evaluated and measured in order to facilitate decision making for landfill leachate management and treatment. Leachate pollution index (LPI) provides quantitative measures of the potential environmental pollution by landfill leachate and information about the environmental quality adjacent to a particular landfill. According to LPI values, most developing countries show high pollution potentials from leachate, mainly due to high organic waste composition and low level of waste management techniques. A special focus on leachate characterization studies with LPI and its integration to treatment, which has not been focused in previous reviews on landfill leachate, is given here. Further, the current review provides a summary related to leachate generation, composition, characterization, risk assessment and treatment together with challenges and perspectives in the sector with its focus to developing nations. Potential commercial and industrial applications of landfill leachate is discussed in the study to provide insights into its sustainable management which is original for the study.

Development of food-origin biochars for the adsorption of selected volatile organic compounds (VOCs) for environmental matrices

Four novel fruit-derived biochars were developed: pomegranate peels (PB), prickly pear peels (PPB), carob (CB), and locust bean gum (LBGB). The feedstocks were pyrolyzed at 350 and 550 ℃ (under N₂), respectively, and characterized using Scanning Electron Microscopy (SEM), Elemental Analysis (EA), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Brunauer-Emmett-Teller (B.E.T) analysis, and Thermogravimetric analysis (TGA). A systematic and comprehensive comparison for the adsorption of selected volatile organic compounds (VOCs) by biochar was established. Cresol, dimethyl trisulfide (DMTS), hexane, and benzene were examined as a function of contact time (30-480 min), mass (0.1-1 g), concentration levels (50-1000 ppb_v), efficiency, and reusability, using the headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) method. PB 550 ℃ revealed a specific surface area of 8.3 m² g^-1, the fastest complete removal, an ideal mass of 1 g, 3-times reuse, and ∼ 99% removal of 500 ppb_v benzene, cresol, DMTS, and 100 ppb_v hexane.

Use of biochar for the sorption of volatile organic compounds (VOCs) emitted from cattle manure

The ability of biochar to be used as filter or as additive for the adsorption of volatile organic compounds (VOCs) emitted from cattle manure is investigated. The employed biochar was produced from cattle manure after slow pyrolysis at 550 °C (under nitrogen). Towards this, in-house-made glass emission reactors were filled with fresh cattle manure samples and a thin layer of biochar (10% w/w) was placed on the top of the manure layer. The mixture was left for 24 h to equilibrate and air samples were collected from the headspace air. The samples were then analyzed using the headspace solid-phase micro-extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) method. Cattle manure emissions are considered unpleasant and odoriferous. The respective changes in the emitted cattle manure VOCs were reported; these included mainly reduction in sulfur- (thiols and sulfides) and oxygen-containing VOCs (alcohols, ketones, phenolics), showing a promising application of biochar for the removal of such compounds from manure wastes. Also, five VOCs were selected as sorbents for further laboratory studies: hexane, dimethyl trisulfide, phenol, p-cresol, and 2-methyl-3-pentanone. The results of cattle manure-derived biochar, revealed a reduction in their emitted concentrations (low ppb_v). The present application highlights a straightforward example of cyclic economy, where a waste product is reused after being processed; its re-usage as odor adsorbent serves again the agriculture sector.

Production and beneficial impact of biochar for environmental application: A comprehensive review

This review focuses on a holistic view of biochar, production from feedstock's, engineering production strategies, its applications and future prospects. This article reveals a systematic emphasis on the continuation and development of biochar and its production methods such as Physical engineering, chemical and bio-engineering techniques. In addition, biochar alternatives such as nutrient formations and surface area made it a promising cheap source of carbon-based products such as anaerobic digestion, gasification, and pyrolysis, commercially available wastewater treatment, carbons, energy storage, microbial fuel cell electrodes, and super-capacitors repair have been reviewed. This paper also covers the knowledge blanks of strategies and ideas for the future in the field of engineering biochar production techniques and application as well as expand the technology used in the circular bio-economy.

Ethylbenzene and toluene interactions with biochar from municipal solid waste in single and dual systems

The present study investigated adsorptive removal of toluene and ethylbenzene from the aqueous media via using biochar derived from municipal solid waste (termed "MSW-BC") in a single and binary contaminant system at 25-45 °C. The adsorption was evaluated at different pH (3-10), experimental time (up to 24 h), and initial adsorbate concentrations (10-600 μg/L) in single and binary contaminant system. A fixed-bed column experiment was also conducted using MSW-BC (0.25%) and influent concentration of toluene and ethylbenzene (4 mg/L) at 2 mL/min of flow rate. The adsorption of toluene and ethylbenzene on the MSW-BC was mildly dependent on the pH, and the peak adsorption ability (44-47 μg/g) was recorded at a baseline pH of ~8 in mono and dual contaminant system. Langmuir and Hill are the models that match the isotherm results in a single contaminant environment for both toluene (R² of 0.97 and 0.99, respectively) and ethylbenzene (R² of 0.99 and 0.99, respectively) adsorption. In the binary system, the isotherm models matched in the order of Langmuir > Hill > Freundlich for toluene, whereas Hill > Freundlich > Langmuir for ethylbenzene. The adsorption in the batch experiment was likely to take place via cooperative and multilayer adsorption onto MSW-BC involving hydrophobic, π- π and n- π attractions, specific interaction such as hydrogen-π and cation-π interactions, and van der Waals interactions. The thermodynamic results indicate exothermic adsorption occurred by physical attractions between toluene and ethylbenzene, and MSW-BC. The breakthrough behavior of toluene and ethylbenzene was successfully described with Yoon-Nelson and Thomas models. The data demonstrate that the low-cost adsorbent derived from the municipal solid waste can be utilized to remove toluene and ethylbenzene in landfill leachate.

Computational and experimental assessment of pH and specific ions on the solute solvent interactions of clay-biochar composites towards tetracycline adsorption: Implications on wastewater treatment

Experimental and computational investigations have been conducted in this study to assess the influence of municipal waste pyrolyzed biochar impregnated clay composites on antibiotic removal as a material for wastewater treatment and simultaneous value-addition for waste. The surface potential (zeta potential) of the pristine biochar and composite samples are found to be within the range ~10 to ~ -40 mV in the pH range 2-10. The presence of different inorganic salt solutions influences the electrophoretic mobility of the dispersed phase in a suspension, as well as its zeta potential. In addition of Na⁺ salt solutions, the Na⁺ ions undergo electrostatic interaction with the negatively charged biochar samples and form a double layer at the interface of biochar and ionic salt solution. Molecular dynamics simulations have been employed to understand experimental findings, ions adsorption and solute-solvent interactions at the molecular level of two biochar B7 (seven benzene rings, one methoxy, one aldehyde and two hydroxyls groups) and B17 (seventeen benzene rings, one methoxy, two hydroxyls and two carboxylic acid groups) in salts aqueous solutions. The results confirm that hydroxyls and carboxylate groups of biochar are responsible for solute-solvent interactions. Successful removal of tetracycline antibiotics is observed with 26 mg/g maximum adsorption capacity with montmorillonite biochar composite. This study confirms that interactions between amide and hydroxyl groups of tetracycline with hydroxyl and carboxylate groups of biochar play the key role in the adsorption process. The solution pH and presence of different background electrolytes effectively influence the process of solute-solvent interactions as well as adsorption efficacy towards tetracycline adsorption.

Efficient removal of volatile organic compound by ball-milled biochars from different preparing conditions

Adsorption is an important technology to deal with volatile organic compounds (VOCs), and biochar has attracted much attention as a new type of adsorbent for VOCs. In this study, rice husk, corn stover and pine wood sawdust biochars from different pyrolysis temperatures (300 °C, 500 °C and 700 °C) were synthesized and treated by ball milling. The pristine and ball-milled biochars were used as adsorbents for acetone and toluene removal. Results showed that wood biochar had higher adsorption capacity for VOCs. After ball milling, the BET specific surface area and the oxygen functional group content of biochars increased. With these changes, all the ball-milled biochars showed higher adsorption rate than the pristine biochars. The ball-milled biochars under pyrolysis temperature of 300 °C showed the best adsorption performance for acetone (304 mg g^-1), which was 1.7-fold greater than that of pristine biochar. Increasing the surface area by ball milling is conducive to the diffusion of hydrophobic VOCs molecules such as toluene to the adsorption sites in the biochar. However, for hydrophilic VOCs such as acetone, higher oxygen functional groups were the main reason for the enhanced adsorption by ball milling. Therefore, ball-milled biochar can be used as a potential adsorbent material in VOCs treatment.

Bioconversion of municipal solid waste into bio-based products: A review on valorisation and sustainable approach for circular bioeconomy

Municipal solid waste management is one of the major issues throughout the world. Inappropriate management of municipal solid waste (MSW) can pose a major hazard. Anaerobic processing of MSW followed by methane and biogas generation is one of the numerous sustainable energy source options. Compared with other technologies applicable for the treatment of MSW, factors like economic aspects, energy savings, and ecological advantages make anaerobic processing an attractive choice. This review discusses the framework for evaluating conversion of municipal solid waste to energy and waste derived bioeconomy in order to address the sustainable development goals. Further, this review will provide an innovative work foundation to improve the accuracy of structuring, quality control, and pre-treatment for the ideal treatment of different segments of MSW to achieve a sustainable circular bioeconomy. The increasing advancements in three essential conversion pathways, in particular the thermochemical, biochemical, and physiochemical conversion methods, are assessed. Generation of wastes should be limited and resource utilization must be minimised to make total progress in a circular bioeconomy.

Biochar based sorptive remediation of steroidal estrogen contaminated aqueous systems: A critical review

Remediation of steroidal estrogens from aqueous ecosystems is of prevailing concern due to their potential impact on organisms even at trace concentrations. Biochar (BC) is capable of estrogen removal due to its rich porosity and surface functionality. The presented review emphasizes on the adsorption mechanisms, isotherms, kinetics, ionic strength and the effect of matrix components associated with the removal of steroidal estrogens. The dominant sorption mechanisms reported for estrogen were π-π electron donor-acceptor interactions and hydrogen bonding. Natural organic matter and ionic species were seen to influence the hydrophobicity of the estrogen in multiple ways. Zinc activation and magnetization of the BC increased the surface area and surface functionalities leading to high adsorption capacities. The contribution by persistent free radicals and the arene network of BC have promoted the catalytic degradation of adsorbates via electron transfer mechanisms. The presence of surface functional groups and the redox activity of BC facilitates the bacterial degradation of estrogens. The sorptive removal of estrogens from aqueous systems has been minimally reviewed as a part of a collective evaluation of micropollutants. However, to the best of our knowledge, a critique focusing specifically and comprehensively on BC-based removal of steroidal estrogens does not exist. The presented review is a critical assessment of the existing literature on BC based steroidal estrogen adsorption and attempts to converge the scattered knowledge regarding its mechanistic interpretations. Sorption studies using natural water matrices containing residue level concentrations, and dynamic sorption experiments can be identified as future research directions.

In-situ biodegradation of volatile organic compounds in landfill by sewage sludge modified waste-char

VOCs are the major harmful pollutants released from MSW landfills, which are toxicity to human health. In order to in-situ biodegradation of VOCs released from landfill, two novel laboratory-scale biocovers, including waste-char obtained from MSW pyrolysis (WC), and sewage sludge modified the WC (SWC), are used to degradate VOCs. The removal performances of VOCs as well as the bacterial community in the WC and SWC are investigated in a simulated landfill systems with the contrast experiment of a landfill cover soil (LCS) for 60 days. Meanwhile, the adsorption-biodegradation of VOCs model compounds over the LCS, WC, and SWC are also tested in fixed-bed adsorption reactor and in-situ FTIR. The VOCs removal efficiencies by the SWC are maintained above 85% for a long-term, much higher than that of the LCS and WC. The higher removal efficiencies and long-term stability for VOCs degradation in SWC are attributed to a strongly positive synergistic between adsorption and biodegradation that the gaseous VOCs released from MSW is effectively adsorbed by the SWC due to its higher VOCs adsorption capacity, and then the adsorbed-VOCs is converted into CO₂ and H₂O by the microorganisms that consuming the adsorbed-VOCs as energy and carbon sources. Subsequently, the decrease of the adsorbed-VOCs in SWC would also promote the transformation of the gaseous VOCs into the adsorbed VOCs and accelerate the growth of microorganisms by taking the adsorbed-VOCs as the energy and carbon source, resulted in a higher adsorption rate and degradation rate for VOCs.

Crayfish shell biochar modified with magnesium chloride and its effect on lead removal in aqueous solution

In this study, crayfish shell was pyrolyzed at 600 °C to obtain an unmodified biochar (CS600). MgCl₂ was used as a modifier to pretreat crayfish shell to produce a modified biochar (CS600-MgCl₂) under the same pyrolysis conditions. The two biochars were characterized for physicochemical properties and evaluated for lead (Pb²⁺) sorption ability to determine the modification mechanism. Mono-element batch adsorption experiments were conducted to compare the sorption performances of CS600 and CS600-MgCl₂ to Pb²⁺ in aqueous solutions. All the experiments were carried out at pH of 7. According to the Freundlich-Langmuir model, CS600-MgCl₂ had a higher adsorption capacity (152.3 mg/g) than CS600 (134.3 mg/g). FTIR, SEM, XRD, BET, and ICP analyses were applied to inform the interpretation of the mechanism. CS600 was calcium-rich and mainly removed Pb²⁺ through the ion exchange mechanism by replacing Ca²⁺ in the biochar. The increased Pb²⁺ adsorption capacity of CS600-MgCl₂ was mainly due to the enlarged specific surface area and the formation of Mg₃(OH)₅Cl·4H₂O on the modified biochar. Findings of this study suggest that both CS600 and CS600-MgCl₂ can be used to remove heavy metal ions from wastewater and MgCl₂ can improve the sorption performance of biochar.

A Review of Non-Soil Biochar Applications

Biochar is the solid residue that is recovered after the thermal cracking of biomasses in an oxygen-free atmosphere. Biochar has been used for many years as a soil amendment and in general soil applications. Nonetheless, biochar is far more than a mere soil amendment. In this review, we report all the non-soil applications of biochar including environmental remediation, energy storage, composites, and catalyst production. We provide a general overview of the recent uses of biochar in material science, thus presenting this cheap and waste-derived material as a high value-added and carbonaceous source.

Activated carbon biochar from municipal waste as a sorptive agent for the removal of polyaromatic hydrocarbons (PAHs), phenols and petroleum based compounds in contaminated liquids

Wastewater (WW) sludge cake is problematic to dispose of with treatment unable to remove organic pollutants. Typical disposal options include landfill or deposition on agricultural land, at considerable expense and environmental impact. Pyrolysis can recycle this waste to biochar however, additional unwanted organic pollutants are generated, differing in composition and volume according to the feedstock. These pollutants can be captured in solvent impingers or 'scrubbers' to avoid environmental release but lead to alternative waste. Both activated carbon and biochar are proven clean-up methods for organic pollutants with pine wood biochar showing changes in extraction selectivity with preparation temperature. Activated carbon biochar (ACB) from pine wood has also been successfully compared as a substitute at reduced cost and improved efficacy. To our knowledge, ACB from sludge cake has remained untested along with its application to clean-up solvent scrubbers. We have investigated this material from two WW treatment plants (UK and Ghana) as a sorbent, generated at 400 and 700 °C, to minimise contamination of liquids from pyrolysis and, petrochemicals in the event of a spill. This study confirmed the use and selective production of ACB for preferential clean-up of specific pollutants. Despite high temperature pine wood ACB proving most effective in removing petrochemical mixtures (>76%) extractions of equivalent repeatability and reasonable recovery were achieved with low temperature sludge cake ACB. This re-use of waste sludge cake offers improved thermochemical (recycling) and WW process efficiency, limiting the environmental impact and overall operational costs, minimising waste for disposal.

Removal of Arsenic(III) from water using magnetite precipitated onto Douglas fir biochar

Magnetic Fe₃O₄/Douglas fir biochar composites (MBC) were prepared with a 29.2% wt. Fe₃O₄ loading and used to treat As(III)-contaminated water. Toxicity of As(III) (inorganic) is significantly greater than As(V) and more difficult to remove from water. Removal efficiency was optimized verses pH, contact time and initial concentration. Column sorption and regeneration were also studied. Adsorption kinetics data best fitted the pseudo second order model (R² > 0.99). Adsorption was analyzed with three isotherm models at 20, 25 and 40 °C. The Sips isotherm showed the best fit at 25 °C with a 5.49 mg/g adsorption capacity, which is comparable with other adsorbents. MBC gave faster kinetics (~1-1.5 h) at pH 7 and ambient temperature than previous adsorbents. The Gibbs free energy (ΔG) of this spontaneous As(III) adsorption was -35 kJ/mol and ΔH = 70 kJ/mol was endothermic. Experiments were performed on industrial and laboratory wastewater samples in the presence of other co-existing contaminants (pharmaceutical residues, heavy metals ions and oxi-anions). The composite reduced the arsenic concentrations below the WHO's safe limit of 0.2 mg/L for waste water discharge. X-ray photoelectron spectroscopy (XPS) studies found As(III) and less toxic As(V) on Fe₃O₄ surfaces indicating adsorbed (or adsorbing) As(III) oxidation occurred upon contact with O₂ and possibly dissolved Fe(III) or upon drying under oxic conditions. Under anoxic conditions magnetite to maghemite transformation drives the oxidation. A pH-dependent surface chemisorption mechanism was proposed governing adsorption aided by XPS studies vs pH.

Editorial: Technically-based use of by-products as a tool to control pollution

This Virtual Special Issue of Journal of Environmental Management dealt with the recycling of waste and by-products, focusing on their use in controlling environmental pollution. The field of research was previously considered as promising, in view of its relevance and the increasing number of papers published in last years. And this Special Issue allows going a step ahead in the matter, with 90 submissions and a number of 48 high quality papers finally accepted and published. We think that it will be useful at a global level, especially for researchers, social partners, and social actors involved in environmental and public health issues related to environmental pollution.

The influence of three acid modifications on the physicochemical characteristics of tea-waste biochar pyrolyzed at different temperatures: a comparative study

Tea-waste biochar produced under different pyrolysis temperatures were subjected to three acid modifications and a comparative evaluation of their key physicochemical characteristics made.