Performance and mechanism of low-frequency ultrasound to regenerate the biological activated carbon

Effects of low frequency ultrasound treatment on dissolved organic nitrogen removal by biological activated carbon: Critical insights into molecular characteristics, microbial traits, and metabolism

Drinking water treatment plants (DWTPs) in China that pioneered the biological activated carbon (BAC) process have reached 10 years of operation. There has been a renewed focus on biofiltration and the performance of old BAC filters for dissolved organic nitrogen (DON) has been poor, requiring replacement and regeneration of the BAC. Therefore, it is necessary to explore a cost-effective way to improve the water quality of the old BAC filters. To address this, low frequency ultrasound is proposed to enhance DON removal efficiency by BAC. In this study, bench and pilot tests were conducted to investigate the effect of low frequency ultrasound on DON removal by 10-year BAC. The results indicated that low frequency ultrasound significantly improved the DON removal rate increased from 15.83 % to 85.87 % and considerably inhibited the nitrogenous disinfection by-products (N-DBPs) formation potential, which was attributed to a decrease in the production of lipid-like, carbohydrate-like, and protein/amino sugar-like DON. The biomass on the BAC was significantly reduced after ultrasound treatment, and it decreased from 349.56∼388.98 nmol P/gBAC to 310.12∼377.63 nmol P/gBAC, enabling the biofilm thickness to decrease and the surface to become sparse and porous, which was conducive to oxygen and nutrients transfer. The Rhizobials associated with microbe-derived DON were stripped away during ultrasound treatment, which reduced microbe-derived DON associated with amino acids. Additionally, ultrasound regulated metabolic pathways, including amino acids, tricarboxylic acid (TCA) cycle, and nucleotide metabolism, to improve the osmotic pressure of the biofilm. In short, low frequency ultrasound treatment can enhance BAC biological properties and effectively remove DON and N-DBPs formation potentials, which provides a viable and promising strategy for improving the safety of drinking water in practice.

Study on regeneration characteristics of granular activated carbon using ultrasonic and thermal methods

Dye wastewater is a type of high-concentration, high chromaticity, and high salinity organic wastewater, which is generally treated with activated carbon adsorbent. The effective regeneration of granular activated carbon (GAC) is the key to reducing the operating cost of GAC in the wastewater treatment process. The regeneration characteristics of saturated GAC adsorbed on 288 orange dye wastewater were studied by using the ultrasonic coupled thermal regeneration method. The results showed that the regeneration efficiency of GAC adsorbed on 288 orange dye wastewater increased with the increase of ultrasound power. The optimal ultrasound frequency and regeneration temperature were determined to be 45 kHz and 60 ℃, and the relationship between regeneration times and carbon loss rate was explored. The combination of ultrasound and high-temperature heating methods has successfully improved the regeneration efficiency of GAC and significantly reduced the high-temperature thermal regeneration time of GAC, thereby reducing the mass loss rate of GAC. The performance changes of fresh activated carbon (FAC), saturated activated carbon (SAC), ultrasonic regeneration of activated carbon (UAC), and thermal regeneration of activated carbon (TAC) during the combined regeneration process were explored by characterizing the regenerated GAC. Infrared characterization showed that the C-O group of GAC was significantly weakened after coupling treatment, indicating that ultrasonic treatment can significantly enhance the desorption effect of thermal regeneration. The microjet, shock wave, and cavitation effects generated by ultrasonic treatment restore the specific surface area of GAC, mainly increasing the micropore volume and pore size of GAC, and enhancing the treatment effect of thermal regeneration.

Insight into the temporal dynamics of microbial succession and ecology mechanisms in biological activated carbon tanks

Biological activated carbon (BAC) has long been applied in China to guarantee water quality and to achieve drinking water regulations. However, a knowledge gap remains regarding the temporal dynamics of microbial communities, particularly microbe-based assembly and co-occurrence patterns. Accordingly, this study investigated the evolution of BAC microbial communities using a pilot-scale system and examined by multivariate ecological combined with high-throughput Illumina sequencing and statistical methods. The results showed that BAC microbial diversity reached its peak in 2 years and declined thereafter. Microbial communities composition was accompanied by significant temporal evolution in the BAC biofilm. Deterministic processes gained in importance along with time, especially homogeneous selection which contributed 59.09 %-75.63 % to the community assembly in 8-yr, 9-yr, and 10-yr BAC. According to co-occurrence network analysis, microbial networks have more unstable structures over time, as evidenced by higher modularity, heightened connectivity, and fewer keystones. Moreover, the interaction between microbial taxa tended to have a higher proportion of competitive relationships during the operation of the BAC tank, ranging from 13.51 % to 76.35 %. Based on these dynamic ecological processes, microbial community succession in BAC biofilm might undergo four phases: community establishment (Years 0-2); community stability (Years 2-5); community quasi-degradation (Years 5-8); community degradation (Years 8-10). The performance of BAC was greatly influenced by community development, and contaminant removal gradually decreased as community succession proceeded. These results add to our knowledge of microbial ecology and provide the basis for further research into microbial communities' regulation strategies in BAC tanks.

Removal of highly concentrated methylene blue dye by cellulose nanofiber biocomposites

The contamination of water by dyes in high concentrations is a worldwide concern, and it has prompted the development of efficient, economical, and environmentally friendly materials and technologies for water purification. The hydration and adsorption capacity for methylene blue (MB) in biocomposites (BCs) based on cellulose nanofiber (CNF) (0 to 2 wt%) were studied. BCs were synthesized through a simple and straightforward route and characterized by spectroscopy, microscopic techniques and thermogravimetric analysis, among others. Hydration studies showed that BCs prepared with 2 wt% of CNF can absorb large volumes of water, approximately 2274 % in the case of poly 2-acrylamide-2-methyl-1-propanesulfonic acid (PAMPS)-CNF and 2408 % in poly sodium 4-styrene sulfonate (PSSNa)-CNF. These BCs showed outstanding adsorption capacity for highly concentrated MB solutions (4536 mg g^-1 PAMPS-CNF and 11,930 mg g^-1 PSSNa-CNF). It was confirmed that the adsorption mechanism is through electrostatic interactions. Finally, BCs showed high MB adsorption efficiency after several sorption-desorption cycles and on a simulated textile effluent. Furthermore, the theoretical results showed a preferential interaction between MB and the semiflexible polymer chains at the lowest energy setting. The development and study of a new adsorbent material with high MB removal performance that is easy to prepare, economical and reusable for potential use in water purification treatments was successfully achieved.

Emerging Modification Technologies of Lignin-based Activated Carbon toward Advanced Applications

Lignin-based activated carbon (LAC) is a promising high-quality functional material due to high surface area, abundant porous structure, and various functional groups. Modification is the most important step to functionalize LAC by altering its porous and chemical properties. This Review summarizes the state-of-the-art modification technologies of LAC toward advanced applications. Promising modification approaches are reviewed to display their effects on the preparation of LAC. The multiscale changes in the porosity and the surface chemistry of LAC are fully discussed. Advanced applications are then introduced to show the potential of LAC for supercapacitor electrode, catalyst support, hydrogen storage, and carbon dioxide capture. Finally, the mechanistic structure-function relationships of LAC are elaborated. These results highlight that modification technologies play a special role in altering the properties and defining the functionalities of LAC, which could be a promising porous carbon material toward industrial applications.

Recent Advances on Membranes for Water Purification Based on Carbon Nanomaterials

Every year the problem of water purification becomes more relevant. This is due to the continuous increase in the level of pollution of natural water sources, an increase in the population, and sharp climatic changes. The growth in demand for affordable and clean water is not always comparable to the supply that exists in the water treatment market. In addition, the amount of water pollution increases with the increase in production capacity, the purification of which cannot be fully handled by conventional processes. However, the application of novel nanomaterials will enhance the characteristics of water treatment processes which are one of the most important technological problems. In this review, we considered the application of carbon nanomaterials in membrane water purification. Carbon nanofibers, carbon nanotubes, graphite, graphene oxide, and activated carbon were analyzed as promising materials for membranes. The problems associated with the application of carbon nanomaterials in membrane processes and ways to solve them were discussed. Their efficiency, properties, and characteristics as a modifier for membranes were analyzed. The potential directions, opportunities and challenges for application of various carbon nanomaterials were suggested.

Agricultural waste materials for adsorptive removal of phenols, chromium (VI) and cadmium (II) from wastewater: A review

Management of basic natural resources and the spent industrial and domestic streams to provide a sustainable safe environment for healthy living is a magnum challenge to scientists and environmentalists. The present remedial approach to the wastewater focuses on recovering pure water for reuse and converting the contaminants into a solid matrix for permanent land disposal. However, the ground water aquifers, over a long period slowly leach the contaminants consequently polluting the ground water. Synthetic adsorbents, mainly consisting of polymeric resins, chelating agents, etc. are efficient and have high specificity, but ultimate disposal is a challenge as most of these materials are non-biodegradable. In this context, it is felt appropriate to review the utility of adsorbents based on natural green materials such as agricultural waste and restricted to few model contaminants: phenols, and heavy metals chromium(VI), and cadmium(II) in view of the vast amount of literature available. The article discusses the features of the agricultural waste material-based adsorbents including the mechanism. It is inferred that agricultural waste materials are some of the common renewable sources available across the globe and can be used as sustainable adsorbents. A discussion on challenges for industrial scale implementation and integration with advanced technologies like magnetic-based approaches and nanotechnology to improve the removal efficiency is included for future prospects.

An ultrasound/O3 and UV/O3 process for atrazine manufacturing wastewater treatment: a multiple scale experimental study

An ultraviolet (UV) and ultrasound (US) enhanced ozonation method were developed to investigate their efficiency on the removal of atrazine and chemical oxygen demand (COD) in authentic atrazine manufacturing wastewater. The bench-scale tests suggested a positive effect of UV and US on the degradation of atrazine within a limited energy range. The pilot-scale flow-through system was further tested by using response surface methodology. The results showed that O₃ and its interaction with UV promoted the degradation of both COD and atrazine while its interaction with US inhibited the removal of COD but promoted the removal of atrazine. The optimal removal rate of atrazine (96.9%) was achieved in the condition of 6.86 W/L UV, 1.96 g/L·h O₃ and 294 W/L US. Chloride ions hindered the atrazine degradation, but the generated free chlorine radicals were still able to react with atrazine. In terms of energy-effectiveness, the configuration of 14.7 W/L UV and 1.96 g/L·h O₃ is the best option, which have the electrical energy per order of 181.6 kWh/m³ for atrazine and 0.13 kWh/g COD. These method and findings could be helpful in the development of energy-efficient advanced oxidation processes in treating wastewater with high salinity and COD loadings.

Instructive analysis of engineered carbon materials for potential application in water and wastewater treatment

Water remediation is an essential component for sustainable development. Increasing population and rapid industrialization have contributed to the deterioration of water resources. In particular, effluents from chemical, pharmaceutical, petroleum industries, and anthropogenic activities have led to severe ecological degradation. Many of these detrimental pollutants are highly toxic even at low concentrations, acting as carcinogens and inflicting severe long-lasting effects on human health. This review underscores the potential applications of engineered carbon-based materials for effective wastewater treatment. It focuses on the performance as well as efficiency of activated carbon, graphene nanomaterial, and carbon nanotubes, both with and without chemical functionalization. Plausible mechanisms of action between the chemically functionalized adsorbent and pollutants are also discussed. Based on the keywords from the literature published in the recent five years, a statistical practicality-vs-applicability analysis of these three materials is also provided. The review will provide a deep understanding of the physical or chemical interactions of the wastewater pollutants with carbon materials.

Zn2+ removal from the aqueous environment using a polydopamine/hydroxyapatite/Fe3O4 magnetic composite under ultrasonic waves

In this study, an easily magnetically recoverable polydopamine (PDA)-modified hydroxyapatite (HAp)/Fe₃O₄ magnetic composite (HAp/Fe₃O₄/PDA) was suitably synthesized to exploit its adsorption capacity to remove Zn²⁺ from aqueous solution, and its structural properties were thoroughly examined using different analytical techniques. The effect of multiple parameters like pH, ultrasonic power, ultrasonic time, adsorbent dose, and initial Zn²⁺ concentration on the adsorption efficiency was assessed using RSM-CCD. According to the acquired results, by increasing the adsorbent quantity, ultrasonic power, ultrasonic time, and pH, the Zn²⁺ adsorption efficiency increased and the interaction between the variables of ultrasonic power/Zn²⁺ concentration, pH/Zn²⁺ concentration, pH/absorbent dose, and ultrasonic time/adsorbent dose has a vital role in the Zn²⁺ adsorption. The uptake process of Zn²⁺ onto PDA/HAp/Fe₃O₄ followed Freundlich and pseudo-second order kinetic models. The maximum capacity of Zn²⁺ adsorption (q _m) obtained by PDA/HAp/Fe₃O₄, HAp/Fe₃O₄, and HAp was determined as 46.37 mg g^-1, 40.07 mg g^-1, and 37.57 mg g^-1, respectively. Due to its good performance and recoverability (ten times), the HAp/Fe₃O₄/PDA magnetic composite can be proposed as a good candidate to eliminate Zn²⁺ ions from a water solution.

Implication on selection and replacement of granular activated carbon used in biologically activated carbon filters through meta-omics analysis

Biologically activated carbon (BAC) filters are widely used in China and worldwide as an essential part of advanced water treatment. However, it is unclear how to properly select the granular activated carbon (GAC) used in BAC filters and to determine when GAC should be replaced. In this study, five BAC filters, each filled with a different coconut- or coal-based GAC with different physicochemical properties, were run continuously for 400 days. The structure and function of the microbial community and the quantity of specific enzymes in the BAC filters were investigated through an integrated metagenomic/metaproteomic analysis. The results indicated that GAC adsorption still played a major role in removing organic matter once the filters reached a steady-state, which was attributed to bioregeneration, and the contribution of adsorption might be relatively greater than that of biodegradation. GAC with strong adsorption capacity and high bioregeneration potential selected bacterial communities more phylogenetically closely-related than others. The iodine value could be used as an indicator of BAC performance in terms of organic matter removal in the initial stage of the filters, which is dominated by adsorption. However, it could not be used to assess performance at a later stage when adsorption and biodegradation occurred simultaneously. Pore-size distribution characteristics could be chosen as a potential better indicator compared with the current adsorption indicators, dually representing the adsorption performance and the microbial activity, and the proportion of important pore-size of GAC that is more suitable for BAC filter is suggested. GAC with strongly polar terminal groups is more conducive to the removal of ammonium-nitrogen.

Practical and Sustainable Modification Method on Activated Carbon to Improve the Decolorization Process in the Acetaminophen Pharmaceutical Industry

Decolorization plays an important part in the industrial production of acetaminophen (APAP) drugs. The impurities generated from the APAP pharmaceutical industry decolorization refining process were primarily separated and purified, and their structures were determined by MS and ¹H NMR technology. Then the catalytic effects of three samples of modified powdered activated carbon (PAC) on APAP in heterogeneous solution systems and the adsorption catalysis system were systematically investigated, which indicated that PAC catalyzed the APAP oxidative coupling side reaction and thus increased the impurities in the APAP product. The M-T-RAC (thermal regeneration PAC modified by ammonium sulfate) possessing more acidic surface groups can effectively inhibit this side reaction. Furthermore, according to the different catalytic results of O-T-RAC (thermal regeneration PAC modified by hydrogen peroxide) in solid-liquid catalytic and adsorption catalytic systems, we speculated that the multimer impurities were generated by the oxidative coupling reaction of APAP being oxidized to rated N-acetyl-p-benzoquinone (NAPQI) during decolorization, while free radical polymerization of APAP mainly occurred in the pores of the spent PAC. The pore textural structure and chemical properties of M-T-RAC were further characterized to ensure its feasibility of industrial application. The process of simulating industrial decolorization substantiated the excellent ability of M-T-RAC to inhibit side reactions. This study contributes to the development of green materials for sustainable recycling of activated carbon to reduce pollution and costs, and provides an effective advice for the pharmaceutical process.

Adsorption characteristics of chloramphenicol onto powdered activated carbon and its desorption performance by ultrasound

In this work, the adsorption characteristics, including adsorption kinetic, isotherm and thermodynamics of chloramphenicol (CAP) onto powdered activated carbon (PAC), were carried out, and the feasibility of using ultrasound to regenerate saturated PAC in aqueous solution was evaluated. The adsorption results demonstrated that the adsorption mechanism was a complex process including surface adsorption, external liquid membrane diffusion and intraparticle diffusion as well, and the adsorption process was endothermic and non-spontaneous. The optimal conditions for PAC regeneration were as follows: acoustic density of 0.36 W/mL, saturated carbon dosage of 1.0 g/L and pH value of 10.36. The analysis of thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), Brunauer-Emmett-Teller (BET) surface area, pore size distribution and scanning electron microscopy (SEM) of PAC samples revealed that ultrasound mainly acted on surface functionalities, meso-pores and macro-pores of PAC through hydroxyl radical oxidization, high-pressure shock waves and high-speed microjets due to cavitation effect. This study highlighted that ultrasound could be efficiently desorbing CAP from saturated PAC. Practical applications of this method for PAC regeneration with complex natural matrices under environmentally realistic conditions were conducted and the adsorption capacity of the regenerated PAC decreased.

Impacts of thermal and non-thermal processing on structure and functionality of pectin in fruit- and vegetable- based products: A review

Pectin, a major polysaccharide found in the cell walls of higher plants, plays major roles in determining the physical and nutritional properties of fruit- and vegetable-based products. An in-depth understanding of the effects of processing operations on pectin structure and functionality is critical for designing better products. This review, therefore, focuses on the progress made in understanding the effects of processing on pectin structure, further on pectin functionality, consequently on product properties. The effects of processing on pectin structure are highly dependent on the processing conditions. Targeted control of pectin structure by applying various processing operations could enhance textural, rheological, nutritional properties and cloud stability of products. While it seems that optimizing product quality in terms of physical properties is counteracted by optimizing the nutritional properties. Therefore, understanding plant component biosynthesis mechanisms and processing mechanisms could be a major challenge to balance among the quality indicators of processed products.

Effect of granular activated carbon pore-size distribution on biological activated carbon filter performance

Proper granular activated carbon (GAC) selection could improve the performance of biological activated carbon (BAC) filters through a combination of adsorption and biodegradation, while the GACs used in BAC filters are now mainly selected according to adsorption function, ignoring biodegradation. In this study, sand filter effluent obtained from a drinking water treatment plant was fed into continuous-flow bench-scale BAC columns operated in parallel over 245 days to examine the effects of GAC pore-size distribution on BAC filter performance, in terms of the dissolved organic carbon (DOC) and disinfection byproduct (DBP) precursors. A metagenomic analysis indicated that bacterial community structure played an important role in BAC filter performance. A significant correlation was found between metabolism-related proteins and the volume of micro-level macropores based on metaproteomic analysis. It is suggested that the adsorption saturation was dynamic and that adsorption played a role in the performance of the BAC filters throughout the 245-day operating period. Renewed adsorption capacity, or bioregeneration, was driven by bacterial metabolic activity. Such activity largely depended on the organic matter adsorbed by the GAC, in which micro-level macropores, especially those with diameters of 0.2-10 μm, played an important but previously unrecognized role. The results suggest that more attention should be paid to well-developed pores and pore-size distribution in the production and selection of GAC used for full-scale drinking water biofilters.

Composites for wastewater purification: A review

The review deals with different kinds of composites which have been used for wastewater treatment. The use of different types of composites ranging from nanocomposites, activated charcoal composites, polymer composites, oxide-based composites, hybrid composites, and biosorbent composites, etc. has been dealt with in detail, and presented as a central source of knowledge. The paper incorporates water purification explicitly via adsorption process, which has proven to be economical and efficient. These composites have been explored for treating or elimination of various hazardous substances like heavy metal species, different classes of colored contaminants (dyes), several organic and inorganic pollutants from wastewater. The composites discussed have successfully eliminated Zn²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Hg, etc. In some instances the removal percentage of the contaminants was almost 100%. The presented data reveals the efficiency of composite materials in wastewater treatment over the conventional singular materials.

Comparison of two typical regeneration methods to the spent biological activated carbon in drinking water

The spent biological activated carbon (BAC) should be disposed properly; regeneration was a better choice. Performances of thermal and ultrasonic regeneration to the BAC with various service time (3 years, 5 years, and 10 years) were compared comprehensively; the recovery of the BAC's pore structure, variation of mechanical hardness, influence of bioactivity, and removal efficiency of typical pollutants in the reuse were examined. The results showed that thermal regeneration was an utterly regeneration, and almost all the pore structure was restored, whose recovery rate was above 90% for BAC used 3 years and disfavored by the longer BAC's service time (83% for the BAC used 5 years). Ultrasonic regeneration could recover part of the BAC's pores (including micropores) and the restoration mainly focused on the BAC's surface, so the recovery rate was not influenced by the BAC's service time, and the recovery values of specific surface areas and iodine value were kept at 120 m²/g and 200 mg/g, respectively. In addition, the ultrasonic treatment enhanced the BAC's biological activity even with a significant decrease of the biomass on the BAC. The mechanical hardness of BAC decreased from 95 to 89% for the first regeneration and further to 79% for the second regeneration, whereas relatively lower decrease happened for the ultrasonic regeneration (less than 10% after 5 regeneration cycles). The mass losses in the thermal and ultrasonic regeneration were about 13%, 0.5%, and 25%, 3% for the first and second regeneration, respectively. The thermal-regenerated activated carbon (AC) exhibited excellent adsorption ability, good adherence of biofilm, and maintain higher removal rate for more than 2 years, which were similar with that of the fresh AC, but relatively lower removal performance was found. However, the ultrasonic regenerated BAC retained the biodegradation ability, restored the fast-adsorption ability, and the higher removal process lasted about 6 months. Taking the regeneration cost, operation, variation of the AC's characteristics, and the removal performance in reuse, ultrasonic regeneration was more suitable for the BAC filter and better used as a regular measure to maintain the higher removal performance, whereas thermal regeneration was more applicable to the activated carbon adsorption tank.

Variation in the biological characteristics of BAC during ultrasonic regeneration

Ultrasonic treatment has been shown to have a favorable effect on the regeneration of spent biological activated carbon (BAC) from drinking water treatment plants. In this study, the use of ultrasound as a regeneration method had a significant effect on the recovery of spent BAC after 7.5 years of use; it effectively increased the iodine value from 300 mg/g to 600 mg/g and restored the specific surface area and pore volume of BAC. Ultrasound effectively changed the structure of the biofilm inside and on the surfaces of BAC particles, on the basis of confocal laser scanning microscopy (CLSM) images. The thickness of the surface biofilm attached to BAC reached an "active" level (about 100 μm) at the regeneration frequency of 40 kHz. The dehydrogenase activity significantly improved from 4.50 mg TF/g BAC to 9.13 mg TF/g BAC, and the content of adenosine-triphosphate (ATP) in regenerated BAC was maintained at a high level (2.501 × 10^-6g ATP/g BAC), thus allowing the development of microbial growth. The production of soluble microbial products (SMPs) from regenerated BAC decreased during the reuse process. The removal efficiency of DOC, COD_Mn, NH₄⁺ and NO₃^- control increased by approximately 78%, 71%, 50% and 20%, respectively.

Ag nanoparticle-decorated carbon nanotube sponges for removal of methylene blue from aqueous solution

Fabrication of AgNP-Pdop-CNTS for MB adsorption and regeneration.

Evaluation of Edible Quality of Sorghum Based on Principal Component Analysis

Sorghum (Sorghum bicolor (L.) Moench) is one of the most important cereals in the Northeast China. The physicochemical, pasting, texture, and cooking properties of 21 sorghum varieties were determined, which were mainly cultivated in Northeast China. Then, the evaluation of edible quality of sorghum was based on principal component analysis and fitted with the score of sensory evaluation. Five principal components (PCs) with a cumulative contribution rate of 86.19% could be picked out to describe the taste, pasting, flavor, cooking, and variety of sorghum, respectively. And a comprehensive equation of sorghum edible quality in Northeast China was constructed which was Z = 0.45F1 + 0.25F2 + 0.12F3 + 0.10F4 + 0.08F5. The edible quality of No. 14 and No. 15 was the best. The sensory evaluation was used to verify the above equation with the fitting coefficient of 0.81, which indicated that the equation could be more accurate to evaluate the edible quality of sorghum in Northeast China.

Regeneration of 4-chlorophenol from spent powdered activated carbon by ultrasound

Ultrasound-assisted regeneration of powdered activated carbon (PAC) saturated with 4-chlorophenol (4-CP) was investigated in this work. The variables, i.e., acoustic frequency, density levels, regenerating solution species, spent PAC mass, and the number of repeated cycle, were optimized. The UV-Vis spectra, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and pore structure analysis were used to characterize the regenerated PAC as compared to the virgin and spent PAC. The adsorption experiments indicated that the adsorption kinetics of 4-CP fitted well with the pseudo-second-order model, and the main chemisorption process was nonlinear and heterogeneous. The desorption results showed that the optimized regenerated conditions were identified as 40 kHz of frequency, 0.18 W/mL of sonication intensity, 0.1 M NaOH and 50% (v/v) ethyl alcohol mixture of regeneration solution, and 1 g/L of saturated PAC mass. Under this condition, the regeneration efficiency reached up to 86.81%. Hydroxylated oxidation products especially benzoquinone and hydroquinone were formed during ultrasound regeneration. Ultrasound mainly acted on surface functionalities, mesopores, and macropores of PAC through the hydroxyl radical oxidization resulted from the cavitation effect.

Single-step synthesis of eucalyptus sawdust magnetic activated carbon and its adsorption behavior for methylene blue

Eucalyptus wood-based magnetic activated carbon (MAC) was prepared by single-step carbonization activation magnetization with FeCl₃ and utilized for the adsorption of methylene blue (MB).

Preparation, adsorptive properties and chemical regeneration studies of high-porous activated carbon derived from Platanus orientalis leaves for Cr(VI) removal

Activated carbon (AC) was prepared from Platanus orientalis leaves by H₃PO₄ activation using a microwave heating method and characterized by SEM (scanning electron microscopy), Brunauer-Emmett-Teller (BET) surface area analysis and FTIR (Fourier transform infrared spectroscopy) techniques. AC exhibited a surface area of 1089.67 m²/g and a relatively high pore volume of 1.468 cm³/g. Utilization of AC for the removal of Cr(VI) from aqueous solution was researched. The adsorption efficiency was highly pH dependent and adsorption capacity of AC for Cr(VI) could reach up to 135.24 mg/g. Adsorption equilibrium could be quickly reached within 2 h. A kinetic study indicated that the adsorption of Cr(VI) conformed to the pseudo-second-order model (R² > 0.99). An intraparticle diffusion model was applied to describe the adsorption kinetics, and the results showed that there are other factors that affect the rate. Chemical regeneration for AC saturated with Cr(VI) was performed and HNO₃ displayed the best regeneration performance among the four chemical regeneration agents (HNO₃, H₂SO₄, NaOH, NaCl). The regeneration performance increased at first and then decreased with the rise of HNO₃ concentration, and regeneration reaction could reach equilibrium within 4 h in the first cycle. The FTIR spectra revealed that HNO₃ successfully introduced N-H bonds onto the AC surface in the regeneration process.

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.

Study on regeneration effect and mechanism of high-frequency ultrasound on biological activated carbon

High frequency ultrasonic radiation technology was developed as a novel and efficient means of regenerating spent biological activated carbon (BAC) used in drinking water treatment plants (DWTPs). The results of this study indicated that high frequency ultrasonic treatment could recover the spent BAC, to some extent, with the following optimal conditions: a frequency of 400 kHz, sonication power of 60 W, water temperature of 30 °C, and sonication time of 6 min. Under the above conditions, the iodine value increased from 300 mg/g to 409 mg/g, the volume of total pores and micropores increased from 0.2600 cm³/g and 0.1779 cm³/g to 0.3560 cm³/g and 0.2662 cm³/g, respectively; the specific surface area of micropores and the mean pore diameter expanded from 361.15 m²/g and 2.0975 nm to 449.92 m²/g and 2.1268 nm, respectively. The biological activity increased from 0.0297 mgO₂/gC·h to 0.0521 mgO₂/gC·h, while the biomass decreased from 203 nmolP/gC to 180 nmolP/gC. The results of high throughput 16S rRNA gene amplicon sequencing showed that microorganisms such as Clostridia and Nitrospira were markedly decreased due to high frequency ultrasound. The method used in this study caused the inhibition of certain carbon-attached microbials resulting in a negative effect on the removal rate of ammonia-N during the initial stage of the long-term reuse operation. The removal of UV254 and atrazine were restored from 8.1% and 55% to 21% and 76%, respectively.

Ultrasonic-promoted rapid preparation of PVC/TiO2-BSA nanocomposites: Characterization and photocatalytic degradation of methylene blue

In the present project in order to prevent agglomeration and better dispersion of TiO₂ nanoparticles (NPs) in the poly(vinyl chloride) (PVC) matrix, initially, the surface of TiO₂ NPs was covered by bovine serum albumin protein (BSA) via sonication method. Then, the TiO₂-BSA powders were embedded into the PVC matrix using ultrasonic irradiations. With mechanical and magnetic stirring homogenous mixture was not obtained. So sonication process was very essential and vital. Physical, chemical and structural properties of the samples were investigated with various tools. Morphology studies showed the well distribution of spherical TiO₂ NPs in the PVC matrix. TGA analysis showed that nanocomposites (NCs) have higher thermal stability than the pristine polymer. The photocatalytic activity tests by destroying the methylene blue dye on the pristine TiO₂ NPs, TiO₂-BSA NPs and PVC/TiO₂-BSA NC 6 wt% were examined. The results showed that the photocatalytic activity of TiO₂ NPs was reduced in the presence of BSA and PVC. It can be concluded that the TiO₂-BSA NPs and PVC/TiO₂-BSA NC 6 wt% have UV shielding properties and can protect film from degradation by UV.

A simple method for the sonochemical synthesis of PVA/ZrO2-vitamin B1 nanocomposites: Morphology, mechanical, thermal and wettability investigations

Poly(vinyl alcohol) (PVA) based nanocomposites (NCs) filled by various weight percent of modified ZrO₂ nanoparticles (NPs) with vitamin B₁ (VB₁) up to 7wt% were fabricated via ultrasonication method then was cast to thin films. The ultrasonication was applied for the preparation and modification process asan easy, safe and fast method. Ultrasonic was responsible for great homogeneities of NPs into PVA matrix, which could not be achieved by mechanical or magnetically stirring. The creation of polymer NCs and changes in the structural properties were examined by X-ray diffraction. FT-IR spectroscopy indicated the possible interactions of the ZrO₂-VB₁ NPs with the PVA backbones and also, existence of absorption bands related to PVA and ZrO₂ NPs in the NC structures. The distribution of nano-fillers and uniform morphology of the NCs showed that the ZrO₂-VB₁ NPs were homogeneously dispersed in the polymer matrix in the nanosized scale. UV-Vis analysis shown that the the optical absorption were improved by evolution of ZrO₂-VB₁ NPs content. The tensile strength of PVA film was increased significantly with increasing the ZrO₂-VB₁ NPs content. Thermal gravimetric analysis confirmed that NCs displayed higher thermal stability than the pristine PVA. Also, water contact angle analysis indicated that the hydrophilicity of NC films was enhanced with increasing the concentration of ZrO₂ NPs.

Utilization of ultrasonic irradiation as a green and effective strategy to prepare poly(N-vinyl-2-pyrrolidone)/modified nano-copper (II) oxide nanocomposites

The present paper describes the result of investigations into preparation of novel nanocomposites (NCs) based on poly(N-vinyl-2-pyrrolidone) (PVP) as a biocompatible polymer and modified copper (II) oxide nanoparticles (NPs) as a nano-filler. To achieve optimum NCs properties, different ratios of modified copper (II) oxide NPs (3, 5, and 7wt%) were used to fabricate PVP NCs and also the ultrasonic irradiation was utilized to perform these processes as a fast and effective method. Subsequently, the structure of the obtained nanohybrids was characterized by various techniques. The suitable incorporation between PVP matrix and modified CuO NPs can be seen from the FT-IR spectra. The obtained NCs indicated an efficient thermal improvement in comparison to the pristine polymer. Also, the uniform dispersion of modified CuO NPs in the PVP matrix was detected by FE-SEM and EDX. According to UV absorption spectra, it is clear that these NCs can be used in UV protecting applications.

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.