Microwave-assisted regeneration of activated carbon

Coupling physiochemical adsorption with biodegradation for enhanced removal of microcystin-LR in water

To innovate the design of water treatment technology for algal toxin removal, this research investigated the mechanisms of cyanotoxin microcystin-LR (MC-LR) removal by a coupled adsorption-biodegradation. Eight types of woody carbonaceous adsorbents with and without Sphingopyxis sp. m6, a MC-LR degrading bacterium, were tested for MC-LR removal in water. All adsorbents showed good adsorption capability, removing 40 % to almost 100 % of the MC-LR (4.5 mg/L) within 48 h in batch experiments. Adding Sphingopyxis sp. m6 continuously promoted MC-LR biological removal, and successfully broke the barrier of adsorption capacity of tested adsorbents, removing >90 % of the MC-LR in most of the coupled adsorption-biodegradation tests, especially for those adsorbents had low physiochemical adsorption capacity. Variance partitioning analysis indicated that mesopore was the dominant contributor to adsorption capacity of MC-LR in pure adsorption treatments, which acted synergistically with electrical conductivity, polarity and total functional groups on the absorbent. Pore structure was the key factor beneficial for the growth of Sphingopyxis sp. m6 (51% contribution) and subsequent MC-LR biological removal rate (80 % contribution). Overall, pinewood-based carbonaceous adsorbents (especially pinewood activated carbon) exhibited the highest adsorption capacity towards MC-LR and provided the most favorable conditions for biological removal of MC-LR, largely because of their high mesopore volume, total functional groups and electric conductivity. The research outcomes not only deepened the quantitative understanding of mechanisms for MC-LR removal by the coupled process, but also provided theoretical basis for future materials' selection and modification during the practical application of coupled process.

Regeneration of dye-saturated activated carbon through advanced oxidative processes: A review

Activated carbon (AC) is a porous carbon-rich material that is widely used to remove pollutants, such as synthetic dyes, from contaminated water. Although quite efficient, the use of this technology is limited to the ability of the AC to be regenerated and/or reused. Conventional regeneration procedures are inefficient, requiring the development and/or implementation of new approaches. Advanced Oxidative Processes (AOP) have unique properties that result in high efficiency in wastewater treatment. The use of these technologies in the regeneration of AC has gained considerable prominence due to the ability to remove organic pollutants concentrated in the AC. During this process, the oxidizing species produced interact with the substrates adsorbed on the AC, in a non-selective way, mineralizing them and/or reducing their recalcitrance. Although widely used in wastewater treatment, few reviews focus on the use of AOP as AC regeneration technology, causing an insufficient exchange of information and ideas for strategic development in this area. Therefore, in this review, the authors present an overview of the use of some AOP (Photolysis, Peroxidation, Fenton reaction and Advanced electrochemical oxidative processes) when applied in regeneration of dye-saturated AC, including the mechanisms involved in the different processes, the general aspects that affect individual processes and the different methods established to quantify the effectiveness of regeneration.

Efficient remediation of antibiotic pollutants from the environment by innovative biochar: current updates and prospects

The increased antibiotic consumption and their improper management led to serious antibiotic pollution and its exposure to the environment develops multidrug resistance in microbes against antibiotics. The entry rate of antibiotics to the environment is much higher than its exclusion; therefore, efficient removal is a high priority to reduce the harmful impact of antibiotics on human health and the environment. Recent developments in cost-effective and efficient biochar preparation are noticeable for their effective removal. Moreover, biochar engineering advancements enhanced biochar remediation performance several folds more than in its pristine forms. Biochar engineering provides several new interactions and bonding abilities with antibiotic pollutants to increase remediation efficiency. Especially heteroatoms-doping significantly increased catalysis of biochar. The main focus of this review is to underline the crucial role of biochar in the abatement of emerging antibiotic pollutants. A detailed analysis of both native and engineered biochar is provided in this article for antibiotic remediation. There has also been discussion of how biochar properties relate to feedstock, production conditions and manufacturing technologies, and engineering techniques. It is possible to produce biochar with different surface functionalities by varying the feedstock or by modifying the pristine biochar with different chemicals and preparing composites. Subsequently, the interaction of biochar with antibiotic pollutants was compared and reviewed. Depending on the surface functionalities of biochar, they offer different types of interactions e.g., π-π stacking, electrostatic, and H-bonding to adsorb on the biochar surface. This review demonstrates how biochar and related composites have optimized for maximum removal performance by regulating key parameters. Furthermore, future research directions and opportunities for biochar research are discussed.

Ultrasound and microwave-assisted recycling of spent mercuric chloride catalyst

It is urgent to develop a high-efficient process for recycling the spent mercuric chlorides catalyst (SMC) from vinyl chloride monomer (VCM) production with the implementation of the 'Minamata Convention on mercury'. A ultrasound and microwave-assisted technology were developed to treat SMC in this study. Firstly, organic carbon deposition was separated from SMC by pretreatment (ultrasonic-assisted ethanol extraction). The optimized extraction conditions were: ultrasonic time 2 h, ultrasonic power 700 W, extraction temperature 65°C, and liquid-solid ratio 7:1. Under these conditions, 90% of hazardous Cl-containing organics were separated from SMC. Then the pretreated SMC was treated by microwave heating for mercury removal. Residual mercury concentration of SMC decreased from original 1.33% to only 11.92 mg/kg at the preferred conditions of 500°C for 60 min and the treated SMC passed the Toxicity Characteristics Leaching Procedure (TCLP) test. Simultaneously, catalyst support activated carbon (AC) was regenerated with specific surface area increasing from original 263.85 to 627.5 m²/g. The organics from macropores and surface of AC was removed by pretreatment, intensifying the subsequent Hg removal and regeneration of AC as revealed by the comparative studies. Finally, SMC was subjected to water leaching for recovering metal values. 88.7% of Ba and 95.3% of Ce were leached with ultrasonic power 500 W and ultrasonic time 120 min. SMC was detoxified and valuable components Hg, AC, Ba, Ce were recovered by this new process, which may provide a new idea for industrial treatment of SMC.

Effects of different feedstocks-based biochar on soil remediation: A review

As a promising amendment, biochar has excellent characteristics and can be used as a remediation agent for diverse types of soil pollution. Biochar is mostly made from agricultural wastes, forestry wastes, and biosolids (eg, sewage sludge), but not all the biochar has the same performance in the improvement of soil quality. There is a lack of guidelines devoted to the selection of biochar to be used for different types of soil pollution, and this can undermine the remediation efficiency. To shed light on this sensitive issue, this review focus on the following aspects, (i) how feedstocks affect biochar properties, (ii) the effects of biochar on heavy metals and organic pollutants in soil, and (iii) the impact on greenhouse gas emissions from soil. Generally, the biochars produced from crop residue and woody biomass which are composed of lignin, cellulose, and hemicellulose are more suitable for organic pollution remediation and greenhouse gas emission reduction, while biochar with high ash content are more suitable for cationic organic pollutant and heavy metal pollution (manure and sludge, etc.). Additionally, the effect of biochar on soil microorganisms shows that gram-negative bacteria in soil tend to use WB biochar with high lignin content, while biochar from OW (rich in P, K, Mg, and other nutrients) is more able to promote enzyme activity. Finally, our recommendations on feedstocks selection are presented in the form of a flow diagram, which is precisely intended to be used as a support for decisions on the crucial proportioning conditions to be selected for the preparation of biochar having specific properties and to maximize its efficiency in pollution control.

Biochar derived from fruit by-products using pyrolysis process for the elimination of Pb(II) ion: An updated review

Water pollution is one of the most concerning global environmental problems in this century with the severity and complexity of the issue increases every day. One of the major contributors to water pollution is the discharge of harmful heavy metal wastes into the rivers and water bodies. Without proper treatment, the release of these harmful inorganic waste would endanger the environment by contaminating the food chains of living organisms, hence, leading to potential health risks to humans. The adsorption method has become one of the cost-effective alternative treatments to eliminate heavy metal ions. Since the type of adsorbent material is the most vital factor that determines the effectiveness of the adsorption, continuous efforts have been made in search of cheap adsorbents derived from a variety of waste materials. Fruit waste can be transformed into valuable products, such as biochar, as they are composed of many functional groups, including carboxylic groups and lignin, which is effective in metal binding. The main objective of this study was to review the potential of various types of fruit wastes as an alternative adsorbent for Pb(II) removal. Following a brief overview of the properties and effects of Pb(II), this study discussed the equilibrium isotherms and adsorption kinetic by various adsorption models. The possible adsorption mechanisms and regeneration study for Pb(II) removal were also elaborated in detail to provide a clear understanding of biochar produced using the pyrolysis technique. The future prospects of fruit waste as an adsorbent for the removal of Pb(II) was also highlighted.

Surface Modified Activated Carbons: Sustainable Bio-Based Materials for Environmental Remediation

Global warming and water/air contamination caused by human activities are major challenges in environmental pollution and climate change. The improper discharge of a large amount of agro-forest byproduct is accelerating these issues mainly in developing countries. The burning of agricultural byproducts causes global warming, whereas their improper waste management causes water/air pollution. The conversion of these waste materials into effective smart materials can be considered as a promising strategy in waste management and environmental remediation. Over the past decades, activated carbons (ACs) have been prepared from various agricultural wastes and extensively used as adsorbents. The adsorption capacity of ACs is linked to a well-developed porous structure, large specific surface area, and rich surface functional moieties. Activated carbon needs to increase their adsorption capacity, especially for specific adsorbates, making them suitable for specific applications, and this is possible by surface modifications of their surface chemistry. The modifications of surface chemistry involve the introduction of surface functional groups which can be carried out by various methods such as acid treatment, alkaline treatment, impregnation, ozone treatment, plasma treatment, and so on. Depending on the treatment methods, surface modification mainly affects surface chemistry. In this review, we summarized several modification methods for agricultural-waste-based ACs. In addition, the applications of AC for the adsorption of various pollutants are highlighted.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.

Microwave Irradiation in Technologies of Wastewater and Wastewater Sludge Treatment: A Review

Every year, the human impact on the world’s water sources becomes more pronounced. One of the triggers to this increase is the use of ineffective wastewater and sludge treatment systems. Recently, the number of studies of microwave processing in handling liquid municipal and industrial waste has increased. This paper discusses heat treatment, change in properties, decomposition of substances, removal of metals, demulsification, pyrolysis, biogas processing, disinfection, and other topics. The findings of European, Chinese, Russian, and other authors are summarised and presented in this review. In addition, the most notable Russian patents for microwave installations/devices and reactors suitable for a wide variety of applications are discussed. In this article, the authors look at microwave wastewater and sludge treatment from the perspective of practical application in various fields of human economic activity.

Microwave based regenerating permeable reactive barriers (MW-PRBs): Proof of concept and application for Cs removal

The present study evaluates the concept of permeable reactive barrier (PRB) coupled with microwaves (MWs) as in situ-regenerating technology with focus on Cs-contaminated water. Experimental and modelling results data from batch and column tests were carried out, evaluating several chemical-physical and environmental parameters. Main results showed a very rapid increase in GAC temperature during MW irradiation up to ∼680 °C. This highlights the GAC strong ability to transform MW power into heat due to GAC excellent dielectric properties (ε' = 13.8). Physical characterization revealed that GAC pore volume and specific surface area change with the number of regeneration cycles. GAC regeneration efficiency variation reflects this behaviour with a maximum value of ∼112% (5th cycle). The final GAC weight loss of ∼7% further demonstrates GAC life span preservation during MW irradiation. Results from column tests confirms that GAC can be regenerated by MW also in dynamic condition, due to sublimation/vaporization and vapour stripping Cs removal mechanisms and that the regeneration effectiveness is time-dependent. The breakthrough curve shape confirms significant benefits from MW irradiation. Overall, obtained finding demonstrated the feasibility of the proposed concept, also providing essential data to guide its scaling-up application.

Comprehending adsorption of methylethylketone and toluene and microwave regeneration effectiveness for beaded activated carbon derived from recycled waste bamboo tar

Beaded activated carbons (BACs) were derived from waste bamboo tar through carbonization (500°C for 2 hr) followed by physical activation using carbon dioxide (800-900°C for 2-4 hr). The adsorbent was examined for their physical and chemical properties, adsorption capacities toward methylethylketone (MEK) and toluene, and regenerabilities under microwave heating. It was found that the maximum total surface area reached for bamboo-tar-derived BAC after physical activation was 1364 m² g^-1, and more than 95% of the area was attributed to the microporous structures. Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models were applied to the adsorption isotherm fitting, and the minimum R² for each model was 0.986, 0.915, and 0.943, respectively. The isosteric heats of adsorption calculated based on D-R parameters for methylethylketone and toluene were 44.04 to 51.50 and 45.88 to 73.27 KJ mol^-1, respectively. They were slightly over the range of physisorption and increased with adsorbate loading, which might be related to the micropore filling mechanism. Microwave regeneration under 600 W of power output removed most of the adsorbate (>93.03%) within 8 min. The results of this study are intended to benefit future study on waste-derived adsorbent in environmental applications.

IMPLICATIONS

Recycling waste bamboo tar for the novel adsorbent preparation is shown feasible in this study. Beaded activated carbon (BAC) synthesized from this waste bamboo tar possessed a high specific surface area, which aided in the capturing of volatile organic compounds (VOCs). Three adsorption isotherms, Langmuir, Freundlich, Dubinin-Radushkevich (D-R) models can be applied in interpreting the experimental adsorption data, providing information on adsorption heat and possible adsorption mechanism. A potential microwave regeneration method for BAC is tested, showing high desorption efficiencies with minimum heel formation. These findings can provide a new pathway for waste bamboo tar management and VOC abatement using adsorbents.

Aragón-Tobar C, Gámez S, de la Torre E. Reactivation Process of Activated Carbons: Effect on the Mechanical and Adsorptive Properties

Carbon reactivation is a strategy to reduce waste and cost in many industrial processes, for example, effluent treatment, food industry, and hydrometallurgy. In this work, the effect of physical and chemical reactivation of granular activated carbon (AC) was studied. Spent activated carbon (SAC) was obtained from a carbon in pulp (CIP) leaching process for gold extraction. Chemical and physical reactivations were evaluated using several acid-wash procedures (HCl, HNO₃, H₂SO₄) and thermal treatment (650–950 °C) methods, respectively. The effect of the reactivation processes on the mechanical properties was evaluated determining ball pan hardness and normal abrasion in pulp resistance. The effect on the adsorptive properties was evaluated via the iodine number, the gold adsorption value (k expressed in mg Au/g AC), and Brunauer–Emmett–Teller (BET) surface area. Initial characterization of the SAC showed an iodine number of 734 mg I₂/g AC, a k value of 1.37 mg Au/g AC, and a BET surface area of 869 m²/g. The best reactivation results of the SAC were achieved via acid washing with HNO₃ at 20% v/v and 50 °C over 30 min, and a subsequent thermal reactivation at 850 °C over 1 h. The final reactivated carbon had an iodine number of 1199 mg I₂/g AC, a k value of 14.9 mg Au/g AC, and a BET surface area of 1079 m²/g. Acid wash prior to thermal treatment was critical to reactivate the SAC. The reactivation process had a minor impact (<1% change) on the mechanical properties of the AC.

Graphene-based materials production and application in textile wastewater treatment: color removal and phytotoxicity using Lactuca sativa as bioindicator

The dyes used in textile industries are usually difficult to degrade in aquatic environments, being highly toxic to micro fauna and flora. Thus, textile wastewater treatments have been developed, among them, one that stands out is adsorption process. With the rise of nanomaterials applied to adsorption, graphene oxide (GO) shows promise in the removal of dyes. This work aimed to produce a more economical and environmentally friendly GO by reducing H2SO4 concentration during the synthesis. Adsorption tests were performed with methylene blue (MB) and brilliant blue (BB), adsorbent regeneration tests, as well as a kinetic study using real wastewater, and toxicological assays with lettuce seeds. Results showed that the sample produced with less H2SO4 (GO-21) performed better for MB (99% removal) and BB (29% removal); and recycling test showed that despite the decrease in removal efficiency, it remained high in the first cycles. Kinetics showed that equilibrium was reached in 30 min, removing 67.43% of color and 90.23% of the effluent's turbidity. Phytotoxicity assays indicated that the wastewater treated with GO-21 was the least toxic, compared to other wastewater samples analyzed. Therefore, GO has demonstrated its potential to be an effective and less toxic option to treat textile effluents.[Formula: see text].

An overview of chlorophenols as contaminants and their removal from wastewater by adsorption: A review

In this review article, a significant number of published articles (over three decades) were consulted in order to provide comprehensive literature information about chlorophenols, their sources into the environment, classification, and toxicity, various wastewater treatment methods for their removal as well as the characteristics of their adsorption by various adsorbents. Organizing the scattered available information on a wide range of potentially effective adsorbents in the removal of chlorophenols is the principal objective of this article. Various adsorbents such as natural materials, waste materials from industries, agricultural by-products and biomass-based activated carbon in the removal of various chlorophenols have been compiled and discussed here. Crucial factors like temperature, solution pH, contact time and initial solution concentration are also reported and discussed here. The π-π dispersion interaction mechanism, hydrogen bonding formation mechanism, and the electron donor-acceptor complex mechanism were proposed for the chlorophenols adsorption onto various adsorbents with the help of current literature. Conclusions have been drawn proposing a few suggestions for future research on mitigating the effect of chlorophenols in the environment.

The adsorption, regeneration and engineering applications of biochar for removal organic pollutants: A review

In recent years, with the continuous development of industry and agriculture, the content of organic pollutants in the environment has been increasing, which has caused serious pollution to the environment. Adsorption has proven to be an effective and economically viable method of removing organic contaminants. Since biochar has many advantages such as various types of raw materials, low cost, and recyclability, it can achieve the effect of turning waste into treasure when used for environmental treatment. This paper summarizes the source and production of biochar, points out its research status in the removal of organic pollutants, expounds its adsorption mechanism on organic pollutants, introduces the relevant adsorption parameters, summarizes its regeneration methods, studies its application of engineering, and finally analyses of benefits and describes the development prospects.

Preparation and analysis of straw activated carbon synergetic catalyzed by ZnCl2-H3PO4 through hydrothermal carbonization combined with ultrasonic assisted immersion pyrolysis

In this paper, wheat straw (WS), corn straw (CS) and sorghum straw (SS) were used as raw materials. ZnCl₂ and H₃PO₄ were used as catalysts. Hydrothermal carbonization combined with pyrolysis were used to co-activate with the ultrasonic auxiliary impregnation method in order to prepare straw activated carbon (SAC). Methylene blue adsorption value and iodine value were used as the main evaluation index to optimize the process conditions. The activation process was analyzed and the optimum preparation conditions were obtained. The results showed that it was feasible to combine hydrothermal carbonization with ultrasonic assisted immersion pyrolysis using ZnCl₂ and H₃PO₄ as catalysts for preparing SAC. WS, CS and SS showed similar characteristics in the preparation of SAC. The best preparation conditions of hydrothermal temperature and the impregnation ratio of ZnCl₂ were 200 °C and 2:1. The optimum pyrolysis condition was at a heating rate of 5 °C/min and an impregnation ratio of H₃PO₄ equal to 2:1 with 1 h of pyrolysis at 500 °C. The temperature and time of ultrasonic auxiliary conditions were 40 °C and 30 min. For WSHUPC, CSHUPC and SSHUPC, the MB adsorption values were 165, 166 and 164 mg/g and the iodine values reached 764, 725 and 701 mg/g. It was demonstrated the three kinds of straws were highly efficient precursor for the preparation of activated carbon used to remove dyes from wastewater. The preparation method in this study combines the advantages of physical and chemical activation.

A review on activated carbon adsorption for volatile organic compounds (VOCs)

A number of control methods have been adopted for the removal of hazardous volatile organic compounds (VOCs) from gas streams, particularly adsorption processes which are considered more prominent in terms of feasibility, effectiveness as well as cost competence compared to other methods. In this study, most of the activated-carbon-based adsorbents are critically reviewed in terms of their advantages and limitations for VOC gas adsorption. The choice of adsorbent and process parameters depends mainly on the type of VOC used, its chemical and structural properties, in addition to the adsorbent’s characteristics. The review discusses in detail the application of fixed-bed adsorption systems. A computational simulation study using quantum-chemical conductor like screening model for real solvents is included in this review which determines the efficiency in describing and predicting the adsorption technique required for each process. This review offers a comprehensive discussion of the VOC adsorption techniques and their implementation for different applications.

In-situ regeneration of activated carbon with electric potential swing desorption (EPSD) for the H2S removal from biogas

In-situ regeneration of a granular activated carbon was conducted for the first time using electric potential swing desorption (EPSD) with potentials up to 30 V. The EPSD system was compared against a standard non-potential system using a fixed-bed reactor with a bed of 10 g of activated carbon treating a gas mixture with 10,000 ppm H₂S. Breakthrough times, adsorption desorption volume, capacities, effect of regeneration and desorption kinetics were investigated. The analysis showed that desorption of H₂S using the new EPSD system was 3 times quicker compared with the no potential system. Hence, physical adsorption using EPSD over activated carbon is efficient, safe and environmental friendly and could be used for the in-situ regeneration of granular activated carbon without using a PSA and/or TSA system. Additionally, adsorption and desorption cycles can be obtained with a classical two column system, which could lead towards a more efficient and economic biogas to biomethane process.

Effect and mechanism of microwave-activated ultraviolet-advanced oxidation technology for adsorbent regeneration

To decrease the secondary pollution of volatile organic compounds (VOCs) during adsorbent regeneration by microwave, electrodeless lamp was added in the microwave field to oxidize VOCs in the gas phase. Ultraviolet has a significant improvement on mineralization of VOCs generated from adsorbate during adsorbent regeneration. However, the mechanism and main influence factors on the degradation of VOCs are not clear. The effect of microwave power, regeneration time, airflow rate, and humidity content on the mineralization of adsorbed tetracycline during adsorbent regeneration was studied. Ozone concentration and ultraviolet irradiation intensity were also measured to analyze the mechanism of the microwave-ultraviolet adsorbent regeneration method. Although the electrodeless lamp adsorbed microwave and competed with the regenerated adsorbent, the mineralization percentage of tetracycline increased about 10% with the presence of electrodeless lamp at the same microwave power supply. Besides, humidity content also takes an important role on enhancing the mineralization of tetracycline. The mineralization of tetracycline in the microwave-ultraviolet field consists of three major parts: pyrolysis, ozone oxidation, and free radical oxidation. More than 50% adsorbed tetracycline can be oxidized into H₂O and CO₂ during regeneration in 5 min. These results support the potential use of electrodeless lamp to treat VOCs in the gas phase to decrease the risk of secondary pollution during adsorbent regeneration.

High temperature dielectric properties of spent adsorbent with zinc sulfate by cavity perturbation technique

Dielectric properties of spent adsorbent with zinc sulfate are investigated by cavity perturbation technique at 2450MHz from 20°C to approximately 1000°C. Two weight loss stages are observed for spent adsorbent by thermogravimetric-differential scanning calorimeter (TG-DSC) analysis, and zinc sulfate is decomposed to ZnO·2ZnSO₄ and ZnO at about 750°C and 860°C. Microwave absorption capability of ZnSO₄ increases with increasing temperature and declines after ZnO generation on account of the poor dielectric properties. Dielectric properties of spent adsorbent are dependent on apparent density and noticed an interestingly linearly relationship at room temperature. The three parameters increase gently from 20°C to 400°C, but a sharp increase both in real part and imaginary part are found subsequently due to the volatiles release and regeneration of carbon. And material conductivity is improved, which contributes to the π-electron conduction appearance. Relationship between penetration depth and temperature further elaborate spent adsorbent is an excellent microwave absorber and the microwave absorption capability order of zinc compounds is ZnO·2ZnSO₄, ZnSO₄ and ZnO. Heating characteristics suggest that heating rate is related with dielectric properties of materials. The pore structures of spent adsorbent are improved significantly and the surface is smoother after microwave-regeneration.

A review: Potential and challenges of biologically activated carbon to remove natural organic matter in drinking water purification process

The use of biologically activated carbon (BAC) in drinking water purification is reviewed. In the past BAC is seen mostly as a polishing treatment. However, BAC has the potential to provide solution to recent challenges faced by water utilities arising from change in natural organic matter (NOM) composition in drinking water sources - increased NOM concentration with a larger fraction of hydrophilic compounds and ever increasing trace level organic pollutants. Hydrophilic NOM is not removed by traditional coagulation process and causes bacterial regrowth and increases disinfection by-products (DBPs) formation during disinfection. BAC can offer many advantages by removing hydrophilic fraction and many toxic and endocrine compounds which are not otherwise removed. BAC can also aid the other downstream processes if used as a pre-treatment. Major drawback of BAC was longer empty bed contact time (EBCT) required for an effective NOM removal. This critical review analyses the strategies that have been adopted to enhance the biological activity of the carbon by operational means and summarises the surface modification methods. To maximize the benefit of the BAC, a rethink of current treatment plant configuration is proposed. If the process can be expedited and adopted appropriately, BAC can solve many of the current problems.

Microwave Reactor Concepts: From Resonant Cavities to Traveling Fields

Microwave chemistry has been investigated for nearly thirty years with many notable results being published on apparent process enhancement due to microwave exposure. Conclusive proof of beneficial microwave-chemical interactions is lacking though, as are design rules for successful implementation of microwave-chemical processing systems. In this chapter, the main cause for this is asserted to be the current absence both of suitable instrumentation for research, and processing equipment that merges chemistry with electromagnetic aspects. Several concepts are presented to show how these challenges may be addressed.

Microwave regeneration of phenol-loaded activated carbons obtained from Arundo donax and waste fiberboard

A study was performed for the microwave regeneration of Arundo donax activated carbon (ADAC) and waste fiberboard activated carbon (WFAC) loaded with phenol.

Microwave regeneration of spent activated carbon for the treatment of ester-containing wastewater

In this study, an integrated granular activated carbon (GAC) adsorption/microwave (MW) irradiation process was used for the treatment of ester-containing wastewater from a lithium-ion battery (LIB) factory.

The effects of microwave regeneration on adsorptive performance of functionalized carbon nanotubes

In this study, the microwave regeneration method was applied to investigate the properties and adsorptive performance of functionalized carbon nanotubes (f-CNTs) in different cycles of regeneration/reuse. For this purpose, an organic and hazardous dye (Reactive Blue 19) was chosen as a widely used pollutant. N2 adsorption/desorption isotherms, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize f-CNTs during the regeneration/reuse procedure. The morphology, specific surface area and pore volume of f-CNT samples were not significantly altered. However, the functional groups present on the f-CNTs' surface were gradually removed after successive cycles of regeneration/reuse. A sudden decrease of adsorption capacity (about 20%) after the first cycle of regeneration/reuse was attributed to the elimination of functional groups interacting with the dye molecules because of the molecular-level heating. Relatively high regeneration efficiencies (73.30 to 80.16%) proved that the microwave regeneration method was successful. Very high step stripping efficiencies (80.16 to 98.02%) in four cycles of regeneration/reuse demonstrated that the microwave regeneration method could be utilized in consecutive cycles. After four cycles of regeneration/reuse, the CNTs could not be considered as functionalized.

Physicochemical and porosity characteristics of thermally regenerated activated carbon polluted with biological activated carbon process

The characteristics of thermally regenerated activated carbon (AC) polluted with biological activated carbon (BAC) process were investigated. The results showed that the true micropore and sub-micropore volume, pH value, bulk density, and hardness of regenerated AC decreased compared to the virgin AC, but the total pore volume increased. XPS analysis displayed that the ash contents of Al, Si, and Ca in the regenerated AC respectively increased by 3.83%, 2.62% and 1.8%. FTIR spectrum showed that the surface functional groups of virgin and regenerated AC did not change significantly. Pore size distributions indicated that the AC regeneration process resulted in the decrease of micropore and macropore (D>10 μm) volume and the increase of mesopore and macropore (0.1 μm<D<10 μm) volume in regenerated AC, which are benefit for water treatment. These results will provide a theoretical basis for the reuse of biological waste (spent AC) from BAC process.

Effects of microwave heating on porous structure of regenerated powdered activated carbon used in xylose

The regeneration of spent powdered activated carbons used in xylose decolourization by microwave heating was investigated. Effects of microwave power and microwave heating time on the adsorption capacity of regenerated activated carbons were evaluated. The optimum conditions obtained are as follows: microwave power 800W; microwave heating time 30min. Regenerated activated carbon in this work has high adsorption capacities for the amount of methylene blue of 16 cm3/0.1 g and the iodine number of 1000.06mg/g. The specific surface areas of fresh commercial activated carbon, spent carbon and regenerated activated carbon were calculated according to the Brunauer, Emmett and Teller method, and the pore-size distributions of these carbons were characterized by non-local density functional theory (NLDFT). The results show that the specific surface area and the total pore volume of regenerated activated carbon are 1064 m2/g and 1.181 mL/g, respectively, indicating the feasibility of regeneration of spent powdered activated carbon used in xylose decolourization by microwave heating. The results of surface fractal dimensions also confirm the results of isotherms and NLDFT.

Utilization of oil palm biodiesel solid residue as renewable sources for preparation of granular activated carbon by microwave induced KOH activation

In this work, preparation of granular activated carbon from oil palm biodiesel solid residue, oil palm shell (PSAC) by microwave assisted KOH activation has been attempted. The physical and chemical properties of PSAC were characterized using scanning electron microscopy, volumetric adsorption analyzer and elemental analysis. The adsorption behavior was examined by performing batch adsorption experiments using methylene blue as dye model compound. Equilibrium data were simulated using the Langmuir, Freundlich and Temkin isotherm models. Kinetic modeling was fitted to the pseudo-first-order, pseudo-second-order and Elovich kinetic models, while the adsorption mechanism was determined using the intraparticle diffusion and Boyd equations. The result was satisfactory fitted to the Langmuir isotherm model with a monolayer adsorption capacity of 343.94mg/g at 30°C. The findings support the potential of oil palm shell for preparation of high surface area activated carbon by microwave assisted KOH activation.